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Theses, Dissertations, Professional Papers
Graduate School
1976
Aspects of the diving physiology of muskrats
(Ondatra zibethica) : post-dive oxygen
consumption and lactic acid levels
Eleanor Stetson
The University of Montana
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Stetson, Eleanor, "Aspects of the diving physiology of muskrats (Ondatra zibethica) : post-dive oxygen consumption and lactic acid
levels" (1976). Theses, Dissertations, Professional Papers. Paper 6525.
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physiology OF MUSKRATS
(ONDATRA ZIBETHICA): POST-DIVE OXYGEN
CÙNSÜMPTIC)N"AND"LACTIC ACID LEVELS
aspects of the d iv in g
BY
ELEANOR STETSON
B.A., MOUNT HOLYOKE COLLEGE, 1973
Presented in p artial fu lfillm e n t of the requirements
fo r the degree o f
Master o f Arts
U n iversity o f Montana
1976
Approved by:
Chairman, Board o f Examr^rs
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UMI Number: EP37326
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Stetson, Eleanor, M.A., August 1976
Zoology
Aspects of the Diving Physiology o f Muskrats ( Ondatra z ib e th ic a ):
Post-dive Oxygen Consumption and Lactic Acid Levels (45 p p .)
D ire cto r: Dr. Delbert L. Kilgore^^*"^
The extensive l i t e r a t u r e on the physiological adaptations to
diving does not include much information on semi-aquatic mammals
or on unrestrained animals. Experiments with animals accustomed
to dives o f short duration are needed to determine the f u l l range
o f v a ria tio n in physiological adaptations among d iff e r e n t diving
animals. Comparison o f restrained and unrestrained dives is
necessary to assess the e f f e c t o f r e s tr a in t on an animal's diving
responses.
Muskrats are medium sized semi-aquatic mammals accustomed to
dives o f short duration. Seven animals were used fo r a to ta l of
31 restrained dives and nine animals were used fo r a to ta l o f 46
unrestrained dives. Dives were 0 .5 , 1, 2, 3, 4, or 5 minutes
long. A paramagnetic oxygen analyzer continuously monitored the
fra c tio n a l oxygen concentrations before and a f t e r the dives.
Oxygen consumption was calculated from the fra c tio n a l oxygen con­
centration data. Body oxygen stores were estimated and blood
lev els o f l a c t i c acid were measured before, during and a f t e r 6
restrained dives to determine whether or not the n o n -la ctic acid
oxygen debt of seals, animals accustomed to prolonged dives, is
apparent in muskrats also.
The r a t io o f the oxygen debt, assuming maintenance of the pre­
dive oxygen consumption rate during the d ive, to the actual post­
dive excess oxygen consumption indicates e ith e r an increased
oxygen consumption rate during the dive or an increase a f t e r the
dive not caused by oxygen debt payment. The post-dive excess
oxygen consumption increased with longer dives a f t e r both re ­
strained and unrestrained dives. Regression o f post-dive excess
oxygen on dive time re su lts in s t a t i s t i c a l l y equal regression
equations fo r restrained and unrestrained dives ind icatin g th at
r e s tr a in t has no e ff e c t on the magnitude of the post-dive excess
oxygen consumption. However, a f t e r unrestrained dives the mean
ra te a t which the excess oxygen consumption occurred was always
greater than a f t e r restrained dives.
A v a ria b le n o n -la c tic acid debt appears to e x is t in muskrats
but, because o f the disagreement in the l i t e r a t u r e as to the
fra c tio n o f the l a c t ic acid which is oxidized in recovery, no
d e f in it e conclusions can be made.
n
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TABLE OF CONTENTS
PAGE
ABSTRACT.........................................................................................................
ii
LIST OF ILLUSTRATIONS..............................................................................
iv
LIST OF TABLES............................................................................................
v
ACKNOWLEDGEMENTS........................................................................................
vi
CHAPTER
r
INTRODUCTION................................................................................
1
II
METHODS AND MATERIALS................................................
4
III
Trapping and Maintenance..............................................
Restrained D iv e s ..
........
Unrestrained Dives.............................................................
Measurement of Oxygen Consumption.............................
Lactic Acid Determinations............................................
4
4
6
7
8
RESULTS...........................................................................................
10
Magnitude of Post-dive Excess Oxygen
Consumption.......................................... ; ......................
Post-dive Excess Oxygen Consumption
versus Dive Time...............................
Recovery Time..................................................................
Estimated Oxygen Stores..................................................
Lactic Acid............................................................................
13
16
19
21
IV
DISCUSSION.....................................................................................
25
V
SUMMARY...........................................................................................
31
APPENDIX 1.....................................................................................................
34
APPENDIX 2 .....................................................................................................
36
APPENDIX 3 .....................................................................................................
40
LITERATURE
43
CITED....................................................................................
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10
LIST OF ILLUSTRATIONS
Figure
1.
2.
3.
4.
5.
Page
Restrained dive apparatus (top) and unrestrained
dive apparatus (bottom) drawn to sc a le .........................
5
Typical 2 minute restrained dive curve. Shaded
sections indicate equivalent oxygen consumptions and
show the portion of the post-dive excess oxygen con­
sumption necessary to pay o f f the oxygen debt
11
Relationship between post-dive excess oxygen con­
sumption and dive time fo r restrained dives
15
Relationship between post-dive excess oxygen con­
sumption and dive time fo r unrestrained d ives
17
Oxygen consumption and blood lev els o f l a c t ic acid
before, during and a f t e r a 2.5 minute dive (Exp. la ) 22
IV
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LIST OF TABLES
Table
1.
2.
3.
4.
Page
Post-dive excess oxygen consumption (V02 ) , oxygen
debt (0 0 ), and mean percentage o f V02 accounted
fo r by OD fo r restrained and unrestrained dives
a t each dive tim e.........................
12
Analysis o f variance o f the mean percentage of
V02 accounted fo r by 00 a t d if f e r e n t dive times
and fo r both restrained and unrestrained d ives
14
Mean to ta l recovery time in minutes fo r each dive
time, both restrained and unrestrained d i v e s . .
18
Estimated oxygen stores fo r each muskrat used
in the l a c t ic acid e x p e r i m e n t s . . . . . . ................................
20
5.
Maximal l a c t ic acid (LA) concentration, % o f to ta l
LA increase occurring during the d ive, grams LA
removed in recovery, and oxygen required fo r removal
o f LA fo r l a c t i c acid experiments........................................ 23
6.
Comparison o f post-dive excess oxygen consumption
and the oxygen necessary fo r replenishing oxygen
stores and removing l a c t ic a c id ..........................................
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24
ACKNOWLEDGEMENTS
Special thanks go to Dr. Delbert L. Kilgore who as my major
advisor gave much of his time and assistance a t a l l lev e ls o f th is pro­
je c t.
His constant encouragement and friendship were invaluable.
Thanks are also extended to Dr. Richard Fevold fo r his advice
on the biochemical aspects o f th is study and fo r his c r i t i c a l review of
the manuscript and to Dr. P h il l ip Wright fo r his advice on trapping
muskrats and fo r his review o f the manuscript.
Mr. Robert Twist, D irector o f the R avalli W ild lif e Refuge and
Mr. David Mad ay and Ms. Anne Mad ay are extended thanks fo r allowing
me to trap muskrats on land under t h e i r co n tro l.
A ll my fe llo w graduate students provided help and encourage­
ment
in various ways. Special thanks to a l l who helped me "handle"
my muskrats.
I es p ecially wish to thank the women a t 707 Dickinson fo r
empathy, laughter, encouragement, confidence, and frien d sh ip .
o f them
Because
the bad times were b e tte r and the good times, great.
A f in a l
thank you to Lee Fairbanks fo r his ceaseless support
and encouragement and his b e l i e f th at i t was a l l worthwhile.
VI
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CHAPTER I
INTRODUCTION
The a b i l i t y o f some animals to dive fo r periods of time th at
exceed the length o f dive possible, estimated from t h e i r oxygen stores,
has been the subject of research since the la te 1800's (B e rt, 1870;
Bohr, 1897; Richet, 1899).
The physiological adaptations associated
with the diving habit have been reasonably well studied in seals, but
less is known about the adaptations o f those animals th a t dive fo r only
short periods o f time.
The l i t e r a t u r e on diving has been reviewed by
Irv in g (1939), Scholander (1964), and more recently by Andersen (1966).
The physiological adaptations associated with diving include an
intense submergence bradycardia accompanied by s e le c tiv e peripheral
vasoconstriction, reduced s e n s i t iv it y to carbon dioxide in the blood,
and large oxygen stores re s u ltin g from increased blood volumes, high
muscle myoglobin concentrations, and large blood oxygen capacities
(Andersen, 1966).
The large oxygen storage capacity and the s e lec tiv e
peripheral vasoconstriction make i t possible fo r the animal to maintain
aerobic metabolism in the heart and brain while the major muscle masses
function
anaerobically.
A fte r a dive the animal must consume enough
oxygen to replenish the oxygen stores and to restore the blood l a c t ic
1
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acid lev els to pre-dive le v e ls .
In te r e s t in g ly , Scholander (1940) r e ­
ported the existence o f a small n o n -la c tic acid oxygen debt in seals in
addition to the l a c t i c acid oxygen debt and the oxygen stores debt.
Whether th is n o n -la ctic acid debt exists in other diving animals is not
known, as few measurements of post-dive oxygen consumption and blood
lev els of l a c t ic acid have been made.
Variations in the physiological adaptations to diving o f various
mammals and birds are undoubtedly re fle c te d in t h e i r diving habits.
This
is evidenced by the fa c t th at seals, which are accustomed to prolonged
d iv in g , have a lower post-dive oxygen consumption than expected, in d ic a t­
ing a metabolic ra te during a dive lower than t h e i r pre-dive ra te .
Con­
versely, animals such as cats, not adapted fo r d iv in g , have a higher
post-dive oxygen consumption than expected, perhaps in d ica tin g a meta­
b o lic rate during dives which is higher than t h e i r pre-dive rate (Scho­
lander, 1940).
The f u l l range o f th is response is not known as l i t t l e
work has been done on animals accustomed to dives o f only short duration.
Muskrats (Ondatra z ib e th ic a ) are small mammalian divers accustomed to
diving o f th is type and th is study w i l l
examine the nature of t h e ir
post-dive excess oxygen consumption a f t e r restrained dives and compare
i t to th a t in seals.
Muskrats are su itab le subjects fo r th is study not only because
o f t h e i r diving habits but also because o f t h e i r size.
They are small
enough to allow experimental unrestrained dives to be performed in the
laboratory.
This is important because, despite the volume o f l i t e r a t u r e
on the physiology o f diving mammals and b ird s , few experiments have
involved measurements on unrestrained animals (Murdaugh, e t
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1961;
3
Kooyman, e t
Jones, e_t
1971; Harrison, e
1973; Kooyman, e t
; t 1972; Kooyman & Campbell, 1972;
1973; M ill a r d , e_t
1973).
For
purposes o f comparisons between diving and non-diving animals and among
d if f e r e n t diving animals, the restrained dive is an e x c e lle n t approach
to the problem and, because o f technical d i f f i c u l t i e s , i t is often the
only possible approach.
However, diving animals are usually very ac tive
underwater and i t would be o f in te re s t to know whether data collected
during a restrained dive are good estimates o f the same parameters
during unrestrained dives.
In th is study comparison o f the excess oxygen
consumption a f t e r both restrained and unrestrained dives o f muskrats
w i l l determine the e f f e c t o f r e s t r a in t on data obtained during diving
experiments.
Since muskrats' diving habits are q u ite d if f e r e n t from the d iv ­
ing habits o f seals the n o n -la c tic acid oxygen debt mentioned e a r l i e r
may or may not be evident in muskrats.
The simultaneous measurement o f
post-dive oxygen consumption and blood l a c t i c acid levels in th is study
w i l l elucidate the re la tio n s h ip between these two parameters in muskrats.
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CHAPTER I I
METHODS AND MATERIALS
Trapping and Maintenance
Muskrats ( Ondatra z ib e th ic a ) were trapped from sloughs along
the B itte r ro o t River, south o f Missoula, Montana during the f a l l of
1974 and 1975.
A to ta l of 12 individuals (5 males, 7 females) were used
in these experiments.
to 1.539 kg).
Their mean body mass was 1.011 kg (range 0.638
The animals were in d iv id u a lly housed in cages and main­
tained on le ttu c e , c a rro ts , and Purina dog chow.
provided ad lib itu m .
Drinking water was
A ll experiments were conducted between July 1975
and February 1976.
Restrained Dives
A diving board mounted on a large aquarium (1.22 x 0.40 x
0.51 m) was used fo r the restrained dives (Fig . 1).
The board was a t ­
tached to a metal rod supported on two ball bearings and could be held
level or t i l t e d into the water with ease.
The animal was secured on the
board with cloth straps around each fo o t; these were tie d to small cleats.
Velcro straps were used to re s tra in the animal's body and t a i l and a
padded U -b olt held the animal's neck.
Secured in th is manner the
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Figure 1: Restrained dive apparatus (to p ) and unrestrained
dive apparatus (bottom) drawn to scale.
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TO O X Y G E N
ANALYZER
1. 22
m
j-----------------> T O O 2 A N A L Y Z E R
< -A ir
O
1.80
m
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6
animal's re s p ira to ry movements were unimpeded.
A h a lf gallon p la s tic b o ttle was modified into a hood which f i t
snugly over the animal's head when the animal was above water.
Room
a i r was drawn through the hood a t a ra te o f 3.58 to 6.88 1/min and was
s u f f i c i e n t to prevent any loss o f expired a i r .
The flow of a i r through
the hood was held constant during each experiment.
The fra c tio n a l con­
centration o f oxygen in the excurrent hood a i r (FE0 2 ) was continuously
monitored during an experiment and only a f t e r an animal reached a
restin g level o f metabolism were animals dived. An animal was assumed to
be a t re s t when oxygen consumption remained r e l a t i v e l y steady (±3% to
±
6 % o f re s tin g ) fo r a 7 to 15 minute period.
A fte r a d iv e, the animal
was allowed to return to a t le a s t w ithin 12 to 24% above the pre­
dive oxygen consumption ra te before being removed from the board.
Seven d if f e r e n t animals were used.
Six 0.5 minute dives, six
1 minute dives, eight 2 minute dives, fiv e 3 minute dives, and six 4
minute dives were done fo r a to ta l o f 31 restrained dives.
No animal
was dived more than two times in one day and often only once.
Unrestrained Dives
Experiments on unrestrained diving muskrats were conducted in
a glass-fronted tank (0.77 x 1.84 x 0.96 m) covered with a piece o f
masonite mounted approximately 2 cm below the water surface (F ig . 1 ).
A trapdoor in the masonite, when open, was the animal's only breathing
hole and was the only e x i t and entrance to the tank.
The door was
weighted and hinged and could be raised and lowered by a rope attached
to a p ulley above the tank.
The f u l l body hood consisted of a wooden
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7
box (0.21
top.
X
0.21
X
0.14 m) with a cle a r p la s tic dome 20 cm in height
The volume o f the hood without the animal was 13.6 1.
drawn into and through the box through a series of
bottom on each side.
on
A ir was
holes 2 cm from the
The closed trapdoor formed the flo o r o f
so when the door was opened the animal was fre e to dive.
the box
During the
experiments a i r flow was maintained at 7.44 l/m1n.
Fractional concentration of oxygen in the excurrent a i r was
continuously monitored as in the restrained dive experiments and resting
metabolic rate was ascertained in the same manner.
was established,
was closed.
When a restin g rate
the animal was permitted to d iv e , a f t e r which the door
The animal had no access to the surface and o r d in a r ily
swam continuously during the dive.
The door was opened approximately
5 seconds before the end o f the dive.
Therefore, actual dive times
varied from desired dive time by a few seconds (-1 .8 5 + 0.34 to 4.48±0.72
sec).
A fte r the dive the animal was allowed to return to i t s pre-dive
restin g metabolic ra te before the experiment was terminated.
Nine d if f e r e n t animals were used fo r a to ta l o f 46 dives in ­
cluding six 1 minute dives, eig ht 2 minute dives, eleven 3 minute dives,
fourteen 4 minute dives, and seven 5 minute dives.
No animal was
dived more than three times in one day and usually only once.
Measurement o f Oxygen Consumption
The fra c tio n a l concentration o f oxygen in the excurrent hood
a i r and room a i r (F 102 ) were measured with a Beckman (Model G2) para­
magnetic oxygen analyzer (see Appendix 1 ).
The oxygen analyzer was
c a lib ra te d by varying the pressure in i t s c e ll and the c a lib ra tio n was
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8
checked with a c e r t i f i e d primary gas standard before each run.
The
equation used to c a lcu la te oxygen consumption rate from data obtained
from the oxygen analyzer was th a t o f Tucker (1968; Equation 3 ),
Flow o f a i r through the hoods was measured with a flowmeter
which had previously been c a lib ra te d with a MBS c e r t i f i e d Vol-U-Meter
(Brooks, Model #1058-7A) and was held constant by a sub-atmospheric
pressure regu lato r (Moore Products, Model 44 -20 ).
The post-dive excess oxygen consumption (Voz) is the oxygen con­
sumed above th at which would have been consumed i f the animals had main­
tained a restin g oxygen consumption ra te a f t e r the dive.
The post-dive
excess VQ2 was determined by measuring the area bounded by the post­
dive excess V02 curve above and the hypothetical resting oxygen con­
sumption ra te below with a planimeter and comparing i t to an area with
a known oxygen consumption.
A ll volumes are reported a t standard temperature and pressure
(STP).
L actic Acid Determinations
Blood samples were taken before, during, and a f t e r six re ­
strained dives.
Of these, f i v e dives were 2.5 minutes in duration and
one was 2 .0 minutes.
Because o f the small sample s iz e , each dive was
evaluated in d iv id u a lly .
Blood samples fo r the l a c t i c acid assay were co llected from a
cannula (PE 90) positioned in the femoral a r te ry under a general anes­
th e tic .
The muskrats were anesthetized with sodium pentabarbital
(35
mg/kg body mass) and were allowed to recuperate fo r 20 to 30 hours be-
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
9
fo re being used in the diving experiments.
Clotted cannulae were a
chronic problem, hence sodium heparin was in jec ted intramuscularly
(5 mg/kg body mass) approximately 5 minutes before the cannula was in ­
serted into the a r te r y .
Sixteen to twenty blood samples were co llected during a single
diving experiment.
In most cases, three samples were taken before the
d iv e, three during the dive and the remaining samples were collected at
varying in te rv a ls a f t e r the dive.
minutes a f t e r the dive.
The la s t sample was taken about 90
A 0.25 ml sample was collected each time and
the blood was replaced with heparinized isotonic s a lin e .
Blood samples
were immediately combined with 0.5 ml cold 8% perchloric acid in a
small polyurethane ce n trifu g e tube.
This combination was mixed vig o r­
ously (Beckman/Spinco 154 micromixer) and centrifuged.
The c le a r super­
natant was assayed f o r l a c t i c acid using procedures outlined in Sigma
Technical B u lle tin - 726UV/826UV and employing a Beckman DU spectro­
photometer.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
CHAPTER I I I
RESULTS
Magnitude o f Post-dive Excess Oxygen Consumption
A typ ical pattern o f oxygen consumption before, during and a f t e r
a two minute restrained dive is shown in Figure 2.
The restrained dives
were characterized by an immediate increase in oxygen consumption f o l ­
lowed by a steep decline and then a ra th e r extended plateau during
which the oxygen consumption ra te approached the pre-dive le v e l.
Oxygen
consumption records following unrestrained dives lacked th is plateau and
were characterized by a more gradual increase and decrease in oxygen
consumption.
During a dive an animal should th e o r e t ic a lly incur an oxygen
debt which minimally should equal the oxygen consumed fo r the duration
o f the dive assuming the animal was a t r e s t.
The post-dive excess
oxygen consumption should compensate fo r th is oxygen debt.
The post­
dive excess oxygen consumption and oxygen debt fo r each dive are shown
in Appendix 2.
The post-dive excess oxygen consumption was found to be
q u ite v a ria b le , but increased as did oxygen debt with longer dive times
(Table 1 ).
The oxygen debts incurred during 3 minute and 4 minute un­
restrained dives are nearly the same.
The resting oxygen consumption
10
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 2: Typical 2 minute restrained dive curve. Shaded
sections Indicate equivalent oxygen consumptions
and show the portion of the post-dive excess oxygen
consumption necessary to pay o ff the oxygen debt.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
11
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Table 1: Post-dive excess oxygen consumption (V02 ) , oxygen debt (OD), and mean
percentage of V02 accounted for by OD for restrained and unrestrained
dives at each dive time. VQ2 and OD values are means ± one standard error.
8
(O '
3"
Restrained Dives
i
Unrestrained Dives
3
CD
"n
c
Dive Time
(min)
VO?
O2 Debt
(ml/kg)
(ml/kg)
3 .
OD
X 100
V02
Vo?
(ml/Rg)
O2 Debt
(ml/kg)
OD
VO2
X 100
3"
CD
■CDD
O
Q.
C
a
o
3
■D
0.5
62 ±11
6 ±0.6
11
1.0
93 ±23
11 ±0.3
16
92 ±18
15 ±0.5
18
2.0
189 ±52
25 ±0.7
23
175 ±16
23 ±2,0
15
3.0
302 ±66
35 ±3.0
15
398 ±70
51 ±4.0
18
4.0
321 ±44
48 ±2.0
17
374 ±47
50 ±4.0
17
475 ±59
74 ±8.0
17
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5.0
cn
cn
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13
ra te o f the animals used in these 3 minute dives was uniformly higher
than the average restin g ra te o f a l l the animals, thus increasing the
calculated oxygen debt.
The r a t io between oxygen debt and post-dive excess oxygen con­
sumption indicates th a t proportion o f the post-dive excess oxygen con­
sumption used to pay o f f the restin g oxygen debt during the dive and
corresponds to the shaded sections in Figure 2.
considerably (see Appendix 2 ).
This percentage varies
However, the mean percentages fo r var­
ious dive times range from only 11% to 23% (Table 1 ).
These mean
percentages fo r d if f e r e n t dive times fo r both restrained and unrestrained
dives are not s t a t i s t i c a l l y d if f e r e n t ( p > 0 . 0 5 ) (Table 2 ) .
Also the
mean percentage o f a l l the restrained dives (16.8%) is not s t a t i s t i c a l l y
d if f e r e n t from th a t (16.9%) o f a l l the unrestrained dives (Fs = 0 .0 2 ,
d f = 1 /5 1 , p > 0 . 0 5 ) .
I t is evident th a t post-dive excess oxygen con­
sumption is considerably g reater than the oxygen debt incurred during
the dive assuming resting conditions and th a t the r a t io o f oxygen debt
to post-dive excess oxygen consumption is independent o f dive time or
type o f dive.
Post-dive Excess Oxygen Consumption versus Dive Time
As previously s ta te d , the post-dive excess oxygen consumption
increased with longer dives (Table 1 ).
in Figure 3.
This re la tio n s h ip is also shown
A weighted regression lin e f i t t e d to the data and passing
through the o rig in is described by the equation Y = 92X where Y is the
post-dive excess oxygen consumption in m i l l i l i t e r s per kilogram body
mass and X is the dive time in minutes.
This regression explains 82%
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
7}
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O
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g
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M
I
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1
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Table 2: Analysis of variance of the mean percentage of Vog accounted
for by OD at d iffe re n t dive times and for both restrained and
unrestrained dives. Abbreviations as defined in Table 1.
Percentages were transformed before completing the s ta tis t ic a l
analyses. Method of Sokal & Rohlf, 1969.
c5'
3
CD
Restrained
Unrestrained
C
p.
3
"
CD
Source of Variation
■CDo
Dive Time
a
Error
I
C
o
3
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o
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cn
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3
df
MS
4
58.07
26
73.90
Fs
0.79
df
MS
Fs
4
5.99
0.14
41
42.97
Figure 3: Relationship between post-dive excess oxygen con­
sumption and dive time fo r restrained dives. The
regression is described by Y = 92X. Method fo r
weighted regression through the origin from Steel
& T o rrie , p. 179 (I9 6 0 ).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
15
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16
o f the v a ria tio n in Y and is highly s ig n if ic a n t (Fs = 136.92, d f = 1/3 0 ,
p < 0 .0 0 1 ) .
A te s t of the hypothesis th a t the l in e passes through zero
yielded a Fs value o f 3.07 (d f = 1/2 9, p ;>0.05) in d ica tin g th at the lin e
does pass through zero.
Figure 4 shows the same re la tio n s h ip between mean excess oxygen
consumption and dive time but fo r unrestrained dives.
The weighted re ­
gression lin e through the o rig in is explained by the equation, Y = 93X.
The regression explains
87% o f the v a ria tio n in Y and is highly
s ig n if ic a n t (Fs = 304.64, d f = 1/4 5 , p < 0 . 0 0 1 ) .
Again, the assumption
th a t the regression lin e passes through zero is v a lid (Fs = 0.0 8,
d f = 1 /4 4 , p > 0 . 1 ) .
The slopes o f these two regression lin e s are not s ig n if ic a n t ly
d if f e r e n t (T = 0 .1 0 , d f = 75, p -> 0 .5 ), in d icatin g th at fo r equal length
dives the excess oxygen consumption is s t a t i s t i c a l l y the same fo r both
unrestrained and restrained diving muskrats.
Recovery Time
The to ta l number o f minutes required fo r recovery from each
dive are shown in Appendix 3.
Recovery was assumed to be complete when
the oxygen consumption had reached the pre-dive level or a t le a s t to
w ith in 24% above th a t le v e l.
The recovery time was variable and general­
ly increased with increasing dive time (Table 3 ).
For equal length dives
the number o f minutes to recovery is s ig n if ic a n t ly greater fo r r e ­
strained dives than fo r the unrestrained dives.
T -te s ts were performed
on the four dive times fo r which both restrained and unrestrained data
were a v a ila b le .
For 1 minute, 2 minute, 3 minute, and 4 minute dives
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 4: Relationship between post-dive excess oxygen con­
sumption and dive time for unrestrained dives. The
regression is described by Y = 93X. Method fo r
weighted regression through the o rigin from Steel &
T o rrie, p. 179 (1960).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
17
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Table 3: Mean total recovery time in minutes for each dive
time, both restrained and unrestrained dives.
Values are means ± one standard error of the mean
8
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1
3
Dive Time
(min)
Restrained Dives
(min)
Unrestrained
(min)
CD
3.
3
0.5
18.25 ±3.14
"
CD
1.0
23.00 ±2.57
14.30 ±2.25
■CDD
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2.0
33.80 ±5.83
19.75 ±1.16
3
3.0
52.20 ±8.47
31.30 ±4.74
4.0
44.90 ±5.71
30.60 ±3.36
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the p r o b a b ility th a t the recovery time f o r restrained dives was greater
than th a t fo r unrestrained merely by chance was less than 0.05; 1 minute
dives ( t
=2 .5 5 , d f = 1 0 ), 2 minute dives ( t
= 2 .3 7 , d f = 1 4 ), 3 minute
dives ( t
=2 .3 2 , d f = 1 4 ), 4 minute dives ( t
= 2 .2 6 , d f = 18).
Estimated Oxygen Stores
The estimated oxygen stores fo r each animal used in the l a c t ic
acid experiments are summarized in Table 4.
Oxygen stores include oxygen
in the lung, blood oxygen, and oxygen bound to myoglobin in the muscle.
The oxygen a v a ila b le in the lungs was estimated using S tah l's (1967)
equation fo r to ta l lung capacity (TLC = 53.5M l.06) where M is the mass
in kilograms.
The fra c tio n a l concentration o f oxygen in the lung was
assumed to be 14%.
Oxygen stores in the blood were estimated from blood
volume and the oxygen capacity o f the blood. The blood
volume o f musk­
rats was determined by Irv in g (1934) to be 10% of t h e i r body mass and
the oxygen capacity o f t h e i r blood is 25 ml/100 ml blood ( I r v i n g , 1939).
Of th is to ta l blood volume, one th ir d was assumed to be a r t e r ia l and
95% saturated, the remaining two th ird s to be venous with an oxygen
saturation 5 vol% less than the a r t e r i a l blood (Lenfant, et al_, 1970).
Robinson (1939) estimated th a t 35% o f the body weight in seals
was muscle, but 40% was chosen in th is case as muskrats have less
blubber than do seals.
Muscle myoglobin content was estimated a t 2% o f
the wet weight o f the muscle, a fig u re close to actual measurements ob­
tained from penguins (Weber, ejb
1973) and from sea o tte r s , but lower
than those obtained from seals (Lenfant, e t a%, 1970).
The oxygen-
combining a b i l i t y o f myoglobin is 1.34 ml 02/g myoglobin (Robinson, 1939)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
73
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(g
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Table 4; Estimated oxygen stores fo r each muskrat used in the la c tic
acid experiments. See text for specific information on how
stores were estimated.
CD
8
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O
3
CD
teriment
Animal Mass
(kg)
Lung
(ml)
Oxygen Stores
Blood
Muscle
(ml)
(ml )
Total Oxygen
Stores (ml)
la
0.847
5.3
17.3
9.1
32.7
p.
2a
0.830
6.1
17.0
8.9
32.0
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3a
0.920
5.9
18.8
9.9
35.6
a
4a
1.197
9.1
24.5
12.8
46.4
5a
0.790
5.8
16.2
8.5
30.5
3
1.075
8.1
21.9
11.5
41.5
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21
L actic Acid
The l a c t i c acid concentration in the blood remained low
throughout the dive (Figure 5) in a l l instances except one.
A fte r a
dive there was an immediate increase in blood lev els o f l a c t ic acid.
Only 4 to 13% of the to ta l increase in l a c t i c acid following a dive
occurred during the dive (Table 5 ).
During the dive in which l a c t ic
acid concentration increased s u b s ta n tia lly , 70% o f the to ta l increase in
l a c t i c acid occurred during the dive.
Table 5 also shows the estimated amount o f oxygen th at would be
required to oxidize the accumulated l a c t ic acid a f t e r each dive.
The
to ta l amount o f l a c t ic acid (LA) per kilogram animal mass following a
dive was computed with the formula; 0.75 LAb = LA/kg given by Margaria,
e t _ ^ (1963) where LAb is the amount o f l a c t ic acid in grams per l i t e r
o f blood.
O n e -fifth o f th is to ta l l a c t i c acid is then oxidized to con­
v e rt the remaining 4/5 into glycogen (Scholander, 1940).
The amount of
oxygen required to e f f e c t th is oxidation can be calcu lated , since 3
moles o f oxygen are required to oxidize 1 mole o f l a c t ic acid (Margaria,
et
1933).
The re la tio n s h ip between the sum of the oxygen stores plus the
estimated amount o f oxygen used in the oxidation o f l a c t i c acid and
the t o ta l post-dive excess oxygen consumption is shown in Table 6.
In
a l l cases the oxygen stores plus oxygen used in the l a c t i c acid oxidation
was less than (39 to 90%) the t o ta l excess in oxygen consumption.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Figure 5: Oxygen consumption and blood le v e ls o f l a c t i c acid
before, during and a f t e r a 2.5 minute d iv e . (Exp. l a )
The increase in l a c t i c acid during the dive was assumed
to be l in e a r .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
22
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Table 5: Maximal la c tic acid (LA) concentration, percentage of to tal LA increase occurring
during the dive, grams LA removed in recovery, and oxygen required fo r removal of
LA for la c tic acid experiments.
8
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Experiment
Animal Mass
(kg)
Maximal LA
Concentration
(mg/lOOml blood)
7o LA Increase
During Dive
Grams LA
Removed
During Recovery
Oxygen Required
For Oxidation
of LA (ml)
la
0.847
114.67
12
0.73
108
2a
0.830
100.67
70
0.55
83
3a
0.920
142.43
13
0.91
136
4a
1.197
79.06
13
0.74
110
5a
0.790
142.03
13
0.66
97
3
1.075
125.32
4
0.79
119
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Table 6: Comparison of post-dive excess oxygen consumption and the oxygen
necessary for replenishing oxygen stores and removing la c tic acid.
%
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Experiment
U)
Post-dive Excess
Oxygen Consumption
(ml)
(2)
Oxygen Stores plus
Oxygen for la c tic acid
Oxidation (ml)
(2)
(l)
^ 100
{%)
la
192
141
73
2a
203
115
57
3a
251
172
68
4a
404
156
39
5a
141
128
90
3
194
161
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CHAPTER IV
DISCUSSION
Previous work by Scholander (1940) on seals and by Andersen
(1961) on a llig a t o r s indicates th a t the post-dive excess oxygen consump­
tio n is usually in s u f f i c i e n t to account fo r the oxygen debt incurred
during a dive i f i t is assumed th a t the pre-dive resting ra te is main­
tained throughout the dive.
seals struggled.
This is true even a f t e r dives in which the
Both authors suggested as a possible explanation th at
metabolism (as indicated by oxygen consumption) is reduced during a
dive.
A reduction in metabolism (as measured by reduced body tempera­
tu res ) during diving has a c tu a lly been observed by Scholander, e t al
(1942) in seals, by Jackson (1968) in the t u r t l e , Pseudemys s c r ip t a ,
and by Andersen (1959) in ducks.
However, not a l l diving animals respond to forced dives by re ­
ducing t h e i r
metabolic r a te .
Scholander (1940) found th at in penguins
the post-dive excess oxygen consumption was much g reater than the oxygen
debt incurred during the dive i f a restin g oxygen consumption ra te was
assumed fo r the period o f the d iv e , and the same re s u lt was obtained
when manatees were f o r c ib ly dived (Scholander & Ir v in g , 1941).
instances, the animals struggled during the dives.
In both
Muskrats' metabolic
25
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26
response to diving is s im ila r to th at o f penguins and manatees in th at
the post-dive excess oxygen consumption is 4 to 9 times greater than the
oxygen debt incurred, assuming a restin g oxygen consumption ra te during
the d iv e.
Struggling was never continuous but did occur p e rio d ic a lly
during some of the dives.
There are two possible explanations fo r a post-dive oxygen
consumption which is greater than expected.
The animals are e it h e r ,
not maintaining a re stin g oxygen consumption ra te during the dive or
the post-dive excess oxygen consumption is superimposed on an oxygen
consumption ra te which is g reater than the pre-dive oxygen consumption
r a te .
The factors th a t might increase oxygen consumption ra te during a
dive include a c t i v i t y , thermal stres s, and/or hormonal changes.
Hart
(1971) reports th a t the maximal possible oxygen consumption th a t can be
maintained fo r a t le a s t 20 minutes by a muskrat is 3.5 times t h e i r basal
oxygen consumption r a t e , but fo r shorter periods o f time, e.g . the
length o f these dives, i t is l i k e l y th a t they could maintain t h e i r oxy­
gen consumption ra te a t even higher lev e ls as is possible in humans (20
times normal fo r several minutes).
Yet, a c t i v i t y during the d iv e , in i t s e l f , cannot f u l l y explain
the la r g e r than expected post-dive oxygen consumption observed in musk­
ra ts .
In a number o f dives in which the animal remained e s s e n tia lly
motionless throughout the dive the post-dive oxygen consumption s t i l l
exceeded the oxygen debt, assuming a re stin g oxygen consumption rate
during the d iv e , by a fa c to r o f 2 to 8.
In addition to increases due
to the occasional a c t i v i t y , muskrats have been observed to have an
oxygen consumption ra te in water 1.18 to 1.3 times t h e i r oxygen con­
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
27
sumption ra te in a i r a t the same temperature (Shcheglova, 1964) which
may account fo r a portion o f the increase in oxygen consumption that is
apparent in muskrats even when there is minimal a c t i v i t y .
The only hor­
monal changes l i k e l y to be of any importance are those involved with the
release o f epinephrine.
This causes only a r e l a t i v e l y small increase in
metabolic ra te but i t also might contribute to the increase in oxygen
consumption during dives with minimal a c t i v i t y .
I t is l i k e l y th a t the
increases seen even with only minimal a c t i v i t y during the dive re s u lt
from a combination o f these fac to rs.
These same factors might also a f f e c t oxygen consumption a f t e r
a d iv e , but a c t i v i t y is minimal a f t e r restrained dives, and would prob­
ably not contribute g re a tly to an increase in oxygen consumption.
A fte r
unrestrained dives the animals did commonly groom, so th is a c t i v i t y
could r e s u lt in some o f the increase in oxygen consumption a f t e r unre­
strained dives.
Again, release o f epinephrine could cause a small por­
tio n o f any increase in oxygen consumption ra te .
Physical a c t i v i t y causes the greatest increases in oxygen con­
sumption ra te and while i t may not be able to account fo r a l l the excess
oxygen consumption a f t e r a dive i t probably accounts fo r the major part
of i t .
In the restrained dive experiments, th is physical a c t i v i t y oc­
curred during the dive whereas in the unrestrained dive experiments i t
was most l i k e l y a combination o f the swimming and post-dive grooming.
The major procedural d iffe re n c e between these restrained and
unrestrained dives was in the freedom o f movement allowed the animal.
The length o f the dive was regulated in both instances.
Because o f t h i s ,
any d ifferen ces observed between the restrained and unrestrained dives
should be due to the a c t i v i t y o f swimming, y e t the excess oxygen con­
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
28
sumptions a f t e r restrained and unrestrained dives of equal duration are
q u a n t it a t iv e ly s im ila r .
The increased a c t i v i t y o f the unrestrained
dives appears not to have affe cte d the magnitude o f the excess oxygen
consumption a f t e r the dive.
is not great in muskrats.
also in seals.
Apparently the energetic cost o f swimming
Kooyman,
al_ (1973) found th is to be true
Therefore, when measuring the magnitude o f the post-dive
oxygen consumption in muskrats, a restrained dive is a good approximation
o f the unrestrained s itu a tio n .
Although the excess oxygen consumptions a f t e r restrained and
unrestrained dives are q u a n tita tiv e ly s im ila r , there do appear to be
q u a li t a t i v e d iffe re n c e s .
The ra te a t which th is excess oxygen is con­
sumed a f t e r restrained dives is slower than the ra te a t which i t is con­
sumed a f t e r unrestrained dives.
The recovery a f t e r a restrained dive
o f a muskrat shows the same c h a ra c te r is tic curve as th at obtained from
other diving mammals — an i n i t i a l rapid oxygen consumption ra te followed
by a lower slowly decreasing ra te u n til recovery is complete.
The re ­
covery curve of an unrestrained dive drops more quickly from the i n i t i a l
increase.
Recovery may possibly have been fa s te r a f t e r unrestrained dives
because o f the grooming a c t i v i t y th a t commonly took place a f t e r the dive.
Newman, ejb
(1936) found th a t the ra te of removal o f l a c t ic acid is
fa s te r a f t e r exercise i f some moderate level o f exercise is maintained,
thus the grooming may have aided in the recovery process.
The small amount o f l a c t i c acid th a t appears in the blood
during the dive in comparison to the amount which appears a f t e r the dive
in d icates th a t muskrats, l ik e other diving animals, e x h ib it c ir c u la to r y
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
29
adjustments which is o la te the muscle masses during a d iv e , reserving
oxygen f o r less to le ra n t tissues such as brain and heart.
There is disagreement in the l i t e r a t u r e as to what fra c tio n of
the accumulated l a c t i c acid formed anaerobically is a c tu a lly oxidized to
provide the energy fo r the resynthesis o f the remaining l a c t i c acid into
glycogen.
Meyerhof (1927) determined th is fra c tio n to be 1/3 to 1/6.
Scholander (1940) used 1/5 and th a t fra c tio n was used in th is study also.
Other authors have proposed using 1/10 (Margaria, e;t
(M argaria, e t al_, 1963).
1933) or 1/13
When using one o f these fra ctio n s o f the to ta l
l a c t i c acid to estimate the amount o f oxygen necessary to e f f e c t the
removal o f the l a c t i c ac id , the assumption is made th a t a l l the l a c t ic
acid removed is converted to glycogen.
not tru e .
There is evidence th a t th is is
Stainsby & Welch (1966) and Freyschuss & Strandell
observed the uptake o f l a c t i c acid by muscle in s i t u .
(1967) have
Lactic acid is
also removed from the coronary a r t e r i a l blood in q u a n titie s th a t suggest
th a t i t is u t i l i z e d as an energy source by the heart (McGinty & M i l l e r ,
1932).
The sum o f the oxygen stores and the oxygen necessary fo r l a c t i c
acid oxidation was always less than the actual post-dive excess oxygen
consumption (Table 6 ) .
A v a ria b le n o n -la c tic acid debt appears to e x is t
in muskrats but i f a g reater percentage o f the l a c t i c acid was assumed
to be o xid ize d , the e n tire post-dive excess oxygen consumption can be
accounted fo r by oxygen stores plus oxygen necessary fo r l a c t i c acid
o xid a tio n .
The percentage o f the l a c t i c acid th a t had to be oxidized
to account f o r the e n tir e excess oxygen consumption varied fo r the six
dives performed ( l a , 29%; 2a, 42%; 3a, 32%; 4a, 65%; 5a, 22%; 3, 26%).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
39
Because o f the above d i f f i c u l t i e s in assessing th a t portion of the
l a c t i c acid accumulated during a dive th a t is a c tu a lly oxidized, i t is
d i f f i c u l t to make d e f i n i t e conclusions as to the presence or absence of
a n o n -la c tic acid debt in muskrats.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
CHAPTER V
SUMMARY
The extensive l i t e r a t u r e on the physiological adaptations to
diving does not include much information on semi-aquatic mammals or
on unrestrained animals.
Most o f the research on diving mammals has
been done using seals, animals accustomed to prolonged diving.
The
extent o f the adaptations to diving varies among d if f e r e n t diving an­
imals and probably r e fle c ts the diving habits o f the animal.
Muskrats
are medium-sized semi-aquatic mammals accustomed to dives o f short
duration.
This study examined the post-dive excess oxygen consumption
in muskrats and determined whether the n o n -la c tic acid oxygen debt
observed in seals is also present in muskrats.
Comparisons are also
made o f restrained and unrestrained dives to determine the e ff e c t o f
r e s t r a in t on an animal's physiological responses to diving.
Seven animals were used fo r a to ta l o f th irty -o n e restrained
dives.
Dives were performed with the animal secured on a board which
could be t i l t e d into the water.
in d uration.
Dives were 0 .5 , 1, 2, 3, or 4 minutes
Nine animals were used fo r a t o ta l o f f o r t y - s ix unre­
strained dives.
Unrestrained dives were performed in a large tank
31
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32
■V
w ith only one opening used fo r both an entrance and e x i t and
lasted 1, 2, 3, 4, or 5 minutes.
Dive time was regulated by opening
and closing the trapdoor over the opening to the tank.
During restrained diving experiments the animal's head was
covered by a p la s tic hood and during the unrestrained diving experi­
ments the animal sat in a whole body hood.
Room a i r was drawn through
these hoods and the fra c tio n a l concentration o f oxygen in the excurrent
hood a i r was continuously monitored with a paramagnetic oxygen analyzer
before and a f t e r each dive.
Oxygen consumption was calculated from
the fra c tio n a l oxygen concentration data.
Lactic acid lev els were
determined in blood samples which were taken from the muskrat's femoral
a r te ry before, during, and a f t e r six d if f e r e n t restrained dives.
Body
oxygen stores were estimated from the l i t e r a t u r e .
The post-dive excess oxygen consumption a f t e r a l l dives was
greater than the oxygen debt incurred assuming maintenance o f the pre­
dive oxygen consumption ra te .
This indicates e it h e r an increased
oxygen consumption ra te during the dive or a f t e r the dive.
The in ­
crease in the oxygen consumption ra te in restrained experiments prob­
ably occurs during the dive and is due p a r t i a l l y to in te rm itte n t
strug g lin g.
The increase in unrestrained experiments probably occurs
both during the dive (swimming a c t i v i t y ) and a f t e r the dive (grooming).
The post-dive excess oxygen consumption increased with longer
dives a f t e r both restrained and unrestrained dives.
Regression of
post-dive excess oxygen consumption on dive time re su lts in s t a t i s t i c a l ­
l y equal regression equations f o r restrained and unrestrained dives.
This indicates th a t the a c t i v i t y o f swimming is not e n e rg e tic a lly
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
33
co s tly fo r muskrats and th a t r e s t r a in t has no q u a n tita tiv e e f f e c t on
the post-dive excess oxygen consumption.
However, there appears to be
a q u a lit a t iv e d ifferen ce between restrained and unrestrained dives in
th a t the to ta l time to recovery is always shorter a f t e r unrestrained
dives than a f t e r restrained dives o f the same duration.
Comparison o f the volume o f oxygen necessary to replenish
the oxygen stores plus the l a c t i c acid oxidation oxygen and the actual
post-dive excess oxygen consumption suggests a n o n -la c tic acid debt
in muskrats but, because o f the disagreement in the l i t e r a t u r e as
to the fra c tio n o f the l a c t i c acid which is oxidized in recovery, no
d e f in it e conclusions can be made as to the existence o f a n o n -la c tic
acid oxygen debt in muskrats.
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34
APPENDIX 1
Flow system u t i l i z e d fo r oxygen consumption
measurements.
VR is a vacuum re g u la to r and
\ y is a flowmeter.
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35
<
a.
z>
=)
X
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
36
APPENDIX 2
Post-dive excess oxygen consumption (V0 2 ) , oxygen
debt (OD), and percentage o f V02 accounted fo r
by OD fo r each d iv e , both restrained and unre­
re strain e d .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
37
Restrained Dives
Dive Time
(min)
VO?
(ml/Rg)
0.5
0.5
0.5
0.5
0.5
0.5
51
38
59
114
63
48
5
6
6
9
5
7
10
16
10
8
8
15
1 .0
1.0
1.0
1.0
1.0
1.0
31
70
62
171
157
66
10
10
11
10
11
12
32
14
18
6
7
18
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
31
315
110
161
488
82
176
151
22
27
25
25
27
23
26
23
71
9
23
16
6
28
15
15
3.0
3.0
3.0
3.0
3.0
483
241
389
299
97
30
44
33
41
29
6
18
9
14
30
4.0
4.0
4.0
4.0
4 .0
4.0
286
421
245
482
286
205
44
43
54
43
56
50
15
10
22
9
20
24
02 Debt
(ml/kg)
02 Debt
100
V02
^
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38
U n r e s tr a in e d D ives
Dive Time
(mi n )
V02
(ml/kg)
O2 Debt
(ml/kg)
02 Debt
X 100
V02
1 .0
1.0
1.0
1.0
1.0
1.0
79
72
63
,180
66
93
16
13
16
15
14
14
20
18
25
8
21
15
2.0
2.0
2.0
2.0
2 .0
2 .0
2.0
2.0
174
137
191
178
154
220
244
100
20
27
22
22
17
22
26
31
12
20
12
12
11
10
11
31
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
577
343
699
853
249
134
326
202
317
173
509
57
74
34
35
60
44
49
37
67
62
39
10
22
5
4
24
33
15
18
21
36
8
4.0
4.0
4.0
4.0
4 .0
4 .0
4 .0
4 .0
4.0
4 .0
4 .0
4.0
4.0
4.0
291
360
243
225
162
224
554
496
169
310
339
687
578
583
57
57
41
50
54
52
44
49
51
50
48
44
51
53
20
16
17
22
33
23
8
10
30
16
14
6
9
9
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
39
U n r e s tr a in e d D ives ( c o n t . )
Dive Time
(min)
V02
(ml/kg)
5.0
5.0
5.0
5.0
5.0
5.0
5.0
784
338
552
452
333
452
414
02 Debt
(ml/kg)
59
56
52
59
97
94
99
02 Debt ..
V02
^ 100
8
17
9
13
29
21
24
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40
APPENDIX 3
Recovery time in minutes fo r each re strain e d
and unrestrained d ive.
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41
R e s tra in e d
U n re s tra in e d
Dive Time
(min)
Recovery
Time
Dive Time
(min)
Recove
Time
0.5
0.5
0.5
0.5
0.5
0.5
32
11
13
19
21
15
1.0
1.0
1.0
1.0
1.0
1.0
11
13
9
23
12
19
1.0
1.0
1.0
1.0
1.0
1 .0
18
29
20
30
27
15
2.0
2.0
2.0
2 .0
2.0
2.0
2.0
2 .0
26
55
27
22
62
14
35
31
2.0
2.0
2.0
2.0
2.0
2 .0
2 .0
2 .0
18
17
27
22
22
17
18
19
3.0
3.0
3.0
3.0
3.0
58
47
74
59
23
3.0
3.0
3.0
3 .0
3.0
3.0
3.0
3 .0
3 .0
3 .0
3.0
45
24
42
66
20
14
28
21
29
14
42
4.0
4.0
4.0
4.0
4 .0
4.0
40
45
32
67
56
31
4 .0
4 .0
4 .0
4 .0
4 .0
4.0
4 .0
4.0
4 .0
4.0
4 .0
4.0
4.0
4 .0
25
25
24
18
18
17
51
42
18
28
33
54
42
37
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42
U n re s tra in e d
Dive Time
(min)
Recovery
Time
5.0
5 .0
5 .0
5.0
5 .0
5 .0
5 .0
64
27
38
34
23
25
33
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43
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