Clinical Science and Molecular Medicine (1978), 55,125-128
SHORT COMMUNICATION
Revised standards for normal resting dead-space volume
and venous admixture in men and women
E. A . H A R R I S , E V E R . S E E L Y E A N D R . M . L. W H I T L O C K
Clinical Physiology Department, Green Lane Hospital, Auckland, New Zealand
(Received 19 October 1977; accepted 18 April 1978)
Summary
1. Data have been combined from three previous series to provide revised standards for the
prediction of physiological dead-space volume
(V,), arterial oxygen tension (Pa,o,), alveolar-toarterial oxygen-tension difference (FA,O; - Pa,oJ
and venous admixture fraction (Qva/Qt) in the
sitting position.
2. These standards, based on measurements in
96 healthy men and women aged from 20 to 74
years, largely confirm conclusions drawn from the
first series of 48 subjects.
3. V, is best predicted on age, height, tidal
volume and the reciprocal of respiratory frequency.
Pa,o, PA,^, - Pa,oJ and Qva/Qt are adequately
predicted on age alone.
Key words: alveolar oxygen, dead space, oxygen,
venous admixture.
Introduction
Equations for the prediction of normal dead-space
volume and venous admixture in the sitting
position, based on data for 24 men and 24 women
aged 20-73 years, were presented by Harris,
Hunter, Seelye, Vedder & Whitlock (1973) and
Harris, Kenyon, Nisbet, Seelye & Whitlock (1974).
Since then, similar studies have been made on 24
healthy subjects at rest and on exercise (Bradley,
Harris, Seelye & Whitlock, 1976; Harris, Seelye &
Whitlock, 1976) and on 24 subjects in the sitting
and supine positions (Rae, Withy, Seelye & Harris,
1977), so that values are now available in 96
healthy men and women in the sitting position. We
have analysed this material and now present
revised standards for the prediction of physiological dead-space volume ( V,), arterial oxygen
tension (Pa,oJ, alveolar-to-arterial oxygen-tension
difference (PA,o,
Pa,o,) and the venousadmixture fraction (Qva/&) when air or oxygen is
breathed.
Methods
These were described in detail in the papers cited
above. Sixteen men and 16 women in each of the
age groups 20-30, 39-51 and 60-74 years were
studied, seated comfortably, breathing air or 0, in
the steady state. Inspired and expired gas concentrations of 0,, N, and CO,, expired gas
volumes and respiratory frequency were measured
during two consecutive 3 min periods; during the
second minute of each, 5 ml of arterial blood was
drawn evenly into a heparinized glass syringe from
a radial artery catheter. Complete calculations
were made for each 3 min period, and since no
systematic difference was found between these
duplicates all results were expressed as their mean
value. Dead-space volume was calculated from
the modified Bohr equation:
V , = VT (Pa,co, - PE,coJ/Pa,coz
where V, is dead-space volume (ml), V, tidal
volume (ml) and Pa,coz and PE,coZare respectively arterial and expired-gas CO, tensions (kPa).
In each case, two values for V , were calculated,
one from Pago, expressed at the patient’s oral
temperature and one at 0.8OC higher than this, as
an estimate of pulmonary capillary temperature
(Edwards, Velasquez & Farhi, 1963), which has
been shown to be relevant to V , measurement,
especially during exercise (Bradley et al., 1976).
Correspondence: Dr E. A. Harris, Clinical Physiology
Department, Green Lane Hospital, Auckland, 3, New Zealand.
125
126
E. A . Harris, Eve R . SeeIye aHd R . M. L . Whitlock
Alveolar 0, tension (PA,o,) was calculated for
air-breathing from the alveolar gas equation:
PA,o,= P,,o, - Pa,co, [F,,o, + (1 - FI,o,)lRl
where P,,o, and FI,02are respectively inspired 0,
tension and concentration and R is the gasexchange ratio. When 0, was breathed, Pa,o, Was
taken as
0.9973 (P,
-
6.27) - Pa,co, kPa [O.9973(PB47) - Pa,co, mmHg1
where P, is barometric pressure and 0.9973 the
mean inspired 0, concentration. If during 0,breathing, expired N, concentration ( F E , ~ , )was
greater than 0.0050, P1,o2 was taken as (1 FE,NZ)(PB - 6.27) kPa [I - FE,N2)(PB - 47)
mmHg].
Venous admixture was calculated from the
kquation:
(jva/Qt = (C’C,O~- ca,oj/[(C’c,o, - ca,o21 +
(Ca,o, - CV,o,)l
where C ‘ C , ~ ,and Ca,o, are respectively endpulmonary-capillary and arterial 0, content
[determined from PA,o, and Pa,o, by Kelman’s
(1966) subrodtinel and CC,o, is the mixed-venous
0, content; (Ca,o, - CT,oJ was assumed to be
50 mill.
These experiments yielded, for V,, 96 mean
values when Greathing air and 96 on 0,,and, for
Pa,Oj, (PA,O, - Pa,oJ and Q v a l b , 96 values on
air and 95 ori 0, (one set of data on 0, was
rejected because of gross contamination of the
inspired 0, with air). Since there was no systematic
air - 0, difference in V,, all 192 values were
combined for analysis.
Statistical analysis
Pa,o,, ( P A , 0 2 - Payo,) and Qva/Qt are adequately predicted by age alone for both sexes
combined (Harris et al., 1974). Only air-brehhing
Pa,o, is distributed homoscedastically on age;
limits were calculated from the standard deviation
about regression. Clinically only a low Pa,o, is of
interest, and single-sided limits are therefore used.
Analysis of VD was by multiple regression
(Daniel 8c Woods, 1971)on various combinations
and transformations, as independent variables, of
age, height, CO, output, ventilation and respiratory
frequency, a PDP8-E computer being used.
Goodness of fit and the relevance of each predictor were judged from the multiple correlation,
residual standard deviation, partial regression
coefficients and the effect on V Dof changing eaeh
predictor by four times its standard deviation.
Confidence limits are given as 95, 99 and 99.9%
intervals above the regression plane.
Results
Gas tensions are given in kPa (with mmHg in
parentheses), age in years, height in cm and
volumes in ml.
Dend-space volume
The most satisfactory of 1 1 regressions tested
was that on age, height, tidal volume and reciprocal
of frequency. Four of the 192 measured values of
Vd fell persistently beyond 3 SD from regression;
these four were excluded as probable errors and the
regression was recalculated. Detailed results have
been deposited as Clinical Science and hfolecular
Mkdicine Table nos. 7817 and 8 with the Librarian,
Royal Society of Medicine, Wimpole Street, Londan W J M SAE, from whom copies can be
obtained on request. The recommended equations
are:
Referred to oral temperature
VD = 0.859 (age) + 1-32(height) + 0.264 V , 905lf - 179, n 188, Ry,l,34 0-8640,sy1,23426-01
ml, confidence intervals 43, 61 and 82 ml above
regression.
Referred to ‘pulmonary-capillary’ temperature
VD = 6.834 (age) + 1.26 (height) + 0.296 8791f - 174, n 188,Ry,12340.8926, sy,,234 24.86
ml, confidence intervals 41, 58 and 78 ml above
regression.
vT
These equations are valid for both sexes aged
20-74 years, V, up to 900 ml and f up to 25
breathslmin. n is the number of data sets, Ry1,234
the multiple correlation and syl1234
the residual SD
about regression. All regression coefficients are
highly significant (2P < 0.001).
Venous admixture
The individual data have been deposited as
described above. Table 1 shows mean values and
SD Of Pa,02,(PA,02 - Pa,O,) and &a/@ in each of
the three age-groups, breathing air and breathing
oxygen.
Apart from Pa,o, breathing air, the variance
increases significantly ( P < 0.01 by Ptest) with
age; in other words the distribution with age is
heteroscedastic. Since some of the individual values
-
Normal dead-space and venous admixture
127
TAELE1. Arterial oxygen pressure ,(Pa@,), alveolar to arterial oxygenpressure di~erence(PA@, - Pa,o,) and venous-admixture
fraction (QvafQt) in 96 healthy men and women, seated, breathing air and breathing oxygen
Pa@, and PA,o~
- Pa,o, are expressed in kPa (values in parentheses are mmHg); QvalQt values are percentages.
Breathing 0,
Breathing air
Pa,o,
Age 2&30 years
No. of subjects
Mean
SD
Age 39-5 1 years
No. of subjects
Mean
SD
Age 59-74 years
No. of subjects
Mean
SD
PA,o,- Pa,o,
QvaIQt
pa,o,
PA,O, - ~ a j o ,
QvaIQt
32
86.11
(645 * 88)
2.512
(18.84)
32
3.25
(24.3 8)
2.094
(15.7 1)
32
1.48
31
82.95
(622.18)
3.781
(28.36)
31
6.22
(46.65)
3.943
(29.57)
31
2.76
32
80.78
(605.90)
5.416
(40.62)
32
8.29
(62.18)
5.393
(40.45)
32
3.65
32
13.22
(99.16)
1.028
(7.71)
32
0.756
(5.67)
0.673
(5.05)
32
1.28
32
12.36
(92.7)
1.031
(7.73)
32
1.47
(11.03)
0.797
(5.98)
32
2.96
32
11.55
(86.63)
1.144
(8.58)
32
2.45
(18.38)
1.107
(8.30)
32
4.98
1.095
1.915
of (PA,o, - Pa,oJ and Qva/Qt were negative, a
logarithmic transformation (which might have
achieved homoscedasticity) was impossible. A
straightforward regression analysis *as possible,
therefore, only in the case of Pa,o, breathing air.
This gave:
Pa,o, = 14.1 - 0.390 (age) kPa [Pao, = 105.8
- 2.925 (age) mmHg1, n = 96, r = -0.5352, sy.x
= 1.07 kPa (8.03),confidence limits 1-78, 2.53
and 3.41 kPa (13.35, 18-98 and 25-58 mmHg)
below regression.
Qva/Qt alters little when gas tensions are
expressed at ‘pulmohary capillary’ temperature
(Harris et al., 1976). For predictive purposes the
oral reference temperature is adequate.
Discussion
We explored many more combinations of independent variables for predicting VD than previously
(Harris et al., 1973), yet the present andysis
confirms our original choice. The regression
parameters have changed a little but the confidence
intervals are practically the same. All regressions
examined showed marginally better fits when VD
was referred to ‘pulmonary capillary’ temperature.
This may mean that it is the truer estimate, but it
seems to offer little predictive advantage for resting
2.641
0.939
1.736
2.272
For prediction they recommended a multiple
regression equation on age and PA,o?The present
results show, for a subject of 45 years, a 95%
interval of 1.78 kPa (13.35 mmHg) for Pa,o, and
of 1.46 kPa (10.95 mmHg) for (PA,o, Pa,o j,
bearihg out the results of Gillies et al. (1977). It
probably matters little whether predictioll is made
of (PA,o, - P a , o j on age, we have dofib, or of
Pa,o, on age and PA,o,.
However, in practice, the data needed to calculate
PA,o, are usually not available and a prediction on
age alone is helpful.
It is emphasized that the data when breathing 0,
are for normal, not deep, breaths after at ieast 15
min of 0,-breathing, with expired N, concentration
below 1%. While this is a fairly common procedure
for which a prediction is useful, it does not measure
anatomical venous shunt (Harris et al., 1976).
Acknowledgments
We thank our subjects, the staff of the Clinical
Physiology Department over several years and Mrs
Joan Findlay for indispensable support. The work
was supported by a grant to E.A.H. from the
Medical Research Council of New Zealand.
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