Clinical Science (2003) 105, 683–689 (Printed in Great Britain)
Myogenic, mechanical and structural
characteristics of resistance arterioles from
healthy and ischaemic subjects
P. COATS
Department of Physiology and Pharmacology, University of Strathclyde, Taylor Street, Glasgow G4 0BA, Scotland, U.K.
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In critical limb ischaemia (CLI), the ability to regulate regional blood flow in the diseased portion
of the leg would appear to be severely compromised. Considering this, pressure-dependent
myogenic and mechanical properties of resistance arterioles isolated from control subjects
and from patients with CLI were studied. Using confocal microscopy and pressure myography,
subcutaneous resistance arteriole structure and function were compared between subcutaneous
arterioles isolated from healthy volunteers [control subcutaneous (CS)] and non-diseased proximal
subcutaneous (PS; internal control) and distal subcutaneous (DS) arterioles from the diseased
ischaemic part of the limb from patients with CLI. Significant wall atrophy was observed in DS
arterioles compared with PS and CS arterioles. Passive pressure-dependent mechanical properties
were significantly altered in the diseased arterioles compared with PS and CS arterioles. Active
pressure-dependent myogenic tone was completely absent in DS arterioles. The atrophic structural
remodelling in DS arterioles were correlated with the changes in vascular mechanics, but not with
the ability of these arterioles to contract in response to chemical stimuli. However, active pressure-dependent myogenic tone was absent in the DS arterioles. The combination of altered
pressure-dependent passive mechanical and active myogenic tone goes some way in explaining CLI
sequelae and poor outcome following surgical revascularization experienced by these patients.
INTRODUCTION
The fundamental function of arterioles is to maintain constant blood flow, independent of blood pressure (BP), to
the capillary beds, thus maintaining optimal pressure/
flow relationship and promoting maximal blood gas/
nutrient exchange. An optimal pressure/flow relationship
is maintained predominantly by arteriolar pressuredependent myogenic activity [1,2].
The myogenic component of vascular tone refers to the
correlation between intraluminal pressure and pressuredependent tone [3]. This property, commonly found
in arterioles < 150 µm in diameter, has been studied
extensively and is considered to be the major determinant
of peripheral vascular resistance and regulator of regional
blood flow [1]. For example, the increased vascular
resistance in hypertension has been attributed, in part,
to an increase in myogenic vascular tone [4]. Whether
this is a consequence or a cause of the hypertensive state
remains to be elucidated.
Critical limb ischaemia (CLI) is an advanced state of
peripheral vascular disease that severely compromises
limb functionality and survival. CLI is by definition
a state of hypopressure/hypoperfusion, nonetheless approx. 70 % of patients with CLI present with oedema
confined to the distal ischaemic portion of the affected
leg(s) [5,6]. In many CLI subjects, elevation of the feet
results in capillary collapse and ‘pallor’ of the distal
ischaemic part of the limb [7]. Conversely, on standing,
blood drains unimpeded into the capillary beds of the
Key words: blood pressure, microcirculation, regional blood flow, remodelling.
Abbreviations: BP, blood pressure; CLI, critical limb ischaemia; CS, control subcutaneous; DS, distal subcutaneous; PS, proximal
subcutaneous; PSS, physiological saline solution.
Correspondence: Dr Paul Coats (e-mail [email protected]).
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lower limb [8–10]. Uncontrolled orthostatic-dependent
increases in blood hydrostatic pressure within the distal
portion of the limb are likely to contribute to oedema
development. Similarly, following surgical revascularization, post-operative leg oedema often develops. This
arises following the re-introduction of systemic BP to
the distal portion of the limb. Oedema formation in CLI
is a significant problem as it compresses the nutritive
skin capillaries and accelerates ischaemic necrosis and can
significantly contribute to bypass graft failure and impaired wound healing [8–10].
Considering the relative importance of myogenic
mechanisms of vascular control in the maintenance of
optimal BP/flow relationship, the aim of this study was
to compare both active and passive pressure-dependent
mechanisms of vascular tone in resistance arterioles
between subjects with CLI and age-matched controls.
METHODS
This study was performed in accordance with the declaration of Helsinki [11]. The Glasgow (U.K.) Hospitals
Ethics Review Committee approved this study, and each
subject gave written informed consent.
Control subjects
Twelve (five male and seven female) healthy volunteers
(age, 64 +
− 4 years) with no history of vascular disease,
diabetes or hypertension attended the Clinical Investigations Research Unit at the Western Infirmary, Glasgow
(Table 1). Subcutaneous gluteal fat biopsies (1.5 ×
1.5 × 0.5 cm) were excised under local anaesthesia with
1 % lidocaine and immediately transferred to ice-cold
physiological saline solution [PSS; 119 mM NaCl,
4.5 mM KCl, 25 mM NaHCO3 , 1.0 mM KH2 PO4 ,
1.0 mM MgSO4 ,7H2 O, 6.0 mM glucose and 2.5 mM
CaCl (pH 7.4)]. Resistance-size arterioles were isolated
and cleaned of any adherent tissue under a dissection
microscope (Zeiss Stemi 2000).
CLI subjects
Subcutaneous biopsies were obtained from 12 patients
(seven male and five female; age, 69 +
− 4 years) undergoing amputation for CLI at Glasgow Gartnavel Hospital
(Table 1). In each, CLI was clinically defined by persistently occurring rest pain and/or gangrene of the foot or
toes plus an ankle systolic BP < 50 mmHg and/or toe
systolic BP < 30 mmHg [12]. Immediately following amputation, paired 1 cm3 biopsies were isolated from proximal and distal subcutaneous (PS and DS respectively)
sites. PS biopsies were isolated approx. 2 cm below the
level of amputation. DS biopsies were isolated from
tissue directly inferior to the medial malleolus. Arterioles
isolated from the proximal portion of the amputated
leg represent non-ischaemic internal control vessels and
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Table 1 Clinical details of CLI subjects and controls
∗
Values are means +
− S.E.M. P < 0.05 compared with controls. †No current
plasma measures of serum cholesterol were available for these patients. NIDDM,
non-insulin-dependent diabetes mellitus; HMG-CoA: 3-hydroxy-3-methylglutaryl-CoA;
ACE, angiotensin-converting enzyme.
Parameters
Controls (n = 12)
CLI subjects (n = 12)
Sex (male/female)
Age (years)
Diabetic
Hypertension
Smoker
Creatinine (µmol/l)
Cholesterol (mmol/l)
Glucose (mmol/l)
Systolic BP (mmHg)
Diastolic BP (mmHg)
Drug therapy
ACE inhibitor
Ca2+ channel antagonist
Diuretic
Digoxin
Nitrates
Aspirin
HMG-CoA inhibitor
5/7
64 +
−4
0
0
0
91 +
− 1.7
5.1 +
− 0.2
5.5 +
− 0.2
131 +
−6
68 +
−3
7/5
67 +
−3
4 (NIDDM)
3
6
100 +
− 10.8
−†
9.4 +
− 3.1
∗
110 +
−6
64 +
−3
0
0
0
0
0
0
0
4
2
6
3
2
8
2
those isolated from the distal portion of the leg ischaemic
vessels. This is based on the clinical determination of the
amputation level being at a level where blood perfusion is
normal and complete and rapid healing of the stump can
be reliably predicted. Following removal, each biopsy
was immediately placed in ice-cold PSS and arterioles
were isolated using the same methodology for the control
arterioles.
Isolated arterioles were studied using techniques described previously [13]. Briefly, arterioles were mounted
on a Danish MyoTech P110 pressure myograph system
and secured with two 17 µm nylon sutures to sizematched microcannula. Following mounting, the vessel
lumen was flushed gently with PSS to remove any blood
or debris. A real-time image of the arteriole was captured by a high-resolution charge-coupled-device camera
attached to the microscope’s third ocular tube. The video
image was analysed using MyoView software (Danish
MyoTech), which used edge-detection algorithms to
measure external and internal (lumen) diameters and wall
thickness. Time, mean pressure, longitudinal force, temperature and manual interventions were also recorded.
Data were acquired at intervals of 1 s and recorded on an
IBM personal computer.
Functional studies
Arterioles were bathed in PSS and gassed with 20 %
O2 /5 % CO2 /75 % nitrogen, maintaining a pH of 7.4
at 37 ◦ C. At an intraluminal pressure of 40 mmHg,
Pressure-dependent arteriolar tone
functional viability was assessed by maximum vasoconstriction in response to 60 mM KCl-adjusted PSS
and noradrenaline (1 µM) and endothelium-dependent
relaxation in response to acetylcholine. All arterioles
fulfilled these criteria and none were discarded.
A non-cumulative concentration response was measured to a range of KCl-adjusted PSS concentrations
(4.5 mM, and 10–100 mM in increments of 10 mM). KCl
concentration was adjusted in the PSS from 4.5–100 mM
by equimolar substitution of NaCl for KCl.
Assessment of pressure-dependent
myogenic tone
Arteriolar myogenic responses were studied by increasing intraluminal pressure from 40–120 mmHg in
40 mmHg steps for a period of 5 min at each pressure
step. Previous studies [13] have shown that 40 mmHg
was below the threshold for myogenic activation in these
arterioles. Myogenic contraction consistently reached a
maximum within 30–60 s of the intraluminal pressure
step.
Assessment of vascular mechanics
Following myogenic protocols, the mechanical properties of the arterioles under study were assessed in a Ca2+ free PSS (PSS containing 1 mM EGTA). The intraluminal
pressure was reduced to 1 mmHg and arteriole diameter
was allowed to stabilize for 30 min before a pressure
curve was constructed. Intraluminal pressure was raised
incrementally from 1–120 mmHg, initially (from 1–
40 mmHg) in increments of 5 mmHg and thereafter
in increments of 10 mmHg. At each point along the
pressure curve, arteriole diameter was allowed to stabilize
for a period of 5 min before external diameter, luminal
diameter and wall thickness were measured.
Calculations of vascular mechanics
The pressure-dependent deformation ratio of incremental
distensibility was calculated from the observed change in
arteriole lumen diameter relative to the known increase
in intraluminal pressure using the following formula:
LD/(LD × IP) × 100
where LD is the change in lumen diameter (LD) of the
arteriole following a change in intraluminal pressure IP.
Circumferential stress (σ ), the force generated per unit
area of the arteriole wall as a product of pressure, was
calculated from the internal diameter of the arteriole using
the formula:
σ = (IP × LD)/(2WT)
where WT is wall thickness and IP is intraluminal
pressure.
Circumferential strain (ε), the fractional changes in
lumen diameter as a product of pressure, was calculated
from arteriole lumen diameter measurements using the
formula:
ε = (LD − Do )/Do
where Do is the original diameter, and 1 mmHg was
used as the original diameter in the calculation of ε. To
determine the intrinsic elastic properties of the arteriole
under study, the stress-strain data for individual arterioles
were fitted to an exponential curve (y = ae βε ) to obtain
the slope of the tangential elastic modulus versus stress
using the equation:
σ = σorig eβε
where σ orig is the stress at the original diameter (1 mmHg)
and β is the slope of the tangential elastic modulus.
Morphological measurements
A Noran Odyssey confocal laser-scanning microscope
was then used for in-depth structural as described previously [14]. Briefly, following the functional protocols,
the resistance arterioles were pressure-fixed with 10 %
(v/v) formaldehyde/PBS (pH 7.2 at 37 ◦ C) for 2 h.
Arterioles were then dismounted from the pressure
myograph and rinsed in distilled water to remove
formaldehyde/PBS, cut into segments of 2 mm and
stained with the nuclear dye propidium iodide (10 µg/ml)
for 1 h. MetaMorph 2.5 image-processing software
(Universal Imaging Corporation) was used to measure
wall thickness and lumen diameter and the different wall
layers (adventitia, smooth muscle and endothelium).
Drugs
All drugs and reagents were purchased from Sigma
(Poole, Dorset, UK) and all were prepared on the day
of the experiment and dissolved in distilled water.
Data and statistical analysis
Data are presented as means +
− S.E.M. Contraction data
in response to the vasoconstrictor agonist noradrenaline
are represented as percentage contraction relative to the
maximum contraction evoked by 60 mM KCl-adjusted
PSS. Sensitivity to KCl and noradrenaline (EC50 ) were
compared using Student’s t test. Comparison of cumulative concentration response curves and pressuredependent response curves were by ANOVA for repeated
measures. Passive pressure curve data are presented as
normalized values. Statistical significance was assumed if
P < 0.05. Statistical analysis of the data was performed
using Prism software (GraphPad).
RESULTS
Resistance arteriole morphology
Non-ischaemic arterioles isolated from the control
subjects and from the proximal part of the amputated
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Table 2 Morphological characteristics of subcutaneous
resistance arterioles isolated from control and CLI subjects
∗
Values are means +
− S.E.M. P < 0.05 when DS arterioles are compared with
CS and PS arterioles using Student’s t test. CSA, cross-sectional area.
Resistance arteriole
Morphological characteristics CS (n = 12)
Lumen diameter (µm)
Wall thickness (µm)
Wall CSA (µm2 )
Wall:lumen (%)
116
26
11 716
22
+
−
+
−
+
−
+
−
PS (n = 12)
4
121 +
−
1
27 +
−
906 12 515 +
−
1
21 +
−
Table 3 In-depth structural analysis derived from confocal
microscopy of subcutaneous resistance arterioles isolated
from controls and CLI subjects
∗
Values are means +
− S.E.M. P < 0.05 when DS arterioles are compared with
CS and PS arterioles using Student’s t test. CSA, cross-sectional area.
Resistance arteriole
DS (n = 12)
7
126 +
−9
∗
1
14 +
−1
∗
1134 6591 +
− 709
∗
1
12 +
−1
limb had similar morphological characteristics (Table 2).
However, the morphology of the arterioles isolated from
the diseased ischaemic part of the amputated legs was
significantly different when compared with both the
paired internal controls [proximal subcutaneous (PS)]
and the external control [control subcutaneous (CS);
Table 3]. In-depth structural analysis revealed that there
was a significant reduction in adventitia:lumen and
media:lumen ratios and cross-sectional areas of the DS
arterioles when compared with both the non-ischaemic
PC (internal control) and CS arterioles (Table 3). There
was no difference in the structure of the arterial wall in
PS arterioles when compared with the CS arterioles.
Structural analysis
CS (n = 12)
PS (n = 12)
DS (n = 12)
Adventitia:lumen (%)
Media:lumen (%)
Intima:lumen (%)
CSA
Adventitia
Media
Intima
5.5
11.8
2.5
+
− 1.2
+
− 0.8
+
− 0.3
5.8
11.3
2.2
+
− 0.7
+
− 1.1
+
− 0.3
2.1
6.0
2.9
∗
+
− 0.4
∗
+
− 1.3
+
− 0.9
3163
6593
1275
+
− 241
+
− 519
+
− 129
3315
6929
1272
+
− 307
+
− 612
+
− 201
1327
3132
1647
∗
+
− 214
∗
+
− 318
+
− 263
(Figure 1A). EC50 values were 24 +
− 2 mM, 26 +
− 2 mM
and 26 +
1
mM
respectively.
There
was
no
difference
in
−
the noradrenaline-mediated response measured in the CS
and PS arterioles. However, there was a significant attenuation in the response to noradrenaline in the DS arterioles
when compared with the response observed in both PS
and CS arterioles (Figure 1B). EC50 values to noradrenaline were 48 +
− 12 nM, 63 +
− 21 nM and 189 +
− 61 µM
respectively (P < 0.05, DS compared with CS and PS).
Functional studies
Responses to depolarization-dependent vasoconstriction
highlighted that there was no difference in the response
to KCl-adjusted PSS in CS, PS and DS arterioles
Active pressure-dependent responses
In response to an increase in intraluminal pressure, both
CS and PS arterioles constricted, displaying a classic
Figure 1 Response to cumulative addition of KCl-adjusted PSS (A) and noradrenaline (B) in PS, DS and CS arterioles
Values are means +
− S.E.M. CS, n = 12; PS and DS, n = 12 pairs.
measures (for the comparison of the curves). NA, noradrenaline.
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∗∗
P < 0.01 when DS arterioles are compared with CS and PS arterioles using ANOVA for repeated
Pressure-dependent arteriolar tone
step (contraction at 80–120 mmHg: 5 +
− 2 % and 7 +
−2%
for CS and PS respectively).
Passive pressure-dependent responses
Figure 2 Intraluminal pressure-dependent responses of CS,
PS and DS arterioles
∗
Values are means +
− S.E.M. CS, n = 12; PS and DS, n = 12 pairs. P < 0.05
when DS arterioles are compared with CS and PS arterioles using ANOVA for
repeated measures (for the comparison of the curves).
pressure-dependent myogenic constriction response
(Figure 2). However, DS arterioles failed to show any
active pressure-dependent myogenic activity (Figure 2).
In both CS and PS arterioles, the greatest myogenic
contraction was observed during the 40–80 mmHg
pressure step (contraction at 40–80 mmHg: 22 +
− 4 % and
16 +
5
%
for
CS
and
PS
arterioles
respectively).
Although
−
lumen diameter reduced in response to increasing the
intraluminal pressure from 80–120 mmHg, this was a
smaller contraction when compared with the myogenicinduced contraction observed during the 40–80 mmHg
Incremental distensibility, a direct measure of circumferential compliance, was significantly higher in DS
arterioles (Figure 3A). Both CS and PS arterioles displayed similar distensibility characteristics. The increased
compliance in the DS arterioles resulted in greater
pressure-dependent wall stress and circumferential strain
over the pressure range when compared with that for
both PS and CS arterioles. Plotting wall stress against the
circumferential strain clearly illustrates that DS arterioles
possessed distinct mechanical properties when compared
with those of PS and CS arterioles (Figure 3B). The stressstrain curve derived from DS arterioles was significantly
shifted to the right of the PS and CS arterioles. Also
a significant difference was observed in the tangential
elastic modulus (β: CS, 8.79 +
− 0.5; PS, 8.22 +
− 1.3; and
DS, 5.6 +
0.2;
P
<
0.05,
DS
arterioles
compared
with PS
−
and CS arterioles).
DISCUSSION
The fundamental function of resistance arterioles is to
control the flow of blood to the capillary beds, so that
an optimal pressure/flow relationship is maintained thus
promoting maximal blood gas and nutrient exchange to
the surrounding tissues. This is predominantly achieved
by a putative pressure-sensing mechanism, which stimulates a myogenic response in the vascular smooth muscle
[1,15]. In the present study, the pressure-dependent
differences observed in isolated arterioles from subjects
Figure 3 Relationship between incremental distensibility and intraluminal pressure (A) and stress-strain curves (B) in CS,
PS and DS arterioles
∗
Values are means +
− S.E.M. CS, n = 12; PS and DS, n = 12 pairs. P < 0.05 when DS arterioles are compared with CS and PS arterioles using ANOVA for repeated
measures (for the comparison of the curves).
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with CLI and control subjects can be described by
two different components of reactivity. The first is the
active myogenic response to increasing intraluminal
pressure, and the second is the passive mechanical
response. Subcutaneous resistance arterioles isolated
from the distal hypotensive portion of the ischaemic leg
display no myogenic properties whatsoever. Myogenic
vasoconstriction in response to an increase in intraluminal pressure is a fundamental response of the precapillary resistance arterioles. This response is thought to
regulate blood flow and pressure within the downstream
capillary beds. Many CLI patients display oedema and
uncontrolled orthostatic-dependent changes in fluid
volume within the distal portion of the diseased leg.
The absence of pressure-dependent myogenic tone in
resistance arterioles feeding the capillary beds in the
diseased portion of the leg may explain this observation.
The exact mechanisms underlying intrinsic myogenic
responses have yet to be fully determined [1]. Increases
in arteriolar wall tension/stress, resulting in a stretchdependent smooth muscle depolarization and activation
of membrane-bound enzymes, has been proposed as
the initiating event in arteriolar myogenic contraction.
Consequently, an increase in vascular smooth muscle intracellular Ca2+ and activation of second-messenger pathways culminates in myogenic contraction. With respect
to tension/stress being the primary event in a myogenic
response [1], in DS arterioles, wall stress/tension, as a
product of intraluminal pressure, was significantly greater
than that observed in PS and CS arterioles (Figure 3B).
This, however, did not result in an increase in sensitivity
to raised intraluminal pressure.
In the present study, there was no difference in the
KCl depolarization-mediated vasoconstriction in any
of the arterioles studied (Figure 1A). Voltage-sensitive
Ca2+ channels play a crucial role in myogenic responses
[16,17]. This observation indicates that voltage-sensitive
Ca2+ channel function and basic Ca2+ -dependent mechanisms of contraction are well preserved in the arterioles
isolated from the diseased portion of the leg. Pressuredependent myogenic vasoconstriction and noradrenaline-mediated vasoconstriction utilize similar cellular
signal transduction pathways [1,15]. The myogenic signalling pathway in human subcutaneous arterioles
involves phospholipase C (PLC)- and protein kinase C
(PKC)-dependent processes [13]. The response to noradrenaline in DS arterioles was marginally reduced
when compared with PS and CS arterioles (Figure 1B).
Significantly, this response to noradrenaline in DS
arterioles indicates that the signal transduction pathway
culminating in contraction is functional. Since the fundamental ability to contract, as measured by the response to
KCl, is intact and the common transduction pathway, as
measured by the response to noradrenaline, is functional,
the question arises as to why there is no myogenic re
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sponse whatsoever in DS arterioles? The myogenic
dysfunction observed is likely to be as a result of altered
mechanosensory activity. However, in the present study,
no attempt was made to investigate the primary pressure
sensing event, and clearly there is a need to investigate
this in a future study.
In the distal ischaemic arterioles, where the myogenic
response is absent, the sensory apparatus is presumably
severely impaired, because of the chronic period of
diminished BP (low circumferential stress) and blood
flow (low shear stress), resulting in reduced sensitivity
to intraluminal pressure changes. In hypertensive states,
the exact opposite effect has been reported [4,18].
Prolonged periods of hypertension (high circumferential
stress and high shear stress) would appear to increase
myogenic reactivity and sensitivity to an increase in
intraluminal pressure. However, increased pressure stimulus is unlikely to be the only factor involved. Hypertension is associated with hypertrophy and/or hyperplasia and, consequently, an increase in wall cross-sectional
area and wall:lumen ratio. Therefore an increased
myogenic response in hypertension may be a synergistic
consequence of chronic hypertension and the increased
muscle mass per unit area. In the distal ischaemic portion
of the leg, there is clearly arterial wall atrophy in
DS arterioles. If synergism between structure and wall
tension exists, then atrophy combined with ischaemia
could be a plausible explanation for the deficit in
pressure-dependent myogenic reactivity. However, the
data presented in the present study do not support this
hypothesis, as the ability of DS arterioles to contract in
response to KCl and, to a lesser extent, noradrenaline was
unaffected.
In the present study, arterioles isolated from the
diseased part of the leg can be associated with both
functional and structural adaptations to a period chronic
ischaemia. Pressure-dependent vascular wall stress and, to
a lesser extent, shear stress are recognized as the major determinants of vascular wall structure [19–22]. Therefore it
is not surprising that CLI arterioles isolated from the diseased part of the leg, a low-pressure environment, have reduced wall thickness, reduced cross-sectional area and
reduced wall:lumen ratio when compared with arterioles
isolated from the healthy part of the same leg (Tables 2
and 3). To date, there have been few studies on the effect
of reducing environmental stimuli such as BP and blood
flow on vascular structure and function and certainly
none in human subjects over an extended period.
The magnitude of intrinsic resistance to blood flow/BP
offered by an arteriole can be considered as the sum
of two discrete components: active pressure-dependent
myogenic tone and the passive pressure-dependent mechanical properties of the arteriole. The latter is largely
dependent on the structural properties of the arteriole.
In the present study, it has been clearly shown that
DS arterioles isolated from the diseased part of the
Pressure-dependent arteriolar tone
chronically ischaemic leg have undergone significant
structural remodelling (Tables 2 and 3). Also, it has been
shown that derangement of arteriolar wall architecture
has a direct consequence in terms of the passive lumen
diameter-pressure relationship (Figure 3). The ability to
resist pressure-dependent deformation in DS arterioles
exclusively depends on the structural properties, as
DS arterioles fail to generate any active pressuredependent myogenic tone. Consequently, the passive
resistance offered to changes in intraluminal pressure by
DS arterioles is insufficient to control blood flow/BP
to the downstream capillary beds. Extrapolation of
these observations to the in vivo situation would result
in excessive blood/flow within the delicate capillary
beds, increased blood hydrostatic pressure, impairment
of trans-capillary fluid exchange and oedema formation.
These observations go some way in explaining the clinical observation of uncontrolled orthostatic-dependent
changes in limb volume and post-operative oedema
formation in CLI patients.
In conclusion, the present study has compared the
active and passive properties of arterioles from healthy
control subjects with similar arterioles from patients
with peripheral vascular disease. Agonist- and KClmediated responses as well as active (myogenic) and passive (mechanical) properties have been studied and these
findings related to arterial structural characteristics.
The atrophied resistance arterioles from the diseased
ischaemic part of the leg have retained the ability to produce a contractile response to external chemical stimuli.
However, their ability to respond actively to changes
in intraluminal pressure, a fundamental property of
arterioles, is absent. This dysfunction is a consequence
of absent myogenic function and altered passive
mechanical properties, and this can be associated with a
functional and structural adaptation to the low-pressure
environment. The distal vasculature is able to accommodate the low-pressure environment with ease;
however, the increase in pressure that occurs following
surgical interventions such as angioplasty or bypass subsequently compromises distal vascular function. These
observations are important, since they provide an explanation for post-operative oedema development following
the return of systemic perfusion pressures after revascularization, which often leads to amputation in CLI
patients.
ACKNOWLEDGMENTS
I thank the vascular surgical teams at Glasgow Gartnavel
Hospital and Glasgow Royal Infirmary, Glasgow, U.K.
REFERENCES
1 Davis, M. J. and Hill, M. A. (1999) Signalling mechanisms
underlying the vascular myogenic response. Physiol. Rev.
79, 387–423
2 Mulvany, M. J. and Aalkjaer, C. (1990) Structure and
function of small arterioles. Physiol. Rev. 70, 921–961
3 Davis, M. J. (1993) Microvascular control of capillary
pressure during increase in local arterial and
venous pressure. Am. J. Physiol. 255, H772–H784
4 Dunn, W. R., Wallis, S. J. and Gardiner, S. M. (1998)
Remodelling and enhanced myogenic tone in cerebral
resistance arterioles isolated from genetically hypertensive
Brattleboro rats. J. Vasc. Res. 35, 18–26
5 Kinmonth, J. B. (1967) Investigation of chronic oedema of
the lower limb. Br. J. Surg. 54, 890–891
6 Khiabani, H. Z., Anvar, M. D., Rostad, B., Stranden, E. and
Kroese, A. J. (1999) The distribution of oedema in the
lower limb of patients with chronic critical limb ischaemia:
a study with computed tomography. Vasa 28, 265–270
7 Lowe, G. (1990) Pathophysiology of critical ischaemia. In
Critical Leg Ischaemia (Dormandy, J. A. and Stock, G.,
eds.), pp. 23–41, Springer-Verlag, London
8 McEwan, A. J. and Ledingham, I. M. (1971) Blood flow
characteristics and tissue nutrition in apparently ischaemic
feet. Br. Med. J. 3, 220–224
9 Dormandy, J. A., Nahir, M. and Ascady, G. (1989) Fate of
the patient with chronic leg ischaemia. J. Cardiovasc. Surg.
30, 50–57
10 Thomas, S. and Belli, A. M. (1998) Endovascular methods
of retrieving a failing graft. Crit. Ischaemia 8, 19–29
11 Declaration of Helsinki (1997) Cardiovasc. Res. 35, 2–3
12 Consensus Document Second European Consensus
Document on Chronic Leg Ischaemia. (1991) Circulation
84, 1–26
13 Coats, P., Johnston, F., Macdonald, J., McMurray, J. J. V.
and Hillier, C. (2001) Signalling mechanisms underlying
the myogenic response in human subcutaneous resistance
arterioles. Cardiovasc. Res. 49, 828–837
14 Coats, P., Jarajapu, Y. P. R., Hillier, C., McGrath, J. C. and
Daly, C. (2003) The use of fluorescent nuclear dyes and
laser scanning confocal microscopy to study the cellular
aspects of arterial remodelling in critical limb ischaemia.
Exp. Physiol. 88, 547–554
15 Meininger, G. A. and Davis, M. J. (1992) Cellular
mechanisms involved in the vascular myogenic response.
Am. J. Physiol. 263, H647–H659
16 Hill, M. A. and Meininger, G. A. (1994) Calcium entry and
myogenic phenomena in skeletal muscle arterioles.
Am. J. Physiol. 267, H1085–H1092
17 Wesselman, J. P. M., VanBavel, E., Pfaffendorf, M. and
Spaan, J. A. E. (1996) Voltage-operated calcium channels
are essential for the myogenic responsiveness of cannulated
rat mesenteric small arterioles. J. Vasc. Res. 33, 32–41
18 Falcone, J. C., Granger, H. J. and Meininger, G. A. (1993)
Enhanced myogenic activation in skeletal muscle arterioles
from spontaneously hypertensive rats. Am. J. Physiol. 265,
H1847–H1855
19 Pourageaud, F. and De Mey, J. G. R. (1998) Vasomotor
responses in chronically hyperperfused and hypoperfused
rat mesenteric arteries. Am. J. Physiol. 274, H1301–H1307
20 Delp, M. D., Colleran, P. N., Wilkerson, M. K., McCurdy,
M. R. and Muller-Delp, J. (2000) Structural and functional
remodeling of skeletal muscle microvasculature is induced
by simulated microgravity. Am. J. Physiol. 278,
H1866–H1873
21 Pourageaud, F. and De Mey, J. G. R. (1997) Structural
properties of the rat mesenteric small arteries after 4-wk
exposure to elevated or reduced blood flow. Am. J.
Physiol. 273, H1699–H1706
22 Brownlee, R. D. and Langille, B. L. (1991) Arterial
adaptations to blood flow. Can. J. Physiol. Pharmacol. 69,
978–983
Received 11 June 2003; accepted 23 July 2003
Published as Immediate Publication 23 July 2003, DOI 10.1042/CS20030203
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2003 The Biochemical Society
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