Clinical Science (1995) 89, 467--474 (Printed in Great Britain)
467
Microvascular response to tissue injury and capillary
ultrastructure in the foot skin of Type I diabetic patients
*G. RAYMAN, tR. A. MALIK, tAo K. SHARMA and *J. L. DAY
*Diabetes Centre, Ipswich Hospital, Suffolk, U.K., and tDepartment
Royal Infirmary, Manchester, U.K.
of Medicine, Manchester
(Received 7 April/30 June 1995; accepted 6 July 1995)
1. Microvascular blood flow responses to injury and
capillary ultrastructure were assessed by laser
Doppler flowmetry and detailed light and electron
microscopy respectively in skin biopsied from 28
patients with insulin-dependent diabetes and 17
control subjects.
2. The hyperaemic response induced by biopsy
(P<O.OOI) and heating to 44°C (P<O.OOI) was
significantly lower in the diabetic patients and showed
progressive impairment with the severity of complications (P<O.OOI).
3. Skin capillary basement membrane thickness was
significantly increased in the diabetic patients
(P < 0.001) and also increased with the severity of
complications (P < 0.002). Both the luminal area
(P<O.OOI) and the endothelial cell outer perimeter
(P < 0.0(2), measures of luminal and capillary size,
respectively, were significantly reduced in all diabetic
patients.
4. Basement membrane thickness was related significantly to the impaired hyperaemic response to both
biopsy (P<O.OI) and thermal injury (P<O.OI).
5. Our findings support the hypothesis that structural
abnormalities, which are characterized by an early
reduction in capillary size and later thickening of
basement membrane, form an important mechanism
for the impaired hyperaemic response in diabetic
patients.
INTRODUCTION
Diabetic foot ulceration is a cause of considerable
morbidity and mortality and remains one of the
most frequent reasons for admission of a diabetic
patient to hospital [1, 2]. The ultimate ca~se ?f
tissue necrosis is microcirculatory failure, which In
diabetes is due to microangiopathy interacting with
large vessel disease and neuropathy [1]. There are
now a number of studies which have clearly demonstrated abnormal microvascular function in the form
of an impaired hyperaemic response and raised
capillary pressure in patients with Type I [3-5] and
recently diagnosed Type II diabetes [6]. Further-
more, children with diabetes [7], patients with
impaired glucose tolerance [8, 9] and diabetic
patients with microalbuminuria [10] also demonstrate an abnormality of microvascular function,
suggestive of an early abnormality. Possible explanations for abnormalities of microvascular function
include an impairment in the release and action of
vasoactive mediators such as prostacyclin [11] and
nitric oxide [12]. Moreover, increased levels of the
potent vasoconstrictor endothelin have been demonstrated [13], and the use of an endothelin-l antagonist has been shown to improve tissue blood flow
[14]. Structural abnormalities such as a reduction in
vascular density and/or abnormalities within the
vessel wall may also form an important mechanism
for the abnormalities of microvascular function.
The primary aim of this study was to determine
whether structural abnormalities of the capillaries
are a feature of the skin in the feet of patients with
Type I diabetes and if so, whether such abnormalities relate to abnormalities in skin microvascular
function and the severity of microvascular complications. Skin microvascular responses to both heating
and tissue injury were assessed by laser Doppler
flowmetry and detailed light and electron microscopic morphometric evaluation of capillaries was
undertaken in biopsies from adjacent skin of
diabetic patients with and without complications
and from control subjects.
METHODS
Patient selection
Twenty-eight insulin-dependent diabetic patients
(14 male, 14 female) and 17 healthy control subjects
(nine male, eight female) were studied. Smokers and
subjects with a history of foot lesions were excluded.
Those with evidence of lower limb occlusive vascular disease (ankle/brachial systolic pressure ratio
< 1.0) were excluded. Retinopathy was assessed by
examining the fundi by standard ophthalmoscopy
through dilated pupils, and all patients noted to
have proliferative retinopathy were receiving or had
received laser photocoagulation. Neuropathy was
Key words: blood flow, diabetes, foot ulceration. laser Doppler. microangiopathy.
Abbreviations: ANOVA, analysis of variance; V, volts.
Correspondence: Dr R. A. Malik. Department of Medicine (M7). Manchester Royal Infirmary. Oxford Road. Manchester Mil 9WL. U.K.
468
G. Rayman et al.
assessed by standard neurological examination, taking into account perception of touch, pain and
presence or absence of ankle reflexes and also the
vibration perception threshold using a Biothesiometer (Biomedical Instruments Co., OH, U.S.A.).
Patients with absent ankle reflexes and a vibration
perception threshold above the 90th centile for age
were considered to have neuropathy. Nephropathy
was assessed by standard 24 h urinary protein and
urea and creatinine assessment. Diabetic patients
were matched for duration of diabetes and grouped
into those with no evidence of retinopathy, nephropathy and neuropathy, i.e. uncomplicated (Group I,
n = 12), those with background retinopathy but no
nephropathy or neuropathy (Group II, n = 6) and
those with severe complications, i.e. two or more
complications or proliferative retinopathy on its
own (Group III, n = 10).
Blood flow response to thermal and mechanical injury
Skin microvascular flow was measured using a
Periflux Laser Doppler flowmeter (Model PF 2b,
Perimed, Stockholm, Sweden). The basic technique
and underlying principles have been described in
detail elsewhere [3, 15-17]. All studies were performed in a temperature-controlled environment
(22-24°C) with the patient in a recumbent posture.
For the response to thermal injury, the blood flow
response to heating the skin to 44°C for 30min
using a specially constructed heating probe was
compared with resting flow measured in arbitrary
units of volts (V). Readings were taken from nine
sites and the mean was used for analysis (coefficient
of variation 8.2%). The microvascular response to
mechanical injury was measured immediately after
the biopsy at four points, each 1 mm adjacent to the
site of biopsy. Blood flow measurements were made
for 20 min after biopsy, rotating between each of the
four sites at 1 min intervals. The mean of the peak
blood flow from each measurement site was used for
analysis.
Surgical procedure and specimen preparation
The study was approved by the local ethics
committee and informed consent was obtained from
all patients. Local anaesthetic [0.5 ml Lignocaine
(1%)] was injected into an area proximal to the
biopsy site before biopsy. A 3 mm diameter skin
biopsy was obtained from the dorsum of the foot
between the first and second metatarsals using a
biopsy punch (Stiefel Laboratories Ltd., Bucks,
England, U.K.). All biopsied tissue from control
subjects and diabetic patients underwent exactly the
same fixation procedure. The tissue underwent
immediate primary fixation in glutaraldehyde fixative in cacodylate buffer and secondary fixation in
1% osmium tetroxide. After dehydration in a graded
series of ethanol, the tissue was infiltrated with epon
resin using propylene oxide as an intermediary, and
finally set overnight in catalysed epon in an oven at
60°C.
Morphometric techniques
The investigator performing the morphological
analyses was not aware of the identity of the
specimens. Transverse semi-thin sections (0.75 tlm)
were cut on a Reichert Jung Ultracut microtome
and stained with Toluidine Blue. Light micrographs
were prepared using a Vickers light microscope. The
mean epidermal thickness and vessel (arteriole,
venule and capillary density/rum" of dermal area)
density were assessed using techniques which have
been described previously in detail [18]. Ultra-thin
sections « 0.1 tlm) were prepared using a diamond
knife, stained with methanolic uranyl acetate and
lead citrate and examined under a Philips EM201C
transmission electron microscope. All microvessels
(25-30/biopsy) which were considered to be capillaries according to previously defined criteria [19]
were photographed at a final magnification of
x 10000. Each micrograph was then assessed for
morphological abnormalities defined in a number of
previous investigations [19-21]. The luminal area,
endothelial cell area and endothelial cell outer perimeter were derived by tracing profile lengths (Fig.
1). The basement membrane thickness was derived
from a minimum of 20 orthogonal intercept lengths
per capillary [20]. The endothelial cell profile
number, endothelial cell nuclear number, pericyte
nuclear number per capillary and the endothelial!
pericyte cell nuclear ratio were derived directly from
counts made on each micrograph.
Statistical analysis
All data were normally distributed and were
expressed as the mean and SO. Student's t-test was
performed to assess differences between diabetic
patients and control subjects. An analysis of variance (ANOVA) test for trend across the diabetic
patients was also performed to assess the change in
measured parameters with increasing severity of
complications. Where multiple comparisons against
the control group were performed, the Bonferroni
correction was applied and a significance level of
0.0167 was used. The Pearson product moment
correlation was performed to analyse relationships
between the different parameters assessed.
RESULTS
Clinical status
Clinical details of diabetic patients and normal
subjects are presented in Table 1. The age, systolic
and diastolic blood pressure and duration of
diabetes did not differ significantly between the
groups of patients studied. Blood glucose was higher
in diabetic patients with complications compared
Capillary function and structure in diabetic skin
469
Endothelial cell
nucleus
Pericyte cell
nucleus
Lumen
- - - Endothelial cell
Pericyte cell
profile
Basement membrane
Fig. I. Electron micrograph ( x 4217) of skin capillary from a patient with established microvascular complications and schematic diagram illustrating
the morphometric parameters assessed. The double arrow shows the basement membrane thickness.
Table I. Clinical details of control subjects and diabetic patients, presented as means± SD and ANOVA, for trend
within the diabetic patients with progression of complications
Sex
Age (years)
Diabetes duration (years)
Plasma glucose (mmol{l)
Systolic blood pressure (mmHg)
Diastolic blood pressure (mmHg)
Control subjects
Group 1
Group II
Group III
9M,8F
42.6± 10.4
0.0
<7.0
129.4 ± 14.2
80.3±6.4
SM,7F
40.1 ± 11.4
20.1 ± 11.5
9.0±4.9
130.0± 16.7
80.0± 11.1
4M,2F
46.7 ±8.1
27.7 ± 7.4
13.3±6.1
141.7 ±24.8
80.8±6.6
SM, SF
44.3 ± 13.3
27.4 ± 14.3
14.2±4.4
I36.5± 18.0
79.5±9.6
with those without complications. Diabetic patients
in group I had no evidence of retinopathy, were all
albustix-negative with normal creatinine and had a
vibration perception of 8.7 ± 2.1 V, which was not
significantly different from control subjects
(7.6 ± 3.3V). All patients in group II had background retinopathy only, had no evidence of renal
dysfunction and vibration perception was also not
significantly
greater
than
control
subjects
(10.5±4.7V). In group III, five patients had background retinopathy and the remaining five had
proliferative retinopathy with a significantly elevated
vibration perception (22.8± 12.5V) indicative of
neuropathy, and three patients had albustix-positive
proteinuria but normal creatinine.
Microvascular blood flow
The hyperaemic blood flow response to thermal
injury was reduced in all groups of diabetic patients
(Group I, 1.3±0.2, P<O.OOl; Group II, l.3±Oo4,
P<O.OOl; Group III, 0.7±0.2, P<O.OOl) compared
with control subjects (1.9± 004). Furthermore, it was
decreased with increasing severity of complications
NS
NS
NS
<0.004
NS
NS
(P<O.OOI) (Fig. 2a). The hyperaemic response to
biopsy was also reduced in all groups of diabetic
patients, reaching significance in patients with the
most severe complications (Group I, 0.9 ± 0.2,
P < 0.02, not significant; Group II, 0.9 ± 0.2, P < 0.02,
not significant; Group III, 0.5 ± 0.2, P < 0.001) compared with control subjects (1.2 ± 0.3) and was also
related to increasing severity of complications
(P<O.OOl) (Fig. 2b). The magnitude of the blood
flow response was clearly lower in the biopsy compared with the thermal injury in control subjects
(1.2 ± 0.3 compared with 1.9± 004) as well as diabetic
patients (0.7±0.3 compared with l.l±Oo4). However, the magnitude of the impaired hyperaemic
response, as assessed by the percentage reduction in
mean blood flow to both thermal injury (42.1 %) and
biopsy (41.7%), was almost identical when comparing diabetic patients with control subjects. Furthermore, hyperaemic responses to thermal injury and
biopsy were significantly correlated in the diabetic
patients (r=0.73, P<O.OOl) (Fig. 3). The hyperaemic
response to both types of injury failed to relate to
age, sex, duration of diabetes, blood pressure or
blood glucose at the time of the study.
G. Rayman et al.
470
3.0
(0)
...·:
....·..:
....:.
·.··
·
..
···
...
....:
OL------.----.---,..----,---Control
subjects
(b)
Group I
Group II
Group III
20
-:-··
·1-
Control
subjects
..-:.!
··
Group I
...
..
...
:
Group II
Group III
Fig. 2. Hyperaemic response to thermal injury (a) and biopsy (h) in
control subjectsand each of the groups of diabetic patients, demonstrating the progressive impairment with the severity of
complications
~ 1.2
Relationship between functional and structural
parameters
..
l:l
.~
~ 10
~
~ 0.8
:~
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0.6
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E
r=0.73 P<O.OOI
8 0.4
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s
~
02
0.4
0.6
0.8
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1.2
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1.6
Response to thermal injury [arbitrary units (V)]
mality was that of capillary basement membrane
thickening which progressed with the severity of
complications (Fig. 4). Capillary basement membrane thickness was increased in the diabetic
patients (2.0 ± 0.7 flm) compared with control subjects (1.3 ± 0.3 flm, P < 0.001), and also showed a
progressive increase with the severity of complications (P < 0.002) (Fig. 5). The luminal area was
significantly reduced in all groups of diabetic
patients (48.8 ± 20.0 flm 2 ) compared with control
subjects (80.8±31.9flm 2 , P<O.Ol). Similarly, the
endothelial cell outer perimeter, a measure of capillary size, was also reduced in all groups of diabetic
patients (31.5 ± 4.3 flm) compared with control subjects (39.6 ± 9.0 flm, P < 0.002). Both luminal area
and endothelial cell outer perimeter were significantly reduced in patients with and without complications and did not progress with the severity of
complications (Fig. 6). Cellular abnormalities in the
form of endothelial cell profile and nuclear number,
endothelial cell area, pericyte cell nuclear number
and the endothelial/pericyte cell nuclear ratio did
not differ significantly between control subjects and
diabetic patients (Table 3). None of the morphological parameters related to age, sex, blood pressure,
duration of diabetes or blood glucose at the time of
study.
1.8
Fig. 3. Correlation plot between the hyperaemic response to
thermal injury and biopsy, demonstrating the close relationship
between the two responses
There was no correlation between the impaired
hyperaemic response and large or small vessel
density. Epidermal thickness was directly related to
the hyperaemic response to thermal injury (r = 0.46,
P<0.05) and biopsy (r=0.48, P<O.Ol). There was a
significant inverse correlation between basement
membrane thickness and hyperaemic blood flow
response to both thermal injury (r= -0.53, P<O.Ol)
and biopsy (r= -0.56, P<O.Ol) (Fig. 7). There was
no correlation between the impaired hyperaemic
response and either luminal or endothelial cell outer
perimeter, as the latter two abnormalities were
present to an equal degree in all diabetic patients,
suggesting that they occur early on and do not
progress with severity of complications. Furthermore, there was no correlation between the hyperaemic response and any of the cellular parameters.
Morphometric data
Morphometric data derived at the light microscopic level are presented in Table 2. Large (arteriole and venule) vessel and capillary densities as well
as the small to large vessel ratio did not differ
significantly between the diabetic patients and
control subjects nor between the different groups of
diabetic patients. Epidermal thickness, though
slightly increased in diabetic patients, did in fact
demonstrate a significant trend for reduction in
thickness with the progression of complications
(P<O.OI). Qualitatively, the most prominent abnor-
DISCUSSION
This study demonstrates significant abnormalities
in both the functional and structural integrity of the
microvasculature in the skin of the feet of patients
with Type I diabetes. The hyperaemic response to
thermal injury was found to be impaired in diabetic
patients, in agreement with our original findings [3],
and the degree of functional abnormality was
related to the severity of microvascular disease in
other tissues as assessed by the degree of retino-
Capillary function and structure in diabetic skin
471
Table2. Light microscopic morphometric parameters in control subjects and diabetic patients, presented as means±
SO and ANOVA, for trend within the diabetic patients with progression of complications
Epidermal thickness (Jl m)
Large vessel density (no./mm')
Capillary density (no./mm')
Capillary/large vessel ratio
Control subjects
Group I
Group II
Group III
66.9± 19.1
19.1 ±7.5
59.0 ± 23.6
3.4± 1.5
76.3± 15.8
18.6±5.9
614±24.9
3.4±0.7
74.1±7.7
15.7±0.7
56.8±15.3
3.7± 1.1
58.9±17.3
21.5±10.5
69.9±2S.1
3.6± 1.4
<0.01
NS
NS
NS
Fig. 4. Comparative electron micrographs (x 42n) of skin capillaries from a control subject (a) when compared with the capillaries from diabetic
patients from Group I (b), Group II (c) and Group III (d), illustrating the reduction in luminal (I) and vessel size and the progressive thickening of
basement membrane (bm)
pathy, neuropathy and nephropathy, in agreement
with another previous study [4]. Furthermore, we
also observed an impaired hyperaemic response in
patients who were free from clinical microvascular
complications. In support of this finding, recent
studies have demonstrated abnormal microvascular
function in children with Type I diabetes [7],
recently diagnosed patients with Type II diabetes
[6], patients with impaired glucose tolerance [8, 9]
and diabetic patients with microalbuminuria [10],
all of whom had no overt clinical complications of
diabetes.
G. Rayman et al.
472
4.0
E
-:; 3.0
~
~
£.,
e<= 2.0
-c
E
E
<=
.,
E
rJ
1.0
.···
::I
:
.
-:.
I
'"
0
Control
subjects
Group I
Group II
Group III
Fig. 5. Basement membrane thickness in control subjects and in
each of the groups of diabetic patients, demonstratingthe progressive increase in basement membrane thickness
160
(a)
140
120
1100
.,
'" 80
'"
~
-;;;
<=
.~
--'
60
40
·.···
-i·
20
Control
subjects
(b)
...··
·
·
.:.
:
·
Group I
Group II
Group III
70
E
.s
., 60
E
.".,
0-
SO
~0
~
40
~
Q)
-'=
j
30
...:
...!
...··
·:
:
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20
Control
subjects
Group I
Group II
Group III
Fig. 6. Luminal area (a) and endothelial cell outer perimeter (b) in
control subjectsand each of the groups of diabetic patients, demonstrating the early and maintained reduction in both parameters in
the diabetic patients
We have also demonstrated that the impaired
hyperaemic response occurs not only after thermal
injury but also after mechanical injury due to a
biopsy, and that the two responses are comparable.
The response to mechanical injury was less in
magnitude than to thermal injury. A possible underlying explanation for this may be related to the site
chosen for detecting the hyperaemic response, as the
thermal injury response was measured directly at
the point of injury, whereas the mechanical injury
response was measured in adjacent skin.
A change in vascular density or epidermal thickness may clearly influence the laser Doppler assessment of blood flow [15]. This study has shown that
there is no significant increase in epidermal thickness in diabetic patients, in fact the converse is true,
such that there is a significant trend towards thinner
epidermis among diabetic patients with complications. Large vessel arteriolar/venular and small vessel capillary density also did not differ between
diabetic patients and control subjects, or between
the different groups of diabetic patients. Thus, these
parameters cannot explain the differences in hyperaemic responses observed.
With regard to previous morphological studies,
only a limited number have been performed, often
with inadequate numbers of patients. The great
majority have employed semi-quantitative and often
purely qualitative techniques which provide an
insufficient assessment of detailed pathological
abnormalities [22-27]. Furthermore, in a number of
studies, biopsies have been taken from sites other
than the foot and therefore have no direct relevance
to the problem of foot ulceration [25, 27]. In the
present study, a detailed ultrastructural light and
electron microscopic morphometric analysis was
performed in the foot skin of a large number of
Type I diabetic patients. The capillary basement
membrane thickness was increased in diabetic
patients, especially in those with severe complications, confirming previous observations in patients
with established complications [22-29]. Furthermore, there was a marked reduction in luminal area
and also the endothelial cell outer perimeter in all
groups of diabetic patients, which was apparent very
early on even in patients without complications.
Reduced microvascular dimensions have been
reported in the forearm skin of diabetic patients,
although the study was only conducted at the light
microscopic level and differentiation between
smaller capillaries and larger arterioles and venules
was not made [28]. We could not demonstrate any
cellular abnormality in the form of endothelial cell
hypertrophy, hyperplasia, pericyte cell loss or
change in the endothelial/pericyte cell nuclear ratio
which has previously been demonstrated in the
retina [30], kidney [31] and peripheral nerve [19].
As far as we are aware, this is the first study
which attempts to relate microvascular function in
foot skin with detailed quantitative histomorphometric analysis of skin capillaries from the same site.
We have demonstrated a significant inverse relationship between the impaired hyperaemic response and
capillary basement membrane thickening. A previous semi-quantitative light microscopic study
showed an inverse relationship between vascular
distensibility and the amount of periodic/Schiffpositive material in the walls of small blood vessels,
but failed to differentiate capillaries from other
larger vessels [29]. Ajjam et al. [28] have also
Capillary function and structure in diabetic skin
473
Table 3. Electron microscopic morphometric parameters of skin capillaries in control subjects and diabetic patients,
expressed as mean±SD and ANOVA, for trend within the diabetic patients with progression of complications
Basement membrane thickness (J.1 m)
Lu minal area (J.1 m')
Endothelial cell outer perimeter (J.1 m)
Endothelial cell area (J.1 m')
Endothelial cell profile no.
Endothelial cell nuclear no.
Pericyte cell nuclear no.
Endothelial/pericyte nuclear ratio
(a)
~
1.6
• •-
~ ~ 104..
E
... ~
-5
...
..
Group I
Group II
Group III
P
1.3 ± 0,3
BO.8±31.9
39.6±9.0
40.9 ± 32.4
5.HO.8
1.5±0.4
1.0±0.4
1.7 ±0.7
1.6±0.6
45.0±17.9
3I.H 4.4
34.7 ± 21.0
4.8±0.5
1.3 ±0.2
1.1 ±0.2
1.3±0.2
1.8±0.6
51.8±24.5
31.H6.5
29.4±12.9
5,3 ± 1.0
I.HO.5
0.9±0.1
1.6±0.5
2.5±0.6
51.5±21.1
31.7±2.9
2B.8± 13.5
4.9±0.5
I.HO.5
I.HO.5
I.HO.5
NS
NS
NS
NS
NS
NS
NS
r= -0.53 P<O.OI
1.8
';:
Control subjects
•
•
.~:0 12
•
>-
,; ~ 1.0
~:ii
<::
J!. 0.8
<ii
0.6
g
••
•
0.4 +----,-----r--,--+---,
1.5
2.0
2.5
3.0
3.5
1.0
Basement membrane thickness (J.Im)
(b)
r= -0.56 P<O.OI
1.2
•
~
:§:
1.0
~~
.g..
.J;!
c
E
:0
...
~
•
•
•
0.8
.. ..
1i .E 0.6
~-e
~.!!.
'8<ii
0.4
•
•
•
•
0.2 +-----.-----,,.----r-----,.-=---,
1.0
1.5
2.0
2.5
3.0
3.5
Basement membrane thickness (J.Im)
Fig. 7. Correlation plot demonstrating the association between the
skin blood flow response to thermal injury (a) and biopsy (b) with
capillary basement membrane thickening
demonstrated a reduced vasodilator response to
injected histamine and topically applied ethyl nicotinate and a reduced vessel size, but no mention was
made of any structural/functional relationship. One
electron microscopic study [27] failed to demonstrate any structural abnormality of the forearm
skin capillaries and also failed to find a relationship
between the structure and function of skin vessels.
The findings in the latter study may of course be
related to the patients selected for study, who had
non-insulin-dependent diabetes and were free of
complications, but more importantly they may also
be related to the site of biopsy, i.e. the forearm,
which would not reflect the greater damage
observed in the foot due to higher capillary pressures [32].
<0.002
Blood flow in the microcirculation is regulated at
the level of the resistance vessels; however, when
functional tone is abolished, as with thermal stress,
structural influences will dominate [33]. Indeed,
diabetic patients have been shown to have reduced
microvascular distensibility in muscle after total
paralysis with papaverine [34]. Thus, a reduction in
vascular density or capillary luminal size (due to
smaller capillaries or reduced capillary distension)
could account for the reduction in hyperaemic flow
observed. The present study has demonstrated no
reduction in vascular density in agreement with a
previous study [27]. With regard to capillary structure, an association was observed between the
degree of basement membrane thickening and the
injury response, supporting a possible pathophysiological mechanism for the observed impaired hyperaemic response. Capillary basement membrane
provides structural support for the endothelial cells
and hence maintains the integrity of the vessel; it
has a Young's elastic modulus comparable to that
of collagen [35] and distends with increasing intraluminal capillary pressure [36]. Doubling its width
has been estimated to approximately halve its distensibility [35]. Thus, reduced capillary compliance
due to encasement in thickened basement membrane could explain the inverse relationship between
basement membrane thickness and the impaired
hyperaemic response. It would not explain the
impaired hyperaemic response in diabetic patients
who were free of complications and who had no
significant evidence of basement membrane thickening. However, there was an early and maintained
reduction in both luminal and capillary size which
may be related to the increasing number of abnormalities of vasodilatation that have been demonstrated [11-14]. Since blood flow is related to the
fourth power of the luminal radius, such a difference
could readily account for the difference in hyperaemic response between control subjects and diabetic
patients without complications.
The normal tissue response to injury is a substantial increase in local blood flow to the site of injury,
i.e. the hyperaemic response [37]. An impairment of
this hyperaemic response may contribute to tissue
breakdown with ulceration and delayed healing [1,
38, 39]. This study has demonstrated that this
response is impaired in the foot skin of diabetic
474
G. Rayman et al.
patients even without clinical complications and
progresses with the severity of complications. This
suggests that microvascular abnormalities occur at a
very early stage in the evolution of diabetic complications. The significant structural abnormalities
demonstrated in this study in the form of an initial
reduction in capillary size and later increased basement membrane thickening may underlie the abnormal functional response of the diabetic microvasculature to injury.
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