Abstract
In patients with peripheral arterial occlusive disease (PAOD) a restricted circulation in cutaneous microvessels has been reported. In this study the velocity of erythrocytes (very) in finger nailfold capillaries - a vascular area without upstream macroangiopathy - and also in toe nailfold capillaries - a post-stenotic area âwas investigated using capillary microscopy in apparently healthy subjects and patients with PAOD. Already in finger nailfold capillaries very of patients with PAOD under resting conditions was significantly lower than in capillaries of healthy subjects. This was also true for the circulation in toe capillaries. In addition, the erythrocyte velocities under resting conditions in the toe capillaries were significantly lower than in the finger capillaries. Similar results were found for the duration and the maximum velocity of postocclusive hyperemia. It is concluded that the resting blood flow in the skin microcirculation is impaired in PAOD patients, both under resting conditions and during postocclusive hyperemia in finger as well in toe nailfold capillaries.
Introduction
The cutaneous blood flow can be divided in thermoregulatory shunt flow and nutritive skin capillary flow. Laser-doppler flux measures flow and number of signal-reflecting blood cells integratively and is dominated during measurements in the skin by non-nutritional shunt vessels [1]. Here, capillaroscopy is the only method for the assessment of morphology and perfusion of nutritive skin capillaries at the nail fold of fingers and toes. Capillaries can readily be studied microscopically which enables the investigator to assess morphology, density and flow velocity of erythrocytes [2â4].
Studies about the comparison of nutritional blood flow in cutaneous capillaries in the nail fold of fingers and toes of the same patients are rare. Lambova et al. analyzed the morphology of capillaries at both sites and found that the patterns of toe capillaries differed from the respective patterns of the fingers. They related the differences to less-severe Raynaud phenomenon and lower skin score of systemic sclerosis at the feet [5]. Bongard & Fagrell found no differences in erythrocyte velocities under resting conditions in both the fingers and toes of patients with peripheral arterial occlusive disease (PAOD, 8 patients with PAOD versus 10 healthy subjects were included) [6]. However, a maldistribution and an impaired reactive hyperemia in the affected region was found. On the other hand, De Graaff described a decreased erythrocyte velocity in nail fold capillaries of the toes of patients with PAOD [7].
Thus, the aim of this observational study was to investigate whether there are differences in the erythrocyte velocities in capillaries of finger and toe in patients with PAOD in comparison to apparently healthy subjects.
Material and methods
The study was part of a quality management project performed in the Institute for Clinical Hemostasiology and Transfusion Medicine at the University Saarland in compliance with the Declaration of Helsinki/Somerset West [8].
Twenty patients with peripheral arterial occlusive disease in stage IIb were examined. Mean age was 63±7 years, body height 174±5âcm and a body weight of 76±9âkg. As control nâ=â113 apparently healthy subjects were examined. Their mean age was 58±6 years with a body height of 170±18âcm and a body weight of 71±12âkg. Apparently healthy subjects were those who, according to the Nordkem workshop [9, 10], fulfilled the following criteria: clean anamnesis, physical examination without pathological findings, no pathological somatic risk factors such as diabetes mellitus, arterial hypertension, lipometabolic disorders, no vascular diseases, no medication, the following laboratory parameters within the normal range: albumin and glucose in urine, blood sedimentation rate, hematocrit, plasma cholesterol and triglyceride concentration.
Inravital video capillary microscopy
The microscopic examinations were performed under standardized conditions, for details see previous work [11]. The visualization of erythrocytes in the nail fold capillaries was performed with a reflected light microscope (Zeiss AG, Germany), which was extended with a video system [4].
Due to the absorption of green light by hemoglobin, epi-illuminating light with a wavelength of 480ânm allowed erythrocyte detection. So-called plasma gaps are formed at sites without erythrocytes, and can be observed clearly. The capillary erythrocyte velocity was quantified by frame-to-frame analysis of the video pictures following the motion of the plasma gaps using an image analysis system âCap-Imageâ (Zeintl Engineering Office, Heidelberg, Germany [11]). Details of the assessment and error analysis are described elsewhere [10].
A typical example of the course of a post-occlusive hyperemia shows Fig. 2. The duration of the post-occlusive hyperemia (DrH) is defined as the time interval between the release of bloodstream and the restoration of baseline values at rest of erythrocyte velocity in the selected capillaries of the nail fold.
Scheme of the branch of the digital artery supplying the nailfold capillaries.
Postischemic hyperemia in a nail fold capillary of a healthy subject during resting conditions, stasis and after 3 minutes of stasis.
For all samples arithmetic mean values and standard deviations are given (in case of categorical data percent values). Gaussian distributions were tested using Kolmogorov-Smirnov or DâAgostino & Pearson omnibus normality tests. Comparisons of the different materials and assays were carried out as one-way analysis of variance (when Gaussian distributed) or Kruskal-Wallis analysis as nonparametric test. Bonferroniâs multiple comparison tests (when Gaussian distributed) or Dunns tests (nonparametric) were applied as post hoc analysis. p-values less than 0.05 were considered significant.
Results
Mean erythrocyte velocity in the nail fold of finger and toe
Figure 3 shows the erythrocyte velocity in nail fold capillaries of finger and toe under resting conditions of apparently healthy subjects and patients with PAOD at four time points over the day.
Mean erythrocyte velocities very in [mm/s] under resting conditions in nail fold capillaries of the finger and of toes of patients with peripheral arterial occlusive disease and healthy subjects at four time points over the day (at 9 o'clock, 10.30 o'clock, 1 o'clock and at 3 o'clock).
Under resting conditions, erythrocyte velocities in nail fold capillaries of finger versus toes did not differ (â9.0%, ns) in apparently healthy subjects while the velocities in PAOD patients differed by 41.5% (pâ<â0.05). However, the velocities in healthy subjects were both significantly higher than in patients with PAOD, in finger nail fold capillaries by 54.1% and in toe nail fold capillaries by 70.7% (pâ<â0.01 each).
Figure 4 shows the post-occlusive erythrocyte velocity in nail fold capillaries of finger and toe of apparently healthy subjects and patients with PAOD.
Post-occlusive erythrocyte velocities very in [mm/s] in nail fold capillaries of the finger and toe of patients with peripheral arterial occlusive disease and healthy subjects.
Maximum increase of very during post-occlusive hyperemia as well as the duration is significantly lower in PAOD patients compared to apparently healthy subjects (pâ<â0.05 each).
In apparently healthy volunteers, the capillary erythrocyte velocity in the nail fold under resting conditions of finger and toe did not differ. The examination of the capillary blood flow in the fingers was always performed in a sitting position, while capillary microscopy of the toes in a lying position. This ensured that in both cases the capillaries were at heart level to avoid different influences of local transmural pressures which might influence the capillary perfusion [12, 13]. In addition, skin temperature at both sides was comparable [14].
In contrast to healthy volunteers, PAOD patients showed a significantly reduced erythrocyte velocity in the nail fold capillaries already under resting conditions on both finger and toe. There is a big body of evidence that nitric oxide (NO) is deeply involved in this process [15, 16]. NO has a wide range of biological properties, including relaxation of vascular smooth muscle cells leading to vasodilation [17, 18]. Already during the early phase of atherosclerosis, a decreased production of NO occurs [19â21]. The reduced vasodilation then induces a decreased capillary erythrocyte velocity [22]. Rossi and Carpi also described a reduced erythrocyte velocity in finger nail fold capillaries in patients with peripheral arterial obliterative disease [23]. Also, with other methods a reduced skin microcirculation in atherosclerotic Patients can be detected [24â26].
In particular, the capillary erythrocyte velocity in the post-stenotic capillaries of the toe - all patients had stenoses in the upstream arterial tract of the leg - was significantly reduced. Microcirculatory dysfunction in patients with PAOD was firstly shown by Matsen et al. in 1980 using transcutaneous oxygen pressure measurements [27]. They found significantly lower TcpO2 values in the feet of PAOD patients compared with those of healthy controls. Similar findings were reported by Jung et al. in the post-stenotic of skeletal muscle region (M tibialis anterior) in PAODII patients [28], also in upper extremities [29]. Also, DeGraaff et al. [7] described that the red blood cell velocity in nail fold capillaries of toes decreased with increasing disease severity while supine (pâ=â0.005) and while sitting (pâ=â0.06). That was confirmed by Fagrell's group, who also found a decreased erythrocyte velocity in the toes of PAOD patents [30]. In contrast, Bollinger et al. did not find a restricted erythrocyte velocity under resting conditions. Measurements using laser-Doppler flux at rest were described still to be within the normal range even in advanced disease, since the sample volume of these instruments also contains non-nutritive shunt vessels [6, 31].
In patients with mild disease, the capillary bed at the forefoot does not seem to be markedly abnormal. But the pattern changes with increasing stage of PAOD [32]. Figure 5 shows capillaries in the nail fold of the finger of an apparently healthy subject with ideal hairpin pattern and in comparison, the typical pattern of capillaries in the toe nail fold of a patient with PAODIIb with a markedly restricted painfree walking distance of 60âm.
Pattern of nail fold capillaries in the finger (left) or toe (right).
The considerably increased torquation and anastomization of the capillaries at the toe could - in addition to the reduced perfusion pressure in the post-stenotic arterial area - contribute to the reduction of the erythrocyte velocity in the nail fold capillaries [33].
Also, the pattern of the post-occlusive hyperemia was significantly disturbed in PAOD patients in finger as well as in toe capillaries. The maximum velocity was much lower and the timepoint of maximum velocity was delayed. Similar observations for toe capillaries have been reported earlier [6, 30]. The reduced release of NO also plays a role here. Various mediators such as K+, NO, purines and prostaglandins are involved in the hyperemic response to occlusion. It is assumed that NO is involved in about 30% of the reduction of post-occlusive hyperemia [34], which may partly explain the results found here.
In conclusion, the study revealed a disturbed skin microcirculation in finger nail fold, a vascular area without upstream macroangiopathy, and also but more severe in the post-stenotic region of the toe nail fold in patients with peripheral arterial occlusive disease.