Journal of Non Invasive Vascular Investigation Category: Clinical Type: Research Article
Microcirculation at Different Parts of the Foot in Healthy Subjects
- Stefan Rosfors1*
- 1 Department Of Clinical Science And Education, Section Of Clinical Physiology, Karolinska Institute, Södersjukhuset, Stockholm, Sweden
*Corresponding Author:Stefan Rosfors
Department Of Clinical Science And Education, Section Of Clinical Physiology, Karolinska Institute, Södersjukhuset, Stockholm, Sweden
Received Date: Nov 09, 2016 Accepted Date: Dec 29, 2016 Published Date: Dec 31, 2016
Methods: Microcirculation of the foot was evaluated on 15 healthy subjects (aged 22-37 years) by two methods: Transcutaneous Oxygen Pressure (TcPO2) with and without oxygen provocation and Laser Doppler Flux (LDF) with heat provocation. Four different measuring sites were used: one distal and one proximal point at the dorsal foot (the distal is the standard position), one point at the medial plantar part and one at the anterolateral part of the foot. The measuring points were distributed on parts of the foot supplied by three different end-arteries (so called angiosome).
Results: TcPO2 levels were significantly higher at all three measuring points than at the standard position at the distal dorsal foot. Median TcPO2 was 68 mm Hg at the standard position compared with 76 mm Hg at the dorsal proximal, 73 mm Hg at the medial and 83 mm Hg at the anterolateral electrode position. After oxygen provocation only the proximal dorsal point remained significantly higher than the standard position. Heat-provoked LDF did not differ between different parts of the foot with an increase of more than 400% seen at all probe positions in all subjects. Oxygen inhalation increased TcPO2 to median levels around 200 mm Hg, without affecting LDF. Both TcPO2 and LDF results were unrelated to different angiosome.
Conclusion: In healthy subjects TcPO2 levels are slightly higher at proximal than at distal parts of the foot, but LDF did not differ between different parts of the foot. Although both methods are used to study the microcirculation there are no correlations between TcPO2 and LDF, which reflect that these methods use different mechanisms and different measurement principles.
Local microcirculation of the foot can be described in terms of the angiosome model, a concept that has gained in interest during the last decade . Basically it refers to a block of tissue perfusion by a specific end-artery. At the foot the three main arteries give rise to six end-arteries, each supplying an angiosome; three from the posterior tibial artery, two from the peroneal artery and one from the anterior tibial artery . The angiosome concept of the foot has received special attention regarding choice of target artery for revascularization in order to achieve best ulcer healing.
The aim of this study is to investigate the microcirculation of the foot on healthy subjects with two different methods (TcPO2 and heat-provoked LDF) in order to describe regional differences in parts of the foot supplied by different end-arteries, and to study relationships between results obtained with these two methods.
MATERIAL AND METHODS
Positioning of electrodes/probes and experimental set-up
• Dorsal distal: The distal part of dorsalis pedis angiosome (supplied by the anterior tibial artery), standard position
• Dorsal proximal: The proximal part of the dorsalis pedis angiosome (supplied by the anterior tibial artery)
• Medial: The medial plantar artery angiosome (supplied by the posterior tibial artery)
• Anterolateral: The anterior perforating branch angiosome (supplied by the peroneal artery)
These investigations were made in two steps; first positions 1 and 2 and after replacement of the electrodes/probes positions 3 and 4 were investigated (Figure 1). The patients were studied in supine position. First two LD probes were attached and baseline values were sampled followed by activation of the built-in heater system. The calibrated TcPO2 electrodes were then attached close to the LD probes, heating of the TcPO2 electrodes was started and then sampling for both TcPO2 and LDF, followed by oxygen provocation. Only one limb per patient was studied (randomly 7 right limbs and 8 left limbs).
Transcutaneous Oxygen Pressure (TcPO2)
Laser Doppler Flux (LDF)
Statistics and ethics
The study was approved by the local ethics committee and conducted according to the declaration of Helsinki. Written informed consent was obtained from all participants.
|TcPO2 (mm Hg)|
|TcPO2 breathing oxygen|
|Heat-provoked LDF (PU)|
For TcPO2 it is common to use a fixed electrode position at the dorsum of the foot in the first intermetatarsal space just proximal to the first and second toe (denoted standard position in the present study) . Here a level below 30 mm Hg is proposed to denote critical limb ischemia . Different positions in the vicinity of problem wounds are sometimes used, for example to select patients that are suitable for hyperbaric oxygen therapy . Moreover, the electrodes can be applied at different levels of the foot and the lower limb to assess the proper level for amputation . The present results demonstrated systematically higher levels at the proximal foot (dorsal, medial and anterolateral parts) than at the distal foot. This difference was not related to angiosome, since it was a significant difference between electrode positions also within the same angiosome (i.e., higher levels at the proximal dorsal foot than at the distal dorsal). This is not surprising, on the contrary rather expected since angiosome are supposed to be of importance in patients with compromised circulation and diseased arterial interconnections [4,8]. Thus, in normal subjects there are small, but significant, regional differences in microcirculation assessed with TcPO2. These differences are difficult to explain, but anatomic variations in healthy subjects might play a role.
When the six angiosome of the foot were described, an interest emerged regarding revascularization of patients with critical ischemia and ulcers/gangrene . Some early results suggested a better outcome in terms of wound healing when the procedure was directed towards the vessel feeding the angiosome containing the ulcer (DR- Direct Revascularization), compared to when the procedure included only vessels not feeding the affected angiosome directly (IR- Indirect Revascularisation) . However, in larger series and in reviews the results were much more divergent and the role of the angiosome concept in revascularization of ischemic limbs remains to some extent unclear . For example it has been suggested that the concept has higher relevance regarding ulcer healing in diabetic patients with known poor collateralization compared to non-diabetics . In recent study Rother et al., used microcirculatory methods with angiosome-related measuring points to study the effect of DR and IR in patients with critical limb ischemia . Their results could not support an angiosome concept of the foot regarding changes in microperfusion.
In general the healthy subjects in the present study had basal TcPO2 levels between 60 and 80 mm Hg that increased to 150-200 mm Hg after oxygen inhalation. The low basal LDF (< 20 PU) increased with heat provocation to around 180-200 PU. Oxygen inhalation did not further affect LDF, an expected finding although not earlier described. According to an earlier suggested classification system for interpreting TcPO2 and LDF all healthy controls except one could be denoted as normal . The exception was a 29-year old female with 402% increase in heat-provoked LDF at the standard position and 426% increase at the proximal dorsal probe (normal > 500%). We consider this to be interpreted as within the normal variability range, rather than to implicate microvascular disease.
In the present study apparently healthy subjects were studied. One possible limitation was that no standard methods were used to prove “normality”. In order to control for that only asymptomatic subjects below 40 years without risk factors were chosen. The fact that all the subjects were found to have TcPO2 within the normal range at all measuring points at the foot strongly supports that the subjects were free of both macro- and microvascular disease. Most authors agree that a normal TcPO2 can be used to rule out both macro- and microvascular disease, and 50 mm Hg at foot level is a generally found lower limit of normality [2,14-18]. Another possible limitation was the rather small number of only 15 subjects included. A larger sample would have increased the usefulness of the present study, since then also results regarding differences between age groups could have been assessed and possibly also reference values for various microcirculatory variables.
There was in general no significant relation between TcPO2 values and LDF. This is not surprising since two different measuring principles are used; TcPO2 with measure of oxygen in skin capillaries and LD with assessment of tissue reserve capacity recruiting response from somewhat more deeply located structures which besides capillaries also can include arterioles and venules . TcPO2 and LDF were chosen since they are commonly used in studies of microvascular function, but with limited knowledge regarding relationship between results obtained with these two methods.
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Citation:Rosfors S (2016) Microcirculation at Different Parts of the Foot in Healthy Subjects. J Non invasive Vasc Invest 1: 005.
Copyright: © 2016 Stefan Rosfors, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.