Diagnostics of microvascular tone regulation disorders
The behavior of the microvasculature is traditionally described using the term “vascular tone” (from tonus (Lat.) – “a sound, tone, accent”). Factors of vascular tone regulation cause complex fluctuations in non-recurrent perfusion (passage of blood through the tissue). Several methods have been developed for detection of these. Of particular interest is the vascular response to external stimuli – the so-called functional tests. Microtest can be used effectively with a variety of functional tests.
One of the better documented tests to assess microvascular function is a cold test, which allows detection of microcirculation disorders in their early stages. Of particular interest is a study of microcirculatory reactions of contralateral limb (indirect cold test) as the systemic response to a cold pressor test. In the course of the cold test the left hand cools, and the temperature fluctuations are recorded on the right hand. Typical changes in vascular tone (wavelet plane and the results of the wavelet filtering) registered by Microtest during an indirect cold test (600 ... 780 seconds) are shown below:
Another commonly used functional tests to assess the condition of the skin blood flow is the local heating test. Significant vasodilation in human skin is achieved by local heating up 42°C for 20-30 minutes. The results of the reaction to the heat test are the initial vasodilation phase and the prolonged vasodilation phase. The initial vasodilation is associated with the mechanisms of axon reflex, is most pronounced when heated to 34-35 °C, and may be blocked with local anesthetics administered directly into the heated area of the skin. The second phase is associated with the release of NO from the vascular endothelium. The total extent of the vasodilatory response in a local heat test depends mainly on the second phase, but not on the first phase. Heat test is a quite simple and effective test to evaluate the mechanisms of vascular tone regulation disorders, including endothelial dysfunction. The use of this test in practice has so far been limited due to a number of reasons, but in combination with the WAST method, it can be used in routine clinical tests, particularly for screening and early detection of ED.
The figure shows a typical graph of temperature versus time and a wavelet plane of temperature fluctuations for a healthy person (left) and patients with type 2 diabetes (right) in a heat test (Podtaev, S., Stepanov, R., et al. Microvasc Res 2015 ; 97: 109-114).