Experimental Studies

An Overview

Data presented in the previous section were obtained from NF by microvascular techniques in baseline conditions, i.e., without intervention by experimental stimuli or change in environmental conditions. Here we summarize data of microvascular responses to selected agents likely to affect the microvasculature of the NF.

Most human studies have been clinically oriented and often used for diagnosis, differential diagnosis, or correlated with laboratory data. Investigators aimed to understand pathophysiology by assuming that the same microvascular abnormalities seen in NF may be present in internal organs. They have correlated NF data with those of internal organs that were involved in a given disease, and attempted to study the prognostic significance of microvascular changes.

Selected Stimuli

Cold Exposure

(a) Whole-body exposure. In normal subjects exposed to cold in an experimental chamber, NF capillary blood flow may slow down but will not come to a complete standstill, even after more than 30 minutes. In certain disease states, severe slowing of capillary flow occurs in NF loops within a matter of minutes and rapidly comes to a standstill in all the endrow loops and beyond. Temperatures used range from 10 to 20°C between investigators. Other factors are also important, such as time of the day, clothing, and meals.

(b) Local cold exposure. Cooling of the finger can be accomplished by blowing cold air on the NF, using Peltier element and other techniques, while controlling the finger skin temperature carefully to keep it in desired range and to avoid injury. A short flow stop (measured in seconds) can also occur in normal subjects.

(c) Immersion of contralateral hand in cold water. This has also been used but is less effective.

Reactive Hyperemia

An arterial occlusion of finger blood flow in normal subjects produces cessation of blood flow followed by reactive hyperemia overshooting the basal flow rate. This response curve can be modified in certain disease states. This test has been used with a variety of microvascular techniques, such as RBC velocity measurement and laser Doppler flux.

Response to Drugs

(a) Responses to vasomotor agonists injected IA or IV and to their antagonists.

(b) Responses to drugs used in treatment of certain diseases in which microcirculation is deemed important.

The reader can find more details on experimental studies from works of Bollinger and Fagrell and of Shore [4, 5].

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