Responses in acral and non-acral skin vasomotion and temperature during lowering of ambient temperature.

Arteriovenous anastomoses (AVA) in acral skin (palms and soles) have a huge capacity to shunt blood directly from the arteries to the superficial venous plexus of the extremities. We hypothesized that acral skin, which supplies blood to the superficial venous plexus, has a stronger influence on blood flow adjustments during cooling in thermoneutral subjects than does non-acral skin. Thirteen healthy subjects were exposed to stepwise cooling from 32 °C to 25 °C and 17 °C in a climate chamber. Laser Doppler flux and skin temperature were measured simultaneously from the left and right third finger pulp and bilateral upper arm skin. Coherence and correlation analyses were performed of short-term fluctuations at each temperature interval. The flux from finger pulps showed the synchronous spontaneous fluctuations characteristic of skin areas containing AVAs. Fluctuation frequency, amplitude and synchronicity were all higher at 25 °C than at 32 °C and 17 °C (p<0.02). Bilateral flux from the upper arm skin showed an irregular, asynchronous vasomotor pattern with small amplitudes which were independent of ambient temperature. At 32 °C, ipsilateral median flux values from the right arm (95% confidence intervals) were 492 arbitrary units (au) (417, 537) in finger pulp and 43 au (35, 60) in upper arm skin. Flux values gradually decreased in finger pulp to 246 au (109, 363) at 25 °C, before an abrupt fall occurred at a median room temperature of 24 °C, resulting in a flux value of 79 au (31, 116) at 17 °C. In the upper arm skin a gradual fall throughout the cooling period to 21 au (13, 27) at 17 °C was observed. The fact that the response of blood flow to ambient cooling is stronger in acral skin than in non-acral skin suggests that AVAs have a greater capacity to adjust blood flow in thermoneutral zone than arterioles in non-acral skin.

Thermal responses to whole-body cooling in air with special reference to arteriovenous anastomoses in fingers.

The arteriovenous anastomoses (AVAs) in the distal parts of the extremities play a significant role in the heat exchange with the environment. The aim of the study was to examine the thermal responses to whole-body cooling in air, and especially the behaviour of finger skin temperature (T(f) , rich in AVAs). Eight young men sat in minimal clothing at 32°C air temperature (T(a) ), which was then lowered gradually to 13°C in 100 min. In the beginning of cooling, T(f) was high and fluctuating, and then suddenly exhibited a rapid fall, while temperatures in other skin sites fell fairly linearly along decreasing T(a) to the end of cooling. During the period from start to the rapid fall in T(f) , rectal temperature decreased from 37·4°C (SD 0.2) to 37·2°C (0·2), mean skin temperature (T(sk) ) from 34·6°C (0·5) to 31·2°C (2·0) and whole-body thermal sensation from 'slightly warm/warm' to 'slightly cool/cold'. The start of the steep fall in T(f) varied considerably between individuals in terms of time (2-75 min), T(a) (16·7 - 32·0°C) and T(sk) (28·8 - 34·7°C). On the other hand, the range of T(f) at that point was narrower (32·1 - 35·8°C). The findings stress the importance of taking into account the distal skin temperatures in thermoregulatory studies in addition to the ordinarily used more proximal and central skin sites. Also, it might be advisable to start such experiments with relatively high and fluctuating T(f) to guarantee that the thermal state of the subject is well defined.