Skin blood flow and autonomic reactivity in human poikilothermia.

Autonomic reactivity is pivotal in maintaining a constant body core temperature. Skin vasomotor reflexes and cardiovascular reactivity were investigated in four women (aged 28-37 years) with acquired poikilothermia, during steady-state spontaneous hypothermia (rectal temperature (Tr) = 33.7 +/- 1.0 degrees C [mean +/- SD]) and steady-state normothermia (Tr = 36.7 +/- 0.3 degrees C), as well as in 12 normothermic control subjects. Baseline finger temperature (Tf) during hypothermia was significantly lower than during normothermia (Tf = 32.4 +/- 1.2 compared with 36.2 +/- 0.3 degrees C, respectively), and than in the controls (Tf = 34.8 +/- 0.8 degrees C). No significant differences in baseline skin blood flow and forearm blood flow were found between subjects during hypothermia or normothermia and controls, suggesting a failure of sympathetic drive to counter-regulate hypothermia in the subjects. Skin vasoconstrictor responses to the contralateral cooling test and neck cooling test were markedly attenuated in three subjects, and to the finger cooling test in two subjects, during normothermia compared with hypothermia. Blood pressure responses to the Valsalva manoeuvre and head-up tilting were normal in all subjects, whereas the heart rate response to head-up tilting was blunted in three subjects during hypothermia. The responses of blood pressure and forearm blood flow to the cold pressor test in the subjects during both thermal conditions were comparable with the controls. We conclude that in our subjects, without generalized autonomic failure, poikilothermia has to be attributed predominantly to disorders of the central thermoregulatory pathways. Our findings during hypothermia and normothermia indicate that variations in core and skin temperature significantly affect skin vasomotor reactivity.