Sudomotor function in human poikilothermia

Hypohidrosis predisposes to hyperthermia and may indicate generalized thermoregulatory failure. To assess the sweating capacity in human poikilothermia, we performed a quantitative analysis of the central and peripheral sudomotor pathways in four women with acquired poikilothermia (aged 29 to 38 years) and nine controls. Heat challenge in a climatic chamber (ambient temperature 40 degrees C, 50% relative humidity) for 180 minutes revealed that both sweat secretion and evaporative weight loss were significantly lower in the patients than in the controls (p < 0.01). Temperature thresholds for thermal sweating were markedly elevated in at least two patients, whereas a third patient showed no sweating response. Stimulation of the eccrine sweat glands by intradermally injected acetylcholine during reduced core temperature (34.9 +/- 0.7 degrees C) revealed a significantly reduced sweating response in all patients (p < 0.01); the sudomotor response to pilocarpine iontophoresis was reduced or absent in three patients. We conclude that the generalized thermoregulatory sudomotor failure in these patients was attributable primarily to disorders of the central sudomotor drive; the impaired postganglionic sudomotor response is temperature related and possibly secondary to (long-standing) poikilothermia. Quantification of heat-dissipating capacity is pivotal for diagnosing severe thermolability and may help to prevent serious heat illness.