Acute metabolic response to cold exposure in unipolar and bipolar II patients

The thermoregulatory response to cold exposure was examined in 11 unipolar and 5 bipolar II drug-free outpatients and 12 healthy controls. Subjects were studied in an environmental chamber at 10 C for 60 min. The heat production response was derived from the rate of oxygen consumption measured at 15-min intervals. Rectal and mean skin temperatures were continuously recorded from thermistor probes. Responses of the controls were used to establish a standard range against which the responses of the patients were compared. Six unipolar patients (54.5%) fell outside the standard range (chi 2 = 8.86, df = 1, p less than 0.005). Four of these patients showed a paradoxical decrease in heat production. Responses of the bipolar II patients fell within a narrow segment of the standard range, such that 10 of 12 controls (83.3%) responded outside the segment (chi 2 = 10.12, df = 1, p less than 0.005). These findings indicate that unipolar patients show greater variability and bipolar II patients less variability than controls in thermoregulatory response to cold. These observations extend previous suggestions of hypothalamic-limbic system dysfunction in patients with depression.