BACKGROUND: Epidemiological data suggest that during heat waves the risk of heat illness and related death is increased in people with known medical conditions. Patients with diabetes have impaired thermoregulation and sensory nerve abnormalities that may impair thermal sensations.
PURPOSE: This study tested the hypothesis that the perception to heat stress is altered in obese type 2 diabetics compared to healthy individuals.
METHODS: Nine obese type 2 diabetics (50.1±12y, 45±7.1% fat mass, 7.5±1.8% HbA1C) and nine similarly aged healthy controls (41.1±13.7y, p=0.185; 33.4±7.8% fat mass, p=0.009, 5.3±0.4%; HbA1C, p=0.007) participated. Subjects underwent whole body passive hyperthermia via head-out immersion that increased core body temperature by ~1.4°C. Perception of thermal sensation; scale range: 7 (comfortable) - 13 (so hot I am sick and nauseated), and the physiological strain index that includes the increase in core temperature and heart rate between pre and end periods, were the primary dependent variables.
RESULTS: There were no differences between groups on the increase in core body temperature ([INCREMENT]Tre, 1.4 ± 0.4°; p=0.12), skin temperature ([INCREMENT]Tsk, 6.5 ± 0.8; p=0.3), or heart rate ([INCREMENT]HR from rest, 34 ± 8 bpm; p=0.3) during the 60 min of heat stress. A repeated measures two way ANOVA resulted in no group x time interaction for perception of thermal sensation (p=0.70) or the calculated physiological strain index (p=0.14) during hyperthermia. Pearson product correlation suggested strong correlations with [INCREMENT]Tre, [INCREMENT]HR, [INCREMENT]Tsk, and thermal sensation in both populations. However, a linear stepwise regression analysis revealed that [INCREMENT]Tsk and [INCREMENT]Tre combined were the highest predictors for thermal sensation, with an r =0.69 and accounting for 45% of the variance (Adjusted R2), in diabetics. In the healthy controls, combining [INCREMENT]Tre and [INCREMENT]HR fit the best model for predictors of thermal sensation, with an r = 0.78 and accounting for 77% of the variance.
CONCLUSIONS: These data indicate that obese type 2 diabetics with moderate metabolic control have similar thermal sensation and physiological strain to hyperthermia as healthy individuals. However, the influence of thermoregulatory ([INCREMENT]Tre and [INCREMENT]Tsk) and circulatory ([INCREMENT]HR) strain on thermal perception may differ.