The effect of posture and environmental temperature on cardiovascular reflexes in normal subjects and diabetes mellitus.

This study was undertaken to determine the effects of environmental temperature (17 degrees C or 27 degrees C) and posture on heart rate variability during forced sinus arrhythmia (deep breathing), and of environmental temperature on the heart rate and blood pressure responses to standing, and to the cold pressor test. A group of non-diabetic young subjects (23 +/- 5 years) and a group of older diabetic patients (54 +/- 15 years) were studied. At 27 degrees C, supine resting heart rate and systolic blood pressure were lower than at 17 degrees C in both diabetic and non-diabetic subjects, and heart rate variability was lower than at 17 degrees C in the non-diabetic subjects (p less than 0.01) with seven of 17 abnormal or borderline results (all seven subjects had normal values at 17 degrees C). Room temperature had no effect on supine heart rate variability in the diabetic patients. At 27 degrees C heart rate variability in the upright posture was significantly greater than supine (p less than 0.001) in the non-diabetic subjects. In the diabetic subjects, heart rate variability when standing at 17 degrees C increased such that five patients classified as abnormal when supine had normal values when upright. A similar pattern was observed at 27 degrees C, although only those with normal heart rate variability showed an increase on standing. Room temperature had no effect on the responses to the cold pressor test, or the blood pressure responses to standing, although the heart rate response was greater in both groups at 27 degrees C. This study shows that care should be taken to standardize the conditions under which heart rate variability is determined.