Cardiovascular responses to lower body negative pressure in normal subjects and in patients with diabetes mellitus.

The cardiovascular responses of non-diabetic and diabetic subjects to lower body negative pressure at 1.3, 2.7, and 5.3 kPa (10, 20, and 40 mmHg) were measured. The diabetics fell into two groups--those showing little change in systolic blood pressure with lower body negative pressure at 5.3 kPa (40 mmHg) and those showing falls greater than 2.7 kPa (20 mmHg). The patterns of response in the former group of diabetics and in the non-diabetics were similar. The diabetics who showed a fall in systolic blood pressure with lower body negative pressure nonetheless responded with a forearm vasoconstriction indicating that the vasomotor dysfunction was localised to some other vascular bed. In one subject forearm vasodilatation occurred with lower body negative pressure at 5.3 kPa (40 mmHg) although his response to milder levels of lower body negative pressure appeared normal. It is suggested that the integrity of vasomotor reflexes is most reliably tested by exposure to stepped increases in lower body negative pressure.