EFFECT OF CONTINUOUS NEGATIVE-PRESSURE BREATHING ON SKIN BLOOD-FLOW DURING EXERCISE IN A HOT ENVIRONMENT

To assess the impact of continuous negative-pressure breathing (CNPB) on the regulation of skin blood flow, we measured forearm blood flow ( FBF) by venous-occlusion plethysmography and laser-Doppler flow (LDF) at the anterior chest during exercise in a hot environment (ambient te mperature = 30 degrees C, relative humidity = similar to 30%). Seven m ale subjects exercised in the upright position at an intensity of 60% peak oxygen consumption rate for 40 min with and without CNPB after 20 min of exercise. The esophageal temperature (T-es) in both conditions increased to 38.1 degrees C by the end of exercise, without any signi ficant differences between the two trials. Mean arterial pressure (MAP ) increased by similar to 15 mmHg by 8 min of exercise, without any si gnificant difference between the two trials before CNPB. However, CNPB reduced MAP by similar to 10 mmHg after 24 min of exercise (P < 0.05) . The increase in FBF and LDF in the control condition leveled off aft er 18 min of exercise above a T-es of 37.7 degrees C, whereas in the C NPB trial the increase continued, with a rise in T-es despite the decr ease in MAP. These results suggest that CNPB enhances vasodilation of skin above a T-es of similar to 38 degrees C by stretching intrathorac ic baroreceptors such as cardiopulmonary baroreceptors.