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 temperature = 30°C, relative humidity = ~30%). Seven male 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°C by the end of exercise, without any significant differences between the two trials. Mean arterial pressure (MAP) increased by ~15 mmHg by 8 min of exercise, without any significant difference between the two trials before CNPB. However, CNPB reduced MAP by ~10 mmHg after 24 min of exercise (P < 0.05). The increase in FBF and LDF in the control condition leveled off after 18 min of exercise above a T(es) of 37.7°C, whereas in the CNPB trial the increase continued, with a rise in T(es) despite the decrease in MAP. These results suggest that CNPB enhances vasodilation of skin above a Te, of ~38°C by stretching intrathoracic baroreceptors such as cardiopulmonary baroreceptors.