The role of acute heating in modulating the pressor response to hypoxic stress

Repetitive airway obstruction accompanying Obstructive Sleep Apnea (OSA) produces hypoxic stress, which increases sympathetic nerve activity (SNA) and mean arterial pressure (MAP). Acute hot water immersion offers protective benefits by increasing blood flow while decreasing arterial pressure; while this effect has been repeatedly demonstrated, the effect of thermal stress on the vascular response to hypoxic apnea has not been examined. This project investigates whether acute heating alters the cardiovascular responses to acute hypoxic stress. Subjects wear a heated suit to increase their core body temperature; breath-holds are then performed at three different increments, as the subject's temperature increases (~0.4°C, ~0.8°C and ~1.2°C above baseline). After 60 min of heating, a recovery period begins, and subjects repeat the hypoxic breath-holds as temperature decreases by ~0.4°C, ~0.8°C and ~1.2°C. Measurements of arm blood flow, brachial artery blood pressure, HR, ABP, and SpO2 are monitored throughout the experiment. The data is currently being evaluated: outcome variables will be analyzed using a hypoxia condition-time mixed model, and planned comparisons will be used to examine specific group-time interactions based on hypoxia level and time pre and post heating. Our findings may represent a form of physiologic cross-tolerance that could be a model for potential therapeutic intervention in conditions such as OSA. This will enhance the basic understanding of the physiology of these two stress conditions and provide preliminary insights into the possible use of heat conditioning as therapy for conditions related to vascular dysregulation.