HEMODYNAMIC-RESPONSES TO BRIEF HYPEROXIA IN HEALTHY AND IN MILD HYPERTENSIVE HUMAN-SUBJECTS IN REST AND DURING DYNAMIC EXERCISE

Hemodynamic consequences of the withdrawal of arterial chemoreceptor d rive (ACD) by brief systemic hyperoxia were studied in 16 mild hyperte nsive subjects (HT) and in 16 healthy subjects (NT) in horizontal posi tion at resting metabolic rate. In another 9 mild HT and match NT meas urements were made in resting sitting position and during steady-state mild physical exercise on cycloergometer, (30% of VO2 max.) Tidal vol ume, minute ventilation, end tidal CO2 and O-2 concentration, K+ Na+, pO(2), pCO(2) values in blood were recorded. Impedance reography was u sed for recording stroke volume (SV) and arm blood flow (ABF). Cardiac output (CO), ABF and arterial blood pressure (ABF) values were used f or calculation of the total peripheral resistance (TPR) and vascular r esistance in the arm (AVR). To assess the neurogenic circulatory respo nse to withdrawal of ACD in HT attenuated by oposite peripheral effect s of high oxygen, the values of AVR, ABP, TPR and AVR changes during b rief hyperoxia in NT, assumed to be of peripheral origin, were subtrac ted from respective values in HT, assumed to be of mixed neurogenic an d peripheral origin. In HT hyperoxia applied in sitting position produ ced a brief decrease in systolic and diastolic ABP by 5.4 +/- 0.8% and 3.4 +/- 1.1% respectively, of TPR by 12.4 +/- 3% and of AVP by 4.7 +/ - 4.6%. Decrease in AVR during hyperoxia was significantly greater in sitting than in horizontal position. In NT hyperoxia produced opposite effects in ABP, TPR and AVR, as compared to those in HT. In HT subjec ts during steady-state exercise the TPR decreased by 21 +/- 3,7% reach ing a value no different from that in NT. We suggest, that in primary hypertension neurogenic sympathoexcitatory ACD is augmented and intera cts with the peripheral mechanisms related to tissue oxygen supply.