Hemodynamic responses to brief hyperoxia in healthy and in mild hypertensive human subjects in rest and during...

Hemodynamic consequences of the withdrawal of arterial chemoreceptor drive (ACD) by brief systemic hyperoxia were studied in 16 mild hypertensive subjects (HT) and in 16 healthy subjects (NT) in horizontal position at resting metabolic rate. In another 9 mild HT and match NT measurements were made in resting sitting position and during steady-state mild physical exercise on cycloergometer, (30% of VO2 max.) Tidal volume, minute ventilation, end tidal CO2 and O2 concentration, K+, Na+, pO2, pCO2 values in blood were recorded. Impedance reography was used for recording stroke volume (SV) and arm blood flow (ABF). Cardiac output (CO), ABF and arterial blood pressure (ABF) values were used for calculation of the total peripheral resistance (TPR) and vascular resistance in the arm (AVR). To assess the neurogenic circulatory response to withdrawal of ACD in HT attenuated by opposite peripheral effects of high oxygen, the values of AVR, ABP, TPR and AVR changes during brief hyperoxia in NT, assumed to be of peripheral origin, were subtracted from respective values in HT, assumed to be of mixed neurogenic and peripheral origin. In HT hyperoxia applied in sitting position produced 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 AVR 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 subjects during steady-state exercise the TPR decreased by 21 +/- 3.7% reaching a value no different from that in NT. We suggest, that in primary hypertension neurogenic sympathoexcitatory ACD is augmented and interacts with the peripheral mechanisms related to tissue oxygen supply.