Sympathetic and respiratory responses to hypoxia in essential hypertension

An increased sympathetic nervous response to hypoxia and reduced beta-adren ergic receptor function have been reported in hypertension; This study exam ines the relationship between hypoxia and beta-adrenergic receptor function in sixteen normotensive and eight hypertensive subjects. We measured the a verage arterial oxygen saturation and the end tidal carbon dioxide partial pressure in hypertensive and normotensive groups under normoxia and mild is ocapnic hypoxia (15% O-2, 85% N-2). The ratio of isoproterenol-stimulated c AMP to basal cAMP on lymphocytes was measured in the two groups under normo xia. We also measured plasma norepinephrine levels and calculated the "Chro notropic 25 Dose" of isoproterenol in the two groups under normoxia and hyp oxia. Hypertensives had higher plasma norepinephrine levels for either brea thing condition (F=7.16, p=0.015). Under hypoxia, hypertensives showed a si gnificant decrease in the average arterial oxygen saturation (F=4.92, p=0.0 38) and higher "Chronotropic 25 Dose" implying decreased beta-adrenergic re ceptor sensitivity (F=6.30, p=0.011). These results suggest that hypertensi ves have a diminished ventilatory response and impaired beta-adrenergic res ponse under hypoxia.