Abstract
In young individuals, orthostatic intolerance is associated with marked increases in plasma epinephrine (EPI) concentrations and attenuated rises in plasma norepinephrine (NE) concentrations. This study investigated the cardiovascular, EPI and NE responses of healthy elderly males during orthostatic stress. Twelve men (68 ± 1 yr) with a recent history of orthostatic hypotension and who exhibited orthostatic intolerance (HYPO) during 90° head-up tilt (HUT) were compared with 12 men (69 ± 1 yr) without a history of orthostatic hypotension and who remained normotensive (NORMO) throughout 90° HUT. Beat-by-beat recordings of heart rate (HR), mean (MAP), systolic (SBP), diastolic (DBP), and pulse (PP) pressures were made throughout 90° HUT. Blood samples obtained during supine rest and 90° HUT were analyzed for changes in EPI and NE concentrations, hematocrit, hemoglobin and plasma volume. Compared to supine rest, orthostatic intolerance was characterized by significant reductions (p < 0.0001) in MAP, SBP, DBP, and PP. The HR, MAP, SBP, DBP, and PP at the termination of 90° HUT was significantly lower (p < 0.0001) for HYPO than NORMO. The 90° HUT position resulted in significant increases (p < 0.01) in NE for both HYPO and NORMO, with the rise in NE significantly lower (p < 0.05) in HYPO. There were no differences between groups regarding EPI concentrations at the termination of 90° HUT. These results suggest that the magnitude of arterial pressure (AP) reduction does not influence the EPI response during orthostasis in healthy elderly men. However, marked reductions in AP, leading to orthostatic intolerance, are associated with inadequate increases in NE in these individuals.
