Orthostatic hypotension in aging humans

We tested the hypothesis that hypotension occurred in older adults at the o nset of orthostatic challenge as a result of vagal dysfunction. Responses o f heart rate (HR) and mean arterial pressure (MAP) were compared between 10 healthy older and younger adults during onset and sustained lower body neg ative pressure (LBNP). A younger group was also assessed after blockade of the parasympathetic nervous system with the use of atropine or glycopyrrola te and after blockade of the beta(1)-adrenoceptor by use of metoprolol. Bas eline HR (older vs. younger: 59 +/- 4 vs. 54 +/- 1 beats/min) and MAP (83 /- 2 vs. 89 +/- 3 mmHg) were not significantly different between the groups . During -40 Torr, significant tachycardia occurred at the first HR respons e in the younger subjects without hypotension, whereas significant hypotens ion [change in MAP (Delta MAP) -7 +/- 2 mmHg] was observed in the elderly w ithout tachycardia. After the parasympathetic blockade, tachycardiac respon ses of younger subjects were diminished and associated with a significant h ypotension at the onset of LBNP. However, MAP was not affected after the ca rdiac sympathetic blockade. We concluded that the elderly experienced ortho static hypotension at the onset of orthostatic challenge because of a dimin ished HR response. However, an augmented vasoconstriction helped with the m aintenance of their blood pressure during sustained LBNP.