Arterial Baroreceptor-Cardiac Reflex Sensitivity in the Elderly

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Abstract
Uncertainty still remains regarding the differing effects of blood pressure and age on baroreceptor-cardiac reflex sensitivity in elderly individuals; these differences are at least partly due to the differing methods and subject groups used in previous studies. We sought to resolve these issues by examining baroreflex sensitivity in 54 subjects aged 70±1 years (mean±SE; range, 60 to 81) divided into groups with combined systolic-diastolic hypertension (CH group, n=16), isolated systolic hypertension (ISH group, n=16), or normotension (NT group, n=22). Baroreflex sensitivity was quantified from the pulse interval and blood pressure responses to the Valsalva maneuver and pressor (phenylephrine) and depressor (sodium nitroprusside) stimuli. Baroreflex sensitivity was significantly reduced in the two hypertensive groups but did not differ between them (Valsalva maneuver: CH group, 1.9±0.3 ms/mm Hg; ISH group, 2.8±0.5; NT group, 4.4±0.4; phenylephrine: CH group, 3.1±0.6; ISH group, 3.5±0.7; NT group, 7.7±1.0; sodium nitroprusside: CH group, 2.1±0.3; ISH group, 3.6±0.8; NT group, 5.4±0.3; all P <.05 for comparison with the NT group). Thus, this study demonstrated reductions in baroreflex sensitivity with hypertension in elderly subjects consistent across all methods but with no difference between subjects with combined hypertension and isolated systolic hypertension matched for similar systolic pressure. Baroreflex sensitivity was related only to the level of systolic pressure independent of diastolic pressure or age. If elderly subjects with isolated systolic hypertension have a greater reduction in large-artery compliance than combined hypertensive subjects with similar systolic pressure, this does not appear to lead to further reductions in baroreflex sensitivity in these individuals.