Relationship of baroreflex sensitivity and blood pressure in an older population.

OBJECTIVES: Ageing and hypertension are associated with reduced baroreflex sensitivity (BRS) in young and middle-aged populations. The effects of blood pressure level on BRS in the older population are unclear. We examined the association between blood pressure and BRS in older persons with blood pressure below 180 mmHg.
METHODS: BRS, high (alphaHF 0.15-0.4 Hz) and low (alphaLF 0.04-0.15 Hz) frequency alpha-index, was determined in 75 normotensive subjects (aged 75 +/- 4 years, 41% female, 131 +/- 10/74 +/- 7 mmHg) and 64 untreated hypertensive subjects (aged 76 +/- 5 years, 48% female, 165 +/- 7/ 88 +/- 7 mmHg) by spectral analysis of 20 min continuous blood pressure and heart rate recordings using finger plethysmography. Subjects were recruited from 10 general practices and were taking no cardiovascular medications.
RESULTS: High but not low frequency alpha-index was significantly blunted in hypertensive subjects (alphaHF 5.1 +/- 3.1 versus 8.4 +/- 7.4 ms/mmHg, P< 0.001 and alphaLF 4.7 +/- 3.0 versus 5.8 +/- 3.9 ms/mmHg, P= 0.07). Multivariate analysis of the relationship between age and blood pressure demonstrated systolic and to a lesser extent diastolic blood pressure were significant predictors of variance in BRS for alphaHF [systolic blood pressure (SBP) P< 0.0001, diastolic blood pressure (DBP) P< 0.05, r2 = 0.1] and alphaLF (SBP P=0.01, DBP P<0.05, r2 = 0.04). Age was not a significant predictor for either measure, in the 20 year range studied.
CONCLUSIONS: In an older population blood pressure is associated with reduced BRS, particularly for the high frequency component. Such a change may place older subjects with hypertension at increased risk of orthostatic hypotension, vasovagal syncope and sudden cardiac death.