Influence of aging and other cardiovascular risk factors on baroreflex sensitivity.

OBJECTIVES: To examine the influence of known cardiovascular risk factors (cholesterol, blood glucose levels, arterial pressures, heart rate, and aging) on baroreflex sensitivity. DESIGN: An observational epidemiological study. SETTING: Geriatric Division at the Policlinico Umberto Primo, University of Rome La Sapienza. PARTICIPANTS: Two hundred three subjects whose ages ranged from 9 to 94 years, apparently healthy and free of detectable clinical evidence of atherosclerosis. MEASUREMENTS: All subjects underwent determination of baroreflex sensitivity by phenylephrine infusion (BSphe), and by a noninvasive method derived from spectral analysis of R-R interval and arterial pressure variabilities (alpha index). RESULTS: The population, subdivided into tertiles for each variable studied, had lower BSphe values and lower alpha indexes as a function of age, plasma low-density lipoprotein (LDL) cholesterol, and systolic blood pressure. The alpha index was significantly lower in both groups with elevated LDL cholesterol levels than in those with lower levels (II and III vs I tertile, P <.001), whereas BSphe differed significantly only in the two groups who had extreme levels of LDL (I vs III tertile, P <.001). Multiple regression analysis identified a negative association of the alpha index with age (P <.001), heart rate (P <.01), area under the glucose-response curve (P <.001), and LDL cholesterol (P <.01), but of BSphe only with age (P <.001) and heart rate (P <.01). CONCLUSION: These findings indicate that some risk factors for coronary heart disease adversely influence baroreflex sensitivity.

Influence of age, the autonomic nervous system and anxiety on QT-interval variability.

As QT variability increases and heart rate variability diminishes, the QT variability index (QTVI) - a non-invasive measure of beat-to-beat fluctuations in QT interval on a single ECG lead - shows a trend towards positive values. Increased QT variability is a risk factor for sudden death. Aging lengthens the QT interval and reduces RR-interval variability. In the present study we investigated the influence of aging and the autonomic nervous system on QT-interval variability in healthy subjects. We studied 143 healthy subjects, and divided them into two age ranges (younger and older than 65 years). For each subject we measured two QTVIs: from the q wave to the end of the T wave (QTeVI) and to the apex of the T wave (QTaVI). Both indexes were calculated at baseline and after sympathetic stress. In 10 non-elderly subjects, both QTVIs were determined after beta-adrenoreceptor blockade induced by intravenous infusion of propranolol or sotalol. The QTVI was higher in elderly than in younger subjects (P<0.001). QTVIs obtained during sympathetic stress remained unchanged in the elderly, but became more negative in the younger group (P<0.05). QTeVI and QTaVI at baseline were correlated positively with age (P<0.01) and anxiety scores (P<0.05), but inversely with the low-frequency spectral power of RR-interval variability (P<0.001). QTVIs were higher in subjects with higher anxiety scores. In younger subjects, sotalol infusion increased both QTVIs significantly, whereas propranolol infusion did not. In conclusion, aging increases QT-interval variability. Whether this change is associated with an increased risk of sudden death remains unclear. The association of abnormal QT-interval variability with anxiety and with reduced low-frequency spectral power of heart rate variability merits specific investigation. In healthy non-elderly subjects, acute sympathetic stress (tilt) decreases the QTVI. beta-Adrenoreceptor blockade inhibits this negative trend, thus showing its sympathetic origin. Because a negative trend in QTVI induced by sympathetic stress increases only in younger subjects, it could represent a protective mechanism that is lost with aging.