Effects of Gender and Aging on Differential Autonomic Responses to Orthostatic Maneuvers

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Abstract
There are gender differences in heart rate and blood pressure response to postural change. Also, normal aging is often associated with diminished cardiac autonomic modulation during postural change from supine to upright position. Nevertheless, the exact mechanisms of these physiological alterations are not entirely understood.A total of 362 volunteers (206 females, age range: 10-88 years) underwent continuous, noninvasive, beat-to-beat blood pressure and ECG recordings in supine and upright position. To calculate spontaneous baroreflex sensitivity (BRS), blood pressure and RR interval fluctuations were reconstructed using the time-domain sequential technique. Furthermore, mean systolic and diastolic blood pressure, mean heart rate, and frequency-domain parameters of heart rate variability (low-frequency power [LF], low-frequency power in normalized units [LFn] high-frequency power [HF], high-frequency power in normalized units [HFn], low-/high-frequency ratio [LF/HF], and total power [TP]) were analyzed in both supine and standing positions. To investigate age-related differences, subjects were divided into four equally sized groups (quartile l: 10-33 years; ll: 34-42 years; III: 43-57 years; and lV: 58-88 years), as well as decades (l: 10-19 years; ll: 20-29 years; lll: 30-39 years; lV: 40-49 years; V: 50-59 years; Vl: 60-69 years; Vll: >or= 70 years).A continuous decline in BRS, LF, HF, and TP was observed with increasing age in both male and female subjects, regardless of posture. Gender comparison showed significantly higher values of LF (supine P < 0.001; upright P < 0.05), LFn (supine P < 0.001; upright P < 0.01), and TP (supine P < 0.05; upright P < 0.05) in men than women in supine and standing positions. HF revealed no gender difference and HFn (supine P < 0.001; upright P < 0.05) was larger in women. Log BRS correlated well with log LF and log HF in both supine and standing positions.There are significant differences in postural cardiac autonomic modulation between men and women, and the degree of autonomic response to orthostatic maneuvers varies with normal aging. These results may explain gender- and age-related differences in orthostatic tolerance.

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