Habitual physical activity improves vagal cardiac modulation and carotid baroreflex function in elderly women

The impact of habitual physical activity on vagal-cardiac function and baroreflex sensitivity in elderly women is poorly characterized. This study compared vagal-cardiac modulation and carotid baroreflex (CBR) function in eight physically active (67.6 +/- 1.9 years; peak O-2 uptake 29.1 +/- 2.5 mL/min/kg) versus eight sedentary (67.3 +/- 1.8 years; peak O-2 uptake 18.6 +/- 0.9 mL/min/kg) elderly women. Heart rate (HR) variabilities and maximal changes of HR and mean arterial pressure (MAP) elicited by 5-s pressure pulses between +40 and -80 mmHg applied to the carotid sinus were measured at rest and during carotid baroreceptor unloading effected by -15 mmHg lower-body negative pressure (LBNP). HR variability was greater in active than sedentary women in both low (0.998 +/- 0.286 versus 0.255 +/- 0.063 bpm(2); P = 0.036) and high (0.895 +/- 0.301 versus 0.156 +/- 0.045 bpm(2); P = 0.044) frequency domains. CBR-HR gains (bpm/mmHg) were greater (fitness factor P < 0.001) in active versus sedentary women at rest (-0.146 +/- 0.014 versus -0.088 +/- 0.011) and during LBNP (-0.105 +/- 0.014 versus -0.065 +/- 0.008). CBR-MAP gains (mmHg/mmHg) tended to be greater (fitness factor P = 0.077) in active versus sedentary women at rest (-0.132 +/- 0.013 versus -0.110 +/- 0.011) and during LBNP (-0.129 +/- 0.015 versus -0.113 +/- 0.013). However, LBNP did not potentiate CBR-MAP gains in either sedentary or active women (LBNP factor P = 0.94), and it depressed CBR-HR gains in both groups (LBNP factor P = 0.003). CBR-HR gains in the sedentary women did not differ (sex factor P = 0.65) from gains reported in age-matched sedentary men, although CBR-MAP gains tended to be greater (sex factor P = 0.109) in the men. Thus, tonic vagal modulation indicated by HR variability and dynamic vagal responses assessed by CBR-HR gain were augmented in physically active women. Enhanced vagal-cardiac function may protect against senescence-associated cardiac electrical and hemodynamic instability in elderly women.