Impact of aging on cardiovascular dynamics and heart rate variability during passive head-up tilt.

During aging, arterial stiffness and blood pressure (BP) increase, while heart rate variability (HRV) decreases. We examined age-related hemodynamics in 522 individuals without cardiovascular disease during passive head-up tilt (HUT) using pulse wave analysis, whole-body impedance cardiography, and HRV analysis. Mean age was 44 years, body mass index 26 kg/m, and office BP 138/88 mmHg. Cardiac output was 7% higher in the youngest quartile than the oldest. With increasing age, aortic BP, pulse pressure, pulse wave velocity, wave reflection, and systemic vascular resistance increased, while heart rate, pulse pressure amplification, and aortic reflection time decreased. During HUT, aging was linked to greater reductions in systolic BP, pulse pressure, and stroke volume, as well as diminished heart rate increase and reduced aortic reflection time shortening. HRV in low-frequency (LF) and high-frequency (HF) power decreased with age. However, the supine LF:HF ratio was higher in the oldest quartile than the youngest, a pattern not seen during HUT. In conclusion, higher arterial stiffness and systemic vascular resistance likely contribute to age-related rises in BP and pulse pressure, reduced pulse pressure amplification, and shorter aortic reflection time. Although HRV decreased with age, the supine LF:HF ratio increased, a change absent in the upright position.