Effects of age on ventricular-vascular coupling

Abstract

The effects of age on the interrelation between the physical properties of the arterial tree (aortic input impedance) and left ventricular performance (cardiac output) were studied in 45 subjects, aged 19-62 yr, without apparent cardiovascular disease. Ascending aortic pulsatile pressure and blood flow velocity were measured with a multisensor catheter and cardiac output by green dye or the Fick method. Heart rate and end-diastolic aortic pressure remained unchanged with age; aortic systolic, mean and pulse pressures and aortic radius increased. In subjects younger than 30 yr, early systolic pressure usually exceeded late systolic pressure (type C beat); in subjects older than 50 yr, late systolic pressure usually exceeded early systolic pressure (type A beat). In 55% of subjects aged 30-50 yr, early and late systolic pressures were essentially equal (type B beat). The impedance spectra from all subjects showed fluctuations about the characteristic impedance (index of elastance) that were greater in the older subjects. Peripheral resistance increased 37% (r = 0.47, P < 0.001) over the age range of 20-60 yr; characteristic impedance increased 137% (r = 0.66, P < 0.001). The fundamental impedance modulus increased; the impedance modulus minimum shifted to a higher frequency. These changes in the impedance spectral pattern indicate that the ascending aorta becomes stiffer and the cross section of the peripheral vascular bed decreases with age, causing increased pulse wave velocity and wave reflection. This increase in vascular load may account for the observed decrease in stroke volume (23%, P < 0.025) and cardiac output (20%, P < 0.005) and the development of mild left ventricular hypertrophy and prolonged relaxation with advancing age.