Effects of Increased Preload on Cardiac Function in Younger vs Older Women

Abstract

PURPOSE: Limitations in cardiac preload and/or compliance could underlie diminished stroke volume and ventricular remodeling adaptations to endurance exercise in older women. The present study tested the hypothesis that attenuated cardiac function in older women persists during acute increases in preload, both at rest and during exercise. METHODS: Nine younger (Y, 21-28 y) and ten older (O, 61-73 y) healthy, non-endurance trained women were studied 1) at rest in the supine and seated positions, and 2) during graded upright cycle ergometer exercise (20, 40, 60 and 80% of VO2peak), both before and after acute plasma volume (PV) expansion (via IV infusion of 5% albumin; 10ml/kg). Cardiac responses to postural change, exercise, and PV expansion were measured using echocardiography (rest and low intensity exercise) and open circuit C2H2 (exercise). RESULTS: Under resting normovolemic conditions, stroke volume (SV) was augmented in the supine (vs. upright) posture in both Y (61±9 vs. 52±8 ml/beat, P<0.05) and O (55±10 vs. 49±7 ml/beat, P<0.05) women. Hypervolemia augmented supine SV further in Y (68±4 ml/beat, P<0.05 vs. normovolemia), but not in O (55±10 ml/ beat, P>0.05 vs. normovolemia) women. These resting postural and hypervolemic effects were mediated by changes in end diastolic volume, and not secondary to age group differences in the extent of PV expansion (averaged +16% and +13% in Y and O, respectively) or estimated filling pressures (E/E’). E/A ratio during peak resting preload conditions (i.e., supine hypervolemia), moreover, was positively associated with VO2peak in Y, but not in O women. During upright exercise, hypervolemia increased SV an average of 15 ml/beat across all 4 work intensities in Y women (p<0.05 vs. normovolemia). This was in contrast to O women, who exhibited very small increases in SV during hypervolemic exercise (i.e., <5 ml/beat). CONCLUSIONS: Healthy older women appear to have a reduced ability (relative to younger women) to utilize acute increases in preload to raise left ventricular stroke volume, including during large muscle exercise. These findings likely reflect the combined effects of exceptional lusitropic function in younger women, and a less compliant ventricle in the aged female heart.