Abstract P3106: Sex-specific Limitation Of Cardiac Capacity: Return To Fundamental Structure And Function.

Abstract

Objective: The physiology underlying the sex-specific limitation of cardiac pumping capacity remains unresolved. This study experimentally manipulated the pressure gradient (PG) driving venous return to evidence whether cardiac structure and/or function explain sex differences in cardiac capacity in young and older individuals. Methods: Healthy women and men matched by age and physical activity were included within young ( n =40, age=25±4 yr) and older ( n =55, age=60±8 yr) age groups. Cardiac volumes and output (Q) were assessed via transthoracic echocardiography from moderate to peak exercise under two hemodynamic conditions (‘low’ and ‘high’ PG between lower and upper body) generated via opposite PG identically delivered in a lower body pressure chamber. Main outcomes included sex differences in delta (‘high’ ‘low’ PG) left ventricular (LV) end-diastolic volume (ΔLVEDV), stroke volume (ΔSV) and Q (ΔQ). Results: In young individuals, ‘high’ PG increased exercise LVEDV and SV in men ( P ≤0.002), but not in women ( P ≥0.562), relative to ‘low’ PG. Accordingly, ΔLVEDV, ΔSV and ΔQ were enhanced in young men compared with young women, specifically at the highest exercise intensities ( P ≤0.019). In contrast, right and left atrial volumes were similarly increased by ‘high’ PG in both sexes ( P ≤0.007). ‘High’ PG exclusively prolonged LV filling time during exercise in young men ( P ≤ 0.036). In older women and men, ‘high’ PG did not modify exercise cardiac volumes ( P ≥0.124) and impaired established markers of LV diastolic function ( P ≤0.049). Conclusions: The female young heart is not constrained by venous return or structural factors external to the myocardium. An impaired ability to lengthen LV filling time with augmented venous return may limit female-specific cardiac capacity. With older age, cardiac chambers are not distended and LV diastolic function is impaired with increased PG in both sexes.