Left atrial reservoir pressure-volume relations during exercise in healthy older adults

The left atrium (LA) mediates cardiopulmonary interactions. During ventricular systole, the LA functions as a compliant reservoir that is coupled to the left ventricle (LV) and offloads volume from the pulmonary vasculature. We aimed to describe LA reservoir function using phasic relationships between pulmonary artery wedge pressure (PAWP) and LA volume events. We included healthy adults (7 M/6 F, 56 +/- 8 yr) who were studied at rest and during semirecumbent cycle ergometry at a target of 100 beats/min heart rate. Right heart catheterization was performed to record the PAWP and two-dimensional (2-D) echocardiography was used to measure LA and LV volumes. We manually measured A-wave, x-trough, V-wave, and y-trough PAWP beat-by-beat, as well as minimal, maximal, and precontraction biplane LA volumes. Heart rate increased by 40 +/- 7 beats/min with exercise; stroke volume and cardiac output also rose. Although all phasic PAWP measurements increased with exercise, the x-V pressure pulse during LA filling doubled from 4 +/- 2 to 8 +/- 4 mmHg (P = 0.001). LA minimal volume was unchanged but maximal volume increased from 39 +/- 9 to 48 +/- 9 mL (P < 0.001) with exercise, and so reservoir volume increased from 24 +/- 5 to 32 +/- 8 mL (P < 0.001). As such, calculated LA compliance decreased from 6.8 +/- 3.4 to 4.8 +/- 2.6 mL/mmHg (P = 0.029). The product of V-wave PAWP and LA maximal volume, a surrogate for LA wall stress, increased from 486 +/- 193 to 953 +/- 457 mmHgmL (P < 0.001). In healthy older adults during submaximal exercise, the PAWP waveform shifts upward and its amplitude widens, LA filling increases, LA compliance decreases modestly, and LA wall stress may augment substantially.