Increases in Cardiac Output and Oxygen Consumption During Enhanced External Counterpulsation

Abstract

Background: Regular enhanced external counterpulsation (EECP) improves exercise capacity possibly through a training effect, but the roles of oxygen consumption (VO₂) vs. direct EECP effects (diastolic augmentation, DA-ratio), and their relation to cardiac index (CI) during EECP are unknown.

Methods: We studied eight patients with angina pectoris (median [range] age 72 [53-85], 25% women), who underwent EECP for 35 daily sessions. Before, during and after the first and last sessions, we assessed VO₂, DA-ratio and CI.

Results: At first EECP, CI increased from 2.2 (1.7-2.9) L/min/m² prior to EECP to 3.0 (2.2-3.8) during EECP (p=0.011), and returned to 2.4 (0.8-3.0). Similarly, VO₂ increased during EECP and returned to baseline after EECP. These patterns were reproduced at the last EECP session. Absolute values of CI and VO₂ correlated with each other during but not prior to or after EECP. The increase in CI correlated with the increase in VO₂ by trend: (first session, r 0.52, p=0.19; second session r 0.69, p=0.09), but not with DA-ratio.

Conclusions: Acutely during EECP, there is an increase in cardiac output that is unrelated to direct EECP effects but related to, and may be secondary to, an increase in peripheral O₂ demand. This may represent a training effect.

Keywords: Angina pectoris; Cardiac output; Diastolic augmentation; Enhanced external counterpulsation; Heart failure; Oxygen consumption.