Attenuating intrathoracic pressure swings decreases cardiac output at different intensities of exercise

Intrathoracic pressure (ITP) swings that permit spontaneous ventilation have physiological implications for the heart. We sought to determine the effect of respiration on cardiac output (Q) during semi-supine cycle exercise using a proportional assist ventilator to minimize ITP changes and lower the work of breathing (W-b). Twenty-four participants (12 females) completed three exercise trials at 30%, 60% and 80% peak power (W-max) with unloaded (using a proportional assist ventilator, PAV) and spontaneous breathing. Intrathoracic and intraabdominal pressures were measured with balloon catheters placed in the oesophagus and stomach. Left ventricular (LV) volumes and Q were determined via echocardiography. Heart rate (HR) was measured with electrocardiogram and a customized metabolic cart measured oxygen uptake (VO2). Oesophageal pressure swings decreased from spontaneous to PAV breathing by -2.8 +/- 3.1, -4.9 +/- 5.7 and -8.1 +/- 7.7 cmH(2)O at 30%, 60% and 80% W-max, respectively (P = 0.01). However, the decreases in W-b were similar across exercise intensities (27 +/- 42 vs. 35 +/- 24 vs. 41 +/- 22%, respectively, P = 0.156). During PAV breathing compared to spontaneous breathing, Q decreased by -1.0 +/- 1.3 vs. -1.4 +/- 1.4 vs. -1.5 +/- 1.9 l min(-1) (all P < 0.05) and stroke volume decreased during PAV breathing by -11 +/- 12 vs. -9 +/- 10 vs. -7 +/- 11 ml from spontaneous breathing at 30%, 60% and 80% W-max, respectively (all P < 0.05). HR was lower during PAV breathing by -5 +/- 4 beats min(-1) at 80% W-max (P < 0.0001). Oxygen uptake decreased by 100 ml min(-1) during PAV breathing compared to spontaneous breathing at 80% W-max (P < 0.0001). Overall, attenuating ITPs mitigated LV preload and ejection, thereby suggesting that the ITPs associated with spontaneous respiration impact cardiac function during exercise

Automated summary

This study aimed to investigate the effect of respiration on cardiac output during semi-supine cycle exercise. The results showed that attenuating intrathoracic pressure swings can reduce left ventricular preload and ejection.