Priming the cardiodynamic phase of pulmonary oxygen uptake through voluntary modulations of the respiratory pump at the onset of exercise

Abstract

We examined how different breathing patterns can modulate venous return and alveolar gas transfer during exercise transients in humans. Ten healthy men transitioned from rest to moderate cycling while breathing spontaneously (SP) or with voluntary increases in abdominal (AB) or intrathoracic (RC) pressure swings. We used double body plethysmography to determine blood displacements between the trunk and the extremities (V bs). From continuous signals of airflow and O 2 fraction, we calculated breath-by-breath oxygen uptake at the mouth and used optoelectronic plethysmography to correct for lung O 2 store changes and calculate alveolar O 2 transfer (V O 2 A). Oesophageal (P oes) and gastric (P ga) pressures were monitored using balloontipped catheters. Cardiac stroke volume was measured using impedance cardiography. During the cardiodynamic phase (Φ1) ofV O 2 A-on kinetics (20 s following exercise onset), AB and RC increased total alveolar oxygen transfer compared to SP (227 ± 32, P = 0.019 vs. 235 ± 27, P = 0.001 vs. 206 ± 20 ml, mean ± SD). P ga and P oes swings increased with AB (by 24.4 ± 9.6 cmH 2 O, P < 0.001) and RC (by 14.5 ± 5.7 cmH 2 O, P < 0.001), respectively. AB yielded a greater increase in intra-breath V bs swings compared with RC and SP (+0.30 ± 0.14 vs. +0.16 ± 0.11, P < 0.001 vs. +0.10 ± 0.05 ml, P = 0.006) and increased the sum of stroke volumes compared to SP (4.47 ± 1.28 vs. 3.89 ± 0.96 litres, P = 0.053), while RC produced significant central blood translocation from the extremities compared with SP (by 493 ± 311 ml, P < 0.001). Our findings indicate that combining exercise onset with AB or RC increases venous return, thus increasing mass oxygen transport above metabolic consumption during Φ1 and limiting the oxygen deficit incurred.

Blood shifts between body compartments during submaximal exercise with induced expiratory flow limitation in healthy humans

“…the increase in right ventricular filling would reduce left ventricular compliance) and increase afterload (Cheyne et al., 2020), although these effects remain unclear during exercise (Cheyne et al., 2018). In previous work, we found that during exercise, ‘abdominal’ and ‘rib cage’ breathing manoeuvres, designed to increase intra‐abdominal and intrathoracic pressure swings selectively by emphasizing the action of the diaphragm and the rib cage muscles, respectively, resulted in an increase in Vbs swings compared with spontaneous breathing (Stucky et al., 2021; Uva et al., 2016).…”

“…Mathematical subtraction of the two signals yielded the volume of blood shifted between the trunk and the extremities (volume of blood shift; Vbs) (Aliverti et al, 2009(Aliverti et al, , 2010Uva et al, 2016;LoMauro & Aliverti, 2018;Stucky et al, 2021). Prior to the computation of Vbs, a validated algorithm was used to (1) correct the drift in the ∆Vb signal due to changes in thermodynamic conditions based on measured values of temperature and humidity and (2) automatically select the level of a wavelet filter applied to remove the remaining drift in ∆Vb due to numerical integration of the flow signal (Stucky et al, 2020).…”

Priming cardiac function with voluntary respiratory maneuvers and effect on early exercise oxygen uptake

“…Elegant physiologic experiments dating back to the 1950s have shown that the fall in ITP during normal inspiration produces a decrease in right atrial pressure and widens the pressure gradient from the peripheral venous circulation to the right atrium, thus augmenting venous return (28). With the RC breathing maneuver specifically, this seems to be the dominant mechanism, with more recent data confirming that deepening the inspiratory fall in ITP with RC breathing at rest augments femoral venous return (21) and results in greater intra-breath blood displacements between the trunk and the extremities during moderate exercise (23,25). With AB in turn, in addition to this ITP-driven increase in the venous pressure gradient, the inspiratory descent of the diaphragm may also contribute to augmented venous return via the consequent increase in IAP (29)(30)(31).…”

“…Previous experimental results suggested that voluntary amplification of the respiratory pump with AB and RC modulates femoral venous blood flow (21) and enhances blood displacements between the extremities and the trunk (22,23,25), indicating a potential for respiratory maneuvers to increase venous return. However, methodological constraints could not evaluate the impact of these interventions on cardiac function per se.…”

“…The increase in Q p immediately following exercise onset results from the integration of several processes including augmentation of venous return via respiratory-driven changes in intrathoracic (ITP) and intra-abdominal pressure (IAP) (21,22). Results from studies using deliberate modulations of the "respiratory pump" by maneuvers indicate that abdominal (AB) and rib cage (RC) breathing can increase venous return (22)(23)(24)(25) leading to greater alveolar O 2 transfer during the cardiodynamic phase of exercise (23). Accordingly, voluntary modulation of respiratory mechanics may increase venous return, increase Q p, and thus enhance pulmonary V O 2 but not locomotory muscle V O 2 .…”