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

New Findings What is the central question of this study? The initial increase in oxygen uptake (V?O2) at exercise onset results from pulmonary perfusion changes secondary to an increased venous return. Breathing mechanics contribute to venous return through abdominal and intrathoracic pressures variation. Can voluntary breathing techniques (abdominal or rib cage breathing) increase venous return and improve V?O2 at exercise onset? What is the main finding and its importance? Abdominal and rib cage breathing increase venous return and V?O2 at exercise onset. This mechanism could be clinically relevant in patients with impaired cardiac function limiting oxygen transport. 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?O2A). Oesophageal (P-oes) and gastric (P-ga) pressures were monitored using balloon-tipped catheters. Cardiac stroke volume was measured using impedance cardiography. During the cardiodynamic phase (phi 1) of V?O2A-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 phi 1 and limiting the oxygen deficit incurred.