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

Experimental Physiology 28 December 2020


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 (Vbs). From continuous signals of airflow and O2 fraction, we calculated breath‐by‐breath oxygen uptake at the mouth and used optoelectronic plethysmography to correct for lung O2 stores changes and calculate alveolar O2 transfer. Oesophageal (Poes) and gastric (Pga) pressures were monitored using balloon‐tipped catheters. Cardiac stroke volume was measured using impedance cardiography. During the cardiodynamic phase (Φ1) of ‐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). Pga and Poes swings increased with AB (by 24.4±9.6 cm H2O, p<0.001) and RC (by 14.5±5.7 cm H2O, p<0.001), respectively. AB yielded a greater increase in intra‐breath Vbs 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 L, 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.