The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise.

NEW FINDINGS: What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease. ABSTRACT: We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P < 0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P = 0.151) but was significantly lower during medium (25%, P = 0.02) and high (36%, P < 0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P < 0.05). The EMGdi was significantly lower in medium and high PAV conditions (P = 0.035 and P < 0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r = 0.61, P = 0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

Quantifying the mechanical work of breathing in men and women during rowing.

PURPOSE: To quantify the mechanical work of breathing (Wb) during an indoor rowing test in men and women. Additionally, to compare sex-based differences in the Wb and its components through a rowing test. METHODS: Fifteen collegiate rowers were recruited (8 women/7 men) and performed a 2000 m rowing test on a rowing ergometer. Esophageal pressure was measured during exercise via balloon catheterization, after which pressure-volume curves were used to calculate total, inspiratory resistive and elastic, and total expiratory Wb. RESULTS: Men had significantly higher values of instantaneous and cumulative total Wb at and beyond 37.5% (430.4 ± 42.5 vs. 282.1 ± 45.1 J min-1, P < 0.05) and 62.5% (1946.8 ± 150.9 vs. 1360.1 ± 197.2 J, P < 0.05) total exercise time, respectively. However, when compared at the same minute ventilation, women had higher values of total (at and above ~ 140 L min-1), inspiratory resistive (at and above ~ 120 L min-1), and inspiratory elastic (at and above ~ 135 L min-1) Wb, whereas men presented higher total expiratory Wb compared to women at any ventilation. CONCLUSION: Although female rowers present higher relative values of inspiratory resistive and elastic Wb, their male counterparts develop greater ventilatory efforts during a 2000 m rowing test, resulting in a larger total mechanical Wb. We interpret these findings to mean that the Wb reflects both anatomical (i.e., airways and lung sizes) and respiratory (i.e., minute ventilation) sex differences during rowing.