Partitioning the work of breathing during running and cycling using optoelectronic plethysmography

Abstract

Work of breathing (Wb) derived from a single lung volume and pleural pressure is limited and does not fully characterize the mechanical work done by the respiratory musculature. It has long been known abdominal activation increases with increasing exercise intensity, yet the mechanical work done by these muscles is not reflected in Wb. Using Optoelectronic plethysmography (OEP) we sought to show first, the volumes obtained from OEP (VCW) were comparable to volumes obtained from flow integration (Vt) during cycling and running, and second, to show partitioned volume from OEP could be utilized to quantify the mechanical work done by the ribcage (WBRC) and abdomen (WBAB) during exercise. We fit 11 subjects (6 males/ 5 females) with reflective markers and balloon catheters. Subjects completed an incremental ramp cycling test to exhaustion and a series of submaximal running trials. We found good agreement between VCW vs Vt during cycling (p>0.05) and running (p>0.05). From rest to maximal-exercise, WBAB increased by 84% (range: 30 - 99%;WBAB: 1 ± 1 J/min to 61 ± 52 J/min). The relative contribution of the abdomen increased from 17 ± 9% at rest to 26 ± 16% during maximal-exercise. Our study highlights and provides a quantitative measure of the role of the abdominal muscles during exercise. Incorporating the work done by the abdomen allows for a greater understanding of the mechanical tasks required by the respiratory muscles and could provide further insight into how the respiratory system functions during disease and injury.