Partitioning The Work Of Breathing During Running And Cycling Using Optoelectronic Plethysmography

Abstract

Work of breathing (B) 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 B. Optoelectronic plethysmography (OEP) is a 3-dimentional motion analysis tool that measures the positions and displacements of reflective markers on the thorax and abdomen to calculate volume changes. Importantly, OEP permits an assessment of the ribcage and abdominal contribution to volume changes during breathing. PURPOSE: We sought to: (1) show the volumes measured using OEP (VCW) were comparable to volumes from flow integration (Vt) during cycling and running, and (2) to demonstrate that partitioned ribcage and abdominal volume from OEP could be utilized to quantify the mechanical work done by the ribcage (BRC) and abdomen (BAB) during exercise. METHODS: We fit 11 subjects (6 males/5 females; age, 26 ± 3 years; body mass, 73 ± 10 kg; height, 177 ± 6 cm; maximal oxygen uptake, 55.2 ± 9.8 ml/kg/min) with 89 reflective markers, and esophageal and gastric balloon catheters. Subjects completed an incremental cycling test to exhaustion and a series of submaximal treadmill running trials. RESULTS: We found good agreement between VCW vs. Vt during cycling (bias = 0.002) (p > 0.05) and running (bias = 0.016) (p > 0.05). From rest to maximal-exercise, BAB increased by 84% (range: 30-99%; BAB: 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. CONCLUSION: 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 under physiologically relevant conditions such as exercise. Moreover, our approach could be used to gain insight into how the respiratory system functions under pathophysiological conditions and injury.