Quantifying the work and power of breathing during exercise: a comparison of methods

The work and power of breathing (Wb & Pb, respectively) have been extensively studied in humans during exercise. Through the measurement of the Wb & Pb during exercise, we yield insight into the energetic demands of the respiratory muscles across a wide range of minute ventilations. It must be noted, however, that the methodological approach to quantifying Wb & Pb is very inconsistent in the literature. The 3 most popular methods of calculating Wb & Pb are: (1) the integrated pressure‐volume (PV) loop; (2) the Otis diagram; and (3) the Campbell diagram. Each of these methods are based on different theoretical assumptions and, as such, do not necessarily provide a consistent measure of Wb & Pb. A comparison of the Wb & Pb measured via these 3 methods during exercise is presently lacking. PURPOSE To compare values of the Wb & Pb obtained during incremental exercise as determined by the integrated PV, Otis and Campbell methods. METHODS Twenty‐three young, healthy adults (10 women; 21 ± 1 yrs) visited the laboratory on two separate occasions. The first occasion was used to obtain informed consent and to screen participants for normal pulmonary function (>85% age‐predicted). On the second visit, participants were instrumented with an esophageal balloon catheter to estimate variations in pleural pressure. Quasi‐static relaxation curves were obtained to measure chest wall recoil pressure. Participants then completed an incremental cycling protocol until volitional exhaustion. The total Wb & Pb were computed according to the numerical procedures for the integrated PV, Otis and Campbell methods. The Wb & Pb of each method were compared at standardized minute ventilations obtained during incremental. RESULTS The total Wb & Pb as determined via the Campbell method was systematically higher than the other two methods (integrated PV & Otis) at any given minute ventilation during exercise (Figure ; P < 0.05). Interestingly, the integrated PV method produced values for total Wb & Pb that were lower than those of the Otis method for minute ventilations below 80 L·min −1 , yet were higher at minute ventilations greater than 110 L·min −1 (Figure ; P <0.05). When expressed as a percentage of the values obtained via the Campbell diagram, it was clear that the Otis method constituted a decreasing proportion of total Wb & Pb as minute ventilation increased (Figure ; P <0.05), whereas the integrated PV method yielded values that represented an increasing proportion during exercise ( P <0.05). CONCLUSION The Campbell method produced the highest values at any given minute ventilation. Importantly, however, the Otis method tended to progressively underestimate the total Wb & Pb relative to the Campbell, while the opposite was true of the integrated PV method, as minute ventilation increased during exercise. Investigators must be cognizant of these differences when choosing a method to quantify the Wb & Pb during exercise. Support or Funding Information This research was funded by preliminary data funds provided by Northern Arizona University (JWD). TJC was supported by the Irene Diamond Fund/American Federation for Aging Research Postdoctoral Transition Award during the time of this study. The power of breathing (Pb) determined by the integrated pressure‐volume (PV), Otis and Campbell methods. Values represent means ± 95% confidence intervals. The left panel ( A ) represents the total Pb values obtained via the 3 different methods. The right panel ( B ) illustrates the percentage of the Campbell method's total Pb that is constituted by the integrated PV and Otis methods, separately. Only portions where no significant differences (NS) were observed have been illustrated. Figure 1