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 1A; 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 1B; 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 1B; 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.