A Comparison of Pattern of Breathing during Incremental Exercise in Patients with Pulmonary Fibrosis and Primary Pulmonary Hypertension

Abstract

It has previously been proposed that the pattern of breathing during exercise, and particularly maximum tidal volume, can be used to distinguish between interstitial lung disease and pulmonary vascular disease; however this has never been formally investigated. This study looks at the impact of incremental exercise on a bicycle ergometer and the impact that such exercise has on breathing pattern, specifically maximum tidal volume. Method: We retrospectively reviewed the incremental exercise tests of 10 patients with pulmonary fibrosis (PF) and 9 with primary pulmonary hypertension (PPH). Patients were exercised using a bicycle ergometer, seated, and breathing into a mouthpiece. Results: The VE/VCO2 relationship was linear in all patients, but PPH patients had higher VE/VCO2 slopes (0.058±0.03) mean ±SD than PF patients (0.039±0.01, P<0.04). The respiratory rate/VE slopes were also higher in PPH patients (0.48±0.17) than in PF patients (0.30±0.14, P<0.02). There was no correlation between the VTmax/IC at the end of exercise and the IC %predicted in either group. However, VTmax as % of IC at the end of exercise in PPH patients (59.1±7.6) was lower than in PF patients (87.0±14.5%, P<0.001). Conclusion: The pattern of breathing during exercise, specifically maximum tidal volume, is different in patients with primary pulmonary hypertension compared with pulmonary fibrosis patients. These changes in the breathing pattern are unrelated to underlying static and dynamic lung function. Thus, the conclusion is that patients who have lung diseases which restrict their breathing often compensate, likely in an effort to avoid dyspnea, by modifying their natural breathing into a more tightly constrained pattern.