Respiration and respiratory maneuvers affect cardiac output. Inspiratory muscle training (IMT) increases the negative thoracic pressure, which could have an impact on intra-thoracic hemodynamics and thereby influence the cardiac output (CO). The objective of our study was to determine changes in pulmonary arterial (PA) hemodynamics and the CO during IMT in patients with suspected pulmonary hypertension. A new method for measuring the oxygen cost of breathing during IMT was also developed. 22 patients were included in this prospective study. They performed IMT during right heart catheterization. Mixed-venous blood gas analysis was performed before and at the end of IMT to calculate the oxygen cost of breathing. The baseline PA pressure was systolic/diastolic/mean (s/d/m) 41 ± 20/13 ± 20/25 ± 11 mmHg. The CO was 5.3 ± 1.5 l/min. The IMT was set to 2.3 ± 0.6 kPa (23.7 ± 5.7 cmH2O). The PA pressure at the end of IMT was s/d/m 44/10/22 mmHg s/d/m. Though there was a trend towards a lower diastolic pressure, this change was not statistically significant (p=0.06). CO (6.2 ± 1.1 l/min) did not change due to IMT. The mixed-venous hemoglobin oxygen saturation was 71.8 ± 2.3% before IMT, with a significant reduction to 65.8 ± 5.9% (p=0.027) at the end of IMT. IMT as performed in our study neither changed the mean PA pressure nor the CO. Measuring the oxygen cost of breathing is feasible by the method described in our paper.
Sven Stieglitz, Sandhya Matthes, Christina Priegnitz, Lars Hagmeyer, Winfried Randerath