Pleural pressure changes during exercise do not affect measurement of mean pulmonary vascular pressures

Abstract

SummaryThis study was designed to evaluate the influence of pleural pressure on mean pulmonary vascular pressures in exercising horses. Pulmonary artery (Pa), pulmonary wedge (Pw) and oesophageal pressures (Pes) were measured with transducer tip catheters in 6 Standardbred horses at rest and during treadmill exercise at 75, 90 and 100% of maximal heart rate. Oesophageal pressure (Pes) measurements were used to estimate pleural pressure. Vascular pressures were determined in 4 ways: 1) mean transmural vascular pressure (Ptm) at Pesequal to resting end expiratory pressure; 2) mean Ptmat Pesequal to mean Pesfor the data collection period; 3) mean Ptmwithout selection of specific data points and 4) mean pulmonary vascular pressure relative to atmospheric pressure (conventional method). Despite large fluctuations associated with breathing, mean Pesduring exercise remained close to zero, suggesting that pleural pressure fluctuates equally about zero. The swings in Peswere associated with approximately equal swings in vascular pressure so that, despite the marked fluctuations, mean Paand Pwdetermined with the 4 methods were not significantly different. The results indicate that during exercise it is valid to report mean pulmonary vascular pressures without accounting for the fluctuations in pleural pressure.