Differences in the respiratory swings in COPD and ILD candidates for lung transplantation: a critical concern interpreting central pulmonary pressures

Abstract

Abstract Background In different clinical scenarios (i.e., obesity, COPD, exercise, mechanical ventilation), the swings in intrathoracic pressure are much larger, and end-expiratory (Pee) pressure can be significantly greater than atmospheric pressure. In these scenarios, the intravascular (Piv) pulmonary pressure can overestimate the true transmural (tm) value and it is recommended to read the average of Piv over a few respiratory cycles (Pmrc) [1–3]. Purpose To analyze the respiratory swings and the effect of esophageal pressure (PES) (as a surrogate of intrathoracic pressure) on the reading of Piv tracings during the RHC at rest in COPD and interstitial lung disease (ILD) candidates for lung transplantation (LTx). Methods Thirty-one COPD (15) and ILD (16) candidates for LTx underwent RHC. End-expiratory and mean respiratory cycle measurements were obtained. The respiratory swing was estimated as the difference between maximum-minimum values of Piv. Ten patients (5 COPD/5 ILD) underwent simultaneous RHC and PES (Micro-balloon Esophageal Catheter, LATITUDE) to assess the Ptm (Piv − PES) [4]. Results Both demographic (11F/20M, 60±7 yrs, 25±4 kg/m2) and hemodynamic data (mPAP 24±9 mmHg, pulmonary arterial occlusion pressure [PAOP] 8.6±4 mmHg, right atrial pressure [RAP] 5.2±3.9 mmHg, pulmonary vascular resistance 3.5±2.6 Wu) did not show significant differences between ILD and COPD except the cardiac index (ILD: 2.8±0.8 vs. COPD: 2.4±0.3 L/min/m2). Intravascular RAPee and PAOPee were higher than mrc values in both groups (Fig 1). However, transmural RAPee and PAOPee were similar to and correlated with (r=0.62 and 0.69, respectively; p<0.05) transmural Pmrc values. PESee values were positive in COPD and ILD (3.0±2.2 vs. 3.3±2.0 mmHg, NS). All ILD had negative PESmrc values and were lower than COPD patients (−1.76±1.7 vs. 0.78±1.6 mmHg, p<0.05). ILD PES swings were higher than COPD (10.9±3.7 vs. 8.3±1.4 mmHg), although it did not reach statistical significance (p=0.08). The lower forced vital capacity (%), the more negative the PESmrc (Fig 2A). ILD pts showed higher transmural to intravascular Pmrc (p<0.05) (Fig 2B). Conclusion End-expiratory intravascular RAP and PAOP overestimates the mean respiratory cycle pressures in COPD and ILD candidates for LTx. Averaging pulmonary vascular pressure tracings over the respiratory cycle would be accurate in COPD but could underestimate transmural values in ILD candidates for LTx. The reading of mean respiratory cycle pressure could not be enough to correct the pulmonary pressures measurement error associated with the presence of large swings of intrathoracic pressure. Funding Acknowledgement Type of funding sources: None.