Effects of airway pressure and lung volume on left ventricular transmural pressure-volume relationships in humans

Positive airway pressure, combined with increased lung volume, decreases left ventricular compliance in dogs. To determine whether airway pressure or lung volume influences left ventricular diastolic properties in humans, we examined two consecutive cineangiograms with simultaneous esophageal and left ventricular pressure recordings in 14 patients. Both studies were performed during sustained inspiration, one with atmospheric airway pressure, and one with positive airway pressure (9.1 +/- 2.4 mm Hg). Positive pressure caused higher transpulmonary (airway minus esophageal) pressure and therefore greater lung volume in 10 of 14 patients, while four patients had lower transpulmonary pressures due to decreased inspiratory effort. When positive airway pressure and increased lung volume were present together (n = 10), left ventricular transmural (ventricular minus esophageal) pressure-volume curves revealed higher transmural pressures at comparable diastolic ventricular volumes. For example, at end-diastole mean left ventricular transmural pressure was 25.2 +/- 12.9 mm Hg (compared to 20.8 +/- 12.3 mm Hg during control studies, p less than 0.05), while ventricular volume was unchanged (189 +/- 87 compared to 185 +/- 81 ml, p = NS). When all 14 patients were considered together, this effect was linked more closely to higher transpulmonary pressure than to positive airway pressure. We conclude that human left ventricular transmural pressure-volume relationships are influenced by airway pressure and lung volume. Our findings further suggest that lung volume may be more important than airway pressure in this regard.