title: Influence of the heart on the vertical gradient of transpulmonary pressure in dogs.
abstract: Estimations were made of the vertical gradient of transpulmonary pressure (VGTP) from measurements of esophageal pressure in nine head-up dogs at functional residual capacity (FRC) when alive, when dead, and after total bilateral pneumothorax. The VGTP of 0.4 cmH2O/cm height in the alive state was abolished by pneumothorax, and roentgenograms showed that the heart moved in a caudal-dorsal direction. There was a small but significant increase in the VGTP on going from FRC to near total lung capacity (TLC) in alive head-up dogs. In eight dead head-up dogs heart weight was increased by replacing various amounts of heart blood with Hg. The VGTP was significantly increased from 0.28 to 0.51 cmH2O/cm height. The fractional increase in the VGTP was similar to the fractional increase in heart weight. In five dogs extrapolation to zero heart weight gave an average VGTP of 0.14 cmH2O/cm height. We conclude that the lungs help support the heart in the head-up dog and that the VGTP is in part determined by the pressure distribution required for this support.
mesh_terms: D000818:Animals; D004285:Dogs; D005652:Functional Residual Capacity; D006321:Heart / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D009206:Myocardium / Q000473:pathology; D009929:Organ Size; D011030:Pneumothorax / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology; D011187:Posture; D011312:Pressure; D013902:Radiography, Thoracic; D012119:Respiration; D014109:Total Lung Capacity