title: The contribution of heart beat to gas mixing in the lungs of dogs.
abstract: The mixing efficiency for two gases of different gaseous diffusivity, helium (He) and sulphur hexafluoride (SF6) have been studied in anaesthetised dogs, closed and open chested, with and without the heart beating. Equilibration of He and SF6 was studied during rebreathing at frequency of 0.5 Hz and a tidal volume of either 0.3 or 0.5 L. Circulation and gas exchange were taken over by a complete heart and lung bypass circuit during the periods when the heart was stopped. The number of breaths required to reach 99% equilibration (n99) ranged from 4 to 14 for He and from 6 to 17 for SF6. There was no significant change in mixing efficiency in any situation. Stopping the heart increased the n99 for He by only 0.4 +/- 11% (1 SD) (n = 21). Opening the chest increased n99 by 1.4 +/- 13% with the heart beating and 2.5 +/- 19% with the heart stopped. The n99 for SF6 was 30 +/- 22% higher than that for He with the chest closed with or without the heart beating. This increased to 37% with the chest opened but was not altered by stopping the heart. The findings for the final phase equilibration rate constant were similar. We conclude that the beating action of the heart does not affect gas mixing in the lungs in the tidal breathing range.
mesh_terms: D000818:Animals; D004285:Dogs; D005459:Fluorides / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D006371:Helium / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D013459:Sulfur Hexafluoride / Q000502:physiology*
chemical_list: D006371:Helium; D005459:Fluorides; D013459:Sulfur Hexafluoride