• Pierre Michelet, Serge Carreira, Alexandre Demoule, Julien Amour, Olivier Langeron, Bruno Riou, and Catherine Coirault.
• From the Sorbonne Universités, UPMC Univ Paris-06, UMRS INSERM 1166, IHU ICAN (P.M., J.A., B.R.), UMRS INSERM 1158 (A.D.), UMRS INSERM 974, Centre de Recherche en Myologie (C.C.), Paris, France; Department of Emergency Medicine and Surgery (B.R.), and Department of Anesthesiology and Critical Care (S.C., O.L.), Groupe hospitalier Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, Paris, France; Université de la Méditerranée, Department of Emergency Medicine and Surgery, Hôpital de la Timone, Assistance Publique-Hôpitaux de Marseille, Marseille, France (P.M.).
• Anesthesiology. 2015 Apr 1;122(4):876-83.

BackgroundAcute respiratory acidosis is associated with alterations in diaphragm performance. The authors compared the effects of respiratory acidosis and metabolic acidosis in the rat diaphragm in vitro.MethodsDiaphragmatic strips were stimulated in vitro, and mechanical and energetic variables were measured, cross-bridge kinetics calculated, and the effects of fatigue evaluated. An extracellular pH of 7.00 was obtained by increasing carbon dioxide tension (from 25 to 104 mmHg) in the respiratory acidosis group (n = 12) or lowering bicarbonate concentration (from 24.5 to 5.5 mM) in the metabolic acidosis group (n = 12) and the results compared with a control group (n = 12, pH = 7.40) after 20-min exposure.ResultsRespiratory acidosis induced a significant decrease in maximum shortening velocity (-33%, P < 0.001), active isometric force (-36%, P < 0.001), and peak power output (-59%, P < 0.001), slowed relaxation, and decreased the number of cross-bridges (-35%, P < 0.001) but not the force per cross-bridge, and impaired recovery from fatigue. Respiratory acidosis impaired more relaxation than contraction, as shown by impairment in contraction-relaxation coupling under isotonic (-26%, P < 0.001) or isometric (-44%, P < 0.001) conditions. In contrast, no significant differences in diaphragmatic contraction, relaxation, or contraction-relaxation coupling were observed in the metabolic acidosis group.ConclusionsIn rat diaphragm, acute (20 min) respiratory acidosis induced a marked decrease in the diaphragm contractility, which was not observed in metabolic acidosis.

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