title: Sigmoidal equation for lung and chest wall volume-pressure curves in acute respiratory failure.
abstract: To assess incidence and magnitude of the "lower inflection point" of the chest wall, the sigmoidal equation was used in 36 consecutive patients intubated and mechanically ventilated with acute lung injury (ALI). They were 21 primary and 5 secondary ALI, 6 unilateral pneumonia, and 4 cardiogenic pulmonary edema. The lower inflection point was estimated as the point of maximal compliance increase. The low constant flow inflation method and esophageal pressure were used to partition the volume-pressure curves into their chest wall and lung components on zero end-expiratory pressure. The sigmoidal equation had an excellent fit with coefficients of determination >0.90 in all instances. The point of maximal compliance increase of the chest wall ranged from 0 to 8.3 cmH2O (median 1 cmH2O) with no difference between ALI groups. The chest wall significantly contributed to the lower inflection point of the respiratory system in eight patients only. The occurrence of a significant contribution of the chest wall to the lower inflection point of the respiratory system is lower than anticipated. The sigmoidal equation is able to determine precisely the point of the maximal compliance increase of lung and chest wall.
authors.affiliation: Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix-Rousse, 69004 Lyon, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Pereira
authors.forename: Julien
authors.initials: J
authors.lastname: Bohé
authors.forename: Sylvaine
authors.initials: S
authors.lastname: Rosselli
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Combourieu
authors.forename: Christian
authors.initials: C
authors.lastname: Pommier
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Perdrix
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Richard
authors.forename: Michel
authors.initials: M
authors.lastname: Badet
authors.forename: Sandrine
authors.initials: S
authors.lastname: Gaillard
authors.forename: François
authors.initials: F
authors.lastname: Philit
authors.forename: Claude
authors.initials: C
authors.lastname: Guérin
mesh_terms: D000368:Aged; D003187:Compliance; D006801:Humans; D008168:Lung / Q000502:physiology*; D008176:Lung Volume Measurements; D008875:Middle Aged; D008954:Models, Biological; D011175:Positive-Pressure Respiration / Q000379:methods*; D011312:Pressure; D011446:Prospective Studies; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy*; D035441:Thoracic Wall / Q000502:physiology*