Sigmoidal equation for lung and chest wall volume-pressure curves in acute respiratory failure.
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.
Pereira
Cécile
C
Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix-Rousse, 69004 Lyon, France.
Bohé
Julien
J
Rosselli
Sylvaine
S
Combourieu
Emmanuel
E
Pommier
Christian
C
Perdrix
Jean-Pierre
JP
Richard
Jean-Christophe
JC
Badet
Michel
M
Gaillard
Sandrine
S
Philit
François
F
Guérin
Claude
C
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*