Assessment of airway closure from deflation lung volume-pressure curve: sigmoidal equation revisited.
OBJECTIVE
To assess a sigmoidal equation for describing airway closure.


METHODS
Experimental study.


METHODS
University laboratory.


METHODS
Eight piglets mechanically ventilated on zero end-expiratory pressure (ZEEP).


METHODS
Control and lung saline lavage.


RESULTS
Lungs were inflated up to transpulmonary pressure of 30 cmH(2)O at constant flow (0.12l s(-1)) then deflated at the same flow rate up to the point at which oesophageal pressure was constant, which was assumed to represent complete airway closure. The deflation volume-transpulmonary pressure curve was fitted to: (1) a sigmoidal equation focusing on inflexion point and pressure at maximal compliance increase and (2) an exponential equation above an inflexion point determined by eyeballing. Data deviate from the exponential equation at the point of airway closure onset. The zero-volume intercept was determined. Complete airway closure was reached at -8.3+/-3.5cmH(2)O in control conditions and at -1.3+/-3.7 cmH(2)O after lavage (p < 0.05). Between control and lavage, onset of airway closure was 3.0+/-1.9 vs. 6.0+/-2.8 cmH(2)O (p <0.05), inflexion point 3.2+/-1.8 vs. 7.7+/-2.6 cmH(2)O (p <0.001), pressure at maximal compliance increase -1.9+/-0.7 vs. -0.03+/-2.1cmH(2)O (p <0.05) and zero-volume intercept -1.5+/-1.4 vs. 0.3+/-2.3cmH(2)O (p <0.05).


CONCLUSIONS
During mechanical ventilation airways stay open and close around ZEEP in control but are closed above ZEEP after lavage. Inflexion point might reflect onset of airways closure in control. Pressure at maximal compliance increase was not a marker of complete airways closure. In control and lavage, pressure at maximal compliance increase and zero-volume intercept were reasonably equivalent.
Bayle
Frédérique
F
Hôpital de la Croix-Rousse, Service de Réanimation Médicale et d'Assistance Respiratoire, 103 Grande Rue de la Croix-Rousse, 69004 Lyon, France.
Guérin
Claude
C
Debord
Sophie
S
Badet
Michel
M
Lemasson
Stéphane
S
Poupelin
Jean-Charles
JC
Richard
Jean-Christophe
JC
D000402:Airway Obstruction / Q000503:physiopathology*; D000818:Animals; D005260:Female; D005602:France; D007442:Intubation, Intratracheal; D008176:Lung Volume Measurements; D015233:Models, Statistical; D012128:Respiratory Distress Syndrome / Q000503:physiopathology; D013552:Swine