title: The role of time and pressure on alveolar recruitment.
abstract: Inappropriate mechanical ventilation in patients with acute respiratory distress syndrome can lead to ventilator-induced lung injury (VILI) and increase the morbidity and mortality. Reopening collapsed lung units may significantly reduce VILI, but the mechanisms governing lung recruitment are unclear. We thus investigated the dynamics of lung recruitment at the alveolar level. Rats (n = 6) were anesthetized and mechanically ventilated. The lungs were then lavaged with saline to simulate acute respiratory distress syndrome (ARDS). A left thoracotomy was performed, and an in vivo microscope was placed on the lung surface. The lung was recruited to three recruitment pressures (RP) of 20, 30, or 40 cmH(2)O for 40 s while subpleural alveoli were continuously filmed. Following measurement of microscopic alveolar recruitment, the lungs were excised, and macroscopic gross lung recruitment was digitally filmed. Recruitment was quantified by computer image analysis, and data were interpreted using a mathematical model. The majority of alveolar recruitment (78.3 +/- 7.4 and 84.6 +/- 5.1%) occurred in the first 2 s (T2) following application of RP 30 and 40, respectively. Only 51.9 +/- 5.4% of the microscopic field was recruited by T2 with RP 20. There was limited recruitment from T2 to T40 at all RPs. The majority of gross lung recruitment also occurred by T2 with gradual recruitment to T40. The data were accurately predicted by a mathematical model incorporating the effects of both pressure and time. Alveolar recruitment is determined by the magnitude of recruiting pressure and length of time pressure is applied, a concept supported by our mathematical model. Such a temporal dependence of alveolar recruitment needs to be considered when recruitment maneuvers for clinical application are designed.
authors.affiliation: Department of Surgery, SUNY Upstate Medical University, Syracuse, New York 13210, USA. albertsc@upstate.edu
authors.forename: Scott P
authors.initials: SP
authors.lastname: Albert
authors.forename: Joseph
authors.initials: J
authors.lastname: DiRocco
authors.forename: Gilman B
authors.initials: GB
authors.lastname: Allen
authors.forename: Jason H T
authors.initials: JH
authors.lastname: Bates
authors.forename: Ryan
authors.initials: R
authors.lastname: Lafollette
authors.forename: Brian D
authors.initials: BD
authors.lastname: Kubiak
authors.forename: John
authors.initials: J
authors.lastname: Fischer
authors.forename: Sean
authors.initials: S
authors.lastname: Maroney
authors.forename: Gary F
authors.initials: GF
authors.lastname: Nieman
mesh_terms: D055371:Acute Lung Injury / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D004195:Disease Models, Animal; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D015233:Models, Statistical; D011175:Positive-Pressure Respiration / Q000009:adverse effects* / Q000379:methods; D011650:Pulmonary Alveoli / Q000473:pathology* / Q000503:physiopathology; D012123:Pulmonary Ventilation / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012128:Respiratory Distress Syndrome / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D013997:Time Factors