Journal
CLINICS
Volume 66, Issue 7, Pages 1157-1163Publisher
HOSPITAL CLINICAS, UNIV SAO PAULO
DOI: 10.1590/S1807-59322011000700006
Keywords
Lung mechanics; Lung volume measurements; Respiration artificial; Respiratory mechanics; Respiratory physiology
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Funding
- NHLBI NIH HHS [K24 HL093218, P01 HL095491, R01 HL086717, R01 HL090897, R01 HL085188] Funding Source: Medline
- NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [K24HL093218, R01HL085188, P01HL095491, R01HL090897, R01HL086717] Funding Source: NIH RePORTER
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OBJECTIVE: Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis. METHODS: Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e(-k.P), and a sigmoid equation, V = a+b/(1+e(-(P-c)/d)). RESULTS: The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5 +/- 5.7 cm H(2)O) than that of controls (3.6 +/- 2.4 cm H(2)O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded. CONCLUSION: The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition.
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