A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications

Abstract

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 H2O) than that of controls (3.6±2.4 cm H2O). 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.

Lung volume quantified by MRI reflects extracellular-matrix deposition and altered pulmonary function in bleomycin models of fibrosis: effects of SOM230

“…These changes in lung structure lead to a severe impairment of lung function related to a decreased elasticity. Indeed, increased lung elastance as well as decreased compliance (the reciprocal of elastance) have been shown in humans (19,26,38) and in small rodent pulmonary fibrosis models (1,7,12,15,30,53,57,58). Moreover, changes in tidal volume and breathing cycle times have been shown in a mouse fibrosis model (33).…”

Entropy Production and the Pressure–Volume Curve of the Lung

“…It has been observed that Equation (6) also provide good fits to the P – V curve of both fibrotic (Ferreira et al, 2011 ) and emphysematous (Soutiere and Mitzner, 2004 ; Pérez-Rial et al, 2014 ) lungs. The altered P – V curves in these diseases can thus be mimicked simply by adjusting the parameters in Equation (6).…”

“…Following the results observed in Ferreira et al ( 2011 ), Soutiere and Mitzner ( 2004 ), and Pérez-Rial et al ( 2014 ), we model fibrosis by increasing b , while emphysema is modeled by decreasing b . Specifically, we let b vary with disease state according to where c is the fraction of lung parenchymal tissue affected by disease (a measure of disease severity), b 0 is the value of b for a healthy lung, and f ( c ) is a dimensionless function capturing the influence of the disease.…”

Theoretical open-loop model of respiratory mechanics in the extremely preterm infant

“…The first term V el represents the volume due to aggregate elasticity of the lung unit structure, which is modeled here as a saturated exponential [ 26 – 28 ] where k characterizes the lung stiffness. This representation has been found to suffice in cases of a healthy or surfactant-treated lung.…”

“…Both scenarios indicate a lower compliance and greater pressure required to increase the lung volume in the region of operating pressure. In certain pathological situations such as ARDS, a sigmoidal representation of V A ( P el ) with a low compliance region at low P el [ 28 , 31 – 34 ] could be captured in the parameterization of F rec .…”