1. We assessed lung density, determined by computerized tomography, as a measure of emphysema and related this to lung function and measurement of the elastic recoil of the lung in normal subjects and patients with chronic obstructive lung disease. 2. We found a significant correlation between measurements of elastic recoil pressure at 90% of total lung capacity and both the forced expiratory volume in 1 s ( r = 0.80, P <0.001) and the transfer factor for carbon monoxide ( r = 0.70, P <0.001). Measurements of elastic recoil of the lung also correlated with lung density as measured by computerized tomography scanning ( P <0.001). 3. Multiple regression analysis demonstrated a correlation between the density of the lowest fifth percentile of the computerized tomography lung-density histogram, and both the natural logarithm of the shape parameter of the pressure-volume curve ( P <0.01), and the transfer factor for carbon monoxide ( P <0.01). However, the mean computerized tomography lung density correlated, in addition, with the elastic recoil pressure of the lungs at 90% of total lung capacity ( P <0.001). 4. Since the elastic recoil pressure correlates with computerized tomography lung density, and hence with emphysema, and since elastic recoil pressure also correlates with the forced expiratory volume in 1 s, these results suggest that loss of elastic recoil is one determinant of airflow limitation in patients with chronic obstructive lung disease.
1. Exponential analysis of lung pressure-volume curves is used to deal with the non-linearity of the pressure-volume relationship. A major problem of this procedure is to define the lower volume limit for exponential curve fitting. 2. In 12 healthy subjects and 24 patients with chronic airflow obstruction, a cubic function was fitted to the quasi-static pressure-volume curves to define an inflection point. 3. The exponential function of Colebatch et al . (Colebatch, H.J.H., Ng, C.K.Y. & Nikov, N. J. Applied Physiol. 1979; 46, 387–93) was then fitted to the data for volumes above the inflection point. 4. Exponential analysis with a cubic determination of an inflection point provides an objective way to describe the elastic properties of the human lungs in vivo .