Comparison of five methods of analyzing respiratory pressure-volume curves

Five methods of analyzing the deflation limb of respiratory pressure-volume (PV) curves obtained from seven groups of rats that had undergone various treatments were compared. The five methods utilized measurements of: y intercept and slope with simple exponential curve fitting; area under the curve; volumes at fixed pressures; shape constant, k, of the sigmoid curve described by Paiva et al. (Respir. Physiol. 23:317, 1975); and quasi-static compliance. The seven groups of rats were treated as follows: control (n = 10); high tar/nicotine cigarette smoke exposure (n = 10); low tar/nicotine cigarette smoke exposure (n = 9); intratracheal elastase (n = 10); intratracheal elastase plus sham smoke exposure (n = 10); intratracheal elastase plus high tar/nicotine cigarette smoke exposure (n = 9); and intratracheal elastase plus low tar/nicotine cigarette smoke exposure (n = 10). Elastase treatment caused a leftward and upward shift of the PV curve and this shift was augmented by exposure to either high tar/nicotine or low tar/nicotine cigarette smoke. Using Duncan's multiple range test, we found that the y-intercept measurement of method 1, the area under the curve, volumes at fixed pressures, and quasi-static compliance methods were better able to differentiate PV curves between groups than were the slope measurement of method 1 and the shape constant measurement of method 4.