MEASUREMENT OF INFANT PULMONARY MECHANICS - COMPARATIVE-ANALYSIS OF TECHNIQUES

In spontaneously breathing, intubated infants, lung elastance (E) and resistance (R) can be derived from the general equation of motion of t he lung, P-tp = E . V + R . V + I . V + K, where P is the pressure app lied to the system, E is the elastance (the reciprocal of the complian ce), V is the volume, R is the resistance to airflow (V), I is the ine rtance, (V) is gas acceleration, and K is a constant representing alve olar pressure. However, differences in the methods of analysis may res ult in variations in the derived values of E and R. Eighteen non-sedat ed intubated infants, with a mean post-conceptual age of 32.3 weeks an d mean weight of 1.51 kg, were studied to compare values in E and R de rived by 7 different methods of analysis. For each infant, the same 7 consecutive breaths were analyzed by the following methods: 1) linear regression of P-tp on tidal volume (V-T); 2) a Mead-Whittenberger anal ysis, 3) a 2-factor linear regression of P-tp with (V) and V-T; 4) a 3 -factor regression of P-tp with V, V-T, and V; 5) a 3-factor linear re gression tp of P-tp with V, V-T, and a (V)(2) factor (to incorporate a turbulent flow factor); 6) a 4-factor model regression of P-tp with V , V-T, V, and (V)(2); and 7) a transformation regression plot of P-tp/ V-T versus V/V-T. In addition, the lung impedance was calculated from the values of E and R derived by each method. There was no significant difference between the measurements of E and R in methods 2-6 (by MAN COVA, with the subjects being covariates). Methods 1 and 7 had a signi ficantly elevated E; in addition, Method 7 also had an elevated R. Fur thermore, there were no differences between the impedance values deriv ed from the different methods. We conclude that in this group of spont aneously breathing, intubated infants with a spectrum of pathology, th e results of a 2-factor regression analysis are comparable to more com plex models of the mechanics of the lung. (C) 1997 Wiley-Liss, Inc.