Number of open lung units during an inflation‐deflation cycle based on differences between small loop and quasi‐static compliance of P L –V L curves

Abstract

In excised rat lungs, the compliance of small sinusoidal perturbations superimposed on a quasi-static PL–VL curve differs from the quasi-static compliance in several regions along the curve. Assuming the lung is composed of individual lung units which can be in either an “open” or “closed” state, lung volume (VL) can be represented by the product of the average volume of an open lung unit (VU) and the number of open units (No). The quasi-static compliance of the lung (CTOT=dVL/dPL) can then be written as: dVL/dPL = No dVU/dPL + VU dNo/dPL. In this expression No dVU/dPL represents loop compliance (CL), and VU dNo/dPL represents a compliance resulting from the opening and closing of lung units. The anatomical structure of a lung unit has not yet been identified. By comparing CTOT with CL, a system of differential equations can be evaluated to predict how normalized values (indicated by ∗) of VU∗ and No∗ are related to VL∗ during a complete inflation-deflation cycle ([No∗]dVU∗/dPL= CL∗ and [VU∗]dNo∗/dPL= CTOT∗ − CL∗. Results show that VU∗ and No∗ approximately follow the relationships VU∗ = VL∗0.3 and No∗ = VL∗0.7 during both lung inflation and deflation between transpulmonary pressures of +30 and 0 cm H2O. Funded by NIOSH. Disclaimer: The findings and conclusions of this abstract have not been formally disseminated by NIOSH and should not be construed to represent any agency determination or policy.