Effect of elastase or histamine on single-breath N2 washouts in the rat

A method for performing single-breath N2 washouts (SBNW) in rats was developed and the test's usefulness was studied using two experimentally induced models of lung disease. Rats were anesthetized, intubated with oral tracheal and esophageal catheters, and tested by plethysmography. The SBNW expirogram was recorded during exhalation after inhaling 100% O2 from residual volume. The slope of phase III (slope III), closing volume (CV), and closing capacity (CC) were calculated. Changes in the SBNW expirogram were compared with changes in breathing pattern, dynamic and quasistatic lung mechanics, lung volumes, and forced expiratory indices. Pre- and postinstillation tests were performed on rats treated with elastase or histamine and on untreated controls. The SBNW indices were altered at significant levels equal to those of other indices of lung function, and different patterns of change were induced by the two disease models. Elastase increased CV and CC, but slope III was unchanged. Other tests suggested loss of elastic recoil and expiratory flow limitation. Histamine increased slope III, but CV and CC were unchanged. Other tests suggested large airway constriction. These results suggested the usefulness of the SBNW in rats, but the relationships between SBNW changes and underlying physiological phenomena remain to be defined.