Non-invasive measurement of total respiratory compliance and resistance in cats

We adapted non-invasive techniques developed for human infants to measure total respiratory system compliance (Crs) and resistance (Rrs) in 21 healthy cats. The animals breathed through a face mask attached to a respiratory circuit and measurements were taken of changes in lung volume and airway pressure during brief occlusions of the airway at different lung volumes. The slope of the plot of change in volume against airway pressure yielded the multiple occlusion Crs with a mean (±95%CI) value of 6.8 (6.3-7.3) ml/cm H₂O. In 12 animals measurements were made by the single breath technique in which occlusion was made early in expiration and on release, a plot of the subsequent relaxed expiratory flow and volume yielded the time constant (τrs), Crs and Rrs with mean (±95%CI) values of 0.27 (0.22-0.31) s, 7.0 (6.1-7.8) ml/cm H₂O, and 38.7 (33.7-43.6) cm H₂O/l/s, respectively. Rrs was significantly correlated inversely with forced expiratory flow at resting lung volume (V'maxFRC).