Non-invasive forced expiratory flow-volume curves to measure lung function in cats

Forced expiratory flow-volume curves were performed in 15 cats using the non-invasive thoracic compression techniques developed for use in human infants. Cats breathed through a face mask and pneumotachygraph from which flow and volume were obtained. Thoracic compression was applied from an inflatable bag in a non-expandable jacket surrounding the animal. Bag inflation at end inspiration was initiated by a computer pulse to a pressurized chamber. Processed signals from the pneumotachygraph determined maximum-forced expiratory flow at lung volume equivalent to functional residual capacity (FRC), termed V′maxFRC. Different compression pressures were used, and the highest value from a technically satisfactory flow-volume loop was taken as the result. Mean (±95% CI) V′maxFRC was 422 (369-475) ml/s. Compared with infants of similar weight (V′maxFRC approximately 180 ml/s), cats had a much higher V′maxFRC. Tests repeated another day showed a mean (±95% CI) percentage difference between paired tests to be 2.8 (−12.6, +18.3)%. Non-invasive forced expiratory flow-volume measurements can be reliably obtained in sedated cats.