The relationship between tidal volume and inspiratory time during PAV (open circle) and CPAP (filled circle) before lung lavage (A), after lung lavage (B) and after instillation of surfactant (C) (the X-axis is the dependent variable, and Y-axis the independent variable). Each point represents the mean value of 10 breaths. The regression curve (continuous curve) for all mean values is presented with a correlation coefficient (r). A low correlation between tidal volume and inspiratory time is observed in cats with healthy lungs with tidal volume in a normal range (A). The correlation between tidal volume and inspiratory time is increased after surfactant instillation (C).