M-Mode and Tissue Doppler Ultrasonographic Assessment of Diaphragmatic Function in Dogs With and Without Respiratory Distress

The diaphragm plays a central role in respiration, and its dysfunction may contribute to respiratory distress (RD). Although ultrasound is widely used to assess diaphragmatic function in humans, its value in veterinary patients remains poorly defined. Fifty-eight dogs undergoing cardiorespiratory evaluation were classified as normal (<i>n</i> = 31) or with RD (<i>n</i> = 27) based on clinical scores. All underwent standardised echodiaphragmatic assessment (M-mode and tissue Doppler imaging, TDI), and interobserver measurement reproducibility was analysed. Demographic characteristics did not differ significantly between groups. Respiratory rate (RR) and body weight were the main factors influencing echodiaphragmatic parameters, with RR being the most relevant. Both groups exhibited mild asymmetry between hemidiaphragms. The mean left-right excursion difference was 4.9% (-79.9 to 79.4%) in the no-RD group and 15.2% (-63.2 to 69.6%) in RD dogs. Significant differences between groups were observed for RR (<i>p</i> = 0.039), as well as TDI-derived peak contraction velocity (<i>p</i> = 0.019) and peak relaxation velocity (<i>p</i> = 0.01). However, no single echodiaphragmatic variable demonstrated strong discriminatory ability for RD in ROC or multivariable logistic analyses. Interobserver reproducibility was excellent for all measurements (intraclass correlation coefficient > 87%). In conclusion, M-mode and TDI provide reliable quantitative evaluation of diaphragmatic motion in dogs. A mild dynamic asymmetry exists between hemidiaphragms, but RD is not necessarily indicative of diaphragmatic dysfunction. Respiratory rate remains the main factor influencing echodiaphragmatic parameters.