Diaphragm ultrasound as a tool to study respiratory function in dogs: a validation study correlating sonographic findings with oesophageal pressure and spirometry during mechanical ventilation and spontaneous breathing.

This prospective observational study investigated the correlation between diaphragmatic ultrasound indices (movement and thickening fraction) and trans-diaphragmatic, oesophageal, or transpulmonary pressures, as well as tidal volumes, in anaesthetised dogs. Fifty-seven dogs of various breeds undergoing different procedures were studied under mechanical ventilation at three tidal volumes (5, 10, and 20ml/kg) and during spontaneous breathing post-ventilation. Diaphragmatic movement was evaluated with a microconvex probe in M-mode using the transversal plane during mechanical ventilation, and both transversal and longitudinal planes during spontaneous breathing. Diaphragmatic thickening fraction was assessed with a linear probe using M-mode and B-mode scans during spontaneous breathing. Oesophageal and gastric pressures were measured via a nasogastric feeding tube, with data collected across three respiratory cycles. Transpulmonary pressure strongly correlated with diaphragmatic excursion during mechanical ventilation (rho =.81; P <.001). Moderate correlations were observed between tidal volume and diaphragmatic excursion during spontaneous breathing (rho =.72 for longitudinal and.70 for transversal planes; P <.001). Fair correlations were found between oesophageal pressure and diaphragmatic slope during spontaneous breathing (rho =.56 for longitudinal and.46 for transversal planes; P <.001). Longitudinal and transversal planes strongly correlated for excursion (rho =.94; P <.001) and slope (rho =.91; P <.001), with no fixed bias. Diaphragmatic thickening fraction did not correlate with oesophageal pressure (rho =.26 for B-mode and.129 for M-mode; P =.051 and.34, respectively). These findings highlight ultrasound as a promising tool for assessing diaphragmatic function in veterinary medicine.