Computed tomographic diaphragmatic thickness: a promising method for the evaluation of diaphragmatic muscle in cardiopulmonary diseased cats

Abstract

Diaphragmatic dysfunction (DD) is defined as a weakening of the diaphragmatic muscle and can be an undetected cause of dyspnea. The objectives of this study were to explore the appropriate diaphragmatic location, measure diaphragmatic thickness (DT), evaluate the effect of intrinsic factors on DT, and compare DT between healthy and diseased cats, using 33 healthy cats and 15 diseased cats. A retrospective, analytical, case-control study using thoraco-abdominal feline computed tomography (CT) was performed. Two radiologists independently reviewed all images to verify inter- and intra-observer reliabilities and the best position for measuring DT. The effects of sex, age, and body weight were also studied, and cutoff values for detecting DT abnormalities were established. The results showed that the appropriate location for DT measurement was at the ventral border of the cranial endplate of the first lumbar vertebral body (L1) due to its highest intra- and inter-observer reliabilities. At this location, a significant difference in DT between the right and left hemidiaphragms (p = 0.01) was observed. Only sex had an impact on DT values. Interestingly, the DTs of cardiorespiratory-affected cats, both on the right and left sides, were significantly thinner than those of healthy cats. In conclusion, CT imaging is a reliable imaging method for determining diaphragmatic muscular atrophy. The ventral border of the cranial endplate of L1 is recommended for measuring the DT, and sex was the only factor affecting the DT measurement.

Keywords: cardiorespiratory; computed tomography; diaphragm; feline; measurement.

Figure 1

Axial computed tomography image demonstrating diaphragmatic thickness measurement from three different points: (1) at the level of the ventral border of the cranial endplate of L1, (2) the paramedian of each cupula, and (3) the most lateral of the costal part of the diaphragm. A represents the left diaphragm, and B represents the right diaphragm.

Figure 2

Axial computed tomography demonstrating measurement methods for the thickness of the rectus abdominis muscle (A) and the surface of epaxial muscle (B) at the level of the L4 vertebra: RR represents the thickness of the rectus abdominis muscle on the right side, LR represents the thickness of the rectus abdominis muscle on the left side, RE represents the surface of the right epaxial muscle, and LE represents the surface of the left epaxial muscle.

Figure 3

Correlations between the diaphragmatic thickness (DT) and intrinsic factors of cats such as age (A,B; A = right hemidiaphragm, B = left hemidiaphragm), BW (C,D; C = right hemidiaphragm, D = left hemidiaphragm), and sex (E,F; E = male, F = female) of healthy cats. *Significant difference; p < 0.05.

Figure 4

Receiver-operating characteristic curves show the area under the curve (AUC) and p-value of significance for the diagnosis of diaphragmatic dysfunction of the right hemidiaphragm (A) and left hemidiaphragm (B).