Résumé :
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Most of DMD (Duchenne muscular dystrophy) patients die from respiratory failure. Their canine homologues, GRMD (Golden retriever muscular dystrophy) dogs, also develop respiratory dysfunction. The evaluation of this function seems essential during pre-clinical trials.This study aimed to assess the ability of 2 tools to detect and quantify respiratory dysfunction in GRMD dogs. The first one was named diaphragm kinematics. Awake dogs underwent a profile radioscopy of the diaphragmatic region, during Tidal breathing. Image analysis provided 2 indexes: 1) the diaphragm range of motion (ROM) at the ventral point of the caudal vena cava's foramen (CVCF), and 2) an index quantifying the diaphragmatic retraction: the angle between a perpendicular to the vertebral axis crossing the ventral point of CVCF, and a line linking this point to the caudo-ventral edge of the 10th thoracic vertebra. The second test was the recording of Tidal breathing flow-volume loops (TBFVL), using a spirometer linked to a facemask, on awake dogs. Twenty-three variables and ratios were studied. Clinically stable adult dogs (4 healthy and 4 GRMD) were tested 3 times with both methods. A repeated measures ANOVA assessed intra- and inter-tests repeatability. Diaphragm kinematics was tested on 5 healthy and 9 GRMD adults, and TBFVL on 8 healthy and 11 GRMD adults. An ANOVA was used to screen the variables for their ability to detect abnormalities in GRMD dogs.Both methods were repeatable from a cycle and from a day to another (p>0.05). GRMD dogs had a 50% reduced ROM of the diaphragm (p<0.0001), which was also caudally retracted (p<0.0001). The only TBFVL indexes able to distinguish GRMD from healthy dogs were flow ratios. GRMD dogs had a lower (p=0.008) peak inspiratory flow/peak expiratory flow (PEF). The flows at 50 and 75% of expiratory volume, normalized by the PEF, were significantly lower in GRMD dogs (p=0.018 and p=0.0008). These changes may reflect the compensatory recruitment of abdominal muscles to support the weak diaphragm. This hypothesis needs to be confirmed combining TBFVL recording and a monitoring of the presumed compensatory muscles.This is the first study investigating respiration in GRMD dogs. Both methods were able to non-invasively quantify abnormalities in GRMD adults. These tools are being tested in growing dogs, to describe quantitatively respiratory evolution. The next step will be to assess the ability of these tests to be used during pre-clinical trials.
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