"Respiratory dysfunction in unsedated dog with golden retriever muscular dystrophy"

This study dealt with studying Golden retriever muscular dystrophy (GRMD), or a genetic disease affecting golden retrievers where they have decreased levels of muscle dystrophin. Dystrophin is a protein, connecting the cytoskeleton of muscle fiber to the extracellular matrix, that is crucial in contracting and relaxing of muscles. Reduced dystrophin results in progressive weakness and loss of muscle mass. The researchers performed three tests, an arterial blood gas analysis, tidal breathing spirometry, and respiratory inductance plethysmography (RIP), on eleven dogs with a mild form of GRMD and eleven carrier dogs, who were used as the control. These control dogs were matched to the dogs affected with GRMD by age and many even came from the same litter. None of the dogs were sedated during the study.

Arterial blood gas analysis measures the acidity and levels of oxygen and carbon dioxide in the blood (taken from an artery) to identify how well the lungs can conduct gas exchange in blood. The results indicated greater levels of HCO3 and higher partial pressures of CO2 (PaCO2) in dogs affected with GRMD. There were no significant differences in PaO2, pH, or lactate concentration.

Tidal breathing spirometry measures lung function, specifically the amount and rate of air being inhaled and exhaled at rest. It was concluded from these results that GRMD dogs had higher peak expiratory flow and elevated ratio of flow values early in expiration to values late in expiration.

RIP measures the movement of the chest and abdominal wall to analyze breathing. These results were consistent with the spirometry data that affirmed GRMD dogs had higher peak expiratory flow. Additionally, the RIP test revealed abnormal abdominal movement and asynchronous breathing in most (70%) of GRMD dogs. Paradoxical abdominal motion was seen in early inspiration/late expiration and two abdominal expansions occurred for each expansion of the rib cage. Some discrepancies did exist between the flow values of spirometry and RIP testing because it was not possible to evaluate rib cage/abdominal motion needed for the RIP test simultaneously to the spirometry testing, as it would ideally be done. However, there was still a relatively strong correlation between the results of the two tests.

GRMD is considered a model for the human disease, Duchenne muscular dystrophy. Therefore, the increased peak tidal expiratory flow and abnormal pattern of abdominal movement that was found was of particular interest to the researchers because this is not the case for humans with Duchenne muscular dystrophy. The researchers explained possible reasons for this occurrence in dogs with GRMD. One such hypothesis was that the dogs experienced hyperinflation, and as a result increased elastic recoil in their lungs. In other words, hyperinflation due to a lower airway obstruction may cause the chest wall to recoil inward and, thus, augmenting the lung recoil driving tidal expiratory flow. This is supported by the asynchronous breathing because hyperinflation and airway obstruction has been found to be present in people with chronic obstructive pulmonary disease.

This research study demonstrated that these three methods or tests are successful in monitoring respiratory function in dogs with GRMD without using sedation. Arterial blood gas analysis might be best used in monitoring individual dogs, with the control being their own baseline value, or in evaluating respiratory function specifically during the advance stages of the disease. These results may prove valuable during clinical trials to observe the progression of pulmonary dysfunction; therefore, aiding the understanding and treatment of Duchenne muscular dystrophy in humans.

DeVanna, J., Kornegay, J., Bogan, D., Bogan, J., Dow, J., Hawkins, E. 2013 Respiratory dysfunction in unsedated dogs with golden retriever muscular dystrophy. Science Direct 24(1): 63-73.

http://www.sciencedirect.com/science/article/pii/S0960896613009814