Association of brachycephaly, sleep-disordered breathing, and inflammatory response in dogs

Sleep is fundamental to the welfare of all animals, including dogs. Various important processes take place during sleep, and while complete sleeplessness leads to death, sleep fragmentation is also harmful. Brachycephaly, the severely shortened snout and skull in the absence of a concurrent decrease in the volume of the soft tissues of the upper airways, causes many welfare concerns, including sleep-disordered breathing (SDB). In obstructive SDB, the most common form of SDB in dogs, repeated episodes of partial or complete blockages of airflow occur during sleep. This leads to intermittent hypoxemia. Sleep-disordered breathing resembles obstructive sleep apnea in humans, which is associated with various comorbidities and a higher mortality rate. Intermittent hypoxemia is associated with chronic low-grade inflammation, an independent risk factor for a higher mortality rate in people. Research into SDB in dogs has been limited, largely due to arduous diagnostic methods, but in recent years, new developments have taken place. Risk factors for SDB include brachycephaly, moderate or severe signs of brachycephalic obstructive airway syndrome, and excess weight. As SDB negatively affects welfare on multiple levels and is at least partly treatable with surgical and conservative methods, easier methods are needed to diagnose the individuals in need of treatment. On a population level, the future of brachycephalic breeds needs to be critically evaluated.