[Thermoregulation as a factor in the pathophysiology of the brachycephalic upper airway syndrome in dogs].

The change in body temperature of 21 brachycephalic and 15 normocephalic dogs was recorded using a rectal temperature probe during a standardised 10-minute run on a treadmill and in the subsequent 10-minute recovery phase. While the basal body temperature of the two groups did not differ, the body temperature increase at all representative time points was significantly different (5 min: 0,39 ± 0,17°C vs 0,21 ± 0,12°C; 10 min: 0,59 ± 0,20°C vs 0,25 ± 0,13°C; 15 min: 0,52 ± 0,20°C vs 0,21 ± 0,14°C; 20 min: 0,44 ± 0,24°C vs 0,15 ± 0,15°C) and correlated with both the phenotypic head shape and radiologically measured skull indices. While the body temperature increased significantly faster in brachycephalic dogs than in normocephalic dogs during the treadmill phase, the dogs in both groups cooled down at the same rate during the recovery phase. We interpret the difference in temperature change as an insufficient response by brachycephalic dogs to physical exertion and postulate an alternative pathway in the pathophysiology of the brachycephalic upper airway syndrome (BOAS): the shortening of the nasal skull reduces the thermoregulatory surfaces of the nasal conchae. Physical exertion and high environmental temperatures lead to a sharp rise in body temperature, which is compensated for by increased breathing and panting. This leads to increased negative pressure in the upper airways, causing the soft tissues, such as the nasal entrance cartilage, soft palate and laryngeal pockets, to be sucked into the upper airways and triggering the typical BOAS symptoms.