Canine Brachycephalic Obstructive Airway Syndrome impacts respiratory and hemodynamic physiological adaptations during pregnancy

Brachycephalic obstructive airway syndrome (BOAS) has a negative impact on animal welfare and quality of life, with perturbing signs of respiratory distress and both clinical and reproductive issues. Therefore, the aim of this study was to compare the respiratory pattern, uterine hemodynamic profile, and placenta development during different stages of pregnancy in bitches with or without symptoms of the brachycephalic obstructive airway syndrome. Bitches were grouped according to the symptomatic manifestation of BOAS before breeding, as Brachycephalic Syndrome Group (n = 10) and Non-brachycephalic Syndrome (Control) Group (n = 10). Along gestation (early, mid and late stage), females were examined for clinical evaluations (heart and respiratory rates, body temperature, capillary refill time, hydration and mucosal color score, blood pressure and peripheral oxygen saturation), arterial blood acid-base balance and obstetric B-mode and uterine and umbilical artery dopplervelocimetry. BOAS bitches had higher (P < 0.05) early-pregnancy heart rate, and increased (P < 0.05) respiratory rate at late-pregnancy, tendency to acidemia and lower base excess (BE) and bicarbonate concentration until mid-pregnancy, while PCO₂ remained unchanged. Fetus of BOAS females had slower (P < 0.05) placental growth and improvement of umbilical artery blood flow along gestation, although uterine artery vascularization remained unchanged. In conclusion, pregnant BOAS bitches have altered respiratory pattern and acid-base balance during pregnancy; however, without negatively impacting hemodynamics of the umbilical artery. Adaptations within the fetal-placental unit were sufficient to meet physiological pregnancy demands and partially support proper fetal growth.