Heart rate variability in dogs with brachycephalic obstructive airway syndrome evaluated during wakefulness and sleep

Background Brachycephalic obstructive airway syndrome (BOAS) affects the upper airways of brachycephalic dogs and might alter heart rate variability (HRV). Hypothesis/Objectives This study aimed to evaluate HRV in dogs with BOAS during wakefulness and sleep. Animals Forty-six client-owned dogs: 34 brachycephalic (with and without BOAS) and 12 non-brachycephalic controls. Methods A prospective cross-sectional study utilizing 24-h Holter monitoring and segments recorded during wakefulness and sleep. The evaluated variables included heart rate, mean RR interval, the longest sinus pause, and HRV indices calculated over 24 h, as well as during segments of wakefulness and sleep: corrected standard deviation of NN intervals (cSDNN), corrected root mean square of successive differences (cRMSSD), the vagal tone index (VVTI), and Poincaré plot analysis. Results In the 24-h Holter analysis, BOAS dogs showed significantly higher values than controls, particularly in cSDNN (0.365 [IQR: 0.306-0.465] vs 0.246 [IQR: 0.208-0.359] ms, P = .0058) and cRMSSD (0.476 [IQR: 0.409-0.599] vs 0.312 [IQR: 0.259-0.462] ms, P = .0119). Sleep was associated with higher cSDNN, cRMSSD, and VVTI in all groups (StateSleep estimates: 0.105 [95% CI, 0.062-0.149], 0.426 [95% CI, 0.264-0.588], and 1.758 [95% CI, 1.378-2.139], respectively; all P < .001), with no significant group-by-state interaction for these variables. Presence of BOAS was moderately correlated with the longest sinus pause (r = 0.4197, P = .0023), cSDNN (r = 0.4600, P = .0006), and cRMSSD (r = 0.4214, P = .0018). Conclusions and clinical importance The presence of BOAS influences autonomic modulation more than the dogs’ craniofacial conformation. Differences in HRV were more pronounced in awake dogs, likely due to chronic respiratory alterations and intermittent hypoxia.