The effect of inhaled heliox on peak flow rates in normal and brachycephalic dogs

Background Heliox, a mixture of helium and oxygen, alleviates airway obstruction in people and improves air flow, and its use has been proposed in dogs. Brachycephalic dogs have naturally occurring airway obstruction where heliox might be a useful therapeutic option. Objective The purposes of this study were to (1) determine the impact of breathing heliox on peak inspiratory and expiratory flows (PIF/PEF) in healthy dogs and (2) determine if brachycephalic dogs and mesocephalic dogs have similar responses to inhaled heliox. Animals Eleven healthy dogs: 5 mesocephalic and 6 brachycephalic dogs. Methods A prospective study. Tidal breathing flow‐volume loops were recorded when dogs were breathing room air (nitrogen‐oxygen) and heliox. Peak inspiratory and expiratory flow rates were recorded and the subjective shape of loops assessed. Peak inspiratory and expiratory flows pre‐ and post‐heliox were compared using a Mann‐Whitney Rank sum test with a P‐value of <.05 considered significant. Results In inhaled heliox, PIF and PEF were evaluated by tidal breathing flow‐volume loops. In mesocephalic dogs, PIF increased from a median of 820 mL/s (range, 494‐1010 mL/s) to 1386 mL/s; P = .02; and for PEF from 688 mL/s to 1793 mL/s (P = .04), whereas in brachycephalic dogs, the median PIF increased from 282 mL/s to 694 mL/s; P = .01 and the median PEF increased from 212 mL/s to 517 mL/sec; P = .03. Brachycephalic dogs showed normalization of loop shapes. Conclusions and clinical importance Heliox improves flow rate and appears to improve flow patterns in brachycephalic dogs.