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Intrapulmonary shunting in asthmatic athletes Chao, Jennifer Chung-chi


This study investigated the presence of intrapulmonary shunt in asthmatic athletes during exercise. The effects of airway obstruction on the onset of intrapulmonary shunt were examined by comparing two conditions of airway obstruction: induced airway obstruction and reversed airway obstruction. The study also examined the effect of body position on intrapulmonary shunt recruitment by comparing three positions at rest: supine, head-down tilt and upright. We hypothesized that induced airway obstruction would trigger an earlier onset of intrapulmonary shunt during exercise when compared to reversed airway obstruction; we also hypothesized that the head-down tilt position will recruit intrapulmonary shunt at rest. Ten asthmatic, highly aerobically trained (VO₂max = 62.6 ± 6.7 ml/kg/min) males completed 3 resting stages and 6 stages of incremental exercise under both conditions of airway obstruction. Agitated saline contrast echocardiography was used to determine the presence of intrapulmonary shunt. Ten of ten subjects demonstrated intrapulmonary shunt during exercise; three of ten subjects demonstrated shunt at rest. Nine of ten subjects demonstrated shunt onset at the same workload for both conditions; one individual showed a delay in shunt onset with the reversed airway obstruction condition. Mean shunt onset under induced airway obstruction and reversed airway obstruction was 41.4 ± 7.9 %VO2max and 42.5 ± 8.1 %VO₂max, respectively; no significant difference in mean shunt onset was found. Among the 3 subjects who shunted at rest, 2 subjects shunted at resting supine and 1 subject at both supine and head-down tilt. Conditions of airway obstruction did not have an influence at shunt onset at rest. Intrapulmonary shunting during exercise is evident in asthmatic athletes and appears to occur at low workloads but is not consistently influenced by acute conditions of airway obstruction or body position.

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