Effects of external nasal support on pulmonary gas exchange and EIPH in the horse

In the horse during high-speed running, partial collapse of the unsupported nasal airways may contribute to elevated inspiratory resistance. This effe ct would be expected to increase respiratory muscle work and augment negati ve intrapulmonary pressure swings which in turn might exacerbate exercise-i nduced pulmonary hemorrhage (EIPH). To investigate this issue, six Thorough breds and one Quarter Horse were evaluated while running at high speed (12/-1 m/s) under control conditions (C) and wearing an external nasal dilator (ND) in individual, randomly ordered trials two weeks apart, Whole-body ga s exchange (oxygen uptake, (V) over dot O-2, carbon dioxide output, (V) ove r dot CO2), arterial blood gases, acid-base and blood temperature were meas ured. Compared with C, ND significantly reduced (V) over dot O-2 (C, 59.9+/ -5.3; ND, 56.4+/-5.0 L/min, P < 0.05) and (V) over dot CO2 However, neither arterial blood gases, acid-base, blood temperature nor plasma lactate were changed significantly. Bronchoalveolar lavage (BAL) revealed a 33% (P < 0. 05) reduction in EIPH (quantified as red blood cells/ml BAL fluid) in the N D trial, These data demonstrate that nasal dilation can lower whole body (V ) over dot O-2, and reduce EIPH. It is possible that these effects are seco ndary to a decreased inspiratory resistance, lowered inspiratory muscle wor k and altered intrapulmonary pressures.