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 effect would be expected to increase respiratory muscle work and augment negative intrapulmonary pressure swings which in turn might exacerbate exercise-induced pulmonary hemorrhage (EIPH). To investigate this issue, six Thoroughbreds 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 gas exchange (oxygen uptake, V̇O2, carbon dioxide output, V̇CO2), arterial blood gases, acid-base and blood temperature were measured. Compared with C, ND significantly reduced V̇O2 (C, 59.9±5.3; ND, 56.4±5.0 L/min, P < 0.05) and V̇CO2. 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 ND trial. These data demonstrate that nasal dilation can lower whole body V̇O2 and reduce EIPH. It is possible that these effects are secondary to a decreased inspiratory resistance, lowered inspiratory muscle work and altered intrapulmonary pressures.