Inclined running increases pulmonary haemorrhage in the Thoroughbred horse.
BACKGROUND
Capillary stress failure-induced (exercise-induced) pulmonary haemorrhage (EIPH) during intense running in horses is thought to involve both intravascular (i.e. mean pulmonary arterial pressure [Ppa] > 100 mmHg) and extravascular (e.g. negative inspiratory pressure swings) mechanisms.


OBJECTIVE
That inclined running would reduce breathing frequency (coupled to stride frequency) and increase tidal volume thus increasing lung volume changes and intrapleural pressure swings resulting in more pronounced EIPH.


METHODS
Six Thoroughbred horses were run to volitional fatigue (incremental step test) on a level (L) and inclined (I; 10%) treadmill in random order. Pulmonary minute ventilation, arterial blood gases and mean Ppa were obtained during each run while EIPH severity was quantified via bronchoalveolar lavage (BAL) 30 mins post run.


RESULTS
Time to fatigue did not differ between trials (P > 0.05). At end-exercise, breathing frequency was reduced (L, 127.8 +/- 3.0; I, 122.6 +/- 2.1 breaths/min; P < 0.05) and tidal volume increased (L, 11.5 +/- 0.6; I, 13.1 +/- 0.5 L; P < 0.05) during inclined running. No differences existed in end-exercise plasma [lactate] between trials (L, 24.5 +/- 2.9; I, 26.2 +/- 3.4 mmol/l, P > 0.05); however, the mean peak Ppa was reduced during the inclined run (L, 105+5; I, 96 +/- 4 mmHg, P < 0.05). In the face of reduced Ppa, EIPH severity was increased significantly (P < 0.05) during the inclined vs. level run (L, 37.0 +/- 11.7; I, 49.6 +/- 17.0 x 10(6) red blood cells/ml BAL fluid).


CONCLUSIONS
Although inclined running lowered peak Ppa, EIPH severity was increased. It is likely that this effect resulted, in part, from an altered ventilatory pattern (i.e. increased tidal volumes and associated intrapleural pressure changes).


CONCLUSIONS
This conclusion supports an important role for extravascular factors in the aetiology of EIPH.
D000818:Animals; D006470:Hemorrhage / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D006734:Horse Diseases / Q000209:etiology* / Q000503:physiopathology; D006736:Horses / Q000502:physiology; D008171:Lung Diseases / Q000209:etiology / Q000503:physiopathology / Q000662:veterinary*; D008297:Male; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D011897:Random Allocation