Exercise-induced pulmonary haemorrhage during submaximal exercise.
BACKGROUND
Maximally exercising horses achieve mean pulmonary artery pressures (Ppa(mean)) that exceed the minimum threshold (75 mmHg) estimated for pulmonary capillary rupture and exercise-induced pulmonary haemorrhage (EIPH). EIPH is not expected to occur during moderate submaximal exercise (i.e. 40-60% VO2max) since Ppa(mean) remains well below this threshold.


OBJECTIVE
Prolonged submaximal exercise (trotting) would precipitate locomotory respiratory uncoupling and cause EIPH. This would be present as a result of the most negative intrapleural pressures (as estimated by the minimum oesophageal pressure; Poes(min)) occurring simultaneously with the most positive Ppa (Ppa(peak)) to produce estimated maximal pulmonary artery transmural pressures (PATMPmax) that surpass the EIPH threshold.


METHODS
Five Thoroughbred horses trotted to fatigue (approximately 25 min) at 5 m/sec on a 10% incline. Ventilation (V(E)), Poes, and Ppa were measured at 5 min intervals, and bronchoalveolar lavage (BAL) red blood cells (RBCs) were quantified 45 min post exercise.


RESULTS
BAL revealed an increased EIPH (rest: 2.0 +/- 1 x 10(5), exercise: 17 +/- 10 x 10(5) RBCs/ml BALF; P<0.05), despite the highest Ppamean reaching only mean +/- s.e. 55 +/- 3 mmHg, while V(E), tidal volume and Poes(min) approached 70-80% of the values achieved at maximal running speeds (10% incline: 12-13 m/sec) by these same horses. The resulting PATMPmax was well above the level considered causative of EIPH.


CONCLUSIONS
The finding of significant EIPH during submaximal exercise broadens the spectrum of performance horses susceptible to EIPH and supports studies that suggest that extravascular factors are of primary importance in the aetiology of EIPH.


CONCLUSIONS
Consideration of strategies such as the equine nasal strip for reducing negative extravascular pressures is warranted even for exercise at moderate intensities.
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T S
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Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas 66506, USA.
McDonough
P
P
Padilla
D J
DJ
Gentile
J M
JM
Edwards
K L
KL
Erickson
H H
HH
Poole
D C
DC
D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D004906:Erythrocyte Count / Q000662:veterinary; D006470:Hemorrhage / Q000209:etiology / Q000662:veterinary*; D006734:Horse Diseases / Q000209:etiology*; D006736:Horses; D008171:Lung Diseases / Q000209:etiology / Q000662:veterinary*; D008297:Male; D010101:Oxygen Consumption; D010805:Physical Conditioning, Animal / Q000009:adverse effects / Q000502:physiology; D011651:Pulmonary Artery / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology; D011669:Pulmonary Wedge Pressure / Q000502:physiology