The effect of inspired gas density on pulmonary artery transmural pressure and exercise induced pulmonary haemorrhage.
BACKGROUND
Pulmonary capillary stress failure, largely as a result of high pulmonary vascular pressures, has been implicated in the aetiology of EIPH. However, the role of the respiratory system in determining the magnitude of EIPH has received little attention.


OBJECTIVE
Horses breathing a gas of greater density than air will exhibit greater transmural pulmonary arterial pressures (TPAP) and more severe EIPH, and horses breathing a gas of lower density than air will exhibit lower TPAP and less severe EIPH, both compared with horses breathing air.


METHODS
Following a warm-up, 8 Thoroughbred horses were exercised for 1 min at 10, 11 and 12 m/sec (5 degrees incline) breathing air or 21% oxygen/79% helium or 21% oxygen/79% argon in a randomised order. Heart rate, respiratory rate, pulmonary arterial pressure and oesophageal pressure were measured during exercise. Bronchoalveolar lavage fluid (BALF) was collected from the dorsocaudal regions of the left and right lungs 40 min post exercise and red blood cell (RBC) counts were performed.


RESULTS
The exercise tests induced mild EIPH. Maximum changes in oesophageal pressure were lower on helium-oxygen compared to argon-oxygen (P<0.001). TPAP and median RBC counts did not differ between gas mixtures. BALF RBC counts from the left lung correlated with counts from the right lung (P<0.0001). However BALF RBC counts from the left lung were higher than those from the right lung (P = 0.004).


CONCLUSIONS
As alterations in pulmonary arterial and oesophageal pressure caused by changes in inspired gas density were of similar magnitude, TPAP remained unchanged and there was no significant effect on EIPH severity.


CONCLUSIONS
Manipulations that decrease swings in intrapleural pressure may only decrease the degree of EIPH in horses severely affected by the condition.
Deaton
C M
CM
Animal Health Trust, Lanwades Park, Kentford, Suffolk, UK.
Brown-Feltner
H
H
Henley
W E
WE
Roberts
C A
CA
Lekeux
P
P
Schroter
R C
RC
Marlin
D J
DJ
D000388:Air; D000818:Animals; D001128:Argon / Q000378:metabolism; D001784:Blood Gas Analysis / Q000662:veterinary; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D004906:Erythrocyte Count / Q000662:veterinary; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006371:Helium / Q000378:metabolism; D006470:Hemorrhage / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D006734:Horse Diseases / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D006736:Horses; D008171:Lung Diseases / Q000209:etiology / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D010805:Physical Conditioning, Animal / Q000009:adverse effects / Q000502:physiology; D011651:Pulmonary Artery / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology
D006371:Helium; D001128:Argon; D010100:Oxygen