RT Journal Article
SR Electronic
T1 Airway blood flow and bronchovascular congestion in sheep
JF European Respiratory Journal
JO Eur Respir J
FD European Respiratory Society
SP 1300
OP 1307
DO 10.1183/09031936.94.07071300
VO 7
IS 7
A1 EM Baile
A1 A Sotres-Vega
A1 PD Pare
YR 1994
UL http://erj.ersjournals.com/content/7/7/1300.abstract
AB Vascular congestion could play an important role in causing airway narrowing in asthma. However, the effects of altered bronchial vascular volume and blood flow on airway morphology and pulmonary resistance have not been studied. The aim of this study was to measure airway calibre and vascular volume during inhalation of reputed dilators and constrictors of the airway vasculature in sheep. After baseline measurements of pulmonary resistance (RL) and airway blood flow (Qaw), anaesthetized sheep inhaled an aerosol of either: 0.9% saline (n = 6); histamine 16 mg.ml-1 (n = 5); phenylephrine 0.1-10 mg.ml-1 (n = 6), or methoxamine 1 mg.ml-1 (n = 5). RL and Qaw were measured at the time of peak bronchoconstriction, and the sheep were rapidly killed and lung blood loss prevented. Right lung Qaw was calculated and left lung processed for histology; measurements of cartilaginous airway size, wall thickness and fraction of the wall occupied by blood were made using morphometric techniques. Results showed that 20-30% of the airway wall was occupied by blood vessels. Inhalation of histamine caused an increase in Qaw and RL, and a 50% increase in the vascular volume fraction of the airway wall, whereas inhaled alpha-agonists did not reduce Qaw or vascular volume fraction. We conclude that the major cause of airway narrowing after inhalation of histamine is contraction of the smooth muscle, and the bronchovascular congestion contributes little to airway narrowing in cartilaginous airways of sheep. In addition inhaled alpha-agonists do not constrict the bronchial microvasculature under baseline conditions. Therefore, our results do not support the hypothesis that protection against bronchoconstriction provided by alpha-agonists is due to vasoconstriction.