In the larger airways, the blood circulation forms a subepithelial (mucosal) and outer (peribronchial) microvascular network. This raises the possibility that blood flow in these two networks is regulated independently. We used hypoxemia as a stimulus to induce changes in tracheal mucosal blood flow normalized for systemic arterial pressure (Q̇(tr n)) measured with an inert soluble gas technique and total bronchial blood flow (Q̇(br)) and normalized Q̇(br)(Q̇(brn)) measured with an electromagnetic flow probe in anesthetized sheep. Fifteen minutes of hypoxemia [PO2 40 ± 7 (SD) Torr] decreased mean Q̇(tr n) from 1.1 ± 0.4 to 0.8 ± 0.4 ml · min-1 · mmHg-1 · 102 (-27%; P < 0.05; n = 7) and increased mean Q̇(br n) from 12.1 ± 3.2 to 17.1 ± 5.4 ml · min-1 · mmHg-1 · 102 (+41%; P < 0.05; n = 6). The rise in Q̇(br) correlated with cardiac output (r = 0.68; P < 0.05). Phentolamine pretreatment (0.1 mg/kg iv) blunted the hypoxemia-related decrease of mean Q̇(tr n) (-8%; P = NS). Tyramine (2.5 mg) applied locally to the trachea decreased mean Q̇(tr n) significantly after 30 and 45 min by 31 and 19%, respectively (P < 0.05). 6-Hydroxydopamine (0.2 mg 4 times for 1 h locally applied) prevented the hypoxemia-induced as well as local tyramine-induced decrease in mean Q̇(tr n) (0 and 0%). We conclude that, during arterial hypoxemia, 1) an increase in total airway blood flow is associated with a decrease in airway mucosal blood flow, 2) total airway blood flow correlates with cardiac output, and 3) the decrease in Q̇(tr n) is at least partly mediated by local catecholamine release. These findings suggest an independent adrenergic regulation of airway mucosal blood flow.
- adrenergic nervous system
- bronchial circulation
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation