CHANGES IN TRACHEAL MUCOSAL THICKNESS AND BLOOD-FLOW IN SHEEP

Airway narrowing may be produced by increasing the blood volume of the airway mucosa. Here changes in tracheal mucosal thickness (MT(tr)) were measured in 10 anesthetized sheep. Arteries to the cervical trachea were isolated, and blood flow (Q(tr)) was measured with an electromagnetic flow probe. Simultaneous changes in MT(tr) were measured with a mechanical probe over a fixed cartilage. Arterial injections of phenylephrine produced dose-related falls in Q(tr) and MT(tr) with a maximum peak fall in MT(tr) of -104 +/- 18 (SE)-mu-m. Methacholine, bradykinin, albuterol, and histamine produced dose-related increases in Q(tr). The largest peak increase in MT(tr) of 308 +/- 121-mu-m was seen with bradykinin. For methacholine, albuterol, and histamine the largest increases in MT(tr) were 154 +/- 47, 45 +/- 10, and 153 +/- 31-mu-m, respectively. The increases in MT(tr) were not always closely dose related. The peak changes in MT(tr) occurred substantially later than those in Q(tr) for all the drugs and up to 120 s later for methacholine and bradykinin. Generally, changes in MT(tr) and Q(tr) persisted for < 10 min; at the higher doses of bradykinin increases in MT(tr) lasted for up to 15 min. Changes in MT(tr) were most closely associated in time with changes in Q(tr) for the vasoconstrictor phenylephrine. These changes in MT(tr) would alter airway resistance little in the normal trachea and by substantially more in smaller airways such as the bronchi or in the narrowed trachea. Changes in mucosal thickness may be due not only to changes in tracheal blood volume but may also reflect the effects of tissue edema and mucus secretion.