AIRWAY MUCOSAL BLOOD-FLOW IN HUMANS - RESPONSE TO ADRENERGIC AGONISTS

We measured the uptake of the soluble inert gas dimethyl ether (DME) f rom a segment of the conducting airways to estimate mucosal blood flow (Q(aw)) noninvasively. The subjects inhaled, from the functional resi dual capacity position, a 300-ml gas mixture containing 35% DME, 8% he lium, 35% oxygen, and the balance nitrogen; they held their breath for 5 s and then exhaled into a spirometer. During exhalation, the instan taneous concentrations of DME and helium were recorded together with e xpired gas volume. The maneuver was repeated with breathhold times of 5, 10, 15, and 20 s. We calculated Q(aw) using the time-dependent decr ease in DME concentration in relation to the helium concentration in a n expired volume fraction between 80 and 130 mi (representing an anato mic dead-space segment distal to the glottis) and the mean DME concent ration. In 10 healthy nonsmokers, mean (+/- SE) Q(aw) was 8.0 +/- 1.3 ml/min, or 8 +/- 2 mu l/min/cm(2) mucosal surface. We obtained a value of 12 +/- 3 mu l/min/cm(2) in a validation experiment in sheep. Inhal ed methoxamine (nebulized dose 10 mg) caused a 65 +/- 19% decrease (p < 0.05), and albuterol (nebulized dose 2.5 mg) a 92 +/- 17% increase ( p < 0.05), in mean Q(aw) in seven subjects, with the maximum changes o ccurring immediately or 15 min postinhalation. We conclude that the DM E uptake method is an acceptable noninvasive means of estimating airwa y mucosal blood flow in humans and its modification by vasoactive subs tances.