FIG. 6.

Left panel: specific ventilation maps in a sagittal slice of the right lung in a healthy control (top row) and a mild asthmatic (bottom row) at baseline, and following methacholine-induced bronchoconstriction. In these sagittal images, the head is to the right, and the dorsal lung is toward the bottom of the images. Administration of the predetermined methacholine PC20 dose altered the pattern of specific ventilation, mostly in the dependent lung. Right panel: fraction of constricted lung in the dependent, middle, and nondependent lung thirds, constriction defined as a decrease in specific ventilation of ≥50%, for the two healthy (circles, blue lines) and two asthmatics studied (square, orange line).