Regional and overall inequality of ventilation and blood flow in patients with chronic airflow obstruction.

Measurements of the topographical distribution of pulmonary blood flow and ventilation have been made in 26 subjects with chronic irreversible obstructive lung disease using a radioactive xenon scanning technique. The distribution of blood flow was found to range between a normal gradient and the reverse of normal. Differences between left and right lungs were present in patients with associated bronchiectasis, previous lobectomy, and obvious radiological emphysema but not in most of those subjects with no obvious destructive changes. Ventilation was commonly decreased towards the base of the lung, that is the reverse of the normal pattern. Acetylcholine altered the blood flow distribution pattern in three out of nine subjects and this may represent vasodilatation in hypoxic regions of the lung. Repeatability of the scanning technique was found to be 10% (one standard deviation) for blood flow measurements and 11% for single-breath ventilation measurements. Examination of the expired xenon plateaux following a single inhalation of xenon in air consistently revealed a fall in count rate with expired volume, indicating the presence of poorly ventilated alveoli. However, there was a poor correlation between the degree of ventilatory inequality revealed by external counting on the one hand and the slope of the expired plateau on the other. The shape of the expired xenon plateau following xenon injection was usually horizontal and correlated poorly with the topographical distribution of blood flow. This is evidence that the extent of the inequality of ventilation-perfusion ratios at the alveolar level in patients with chronic lung disease cannot be obtained by external counters.