Collateral ventilation in human subjects

The mechanics of collateral ventilation were studied in awake topically anesthetized young normal volunteers and in patients undergoing diagnostic bronchoscopy. A fiberoptic bronchoscope was passed peripherally to completely obstruct a segmental bronchus. A double lumen catheter was passed through the suction channel of the bronchoscope and air was infused at a constant rate through one lumen, while the pressure in the obstructed segment was measured through the other lumen. At the end of a normal expiration, the subject was instructed to hold his breath while the measurements were made. At functional residual capacity the flow of air into the obstructed segment was stopped and the fall in pressure within the segment was observed. The time constant for collateral ventilation (Tcoll) was defined as the time for the pressure in the obstructed segment to fall 63% when the flow of air into the segment was stopped. The rate constant (K = 1/Tcoll) was less than 0.2 sec^-1 in the young normal volunteers. In patients with a clinical diagnosis of emphysema, K was greater than 2.0 sec^-1. We conclude that collateral channels between segments may play a role in the distribution of ventilation in patients with chronic obstructive pulmonary disease.