COLLATERAL VENTILATION AND MIDDLE LOBE SYNDROME

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Abstract
The mechanics of collateral ventilation in the right middle lobe of 5 young, normal volunteers were studied using a bronchoscopic wedge technique. The results were compared with those from an upper lobe of the same subjects. At functional residual capacity, the resistance to collateral ventilation in the right middle lobe was 4042 .+-. 559 cm H2O/l/s (mean .+-. SE), whereas that of the upper lobes was 799 .+-. 168 cm H2O/l/s. The time constant for collateral ventilation could not be measured in the right middle lobe of any of the subjects because it exceeded their breath-holding times of 6-16 s. The time constant for collateral ventilation in the upper lobes was 4.5 .+-. 1.0 s. Collateral ventilation in the right middle lobe of young normal subjects is possibly characterized by a high resistance and a long-time constant relative to the upper lobes. This is probably explained by a greater ratio of pleural surface to nonpleural surface in the right middle lobe as compared to the upper lobes. Ineffective collateral ventilation is possibly a major factor in the pathophysiology of the Middle Lobe Syndrome.

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