Collateral Ventilation and Gas Exchange during Airway Occlusion in the Normal Human Lung

Abstract

The effectiveness of collateral ventilation in maintaining alveolar gas tensions in obstructed lung segments was investigated using fiberoptic bronchoscopy to place an occluding catheter-tip balloon in selected lobar and segmental bronchi in supine normal human subjects. Gas tensions from beyond the occlusion were measured with a respiratory mass spectrometer. Collateral ventilation is known to be minimal between lobes; therefore, values measured in obstructed lobes provide a control. No significant difference was found between the partial pressures of oxygen or carbon dioxide measured in obstructed lobes and in obstructed segments. In both cases respiratory gas tensions approached reported values for mixed venous levels. The time taken to attain a steady state of gas composition in the obstructed lung was rapid (approximately 50 s), and it was no different for lobes and segments. In addition, collateral ventilation was assessed by measuring the amount of helium reaching occluded lobes and segments when subjects breathed a mixture of 21% oxygen and 79% helium. The rate of rise in helium concentration was less than 1%/min in both lobes and segments, a figure that may be explained by delivery of helium in recirculated blood rather than by collateral ventilation. We conclude that intersegmental collateral ventilation has a negligible role in the maintenance of alveolar gas tensions in supine normal humans during tidal breathing.

The use of positive pressure devices by physiotherapists

“…The work of KIKUCHI et al [56] found surfactant blocked collateral pores but postulated these opened in the presence of lung pathology. This work was supported by MORELL et al [57] in 1993 who found that in normal lungs, 80% of the collateral pores are ®lled with surfactant and that they are indeed very small, in the order of 2.6 mm. It has been suggested that different channels provide collateral ventilation at different states of lung in¯ation and that the bronchoalveolar channels of Martin are the most important in collateral ventilation [56].…”

Responsiveness and variability of airflow obstruction in chronic obstructive pulmonary disease. Clinicopathologic correlative studies.

“…We conclude that collateral ventilation occurs to a much greater extent in the emphysematous than in the normal lung and may be responsible for the relative preservation of gas exchange characteristic of this condition. Morrell Resistance to collateral flow of gas is known to be high in the normal human lung (1,2), and we previously confirmed directly that the contribution of intersegmental collateral ventilation to gas exchange in the normal lung is small (3). However, collateral resistance (Rcoll) may be lower than airway resistance in emphysematous lungs (4), and under these circumstances there may be a greater tendency for gas to flow by collateral channels into obstructed regions of lung.…”

Pulmonary Fissure Integrity and Collateral Ventilation in COPD Patients

“…As Cetti et al [6] pointed out, this may oversimplify the collateral ventilation. Alternatively, Morrell et al [29] proposed to measure collateral ventilation by occluding a lobe or segment with a balloon catheter under the guidance of a bronchoscope; however, their measurement showed the existence of collateral ventilation even for normal segment, suggesting the potential unreliability of this method. In particular, Sciurba et al analyzed both fissure integrity and emphysema heterogeneity as a surrogate for interlobar collaterals in their study [10].…”