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High lung volume increases stress failure in pulmonary capillaries
Z Fu1, M L Costello, K Tsukimoto
1Department of Medicine, University of California, San Diego, La Jolla 92093-0623.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 1, 1992
Summary
High lung volumes increase stress failure in pulmonary capillaries, leading to endothelial and epithelial breaks. This occurs more frequently at higher lung volumes, suggesting a mechanism for increased lung permeability.
Area of Science:
- Pulmonary physiology
- Microcirculation
- Lung mechanics
Background:
- Pulmonary capillaries can undergo stress failure at high transmural pressures (Ptm), causing endothelial and epithelial damage.
- Previous studies indicated stress failure occurs at approximately 40 mmHg Ptm.
Purpose of the Study:
- To investigate if stress failure of pulmonary capillaries is more frequent at high lung volumes compared to low lung volumes for a given Ptm.
- To elucidate the relationship between lung inflation state and capillary wall integrity.
Main Methods:
- Anesthetized rabbits' lungs were inflated to high (20 cmH2O) or low (5 cmH2O) transpulmonary pressure.
- Pulmonary capillaries were perfused with autologous blood at either 32.5 or 2.5 cmH2O Ptm.
- Lung samples were fixed and examined using transmission and scanning electron microscopy.
Main Results:
- Stress failure of capillary walls, including endothelial and epithelial breaks, significantly increased at higher lung volumes for both tested Ptm values.
- At 32.5 cmH2O Ptm, endothelial breaks per mm were 7.1 (high volume) vs. 0.7 (low volume); epithelial breaks were 8.5 (high volume) vs. 0.9 (low volume).
- Higher lung volumes also led to increased blood-gas barrier thickness and evidence of interstitial edema, including epithelial ballooning.
Conclusions:
- High lung volumes exacerbate stress failure in pulmonary capillaries, increasing the frequency and altering the orientation of wall breaks.
- These findings suggest a physiological mechanism linking high lung inflation states to increased pulmonary capillary permeability.
- The observed edema and epithelial ballooning at higher Ptm and lung volumes further support the detrimental effects of high lung volumes on capillary integrity.