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Nitric oxide diffusing capacity and alveolar microvascular recruitment in sarcoidosis
Anagha R Phansalkar1, Chad M Hanson, Ahmed R Shakir
1Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9034, USA.
American Journal of Respiratory and Critical Care Medicine
|February 24, 2004
Summary
Pulmonary sarcoidosis impairs gas diffusion primarily in the lung membrane, affecting carbon monoxide transfer. A modified rebreathing method accurately estimates diffusion capacity in these patients.
Area of Science:
- Pulmonary Medicine
- Respiratory Physiology
- Cardiopulmonary Function
Background:
- Accurate assessment of lung diffusing capacity is crucial for diagnosing and managing respiratory diseases.
- The Roughton-Forster (RF) method is standard for estimating membrane diffusing capacity for carbon monoxide (DMCO) and vital capacity (VC).
- A modified RF method using simultaneous measurements of diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) has been proposed.
Purpose of the Study:
- To validate the modified RF method for estimating DMCO and VC in patients with pulmonary sarcoidosis.
- To investigate whether sarcoidosis affects the recruitment of diffusing capacity in relation to cardiac output.
Main Methods:
- Measurements included diffusing capacities for carbon monoxide (DLCO) and nitric oxide (DLNO), lung volumes, and cardiac output using a rebreathing technique.
- DMCO and VC were estimated using both the standard RF method and a modified RF method at varying alveolar O2 tensions.
- The relationship between DLCO and cardiac output was analyzed in normal subjects and patients with stages II-III pulmonary sarcoidosis.
Main Results:
- Estimates of DMCO and VC by the standard and modified RF methods showed close agreement in both normal subjects and sarcoidosis patients.
- In sarcoidosis patients, DMCO was disproportionately reduced relative to VC at any given cardiac output.
- The slope of the DLCO-cardiac output relationship was significantly lower in sarcoidosis patients compared to normal subjects.
Conclusions:
- The modified RF method accurately estimates DMCO and VC in patients with pulmonary sarcoidosis.
- In sarcoidosis, impaired gas diffusion is primarily due to limitations in the lung membrane.
- Sarcoidosis also modestly impairs the recruitment of microvascular reserves in response to increased cardiac output.