Abnormal wasted ventilation fraction and normal pulmonary hemodynamics during exercise in patients with exertional dyspnea

Our plain-English summary of Abnormal wasted ventilation fraction and normal pulmonary hemodynamics during exercise in patients with exertional dyspnea, by Z. Mohsenifar, H.V. Brown, S.K. Koerner (Respiration; International Review of Thoracic Diseases, 1982).

The study

• Authors: Z. Mohsenifar, H.V. Brown, S.K. Koerner
• Journal: Respiration; International Review of Thoracic Diseases
• Published: 1982;43(4):263-70
• Read it: PubMed · Publisher

Abstract

We have previously reported a drop on wasted ventilation fraction (VD/VT) during exercise in patients with pulmonary vaso-occlusive diseases associated with collagen vascular disorders, despite an abnormally high mean pulmonary artery pressure and pulmonary vascular resistance at rest and during exercise. To further evaluate the diagnostic value of VD/VT measurements, we studied 8 subjects with normal spirometry, lung volumes and single-breath diffusing capacity who had previously demonstrated a high VD/VT at rest and during exercise. We found normal pulmonary hemodynamics in these subjects despite an abnormal rest and exercise VD/VT. Our findings effectively exclude hemodynamically significant pulmonary vascular obstruction, and do not support the use of VD/VT as a screening method for detecting diffuse pulmonary vaso-occlusive diseases.

In plain English

This small study at Cedars-Sinai Medical Center, Los Angeles, examined 8 men aged 55 to 70 with shortness of breath on exertion. All had a history of asbestos exposure, averaging 18 years. Seven had minimal pleural plaques on chest X-ray; one had a normal X-ray. All were smokers. FVC, FEV1, lung volumes and diffusing capacity were normal, but mid-expiratory airflow was reduced in 6, which the authors said suggested small-airways dysfunction. The authors measured the wasted ventilation fraction (VD/VT, the share of each breath not used for gas exchange). They also measured lung artery pressures by catheter at rest and during light cycling. At rest, VD/VT was abnormally high in 6 of the 8 men. During exercise, average VD/VT stayed abnormally high. Yet lung artery pressures were normal in all. The authors concluded that VD/VT is not a reliable screening method for significant blockage of the lung's blood vessels. As possible explanations for the high VD/VT, they raised this airway dysfunction and called subclinical asbestos-related lung changes conceivable. None of the men had X-ray or clinical findings of asbestosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Small clinical physiology study (case series) of 8 patients, using lung function tests, right heart catheterization and exercise testing on a cycle, to examine how specific an abnormal VD/VT is
• Who was studied: 8 men aged 55 to 70 with shortness of breath on exertion, Division of Pulmonary Medicine, Cedars-Sinai Medical Center, Los Angeles. None had a history of heart or lung disease. Seven of the 8 had minimal pleural plaques on chest X-ray and the eighth had a normal chest X-ray. Study dates are not given.
• Exposure: History of asbestos exposure, mean 18 years (standard deviation 8 years). Fiber types, products and jobs are not described. All patients were also smokers.
• Main results:
  • Seven of the 8 patients had minimal pleural plaques on chest X-ray; the eighth had a normal chest X-ray.
  • All patients were smokers, with a mean smoking history of 37 pack-years.
  • All 8 patients had normal FVC, FEV1 and lung volumes.
  • Mid-expiratory flow (MMFR, FEF25-75%) was reduced in 6 of the 8 patients (less than 65% of predicted), with a mean of 65% of predicted (standard deviation 21%). The authors said this suggested small-airways dysfunction.
  • Single-breath diffusing capacity was normal (over 75% of predicted) in all patients.
  • At rest, VD/VT was abnormally elevated in 6 patients and normal in 2 (cases 5 and 8). The mean resting VD/VT was 0.43 (standard deviation 0.05).
  • At rest, pulmonary artery pressure, wedge pressure, cardiac index and pulmonary vascular resistance were normal in all patients.
  • Exercise at 30 W increased cardiac output 1.8-fold and oxygen uptake 2.7-fold.
  • During exercise, VD/VT increased in 1 patient (case 5), remained unchanged in 2 (cases 4 and 6), and decreased minimally in 4 while remaining abnormally elevated. The 2 patients with normal resting VD/VT (cases 5 and 8) had abnormal VD/VT during exercise.
  • Mean exercise VD/VT for all 8 subjects was 0.39 (standard deviation 0.05), which the authors describe as abnormally elevated.
  • During exercise, pulmonary artery pressure and wedge pressure were normal in all subjects.
  • The authors could not detect any correlation between the change in pulmonary artery pressure and VD/VT.
  • None of the patients had X-ray or clinical findings suggestive of asbestosis. The authors considered it conceivable that subclinical interstitial changes due to asbestosis caused the high VD/VT. They also raised small-airways dysfunction and uneven blood flow during exercise as possible explanations.
• The authors' conclusion: The authors concluded that an abnormal VD/VT response to exercise cannot predict abnormal pulmonary hemodynamics. They concluded that VD/VT is not a reliable screening method for detecting hemodynamically significant pulmonary vaso-occlusive diseases, and that other methods, such as measuring pulmonary artery pressure at rest and during exercise, are needed.
• Limitations the authors state:
  • Rest and exercise perfusion scans, offered as evidence that blood flow may have been unevenly distributed, were done in only 2 subjects (cases 3 and 4). The authors call these data preliminary.

Topics

Medical terms in this study, explained in our Lexicon: Dyspnea, Collagen, Spirometry, Diffusing Capacity (DLCO).

Related studies

• Lung function impairment as a guide to exercise limitation in work-related lung disorders — J.E. Cotes, J. Zejda, et al. (1988)
• Persistent Dyspnea in a 74-Year-Old Man With Normal Spirometry and Lung Volumes — W.H. Chong, B. Saha, et al. (2021)
• Asbestos-induced pleural fibrosis and impaired exercise physiology — J.F. Shih, J.S. Wilson, et al. (1994)
• Exercise alveolar-arterial oxygen pressure difference in interstitial lung disease — C. Risk, G.R. Epler, et al. (1984)
• Cardiorespiratory responses to incremental exercise in patients with asbestos-related pleural thickening and normal or slightly abnormal lung function — A. Miller, A. Bhuptani, et al. (1993)
• Lung function and exercise performance in smoking and nonsmoking asbestos-exposed workers — D.Y. Sue, A. Oren, et al. (1985)

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