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Communications to the Editor |

Supranormal Expiratory Flow Rates in Patients With Interstitial Lung Disease FREE TO VIEW

Jerome Reich, MD, FCCP
Author and Funding Information

Affiliations: Portland, OR,  Vermont Lung Center Colchester, VT

Correspondence to: Jerome Reich, MD, FCCP, 5051 SW Barnes Rd, Portland, OR 97221-1517; e-mail: Reichje@dnamail.com



Chest. 2000;118(6):1836. doi:10.1378/chest.118.6.1836
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To the Editor:

I wondered, in assessing the likelihood of interstitial lung disease in their patient, whether Wagers et al (February 2000)1might comment on the following: (1) What is the usefulness of the high expiratory flow rates—FEV1/FVC ratio of 0.89, 119% of predicted—as a noninvasive index of increased retractile forces in the lung, a point not commonly adverted to in standard references. Gold2 stated, “Thus, in early interstitial lung disease, even before lung volumes are decreased, the flow-volume curve usually shows supranormal expiratory airflow.” (2) Please comment also on the utility of correcting the carbon monoxide diffusing capacity of the lung for alveolar volume in distinguishing between interstitial lung disease and other causes of reduction in the alveolar volume. It is my recollection that this has not been found to be as discriminating as hoped. (3) What is the meaning of the term height-to-rate ratio? Was “height-to-weight ratio” intended?

References

Wagers, SS, Bouder, G, Kaminsky, DA, et al (2000) The invaluable pressure-volume curve.Chest117,578-583. [CrossRef] [PubMed]
 
Gold, WM Pulmonary function testing. Murray, JF Nadel, JA eds.Textbook of respiratory medicine 2nd ed.1994,798-900 WB Saunders. Philadelphia, PA:
 
To the Editor:

We would like to thank Dr. Jerome Reich for his interest and comments on our article. The FEV1/FVC ratio has been taught to all of us in medical school as showing a “restrictive pattern” when it is normal or above normal. This is no doubt in part due to statements such as the one you quote, found in many seminal references on pulmonary function testing. A recent article by Aaron et al1 reported the positive predicted value of a low FVC and a normal or above-normal FEV1/FVC ratio to be only 58% for the determination restriction, as confirmed by lung volumes necessitating the measurement of total lung capacity (TLC) when a restrictive pattern is found. This was the pattern seen in our patient. These authors concluded that spirometry is good at ruling out a restrictive defect, as < 3% of those with a normal vital capacity in their study subsequently were shown to have restrictive defect by TLC measurement; in those with a low vital capacity and a restrictive pattern, measurement of a TLC is necessary.

As to the second comment, we agree; perhaps we should have emphasized this point more in our article. For further elaboration, see the American Thoracic Society guides on single-breath diffusing capacity. Lastly, you are correct. It should read “height-to-weight ratio.” We would also like to point out that the legend on Figure 4 reads “as percentage of predicted TLC,” and it should read “percentage of TLC.”

References
Aaron, SD, Dales, RE, Cardinal, P How accurate is spirometry at predicting restrictive pulmonary impairment?Chest1999;115,869-873. [CrossRef] [PubMed]
 

Figures

Tables

References

Wagers, SS, Bouder, G, Kaminsky, DA, et al (2000) The invaluable pressure-volume curve.Chest117,578-583. [CrossRef] [PubMed]
 
Gold, WM Pulmonary function testing. Murray, JF Nadel, JA eds.Textbook of respiratory medicine 2nd ed.1994,798-900 WB Saunders. Philadelphia, PA:
 
Aaron, SD, Dales, RE, Cardinal, P How accurate is spirometry at predicting restrictive pulmonary impairment?Chest1999;115,869-873. [CrossRef] [PubMed]
 
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