Volume Adjustment of Maximal Midexpiratory Flow: Importance of Changes in Total Lung Capacity

doi:10.1378/chest.78.4.595

Chest

Volume 78, Issue 4, October 1980, Pages 595-600

https://doi.org/10.1378/chest.78.4.595 Get rights and content

In 21 of 100 consecutive subjects demonstrating ≥ 10 percent Increase In one second forced expired volume following 200 µg inhaled salbutamol, the forced expired flow over the middle half of the vital capacity (FEF25–75%) was unchanged (n = 16) or fell ≥ 10 percent (n = 5). Volume adjustment of FEF25–75%, to the same volume below total lung capacity (TLC) before and after administration of the bronchodilator resulted in significant increases in 18 of these 21 subjects. The volume-adjusted FEF25–75% increased more (98 percent) following 1500 µg inhaled metaproterenol in ten asthmatic subjects, and decreased more (53 percent) following inhalation of histamine in eight subjects, than did the standard FEF25–75% (44 percent increase and 34 percent decrease respectively). When the small changes in TLC which were seen following metaproterenol (4.4 ± 4.1 percent reduction, p < 0.01) and histamine (11.0 ± 7.2 percent increase, p < 0.001) were considered, and FEF25–75% volume adjusted so it was measured at the same absolute lung volume, greater changes were seen (198 percent increase after use of metaproterenol, and 75 percent decrease after use of histamine). When FEF25–75% is being examined following administration of a bronchodilator or a bronchoprovocation challenge, it should be volume-adjusted to absolute lung volume. When TLC cannot easily be determined repeatedly (eg routine pulmonary function studies), volume adjustment to the same volume below TLC is advised.

Section snippets

Study 1

Consecutive routine pulmonary function studies were reviewed until 100 studies were found in which the FEV₁ improved by 10 percent or more following inhalation of 200 µg of salbutamol. The FEF25–75% following inhaled salbutamol was then reviewed for these 100 pulmonary function tests, and was recorded as improved (≥ 10 percent increase), unchanged (< 10 percent change), or reduced (≥ 10 percent decrease). In studies where the FEF25–75% improved less than 10 percent following inhalation of

Study 1

From 330 consecutive routine pulmonary function studies, 100 studies were found in which the FEV₁ improved ≥ 10 percent after therapy with 200 μg salbutamol. In these 100 studies, the FEF25–75% improved ≥ 10 percent in 79, was unchanged (< 10 percent) in 16, and decreased by ≥ 10 percent in five. In the 21 studies where the FEF25–75% failed to show improvement, volume adjustment by method 1 resulted in ≥ 10 percent improvement in 18; the mean improvement in volume-adjusted FEF25–75% in these 21

Discussion

This investigation has confirmed and expanded on the value of volume-adjustment of the FEF25–75%, not only for the demonstration of bronchodilatation on routine pulmonary function studies and in bronchodilator research, but also in bronchoprovocation studies. Furthermore, small changes in TLC, when taken into account, can result in large changes in the volume-adjusted FEF25–75% and should be considered when volume-adjusting FEF25–75%.

In routine pulmonary function tests, we have identified a 21

ACKNOWLEDGMENTS

We wish to thank Mrs. R. Day and Mr. A. Campbell for help in preparing the manuscript, and Mrs. B. P. C. Gore for technical assistance.

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Patients with suspected reversible airways obstruction (RAO) sometimes report subjective benefit after bronchodilator treatment despite no objective spirometric improvement. One possible explanation for this is improvement in volume-related or plethysmographic parameters in the absence of spirometric improvement. One hundred patients with RAO were assessed before and after inhaled bronchodilator to determine the prevalence of improvement by plethysmographic parameters in the absence of improvement in spirometric parameters. Spirometry alone (FEV₁, FVC, and FEF25-75%) identified reversibility of airflow limitation in 82 patients. Reversibility was identified by body plethysmography (specific conductance [SGaw], thoracic gas volume [TGV], and isovolume maximum expiratory flow rates [IVMEF]) in 15 of the remaining patients. The percent predicted FEF25-75% at baseline was higher in patients who required plethysmography to identify reversibility, but could not be used to predict the lack of a spirometric response for any individual patient. We conclude that spirometry alone fails to identify reversibility in approximately 15 percent of patients, and that most of these patients can be identified by additional plethysmographic measurements of volume-related parameters. At any one point in time, multiple tests must be used together to adequately identify the majority of patients with reversible airways obstruction. Improvement in volume-related parameters may explain why some patients with RAO improve subjectively with bronchodilators but show no spirometric improvement.
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Pulmonary Service, Department of Medicine, University Hospital, University of Saskatchewan, Saskatoon, Canada

Supported in part by a grant from the Medical Research Council of Canada.

Manuscript received September 29; revision accepted November 12.

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Chest

Clinical InvestigationsVolume Adjustment of Maximal Midexpiratory Flow: Importance of Changes in Total Lung Capacity

Section snippets

Study 1

Study 1

Discussion

ACKNOWLEDGMENTS

Chest

Chest

Am J Med

J Allergy Clin Immunol

J Allergy Clin Immunol

J Allergy Clin Immunol

Lancet

Am J Med

Maximal midexpiratory flow

Am Rev Tuberc

Decreases of forced expiratory flow after a bronchodilator aerosol

The Physiologist

A method for interpreting acute response to bronchodilators from the spirogram

Am Rev Respir Dis

Bronchial reactivity to inhaled histamine: A method and clinical survey

Clin Allergy

Clinical Investigations
Volume Adjustment of Maximal Midexpiratory Flow: Importance of Changes in Total Lung Capacity