Chest
Volume 63, Issue 2, February 1973, Pages 171-176
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Clinical Investigations
The Flow Volume Loop: Normal Standards and Abnormalities in Chronic Obstructive Pulmonary Disease

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The flow-volume loop is a test of ventilatory function in which a graphic recording of maximal flow rates is displayed at all lung volumes during a maximal effort forced expiratory and inspiratory vital capacity maneuver. The test is easy to demonstrate, administer, and analyze. Pulmonary diseases produce characteristic flow-volume loop abnormalities. The visualization of abnormalities and calculation of instantaneous flow rates at specific lung volumes make this test useful in screening for pulmonary disease, assessing the pulmonary effect of drugs, and following progression or regression of pulmonary disease. Normal standards for loop vital capacity, volume expired or inspired to achieve peak flow rate, expiratory and inspiratory peak flow rates, flow rates at 25 percent, 50 percent, and 75 percent of the vital capacity, and prediction equations for these indices are reported. Patterns of abnormality detected in the chronic obstructive pulmonary diseases, bronchial asthma, chronic bronchitis, and pulmonary emphysema are described. Alteration of position from sitting to standing or supine for performance of the test did not significantly alter mean flow-volume loop indices.

Section snippets

METHOD

The flow-volume loop is a test of ventilatory function in which velocity of airflow is plotted against volume during a maximal effort expiratory and inspiratory vital capacity maneuver. Two hundred and forty-seven normal subjects, 11 patients with pulmonary emphysema, 10 patients with chronic bronchitis, and 10 patients with bronchial asthma were studied. Patients with bronchial asthma performed the test before and after administration of the bronchodilator, isoproterenol. Subjects were chosen

RESULTS

Analysis of variance for indices measured from ten consecutive flow-volume loops showed that only two similar flow-volume loops per subject would need to be performed in order to obtain reliable indices. Since there is visual display of the test results, the similarity or dissimilarity between two flow-volume loops can be assessed at the completion of the test, allowing additional flow-volume loops to be performed when needed.

Age distribution, anthropomorphic characteristics, pulmonary function

DISCUSSION

The flow-volume loop is a ventilatory test which is reproducible, easy to demonstrate, administer, monitor, and calculate. Availability of prediction equations for normalcy of indices calculated from the flow-volume loop using simple anthropomorphic data makes the test useful in screening for pulmonary disease and assessing progression or regression of disease. Prediction equations were derived for VC, and points on the expiratory and inspiratory curve at 25 percent, 50 percent, and 75 percent

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Supported by a grant from the John A. Hartford Foundation and Public Health Service Grant S-M01-RR-3-13, from the Division of Research Resources.

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