Chest
Volume 71, Issue 3, March 1977, Pages 361-365
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CLINICAL INVESTIGATIONS
Occult Pulmonary Abnormalities in Asymptomatic Asthmatic Children

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The pulmonary status of 178 asymptomatic asthmatic children with normal time-volume spirograms was further evaluated using flow-volume loops, body plethysmographic studies, and blood gas tensions in arterialized capillary bood. Residual volume (RV) was abnormal in 26 percent, total lung capacity (TLC) in 33 percent, RV/TLC% in 41 percent, and arterial oxygen pressure in 23 percent of them. All values for expiratory flow measured relative to observed vital capacity (VC), (ie, the forced expiratory volume in one second [FEV1], the mean forced expiratory flow during the middle half of the forced vital capacity [FEF25-75%; FVC], the FEV1/VC, and the instantaneous forced expiratory flow after 75 percent and after 50 percent of the FVC has been exhaled) were normal, and VC was subnormal in only five instances, but flow rates measured relative to TLC were abnormal in 26 percent of the patients. Some abnormality of pulmonary function was present in all but 13 percent of these asymptomatic children. Reliance upon conventional evaluation of pulmonary function by forced expiratory spirograms and freedom from wheezing may frequently give the clinician a false impression of the true condition of the lungs of the asthmatic child.

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Materials and Methods

Tests of pulmonary function were performed in 178 asthmatic children when they came for regular outpatient visits. Sixty-two were girls, and 116 were boys, and their ages ranged from 5 to 17 years, with a modal age of eight years (Fig 1).

All of the children were free from dyspnea and expiratory wheezing when tested and had been so for at least one month. All of the patients fell into either type C (76 percent) or type D (24 percent) of the classification of Hill and associates,8 and several

Results

An overall pattern of residual abnormalities of pulmonary function was observed repeatedly, hypoxemia with increased residual volume (RV) and TLC and with a normally sized VC. Mean values for tests are given in Table 1.

Discussion

The results of this study clearly slow the limitations of the routine spirogram in detecting residual abnormalities of pulmonary function in the asymptomatic asthmatic child. The FEF25-75% has been previously noted to be a highly sensitive indicator of compromised expiratory flow in asthmatic children;3, 7 that these children all had normal values for FEF25-75% implies that they were truly in remission when studied.

The incidence of abnormalities in static lung volume was higher than one may

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Presented in part at the annual meeting of the American Thoracic Society, New York City, May, 1974.

Supported in part by a grant from the Canadian Cystic Fibrosis Association.

Manuscript received June 7; revision accepted July 30.

Reprint requests: Dr. Levison, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada

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