We have encountered a number of otherwise typical asthmatics who had restrictive ventilatory impairment in contrast to the expected obstructive pattern. We undertook the study to determine the percentage of asthma patients who had restrictive impairment, and to evaluate possible mechanisms.
Retrospective study designed to review full PFT’s of 443 patients with asthma from January 2000 to September 2003. All PFT’s were divided into four categories- normal, obstruction, obstruction with restriction and restriction. PFT’s showing restriction were further classified based on other indicators of restrictive impairment, such as decreased diffusion capacity (DL) as an indication of occult ILD, and high body mass index (BMI). Spirometry and DL adhered to ATS standards. FRC was reviewed to exclude air trapping. PFT’s of patients with obesity (BMI> 30) were further investigated. If FVC normalized either after BD or at another time when BMI remained elevated, restriction was attributed to asthma rather then to obesity.
In our population of 443 patients, 311(70%) demonstrated either obstruction or normal PFT’s, 37 (8%) demonstrated a combined restrictive and obstructive pattern and 95 (21%) demonstrated only a restrictive pattern, which was the focus of our study. Of the restrictive population, 19 (20%) had normal BMI and normal DL, and 8 (8%) had high BMI with normalization of FVC as mentioned above. The remaining 68 patients (72%) with restriction had high BMI and/or low DL. There were 27 patients (68%) whose restrictive impairment was attributed to asthma, and could not be explained by other disorders (obesity, ILD, pleural effusion etc.). Plethysmographic FRC was increased in only 2 of these 27, demonstrating that “restriction” was not secondary to air trapping.
Of all 443 asthmatics, restriction attributed to asthma was found in 27 (6 %) cases. Asthma may contribute to restriction in 105 additional patients, along with obesity and/or occult ILD.
The finding of restriction does not contraindicate the diagnosis of asthma. Restriction may be explained by airway closure rather then narrowing.
A. Palecki, None.