Evaluation of exercise response in asthmatics: Impulse oscillometry in measurement of respiratory impedance

Abstract

Background: Traditionally, forced expiratory volume in one second (FEV1) was used to evaluate exercise response of patients with asthma; however, patients obviously had panting after exercise, so FEV, was affected commonly. Impulse oscillometry (IOS) is a new technique for measuring respiratory impedance that do not require maximal inspiration and forced expiration. Objective: To study airway resistance with IOS before and after exercise in healthy and asthmatic patients and investigate the significance of exercise excitation and IOS assessment. Design: Synchronically non-randomized case contrast study. Setting: Department of Respiratory Medicine, East Hospital Affiliated to Tongji University. Participants: A total of 14 male patients with bronchial asthma who were regarded as the asthmatic group were selected from Department of Respiratory Medicine of Shanghai East Hospital from January to October 2006. They were in a clinical stationary phase. Another 14 male healthy subjects were selected as the control group and ages of all subjects ranged from 29 to 50 years. All subjects provided the confirmed consent. Methods: IOS was used to measure basic value of respiratory resistance, and then subjects underwent exercise challenge. Nose of subjects was clipped breathing through mouth. Within 3-4 minutes, heart rate was increased to 90% and maintained for 6 minutes during challenge. Respiratory resistance was repeatedly measured at 1, 5, 10, 15 and 20 minutes after exercise, including airway hyperresponse (AHR), total respiratory resistance, central resistance, peripheral resistance and resonance frequency at 5, 20 and 35 Hz of pulse frequency, elasrtic resistance and inertia resistance (X5 and X35) at 5 and 10 Hz of pulse frequency. In addition, difference of AHR at 5 and 35 Hz was calculated, and change ratios of both Rcentral and Rperipheral were calculated as (highest value after exercise-baseline value)/baseline value x 100%. Main Outcome Measure: Basic value of respiratory resistance by using IOS and exercise challenge test. Results: All 14 patients with bronchial asthma and 14 healthy subjects were involved in the final analysis. Peripheral resistance (Rperipheras) was significantly higher than central resistance (Rcentral) in asthmatic patients (P < 0.01). The maximal increase of respiratory impedance occurred from 5 minutes to 10 minutes after exercise in asthmatics. Resonance frequency (Fres) of asthmatics before and after exercise was significantly increased than that of controls (P < 0.01). Change ratios of Fres from asthmatics were higher than that from control group (P < 0.01). After challenge, R5, R5-R20, Zrespir and X5 from asthmatics changed significantly than that from controls (P < 0.01). The increment change value of R5-R20 from all asthmatics was ≥ 0.032 kPa/ (L·s). The change ratio of X5 was 71.4% and asthmatics were ≥ 41%. After exercise Zrespir increased significantly, because obstruction of small bronchi during expiration and impedance increased abruptly. Air trapping was expressed in VT-Zrespir graph in 57.1% patients. There was no difference in the Vr-Zrespir graph of controls before and after exercise. Conclusion: The main site of airflow obstruction was in small airways in asthmatics after exercise challenge. The general acceptance of IOS method was good among the asthmatic patients. The airway response of exercise challenge may be assessed more accurately with IOS that do not require a maximal inspiration and forced expiration.