Diagnosing Exercise Induced Bronchoconstriction

Abstract

Eucapnic Voluntary Hyperpnoea (EVH) is a sensitive indirect airway challenge to assist in the diagnosis of Exercise Induced Bronchoconstriction (EIB). However, it has been previously reported that a positive EVH challenge may not necessarily predictive a positive exercise challenge (EX). EX have previously shown varying sensitivity due to differences in control over the inspired air water content, with studies being conducted in ambient lab conditions or using medical grade dry air. PURPOSE: To compare the EVH challenge with an EX in a controlled dry air environment, to see if a standardised EX can be used in the diagnosis or EIB. METHODS: Thirty-one healthy participants (10 female; 21 males, age 36 ± 10 yrs, exercising 7.7 ± 3.0 hrs per week) gave informed consent. Eight had a history of asthma but were not taking preventative medication. Participants completed an EVH and an EX on a cycle ergometer in a randomised order. The EVH required participants to breathe a gas mixture (5% CO2, 21% O2 and 74% N2, <2%RH) at a rate equivalent to 85% predicted MVV. The EX was conducted in an environmental chamber (16°c, 25%RH). Following a 4-min set warm up participants completed 6-mins of cycling at a work rate associated with 85% HRmax. Tests were deemed positive if there was a fall in FEV1 of ≥ 10% following the challenge. Results were analysed using paired t-tests and Pearson’s correlation and are presented as mean ± SD. RESULTS: Seven participants were positive to EVH. Of these, only two had a positive response to Ex. No differences in baseline FEV1 between EVH and EX were found (EVH:4.06 ± 0.79, EX: 4.06 ± 0.77 L, p = 0.746). There was a strong correlation between the % fall in FEV1 post EVH and EX (r = 0.520, p = 0.003). However, the % fall in FEV1 post EVH was significantly greater that post EX (EVH: -7.5 ± 5.4, EX: -2.0 ± 3.8 %, p < 0.001). The total amount of air expired was significantly higher in 6 mins EVH compared to 6 mins EX (EVH: 686.5 ± 141.7, EX: 617.9 ± 83.1 L, p = 0.002). CONCLUSION: A positive EVH challenge may not be predictive of a positive Exercise Challenge in a dry environment. EVH may have a greater sensitivity due to the lower water content of inspired air and a greater VE. This suggests that a mild positive EVH challenge (a fall in FEV1 of 10-15%), may not be predictive of EIB.