Forced expiratory time and bronchial hyperresponsiveness to methacholine.

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Pulmonary function tests (PFTs) typically precede methacholine inhalation challenges (MICs).
• Abnormal baseline forced expiratory times (FET100%) have been observed in patients with positive MICs, contrary to normal spirometry (FEV1, FEF25%-27%, FVC).

Purpose of the Study:

• To prospectively evaluate the correlation between abnormalities in baseline pre-MIC FET100% and positive versus negative MIC results.
• To determine if FET100% can predict a positive MIC in individuals suspected of having asthma.

Main Methods:

• Prospective analysis of baseline pre-MIC FET100% and MIC results in patients with suspected asthma, normal lung exams, spirometry, and chest X-rays.
• Used a PC20 FEV1 threshold of ≤8mg/ml methacholine to define positive and negative MICs.
• Compared mean FET100% and incidence of FET100% <4 seconds between positive (n=115) and negative (n=69) MIC groups.

Main Results:

• The mean FET100% was significantly shorter in the positive MIC group (3.57±1.68 sec) compared to the negative group (4.73±1.60 sec) (p <0.0001).
• A significantly higher incidence of FET100% <4 seconds was found in the positive MIC group (55.65%) versus the negative group (30.43%) (p<0.001).
• Positive MICs were significantly more frequent in patients with FET100% <4 seconds (75.29%) compared to those with FET100% ≥4 seconds (51.52%) (p<0.001).

Conclusions:

• Shortened baseline FET100% <6 seconds is common in this patient population.
• A baseline FET100% <4 seconds strongly correlates with an increased likelihood of a positive methacholine inhalation challenge.
• FET100% may serve as a useful predictive marker for bronchial hyperresponsiveness.