Methacholine challenges: comparison of different tidal breathing challenge methods.

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Clinical Diagnostics

Background:

• Current guidelines recommend tidal breathing methacholine challenges to mitigate deep inhalation's bronchoprotective effects.
• Variability in methacholine challenge methodologies may impact diagnostic accuracy and comparability.
• Optimizing tidal breathing challenge protocols is crucial for reliable asthma assessment.

Purpose of the Study:

• To compare different tidal breathing methacholine challenge methods.
• To assess agreement between tidal dosimetric and continuous output challenges.
• To evaluate the repeatability of various methacholine challenge techniques.

Main Methods:

• Fifteen asthma patients with pre-bronchodilator FEV1 ≥65% predicted and PD20 <1.2 mg performed methacholine challenges.
• Methods included standard dosimetric, adjusted dosimetric (nebulizer output time adjusted), and continuous output challenges.
• Repeatability was assessed by performing adjusted dosimetric and continuous output challenges twice on separate days.

Main Results:

• The adjusted dosimetric challenge showed good repeatability (ICC 0.62 for PD20).
• Adjusted dosimetric and continuous output challenges correlated (r=0.69, ICC 0.65) but yielded different PD20 values (mean ratio 2.31).
• Standard dosimetric challenge results were comparable to adjusted dosimetric challenges (mean ratio 0.90, ICC 0.82).

Conclusions:

• Tidal dosimetric methacholine challenge with adjusted nebulizer output time demonstrates good repeatability.
• Results from adjusted dosimetric and continuous output methacholine challenge methods are not directly interchangeable.
• Methodological differences in tidal breathing methacholine challenges necessitate careful consideration for clinical interpretation.