Bronchial challenge: ventilation during 'tidal volume breathing' inhalation is not constant

Area of Science:

• Respiratory Physiology
• Pulmonary Function Testing

Background:

• Bronchial challenge (BC) testing is essential for diagnosing airway hyperresponsiveness.
• Improving the repeatability of both non-specific and specific BC is a significant clinical goal.
• Tidal volume breathing BC (tBC) involves inhaling a bronchoconstrictor throughout the inspiratory phase.

Purpose of the Study:

• To assess the repeatability and variability of ventilation (VE) during tidal volume breathing bronchial challenge (tBC).
• To identify factors contributing to variability in tBC to inform standardization efforts.

Main Methods:

• A standard Cockcroft technique was adapted, using a patient-operated Pari nebulizer for histamine challenge.
• Ventilation (VE) was measured for 2 minutes at each histamine concentration across 187 tBCs.
• Thirty-four patients underwent two separate tBC challenges to assess within-subject and between-subject variability.

Main Results:

• Significant between-subject (SD = 37%) and within-subject (SD = 21%) variations in VE were observed.
• Ventilation during inhalation of the threshold dose (VE-threshold) was significantly lower than during the preceding dose (VE-threshold-1).
• Within-subject SD for VE was 21% across paired challenges, with between-subject SD at 32%.

Conclusions:

• The current tidal volume breathing BC (tBC) protocol exhibits considerable variability in ventilation, impacting test repeatability.
• Further standardization of the respiratory pattern during tBC is necessary.
• Investigating respiratory frequency and inspiratory time may be key to improving tBC standardization and reliability.