Airway responsiveness in infants: comparison of inhaled and nasally instilled methacholine

Area of Science:

• Pediatric Pulmonology
• Respiratory Physiology
• Allergy and Immunology

Background:

• Infant airway responsiveness is typically assessed during sleep via nasal inhalation of bronchial challenge agents.
• Nasal airway stimulation can potentially cause bronchoconstriction, creating ambiguity in interpreting infant responses.
• Distinguishing between lower airway effects and nasal receptor stimulation is crucial for accurate assessment.

Purpose of the Study:

• To differentiate the effects of lower airway deposition versus nasal receptor stimulation on infant airway responsiveness.
• To compare the impact of inhaled methacholine aerosol with direct nasal instillation of methacholine on partial expiratory flow-volume (PEFV) curves in healthy infants.

Main Methods:

• Six healthy infants underwent evaluation of PEFV curves during sleep.
• Methacholine was administered via two methods: nasal aerosol inhalation and direct nasal liquid instillation.
• Changes in PEFV curves, peak expiratory flow, maximal flow at functional residual capacity (VmaxFRC), and oxygen saturation (SaO2) were measured.

Main Results:

• Inhaled methacholine aerosol led to decreased peak expiratory flow, concave PEFV curves, and reduced SaO2.
• Direct nasal instillation of higher methacholine concentrations did not alter VmaxFRC or SaO2, but caused peak flow reduction and flattening at higher lung volumes.
• Nasal instillation effects were consistent with increased nasal resistance, not lower airway changes.

Conclusions:

• Bronchoconstriction observed after inhaled methacholine in infants is not caused by nasal receptor stimulation.
• The findings support that inhaled methacholine primarily affects the lower airways in infants.
• This study clarifies the mechanism of airway responsiveness testing in infants.