Flow-pressure looping during plethysmography in wheezy infants.

Area of Science:

• Pediatric Pulmonology
• Respiratory Physiology
• Medical Instrumentation

Background:

• Flow-pressure (F-P) loops can exhibit expiratory looping in infants.
• This phenomenon occurs during airway resistance measurements using whole-body plethysmography under controlled conditions.

Purpose of the Study:

• To investigate the relationship between expiratory F-P loop morphology and airway obstruction severity in infants.
• To explore the physiological basis of expiratory looping in pediatric airway disease.

Main Methods:

• Whole-body plethysmography was used to measure airway resistance in 13 infants with varying airway obstruction.
• Flow-pressure relationships were analyzed for expiratory looping.
• Specific airway conductance (SGaw) and forced expiratory time constant (t) were measured.

Main Results:

• Marked expiratory looping was observed in some infants.
• A negative correlation (r = 0.72) was found between looping severity and SGaw.
• A strong correlation (r = 0.85) existed between the phase lag angle tangent (theta) and the lung time constant (t).

Conclusions:

• Expiratory looping in infants is likely caused by small airway closure during forced expiration.
• This closure leads to increased airway resistance and prolonged lung time constants.
• The findings support a simple resistance-capacitance (RC) electrical network model for expiratory lung mechanics in infants.