The classical Starling resistor model often does not predict inspiratory airflow patterns in the human upper airway

Area of Science:

• Respiratory mechanics
• Sleep medicine
• Biophysics

Background:

• The classical Starling resistor model assumes constant inspiratory airflow.
• Clinical sleep studies reveal an initial airflow peak preceding a plateau.
• This peak is often dismissed as a transient phenomenon.

Purpose of the Study:

• To investigate the nature of the initial inspiratory airflow peak in the human upper airway.
• To test the hypothesis that the peak is a transient phenomenon.
• To compare airflow dynamics during fast versus slow inspirations.

Main Methods:

• Developed a method to simulate fast and slow inspirations in eight subjects (4 obstructive sleep apnea, 4 controls) during NREM sleep.
• Utilized an "iron lung" and positive airway pressure (PAP) machine with an epiglottic catheter for pressure measurement.
• Constructed pressure-flow curves for flow-limited breaths following induced central apnea.

Main Results:

• All subjects displayed an initial airflow peak followed by a flow decrease at more negative pressures, indicating negative effort dependence (NED).
• The rate of downstream pressure change (slow vs. fast) did not significantly alter the peak to plateau airflow ratio (%NED: 22 ± 13% slow vs. 20 ± 5% fast).
• This suggests the initial peak is an intrinsic property, not a transient effect.

Conclusions:

• The initial peak in inspiratory airflow is a distinct mechanical property of the upper airway, not a transient.
• The human upper airway exhibits significant negative effort dependence (NED), diverging from the classical Starling resistor model.
• Findings necessitate a revised understanding of upper airway airflow dynamics during breathing.