Maximum expiratory flow changes induced by longitudinal tension on trachea in normal subjects

Area of Science:

• Respiratory Physiology
• Pulmonary Mechanics

Background:

• Maximal expiratory flow (Vmax) can be influenced by posture.
• Previous observations noted Vmax increases with neck hypertension.

Purpose of the Study:

• To investigate the effect of neck hyperextension on maximal expiratory flow volume (MEFV) curves in healthy subjects.
• To determine the mechanism behind Vmax changes during neck hyperextension.

Main Methods:

• Obtained MEFV curves in 15 healthy young subjects in regular and hyperextended neck postures.
• Utilized radiographic studies to assess tracheal changes.
• Confirmed findings in anesthetized tracheostomized dogs.

Main Results:

• Eleven subjects showed increased Vmax during neck hyperextension at high lung volumes.
• MEFV curves exhibited obliteration of concavity during hyperextension.
• Radiography revealed tracheal elongation with a fixed carina.
• Increased tracheal longitudinal tension in dogs also increased Vmax.

Conclusions:

• The trachea is proposed as the flow-limiting segment at high lung volumes in young adults.
• Tracheal elongation during neck hyperextension stiffens the trachea, increasing its tube-wave speed and thus Vmax.
• This mechanism was supported by animal studies demonstrating increased Vmax with enhanced tracheal tension.