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Force, torque, and stress relaxation with direct laryngoscopy
R H Hastings1, E D Hon, C Nghiem
1Department of Anesthesiology, University of California San Diego, USA.
Anesthesia and Analgesia
|March 1, 1996
Summary
Anesthetists apply force and torque during laryngoscopy. This study measured these forces, finding torque may limit glottic exposure and exhibits stress relaxation in pharyngeal tissues.
Area of Science:
- Anesthesiology
- Biomedical Engineering
- Physiology
Background:
- Direct laryngoscopy involves applying axial force to the laryngoscope handle.
- Balancing torque requires a perpendicular force, a factor not previously measured.
- Understanding these forces is crucial for optimizing airway management.
Purpose of the Study:
- To simultaneously measure axial force and torque during direct laryngoscopy.
- To investigate the relationship between applied forces and potential limitations in glottic exposure.
- To analyze the viscoelastic properties of pharyngeal tissues during laryngoscopy.
Main Methods:
- Utilized a novel laryngoscope handle designed for simultaneous force and torque measurement.
- Measured peak force, peak torque, and estimated perpendicular force in 58 ASA grade I and II patients.
- Analyzed force and torque decay over time to assess stress relaxation.
Main Results:
- Peak axial force averaged 38 +/- 2 N; peak torque averaged 4 +/- 0.2 Nm.
- Estimated perpendicular force was 40 +/- 2 N.
- Force and torque decreased monoexponentially to ~70% of peak values (half-time 4 +/- 0.3 s), indicating stress relaxation.
Conclusions:
- Torque, potentially a limiting factor in laryngoscopy, was measured for the first time.
- Stress relaxation of pharyngeal tissues, a viscous property, was observed despite muscle relaxant use.
- These findings offer insights into the biomechanics of direct laryngoscopy and airway management.