Measurement of the Sensitivity of Upper Airway Reflexes

Abstract

We describe a method for measurement of the sensitivity of upper airway reflexes. The technique is based upon delivery of an irritant chemical stimulus (dilute concentrations of ammonia vapour) to the upper airway. The technique is non-invasive and uses equipment which is portable, allowing measurements to be made in the clinical environment.

Effects of topical benzocaine and lignocaine on upper airway reflex sensitivity

“…Measurement of upper airway reflex sensitivity was made using a previously described method which uses low concentrations of ammonia vapour as a chemical stimulus to the upper airway during inspiration [7] (Fig. I).…”

“…The calibration of the system has previously been described [7]. Briefly, the flow of ammonia at the outlet of the cyclopropane flowmeter is calibrated using a bubble flowmeter.…”

“…The final ammonia concentration at flow settings on the cyclopropane flowmeter from zero to 1000 ml.min-' in 100 ml increments is determined and the time required for the concentration of ammonia to reach 95% of the final concentration is also measured. The breathing system is able to deliver accurate concentrations of ammonia vapour in the range CL3500 ppm and the time to 95% of the final ammonia concentration is no longer than 105 s [7]. A pneumatic two-way valve allows the subject to breathe room air via a second limb of the system; on switching the pneumatic valve the subject takes a single breath from the ammonia-containing limb.…”

“…A period for equilibration of 2 min was allowed during which the volunteer breathed room air before recording the effects of an ammonia stimulus [7].…”

“…The only other related work involved experiments on anaesthetised cats and piglets [5. 61. With the development in our laboratory of a method to measure the sensitivity of upper airway reflex sensitivity accurately using low concentrations of ammonia vapour [7], we were able to investigate the effects of benzocaine lozenges, lignocaine administered directly onto the vocal cords and lignocaine administered via a nebuliser. The aim of this investigation was to measure the reduction in sensitivity of upper airway reflexes and also to examine the duration of any effect seen.…”