TAU Trends in Research June 1999

Lessons from a Computerized Nose

Anatomy of the human nasal cavity conditions air before it reaches the lungs

Humans can live in tropical or Arctic climates, and can shift from one extreme environment to another in very short time intervals, without injuring their respiratory system. Part of the secret lies in the complex structure and function of the human nasal cavities which are designed to take incoming air hot or cold, dry or wet and to bring it to lung-like body temperature and humidity (100% saturation) before it ever reaches the lungs. Although the nasal cavity can usually adequately condition the incoming ambient air even before it reaches the pharynx, virtually independent of external conditions, rapid breathing requires additional air-conditioning steps in the intrathoracic airways. The increasing popularity of surgical and pharmacological interventions, and increasing exposures to air-borne pollution, require a better understanding of the dynamics and spatial distribution of the transport processes in the nasal cavity. Unfortunately, the complex structure and relative inaccessibility of the nasal cavity largely prevent detailed in vivo studies and limit the development of objective techniques for functional evaluation.

To overcome these limitations, Prof. David Elad and his colleagues at the TAU Department of Biomedical Engineering have developed a computerized model to study the dynamics of heat and water vapor flux between the interior of the mucosal lining of the nasal cavity and the inspired air. Existing imaging techniques reveal substantial variations between the nasal cavities of healthy subjects, and one cannot define a normal nose. The researchers thus devised a more general model that reproduces the essential features of the nasal cavity, while allowing for the removal or addition of various features needed for a comprehensive analysis.

Temperature distribution in the researchers' nose-like model

In their two-dimensional model, inhaled air was found to be warmed and humidified nearly to 90% of alveolar conditions before reaching the nasopharynx. The turbinates increased the rate of local heat and moisture transport by improving mixing and by maintaining thin boundary layers. The faster air speeds associated with rapid breathing significantly reduced the instantaneous heat and water vapor transfer to the inspired air. There seems to be ample time for heating and humidification under normal conditions; however, deficiencies in the blood supply or surface moistening can reduce the rate of heat or moisture flux into the inspired air.

Although almost one million rhinosinus surgical procedures are performed each year in the U.S., and over 20,000 are performed annually in Israel, there are still no satisfactory, objective techniques for the comprehensive evaluation of nasal function before and after intervention. In order to address such questions, the TAU researchers are building an experimental device for noninvasive data measurements outside of the nasal cavity and extending their computational studies to a more realistic three-dimensional model, an example of the computed temperature distribution within the nasal cavity is shown in the accompanying figure.

This study, funded in part by the U.S.-Israel Binational Science Foundation, should expand our basic knowledge and provide reference values to facilitate the medical followup, exploration and monitoring of post-operative improvement. It may also help resolve such surgical controversies as how much should be excised from hypertrophic turbinates or how should a stenotic valve should be corrected.

For further information please contact:

Prof. David Elad, D.Sc.
Department of Biomedical Engineering
Faculty of Engineering
Tel Aviv University
Ramat Aviv, Tel Aviv 69978
ISRAEL

Tel:	972-3-640-8476
Fax:	972-3-640-7939
E-Mail:	elad@eng.tau.ac.il