Comparison of air warming in the human airway with a thermodynamic model
- 51 Downloads
Airway cooling and drying has been proposed as a mechanism of exercise-induced asthma. Of interest in understanding the role of respiratory heat loss are the airway zones enduring the principal cooling and drying stresses. We have compared the axial rise in air temperature in the upper respiratory tract of asthmatics with that occurring in a laminar airflow steady-state model of convective heat transfer. The latter allowed an assessment of the contribution of airway geometry to the overall air warming process and gave some indication of the likely in vivo air temperature during hyperventilation, which due to the nature of our patients we could not measure directly. In vivo measurements were performed during a fibre-optic bronchoscopy. Eleven patients (67 years ±0·76) inhaled ambient air (23·2°C) and cold air (−17·5°C) nasally at a ventilation of 10 l min−1. During cold air inhalation the air temperature of the pharynx was 32·7°C (1·0) and at the third-generation bronchi 37°C (0·5), whereas with ambient air these were 35·8°C (0·8) and 37·7°C (0·6), respectively. For the same inspired ambient air condition the corresponding air temperatures in the thermodynamic model were approximately 27°C and 32°C. The axial rise in air temperature in both the model and in vivo state were characterised by a rapid early warming phase regardless of airflow rate. We conclude that the region proximal to the pharynx will endure the most severe cooling during a hyperventilation challenge.
KeywordsAirway model In vivo air temperature Respiratory convective heat transfer Respiratory heat loss
Unable to display preview. Download preview PDF.
- Anderson, S. D., Schoffel, R. E., Black, J. L. andDaviskas, E. (1985) Airway cooling as the stimulus to exercise induced asthma—a re-evaluation.Eur. J. Respirat. Dis.,67, 20–30.Google Scholar
- ben Jebria, A. andKays, C. (1987) Effective carbon dioxide washout by high-frequency mechanical ventilation.Med. & Biol. Eng. & Comput.,25, 655–660.Google Scholar
- Cole, P. (1953) Further observations on the conditioning of respiratory air.J. Laryng. & Otol.,67, 669–675.Google Scholar
- Deal, E. C., McFadden, E. R., Ingram, R. H., Strauss, R. H. andJaeger, J. J. (1979) Role of respiratory heat exchange in the production of exercise induced asthma.J. Appl. Physiol.,46, 467–475.Google Scholar
- Hahn, A., Anderson, S. D., Morton, A. R., Black, J. L. andFitch, K. D. (1984) A reinterpretation of the effect of temperature and water content of inspired air and exercise induced asthma.Am. Rev. Respirat. Dis.,130, 575–579.Google Scholar
- Ingelstedt, S. (1956) Studies on the conditioning of air in the respiratory tract.Acta. Otolaryng.,1, Suppl. 131.Google Scholar
- McFadden, E. R., Dennison, D. M., Waller, J. R., Assoufi, B., Peacock, A. andSopwith, T. (1982) Direct recordings of the temperature in the tracheobronchial tree in normal man.J. Appl. Physiol.,58, 564–570.Google Scholar
- McFadden, E. R., Lenner, K. A. M. andStroli, K. P. (1986) Post exertional airway rewarming and thermally induced asthma.Am. Rev. Respirat. Dis.,78, 18–25.Google Scholar