Submitted on June 13, 2005
Accepted on October 19, 2005
The viscoelasticity of the trachea and its effects on flow limitation
Nikolai Aljuri1*, Jose G. Venegas2, and Lutz Freitag3
1 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA; Department of Anaesthesia, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
2 Department of Anaesthesia, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA; Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
3 Institute for Experimental Pneumology, Lungenklinik Hemer, Hemer, Germany
* To whom correspondence should be addressed. E-mail: nikko{at}mit.edu.
To test the hypothesis that peek expiratory flow is determined by the wave-speed limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area (the tube law, TL) of six excised human tracheae under controlled conditions of static (no-flow) and forced expiratory flow. We found that tube laws of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro et all (11) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow (DTL) was significantly stiffer than the static TL (STL). As a result, the stiffer DTL predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant STL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and "supra-maximal" expiratory flows seen at the onset of forced expiration.
