Dynamic response characteristics of upper respiratory system

Abstract

A theoretical model is presented to study the general dynamic characteristics of the upper human respiratory system for a healthy as well as an unhealthy lung. The model is formulated by using perturbation technique on the fluid momentum and continuity equations taking into consideration the structural dynamic features of the air passage walls. A recursion formula is generated to compute the input impedance along the principal path. Also the distributed pressure response along a single pathway in the breathing system is investigated for different frequencies. The results indicate that for a healthy lung the magnitude of the impedance at the throat decreases to a minimum value at a frequency of 379 Hz, then increases again, and continues to fluctuate between maximum and minimum values. This prediction agrees very well with available experimental data and disputes earlier theoretical observations of double minimum values. However, it is indicated that a lung with some abnormality at a Horsfield order of 24 and above has its first minimum at a frequency of 238 Hz. A detailed explanation of the dynamic characteristics in terms of the impedance ration and the pressure distribution is presented in the paper.