Abdellaziz Ben Jebria

Effect of breathing dry warm air on respiratory water loss at rest and during exercise

The changes in respiratory water loss with time, expressed as the mass of water vapour lost per liter BTPS of ventilation (MH2O), and expired temperature (TE), used to calculate the relative humidity (ERH), were investigated in ten normal subjects while breathing warm dry air by mouth (PIH2O = 0 kPa; TI = 30 degrees C): at rest for a period of 35 min; during 15 min light muscular exercise (50 W); at increasing work load from 50 to 100 W between the 5th and 10th min of the exercise. The data collected were compared to those obtained in room air conditions (PIH2O = 0.68-1.3 kPa) and under conditions with slightly heated inspired air (TI = 28-30 degrees C). At rest, when breathing dry warm air MH2O and ERH fell during the first 15 min, while they recovered their initial values during the last 20 min. In contrast no differences in MH2O or ERH were observed when breathing ambient warm air. At constant and moderate work load for 15 min, the respiratory water loss fell significantly (compared to the 5th min) at the 10th and the 15th min when breathing warm dry air. The added hyperpnea which was obtained by increasing work load from 50 to 100 W between the 5th and 10th min of exercise did not further reduce MH2O and ERH. The transient fall in MH2O and ERH, which lasted at least 15 min either at rest or during muscular exercise, suggested that the mechanism underlying humidification of expired gas is overwhelmed by thermal stress. Since the upper airways mucosa is unable to saturate expired gas, this also suggested that the mucosa is dehydrated and probably hyperosmotic. The progressive recovery in MH2O and ERH after 15 min of warm dry air breathing at rest, suggest operation of a slow adaptive mechanism.

A mechanical approach to the longitudinal dispersion of gas flowing in human airways

The aim of this work is to contribute to elucidating the mechanism underlying gas mixing in the human pulmonary airways. For this purpose, a particular attempt is made to analyse the fluid mechanical aspects of gaseous dispersion using bolus response methods. The experiments were performed on five normal subjects by injection of 10 cm3 bolus of He, Ar and SF6 into the latter part of the inspired airstream, in such a way that the whole bolus entered the inspiratory flow and was recovered during the following expiration. The results, presented in a logarithmic plot of dimensionless variance (dispersion of the output bolus) against the Peclet number, show that gaseous dispersion is only slightly dependent on the nature of the tracer gas but is strongly related to flow velocity. This is in agreement with the theory of turbulent or disturbed dispersion; however, it seems that Taylor laminar dispersion does not play a significant role in the airways.

Simulations of steady quaternary gas diffusion between alveolar and blood compartments

Abstract Ficks law is usually employed to analyze diffusion phenomena in the lung. However, this law is only strictly applicable to two component mixtures. When there are more than two gases in the mixture, Stefans equations are more appropriate. Under physiological conditions during respiration, at least three gases are involved (O 2 , CO 2 , N 2 ). Furthermore, helium is often added in studies on the effect of density on pulmonary mixing. Features of quaternary gas diffusion (O 2 , CO 2 , N 2 , He), and computer simulations of physiologically relevant conditions are presented. The results of the simulations were found to be in agreement with results from studies on normal and disease lungs.

Gas Mixing in the Human Upper Airways

The longitudinal dispersion of gas in the upper airways (oropharynx and larynx) was studied in 5 healthy subjects by measuring the response after injection of a bolus of 133Xe into the insp

Effect of resident gas density on CO2 elimination during high-frequency oscillation: A model study☆

In order to throw more light on the mechanisms governing the efficiency of intrapulmonary gas mixing during high-frequency oscillatory ventilation, an experimental, and theoretical, study was carried out on a model casting of the airways of a human lung that closely resembled the respiratory tract. The experiments were carried out under various conditions during high-frequency oscillation (HFO), by using alveolor resident gas mixtures of different densities. The efficiency of gas mixing was assessed by measuring the time constants of the CO2 alveolar washout which were compared to those obtained from simulations on a theoretical model based on a turbulent diffusional resistance concept. Our results showed that the decay in CO2 concentration was highly dependent on both frequency (f) and tidal volume (VT). Tidal volume was found to have a greater effect on efficiency of gas mixing than frequency. Moreover, even though there were statistically significant differences in the time courses of CO2 washout between N2 and He, N2 and SF6 or between He and SF6, this could not imply that gas mixing was limited by diffusion. Agreement between the experimental time constants of CO2 elimination during HFO and the predicted mixing time constants was satisfactory. It is concluded that turbulent augmented diffusion is the main factor responsible for effective gas transport during high-frequency oscillatory ventilation.

Analytical simulation of lingitudinal gas mixing in the human central airways

In order to study gaseous mixing in the proximal respiratory airways during stationary breathing, a simple mathematical model with an analytical solution of the corresponding equation is presented. Calculations were carried out by solving the differential equation analytically according to the system response to a unit impulse combined with the convolution method. It seems that this analytical method gives similar results to those obtained by the numerical ones; however, our method is computationally simple and can provide a reasonable tool to study gas transport in the airways.