Biomedical subjects

A Ben-Jebria

Publications and source records attributed to A Ben-Jebria.

29 records · Page 2Linked to original sources

PubMed1992

Simulation of ozone uptake distribution in the human airways by orthogonal collocation on finite elements.

Ozone transport in a rigid single-pathway anatomic model of the lung was analyzed by a stable convergent numerical algorithm, the method of orthogonal collocation on finite elements. The simulations predicted the dynamic behavior of gas phase concentration profiles for both ozone and an insoluble inert gas. An internal quasi-stationary diffusion front was observed during early inspiration for both gases. In addition, the absorptive distribution of ozone in lung airways was computed as a total dose as well as a tissue dose. The total dose of ozone decreased along the airway path from the mouth. However, the tissue dose of ozone increased along the conducting airways, reached a maximal dose in the terminal bronchioles, and decreased sharply in the respiratory airways.

Algorithms↗

PubMed1992

Longitudinal distribution of ozone absorption in the lung: quiet respiration in healthy subjects.

The objective of this research was to develop a bolus-response method for the noninvasive determination of O3 distribution in the human lung. A previously developed O3 analyzer and bolus generator were incorporated in a computer-controlled inhalation system, and measurements of O3 absorption from inhaled 10-ml boluses with a peak O3 concentration of 4 ppm were carried out on nine previously unexposed healthy male subjects engaged in quiet oral breathing. The fraction of O3 absorbed during a single breath was measured over a range of airway penetrations from 20 to 200 ml, with inspiratory and expiratory flows fixed at a nominal value of 250 ml/s. The resulting data indicated that 50% of the inhaled O3 was absorbed at a penetration of 70 ml, which roughly corresponds to the upper airways, and essentially complete absorption occurred at a penetration of 180 ml, which roughly corresponds to the 16th airway generation, the beginning of the proximal alveolar region. This compares favorably with the results of direct-sampling methods, which indicated that 40.4% of continuously inhaled O3 is removed by the extrathoracic airways (Gerrity et al. J. Appl. Physiol. 65: 393-400, 1988). The computation of an absorption rate constant, Ka, revealed that the efficiency of O3 uptake increased with longitudinal position throughout most of the conducting airways but began to fall off at a penetration of 160 ml.

Absorption↗

PubMed1992

Effect of in vitro nitrogen dioxide exposure on human bronchial smooth muscle response.

The aim of this study was to develop an in vitro system in which an isolated bronchus from human lung was exposed, during 30 min, to a constant flow of either air or nitrogen dioxide (NO2), and to examine subsequently the contractile response of airway smooth muscle rings to carbachol, histamine, and substance P. Two proximal bronchi were mounted in an organ bath, perfused externally with Krebs-Henseleit solution and ventilated with clean air, 1.0 or 2.0 ppm NO2. The exposed bronchi were then cut into rings and mounted in a computerized organ bath system. Contractile responses to agonists were measured isometrically. In each ring, a cumulative concentration response curve was obtained to the desired agonist. We found that in vitro exposure of human lumen bronchus to a constant flow of air did not alter the contractility of the smooth muscle. Whereas in vitro exposure of the bronchus to 1.0 ppm NO2 did not significantly increase the efficacy or the potency of carbachol, exposure to 2.0 ppm NO2 increased airway smooth muscle contractions in response to carbachol, histamine, and substance P. These results indicate that our experimental preparation is well suited to study the respiratory toxicity of inhaled pollutants in order to understand further the mechanisms underlying toxicant-induced airway hyperresponsiveness.

Acetylcholine↗

PubMed1991

Gas mixing in lung model ventilated by high frequency oscillation: effect of tidal volume, frequency and molecular diffusivity.

The efficiency of gas mixing during sinusoidal oscillatory flow in a model of human lung cast was assessed by using a multibreath carbon dioxide washout manoeuvre. The experiments were performed at high frequencies (5, 10, 15 and 20 Hz) and low tidal volumes (50, 90 and 120 cm3). A particular effort was made to analyse the influence of flow oscillation conditions (f and VT) as well as the effect of resident alveolar gas density (molecular diffusion) on the effective diffusion coefficient (Deff). This longitudinal mixing parameter was found to be strongly dependent on the tidal volume (approximately proportional to VT1.4) and weakly dependent on the frequency (approximately proportional to f0.5). However, molecular diffusion was not, in general, a limiting factor in the gas transport process during high-frequency oscillation (HFO).

Humans↗

PubMed1991

Ozone absorption into excised porcine and sheep tracheae by a bolus-response method.

The absorption of ozone (O3) into excised porcine and sheep tracheae was characterized by a bolus-response experiment in which a bolus with a peak O3 concentration of 1 ppm was rapidly injected into a steadily flowing airstream entering the trachea. Using a fast-responding chemiluminescent analyzer of our design, the O3 concentration curves at the proximal end (i.e., the bolus input) and at the distal end (i.e., the response) of the trachea were monitored. Each concentration curve was numerically integrated, and the fraction of O3 absorbed in the trachea was obtained by subtracting from unity the ratio of the response integral to the bolus input integral. Average values of ozone-absorbed fraction decreased from about 0.50 to 0.15 at increasing airflows from 50 to 200 ml/sec. A diffusion theory that includes the effects of bulk convection, axial dispersion, and first-order absorption was developed to relate the fractional absorption to an overall mass transfer coefficient (K). The results indicate that K is independent of airflow, suggesting that the diffusion resistance in mucus is much greater than that in the gas phase. The time-weighted integrals of the concentration curves were also computed, allowing the mean residence time of O3 in the trachea (delta tau) to be determined. As predicted by the diffusion theory, delta tau was inversely related to the rate of O3 absorption.

Absorption↗

PubMed1991

Noninvasive determination of respiratory ozone absorption: development of a fast-responding ozone analyzer.

We developed a chemiluminescent ozone analyzer and constructed an ozone bolus generator with the eventual goal of using a bolus-response method to measure noninvasively the longitudinal distribution of ozone absorption in human lungs. Because the analyzer will be used to sample gases within a single breath, it must have a sufficiently rapid response to monitor changes in ozone concentration during a four-second breathing period, yet its sampling flow must be small enough that it does not interfere with quiet respiratory flows of 300 mL/sec. Our analyzer, which is based on the chemiluminescent reaction between 2-methyl-2-butene and ozone, has favorable performance characteristics: a 90 percent step-response time of 110 msec; a linear calibration from 0.03 to 10 parts per million (ppm)2 with a sensitivity of 2.3 nA/ppm; a signal-to-noise ratio of 30 evaluated at 0.5 ppm; and a minimum detection limit of 0.017 ppm. At an airflow corresponding to quiet breathing, the ozone generator is capable of producing single boluses with a peak ozone fraction as high as 4 ppm, but containing only 0.35 micrograms of ozone dispersed over a small volume of 19 mL. To test the combination of ozone analyzer and bolus generator, we performed bolus-response experiments at steady airflows of 50 to 200 mL/sec in excised pig and sheep tracheas. In spite of the small surface area available for radial diffusion, we found that 25 to 50 percent of the ozone introduced into the trachea was absorbed. By comparing the mathematical moments of the bolus input and the response curves to the predictions of a diffusion theory, we computed an absorption coefficient (K). The values of K increased with increasing airflow, implying that ozone absorption is limited by diffusion processes in the airway lumen as well as in the surrounding tissue.

Absorption↗

PubMed1990

Dynamics of sulfur dioxide absorption in excised porcine tracheae.

The absorption of sulfur dioxide (SO2) into excised porcine tracheae was characterized by a step-response experiment in which SO2 outlet concentration was monitored during the 30-min interval following introduction of inlet concentrations of 0.1-0.6 ppm at steady air flows of 2.7-11.0 liter/min. These data were analyzed with a diffusion-reaction theory incorporating three independent parameters--a gas phase mass transfer coefficient, kg, a tissue phase diffusivity x solubility product, D(alpha RT)2, and a tissue phase reaction constant, kr. While single values of 17 sec-1 for kr and 0.28 m2/sec for D(alpha RT)2 were sufficient to simulate all the data, it was necessary to vary kg from a 0.032 to 0.121 m/sec in direct proportion to the gas flow. Based on these parameter values, gas phase resistance accounts for about one-fourth of the total resistance to absorption in gas and tissue phases combined. All three parameters were independent of inlet concentration, implying that diffusion, solubility, and irreversible reaction of SO2 in tissue are all linear processes.

Absorption↗

PubMedDate not supplied

A portable inhalation system for personal exposure to ozone.

A low-cost portable inhalation system was developed for exposing an individual subject to 60-600 parts per billion of ozone in a 30-l clear-plastic head dome. The inhalation system had the following novel features: a canister vacuum cleaner that supplied room air without the need for precleaning or humidification; a 7% oxygen-in-nitrogen feed to a commercial ultraviolet ozonator that avoided an excess production of ozone; a compact inline mixer that assured homogeneous mixing of the 200-300 liters per minute room air supply with the 0.5-1.0 liters per minute of ozonated gas flow, positioning of gas inlet and exhaust hoses on the head dome that provided fresh gas delivery in the vicinity of the mouth; a quick-disconnect neck seal that allowed rapid donning of the head dome by the subject, and mounting of most system components on a small mobile cart. Temperature, humidity, and ozone and carbon dioxide concentrations were measured inside the dome while a subject exercised on a bicycle ergometer. An air flow of 200 liters per minute between rest and light exercise created a suitable microenvironment in the dome. During moderate and heavy exercise, however, a higher flow of 300 liters per minute should be used to suppress the build-up of carbon dioxide and humidity.

Adult↗

PubMedDate not supplied

Longitudinal distribution of ozone absorption in the lung: effect of continuous inhalation exposure.

The effect of continuous exposure to ozone on the absorption of ozone in the conducting airways of human lungs was investigated with a bolus-response method. Eleven healthy nonsmoking college students (8 males, 3 females) were exposed at rest for 2 h on 3 separate days to air containing 0 ppm, 0.12 ppm, and 0.36 ppm ozone. A personal inhalation chamber equipped with a head-only clear plastic dome was used for exposure. Every 30 min a subject removed the dome and orally inhaled a series of five ozone-air boluses, each in a separate breath. Penetration of the boluses distal to the lips was targeted in the range of 70-120 ml (corresponding to the central conducting airways). By integrating the inhaled and exhaled-ozone concentration curves, we obtained the absorbed fraction (lambda) and the dispersion (sigma2) of the ozone bolus for each test breath. In addition, the subtraction of baseline measurements made just before exposure enabled us to determine the changes in absorbed fraction (deltalambda) and in dispersion (deltasigma2) that resulted from exposure alone. Absorbed fraction decreased, but sigma2 increased during O3 exposure, and the differences in deltalambda and in deltasigma2 between breathing air and exposure to either 0.12 ppm or 0.36 ppm O3 were significant. We concluded that exposure of the conducting airways to O3 reduced their capacity to absorb O3, possibly by the depletion of biochemical substrates that are normally oxidized by O3.

Administration, Inhalation↗

PubMedDate not supplied

A respiratory ozone analyzer optimized for high resolution and swift dynamic response during exercise conditions.

The breath-to-breath determination of total respiratory ozone (O3) uptake requires the monitoring of O3 concentration at the airway opening with an instrument that responds rapidly relative to the frequency of respiration. Originally, the authors developed an analyzer that used the homogeneous chemiluminescent reaction of O3 with 2-methyl-2-butene, but it was suitable only for monitoring O3 during quiet breathing and light exercise (Ben-Jebria and Ultman, Rev Sci Instrum 1989; 60:3004-11, and Ben-Jebria et al., Rev Sci Instrum 1990; 61:3435-39). The improvement of performance characteristics of the aforementioned analyzer enabled the authors to use the newly constructed and self-contained instrument, which used ethylene as the reactant gas, for respiratory O3 monitoring during moderate-to-heavy exercise. Operating at a reaction chamber pressure of 350 torr, an ethylene/sample flow ratio of 4:1, and a sampling flow of 0.6 lpm, the authors achieved an optimum analyzer performance (i.e., 10-90% step-response of 70 msec and a minimum resolution of 0.006 ppm O3). Furthermore, the new instrument did not exhibit the nonlinear calibration and the CO2 interference suffered by the original analyzer. To demonstrate the quality of the new O3 analyzer in a respiratory application (i.e., total O3 uptake), the authors measured a series of single breaths on two subjects who breathed 0.11 and 0.43 ppm O3-in-air mixtures for 15 min during rest, and during moderate and heavy exercise.

Breath Tests↗

PubMedDate not supplied

Longitudinal distribution of ozone absorption in the lung: effects of nitrogen dioxide, sulfur dioxide, and ozone exposures.

Investigators used an ozone bolus inhalation method to study the effects of continuous exposure to ozone, nitrogen dioxide, and sulfur dioxide on ozone absorption in the conducting airways of human lungs. Healthy, young nonsmokers (6 males, 6 females) were exposed on separate days for 2 h to air containing 0.36 ppm nitrogen dioxide, 0.75 ppm nitrogen dioxide, 0.36 ppm sulfur dioxide, or 0.36 ppm ozone. Every 30 min, the subject interrupted exposure for approximately 5 min, during which he or she orally inhaled five ozone boluses-each in a separate breath. Investigators targeted penetration of the boluses distal to the lips in the 70-130-ml range, which corresponded to the lower conducting airways. The authors computed the change in absorption resulting from exposure (delta lambda) by comparing the amount of each ozone bolus that was absorbed with a corresponding value obtained prior to exposure. Results indicated that ozone exposure caused delta lambda to decrease relative to air exposure (p < .01), whereas both nitrogen dioxide and sulfur dioxide exposures caused an increase in delta lambda that was not significantly different from air exposure. This resulted, at least in part, to an artifact caused by preexposure to ozone boluses. The authors concluded that exposure of the lower conducting airways to nitrogen dioxide or sulfur dioxide increased their capacity to absorb ozone because more of the biochemical substrates that are normally oxidized by ozone were made available. During continuous ozone exposure, this excess of substrate is depleted and the absorption of ozone boluses decreases.

Absorption↗