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Biomedical subjects

J S Ultman

Publications and source records attributed to J S Ultman.

At least 19 recordsLinked 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↗
PubMed1991

Differential pathlength factor for diffuse photon scattering through tissue by a pulse-response method.

Although near-infrared (NIR) spectroscopy may one day provide a noninvasive measurement of oxidative metabolism in tissue, the method cannot be fully quantitative until the mean pathlength traveled by photons between reference and output detectors (i.e, optrodes) is known. In NIR spectroscopy, photons are transported primarily by diffuse scattering, and their mean pathlength can be expressed by a differential path factor (DPF) whose value is greater than the interoptrode distance. Beginning with a P1 diffusion approximation of the Boltzmann equation, one-dimensional photon currents originating from plane, line, and point photon sources were analyzed. DPF was formulated from the attenuation of light intensity generated by constant sources, and an equation for the mean time of flight of photons between reference and output optrodes, delta tau, was derived for arbitrarily pulsed sources. The results indicate that (1) the attenuation of light in tissue does not, in general, vary with interoptrode distance in the manner predicted by Beer's law; (2) the relationship between DPF and interoptrode distance is nonlinear and geometry-dependent; and (3) in spite of these nonidealities, DPF is equal to the product of delta tau and the speed of light.

Metabolism↗
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

Mechanically induced pendelluft flow in a model airway bifurcation during high frequency oscillation.

A single bifurcation with adjustable branch compliances, resistances and inertances was used to study the generation of pendelluft flows during ventilation at tidal volumes of 5-15 ml and frequencies of 6-26 Hz, corresponding to parent branch Reynolds numbers of 400-8000 and Womersley parameter values of 12-25. Pendelluft was quantified by the ratio of tidal volume sum in sibling branches to tidal volume in the parent branch. This tidal volume fraction being greater than one in all experiments where an asymmetry in branch mechanics was imposed, indicated that some degree of pendelluft was always present. Asymmetries in compliance and in inertance produced much greater pendelluft than an asymmetry in resistance. The largest tidal volume fraction, equal to 2.75, was recorded when inertance in both sibling branches was high, resistance was low, and compliances differed by a factor of five. Tidal volume fraction always peaked at an optimal frequency between 12-24 Hz, similar to the frequencies at which physiologic transport optima have previously been observed.

Airway Resistance↗
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↗
PubMed1988

Longitudinal mixing in dog lungs during high-frequency forced flow oscillation.

Longitudinal mixing in the conducting airways of eight intubated anesthetized beagles (10.8 +/- 0.9 kg) was studied at functional residual capacity in the presence of forced sinusoidal flow oscillations and in the absence of fresh air bias flow. The ranges of oscillation conditions were: frequencies, f, from 3 to 18 Hz and minute volumes, Vosc, from 50 to 150 ml/sec, corresponding to tidal volumes, Vosc/f, from 0.3 to 4.5 ml/kg body mass. Oscillations were imposed during a breath holding interval incorporated into a modified single-breath nitrogen (N2) washout maneuver. The expired N2 fraction curves were analyzed with a Fickian diffusion model by adjusting the value of a global mixing parameter, (DA2), to achieve an optimal fit of the model to the data. The mixing parameter was an increasing function of minute volume and a decreasing function of frequency, which is well represented by the equation: (DA2) = 2.72 Vosc 1.74 f-1.57 By comparison to available theory and previous measurements in physical systems, this formula implies that Taylor-type dispersion is the dominant mixing mechanism in the conducting airways. Also, the diffusion model predicted, and the data verified, the existence of a mouth-ward 'diffusion flow' during breath holding. This effect, caused by the non-uniform nature of the summed airway cross-section, is directly correlated with the value of (DA2).

Animals↗
PubMed1988

Pendelluft and mixing in a single bifurcation lung model during high-frequency oscillation.

A single bifurcation with an adjustable daughter branch compliance ratio (VR) was used to simultaneously study pendelluft and longitudinal mixing during flow oscillations at frequencies (f) of 1-15 Hz and amplitudes (VOp) of 25-150 ml/s. Mixing coefficients (Deff) were determined from the dispersion of a CO2 bolus centered at the bifurcation point, and pendelluft volume was computed as a fraction of mother branch tidal volume (PVF) using measurements of airflow in the daughter branches. Plotted against frequency, PVF was a bell-shaped curve insensitive to the value of VOp. When VR = 2, a PVF peak of 0.25 appeared at f = 3 Hz, and when VR = 5, a PVF peak of 0.75 appeared at f = 4 Hz. After normalization by control values at VR = 1, Deff curves were also bell shaped, insensitive to the value of VOp and with peaks appearing at the same frequencies as the PVF peaks. The normalized Deff peak values were 1.7 when VR = 2 and 4.0 when VR = 5. The similarities in the PVF and Deff curves imply a direct relationship between pendelluft and enhanced mixing.

Algorithms↗
PubMed1988

Bronchial distribution of gas mixing in a model of the upper and central airways.

Longitudinal mixing of He, O2, and sulfur hexafluoride boluses with air flowing through a three-generation tracheobronchial airway model was evaluated as the increase in volume variance of gas concentration distributions monitored at upstream and downstream sampling ports. Mixing was partitioned between tracheal and branched regions of the model at steady inspiratory and expiratory airflows from 0.044 to 0.884 l/s, both in the absence and in the presence of a removable larynx cast. During inspiration in the absence of the larynx, mixing increased as airflow increased, reaching a peak value at 0.2 l/s, and decreasing as airflow increased further. This mixing peak was higher in the branched region than in the tracheal region and was inversely related to the diffusion coefficient of the indicator gas-air mixture. During inspiration in the presence of the larynx, a mixing peak was observed in the tracheal region, but mixing peaks in the branched region were eliminated by turbulence propagated downstream from the larynx. During expiration, laryngeal turbulence was propagated far enough downstream (i.e., proximal to the trachea) that mixing peaks could be observed in both tracheal and branched regions whether or not the larynx cast was present.

Bronchi↗
PubMed1988

Electrically heated simulator for relative evaluation of alternative infant incubator environments.

A 10.9-cm diameter, copper ellipsoid was electrically heated to provide a simulation of sensible heat transfer from a newborn infant. The use of this simulator to determine mean radiant temperature and convective heat-transfer coefficient was demonstrated in three commercial incubators: the Isolette (Model C-86, Narco/Air Shields); the Armstrong Care-ette (Ohio Medical Products); and the I. C. (Ohmeda). The relative performance of these environmental therapeutic devices in shielding an infant against radiant heat loss was judged by the deviation of mean radiant temperature from incubator air temperature, which was varied from 32-36 degrees C. Whereas the I. C. incubator exhibited a radiant temperature always 0.5 degrees C less than air temperature, the Care-ette incubator showed radiant temperatures of 4.0-5.5 degrees C below air temperature, and the Isolette displayed radiant temperatures of 2.7-4.7 degrees C (inner wall removed) and 2.0-3.8 degrees C (inner wall inserted) below air temperature. The relative performance of the incubators in preventing convective heat loss was judged from the magnitude of the convective heat-transfer coefficient, hv. The I. C. incubator had an hv = 4.52 W/m2/degrees C; the Care-ette, 5.55 W/m2/degrees C; and the Isolette 7.19 W/m2/degrees C (inner wall removed) and 6.23 W/m2/degrees C (inner wall inserted). Although an ellipsoid simulator is not an anatomically correct substitute for an infant, it does provide a reliable and convenient comparison of steady-state heat transfer characteristics of alternative environmental devices.

Body Temperature Regulation↗
PubMed1987

Computational model for insensible water loss from the newborn.

A mathematical model for predicting insensible water loss from the newborn infant has been developed, and its adjustable parameters have been evaluated using existing data for respiratory and transepidermal water loss components. Subsequently, the model was verified by using an independent set of available data on total insensible loss from naked infants who were not mechanically ventilated and who did not sweat. Under these conditions, the model was capable of correctly predicting the influence of ambient humidity, gestational age, and postnatal age, and in general, the predictions had a precision of +/- 14%, but they tended to underestimate insensible water loss by -16%. The straightforward algebraic form of the model makes it suitable for computerized calculations, which can be readily available at the bedside and quickly updated to account for changes in infant or environmental variables. The model is useful both for anticipating the abnormally large insensible water loss of the premature infant early in life and for computing expected changes in insensible water loss as a result of intentional manipulation of environmental factors, such as incubator temperature or supplemental humidification.

Computer Simulation↗
PubMed1985

Inert gas mixing in the upper and central airways of man.

The dispersion of an inert bolus of helium (He) or sulfur hexafluoride (SF6) was used as a direct, non-invasive measure of longitudinal gas mixing in the conducting airways of three human subjects. Penetration volume was determined as the milliliters of air inspired after bolus injection, and by computing the increase in mixing between bolus penetrations of 30 and 90 ml, mixing was characterized in the intervening upper airway compartment. Mixing in a central airway compartment was similarly evaluated as the increased mixing between bolus penetrations of 90 and 150 ml. To investigate mixing mechanisms during inspiration, inspiratory flow rate was varied between 0.2 and 1.8 L . sec-1 while the expiratory flow rate was held constant at 0.4 L . sec-1 and conversely, expiratory mixing mechanisms were studied at a fixed inspiratory flow of 0.4 L . sec-1 by varying expiratory flow from 0.2 to 2.4 L . sec-1. Under all eight experimental conditions (i.e. two inert gases X two airway compartments X two variable flow half-cycles), the extent of SF6 mixing was found to be three times that of He, and this is indicative of a dispersion process in which radial diffusion limits longitudinal mixing. This was further supported by the positive correlation between mixing and expiratory flow in the upper airway compartment. Mixing in this compartment did not vary with inspiratory flow, possibly because of the influence of turbulence generated by the glottis. In the central airways, the effect of changes in both inspiratory and expiratory flow was insignificant.

Adult↗
PubMed1983

Single breath cardiac output--enhanced sampling and analysis techniques.

The single breath method for measuring cardiac output (Q) was enhanced using new computer sampling and analysis techniques. The carbon dioxide (CO2) elimination rate was measured breath by breath using computer integration of expired flow rate and CO2 concentration. The concentration of CO2 in the arterial blood was determined from the CO2 partial pressure at the end of a normal breath. The concentration of CO2 in mixed venous blood was determined with a modification of the single breath method. The variability and relative accuracy of measurement of cardiac output were evaluated using four healthy men who exercised at three work rates from 0.5 L X min-1 (rest) to 2 L X min-1 oxygen consumption (VO2). Repeatability of measurements was assessed by making repeated measurements on one subject at a steady state exercise work rate. The coefficients of variation for repeated measurements made at 0.5 L X min-1 (rest), 1.0 L X min-1 VO2, and 2.0 L X min VO2 were 18.2, 10.5% and 8.8%, respectively. Regression lines relating cardiac output and oxygen consumption from three separate studies, employing the direct Fick method, and the described method were all similar. The probability of a successful breathing maneuver was increased to nearly 100%. Success was defined as a linear regression correlation coefficient (r2), relating instantaneous exchange ratio and CO2 during the breathing maneuver, of greater than 0.9.

Adult↗
PubMed1979

Longitudinal mixing in pulmonary airways: comparison of inspiration and expiration.

The increase in dispersion of an inert tracer bolus of helium (He) or sulfur hexafluoride (SF6) was used as a direct and noninvasive measure of longitudinal mixing in the conducting airways. Over a 0- to 260-ml range of bolus penetration, a change in the inspiratory flow from 0.35 to 1.2 l/s did not affect the dispersion of He and SF6, this implies that pure convective dispersion is the dominant inspiratory mixing process. The same change in expiratory flow caused a significant increase in SF6 dispersion only; this indicates that Taylor dispersion is important during expiration. In experiments performed at a fixed penetration of 160 ml and with SF6 only, the inspiratory and the expiratory flows were independently varied from 0.18 to 5.4 l/s. Though the bolus dispersion exhibited a mildly negative correlation with inspiratory flow, it was linearly correlated with expiratory flow. From the former result we conclude that although inspiratory mixing occurs primarily by convective dispersion, there is also a small degree of turbulent dispersion. The latter result confirms that expiratory mixing is primarily due to Taylor dispersion.

Helium↗