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D K Sponholtz

Publications and source records attributed to D K Sponholtz.

7 recordsLinked to original sources
PubMed1982

Estimation of gas-phase diffusivities in hyperbaric environments.

Diffusion of a particular gas in a mixture of three or more gases depends on diffusion characteristics and concentrations of the other gases and also on environmental pressure. 1) Estimates of gas-phase diffusivities in hyperbaric environments can be calculated from binary coefficients by the Wilke equation. Sample calculations show that addition of carbon dioxide and water to inspired gas has very little effect on diffusivity of oxygen but that neglect of lesser components of a mixture, such as the nitrogen in "trimix" or the helium in crude neon, would lead to errors of 10% to 20%. 2) It is not possible to match a compressed air environment with a helium-oxygen or a helium-oxygen-nitrogen environment for both density and diffusivity. Diffusivities of oxygen and carbon dioxide in a helium mixture can be less than half the values in compressed air having the same density. In a plot of diffusivity vs. gas density, most useful mixtures are included in a hyperbolic-shaped band; diffusivity falls to below 25% of the room air value when density is 5 times normal.

Atmospheric Pressure↗
PubMed1981

Hindrance to diffusive gas mixing in the lung in hyperbaric environments.

Diffusivity of a gas is inversely proportional to atmospheric pressure. We studied pulmonary gas mixing in hyperbaric environments (5.5 and 9.5 ATA) as a means of understanding the role played by diffusion in normal situations and also as a means of determining whether persons in hyperbaric environments will be handicapped by poor diffusive mixing. Our subjects took single breaths of a mixture of indicator gases (5% each of SF6, Ar, Ne, and He; 20% O2, balance N2). Recordings of expired volumes and concentrations showed that heavier indicators were less well mixed than lighter ones, as evidenced by a slower fall during the transition between dead space and "alveolar" gas and a steeper slope of the alveolar plateau. Differences between light and heavy gases increased as pressure increased. Amounts of the indicators retained in the functional residual capacity (FRC) or residual volume after a single breath had a weak positive relation to diffusivity; the amounts (A) in the FRC (as fraction of inspired amounts) were well fitted by a simple equation. ARFC/AI = 0.55 - (0.0010/D), where D is molecular diffusivity. We conclude that the changes of distribution of inspired gas that occur with large changes of diffusivity have only a minor effect on the amount of gas exchanged between the inspirate and residual gas in the FRC.

Atmospheric Pressure↗
PubMed1981

Effectiveness of a breath during exercise in a hyperbaric environment.

During vigorous foot-pedal exercise at 6.75 ATA, three subjects had lower total ventilation, larger functional residual capacity (FRC), and higher PCO2 in end-expired and mixed-expired gas than during the same exercise at 1.5 ATA. Compartmental analysis of multiple breath washin suggested that ventilation was more evenly distributed during the high pressure exercise. Mass-balance analysis of inert indicator gases in single breaths showed that at a given pressure, low-diffusivity gases did not mix in the lung as well as high-diffusivity gases. It did not follow, however, that a particular gas was better mixed at low pressure than when its diffusivity was decreased by high pressure; the data showed just the opposite during exercise. The apparent paradox seems to be explained by the change of other conditions for mixing at high pressure, especially the enlargement of the FRC.

Atmospheric Pressure↗
PubMed1979

Diffusion-dependence of pulmonary gas mixing at 5.5 and 9.5 ATA.

Gas-phase diffusivity is inversely proportional to pressure, so mixing of inspired gas in the lung can be expected to be poor in hyperbaric environments. Subjects performed multiple-breath wash-in of a mixture (4% each of SF6, Ar, Ne, and He; 21% O2, 63% N2) at 1.5, 5.5, and 9.5 ATA. At the higher pressures there were marked differences of concentrations between the indicator gases, measured by mass spectrometer at the mouth during a single expiration. Compared to heavier gases, light gases fell from dead space concentration to the "alveolar" level sooner, had a flatter plateau, and had a lower average expired concentration, indicating that more of the light gases were retained in the Functional Residual Capacity (FRC) after the breath. However, wash-in rates for the indicators were about the same; a rapid initial rate for He diminished so that it was about the same as the SF6 rate, because in later breaths a back pressure developed for He. The findings illustrate the basic principle that the amount of gas that diffuses from one location to another in a container depends not only on diffusivity, but also in an interdependent manner on concentration gradient, time for diffusion, and configuration of the container.

Argon↗
PubMed1979

Effects of immersion and static lung loading on submerged exercise at depth.

The effects of static lung loading in the range +20 cmH2O to -20 cmH2O was investigated in 3 male subjects breathing air during submerged exercise in the prone position at pressures ranging from 1.45 ATA to 6.76 ATA. Both maximal and submaximal exercise was performed and dry controls were done at 1.45 ATA. A low-resistance bag-in-a-box breathing apparatus (less than 1.25 cmH2O/liter/s at 8 g/liter density) was used. Static lung loading had little effect on maximal or submaximal VO2, VCO2, VE, heart rate, or end-tidal PCO2, while increased breathing gas density did affect these parameters to a larger extent. Imersion per se reduced the VE at a given level of VO2 and increased both the VT and VA at a given VE. Increasingly positive static lung load increased VC and ERV both during rest and exercise. Exercise-induced dyspnea was experienced and scored. At submaximal VO2 levels up to 2.5 liter/min this dyspnea did not limit exercise at any depth, but during maximal exertion at 6.76 ATA (VO2 from 3.45--3.77 liter/min), dyspnea became work limiting in several cases. Static load had a marked effect on dyspnea and a load of +10 cmH2O produced the least dyspnea, enabling all subjects to perform maximal exertions for 5 min at 6.76 ATA. The 15-s MVV was performed at all depths and static loads and neither it nor the VE/MVV ratio correlated with the degree of dyspnea.

Adult↗
PubMed1978

Chamber-based system for physiological monitoring of submerged exercising subjects.

A system has been designed which allows for measurement of cardiorespiratory parameters in the fully submerged subject performing graded exercise. It consists of a horizontal wet chamber; a waterproofed, electrically braked bicycle ergometer; and a low-resistance "bag-in-a-box" breathing apparatus. Chamber and breathing apparatus design allow for a great deal of flexibility in both positioning of the subject and instrumentation. The 200-liter "bag-in-a-box" configuration provides the subject with humidified gas through 2.5 in. i.d. tubing. A rolling seal spirometer provides the lung counter volume. Provision is made for breath-by-breath gas analysis with a mass spectrometer. Hydrostatic pressure on the diver's thorax relative to chamber pressure can be easily and reproducibly varied over a wide range of positive and negative static lung loads. This system has been used on over 100 man-dives to depths equivalent to 6.5 ATA with oxygen consumptions up to 4.0 liters/min.

Humans↗