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S M Mastenbrook

Publications and source records attributed to S M Mastenbrook.

6 recordsLinked to original sources
PubMed1983

Graphical analysis of multiple inert gas elimination data.

A plot of measured retention-excretion ratios [(Ri/Ei)obs] vs. reciprocal solubility (1/lambda i) for selected inert gases allows quick detection of shunt and ventilation-perfusion (V/Q) inhomogeneity in the lung. We derive simple rules for constructing a smooth R/E function from the data, using a multicompartmental model of the lung. If mixed venous inert gas measurements are available, the values [lambda i(1-Ri)/Ei]obs for the infused gases can be used to estimate the overall VT/QT ratio and provide an additional test of the consistency of the data. For any set of equilibrium compartments ventilated and perfused in parallel, we show that d(R/E)/d(1/lambda) cannot be negative, nor can d2(R/E)/d(1/lambda)2 be greater than zero. A rectilinear R/E function implies a narrow distribution of V/Q among the gas exchange compartments, whereas a downward-concave curve implies a broader distribution. The shunt perfusion and dead-space ventilation can be estimated from the asymptotes of the R/E function. The range of V/Q for the gas exchange compartments can also be bracketed if a well-defined region of curvature is present in the graph. Finally, from the R/E vs. 1/lambda graph and (if mixed venous data are available) from the lambda(1-R)/E values, we can determine quickly whether the data deserve the detailed numerical analysis outlined in our companion paper.

Humans↗
PubMed1983

Parametric estimation of ventilation-perfusion ratio distributions.

We present a model and rigorous statistical approach for recovery of ventilation-perfusion ratio (V/Q) distribution parameters from multiple inert gas elimination data. We model the lung as a parallel combination of shunt, dead space, and one to three log-normal distributions of gas exchange units. This model provides a natural set of parameters for characterizing V/Q distributions. The log-normal terms are adjustable to represent smooth or sharp peaks in the distribution. Since the peak locations and widths are explicit in the model, very few parameters are needed. We select and estimate the significant parameters of the model by use of standard statistical tests and constrained least squares. This method provides two major advances in V/Q distribution estimation: 1) it allows flexible pooling and statistical comparisons of multiple experiments, and 2) it simultaneously gives both point estimates and 95% probability intervals for the V/Q distribution parameters. We present results of our procedure for data from humans in health, stress, and pulmonary disease. A program package, VQPAR, in FORTRAN is available for implementing the procedure.

Bayes Theorem↗
PubMed1982

Ventilation-perfusion ratio distributions by mass spectrometry with membrane catheters.

We previously developed a quadrupole mass spectrometer system for measuring gas phase concentrations of multiple inert gases at trace levels. A new inlet with two silicone rubber membrane catheters now allows quantitative analysis of the inert gas concentrations in both blood and gas phase samples. We have determined the sensitivity, linearity, and reproducibility of this system by measuring blood-to-gas phase calibration curves for the following inert gases: sulfur hexafluoride, krypton, Freon 12, enflurane, diethyl ether, and acetone. We have used our mass spectrometer system to obtain multiple inert gas elimination data from three anesthetized, spontaneously breathing dogs. We conclude that our dual-membrane mass spectrometer system provides useful measurements of trace multiple inert gas concentrations in both blood and gas phase samples. Furthermore, the inert gases in blood can be measured directly without having to extract them into a gas phase, and the multiple inert gas elimination data acquired with our system can be used to provide estimates of ventilation-perfusion ratio distributions. Our mass spectrometer technique provides an alternative to the gas chromatographic approach for these measurements.

Anesthesia, General↗
PubMed1980

Pulmonary control systems in exercise.

We reviewed the response and regulation of alveolar ventilation, chest wall mechanics, and alveolar-to-arterial gas exchange to the demands imposed by increases in tissue metabolic rate. The primary mediator of iso-capnic exercise hyperpnea remains a dilemma--with conflicting evidence presented on both sides of a "CO2 flow" humoral hypothesis versus a "neurogenic" non-humoral hypothesis. The increased expiratory flows and tidal volumes at any given level of hyperpnea are achieved at a "minimum" of increased mechanical work exerted on the lung and chest wall, owing to a control system that has multiple levels of nervous integration (from cortex to spinal motor neuron) readily accessible to a wide variety of sensory information concerning the mechanical status of the lung and respiratory muscles. The maintenance of arterial PO2 in the face of a falling CVO2 during exercise was attributed to a precise regulation over factors that limit diffusion equilibrium and intra- and interregional ventilation: perfusion distributions in the lung. Finally, we noted that the near-optimal nature of these responses and their control during exercise had many exceptions in the real world of physical exercise outside of the laboratory.

Carbon Dioxide↗