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Biomedical subjects

G D Swanson

Publications and source records attributed to G D Swanson.

At least 37 records · Page 2Linked to original sources
PubMed1986

Computerized estimation of lactate threshold.

Traditional approaches to estimating a lactate threshold during a progressive exercise test have utilized visual inspection of the data. We describe a computerized approach which utilizes a log-log transformation to yield two approximately linear segments. Linear regression lines are fit to these segments and the intersection of the two lines yields an estimate of the lactate threshold. An approximate 95% confidence interval is also generated.

Algorithms↗
PubMed1986

Importance of oscillations in alveolar gas concentrations in the analysis of rebreathing data.

Cyclic rebreathing of a soluble inert gas can be used to estimate lung tissue volume (Vt) and pulmonary blood flow (Qc). A recently proposed method for analyzing such cyclic data (Respir. Physiol. 48: 255-279, 1982) mathematically assumes that ventilation is a continuous process. However, neglecting the cyclic nature of ventilation may prevent the accurate estimation of Vt and Qc. We evaluated this possibility by simulating the uptake of soluble inert gases during rebreathing using a cyclic model of gas exchange. Under cyclic uptake conditions alveolar gases follow an oscillating time course, because gas concentrations tend to increase during inspiration and to decrease during expiration. We found that neglecting these alveolar gas oscillations leads to the underestimation of soluble gas uptake by blood, particularly during the early rebreathing breaths. When continuous ventilation is assumed Vt and Qc are overestimated unless rapid rebreathing rates, large tidal volumes, and gases of moderately low solubility are used. Under these conditions the amplitude of the cyclic oscillations is minimized, the alveolar time course more closely resembles that expected from continuous ventilation, and the resulting errors are minimized. Alternatively, when the effect of oscillating alveolar gas concentrations on mass transfer are considered, these estimation errors can be eliminated without restricting rebreathing rate or gas solubility. We conclude that failure to consider the effect of cyclic rebreathing on the time course of alveolar gas concentrations may result in significant errors when evaluating rebreathing data for Vt and Qc.

Lung Volume Measurements↗
PubMed1985

On the estimation of hypoxic ventilatory response.

The shape parameter, A, has been used to assess hypoxic sensitivity (ventilatory response, VE, to lowered alveolar oxygen tension, PAO2) in the model of the form VE = VEO + A/(PAO2 - C) where C is held constant at 32. In this paper we examine the consequence of holding C constant versus estimating both A and C from the data. Using computer-simulated data from 59 subjects whose A and C values had been previously determined, we indicate that when the actual C value is substantially different from 32, the model with C = 32 does not fit the data. In this case, the estimated A value with C = 32 is highly dependent upon the lowest value of PAO2 obtained in the experimental protocol and can be markedly different from the actual A value. In contrast, when C is also estimated from the subject's data the model fits the data and the estimate of A is unbiased but the precision may be diminished when the actual value of C is low. To improve this precision, we propose a Bayesian estimation scheme that adds a "soft" constraint on C.

Computers↗
PubMed1985

Flexible implant arthroplasty in the proximal interphalangeal joint of the hand.

Between 1966 and 1981, 812 proximal interphalangeal joints were reconstructed by the senior author using the flexible silicone rubber implant resection arthroplasty method. Within this series, a group of 182 patients with 424 proximal interphalangeal joint implants were available for a detailed clinical and roentgenographic review. Increased motion in a more functional arc with good pain relief and a favorable bone response pattern were noted in most cases after surgery. Complications were rare and included implant dislocation or fracture, recurrence of deformity, and infection. The highest complication rate was noted in implant reconstructions performed to correct rheumatoid swan-neck deformities.

Adult↗
PubMed1985

On the maximum likelihood estimation of respiratory response slopes.

Several approaches have been suggested for estimating a respiratory response slope when both x and y variables are observed with error. Recently, a maximum likelihood estimate under the assumption of a bivariate normal distribution has been proposed. A method of moments solution yields a slope estimate of y/x as long as the underlying process mean is nonzero. This paper extends the maximum likelihood approach to the case where the process mean is zero. In this case, certain additional error assumptions must be made to yield a unique estimate. These concepts are applied to the problem of estimating an effective lung volume for steady-state breath-to-breath gas exchange data during exercise.

Lung Volume Measurements↗
PubMed1985

Unicompartmental and bicompartmental arthroplasty of the knee with a finned metal tibial-plateau implant.

We followed a series of ten patients (ten knees) who had a unicompartmental and twenty patients (twenty-two knees) who had a bicompartmental arthroplasty of the knee, in which a finned metal tibial-plateau implant had been used, for two to fourteen years (average, five years) postoperatively. According to the modified criteria of MacIntosh and Hunter, thirty knees (94 per cent) had a good result and two (6 per cent), a fair result. There were two complications: one intraoperative and one postoperative fracture of the tibial plateau. One patient with rheumatoid arthritis required a revision to a total knee arthroplasty at six months because of rapid progression of disease in the contralateral, untreated compartment. Our results suggest that with the proper indications this arthroplasty has a place in reconstructive surgery of the arthritic knee joint.

Adult↗
PubMed1984

Statistical identification of compartmental models with application to plasma protein kinetics.

A numerical method for fitting linear compartmental models to data is presented which is similar to the method proposed by Jennrich and Bright (R. I. Jennrich and P. B. Bright, Technometrics 18, 385 (1976] and Feldman (H. A. Feldman. Amer. J. Physiol. 233, R1 (1977] but avoids some of the numerical difficulties. The method is direct and does not use numerical integration thereby avoiding time consuming and expensive calculations. Emphasis is on statistical procedures for model selection. In addition to the usual F tests for comparing two models, Akaike's Information Criterion (AIC) is introduced for choosing from among several models. The combined use AIC with an F test, chi-square test, or confidence intervals on estimated parameters gives a practical method to obtain a balance between underfitting and overfitting. Application to models of plasma protein kinetics illustrates the method.

Animals↗
PubMed1984

Estimation of response slopes in respiratory control.

The ventilatory response to changes in alveolar (arterial) CO2 is widely used as an index of respiratory control behavior. Methods for estimating these response slopes should incorporate the possibility that there may be errors in both the independent (partial pressure of CO2) and dependent (ventilation) variables. In a recent paper Daubenspeck and Ogden (J. Appl. Physiol. Respirat. Environ. Exercise Physiol. 45:823-829, 1978) have suggested problems inherent in the traditional technique of reduced major axis and have suggested a more contemporary technique of directional statistics. We have previously analyzed both techniques and developed a method to overcome the problems of reduced major axis and problems inherent in the use of directional statistics. Under the assumption of a bivariate normal distribution, we demonstrate that our slope estimate is similar to the maximum likelihood estimate proposed by Mardia et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 54: 309-313, 1983) for this problem. In addition, we demonstrate a bootstrap statistical approach when the distributions are not normally distributed. These concepts are illustrated using O2-CO2 interaction data.

Carbon Dioxide↗
PubMed1984

Temporal delay of venous blood correlates with onset of exercise hyperpnea.

We tested the hypothesis that humoral factors contribute to the onset of exercise hyperpnea in an electrically induced model of isocapnic exercise in alpha-chloralose-anesthetized dogs. A cannula placed in the inferior vena cava (IVC) permitted hindlimb venous blood to flow either directly to the lungs or through a variable-length extracorporeal circuit. Mean transit times (MTT) of blood from exercising hindlimbs were measured from the arrival at the pulmonary artery of green dye injected into the saphenous vein. Onset of hyperpnea was determined by the half time of the ventilatory response (T 1/2), the time required to reach 50% of the steady-state ventilation. In seven dogs, T 1/2 was directly related to MTT (P less than 0.001), suggesting that blood-borne substances released at the onset of exercise contribute to the hyperpneic response. The T 1/2-MTT relation persisted following L2 cord transection (n = 4), suggesting that intraspinal afferents are not required for this response. Chemoreceptor denervation (n = 4) slowed the onset of exercise hyperpnea but did not alter the T 1/2-MTT relation. In this model of electrically induced "exercise" in which neurogenic influences have been minimized, humoral factors alone may stimulate ventilation sufficiently to produce arterial isocapnia.

Animals↗
PubMed1984

Silicone implants in dogs. A ten-year histopathologic study.

The biocompatibility of implanted materials is important to the successful long-term results obtained in reconstructive surgery with these materials. Recently, interest has emerged regarding host response to the wear debris of implanted material. Since 1962 flexible implant materials have been studied in the Orthopaedic Research Department at Blodgett Memorial Medical Center. An important aspect of this study has been a concern for host tolerance and the evaluation of biologic responses to implanted silicone elastomer. Three dogs in which implants of silicone elastomer had been in place for more than ten years were carefully studied by complete autopsy. A benign foreign-body giant cell response to local silicone wear debris was observed. No silicone particles or macrophage giant cell reactions were found in any distant organs. The host response to silicone wear debris was benign, and no adverse systemic influences were noted.

Amputation Stumps↗
PubMed1983

Model utility in the study of cardiorespiratory control.

This study investigates the utility of differing modeling approaches to the study of cardiorespiratory control. Models are classified in terms of intended purpose. A structural model predicts behavior based on a hypothetical physiological structure. An empirical model summarizes observed behavior. A functional model attempts to relate physiological structure to observed behavior. Models from the literature for exercising man illustrate these concepts and motivate the importance of experimental design in terms of the dynamic variation of a work-rate input.

Biomedical Engineering↗
PubMed1983

A computerized mass spectrometer and flowmeter system for respiratory gas measurements.

Instrumentation systems for breath-to-breath analysis of respiratory gas exchange have been faulted by phase lags between various flow and composition signals and by difficulties in gathering and processing large amounts of data. The system described here represents an attempt to overcome these problems. Phase delays have been minimized by using a direct, piezoelectrically operated mass spectrometer inlet rather than an inlet capillary, by locating the mass spectrometer inlet and flow sensors in the same plane, and by incorporating design features which enhance the mass spectrometer response. Convenience in system operation and data analysis has been enhanced by integrating a computer into the system design so that the computer performs on-line data analysis and control functions and provides the primary interface between the experimenter and the instruments. Miniaturization of the instruments permits close coupling to an exercising subject.

Calibration↗
PubMed1983

Optimal frequency locations for estimating model parameters in studies on respiratory control.

Sinusoidal work rate inputs yield a dynamic ventilatory response which can be fitted to a mathematical model. The model structure leads to inferences about the underlying physiology of the respiratory control mechanism. A particular problem of interest in model parameter estimation concerns the location of the test frequencies. The effects of estimating the parameters of a relatively complex model developed by Fujihara et al. using arbitrary frequency locations from a study by Casaburi et al. versus using the frequencies derived from an optimization method presented in a recent paper by Engeman et al. were examined. The Fujihara model is indicated to be much more likely to be justified when optimal sinusoids are used to generate the data than when Casaburi's arbitrary frequencies are used. The implications are that more descriptive models of respiratory control may be developed with the aid of optimal frequency design for the input sinusoids.

Humans↗