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Biomedical subjects

G C Butler

Publications and source records attributed to G C Butler.

At least 37 records · Page 2Linked to original sources
PubMed1993

Heart rate variability and fractal dimension during orthostatic challenges.

Heart rate variability (HRV) spectral analysis has been used as a tool for short-term assessment of parasympathetic (PNS) and sympathetic nervous system (SNS) control of heart rate. However, it has been suggested that the PNS and SNS indicators are superimposed on a broad-band noise spectrum in which the power spectral densities are inversely proportional to their frequency (1/f beta). In this study, we have used coarse-graining spectral analysis to extract the harmonic components for calculation of PNS and SNS indicators and to obtain the slope (beta) of the 1/f beta component to estimate fractal dimension (DF) of a trail of HRV. DF was regarded as an indicator of cardiovascular system complexity. Ten healthy young subjects (6 women and 4 men) were studied in supine rest and with sequential applications of four levels of lower body negative pressure (LBNP; -10, -20, -30, and -50 mmHg) and head-up tilt (HUT; 10, 20, 30, and 70 degrees). In the 20 tests, there were six occurrences of presyncopal symptoms that required the test to be terminated before the planned end point. At low levels of LBNP or HUT, arterial pulse pressure (PP) was not changed from rest, and calculated DF was very high (beta approximately 1.00). At the higher levels of LBNP and HUT, PP decreased. Coincident with this reduction in PP, PNS activity decreased, SNS activity increased, and DF was reduced, each with a significant linear relationship to the change in PP (PNS: r = 0.56; SNS: r = 0.57; DF: r = 0.70, P < 0.01). Each occurrence of presyncope was associated a low PNS indicator as well as DF < 2.50 (beta > or = 1.80). These data indicate that the cardiovascular system is operating at a reduced level of complexity and further suggest that reduced complexity might not be compatible with cardiovascular homeostasis.

Adult↗
PubMed1993

Effect of recombinant human erythropoietin on platelet production in dialysis patients.

Two hundred forty-four anemic hemodialysis patients were randomized into recombinant erythropoietin and placebo-treated groups during a 12-wk double-blind phase, followed by a 24-wk open-label period. Mean platelet count rose from the baseline value of 242 x 10(9)/L to 264 x 10(9)/L on day 5 of epoetin therapy (P < 0.001, paired t test). Mean platelet count peaked at 290 x 10(9)/L on day 40 and remained at a significantly elevated level below the peak thereafter. The peak platelet count did not exceed the normal range in a majority of cases. Platelet count was unaffected by placebo. Patients without an erythropoietic response during the first few weeks of therapy exhibited a rise in platelet count comparable to that in patients with a satisfactory erythropoiesis. Patients with low initial serum ferritin concentrations had baseline platelet counts comparable to those with normal or high ferritin values and showed a similar rise in platelet count during therapy. As a group, patients with baseline platelet counts above 400 x 10(9)/L showed no rise in platelet count, whereas those with normal or reduced platelet counts showed a marked thrombopoietic response to epoetin. Erythropoietin therapy did not significantly alter the incidence of blood access thrombosis when compared with placebo treatment.

Anemia↗
PubMed1992

Probing heart rate and blood pressure control mechanisms during graded levels of lower body negative pressure (LBNP).

Following space flight or head down tilt bed rest, cardiovascular deconditioning is often observed as a failure to maintain arterial blood pressure with symptoms of presyncope or syncope. LBNP can be used as a stressor of the cardiovascular system to observe the regulatory process. We have recently developed a new method to study cardiovascular control. Coarse graining spectral analysis (CGSA), allows simultaneous extraction of the harmonic components to evaluate sympathetic and parasympathetic nervous activities, and of the underlying complexity of the physiological response as given by the slope (beta) or fractal dimension (DF). The recognition that system complexity plays a major role in maintenance of cardiovascular stability is a relatively new concept. It was the purpose of the present study to examine the underlying complexity of heart rate and systolic blood pressure (SBP) variablities as indicated by the DF and power spectral analysis. Eight healthy men completed a test protocol of 20 min supine rest followed sequentially by 10 min at -5, -15, -25, -40, and -50 mmHg LBNP, and 10 min supine recovery. At rest, DF of R-R interval was 3.57 (beta = 1.56 +/- 0.12). There was a progressive decline in DF with LBNP, until at -50 mmHg, DF decreased to 1.2 (beta = 2.66 +/- 0.09). The DF for SBP was 1.3 (beta = 2.1 +/- 0.18) at rest, and was not significantly changed during LBNP. In the mid- and high-frequency ranges of the spectra, there was a moderately high degree of coherence between the variability in R-R interval and SBP. These findings indicate that short term SBP has a relatively low and unchanged complexity compared to heart rate. The changes in DF of heart rate variability were marked with increasing levels of LBNP. The results of this, and our previous study, indicate that a decline of DF to a critical level (near 1.4) is associated with orthostatic hypotension. These data show the utility of simple, non-invasive methods of data collection in conjunction with sophisticated data analysis techniques to point to possible mechanisms of orthostatic hypotension.

Adult↗
PubMed1991

Kinetics of ventilation and gas exchange during supine and upright cycle exercise.

The dynamics of ventilation (VE), oxygen uptake (VO2), carbon dioxide output (VCO2), and heart rate (fc) were studied in 12 healthy young men during upright and supine exercise. Responses to maximal and to two different types of submaximal exercise tests were contrasted. During incremental exercise to exhaustion, the maximal work rate, VO2max, VEmax, fc,max, and ventilatory threshold were all significantly reduced in supine compared to upright exercise (P less than 0.01-0.001). Following step increases or decreases in work rate between 25 W and 105 W, both VO2 and VCO2 responded more slowly in supine than upright exercise. Dynamics were also studied in two different pseudorandom binary-sequence (PRBS) exercise tests, with the work rate varying between 25 W and 105 W with either 5-s or 30-s durations of each PRBS unit. In both of these tests, there were no differences caused by body position in the amplitude or phase shifts obtained from Fourier analysis for any observed variable. These data show that the body position alters the dynamic response to the more traditional step increase in work rate, but not during PRBS exercise. It is speculated that the elevation of cardiac output observed with supine exercise in combination with the continuously varying work-rate pattern of the PRBS exercise allowed adequate, perhaps near steady-state, perfusion of the working muscles in these tests, whereas at the onset of a step increase in work rate, greater demands were placed on the mechanisms of blood flow redistribution.

Adult↗
PubMed1991

Reduced orthostatic tolerance following 4 h head-down tilt.

The cardiovascular responses to a 10-min 1.22 rad (70 degrees) head-up tilt orthostatic tolerance test (OST) was observed in eight healthy men following each of a 5-min supine baseline (control), 4 h of 0.1 rad (6 degrees) head-down tilt (HDT), or 4 h 0.52 rad (30 degrees) head-up tilt (HUT). An important clinical observation was presyncopal symptoms in six of eight subjects following 4 h HDT, but in no subjects following 4 h HUT. Immediately prior to the OST, there were no differences in heart rate, stroke volume, cardiac output, mean arterial pressure and total peripheral resistance for HDT and HUT. However, stroke volume and cardiac output were greater for the control group. Mean arterial pressure for the control group was less than HDT but not HUT. Over the full 10-min period of OST, the mean arterial pressure was not different between groups. Heart rate increased to the same level for all three treatments. Stroke volume decreased across the full time period for control and HDT, but only at 3 and 9 min for HUT. There was a higher total peripheral resistance in the HDT group than control or HUT. The pre-ejection period to left ventricular ejection time ratio was less in HDT than for control or HUT groups. These data indicate a rapid adaptation of the cardiovascular system to 4 h HDT that appears to be inappropriate on reapplication of a head to foot gravity vector. We speculate that the cause of the impaired orthostatic tolerance is decreased tone in venous capacitance vessels so that venous return is inadequate.

Adult↗
PubMed1990

Effect of hypoxia on VO2 kinetics during pseudorandom binary sequence exercise.

The dynamic response characteristics of the oxygen uptake (VO2) response were investigated during upright cycle ergometer exercise in six healthy male volunteers. The exercise test consisted of a pseudorandom binary sequence (PRBS) with 15 units per sequence, each unit 15 s long, for a total period of 225 s. Six identical sequences were completed in a single test session. Each subject exercised under both normoxic and hypoxic (FIO2 = 14%) conditions. VO2 was measured breath-by-breath. The data were analyzed in the frequency domain by Fourier analysis to yield amplitude and phase shift coefficients for the relationship between the input work rate and the output responses of VO2 and heart rate (HR). The amplitude of the VO2/work rate was significantly reduced by hypoxia compared to normoxia over a wide range of frequencies. The mean VO2 was not different between hypoxia and normoxia. The phase shift for the VO2/work rate response was significantly greater for hypoxia than normoxia. The amplitude of the HR/work rate relationship was not significantly altered by hypoxia; however, the mean HR was higher during hypoxia. The phase shift of the HR/work rate response was significantly different between hypoxia and normoxia only at certain frequencies. These data indicate that the effects of hypoxia on the cardiorespiratory response to exercise can be characterized by the use of PRBS exercise and Fourier analysis techniques. A significant reduction in the ability of the cardiorespiratory system to adapt to changes in work rate appears to be caused by a reduction in the arterial O2 content.

Adult↗
PubMed1990

Cardiovascular response to 4 hours of 6 degrees head-down tilt or of 30 degrees head-up tilt bed rest.

The cardiovascular responses to 4 h of 6 degrees head-down tilt (HDT) were compared to those of 4 h of 30 degrees head-up tilt (HUT) following a period of 1 h baseline in the 30 degrees HUT position. Eight healthy males completed each tilt position. Immediately on assuming HDT, heart rate decreased slightly from baseline, but did not differ from HUT. Stroke volume and cardiac output both increased significantly by as much as 54% and 26%, respectively, in the first minute of HDT. The difference between HDT and HUT was no longer present after 30 min. Mean arterial blood pressure was unchanged throughout 4 h or HUT or HDT. The ratio of pre-injection period to left ventricular ejection time was significantly decreased across all 4 h of HDT. Plasma volume was slightly elevated over the 4 h of HDT, while plasma hemoglobin concentration was significantly reduced. No evidence of a diuresis was found with 4 h HDT. Plasma catecholamines were not different between HDT and HUT. The present results show that the immediate transition from a HUT to a HDT position causes a dramatic change in cardiovascular variables. These changes are generally transient with baseline values resumed by many variables within 30 min of exposure to 6 degrees HDT.

Adult↗
PubMed1978

Approaches for protection standards for ionizing radiation and combustion pollutants.

The question "can the approach used for radiation protection standards, i.e., to extrapolate dose--response relationships to low doses, be applied to combustion pollutants?" provided a basis for discussion. The linear, nonthreshold model postulated by ICRP and UNSCEAR for late effects of ionizing radiation is described and discussed. The utility and problems of applying this model to the effects of air pollutants constitute the focus of this paper. The conclusion is that, in the absence of evidence to the contrary, one should assume the same type of dose--effect relation for chemical air pollutants as for ionizing radiation.

Air Pollutants↗
PubMed1966

Effect of Bromouracil-containing Deoxyribonucleic Acid on Bacillus subtilis.

Gimlin, Dixie M. (Oklahoma State University, Stillwater), Sue D. Hardman, Betty N. Kelley, Grace C. Butler, and Franklin R. Leach. Effect of bromouracil-containing deoxyribonucleic acid on Bacillus subtilis. J. Bacteriol. 92:366-374. 1966.-Replacement of one-half of the thymine with bromouracil in Bacillus subtilis transforming deoxyribonucleic acid (DNA) resulted in a slight decrease in transforming activity, but, when used at high concentrations, this DNA preparation inhibited cell growth. Acid-hydrolyzed DNA, or addition of equivalent concentrations of the free base bromouracil in a transforming mixture, was without effect on cell growth. Treatment of the DNA preparation with deoxyribonuclease completely destroyed transforming activity and killing effect, whereas treatments with ribonuclease and trypsin were without effect on either transformation or killing activity. Growth of competent B. subtilis cells in test tubes was inhibited by high concentrations of both normal and bromouracil-containing DNA, with the bromouracil-containing DNA being significantly more inhibitory. This type of inhibition was also reflected in the time of division of the cells. The inhibitory effect was not due to viscosity, or to mutagenicity. The time course of killing paralleled transformation, and competency was required. These results can be interpreted as being due to uptake of homologous but imperfect DNA (containing bromouracil instead of thymine) by means of the systems involved in transformation, followed by either integration (resulting in lethal transformation, activation of a defective, nonlytic but lethal prophage) or interference with the recombination mechanism.

Journal Article↗