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Biomedical subjects

W G McTaggart

Publications and source records attributed to W G McTaggart.

At least 19 recordsLinked to original sources
PubMed1997

Cardiovascular effects of a sustained -Gz force in the horizontal position.

INTRODUCTION: The purpose of this investigation was to study the effect of a sustained -Gz force applied in the horizontal position on the cardiovascular system and the distribution of body fluids. METHODS: The study was conducted on four men who were submitted to two protocols. The principal difference between the two protocols was that in Protocol A the subjects remained supine, whereas in protocol B the subjects were submitted to a small -Gz force (0.38 G) for a relatively prolonged period while remaining supine. The -Gz force was generated by a short arm centrifuge (AGS or artificial gravity simulator) which has four beds radially oriented on a circular platform and allows variation of the Gz force by controlling the angular velocity. The cardiovascular and fluid distribution responses were sampled approximately every 2 min during the whole duration of the experiment (205 min). The variables recorded were thoracic impedance (Tz), stroke volume (SV), heart rate (HR), first derivative of the thoracic impedance change (dz.dt-1), and systolic (SBP) and diastolic (DBP) arterial BPs. RESULTS: Changes in these variables within each protocol and across protocols were analyzed statistically by group comparisons. This analysis showed that changing from the standing to the supine position causes an increase in SV and a decrease in HR and SBP and DBP. Adding a -Gz force produces the same qualitative effects but causes a greater increase in SV and a greater decrease in systolic and diastolic BPs, even though the -Gz force was only a fraction of 1 G. CONCLUSION: Changing position from vertical to horizontal position and the application of a -G force produce similar cardiovascular and body fluid effects but these effects are amplified by -Gz. An attempt to find an explanation to those changes has led us to hypothesize that a combination of factors such as central venous pressure and sequestering fluids in some part of the thorax must play an important role in the characteristics of those changes. Further research on the physiological effects of prolonged -Gz may be relevant to studies in simulated microgravity.

Adult↗
PubMed1994

Artificial gravity as a countermeasure of physiological deconditioning in space.

The displacement of humans from our planet to space and back to our planet or to another planet necessarily causes the exposure to transitional gravitational forces which create a need for countermeasures of physiological deconditioning. One of the alternative approaches to counteracting physiological deconditioning is the simulation of a gravitational field. An apparatus named the artificial gravity simulator (AGS) has been designed and constructed. The AGS is a short radius rotating platform capable of producing a +Gz 100% gradient of a variable magnitude up to 3-g. It supports four beds for testing four subjects at a time. The AGS is suitable for short and long duration experiments on various physiological systems. At present it is being used to study the cardiovascular response to various g-levels and exposure times.

Cardiovascular Deconditioning↗
PubMed1993

The cardiovascular response to the AGS.

An instrument, the AGS (artificial gravity simulator), has been built to produce artificial gravity. This paper reports preliminary results of experiments on human subjects conducted to study the cardiovascular response to various g-levels and exposure times.

Cardiovascular Deconditioning↗
PubMed1992

Lipid profiles in spinal cord injury.

Measurement of blood levels of total cholesterol and lipoproteins (HDL and LDL) were conducted on 96 men with spinal cord injury, 46 paraplegics and 50 quadriplegics. All these patients were studied in the stabilized phase of the disease as a follow up to the rehabilitation process. The study was designed to compare results with a normal, able bodied population and to investigate if any abnormal finding could be related to the age at onset of the spinal cord injury, the duration of the disease or the level of the lesion. Compared to the normal, able bodied population, this study indicates that patients with a spinal cord injury do not have higher levels of cholesterol or LDL, nor lower levels of HDL. Levels of total cholesterol increase with aging, as in the normal population, but have no relation to the duration of the disease or the level of the lesion. Blood levels of HDL and LDL do not seem to be related either to the duration of the disease or to the level of the lesion.

Adult↗
PubMed1992

Coronary risk in spinal cord injury: assessment following a multivariate approach.

A group of 96 men with spinal cord injury was studied to find out if patients with spinal cord injury were at an increased risk of coronary heart disease. A multivariate approach based on data produced by the Framingham study was used to estimate the probability of developing coronary artery disease within six years. Data obtained from the 96 patients were compared with data obtained from 96 nontrained, able-bodied men matched according to age. The results of this study suggest that patients with spinal cord injury show a risk of coronary artery disease similar to that estimated in non-trained, age-matched, able-bodied individuals. The risk increases with age, but it is of the same order as that found in the normal population and does not appear to be related to the duration of the disease. The results are inconclusive in regard to the level of the lesion as an independent factor of risk.

Adult↗
PubMed1989

Energy requirements of gamefield exercises designed for wheelchair-bound persons.

This report presents energy requirements of three athletic exercises (power ramp, climber, and chin-ups) in a free-wheeling gamefield developed by the City of Houston for wheelchair-bound persons. Heart rate was monitored by telemetry. Expired gas samples were collected in Douglas bags. Oxygen and CO2 concentrations were determined by mass spectrometry and expired gas volumes by a wet gas meter. Pulmonary ventilation, O2 consumption, and CO2 production were calculated from expired gas samples. Laboratory studies were conducted on eight men with paraplegia and ten untrained, healthy, able-bodied men. The same persons were tested on the gamefield while propelling a wheelchair over the power ramp, the climber, and doing chin-ups. Age and weight were 32 +/- 4yrs vs 31 +/- 6yrs and 79.6kg vs 79.0kg, respectively, for paraplegic and healthy men. Paraplegic men had average heart rates of 133 +/- 11bpm, 133 +/- 19bpm, and 135 +/- 21bpm, respectively, for the power ramp, climber, and chin-ups. Heart rate values for able-bodied men were 136 +/- 26bpm, 139 +/- 24bpm, and 136 +/- 26bpm, respectively, for the same three exercises. The paraplegic men's VO2 measurements were 13.2 +/- 2.2, 11.5 +/- 2.8, and 6.4 +/- 2.9ml/min/kg, respectively, for the power ramp, climber, and chin-ups. The able-bodied men's VO2 measurements were 15.8 +/- 2.8, 15.4 +/- 3.6, and 9.2 +/- 2.8 ml/min/kg for the same exercises. Patients with paraplegia seemed to outperform able-bodied men in all events. Gamefield exercises appeared to tax the cardiorespiratory system at a level comparable to that usually prescribed for training purposes.

Adult↗
PubMed1988

Effects of unilateral, low-frequency, neuromuscular stimulation on superficial circulation in lower extremities of patients with peripheral vascular disease.

The effects of unilateral, low-frequency, neuromuscular stimulation on the circulation in skin of the lower extremities were studied in eight subjects with peripheral vascular disease and eight control subjects with normal peripheral vasculature. Sixty minutes of stimulation (at 2 Hz), of sufficient intensity to produce visible contraction of musculature, was applied through cutaneous electrodes placed over the common peroneal nerve and dorsum of the foot. Systolic and diastolic blood pressure, heart rate, bilateral great-toe photoplethysmographic waveform, and bilateral pedal skin temperature were recorded at 30-min intervals during stimulation and 30 min after stimulation. Mean differences in recordings before and after stimulation were then calculated for each parameter, showing in subjects with peripheral vascular disease significant increases of 5.3 +/- 2.1 mm and 0.5 +/- 0.1 degree C for ipsilateral photoplethysmographic waveform amplitude and pedal skin temperature, respectively. Mean differences for the remaining parameters were not significant. Recorded parameters in the control group did not change after stimulation. These results demonstrate that low-frequency, neuromuscular stimulation produces regional cutaneous vasodilation in subjects with peripheral vascular disease. No evidence of generalized vasodilation after neuromuscular stimulation was found.

Adult↗
PubMed1988

Electric impedance measurements in quadriplegia.

Previous experimental studies have shown that measurements of electric impedance of the whole human body relate to body fluid volumes. Measurements using two properly selected current frequencies have been purported to be useful in determining the sizes of extracellular and total body fluids. In this study, measurements of whole body impedance were performed on 20 healthy able-bodied subjects and 20 patients with quadriplegia at the frequencies of 1.5kHz and 150kHz. Differences found between the two groups suggest that the ratio of interstitial body fluids to total body fluids in quadriplegic patients is higher than in healthy subjects. This finding is consistent with previous body composition studies conducted on quadriplegic patients using a radioisotope technique, which have suggested a relative increase of extracellular space.

Adult↗
PubMed1985

Body composition in spinal cord injury.

A study of body composition was conducted on 45 patients with spinal cord injury (SCI) and 12 able-bodied healthy subjects who served as controls. Body composition was assessed in terms of water (W), fat (F), protein (P), and mineral (M) content. SCI patients exhibited lower absolute amounts of W, F, and P, but no differences in the the amounts of these components when expressed relative (percentage) to gross body weight (BW). As estimated in this study, the amount of bone mass constituted a higher percentage of the gross BW. This suggests that, although SCI patients lose calcium in the early stages of the disease, the loss of weight that follows SCI is principally due to the loss of W, F, and P.

Adipose Tissue↗
PubMed1985

Body sodium and potassium in men with spinal cord injury.

As part of a broad study on the body composition of patients with extensive muscular paralysis, total body water (TBW), extracellular fluid (ECF), exchangeable sodium (Nae), and exchangeable potassium (Ke) were measured in 22 paraplegic and 23 quadriplegic patients. These data were compared with similar measurements obtained on 12 healthy men. Patients with spinal cord injury (SCI) showed a drastic loss of K+, more pronounced in quadriplegic than in paraplegic patients. Sodium was retained and associated with a relatively increased ECF volume. The high correlation between TBW and total "exchangeable base" (Nae + Ke) reported in previous studies on healthy subjects and patients with varied diseases was also observed in SCI patients. Analysis of the present data suggests that the physiologic mechanism which maintains the tonicity of the body fluids is not affected in SCI. This analysis does not provide any clue as to the identification of the mechanism that might explain the relative expansion of the extracellular space in the presence of K+ depletion.

Adolescent↗
PubMed1984

Total body water and its distribution in men with spinal cord injury.

During the first months after spinal cord injury there is a drastic loss in body weight. Total body water (TBW) and extracellular water (ECW) were determined in 12 normal healthy men, in 22 paraplegic men and in 23 quadriplegic men. TBW was decreased in both groups of patients, paralleling the loss in body weight, though not totally accounting for the weight loss. ECW was decreased in absolute terms but increased in relation to body weight and height. The amount of intracellular water, obtained by subtracting ECW from TBW, was decreased. This study provides a quantitative estimation of the reduction in body cell mass following spinal cord injury and reveals an expansion of the extracellular space. The mechanism and functional significance of this expansion are not clear at this time.

Adult↗
PubMed1975

Improved method for densitometry of electrophoretic lipoprotein fraction.

We evaluated a method for the densitometric quantitation of the electrophoretic lipoprotein fractions that sets the limit of integration at the beta-lipoprotein peak maximum. Results were compared with the more conventional method of placing the limit of integration in the valley between the beta- and pre-beta-lipoprotein peaks. The criterion of symmetrical beta-lipoprotein peaks imposed by the method was tested, and manual determination of the beta peak maximum was compared to automatic computer analysis. Computer-generated curves stimulating increasing overlap of constant shape beta and pre-beta peaks were analyzed by the two methods. The conventional method introduces an error that increases with increasing overlap, but with the present method results agreed with those for completely resolved peaks. The beta peak was best approximated by an isosceles triangle (at least for the electrophoresis technique used in these studies), indicating symmetry of the beta peak. Values for the area under the lipoprotein peaks obtained by manual and computer placement of the integration limits agreed well (gamma = .892 to .998; SE of estimate = .0264 to .0306). The "beta peak maximum" method of densitometric quantitation avoids the problems associated with partial resolution of the beta- and pre-beta-lipoproteins. It is equally adaptable to either visual placement of the limits of integration or computer analysis.

Computers↗