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Biomedical subjects

D Cardús

Publications and source records attributed to D Cardús.

17 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↗
PubMed1995

Electrical impedance measurements in the arm and the leg during a thirty day bed rest study.

The need to detect, follow and understand the effects of gravity on body fluid distribution is a constant stimulus to the quest for new techniques in this area of research. One of these techniques is electrical bioimpedance spectroscopy (BIS). Although not new, this is a technique whose applications to biomedical research are fairly recent. What is new is the development of instrumentation that has made practical the use of impedance spectroscopy in the biomedical setting, particularly in studies involving human subjects. The purpose of this paper is to report impedance spectroscopy observations made on a subject who was submitted to bed rest for a period of thirty days. These observations were made as part of a study on muscle atrophy during a thirty day head down bed rest. Since bed rest studies are very costly in human and financial terms, and technically difficult to realize, we felt that even though the present study deals only with a single case it was worthy of reporting because it illustrates kinds of questions impedance spectroscopy may help to answer in microgravity research.

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↗
PubMed1994

Artificial gravity in space and in medical research.

The history of manned space flight has repeatedly documented the fact that prolonged sojourn in space causes physiological deconditioning. Physiological deterioration has raised a legitimate concern about man's ability to adequately perform in the course of long missions and even the possibility of leading to circumstances threatening survival. One of the possible countermeasures of physiological deconditioning, theoretically more complete than others presently used since it affects all bodily systems, is artificial gravity. Space stations and spacecrafts can be equipped with artificial gravity, but is artificial gravity necessary? The term "necessary" must be qualified because a meaningful answer to the question depends entirely on further defining the purpose of space travel. If man intends to stay only temporarily in space, then he must keep himself in good physical condition so as to be able to return to earth or to land on any other planetary surface without undue exposure to major physiological problems resulting from transition through variable gravitational fields. Such a situation makes artificial gravity highly desirable, although perhaps not absolutely necessary in the case of relative short exposure to microgravity, but certainly necessary in interplanetary flight and planetary landings. If the intent is to remain indefinitely in space, to colonize space, then artificial gravity may not be necessary, but in this case the consequences of long term effects of adaptation to weightlessness will have to be weighed against the biological evolutionary outcomes that are to be expected. At the moment, plans for establishing permanent colonies in space seem still remote. More likely, the initial phase of exploration of the uncharted solar system will take place through successive, scope limited, research ventures ending with return to earth. This will require man to be ready to operate in gravitational fields of variable intensity. Equipping spacecrafts or space stations with some means of artificial gravity in this initial phase is, therefore, necessary without question. In a strict sense artificial gravity is conceived as a means of replacing natural gravity in space by the centripetal acceleration generated by some sort of rotating device. Rotating devices create an inertial force which has effects on bodies similar to those caused by terrestrial gravity, but artificial gravity by a rotation device is not the same as terrestrial gravity, as we shall see. Present research in artificial gravity for space exploration is projected in two main directions: artificial gravity for whole space stations and artificial gravity produced by short arm centrifuges designed for human use in space.

Adolescent↗
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

When are additive models valid for evaluating proposed research?

This paper is concerned with a comparison of two broad classes of mathematical models, additive and multiplicative, for selecting the best among a number of competing project proposals addressed to a defined research objective. The analysis is predicated on the view that, though additive models are widely utilized, they are theoretically inferior to multiplicative ones. In an effort to more clearly understand when the use of additive models might be acceptable despite their logical flaws, conditions are investigated under which they yield results that are essentially equivalent to those produced by multiplicative models.

Cost-Benefit Analysis↗
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

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↗
PubMed1981

Proposed rehabilitation research or demonstration projects: estimating target population size.

In connection with developing a benefit-cost approach to evaluating proposed rehabilitation research or demonstration projects, the need to estimate the numerical size of the associated target population is explained and a process is described for making such estimates. The process consists of 7 steps: (1) delineating project objectives, (2) specifying target group(s) in operational terms, (3) determining whether satisfactory target population prevalence estimates are available, (4) in the absence of such estimates, identifying a critical parent population and establishing its prevalence, (5) identifying an accessible population, (6) enumerating the number and proportion of target group members in the accessible population, (7) calculating the estimated target population by multiplying data yielded in steps (4) and (6), adjusting for inferred biases and indicating uncertainties of estimation. Consideration is given to the kinds of data bases upon which this estimation process depends, to the feasibility of providing such estimates, and to their probable accuracy.

Cost-Benefit Analysis↗
PubMed1981

Quality of life in benefit-cost analyses of rehabilitation research.

Traditionally, benefit-cost (B-C) models have been limited to the consideration of monetary benefits. This approach has been motivated by the fact that nonmonetary benefits are difficult to define and to quantify. Derived from the general theory of B-C analysis, a model is described which includes 3 categories of benefits, identified by a Delphi-like procedure administered to a broad representation of persons involved in the rehabilitation process. Whereas monetary benefits have the dollar readily available as a unit of measurement, scales for nonmonetary benefits must be developed. Methods for estimating the value and the relative importance of the various benefits are analyzed and a procedure for combining monetary and nonmonetary benefits is proposed.

Delphi Technique↗