Biomolecular Interaction, Recognition and Dynamics. Proceedings of a workshop. Barcelona, Spain, October 23-25, 1997.
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Electrical ventricular defibrillation.
Ventricular fibrillation is the condition in which all of the muscle fibers in the ventricles of the heart contract and relax randomly and do not propel blood from the heart. This condition, which is the major cause of sudden death from a heart attack, can be reversed by passage of a single pulse of current through the heart using electrodes applied to the chest wall; this technique is known as ventricular defibrillation. World-wide clinical experience has shown that with existing defibrillators, successful defibrillation of subjects weighing over 100 kg is infrequent. It should not be concluded, however, that defibrillation cannot be achieved in such subjects. To illustrate this point, data will be presented to show that it is possible to establish a dose concept in which the output required from a defibrillator can be specified in terms of the weight of the subject. This dose concept evolved slowly from studies reported by investigators in various countries. For example, the present-day techniques of ventricular defibrillation are due to the investigations of researchers all over the world. Prevost and Battelli (1898) in Switzerland first showed that electric current can both induce ventricular fibrillation and achieve defibrillation. The studies of Kouwenhoven in the 1930's in the USA showed that 60 Hz alternating current can be used for defibrillation. The first human defibrillations in 1947 and 1952 used this type of current; these studies were reported by Beck and Zoll in the USA. The present-day technique for defibrillation derives from the animal studies reported by Gurvich and Yuniev 1946 in Russia. Finally, Lown et al. in the early 1960's applied the technique to man. Exciting new developments are underway in ventricular defibrillation. Not only are higher output defibrillators beginning to appear, but automatic and fully implantable defibrillators are being involved. In this paper, the present state of the art of defibrillation will be reported and future trends will be described.
Animals↗
The artificial heart - progress, problems, and further development.
The state of the art in the development of artificial heart research based on more than 100 own animal experiments and information from the other groups working in the same field is laid out. Consideration is given to a variety of special problems. The use of biomaterials (blood compatibility and mechanical strength and durability), the flow pattern in the pumps (clot formation), and special hemodynamical effects are discussed as well as different driving systems and percutane energy transmission (avoidance of infection). Respective measurements show the hemodynamics in the systemic and pulmonary circulation, especially the difficulties of the venous inflow and the regulation of the pumps. The effect of an active artificial atrium and new ways of computerized regulation using noninvasively measured parameters are described. Other pathophysiologic findings (lung, kidney, acid-base metabolism, gastrointestinal tract, blood) are dealt with according to their importance. The miniaturization of the driving system and new methods of energy supply necessary for a totally implantable artificial heart system, envisaged for the future, are also pointed out.
Adaptation, Physiological↗
Factors correlated with hypermetabolism in patients with amyotrophic lateral sclerosis.
BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a severe disease characterized by neurogenic amyotrophy and degeneration of upper and lower motor neurons. Although ALS patients usually experience reductions in fat-free mass (FFM), hypermetabolism via an undetermined source has also been reported. OBJECTIVE: The objective was to clarify the metabolic level of ALS patients. DESIGN: We measured the resting energy expenditure (REE) of 62 patients (32 men and 30 women) with ALS and investigated the factors correlated with metabolic level. Nutritional evaluation included bioelectrical impedance analysis, indirect calorimetry, and calculation of the body mass index. Neurologic assessment included an evaluation of peripheral and central neurologic deficit. Forced vital capacity was measured and smoking status was noted. A complete blood cell count was made and thyroid hormone and C-reactive protein concentrations were measured. RESULTS: Patients were hypermetabolic, by an average of approximately 10% more than in a reference healthy population. FFM, age, and the neutrophil count were significantly associated with REE. The only variable that contributed to the prediction of REE, REE/Z100 kHz (bioimpedance at 100 kHz), REE adjusted for FFM, or the ratio of measured REE to calculated REE was the neutrophil count, which explained only a small percentage of variance in the multiple regression analysis. Hypermetabolism was not associated with a reduction in respiratory function, tobacco use, hyperthyroidism, spasticity and fasciculation intensities, or infection. CONCLUSIONS: Our study corroborates the surprising finding that ALS patients are hypermetabolic. FFM, age, sex, manual muscular testing, the modified Norris limb score, weight, and an increase in circulating neutrophil counts correlated with the hypermetabolic state. Other factors may play a role in pathophysiologic processes that involve mitochondrial energy production or even sympathoadrenergic activation.
Adult↗
De novo lipogenesis predicts short-term body-composition response by bioelectrical impedance analysis to oral nutritional supplements in HIV-associated wasting.
We studied the effects of enteral supplements on protein and energy intakes, body composition, energy expenditure, and gastrointestinal histology in 49 subjects with human immunodeficiency virus-associated weight loss (12.7 +/- 0.9% of body wt). We also determined whether a stable-isotope mass spectrometric measurement at baseline might predict the short-term response of fat-free mass (FFM) measured by bioelectrical impedance analysis. Thirty-nine subjects completed the study after being randomly assigned to receive either a whole-protein-based (n = 22) or a peptide-based (n = 17) formula. A nonsupplemented, nonrandomly assigned group (n = 13) was followed concurrently. Both formulas were well tolerated. Voluntary intakes of energy and protein from nonsupplement sources decreased significantly during supplementation [by 819-1638 kJ (196-382 kcal)/d and 5.6-14.4 g protein/d, respectively; P < 0.01] but to a lesser extent than the intake from the supplement [2300-2510 kJ(550-600 kcal)/d and 19-28 g protein/d, respectively], so that net increases in intakes of protein and energy (P < 0.03), as well as of several vitamins and trace elements were increased. Nevertheless, the mean FFM did not increase for the group as a whole, although there was considerable interindividual heterogeneity. Changes in FFM at 6 wk were significantly inversely correlated (r = 0.65, P < 0.01) with baseline synthesis of fat (de novo hepatic lipogenesis), but not with other potential measures of energy intake (insulin-like growth factor 1 or its binding protein) or inflammation (soluble tumor necrosis factor receptors I or II). The prospective identification of FFM response by measurement of de novo hepatic lipogenesis supported the hypothesis that the subset of wasting patients whose FFM is unresponsive to nutrient supplementation have altered nutrient metabolism.
Adult↗
Effect of gender, body composition, and equilibration time on the 2H-to-18O dilution space ratio.
Physiological sources of variation in the 2H-to-18O dilution space ratio (DSR) were examined in 34 males and 20 females (4-78 yr; 14.7-143.2 kg; 1.8-61.0% body fat). Dilution spaces were obtained by time 0 extrapolation of isotope washout over 10-14 days, and body composition was obtained by underwater weight (adults) or bioelectrical impedance (children). The mean DSR was 1.050 +/- 0.015 (range 1.029-1.111), significantly higher (P < 0.001) than the traditionally assumed value of 1.029 based on exchange over 4 h. Use of the value 1.029 causes a systematic 8% overestimate of energy expenditure from doubly labeled water, relative to use of the value 1.05. The DSR was not related to body composition or age but was significantly higher (P < 0.05) in males (1.052 +/- 0.016) than in females (1.044 +/- 0.012). This gender effect was not explained by differences in the number of exchangeable hydrogens in the body. We conclude 1) variation in the 2H-to-18O DSR is not explained by body composition but is influenced by the chemical availability of exchangeable hydrogens to undergo exchange; 2) because the DSR is not easily predicted, use of the observed dilution spaces are recommended; 3) if a fixed DSR is used, values of 1.044 and 1.052 are recommended in females and males, respectively.
Adipose Tissue↗
Theory and applications of biotelemetry.
In this study, biotelemetry and its evolution is explained in detail. Bioelectric and physiological variables could be measured by biotelemetry systems. The development of a biotelemetry system and its principal operation are presented. The components of a biotelemetry system are explained. Biomedical data has been telemetered through every medium between two sites by using a variety of modulated energy forms. Designing of the link between transmitter and receiver is described. Important factors in designing a backpack or implanted telemeter are explained. The main features of implanted biotelemetry units are determined. Single-channel and multichannel biotelemetry systems are defined. The types of telemetry, and a comparison thereof, are given. The power sources of biotelemetry systems and features of different power sources are explained. A survey of biotelemetry applications on humans and animals is presented and advantages of using biotelemetry systems are determined.
Animals↗
Assessing regional muscle mass with segmental measurements of bioelectrical impedance in obese women during weight loss.
Tetrapolar bioelectrical impedance analysis (BIA) offers the possibility of determining the bioconductor volume in discrete segments of the body, because the resistivities of bone, fat, and skeletal muscle differ considerably. We tested this hypothesis by measuring BIA and anthropometry of defined segments of the right thighs of women before and during a controlled weight-loss program. Eight women, aged 22 to 32 years, with a body mass index of 37.8 +/- 1.6 (mean +/- SE) kg/m2 underwent determinations of body composition with dual-energy X-ray absorptiometry (DXA) and regional BIA measurements (800 microA at 50 kHz) before the program, and monthly thereafter for four months during weight loss. BIA measurements were made with spot-detector electrodes positioned 10 cm apart on the anterior of the thigh, and source electrodes placed on the right hand and foot. The physical volume of the thigh segment decreased by 29 +/- 3% (p < 0.0001), with a modest change in its electrical volume (8 +/- 0.2%; p < 0.05) during weight loss. Muscle (181 +/- 49 g; p < 0.05) and fat mass (702 +/- 95 g; p < 0.001) also declined. The electrical or bioconductor volume correlated with DXA determinations of muscle mass (r = 0.91, p < 0.0001), whereas physical volume correlated with fat mass (r = 0.95, p < 0.0001). These findings support the hypothesis that BIA is a valid method to assess regional muscle mass in humans.
Absorptiometry, Photon↗
Fundamental and practical aspects of therapeutic uses of pulsed electromagnetic fields (PEMFs).
The beneficial therapeutic effects of selected low-energy, time-varying magnetic fields, called PEMFs, have been documented with increasing frequency since 1973. Initially, this form of athermal energy was used mainly as a salvage for patients with long-standing juvenile and adult nonunions. Many of these individuals were candidates for amputation. Their clearly documented resistance to the usual forms of surgical treatment, including bone grafting, served as a reasonable control in judging the efficacy of this new therapeutic method, particularly when PEMFs were the sole change in patient management. More recently, the biological effectiveness of this approach in augmenting bone healing has been confirmed by several highly significant double-blind and controlled prospective studies in less challenging clinical circumstances. Furthermore, double-blind evidence of therapeutic effects in other clinical disorders has emerged. These data, coupled with well-controlled laboratory findings on pertinent mechanisms of action, have begun to place PEMFs on a therapeutic par with surgically invasive methods but at considerably less risk and cost. As a result of these clinical observations and concerns about electromagnetic "pollution", interactions of nonionizing electromagnetic fields with biological processes have been the subject of increasing investigational activity. Over the past decade, the number of publications on these topics has risen exponentially. They now include textbooks, speciality journals, regular reviews by government agencies, in addition to individual articles, appearing in the wide spectrum of peer-reviewed, scientific sources. In a recent editorial in Current Contents, the editor reviews the frontiers of biomedical engineering focusing on Science Citation Index methods for identifying core research endeavors. Dr. Garfield chose PEMFs from among other biomedical engineering efforts as an example of a rapidly emerging discipline. Three new societies in the bioelectromagnetics, bioelectrochemistry, and bioelectrical growth and repair have been organized during this time, along with a number of national and international committees and conferences. These activities augment a continuing interest by the IEEE in the U.S. and the IEE in the U.K. This review focuses on the principles and practice behind the therapeutic use of "PEMFs". This term is restricted to time-varying magnetic field characteristics that induce voltage waveform patterns in bone similar to those resulting from mechanical deformation. These asymmetric, broad-band pulses affect a number of biologic processes athermally. Many of these processes appear to have the ability to modify selected pathologic states in the musculoskeletal and other systems.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗