Showing papers in "Annals of Biomedical Engineering in 1974"
TL;DR: The optimal pulse duration for reducing the possibility of tissue damage was concluded to be less than or equal to 0.01 msec for intramuscular stimulation in the test situation.
Abstract: The peak current, peak voltage, charge transfer and energy dissipation necessary for equivalent stimulation were measured for several pulse durations in the range from 0.01 to 1.0 msec. The unidirectional, regulated current, rectangular waveform was studied for subcutaneous nerve and intramuscular stimulation in animals and for surface stimulation in humans. In addition, the unidirectional, regulated current, exponential waveform was studied in humans and was compared with the rectangular waveform. The question of the relationship between charge transfer and energy dissipation and possible tissue damage due to the electrochemical formation of toxic compounds or a temperature rise in the surrounding tissue was examined. The optimal pulse duration for reducing the possibility of tissue damage was concluded to be less than or equal to 0.01 msec for intramuscular stimulation in the test situation. No conclusion was made as to the optimal duration for nerve or surface stimulation. Excitation of muscle fibers was found to take place indirectly by was of muscle nerves during intramuscular stimulation. The exponential waveform required less charge transfer and energy dissipation than the rectangular waveform, but higher peak currents.
154 citations
TL;DR: In this paper, the behavior of anisotropic compact bone in tension at a range of strain rates was examined and the modulus of elasticity, breaking stress and breaking strain were found to vary with strain rate.
Abstract: The paper examines the behavior of anisotropic compact bone in tension at a range of strain rates. Specimens of fresh bovine bone were loaded at strain rates between. 001 and 200 sec−1. This bone was shown to exhibit considerable plasticity throughout the range, except when tested in a direction normal to the long axis. The modulus of elasticity, breaking stress and breaking strain were found to vary with strain rate. There is a maximum energy absorbtion capability at a strain rate of .1 sec−1.
131 citations
TL;DR: The performance of the model was correlated with experimental data that describe the hemodynamic responses to thoracic aortic constriction, exercise, circulatory shock following endotoxin administration, and other situations, indicating that redistribution of blood flow following arterial resistance changes can theoretically have a very strong effect on the level of cardiac output.
Abstract: Most data indicate that cardiac output is normally controlled by the systemic circulation rather than by the heart. This manuscript extends that concept by analyzing the systemic circulation with a mathematical model comprised of two dissimilar blood flow channels. The concept and the model are not new and have, in fact, a strong anatomical and historical basis. However, re-examination using a quantitative, computerized analysis scaled to human dimensions is made in the face of new experimental data.
48 citations
TL;DR: Following a series of unsuccessful experiments employing nonsinusoidal waveforms with penile, perineal, and suprapubic electrodes, three rectal probes were designed and constructed which enabled them to define two directed current patterns: longitudinal current and circular current.
Abstract: The scientific literature concerning electroejaculation of simian primates contains many reports of successful collection of seminal fluid through electrostimulation with penile and rectal electrodes. In none of these reports is there a sufficient discussion of the important electrical parameters involved, such as the amplitude and density of electric current and the impedance of the electrode/tissue interface. Without such information it is difficult, if not impossible, for investigators in other laboratories to duplicate the stimulation regimen successfully and without injury to the animal. This assumes even greater importance when such techniques are considered for application to human beings.
45 citations
TL;DR: All the models produced in this work produce similar diagnostic results, indicating that the development of increasingly more sophisticated models of this type may be a fruitless exercise.
Abstract: This work presents an underlying mathematical framework within which mathematical medical diagnosis can be discussed. Ten mathematical models of disease diagnosis, including those which have been most commonly used or suggested, are derived and compared within this framework.
43 citations
TL;DR: An analytic model is developed to simulate heat transfer in man under immersed conditions to develop the basic thermal network with initial conditions and input parameters that is used by the WETMAN program in determining the diver's thermal response to a given environmental situation.
Abstract: An analytic model is developed to simulate heat transfer in man under immersed conditions. The biothermal model is divided into two distinct subsystems: the physical-controlled system and the dynamic-controlling system. The controlled system consists of the physical portions of the body and the interacting thermal exchange paths. The controlling system contains the associated afferent and efferent signals, the central hypothalamic thermointegrator, and the control modes used to maintain homeostatic thermal conditions in the body. The controlled system in the analytic model is simulated by the SIZE program. The controlling system is modeled by the WETMAN computer program. The SIZE program is used to develop the basic thermal network with initial conditions and input parameters that is used by the WETMAN program in determining the diver's thermal response to a given environmental situation. Three types of experimental data are used to substantiate the analytic model: neck-immersed seminude subjects in cool to temperate water; neck-immersed “wet-suited” subjects in cold water; and totally immersed “wet-suited” subjects in cold water. These types of data encompass a wide range of water temperature, protective clothing, breathing gas mixtures, and duration time of immersion.
39 citations
TL;DR: A numerical analysis is carried out for oscillatory flow of a viscous incompressible fluid through thin-walled elastic tubes with small curvature, resulting in a resulting asymmetrical flow pattern and the secondary flow pattern induced by centrifugal effects due to curvature.
Abstract: A numerical analysis is carried out for oscillatory flow of a viscous incompressible fluid through thin-walled elastic tubes with small curvature. A wave propagation analysis for sinusoidal input pressure disturbance yields a resulting asymmetrical flow pattern and the secondary flow pattern induced by centrifugal effects due to curvature. Essential differences between the effects of curvature on steady and oscillatory flows are obtained. A complicated quadrihelical secondary flow pattern is obtained. The flow pattern and computed wall shear in curved tubes are determined and compared with those of oscillatory flow through straight elastic tubes. Parameters in the computation are chosen to correspond to physiological flows at arterial sites of small curvature.
27 citations
TL;DR: The comparison of data obtained without electrode shifting and with readjustment of the electrodes to the same premarked position has convinced us that one of the main causes for the variability is the unpredictable displacement of different tissues between the electrodes and the stimulated nerve.
Abstract: One of the essential deficiencies of functional electrical stimulation (FES) as a method of rehabilitation of hemiplegic patients is the great variability of responses. This paper treats quantitatively the variability of isometric responses. The parameters chosen for the evaluation of variability were the dynamics of isometric moment and the static value of the moment during maintained stimulation. Experiments were performed to evaluate both surface and implanted stimulation, as both of these methods have reached the stage of clinical application. It was established that the variability is quite large, relative dispersion being ν≐0.35. Using a closed-loop controller of FES of muscles it was shown that such an actuator is too variable to be used as an efficient orthosis. No significant difference was found between surface and implanted FES. The comparison of data obtained without electrode shifting and with readjustment of the electrodes to the same premarked position has convinced us that one of the main causes for the variability is the unpredictable displacement of different tissues between the electrodes and the stimulated nerve. The influence of reflex action and supraspinal centers was studied on a patient with compression of the peroneal nerve. It was found that this influence is strongly subjective. In some hemiplegics this influence was detectable, though on the average less important than the technological-anatomical properties of the contact between the electrodes and the nerve. Better reproducibility is expected with the introduction of improved electrode technology.
26 citations
TL;DR: In this paper, the authors extended the concept of bone mineral measurement using soft γ-rays to determine the area and shape of the compacta cross-section and the corresponding mean linear absorption coefficient.
Abstract: Cameron's concept of bone mineral measurement using soft γ-rays has been extended to determine the area and shape of the compacta cross-section and the corresponding mean linear absorption coefficient. By repeating the linear scanning process at the same section for different directions a polygon is defined which circumscribes the outer contour of the bone section. With the aid of a PDP 11–45 computer and an iterative technique the compacta area and the mean linear absorption coefficient are evaluated. In addition the computer synthesizes iteratively an image of the actual compacta cross-section. Thanks to the redundancy of the absorption data the values for the total mineral content, the compacta area and the mean density can be determined as many times as the scanning process has been carried out. The fluctuations of these values from their averages can apparently be interpreted as a measure of the consistency of the data. To validate the method and assess the accuracy and statistical fluctuations of the measurements an aluminum tube with circular cross-section has been used as a model for a bone. The data indicate that the total mineral content, the compacta area and the mean density can be determined with an error on the order of 1%. Data from measurements on excised human femurs have been obtained and the results are equally consistent as those of the aluminum model.
25 citations
TL;DR: An extensive series of experiments on normal subjects has shown that the rotation of the intrinsic components of the VCG relative to the torso is a consistent indicator of the change of the volume of air in the lungs.
Abstract: Changes in the vectorcardiogram (VCG) during respiration are well-known. An extensive series of experiments on normal subjects has shown that the rotation of the intrinsic components of the VCG relative to the torso is a consistent indicator of the change of the volume of air in the lungs. This has led to a model for the mechanics of the heart-lungs respired-volume system and to a technique for monitoring respiration rate and depth from the VCG.
24 citations
TL;DR: In summary, systemic circulatory mechanics appear to influence cardiac output mainly by redistribution of blood volume between different segments rather than by redistributing blood flow.
Abstract: A previous analytical model of the systemic circulatory system (Grodins,Quarterly Review of Biology, 1959,34, 93–116) was extended based on recent experimental studies. Major units considered are: large arteries, large veins, and the peripheral circulation. The latter is subdivided into three parallel functional units: (1) nutritional bed, (2) shunt pathway and (3) storage area. By addition of simplified linear descriptions for the heart and pulmonary circulation, the overall cardiovascular system was considered. Parameter values were mainly derived from right heart bypass (Grodins, Stuart, and Veenstra, American Journal of Physiology, 1960198, 552–560) and isolated hindlimb (Satoet al., 1971) experiments. An algebraic equation relating cardiac output to systemic circulatory parameters was derived which provided a convenient means of studying effects of parameter changes. This equation predicted that compliances and unstressed volumes have a unidirectional effect on cardiac output but arterial resistance has a variable effect which depends on the values of resistances and compliances of the parallel pathways. Circulatory responses to exercise were considered by changing compliance and resistance of the nutritional bed in accordance with experimental values obtained with a frequency response method (Vega, Ph.D. Thesis, University of Southern California, 1973). Possible mechanisms for blood flow restoration as required by the resistance change are discussed. In summary, systemic circulatory mechanics appear to influence cardiac output mainly by redistribution of blood volume between different segments rather than by redistribution of blood flow.
TL;DR: In this paper, two advanced models of equivalent cardiac generators were formulated and tested, one consisting of two moving dipoles in a bounded spherical volume conductor and the other consisting of a simultaneous moving dipole and quadripole in an identical bounded spherical medium.
Abstract: Two advanced models of equivalent cardiac generators were formulated and tested. The first model consists of two moving dipoles in a bounded spherical volume conductor. The second model consists of a simultaneous moving dipole and quadripole in an identical bounded spherical medium. The development of these models evolves from the derivation of the potential function for a dipole, a quadripole and an octapole in a homogeneous medium with a spherical dielectric boundary using a Taylor series expansion of a potential function due to two point current sources. The nonlinear models were tested in an inverse sense using ideal data and an existing nonlinear estimation scheme. Preliminary results indicate that such models may potentially be useful for characterization of the cardiac generator.
TL;DR: Results strongly suggest that ADP released from red cells cannot account for the increased retention with increased hematocrit and permit, for the first time, a quantitative measure of platelet retention in columns packed with glass beads which is independent of both hemodynamic factors and column geometry.
Abstract: Platelet retention in columns packed with glass beads has been theoretically analyzed in a manner similar to that commonly used to describe the behavior of fixed-bed adsorbers. Combining the results of this analysis with experimental observations has confirmed that the process of platelet deposition from whole blood onto glass bead surfaces is entirely adsorption controlled. In contrast to this finding, a theory often used to predict the performance of a wide range of filtration processes has been utilized to show that platelet deposition from PRP is dominated not by the adsorption step, but by resistances to platelet transport which are confined to the plasma phase. Furthermore, a direct relationship between platelet retention in glass bead columns and hematocrit has been observed using whole blood and ghost cell suspensions. These results, which are in accord with observations made by Zuckeret al. (1972), strongly suggest that ADP released from red cells cannot account for the increased retention with increased hematocrit. This behavior can be explained, however, by recognizing that the efective platelet diffusivity is considerably enhanced by increasing the hematocrit of red cell or ghost cell suspensions and consequently the frequency of cell-cell interactions. As confirmed experimentally, these physical interactions, as opposed to biochemical factors, are primarily responsible for determining the observed changes in platelet retention when the suspending medium is gradually changed from PRP (0% hct) to normal hematocrit values. Furthermore, theoretical and experimental techniques are described which permit, for the first time, a quantitative measure of platelet retention in columns packed with glass beads which is independent of both hemodynamic factors and column geometry. This new measure of platelet retention is shown to relate directly to the affinity of platelets for one another and for solid surfacesin vitro, thereby offering the possibility of using glass bead columns as highly sensitive diagnostic tools for the detection of hemorrhagic disorders.
TL;DR: The mixed data solution using electric and magnetic data gave better results for additive (potential) noise but did not improve the solution in the presence of modelling noise, while the mixedData solution for the Coriolis array reproduced the surface magnetic and electric fields very well, but deviated from the ideal solution.
Abstract: Cardiac electrical activity was modelled by two realistic generators in a spherical conductor with a centric inhomogeneity. The “Selvester” generator consisted of a 19-dipole array; the “Coriolis” generator was a 76-dipole array. Time varying electric and magnetic potentials at the surface of the sphere were calculated for each array. The inverse cardiac generator was a fixed-location, fixed-orientation, nonnegatively constrained multiple dipole array. Inverse dipole moments were calculated using electric data alone, magnetic data alone, and a combination of electric and magnetic data. The inverse solutions were examined in the presence of additive noise and modelling noise. Modelling noise involved translocating or misorienting the inverse dipoles, or assuming an incorrect conductivity for the inhomogeneity. Results for the Selvester and Coriolis simulations were similar. The mixed data solution using electric and magnetic data gave better results for additive (potential) noise but did not improve the solution in the presence of modelling noise. Septal dipoles showed the greatest errors. In the absence of modelling noise, the mixed data solution for the Coriolis array reproduced the surface magnetic and electric fields very well, but deviated from the ideal solution.
TL;DR: The phisiological effects of electricity in the body, electrical safety hazards in the hospital and methods of protecting patients from both macroshock and microshock hazards are described and discussed and recommendations for a relatively inexpensive, but effective and up-to-date electrical safety program for the hospital are recommended.
Abstract: The topic of electrical safety in the hospital has been of considerable interest since it covered that certain catheterized patients can be accidentally electrocuted by currents well below the perceivable level. Prompted by a safety scare that began in 1969, hospitals and manufacturers of medical equipment have since become safety conscious and have taken steps to effectively reduce the safety hazard to both patients and hospital staff. This paper is intended to provide the reader with a basic understanding of electrical safety problems in the hospital. The phisiological effects of electricity in the body, electrical safety hazards in the hospital and methods of protecting patients from both macroshock and microshock hazards are described and discussed. The paper concludes with recommendations for a relatively inexpensive, but effective and up-to-date electrical safety program for the hospital.
TL;DR: In this paper, a method for the calculation of the distribution of vascular volume and flow in a repeating modular organization is presented, based on the measured distribution of the mean transit time obtained by an indicator dilution technique.
Abstract: In this paper, a method for the calculation of the distribution of vascular volume and flow in a repeating modular organization is presented. The calculation is based on the measured distribution of the mean transit time obtained by an indicator dilution technique. Several examples of the distributions of the vascular volume and flow are considered. The existence of higher flow in the capillaries more proximal to the large artery is demonstrated. The calculated volume for the perimeter vessels and for the capillaries agrees qualitatively with direct measurements.
TL;DR: The proposed nonlinear model for testosterone (T) transport and metabolism in the normal adult male suggests that the plasmaT concentration does not always reflect changes in distribution and disposal; and plasma totalT concentration is not by itself a reliable indicator of system pathologies.
Abstract: A nonlinear model is proposed for testosterone (T) transport and metabolism in the normal adult male. The model structure consists of 2 pools: one which includes plasma distribution, direct disposal, and the binding ofT to three plasma proteins; and a second pool for distribution and other disposal ofT. Nonlinearities in the model are manifest in the mass action law dynamics of binding to plasma proteins. A directed random search algorithm was employed to estimate model parameters. The model was fitted to real data by minimization of the least squares output error. The real data consisted of discrete samples of radioactively labeledT in blood following a rapid, pulse injection of labeledT. A quadratic approximation for unboundT in terms of totalT concentration was derived by application of the mass action principle to the multiple hormone-protein binding relationships. This approximation permitted the two model state variables to be expressed as totalT concentration in each pool. This choice guarantees a linear measurement or output model. The model was completely quantified, including a relationship and estimate for the unmeasurable concentration ofT in the lumped intracellular space. These results indicate that: (1) 98% ofT is cleared directly from plasma; (2) the lumped phase boundary between the intra- and extravascular spaces is nearly isotropic toT; and (3) the average steady state intracellular totalT concentration is only 30% of the corresponding plasma totalT concentration in normal man. The predictive value of the model also was explored by performing three simulated experiments, each representing pathologic possibilities. When simulatedT secretion was decreased by 75%, the plasmaT decreased by 70%. When simulated protein concentrations were changed significantly, in opposite directions, the plasmaT concentration fell well below the normal level; but theT concentration in the outer pool remained normal. When the parameter representing transport ofT to the outer pool was decreased, plasmaT did not change, but the outer poolT decreased. Among other things, these results suggest that the plasmaT concentration does not always reflect changes in distribution and disposal; and plasma totalT concentration is not by itself a reliable indicator of system pathologies. Also, low plasmaT concentration and normalT secretion can be consistent with normal concentrations ofT in tissue and hence the target organs for testosterone action.
TL;DR: The need for still another new design of an artificial heart which will not obstruct venous return and will maintain normal venous pressures without compromising lung space is demonstrated.
Abstract: A large number of calves maintained up to two weeks with the Kwan-Gett artificial heart have had elevated central venous pressure with associated ascites, edema, oliguria responding to diuretics, and increased body weight and weight of organs at autopsy. This has been described as right heart failure syndrome and has been a problem limiting survival with the artificial heart. The high venous pressure has been attributed to inadequate pumping characteristics of the heart as well as imperfect fit which obstructs venous return. A new design of an artificial heart was tested on the mock circulation and in one calf with encouraging results. Venous return remained unimpaired during the artificial heart test in the calf. The heart is designed with the following main characteristics.
Although the heart compromised lung space, it demonstrated the need for still another new design which will not obstruct venous return and will maintain normal venous pressures without compromising lung space.
TL;DR: It is concluded that of the materials investigated, vitreous carbon and titanium are preferable in percutaneous connector applications because the higher impedance seen in vitreOUS carbon favors the use of titanium in electrical stimulation.
Abstract: The behavior of solid percutaneous connectors made of gold, stainless steel, vitreous carbon and titanium was studied in humans. Evaluation parameters were biocompatibility studied by conventional histochemical methods, surface degradation studied by scanning electron microscopy, and electrical impedance.
TL;DR: Computer-generated three-dimensional stereo images of the epicardial and endocardial surfaces of the left ventricle were displayed from data obtained with a biplane orthogonal roentgen video system and Continuous tone hidden surface displays of the ventricles were inscribed with isostress contours.
Abstract: Computer-generated three-dimensional stereo images of the epicardial and endocardial surfaces of the left ventricle were displayed from data obtained with a biplane orthogonal roentgen video system. The silhouette of the opacified left ventricle was digitized from a video angiograph. The data were used to calculate the dynamic geometry of the ventricle and parameters such as curvature and stress. Continuous tone hidden surface displays of the ventricle were inscribed with isostress contours. The system is capable of obtaining biplane silhouettes of the ventricle at a rate of 60 pictures/sec. Dynamic displays of the beating ventricle can be obtained by recording sequential frames on a video disc recorder via a scan converter. The resulting sequence of frames can be played back in forward or reverse slow-motion or stop-action for detailed study.
TL;DR: Design criteria for the achievement of effective forward and reverse isolation of hospital patients, with respect to airborne contamination, was developed through model studies of directed vertical sterile air flows.
Abstract: Design criteria for the achievement of effective forward and reverse isolation of hospital patients, with respect to airborne contamination, was developed through model studies of directed vertical sterile air flows. The essential requirements were found to be a low turbulent intensity (of the order of 1%) air column flowing downward at 60 feet per minute and returned through floor gratings about 12 in wide running the full length of the air column along the boundaries of the protected space. The width of the protected space was found to be slightly greater than the width of the air column. A ratio of the air flow collected and recirculated to the column air flow of 1.2 to 1.3 was found to be optimal. Boundary jets or'air curtains were found to be redundant and detrimental under some circumstances.
TL;DR: The derivation indicates explicitly how the differences between the averaging estimator and the true CCVF arise and it has been suggested that the technique be used for this purpose.
Abstract: The relationship between a continuous process such as the EEG of the central nervous system and a point process such as the discharge activity of a single neuron can often be profitably studied by way of the cross covariance function (CCVF). The individual events in the point process can be used to trigger an average response computer so as to obtain the average response of the continuous process to an event in the point process. Under certain circumstances it has been shown that this average response is a useful estimate of the CCVF. Because the technique is simpler to use than conventional methods for estimating the CCVF, it has been suggested that the technique be used for this purpose. However, when the point process is considered in terms of its expectation density, it can be shown that the CCVF estimate obtained by averaging is valid only when the properties of the processes are special enough as not to be encountered in many of the experimental conditions of interest. The derivation indicates explicitly how the differences between the averaging estimator and the true CCVF arise.
TL;DR: The most complete published analysis of the female reproductive system can be found in this article, which is divided into seven main sections: vulva, vagina, cervix, uterus (subdivided into endometrium and myometrium), oviduct, and ovary; a section on placenta completes the work.
Abstract: This book represents the most successful attempt to date to subject the female reproductive system to a detailed and complete morphological analysis. The amount of material assembled and studied is impressive, especially considering that most is human. Each tissue or sample has been evaluated utilizing light microscopic and transmission and scanning electron microscopic methods of investigation, a combination of procedures of morphological analysis which certainly does not represent an easy task and which, also considering the quality of the results, denotes the interest and tremendous involvement of the authors on their compilative work. This is demonstrated also by the fact that, even though the book includes micrographs from other investigators, most of the material compiled in the opus derives from collections assembled and studied by the authors themselves; this is another very laudative aspect of this book that considerably adds to its authoritative value. The work is subdivided into seven main sections, each dealing with one of the main components or organs of the female reproductive tract: vulva, vagina, cervix, uterus (subdivided into endometrium and myometrium), oviduct, and ovary; a section on the placenta completes the work. Each tissue or organ, or organ component is analysed from the points of view of its appearance under normal conditions, variations under different functional situations, pathology and neoplastic transformation; the degree of completeness is simply fantastic considering that even most rarely occurring lesions have been included. This reviewer personally finds the sections on the vulva, vagina, uterus, and oviduct, the most complete published analyses ever prepared on the anatomy, physiology, and pathology of these organs. Due to the impressive amount of human material assembled, the technical difficulties inherent in the procedures employed for the study and yet the remarkable quality, accuracy, and depth of the observations, the completeness of this book can hardly be duplicated in the future. For the above reasons, this authoritative opus represents a classic work and an indispensable source of consultation and reference to anatomists, reproductive physiologists, gynecologists, and pathologists as well as a model to be adhered to for future compilation of truly meaningful \"scientific\" books.
TL;DR: Continuity in description is obtained by characterizing the tracheal airflow by two continuously defined variables, instantaneous amplitude, A(t), and instantaneous frequency,F(t, which can experimentally be uniquely determined at a sampling rate independent of the respiratory rate.
Abstract: The commonly used respiratory variables, minute volume, tidal volume and respiratory rate are discontinuous measures, and thus of limited capability to quantitate transient respiratory responses. Continuity in description is obtained by characterizing the tracheal airflow by two continuously defined variables, instantaneous amplitude,A(t), and instantaneous frequency,F(t), which can experimentally be uniquely determined at a sampling rate independent of the respiratory rate. The two variables are conceptual extensions of currently used discontinuous measures, i.e., the time average ofF(t) recovers respiratory rate, and the time average ofA(t) divided by π closely approximates minute volume. These asymptotic relations were experimentally verified in four human subjects and for different ventilatory states. Respiratory rate and averageF(t) agreed within a relative error of less than 1%. Minute volume was determined from the averageA(t) with an error, slightly dependent on the airflow pattern, of less than 6%. Since the conventionally used quantitation can always be retrieved from the continuous one,A(t) andF(t) may be employed whenever conventional methods break down.
TL;DR: Peak carotid and peak aortic flow acceleration were compared during a variety of cardiovascular interventions in seven acutely instrumented anesthetized dogs and may be of use as an indirect measure of myocardial mechanical performance except during potent peripheral vasodilation.
Abstract: Peak carotid and peak aortic flow acceleration were compared during a variety of cardiovascular interventions in seven acutely instrumented anesthetized (pentobarbital 30 mg/kg, iv) dogs. Flow velocity, recorded with electromagnetic sensors, was processed electronically to give acceleration and the ratio of peak carotid to peak aortic acceleration on a beat-by-beat basis. Occlusion of the left coronary artery, occlusion of the superior vena cava and intravenous administration of sodium bicarbonate and propranolol caused both peak carotid and peak aortic flow acceleration to decrease with little or no change in their ratio. Breathing 100% oxygen and iv infusions of metaraminol, levarterenol, isoproterenol, and acetyl choline and iv injection of serotonin, papaverine, and deslanoside increased peak carotid and peak aortic flow acceleration. The ratio of peak carotid to peak aortic acceleration did not change greatly except with isoproterenol, papaverine, and acetyl choline, when peak carotid flow acceleration increased more than peak aortic flow acceleration causing an increase in their ratio. Intravenous infusion of trimethaphan camphorsulfonate and injection of histamine caused peak carotid flow acceleration to increase and peak aortic flow acceleration to decrease with an increase in their ratio. Peak carotid flow acceleration may be of use as an indirect measure of myocardial mechanical performance except during potent peripheral vasodilation.
TL;DR: Walsh function series were computed for blood pressure waves recorded from anesthetized dogs and it was found that 13 terms of the Walsh series represented 98% of the power in the wave.
Abstract: The rate of convergence of Walsh functions and sine functions to recorded blood pressure waves was determined to evaluate the applicability of Walsh functions for spectral analysis of pulsatile blood pressure. The advantages of Walsh function series for such analysis are that their calculation is much faster and can be performed on small computers.
TL;DR: A mathematical model is derived that describes oxygen concentration in a retinal capillary in terms of the local rate of oxygen utilization and arterial pressure at eye level and provides a mechanism for extrapolating experimental results using idealized exposure patterns to the more complex acceleration patterns encountered by pilots in operational situations.
Abstract: A mathematical model is derived that describes oxygen concentration in a retinal capillary in terms of the local rate of oxygen utilization and arterial pressure at eye level. The model is applied to describe the loss of vision that occurs upon exposure to acceleration stress.
TL;DR: In vitro experiments showed sufficient decrease in the concentrations of ureaet al. in the body fluid, while their concentrations in the recycling dialysate stayed very low, while the adsorbent can be used repeatedly after regeneration.
Abstract: A new hemodialyzing system is proposed in which urea and other toxins are removed from the recirculating dialysate by adsorption on activated carbon in two alternately used adsorber-desorber columns. Desorption of urea and other molecules was performed by passing water and then fresh dialysate through the adsorbent bed. Durations of the periods for adsorption and desorption could be varied using a timer and solenoid valves.In vitro experiments showed sufficient decrease in the concentrations of ureaet al. in the body fluid, while their concentrations in the recycling dialysate stayed very low. The adsorbent can be used repeatedly after regeneration. The new system is considerably more economical than the conventional hemodialyzing system with continuous dilution of dialysate in the cost of construction and the amount of dialysate required.
TL;DR: It was found theoretically again that the increase in the received field strength after an electrically small loop embedded in a biological body was possible when the loop was off-center.
Abstract: It was found theoretically again that the increase in the received field strength after an electrically small loop embedded in a biological body was possible when the loop was off-center. The direction of the magnetic dipole of the off-centered loop should be perpendicular to the radial axis to give a stronger radiated maximum power density. For a loop close to the surface of the sphere, the frequency of the transmitter can be optimized to have stronger power density such that the diameter of the sphere should be an integer times the effective wavelength of the medium. Given the loss tangent, effective wavelength in the medium, and diameter of the sphere, the maximum power density of the loop close to the surface of the sphere is stronger than that of the loop at the center and can be predicted theoretically, as shown in Fig. 2.
TL;DR: A number of bioengineering problems are reviewed which appear feasible but which are not now being done, largely for organizational reasons, to illustrate the point that many worthwhile projects exist now.
Abstract: Bioengineering has many significant contributions to make to improvement in the delivery of health care. However, when major research and development efforts are involved, great care must be exercised in project choice to avoid as far as possible needless expense. Even those programs which ultimately result in very significant benefits at low cost to the average citizen pass a high-cost barrier which may take years to cross. A major mistake is to make decisions on the basis of too short a time span. Nearly all biophysical measurements, many tests, and some drugs have all at one time been too costly for general use. Then as the value of the advance became appreciated, inexpensive means for achieving the same ends were devised. A number of bioengineering problems are reviewed which appear feasible but which are not now being done, largely for organizational reasons, to illustrate the point that many worthwhile projects exist now. The importance of decision making in bioengineering on future health-care quality and costs is apparent. Much of future work will probably be at the molecular level. Since support is now fragmented to the point where continued advancement is in jeopardy, it is important that problems in the support and organization of bioengineering and biomedical research be brought continually to public attention.