Showing papers in "Annals of Biomedical Engineering in 1977"
TL;DR: In this paper, a flow predictor method is proposed to estimate flow at the beginning of the interval only, with an estimated average value for the whole interval, where only one subroutine call is required when a flow is calculated; the expense in computing time is minimal.
Abstract: Compartmentalized models of the circulatory system are used to investigate the dynamics of the movement of blood from one region of the circulation to another. When these models are studied using numerical methods—viz., numerical integration—solution stability can often be achieved only at integration step sizes that are far less than the time intervals of interest. Hence, obtaining solution stability at much larger integration step sizes is desirable. Instability results from a (one-iteration) delay between calculation of the derivative and calculation of the integral. The method described here, applied locally within a model, replaces the usual method of estimating flow at the beginning of the interval only, with an estimated average value for the whole interval. The “flow predictor” method is not general; it requires a knowledge of local resistances and capacitances and their effect on flow. But, only one subroutine call is required when a flow is calculated; the expense in computing time is minimal. Using an example four-compartment model, the maximum stable integration interval with rectangular integration (0.0005 min) was improved by a factor of 106 (to 1000 min) with this method.
169 citations
TL;DR: The feasibility of frequency modulated two-point discrimination as a design concept for electrocutaneous sensory substitution display has been studied and some of the characteristic behavior of cutaneous sensation is discussed relating two- point discrimination with frequency, body sites, and stimulation codes.
Abstract: The feasibility of frequency modulated two-point discrimination as a design concept for electrocutaneous sensory substitution display has been studied. Three stimulation techniques were tested on human subjects: spatial stimulus, temporal stimulus, and frequency on frequency stimulus. The frequency on frequency technique yielded the lowest threshold when compared to the temporal and spatial techniques. In addition, some of the characteristic behavior of cutaneous sensation is discussed relating two-point discrimination with frequency, body sites, and stimulation codes. Implications of the results for clinical applications are reviewed.
83 citations
TL;DR: In this paper, the major problems of implanted percutaneous devices include biocompatibility and infection, and if mechanical forces are reduced to a minimum, prolonged success of these implants can be expected.
Abstract: The major problems of implanted percutaneous devices include biocompatibility and infection. Experience with 127 implants in 43 patients and volunteers of Rancho Los Amigos Hospital is presented and shows that if mechanical forces are reduced to a minimum, prolonged success of these implants can be expected.
52 citations
TL;DR: Tests in vitro indicate that the “safe” charge limit can be at least tripled by the use of imbalanced pulses, which may find application in the field of intramuscular stimulation where the present “ safe’ charge limit for stainless steel electrodes does not permit an adequate range of stimulation intensities.
Abstract: A form of cathodic protection has been developed for controlling the corrosion of stainless steel electrodes during electrical stimulation. The protection is achieved by using biphasic stimulation pulses with a slight (<-1%) charge imbalance in favor of the cathodic phase. Testsin vitro indicate that the “safe” charge limit (the charge density per phase at which corrosion first becomes serious) can be at least tripled by the use of imbalanced pulses. If confirmed by testsin vivo, this result may find application in the field of intramuscular stimulation where the present “safe” charge limit for stainless steel electrodes (#40 μC cm−2) does not permit an adequate range of stimulation intensities.
47 citations
TL;DR: Electrocutaneous tracking was a reliable and sensitive indicator of a code's intrinsic effectiveness for transmitting information cutaneously and multiple electrode codes using spatial modulation were clearly and significantly superior to any single electrode codes examined.
Abstract: Ten electrocutaneous codes suitable for sensory feedback were systematically compared using a random tracking task. The representative sample of codes used single and multiple electrode displays, bipolar and monopolar electrocutaneous stimuli, and frequency, intensity, and spatial modulation. The experimental results from 2 preliminary studies using 4 subjects each, and a full scale study, using 21 subjects, suggested that electrocutaneous tracking was a reliable and sensitive indicator of a code's intrinsic effectiveness for transmitting information cutaneously. In addition, multiple electrode codes using spatial modulation were clearly and significantly superior to any single electrode codes examined. Single electrode codes using frequency modulation were superior to intensity modulation codes whether the pulse stimulus used was monopolar or bipolar. Although subjects rated bipolar stimulation as being slightly more comfortable than monopolar stimulation, they performed better when using monopolar stimulation. Furthermore, sensory adaptation to the monopolar stimulus was considerably less than to the bipolar stimulus. The most effective multiple electrode code was Seven Electrodes in a Linear Array on the Abdomen. The most effective single electrode code was the Low Pulse Rate Modulation Code, wherein the sensory information was embedded in pulse rates between 1 and 15 per second.
46 citations
TL;DR: Intercomparisons are made between three spectrally filtered photographs of experimental burns on guinea pigs and accidental burns on humans to show that these ratios have potential diagnostic value for the determination of burn depth in man.
Abstract: Intercomparisons are made between three spectrally filtered photographs of experimental burns on guinea pigs and accidental burns on humans. The original photographs are taken on Kodak 35 mm Plus X and High Speed Infrared films. The transparencies are digitized and processed by a computer to form three additional photographs, each of which has an optical density proportional to the ratio of the target spectral reflectances. These images are color processed to form a pseudo color photograph which indicates the relative magnitude of the spectral reflectance ratio of the injured tissue. It is shown that these ratios, displayed by color patterns, have potential diagnostic value for the determination of burn depth in man.
43 citations
TL;DR: A method is presented for the use of a unit impulse response and responses to impulse pairs of variable separation in the calculation of the second-degree kernels of a quadratic system.
Abstract: A method is presented for the use of a unit impulse response and responses to impulse pairs of variable separation in the calculation of the second-degree kernels of a quadratic system. A quadratic system may be built from simple linear terms of known dynamics and a multiplier. Computer simulation results on quadratic systems with building elements of various time constants indicate reasonably that the larger time constant term before multiplication dominates in the envelope of the off-diagonal kernel curves as these move perpendicular to and away from the main diagonal. The smaller time constant term before multiplication combines with the effect of the time constant after multiplication to dominate in the kernel curves in the direction of the second-degree impulse response, i.e., parallel to the main diagonal. Such types of insight may be helpful in recognizing essential aspects of (second-degree) kernels; they may be used in simplifying the model structure and, perhaps, add to the physical/physiological understanding of the underlying processes.
32 citations
TL;DR: The experimental validation of this technique and the theoretical basis for obtaining the frequency and coherence of ciliary beat from the autocorrelation function of the spectrum of light scattered from moving cilia are reported.
Abstract: The frequency of ciliary beat was measured by laser light-scattering spectroscopy in cultures of ciliated cells of the rabbit oviduct. Measurements performed by this new method agree with those obtained by high speed cinematography. When beating cilia are illuminated by a laser beam, the scattered light shows a frequency modulation due to the oscillatory motion of cilia. The spectral structure of the scattered light depends on the frequency and time-space coherence of ciliary beat. This paper reports the experimental validation of this technique and the theoretical basis for obtaining the frequency and coherence of ciliary beat from the autocorrelation function of the spectrum of light scattered from moving cilia. Fiber optic light transmission could permit the extension of this method to assess ciliary activityin situ for applications in animal experimentation and clinical studies.
31 citations
TL;DR: In this article, the fluid mechanics of the semicircular canals were examined theoretically and an accurate accounting of the effect of the utricle on fluid flow in the canals was provided.
Abstract: The fluid mechanics of the semicircular canals is examined theoretically. This analysis confirms earlier studies that indicate that the semicircular canal can be modeled as a heavily damped, second-order system. Included for the first time, however, is an accurate accounting of the effect of the utricle on fluid flow in the canals. Using available physiological data, quantitative predictions of canal response to angular acceleration are made.
27 citations
TL;DR: In the model, the proposed schedule will function more effectively for the entire therapy period when additional parameters of drug characteristics, such as the toxicity to the host and drug resistance, are encompassed.
Abstract: A discrete-time kinetic model for chemotherapy was developed to deal with the effects of antitumor drugs on the cell cycle and proliferation kinetics of experimental tumor cell populations in which cell kinetic responses of chemotherapy are represented in terms of perturbation of cell kinetic parameters—cell age, cell size and DNA content distributions. The time-course behavior of these cell kinetic parameters was predicted by solving the discrete-time state equations which characterize the dynamics of tumor-drug interactions. The amount of antitumor drug administered was expressed to be the control function of the state equations and the transition matrix representing two modes of drug action, namely, cell kill and progression delay or accumulation of cells due to drug, was derived. The performance of the model, assessed by examining the effects of cell cycle stage-specific agents such as cytosine arabinoside on spontaneous AKR leukemia, compared favorably with experimental data. Utilizing an optimization scheme in engineering systems studies, an analytical method is described for optimizing the regimen of drug administration so as to maximize the effectiveness of drug dosage schedules and minimize the use of toxic amounts of the drug. The superiority of the schedule designed by an optimization scheme was evident at the termination of therapy, although the schedule designed by experimental trials reduced the number of surviving tumor cells more effectively than the one designed by an optimization scheme during the earlier therapy period. In the model, the proposed schedule will function more effectively for the entire therapy period when additional parameters of drug characteristics, such as the toxicity to the host and drug resistance, are encompassed.
17 citations
TL;DR: It is hypothesize that microwave energy interacts with the remaining portion of the autonomic nervous system within the heart to produce the observed chronotropic effects.
Abstract: Continuous wave (cw) microwave irradiation at 960 MHz has caused bradycardia in isolated, perfused rat hearts maintained at 20°C. The observed bradycardia occurred at microwave dose rates that should have caused mild tachycardia in the heart based on the thermogenic properties of the irradiation. The observed bradycardia, moreover, exhibited neurologic features because atropinized hearts showed strong tachycardia during irradiation and hearts treated with propranolol showed significantly stronger bradycardia during irradiation than that seen without drugs. Use of the liquid-crystal optical-fiber (LCOF) temperature probe has shown, by calorimetric methods, that the microwave-induced bradycardia occurred at dose rates of 1.3 and 2.1 mW/g. We hypothesize that microwave energy interacts with the remaining portion of the autonomic nervous system within the heart to produce the observed chronotropic effects.
TL;DR: Left-ventricular dimensions were measured during a complete cardiac cycle from one-plane cineangiograms and used to calculate the circumferential fiber velocity and circumferent fiber strain and theVCF·ε loop is independent of pressure, making it possible to acquire noninvasively.
Abstract: Left-ventricular dimensions were measured during a complete cardiac cycle from one-plane cineangiograms and used to calculate the circumferential fiber velocity (V
CF) and circumferential fiber strain (e). A velocity-strain (V
CF·e) loop was then constructed for 39 patients. Characteristics of theV
CF·e loop included: peak systolicV
CF(+V
CF), e at +V
CF (eS), systolic time constant τS, absolute peak diastolicV
CF (|−V
CF|), e at |−V
CF| (eD), diastolic time constant τD,V
CF≤|−V
CF|, eD≤eS, and τD≤τS. The first two inequalities combined provided the best criterion of cardiac decompensation. Only 2 of 15 normal patients, 2 of 6 compensated volume overload patients, and 1 of 3 compensated pressure overload patients satisfied the double inequality. However, 6 of 9 decompensated volume overload patients and 5 of 6 congestive cardiomyopathy patients satisfied the double inequality. Physically, this would imply that with depressed cardiac function: +V
CF≤|−V
CF| due to a reduced ability of the ventricle to actively contract, eD≤eS (and τD≤τS) due to an increased viscoelastic stiffness of the ventricle. TheV
CF·e loop is independent of pressure, making it possible to acquire noninvasively.
TL;DR: Compared to the euthyroid sheep, the abnormal animal lacked T4 to T3 conversion, demonstrated a higher T3/T4 secretion rate ratio, and had plasma-liver T3 kinetics increased 2–3 times.
Abstract: Certain system modeling and analysis methods, including identifiability analysis, were applied to the design of experiments and the processing of a posteriori humoral data for quantifying the dynamics of thyroid hormone (both T3 and T4) metabolism in sheep. Two sheep were studied: one euthyroid, and one abnormal; and several alternative hypotheses concerning system structure were tested by fitting alternative models to the resulting data. For the normal sheep, the results indicated that the plasma hormone pool contained 40% of the total T4 with 14% in liver-kidneys-gut, and 47% in muscle-skin; T3 was distributed with 12–20% in plasma, 8–18% in liver-kidneys-gut, and 62–80% in muscle-skin. Also, 40–52% of the normal sheep T3 was generated by conversion of 11–17% of the T4. Compared to the euthyroid sheep, the abnormal animal lacked T4 to T3 conversion, demonstrated a higher T3/T4 secretion rate ratio, and had plasma-liver T3 kinetics increased 2–3 times. The ranges indicated are consistent with all hypotheses tested. A number of other parameters of thyroid hormone metabolism in these sheep also were computed from the data.
TL;DR: A magnetic quasi-multipole expansion differing from the classical magnetic multipole expansion, but having certain computational advantages, was developed and it was found that the first three terms in the MQME could represent MCG's to within 20%.
Abstract: Digital computer models of cardiac excitation and the torso were used to investigate several aspects of the magnetocardiogram (MCG). Cardiac excitation was simulated by 20 current dipoles whose locations and moments are based on experimental data reported by others. Both a homogeneous torso and an inhomogeneous torso containing lung regions with a conductivity of one-half that of the rest of the torso were used. MCG's produced by components of the magnetic field normal to the skin were calculated at 15 sites on a grid over the anterior surface of the thorax. Incorporation of the lung inhomogeneity produced only small changes in the MCG's. Significantly different MCG's were produced by cardiac models which contained free versus fixed orientation current dipoles. A magnetic quasi-multipole expansion (MQME) differing from the classical magnetic multipole expansion, but having certain computational advantages, was developed. It was found that the first three terms in the MQME could represent MCG's to within 20%. A single current dipole model of cardiac excitation was shown to be inadequate for representing the precordial MCG's.
TL;DR: In this article, the electrotactile two point discrimination threshold (TPDT) was considered as a design concept for multichannel artifical sensory communication displays, and data relating TPDT with frequency for three stimulation codes were used for the analysis and specifications of three classes of optimal displays: space optimal, frequency optimal, and space frequency optimal.
Abstract: The electrotactile two point discrimination threshold (TPDT) was considered as a design concept for multichannel artifical sensory communication displays. Data relating two point discrimination threshold with frequency for three stimulation codes were used for the analysis and specifications of three classes of optimal displays: space optimal, frequency optimal, and space-frequency optimal. A table was constructed showing alternative display configurations for various applications, and a design procedure for optimizing each class of display was developed. Possible applications of each display class for various sensory augmentation requirements in rehabilitation of handicapped persons for tactile, kinesthetic, visual, and auditory categories have been identified.
TL;DR: A new membrane oxygenator capable of effective and efficient arterialization of venous blood flowing through etched microchannels has been developed, showing a significant reduction of the apparent viscosity of blood, indicating the peripheral plasma layer effect on the microflow processes.
Abstract: A new membrane oxygenator capable of effective and efficient arterialization of venous blood flowing through etched microchannels has been developed. The design flow capacity can be regulated up to 1.4 liters per minute with a priming volume of 80 cm3. The characteristics of oxygen and carbon dioxide exchange are correlated to the effective channel depth and compared with theoretical predictions. An analysis of the resistance coefficient of blood flowing through the etched microchannels shows a significant reduction (50–65%) of the apparent viscosity of blood, indicating the peripheral plasma layer effect on the microflow processes. The particulate flow results in an anomalous oxygen and carbon dioxide, exchange above theoretical predictions for homogeneous fluids.
TL;DR: The acoustical properties in low oxygen tension sickle cell blood and deoxyhemoglobin S solution are altered, probably due to the crystallization of hemoglobin S.
Abstract: Experimental data are presented to show that the acoustical properties in low oxygen tension sickle cell blood and deoxyhemoglobin S solution are altered, probably due to the crystallization of hemoglobin S. The velocity of propagation is only slightly higher than that of normal blood at the same hemoglobin concentration. The attenuation coefficient shows noted increase and the scattering cross section is found to be about four times larger at 5 MHz. The increase in attenuation has been determined to arise mainly from increased absorption.
TL;DR: It was found that LV power generation and aortic power dissipation increased significantly during assistance and suggest that the short term effects are attributable directly to the device and are not mediated by the autonomic nervous system.
Abstract: The effects of in-series mechanical assistance on left ventricular (LV) afterload and aortic power dissipation were studied in four groups of open chest mongrel dogs: control, acute myocardial ischemia, cholinergic and beta-adrenergic blockade, and combined ischemia and blockade. Aortic root pressure, flow, power, and impedance and LV pressure and power were obtained. Assistance was provided by intraaortic balloon pumping. Times of inflation and deflation of the balloon were controlled to maintain a phase difference of 180° between the fundamental components of aortic root pressure and flow. Differences in hemodynamic parameters before and after 2–5 min of cardiac assistance were calculated. The results confirm other observations regarding effects of in-series assistance on LV and aortic pressure, cardiac output, and peripheral resistance. No consistent changes were obtained in the pulsatile components of aortic input impedance. A significant decrease (14–20%) was observed in the dc component of the impedance in all animals. The results reported here contradict previous reports regarding decreased LV power generation. It was found that LV power generation and aortic power dissipation increased significantly during assistance (LV, 3–17%; aortic, 4–19%). The results of this investigation also appear to conflict with previous reports regarding the role of cardiovascular control in “counteracting” the effects of assistance in the normal experimental preparation. They suggest that the short term effects are attributable directly to the device and are not mediated by the autonomic nervous system.
TL;DR: Head injury models in two geometries with pulse loading were investigated to study the phenomenon of wave propagation in viscoelastic brain tissue and give results that show significantly lower compression and rarefaction levels as compared to the “perfect fluid” twodimensional model.
Abstract: Head injury models in two geometries with pulse loading were investigated to study the phenomenon of wave propagation in viscoelastic brain tissue. One-dimensional and two-dimensional Lagrangian finite-difference computer formulations were used. The brain material was modeled both as a perfect fluid and as a viscoelastic material. A geometric description of the head was obtained from a human skull. The material properties for the bone and brain tissue were obtained by interpreting previously reported experimental data. The one-dimensional model results show signal attenuation and considerable delay in the arvival of activity when viscoelastic properties are used. The two-dimensional viscoelastic model gives results that show significantly lower (≈35%) compression and rarefaction levels as compared to the “perfect fluid” twodimensional model. Locations of possible trauma are identified by comparisons between the computer solutions and experimental measurements.
TL;DR: The data suggest the existence of a pressure regulatory function in the downstream arterial vasculature in type-I animals which established an effective back pressure to arterial perfusion and decouples the arterial pressure-flow characteristics from the remainder of the systemic circulation.
Abstract: Arterial pressure-flow (Pa-\(\dot Q\)) and closing arterial pressure-flow (Pc-\(\dot Q\)) relationships of the systemic vascular bed were determined in anesthetized dogs with the aid of a right heart bypass preparation.Pc was estimated from plateau values of arterial pressure obtained during stop-flow procedures and plotted against the flow which existed immediately prior to the procedure. Two types of arterial pressure-flow relationships were observed. With type I, thePa-\(\dot Q\) curve was steep and extrapolated to a positive arterial pressure at zero flow which was equal to the meanPc occurring over the experimental flow range. With type II, the slope of thePa-\(\dot Q\) curve was relatively shallow and extrapolated to right atrial pressure (0 mm Hg). ThePc-\(\dot Q\) relationships were identical for all dogs. These data suggest the existence of a pressure regulatory function in the downstream arterial vasculature in type-I animals which established an effective back pressure to arterial perfusion and decouples the arterial pressure-flow characteristics from the remainder of the systemic circulation.
TL;DR: In this article, a mathematical model of oxygen and lactic acid transport in skeletal muscle is used to test the effects of reactive hyperemia on oxygen and Lactic acid concentrations following a period of ischemia.
Abstract: A mathematical model of oxygen and lactic acid transport in skeletal muscle is used to test the effects of reactive hyperemia on oxygen and lactic acid concentrations following a period of ischemia. The model is based on the Krogh cylinder as the geometrical representation of the functional unit of transport, i.e., a capillary and the tissue it supplies. Included in the mathematical development of the model are the convective and diffusive transport of the chemical species, the nonlinear aspects of oxygen and lactic acid kinetics, and the reversible reaction of oxygen with hemoglobin in capillary blood and myoglobin in the tissue. The steady-state solution to the model is obtained first as the baseline for the study. Ischemia is then simulated by the cessation of capillary blood flow. This is followed by a reactive hyperemic response that is a function of the occlusion duration. The general effect of reactive hyperemia is to shorten the time intervals for initial return of tissue oxygen levels and the washout of accumulated lactic acid and to maintain tissue oxygen levels above steady-state values.
TL;DR: The paper focuses on the problems and opportunities in the study of biological flows in the various life sciences, both basic and applied, and particular emphasis is given to flows as conveyours of information, the utilization of flows as diagnostic tools, and the interaction between flow and systems considerations.
Abstract: After proposing and briefly assessing the domain, objectives and tools of biofluidmechanics—the use of fluid mechanics for the study of biological flows—the paper focuses on the problems and opportunities in the study of biological flows in the various life sciences, both basic and applied. particular emphasis is given to flows as conveyours of information, the utilization of flows as diagnostic tools, and the interaction between flow and systems considerations. Biological flows also hold potential technological implications both as providers of inspiration for new engineering devices and concepts, and as stimulus to the development of new fundamental techniques in fluid mechanics. Finally, biofluidmechanics is compared to other domains of fluid mechanics (man-made devices and inorganic nature), and the development of the field is briefly considered in terms of social and governmental factors that affect it.
TL;DR: The chief aim of this analysis of well-known kinetic laboratory data was to present numerical computer data suggesting that the slow Na* washout component, seen in laboratory studies, results from the participation of cellular (glandular) structures in the corium, not those in the epidermis.
Abstract: In this study we have applied a multicompartment whole frog skin model to a kinetic analysis of the process of washout of radioactive sodium (Na*) from both the epidermis and the underlying corium (dermis). This work is different from earlier publications from this laboratory in which only epidermis was considered. The whole skin model is designed in accordance with presently known anatomical and physiological information on frog skin. The chief aim of this analysis of well-known kinetic laboratory data was to present numerical computer data suggesting that the slow Na* washout component (t
1/2≅15 min) seen in laboratory studies, results from the participation of cellular (glandular) structures in the corium, not those in the epidermis. In addition, computed data on [Na+] profiles in the model membrane are briefly presented. Although the [Na+] values appear intuitively reasonable, they await experimental confirmation, which requires an analytical technique with a resolution power far superior over that of conventional histochemical methods. The [Na+] gradients are, however, compatible with the known total Na+ content of skin and the overall input-output flows of Na+ across frog skin.
TL;DR: Finite element stress analysis has been applied to examine the stress patterns in a prosthesis requiring fixation in the medullary shaft of a long bone and results indicate that with complete bone ingrowth, the maximum shear stress and the distance necessary for load transfer are both independent of implant length.
Abstract: Finite element stress analysis has been applied to examine the stress patterns in a prosthesis requiring fixation in the medullary shaft of a long bone. No specific prosthesis is considered but rather a generally applicable geometry has been chosen. This consists of a cylindrical section of cortical bone within which is implanted a prosthesis composed of a solid central rod surrounded by a porous coating. The finite element analysis utilized an axisymmetric model to determine the distribution of stresses throughout the system. The effect of changes in length of prosthesis, thickness of porous coating, depth and type of tissue ingrowth, and type of porous coating material were studied under conditions of axisymmetric loading. The results indicate that with complete bone ingrowth, the maximum shear stress and the distance necessary for load transfer are both independent of implant length. However, with incomplete ingrowth, increasing implant length reduces shear. Incomplete growth also produces lower shear stresses but higher shear strains in areas without ingrowth. In addition, a porous polyethylene coating gives a more even load transfer and lower shear than a porous coating of a high modulus material.
TL;DR: A thermistor probe was developed for implantation with the peritoneum in the rat for the continuous measurement of core temperature and has been utilized successfully in experiments involving the peripheral and intracranial administration of drugs and in studies of fever.
Abstract: A thermistor probe was developed for implantation with the peritoneum in the rat for the continuous measurement of core temperature. The implanted probe was exteriorized via a miniature connector mounted on the calvaria and attached via a spring cable to a commercial slip-ring assembly which allowed complete freedom of movement for the animal in a behavioral chamber as its body temperature was measured. In this fashion, artifact-free temperature records were obtained with an accuracy of ±0.1°C for a continuous period as long as 8 weeks. Compared with telemetric devices, this direct method provided a less complex measurement system which is more economicals and is well-suited to short-term behavioral-physiological experiments. This system has been utilized successfully in experiments involving the peripheral and intracranial administration of drugs and in studies of fever.
TL;DR: The results indicate that the half-cycle 60-Hz sinusoid is a reasonable alternative as a defibrillating waveform for low-energy applications where its advantages of waveform unaffected by load impedance, and simplicity of circuit, may be realized.
Abstract: The standard Lown-type capacitor discharge waveform was compared with a single half-cycle 60-Hz sinusoid for effectiveness of defibrillation. Both shock types were used in attempts to defibrillate a series of dogs over a range of intensities from that below the minimum required for defibrillation to values well above those which consistently were successful. An on-line computer was used to monitor energy, peak current, and peak voltage of each shock. The results were plotted as percent success vs each parameter and comparisons were made at the 80% level. The half-cycle sinusoid required 18% more energy but 20% less peak current and 15% less peak voltage for 80% probability of success at these intensity levels. These results indicate that the half-cycle 60-Hz sinusoid is a reasonable alternative as a defibrillating waveform for low-energy applications (open chest surgery, some pediatric cases, and small animal applications) where its advantages of waveform unaffected by load impedance, and simplicity of circuit, may be realized.
TL;DR: The conductive catheter appears to offer a better alternative by altering the common current pathway, so that a larger, more reliably achievable external leakage current limit could be safely specified.
Abstract: A catheter with a conductive wall should enhance patient protection against electrically induced ventricular fibrillation by leaking away externally applied current before it reaches the catheter tip. The hypothesis was tested in five dogs (81 attempts), applying up to 130 V, 60 Hz proximally, using conductive and nonconductive catheters of identical configuration. Fibrillation could not be induced with saline-filled conductive catheters, but the nonconductive catheters usually caused fibrillation. As anticipated, use of a conductive guidewire resulted in fibrillation with both catheter types. A mathematical analysis of catheter behavior is presented which agrees with bench data. Practical implications of the theory include logarithmic attenuation of tip current with increasing immersed length, and a simple means of verifying catheter characteristics. The present instrumentation leakage current limit for invasive measurements is not completely satisfactory, since it increases instrumentation costs without assurance that threshold values will not be exceeded due to other uncontrolled sources. The conductive catheter appears to offer a better alternative by altering the common current pathway, so that a larger, more reliably achievable external leakage current limit could be safely specified.
TL;DR: The results show that the acrylic cement lowered the cerebrospinal fluid pressure at the cranial vault, increased the depth of the position δs, which represents substantial brain contact, and increased the brain elastic response.
Abstract: In controlled experiments in six dogs, we have studied the influence of acrylic cement (applied to the skull) on the mechanical response properties of the brainin vivo. In particular we have been concerned with the brain elastic response which reflects that property of the brain usually referred to by the generic terms “stiff” or “soft.” This response property is directly proportional to the instantaneous elastic modulus, a characteristic response property of viscoelastic materials. As anin vivo response property it was measured as the short-time pressure-depth response using a pressure-depth transducer inserted a short distance (less than 1 mm) into the subpial region, maintaining an intact dura. This quantity was determined before and after the application of the acrylic cement. The results show that the acrylic cement lowered the cerebrospinal fluid (CSF) pressure at the cranial vault, increased the depth of the position δ
s
, which represents substantial brain contact, and increased the brain elastic response.
TL;DR: An automatic control system has been developed that restores and maintains the normal concentration of glucose in blood in nonanesthetized pancreatectomized dogs.
Abstract: Based on a model of the experimentally validated glucoregulatory system operating in the normal dog, an automatic control system has been developed that restores and maintains the normal concentration of glucose in blood in nonanesthetized pancreatectomized dogs. The relative success of the experiments largely validates the model of the disturbed glucoregulatory system.