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Biomedical subjects

S E Dubin

Publications and source records attributed to S E Dubin.

16 recordsLinked to original sources
PubMed1994

Contribution of cerebrospinal fluid to rheoencephalographic waveforms during hypoxic and +Gz stress.

Acceleration (G) forces generated by high performance aircraft induce a redistribution of blood and cerebrospinal fluid (CSF) in the head resulting in decreased visual function, and may lead to G-induced loss of consciousness (G-LOC). CSF provides a critical support function to the brain by equalizing the pressure changes occurring throughout the skull under G-stress, particularly to the venous system. While it has been acknowledged that understanding this role of the CSF system is essential in order to enhance G-tolerance, no such studies have been conducted since the 1940's, due to technical difficulties. We have shown that these can be surmounted through the development of rheoencephalography (REG), or impedance plethysmography of the head, to noninvasively monitor shifts in CSF under both hypoxic (oxygen deprivation in the laboratory) and actual +Gz stress (small centrifuge) conditions. Using surgical and physiologic techniques on New Zealand White rabbits, we have established the following: 1) REG contains information concerning the function of the vascular, CSF, and respiratory systems as they influence both beat-to-beat and bulk movement of cephalic fluids; 2) respiratory effects on cerebral blood volume and CSF pressure can be monitored with the REG; 3) REG waveforms obtained from rabbits under laboratory and +Gz stress conditions were similar to those obtained during human +Gz centrifuge exposures; 4) using (i) brief occlusions of blood flow into the head and (ii) withdrawals of CSF, it was estimated that the relative volumetric contributions of blood and CSF to the REG were 70% and 30%, respectively; and 5) physiologic responses to stress are reflected in changes in the frequency content of the REG.(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration↗
PubMed1990

Cardiac energy considerations during intraaortic balloon pumping.

Cardiac oxygen availability and oxygen consumption were used in a theoretical study as indexes of myocardial energy supply and utilization, respectively. A detailed computer simulation of the closed-loop canine cardiovascular system was utilized to study the dependence of these indexes on timing of the intraaortic balloon pump. Oxygen availability exhibited higher sensitivity to balloon timing than oxygen utilization. While maximum augmentation of oxygen availability was 58 percent, oxygen consumption could be reduced by only 13 percent. Animal experiments were initiated to validate the theoretical results. The results of both the animal experiments and the computer simulation suggested that neither balloon timing which maximizes oxygen availability nor timing which minimizes oxygen consumption correlates with timing which minimizes aortic end diastolic pressure. Thus, end diastolic pressure, presently used as a determinant of proper timing in patients undergoing cardiac assistance, was found to be a poor index of ventricular energy consumption. A performance index comprised of clinically available variables, was formulated to reflect myocardial energy balance. In this performance index, mean diastolic pressure was used to represent energy availability and peak systolic pressure was used as an index of oxygen consumption. Their relationship to oxygen balance and their dependence on timing were studied using the computer simulation of the canine cardiovascular system and animal experiments. Theoretical and experimental results suggest that such an index is capable of representing O2 balance and can be used to control phasing of the device.

Animals↗
PubMed1983

Lithium and symptomatic hyperparathyroidism.

Hyperparathyroidism with or without adenoma has occasionally been reported in association with lithium treatment, and in symptomatic patients depression, psychosis and an exacerbation of existing psychopathology may occur. Three lithium-treated patients with hyperparathyroidism are reported, in whom discontinuation of lithium in one and removal of parathyroid adenomata in two led to both a reduction in plasma calcium levels and an improvement in their psychopathology.

Adenoma↗
PubMed1976

Effects of anticoagulants on packed cell volume measurement.

A comparison was made of different types of anticoagulants on packed cell volume determinations of canine, feline, rabbit, and human blood. It was found that the use of excessive amounts of anticoagulant alters the packed cell volume when measured by the standard centrifuge method. It was also found that the results vary significantly when different anticoagulants are used. The effects are not seen when the packed cell volume is indirectly measured using an electronic cell counter. A balanced combination of ethylenediaminetetraacetic acid salts ameliorates the concentration-dependent effects.

Animals↗
PubMedDate not supplied

Liquid breathing trials and animal studies with a demand-regulated liquid breathing system.

Experimental results of in vivo animal tests conducted on a demand-regulated liquid breathing system are presented. When a liquid replaces gas as the medium in which oxygen and carbon dioxide are transported, several problems not typical in gas respiration occur. The increased mass and viscosity of a liquid as compared with a gas necessitate some means of mechanical assistance. The lower diffusion rates of gases in liquids as compared with gas rates places several constraints on the design of a mechanically assisted liquid breathing system. The liquid breathing system reported in this study has been designed to be demand-regulated, i.e., the animal has control over cycling the pumps which mechanically assist the circulation of an oxygenated liquid to and from the lungs. This system consists of a gas-operated diaphragm pump, demand controller, liquid regenerator with heater and gas scrubber, and ancillary equipment. A demand controller is described which obtains a control signal from an esophageal balloon catheter in the animal and governs operation of the pneumatically driven diaphragm pump.

Airway Resistance↗
PubMedDate not supplied

The effect of shock separation time on multiple-shock defibrillation.

Reports in the literature of studies of the efficacy of multiple, staggered shocks used for cardiac defibrillation have shown widely varying results. Twin half sinusoids, separated by an integral number of 60-Hz half-cycles, were used for transthoracic defibrillation of dogs. The separation of the pulses was varied from 0 to 13 half-cycles (0 to 108 msec). An online computer was used to determine the energy content of each shock and to obtain curves of the percentage of success vs energy, current, and voltage. The results show that 2 pulses, separated by 9 half-cycles (75 msec), require 57 percent of the peak current and 87 percent of the peak voltage required by a single pulse. The energy requirement, however, was 9.9 percent higher with the staggered shock. Other pulse separations required higher voltages and currents. Possible mechanisms for the effect are discussed.

Animals↗
PubMedDate not supplied

Performance optimization of left ventricular assistance. A computer model study.

Performance of temporary parallel left ventricular assistance was investigated and the theoretic conditions leading to optimal behavior of the mechanical system were explored. Computer models of nonpulsatile and pulsatile left ventricular assist devices (LVADs) were incorporated into a previously reported closed-loop simulation of the canine cardiovascular system. Assuming the assisted heart was capable of recovery, LVAD performance was assessed based on both myocardial oxygen balance and cardiac output. With a synchronous LVAD, and operating in a counterpulsation mode, these variables were sensitive to the phasing of pump ejection. Maximum reduction in cardiac oxygen consumption, maximum increase in oxygen availability, and maximum increase in cardiac output with the atrio-aortic device were obtained when pump ejection immediately followed aortic valve closure. These variables were directly proportional to the magnitude of bypass volume. The pulsatile asynchronous and nonpulsatile LVAD models affected oxygen balance in a similar manner, but neither performed so well as the synchronous model when equal bypass volumes were used. Ventricular uptake of blood provided a further 27% decrease in oxygen consumption and further 78% increase in oxygen availability than atrial uptake. In summary, the model predicted that the pulsatile synchronous LVAD, filling from the ventricle during heart systole and ejecting into either the ascending or descending aorta just after ventricular systole, would be most beneficial to both myocardial oxygen balance and cardiac output.

Animals↗