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Biomedical subjects

M W Bungo

Publications and source records attributed to M W Bungo.

At least 19 recordsLinked to original sources
PubMed1997

Adaptive responses of the cardiovascular system to prolonged spaceflight conditions: assessment with Holter monitoring.

This article presents selected findings obtained with Holter monitoring from two crew members of the expedition, performed during a 175-day space mission on board orbital space station "MIR." Using mathematical processing of daily cardiointervals files, 5-minute sections of records were analyzed consecutively. Then, the average daily values of indices, the average-per-every-eight-hours values (morning, evening, night) and mean values per hour were computed. The results of analysis showed that prolonged exposure of man to microgravity conditions leads to important functional alteration in human neuroautonomic regulatory mechanisms. Both crew members had significant increase of heart rate, the rise of stress index, the decrease in power of the spectrum in the range of respiratory sinus arrhythmia. These marked signs of activation of the sympathetic section of the vegetative nervous system showed individual variations. The analysis of the daily collection of cardiointervals with Holter monitoring allows us to understand and forecast the functional feasibilities of the human organism under a variety of stress conditions associated with acute and chronic microgravity exposure.

Adaptation, Physiological↗
PubMed1993

Echocardiograms during six hours of bedrest at head-down and head-up tilt and during space flight.

Left ventricular end-diastolic volume increased after 4 1/2 to 6 hours of space flight, but was significantly decreased after 5 to 6 days of space flight. To determine the role of acute gravitational effects in this phenomenon, responses to a 6-hour bedrest model of 0 gravity (G; 5 degrees head-down tilt) were compared with those of fractional gravity loads of 1/6 G, 1/3 G, and 2/3 G by using head-up tilts of 10 degrees, 20 degrees, and 42 degrees, respectively. On 4 different days, six healthy male subjects were tilted at one of the four angles for 6 hours. Cardiac dimensions and volumes were determined from two-dimensional and M-mode echocardiograms in the left lateral decubitus position at control (0), 2, 4, and 6 hours. Stroke volume decreased with time (P < .05) for all tilt angles when compared with control. Ejection fraction (EF) at -5 degrees was greater than at +20 degrees and +42 degrees (not significant); EF at +10 degrees was greater than at +42 degrees (not significant). For the tilt angles of -5 degrees, +10 degrees, and +20 degrees, mean heart rate decreased during the first 2 hours, and returned to control or was slightly elevated above control (+20 degrees) by 6 hours (not significant). At the +42 degrees angle of tilt, heart rate was increased above control at hours 2, 4, and 6. There were no significant differences in cardiac output at any time point for any tilt angle.(ABSTRACT TRUNCATED AT 250 WORDS)

Bed Rest↗
PubMed1993

Effects of lower-body negative pressure on blood flow with applications to the human cardiovascular system.

The paper reports a theoretical investigation into the effects of lower-body negative pressure on blood flow through the human cardiovascular system. The human cardiovascular system is modelled as a closed network of arteries, arterioles, capillaries, venules and veins of different lengths and cross-sections. The pumping action is provided by the contraction of the ventricles. The model has been analysed using the finite-element method. The pertinent equations incorporating the effects of lower-body negative pressure for the pressures and flow velocities have been derived, and the quantitative results have been computed. Percentage changes in flow velocities, pressure drops and conductances under the application of lower-body negative pressure in the various segments and organs of the entire cardiovascular system are obtained. The lower-body negative pressure has no effect on the flow rates in carotid, ulnar and coronary arteries, nor on the supply of blood to the upper extremities, kidneys, spleen and liver. The major effects are found in the lower extremities.

Blood Vessels↗
PubMed1993

Mathematical modelling of the human cardiovascular system in the presence of stenosis.

This paper reports a theoretical study on the distribution of blood flow in the human cardiovascular system when one or more blood vessels are affected by stenosis. The analysis employs a mathematical model of the entire system based on the finite element method. The arterial-venous network is represented by a large number of interconnected segments in the model. Values for the model parameters are based upon the published data on the physiological and rheological properties of blood. Computational results show how blood flow through various parts of the cardiovascular system is affected by stenosis in different blood vessels. No significant changes in the flow parameters of the cardiovascular system were found to occur when the reduction in the lumen diameter of the stenosed vessels was less than 65%.

Blood Circulation↗
PubMed1992

Mathematical modelling of flow distribution in the human cardiovascular system.

The paper presents a detailed model of the entire human cardiovascular system which aims to study the changes in flow distribution caused by external stimuli, changes in internal parameters, or other factors. The arterial-venous network is represented by 325 interconnected elastic segments. The mathematical description of each segment is based on equations of hydrodynamics and those of stress/strain relationships in elastic materials. Appropriate input functions provide for the pumping of blood by the heart through the system. The analysis employs the finite-element technique which can accommodate any prescribed boundary conditions. Values of model parameters are from available data on physical and rheological properties of blood and blood vessels. As a representative example, simulation results on changes in flow distribution with changes in the elastic properties of blood vessels are discussed. They indicate that the errors in the calculated overall flow rates are not significant even in the extreme case of arteries and veins behaving as rigid tubes.

Blood Flow Velocity↗
PubMed1992

The effects of exercise on blood flow with reference to the human cardiovascular system: a finite element study.

This paper reports on a theoretical investigation into the effects of vasomotion on blood through the human cardiovascular system. The finite element method has been used to analyse the model. Vasoconstriction and vasodilation may be effected either through the action of the central nervous system or autoregulation. One of the conditions responsible for vasomotion is exercise. The proposed model has been solved and quantitative results of flows and pressures due to changing the conductances of specific networks of arterioles, capillaries and venules comprising the arms, legs, stomach and their combinations have been obtained.

Blood Circulation↗
PubMed1992

Treatment of motion sickness in parabolic flight with buccal scopolamine.

Treatment of acute motion sickness induced by parabolic flight with a preparation of scopolamine placed in the buccal pouch was investigated. Twenty-one subjects flew aboard a KC-135 aircraft operated by the National Aeronautics and Space Administration (NASA) which performed parabolic maneuvers resulting in periods of 0-g, 1-g, and 1.8-g. Each subject flew once with a tablet containing scopolamine and once with a placebo in a random order, crossover design. Signs and symptoms of motion sickness were systematically recorded during each parabola by an investigator who was blind to the content of the tablet. Compared with flights using placebo, flights with buccal scopolamine resulted in significantly lower scores for nausea (31%-35% reduction) and vomiting (50% reduction in number of parabolas with vomiting). Side effects of the drug during flight were negligible. We conclude that buccal scopolamine is more effective than a placebo in treating ongoing motion sickness.

Administration, Buccal↗
PubMed1991

Blood and urine responses to ingesting fluids of various salt and glucose concentrations.

Several hours before returning to Earth, Space Shuttle astronauts consume fluid and salt tablets equivalent to a liter of 0.9% saline as a countermeasure to postflight orthostatic intolerance. This countermeasure is not completely successful. Therefore, in search of a countermeasure that would protect against orthostatic intolerance better and for a longer duration, the authors compared the blood and urine responses of five men (21-41 yr) after they drank 1 L of 0.9% saline to their responses after drinking five other solutions: distilled water, 1% glucose, 0.74% saline with 1% glucose, 0.9% saline with 1% glucose, and 1.07% saline. Each subject ingested a different solution on 6 different days and remained seated for the ensuing 4 hours. Heart rate, blood pressures, and urine variables were measured before ingestion of the fluids and every 30 minutes thereafter; blood samples were drawn before, immediately after, and every 60 minutes after ingestion. Change in plasma volume, which was estimated from hemoglobin and hematocrit, was considered the most critical variable. Data for all solutions were compared by analysis of variance. Since plasma volume was increased most after ingestion of 1.07% saline, all variables (at 2 hours, at 3 hours and at 4 hours) were compared between 1.07% saline and 0.9% saline, the current countermeasure. Plasma volume was increased more after 1.07% saline than after 0.9% saline, and this difference was most significant at 4 hours after ingestion (P = .056). Diuresis occurred promptly after ingestion of the two saline-free solutions, water and 1% glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Orthostatic function during a stand test before and after head-up or head-down bedrest.

Astronauts may exhibit orthostatic dysfunction upon returning to 1 g after space flight. Understanding cardiovascular changes at 0 G will provide insights into the mechanisms of the loss of orthostatic tolerance, whether due to space flight or bedrest. Bedrest is one model used to produce cardiovascular changes that are associated with space flight. In the current study, young male adults were placed at -5 degrees, +10, +20, or +42 degrees bedrest (0, 1/6, 1/3, and 2/3g, respectively) for 6 hours on 4 different days. This was preceded and followed by a stand test: 5 minutes in the supine position, and then 5 minutes in the standing position, with the feet 9 inches apart and 6 inches from the wall. Cardiovascular values were measured at 1-minute intervals. Systolic and diastolic pressures were measured using an automated blood pressure device; mean arterial pressure (MAP; mm Hg) was calculated. Heart rate (bpm) and cardiac parameters were measured with a thoracic impedance device. Minute 3, 4, and 5 values were used to determine whether there were time or angle effects. Of six subjects, one reported nausea upon 3 minutes of standing after 6 hours of bedrest at -5 degrees. The same subject was lightheaded in the first minute of standing after 6 hours of bedrest at +10 degrees. Mean heart rate pre-bedrest in the supine position was 63 and increased by 24 bpm on standing. Heart rate post-bedrest in the supine position was 65 and increased by 35 bpm on standing; standing heart rate increased 11 bpm after -5 degrees bedrest. The increases after +10 degrees, +20 degrees, and +42 degrees tilts were 4, 3, and 4 bpm, respectively. Changes in the mean arterial blood pressure were minimal. Results from the stand test pre- and post- 6 hours of bedrest at -5 degrees but not at +10 degrees, +20 degrees, or +42 degrees are similar to those after space flight.

Adult↗
PubMed1991

Pharmacologic considerations for Shuttle astronauts.

Medication usage by crewmembers in the preflight and inflight mission periods is common in the Shuttle Program. The most common medical reports for which medication is used are: space motion sickness (SMS), sleeplessness, headache, and backache. A number of medications are available in the Shuttle Medical Kit to treat these problems. Currently, astronauts test all frequently used medications before mission assignment to identify potential side-effects, problems related to performance, personal likes/dislikes, and individual therapeutic effect. However, microgravity-induced changes in drug pharmacokinetics, in combination with multiple operational factors, may significantly alter crew-member responses inflight. This article discusses those factors that may impact pharmacologic efficacy during Shuttle missions.

Aerospace Medicine↗
PubMed1991

Cardiovascular function in space flight.

Changes in orthostatic heart rate have been noted universally in Soviet and U.S. crewmembers post space flight. The magnitude of these changes appears to be influenced by mission duration, with increasing orthostatic intolerance for the first 7-10 days of flight and then a partial recovery in the orthostatic heart rate response. Fluid loading has been used as a countermeasure to this postflight orthostatic intolerance. Previous reports have documented the effectiveness of this technique, but it has also been noted that the effectiveness of volume expansion diminishes as flight duration exceeds one week. The response of carotid baroreceptor function was investigated utilizing a commercially available neck collar which could apply positive and negative pressure to effect receptor stimulation. Bedrest studies had validated the usefulness and validity of the device. In these studies it was shown that carotid baroreceptor function curves demonstrated less responsiveness to orthostatic stimulation than control individuals. Twelve Space Shuttle crewmembers were examined pre- and postflight from flights lasting from 4-5 days. Plots of baroreceptor function were constructed and plotted as change in R-R interval vs. carotid distending pressure (an orthostatic stimulus). Typical sigmoidal curves were obtained. Postflight the resting heart rate was higher (smaller R-R interval) and the range of R-R value and the slope of the carotid sigmoidal response were both depressed. These changes were not significant immediately postflight (L + O), but did become significant by the second day postflight (L + 2), and remained suppressed for several days thereafter. It is hypothesized that the early adaptation to space flight involves a central fluid shift during the initial days of flight, but subsequent alterations in neural controlling mechanisms (such as carotid baroreceptor function) contribute to orthostatic intolerance.

Adaptation, Physiological↗
PubMed1991

Cardiovascular physiology in space flight.

The effects of space flight on the cardiovascular system have been studied since the first manned flights. In several instances, the results from these investigations have directly contradicted the predictions based on established models. Results suggest associations between space flight's effects on other organ systems and those on the cardiovascular system. Such findings provide new insights into normal human physiology. They must also be considered when planning for the safety and efficiency of space flight crewmembers.

Adaptation, Physiological↗
PubMed1990

Acute and intermediate cardiovascular responses to zero gravity and to fractional gravity levels induced by head-down or head-up tilt.

Determination of early cardiovascular responses to simulated gravity levels between 0 and 1 G will add knowledge of cardiovascular responses to space flight. Cardiovascular responses to 6 hours in a -5 degrees head-down bedrest model of weightlessness (0 G) were compared to those in head-up tilts of +10 degrees, +20 degrees, and +42 degrees (1/6, 1/3, and 2/3 G, respectively). Six healthy young adult males experienced the four angles on separate days. Impedance cardiography was used to measure thoracic fluid index, cardiac output, stroke volume, and peak flow. Although much intersubject variation occurred, the mean thoracic fluid content at -5 degrees decreased during the first hour and remained decreased; 6-hour values were similar to +10 degrees and +20 degrees. Heart rate decreased the first 2 hours for all angles, then increased, converging at 3-4 hours, and reached control by hour 6. Stroke volume decreased for the first 3 hours at -5 degrees, +10 degrees, +20 degrees; values at all four angles converged at hour 3 and increased in unison thereafter. Cardiac output and peak aortic flow reflected the angle at start of tilt; values at all angles converged by the second hour, decreased through the third hour, and increased thereafter. Pulse pressure decreased for the first 3 hours for angles -5 degrees, +10 degrees, and +20 degrees, converged at the fourth hour, and returned to control. Peak flow at +42 degrees was constant for the first 3 hours and increased thereafter. Blood pressure decreased for the first 2 hours, although the greatest decrease occurred at -5 degrees and +42 degrees; thereafter, values at all angles increased in unison and converged at the fourth hour. Total peripheral resistance increased during the first hour at -5 degrees and +20 degrees and decreased from hour 3 to hours 5-6 at the +42 degrees angle. Cardiovascular values were related to tilt angle for the first 2 hours of tilt, but after hour 3 values at all four angles began to converge, suggesting that cardiovascular homeostatic mechanisms seek a common adapted state regardless of effective gravity level (tilt angle) up to 2/3 G.

Bed Rest↗
PubMed1989

Acute hemodynamic responses to weightlessness in humans.

As NASA designs space flights requiring prolonged periods of weightlessness for a broader segment of the population, it will be important to know the acute and sustained effects of weightlessness on the cardiovascular system since this information will contribute to understanding of the clinical pharmacology of drugs administered in space. Due to operational constraints on space flights, earliest effects of weightlessness have not been documented. We examined hemodynamic responses of humans to transitions from acceleration to weightlessness during parabolic flight on NASA's KC-135 aircraft. Impedance cardiography data were collected over four sets of 8-10 parabolas, with a brief rest period between sets. Each parabola included a period of 1.8 Gz, then approximately 20 seconds of weightlessness, and finally a period of 1.6 Gz; the cycle repeated almost immediately for the remainder of the set. Subjects were semi-supine (Shuttle launch posture) for the first set, then randomly supine, sitting and standing for each subsequent set. Transition to weightlessness while standing produced decreased heart rate, increased thoracic fluid content, and increased stroke index. Surprisingly, the onset of weightlessness in the semi-supine posture produced little evidence of a headward fluid shift. Heart rate, stroke index, and cardiac index are virtually unchanged after 20 seconds of weightlessness, and thoracic fluid content is slightly decreased. Semi-supine responses run counter to Shuttle crewmember reports of noticeable fluid shift after minutes to hours in orbit. Apparently, the headward fluid shift commences in the semi-supine posture before launch. is augmented by launch acceleration, but briefly interrupted immediately in orbit, then resumes and is completed over the next hours.

Adult↗
PubMed1989

Pharmacology in space. Part 1. Influence of adaptive changes on pharmacokinetics.

The topic of pharmacology in space, i.e. the administration of drugs during space flight and the subsequent pharmacokinetic handling of the pharmaceuticals, is a new field about which little is known. In a two-part series, Claire Lathers and colleagues highlight some of the current questions in this field. In this first article the physiological and biochemical changes associated with weightlessness in space are discussed. These changes induce adaptive alterations which may influence the pharmacokinetic properties of drugs. The cardiovascular system is of particular relevance here. Also discussed are the classes of pharmacological agent that are most likely to be used during space flight for medical problems and thus, by necessity, will become drugs to be examined in space to determine whether their pharmacokinetic and pharmacodynamic properties are altered. Therapy of the most common spaceflight ailment-motion sickness-will be considered next month in Part 2.

Humans↗