Biomedical subjects

A Gundel

Publications and source records attributed to A Gundel.

At least 19 recordsLinked to original sources

PubMed1999

Heart period and heart period variability during sleep on the MIR space station.

The long-term acclimation of cardiac rhythms to microgravity was studied in four astronauts aboard the Russian space station MIR during wakefulness and sleep. Sleep polygraphies were obtained between the third and the 30th day in space and, in addition, prior to mission on the ground. From each of the sleep polygraphies, beat-to-beat intervals of cardiac rhythms were determined. The response of heart period and heart period variability to the stimulus microgravity was tested during sleep across sleep stages and during waking. A lengthening of heart period by about 100 ms was found in space compared to measurements on the ground. The slowing of heart rate was more pronounced for non-REM sleep than for REM sleep. A systematic change in heart period in relation to the duration of the stay in space could not be detected. An analysis of heart period variability in the high frequency (respiratory sinus arrhythmia) band supports the hypothesis that the decrease of heart rate under microgravity is produced by an increase in parasympathetic activity. Testing the response of cardiac rhythms to microgravity across distinct behavioural states seems to be a powerful tool to investigate the cardiovascular system.

Adult↗

PubMed1999

A circadian oscillator model based on empirical data.

A model based on the van der Pol equation has been developed to predict the pattern of adaptation of aircrew and other travellers to rapid time-zone transitions, when the exposure to light cannot be quantified. The parameters of the model include the stiffness (mu) and the intrinsic period (T0), which together define the free-running period, and the external force (F). The parameter values were estimated by using a simplex minimization technique to fit the output from the model to body temperature data from 12 individuals before, and over a 12-day period immediately after, a 10-h eastward transition between London and Sydney. Data were collected at three equally spaced points during each sleep period and at the end of four 45-min rest periods during the day. The fitting procedure enabled the parameters of the temperature rhythm to be estimated after correcting for the masking effect of sleep. The average estimates of mu (0.38 h) and T0 (24.24 h) were close to earlier estimates based on forced desynchronization experiments, and the mean free-running period, calculated from these, was 24.50 h. The mean value of the external force F (0.54) was surprisingly high, and this may reflect the strong outdoor light levels during the days in Sydney. Estimates of phase, based on the model solutions, suggested that 11 subjects adapted by a phase delay and 1 by a phase advance. However, the amplitude of the rhythms was much reduced at times when the phase was changing rapidly. Simulations using the range of the model parameters for the 12 individuals predicted that adaptation to within 1 h after a 10-h eastward transition would be achieved within between 3 and 11 days. However, since these predictions are dependent on the choice of external force, estimates may need to be more conservative in real-life situations when light exposure cannot be measured.

Adaptation, Physiological↗

PubMed1998

Joint NASA-ESA-DARA Study. Part three: characterization of sleep under ambient CO2-levels of 0.7% and 1.2%.

An experiment was conducted to study sleep quality and sleep architecture in volunteers living in a closed system under elevated ambient CO2 levels of 0.7% and 1.2%. In a closed system, human life is possible only if the CO2 level is permanently adjusted. For the Russian space station MIR, for example, the CO2 levels of the present study are actual upper limits for the adjustment. Sleep architecture was found to be altered in astronauts on the orbiting MIR station. Sleep quantity and quality were reduced. The latency to the first REM sleep was shorter in space and slow wave sleep was redistributed from the first to the second sleep cycle. The elevated CO2 concentration in the atmosphere on MIR may be one of the reasons for those observations regarding sleep in space. Thus, this experiment was also conducted in order to clarify the interpretation of data obtained from astronauts on MIR. In this study sleep polygraphies could be recorded in 4 subjects who lived for 23 d under 0.7% and then for the same period of time under 1.2% CO2. Findings suggest that these levels of ambient CO2 do not reduce sleep quality. Sleep architecture, however, was slightly changed and showed that the amount of slow wave sleep increased with the duration of the exposure to CO2. But it can be excluded that findings on MIR were caused by elevated CO2-levels.

Adult↗

PubMed1998

Joint NASA-ESA-DARA Study. Part three: cardiorespiratory response to elevated CO2 levels during sleep.

Long-term exposure to elevated ambient CO2-levels is a common condition for living in a closed environment such as a spacecraft. In this study, the cardio-respiratory system response to CO2-levels of 0.7% and 1.2% was assessed. The response was investigated during non-REM sleep when the sensitivity of the respiratory system to ambient CO2 is low and only subject to the metabolic respiratory drive. Four subjects were exposed to 0.7% and 1.2% CO2 for 23 d each. Respiration rate and heart rate were determined for the first two phases of slow wave sleep. In addition, the occurrence of central apneas was assessed. Data were analyzed by a repeated measure ANOVA. As a response to CO2 exposure two dynamic effects were observed. Heart rate increased initially with a peak between the second and the sixth night. Over the period of the exposure, respiration rate and heart rate decreased steadily. At least two mechanisms with different time constants must be considered for this dynamic behavior: an uncompensated respiratory acidosis, followed by a phase of relative compensation. At the end of the 23-d exposure, equilibrium in the physiological state had not been reached. Though the experiment did not show severe effects from CO2, it is too early to state that a long-term exposure does not have any consequences for health and well-being.

Adult↗

PubMed1997

The alteration of human sleep and circadian rhythms during spaceflight.

Numerous anecdotes in the past suggest the concept that sleep disturbances in astronauts occur more frequently during spaceflight than on ground. Such disturbances may be caused in part by exogenous factors, but also an altered physiological state under microgravity may add to reducing sleep quality in a spacecraft. The present investigation aims at a better understanding of possible sleep disturbances under microgravity. For the first time, experiments were conducted in which sleep and circadian regulation could be simultaneously assessed in space. Four astronauts took part in this study aboard the Russian MIR station. Sleep was recorded polygraphically on tape together with body temperature. For a comparison, the same parameters were measured during baseline periods preceding the flights. The circadian phase of body temperature was found to be delayed by about 2 h in space compared with baseline data. A free-run was not observed during the first 30 d in space. Sleep was shorter and more disturbed than on earth. In addition, the structure of sleep was significantly altered. In space, the latency to the first REM episode was shorter, and slow-wave sleep was redistributed from the first to the second sleep cycle. Several mechanisms may be responsible for these alterations in sleep regulation and circadian phase. Most likely, altered circadian zeitgebers on MIR and a deficiency in the process S of Borbély's sleep model cause the observed findings. The change in process S may be related to changes in physical activity as a result of weightlessness.

Adult↗

PubMed1997

Two-crew operations: stress and fatigue during long-haul night flights.

BACKGROUND: As part of a research program concerning legal aspects of two-pilot operations on long-haul routes, the purpose of the study was to investigate two-crew extended range operations during a flight roster with two consecutive night flights and a short layover. HYPOTHESIS: Present flight time regulations may not be adequate for two-crew minimum operations. METHODS: The study was conducted in cooperation with a German airline company on the route Frankfurt (FRA)-Mahe (SEZ). There were 11 rotations (22 flights) that were investigated by pre-, in- and post-flight data collection each time from the two pilots. Recordings included sleep, taskload, fatigue and stress by measurement of EEG, ECG, motor activity, and subjective ratings. The average actual flight times were 9:15 h (FRA-SEZ) and 9:53 h (SEZ-FRA). All flights took place at night. The layover duration in Mahe was 13:30 h during day-time. RESULTS: During layover, sleep was shortened by 2 h on average compared with 8-h baseline sleep. The two consecutive night duties resulted in a sleep loss of 9.3 h upon return to home base. Inflight ratings of taskload showed moderate grades, but for fatigue ratings an increasing level was observed. Fatigue was more pronounced during the return flight and several pilots scored their fatigue at a critical level. Motor activity, brainwave activity (occurrences of micro-events) and heart rate indicated drowsiness and a low state of vigilance and alertness during both night flights, but these effects were more pronounced during the second flight. CONCLUSIONS: From the findings it is concluded that a duty roster, as conducted in this study, may impose excessive demands on mental and physiological capacity.

Adult↗

PubMed1995

Sleepiness of civil airline pilots during two consecutive night flights of extended duration.

Sleepiness of civil airline pilots was studied in a two-crew cockpit during two consecutive night flights of about 10 h duration each. Sleepiness was assessed by EEG recordings and subjective ratings during hourly recurrent short experimental phases. On the second night flight, the alertness component that is related to the preceding sleep showed a modification due to reduced quality and quantity of sleep between flights. The daytime sleep during layover was not sufficient to maintain the same alertness level as observed during the initial flight. This result is in coincidence with investigations in shift workers starting a period of night shifts. It is concluded that improvements such as the introduction of a nap schedule should be considered to alleviate spontaneous sleepiness in the cockpit.

Adult↗

PubMed1993

Sleep and circadian rhythm during a short space mission.

An experiment was conducted to assess sleep and circadian regulation in an orbiting spacecraft. In orbit the weakened influence of 24-h zeitgebers could result in delayed circadian phases with the possibility of a transition to free-running circadian rhythms. This and the specific stressors of a space mission may lead to changes in ultradian sleep regulation and in reduced sleep quantity and quality. During the mission sleep was recorded polygraphically on tape, as was body temperature. Daytime alertness was rated subjectively by a mood questionnaire. For comparison the same parameters were measured during a baseline period preceding the space mission. The circadian rhythms of body temperature and alertness were found to be delayed in space compared to baseline. This may mark a phase shift or the transition to a circadian state of free-run. Sleep was shorter and more disturbed. The structure of sleep was significantly altered. In space REM latency was shorter, there was less REM sleep in the second non-REM/REM cycle, and slow-wave sleep was redistributed from the first to the second cycle. The self-assessed mood resembled sleep disturbances and adaptation to the space environment. Reduced sleep quality and quantity are likely to result in fatigue and lower daytime performance. Countermeasures should be adopted to improve sleep of astronauts.

Body Temperature↗

PubMed1992

Topographical changes in the ongoing EEG related to the difficulty of mental tasks.

An experiment was carried out to investigate the hypothesis that task difficulty is reflected in changes in the topographical distribution of the ongoing EEG. Subjects had to perform three different tasks at two difficulty levels each; the Sternberg memory scanning task in an auditory and in a visual mode and a task whose performance required mainly visual scanning. Task difficulty was verified by the measurement of response times. Using a commercial Brain Electrical Activity Mapping device, EEG was recorded from 19 scalp electrodes while the subjects performed the tasks. Spectral matrices of the EEG were calculated to investigate spatial relationships in the EEG. Compared to the lower level, higher task difficulty resulted in EEG changes that led to the identification of two factors. One was the reduction of parietal and occipital alpha activity due to the amount of visual scanning and the other an increase of theta activity in the left frontal electrodes which may be associated with the amount of general mental processing.

Adult↗

PubMed1992

A mathematical model of the human circadian system and its application to jet lag.

A mathematical model of the circadian system is described that is appropriate for application to jet lag. The core of the model is a van der Pol equation with an external force. Approximate solutions of this equation in which the external force is composed of a constant and an oscillating term are investigated. They lead to analytical expressions for the amplitude and period of free-running rhythms and for the frequency limits of the entrainment region. The free-running period increases quadratically with stiffness. Both period and amplitude depend on the value of the constant external force. The width of the range of entrainment is mostly determined by the external force, whereas the relative position of this range follows the intrinsic period of the oscillator. Experiments with forced and spontaneous internal desynchronization were evaluated using these analytical expressions, and estimates were obtained for the intrinsic period of the oscillator, its stiffness, and the external force. A knowledge of these model parameters is essential for predictions about circadian dynamics, and there are practical implications for the assessment of the adaptation after rapid trans-meridian travel.

Body Temperature↗

PubMed1992

[Computer-assisted analysis of the electroencephalogram with a theta ground rhythm variant].

UNLABELLED: From 8 men and 12 women with a slow posterior rhythm on the one hand and from 7 male and 5 female healthy volunteers with a regular alpha-EEG on the other closed-eye-EEGs were registered at 8:00 a.m., 12:00 noon, 4:00 p.m., and 8:00 p.m. and recorded on tape for computer processing. Simultaneously each time the body temperature was measured. RESULTS: In 11 of the 20 patients the slow posterior rhythm shows a right-sided accentuation, in 6 a left-sided. Besides the activity of all frequency-bands favours occipital and occipital-central the right hemisphere. The control group shows only an insignificant right-sided accentuation of alpha-power and alpha-peak-power. The alpha-peak-frequency of the 20 patients is slower than in the controls, the body temperature on the contrary is higher. The physiological circadian shift of the alpha-peak-frequency and of the body temperature does not come up to a similar extent as in the controls. Striking slight is the circadian shift of the frequency of the slow posterior rhythm. Furthermore the day-time related shifts of the alpha-power and of the beta-power take other courses than in the controls. And the maxima of the alpha-power and of the alpha-peak-power are mostly located parietal instead of occipital. All in all the slow posterior rhythm seems to be connected with far-reaching peculiarities of the cerebral function.

Adult↗

PubMed1991

Influence of melatonin treatment on human circadian rhythmicity before and after a simulated 9-hr time shift.

The hormone melatonin is currently proposed by some investigators to be an efficient means for decreasing the impairing effects of jet lag. Eight healthy male subjects, aged 20 to 32, underwent a 9-hr advance shift in the isolation facility of our institute during two periods each of 15 days' duration. In a double-blind, crossover design, subjects took either melatonin or placebo at 1800 hr local time for 3 days before the time shift and at 1400 hr for 4 days afterwards. The time shift was simulated on days 7 and 8 by shortening the sleep period by 6 hr and the following wake period by 3 hr. Body temperature was recorded every 90 min, and urine was collected at 3-hr intervals all day and night. Melatonin treatment enhanced the resynchronization speed of some, but not all, hormone and electrolyte excretion rates for several days after the time shift. The adaptation speed of the temperature rhythm significantly increased during one postshift day. In addition, the circadian temperature rhythm had a significantly higher amplitude under melatonin treatment than under placebo after the time displacement. For the placebo group, the rhythm of 6-hydroxymelatoninsulfate excretion exhibited an advance shift in five subjects, whereas the other three showed a delay shift, and adjustment did not achieve more than one-half of the expected value within 8 days. A significantly different adjustment could be observed in the melatonin-treated group: Seven subjects underwent an advance shift of the expected 9 hr within an average of 8 days. The results suggest that melatonin treatment can accelerate resynchronization of the melatonin excretion rhythm after eastward time zone transitions. The improvement is not, however, sufficiently great that we can recommend melatonin for the alleviation of jet lag.

Adult↗

PubMed1989

Transition between advance and delay responses to eastbound transmeridian flights.

In response to eastbound transmeridian flights, which result in zeitgeber phase advance shifts, adaptation of the circadian system to the new time zone by phase delays and advances are observed. The delay response to an advance zeitgeber shift has been called an antidromic response. For the shift at which the transition from an advance to an antidromic response occurs, the term critical shift is introduced. For the study of critical shifts, a flight experiment across nine time zones and numerical simulations of a van der Pol equation have been evaluated. The interest is focussed on the determination of a range for critical abrupt shifts. An abrupt shift means that the ensemble of zeitgebers including geophysical zeitgebers and the rest-activity cycle is shifted immediately in the new time zone. The range of critical advance shifts has been estimated to reach from +7 to +10 hr. In the literature, results were reported which would imply a much wider range. The discussion of these observations shows that the actual shifts were presumably not abrupt in the quoted experiments. The consequences of critical shifts for jet lag symptoms are investigated. If reduced circadian amplitudes and long times taken for the resynchronization contribute to the feeling of jet lag, the symptoms will be worst for shifts close to the critical one, as numerical simulations revealed. Manipulations of such shifts with the aim to alleviate jet lag are discussed.

Adaptation, Physiological↗

PubMed1989

[EEG studies before and following hemofiltration].

For a sample of 8 men and 3 women, 47-80 years old, closed-eye-EEGs were registered for the first time in the morning before hemofiltration treatment, again thereafter at 1 p.m., and a third time at 7 p.m. The day after treatment EEG-registrations were conducted at the same times. Apart from traditional visual evaluation every EEG was recorded on tape for computer processing. Simultaneously with every EEG-registration the body temperature was measured. For comparison served corresponding data of 17 hemodialysis patients, and of 10 healthy old and 12 healthy young volunteers. The peak-frequency of the hemofiltration patients turned out significantly slower than that of the healthy persons and of the hemodialysis patients. While in the healthy volunteers the peak-frequency increased corresponding with the body temperature from the morning to the evening, the hemofiltration patients lacked such a correlation, although their temperature ascended in the normal way. As to the circadian variations of the activity in the diverse frequency-bands, the hemofiltration patients, and to a less degree the hemodialysis patients, showed especially in the day after treatment distinct deviations from the healthy volunteers.

Aged↗

PubMed1988

[EEG findings in patients with a kidney transplant].

UNLABELLED: For a sample of 22 men and 9 women, 24-59 years old, closed-eye-EEGs were registered three times a day: at 7 a.m., at 1 p.m., and at 7 p.m. Simultaneously with every EEG-registration the body temperature was measured. Apart from traditional visual evaluation every EEG was recorded on tape for computer processing. For comparison served corresponding data of 17 hemodialysis treated (HD), and of 11 hemofiltration treated (HF) patients, of 12 healthy young volunteers (J), and of 10 healthy old volunteers (A). RESULTS: As the illustration shows, the occipital peak-frequency (F) of the renal transplant recipients (NT) resembles that of the J and exceeds negligibly that of the A, whereas considerable differences are revealed compared with the peak-frequencies of the HD- and of the HF-patients. Statistically the peak-frequency of the NT-patients occipital and parietal turns out significantly higher than that of the HD- and HF-patients. According to these findings intraindividually in 5 of the former HD-patients after transplantation a remarkable increase of the peak-frequency is visible. In addition to this the figure demonstrates, that only in the healthy volunteers the peak-frequency (F) ascends corresponding with the body temperature (T) from the morning to the evening, while in the NT-patients similar increases scarcely are recognizable. In contrast to this in the HD- and HF-patients the body temperature rises in the normal way, but there is no corresponding variation of the peak-frequency. In the NT-patients pathological patterns are less frequent than in the HD- and HF-patients, but nevertheless more frequent than in healthy persons.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1987

[Effect of the time of day on the EEG in cerebral arteriosclerosis].

UNLABELLED: The study was conducted with three men and seven women, 72-84 years old, characterized by psychopathological and clinical signs of cerebral arteriosclerosis (A). All patients suffered from disorder of sleep-waking rhythm. With one exception every experiment ran for five days during which closed-eye-EEGs were registered at 8 a.m., 12 noon, 4 p.m., and 8 p.m. of the alert but relaxed patients and recorded on tape for computer processing. Simultaneously with every EEG registration the body temperature was measured. The findings were compared statistically with corresponding data of a former study conducted with ten healthy aged volunteers (G). RESULTS: The dominant peak-frequency of the patients turned out significantly slower than that of the volunteers.--While in healthy persons the peak frequency increased corresponding with the body temperature from the morning to the late afternoon or the early evening respectively, the patients lacked such a correlation, although their temperatures rose gradually in the normal way. In most of the patients the peak-frequency had a remarkable small variety from day to day as well as from scalp-position, and its circadian shift was poor. Psychopathologically these subjects manifested primarily memory loss, general intellectual decline, and in four cases disorientation. On the other hand the EEGs of three women showed substantial greater variety of the peak-frequency from day to day and from scalp-position to scalp-position. Besides the alterations during the day were rather excessive, but lacking any appreciable correspondence with the undisturbed circadian variations of the body temperature. In these three cases psychopathologically personality changes preponderated.

Aged↗

PubMed1987

[Circadian rhythm-related EEG changes in endogenous depressions and manias].

UNLABELLED: From 10 endogenous depressive and 10 manic alert but relaxed patients closed-eye-EEG's were registered at 8.00 a.m., 12.00 noon, 4.00 p.m., and 8.00 p.m., and recorded on tape for computer processing. Simultaneously each time the body temperature was measured. The findings were compared with corresponding former data of 12 healthy young people and 10 healthy aged volunteers. RESULTS: The peak-frequency of the manic patients proved to be significantly higher than that of the depressive ones, and besides slightly exceeded that of the healthy persons. While in the latter temperature and occipital peak-frequency ascend step by step from the morning to the evening, the depressive patients show a resembling increase only in outlines in the peak-frequency, whereas the temperature already decreases from 4.00 p.m. to 8.00 p.m. In the manic patients peak-frequency and temperature and delta-Power reach their acme at 4.00 p.m., but as well the peak-power as the power of alpha- and beta-frequency-bands show a trough just at 4.00 p.m. In the depressive patients, on the other hand, alpha-, theta, and delta-frequency-bands mainly have their summits at 12.00 noon. Finely the manic patients stand out by most significant band-power-variations between the distinct daytimes, while uninterrupted gradual increasing is extreme rare. In the depressive persons both these events scarcely are found. The healthy volunteers have intermediate positions. All in all the results show, that in endogenous depression circadian variations of EEG-parameters appear disorganized, while in mania a modified organization prevails.

Adult↗

PubMed1987

Resynchronization of the circadian system following a 9-hr advance or a delay zeitgeber shift: real flights and simulations by a Van-der-Pol oscillator.

After a flight from Germany to California, eight subjects stayed there for 3 weeks and then were flown back to Germany. After both the westbound and the eastbound flights, body temperature was measured for 2 weeks in the new time zone. Data obtained every 3 hr throughout the day and night were analyzed by the complex demodulation technique to visualize phase adjustments and the nonstationary amplitude of the measured circadian rhythms. The response to the zeitgeber delay was very similar in all subjects and consisted of a phase adjustment of 6 hr in the first 2 days following the flight and a subsequent slow completion of the resynchronization with a rate of 0.5 to 1 hr per day. After the eastbound flight the resynchronization was generally slower, and the circadian amplitudes were more reduced than after the zeitgeber delay. In addition, the advance shift led to different patterns of phase adjustment for the individuals. Shortening and lengthening of circadian periods as well as phase jumps by about 12 hr were observed. Simulations with a Van-der-Pol oscillator forced by a rectangular zeitgeber function clearly reflected the divergence in resynchronization between eastbound and westbound flights. The different resynchronization patterns found after the 9-hr zeitgeber advance, including the corresponding duration of readjustment, could also be well simulated.

Adaptation, Physiological↗