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Biomedical subjects

R L Bondar

Publications and source records attributed to R L Bondar.

29 records · Page 2Linked to original sources
PubMed1991

Cerebral blood flow velocities by transcranial Doppler during parabolic flight.

Microgravity is produced for 20 to 30 seconds in NASA's KC-135 aircraft at the end of a 2 G pullup for each of 40 parabolas per flight. Continuous transcranial Doppler ultrasound, arterial blood pressure, and acceleration levels were recorded for 12 male and 8 female healthy subjects without known cardiovascular or cerebrovascular disease. Recordings were made throughout 10 parabolas per subject in each of the supine, sitting, and standing postures. The data were digitized for off-line analysis using Fast Fourier Transform and other signal processing methods. A phase lag in changes to transcranial Doppler waveforms from the onset of acceleration was more pronounced in the standing position than in the sitting position. There was less of a phase lag in the supine position. These ultrasound changes preceded the more delayed variations in arterial blood pressure. The KC-135 provides a unique short-term environment that allows measurement of the human response to variations in acceleration but limits physiological monitoring of responses to a steady state of microgravity.

Acceleration↗
PubMed1990

Transcranial Doppler studies of flow velocity in middle cerebral artery in weightlessness.

Physiological adaptation to weightlessness requires changes in cardiovascular system parameters to maintain homeostasis in the presence of cephalic fluid shifts. The cerebral circulation must respond immediately to these systemic changes or impairment of cerebral function will occur. Blood flow velocities of the middle cerebral artery were measured by transcranial Doppler (TCD) ultrasound in NASA's KC-135 aircraft from four healthy subjects in the supine position. Transcranial Doppler data with accompanying acceleration information were analyzed in three segments in each parabola. Cardiac cycles for each segment of all 20 parabolas were pooled for individual subjects. A Student's t test on the data revealed statistically significant differences in the mean and peak frequencies, systolic/diastolic ratios and Doppler power between positive 2 gz and microgravity (10(-2) gz) as well as between positive 2 gz and negative 2 gz. Velocity waveform profiles differed for the first one third of each segment, with a more resistive waveform developing during the last two thirds. Changes in systemic arterial resistance and/or raised intracranial pressure may contribute to these TCD waveform changes.

Adaptation, Physiological↗
PubMed1990

Development of methods to analyse transcranial Doppler ultrasound signals recorded in microgravity.

During space flights, several clinical syndromes may be the result of changes in cerebral circulation. The purpose of the paper is to describe the development and initial evaluation of a system for recording, processing and displaying transcranial Doppler ultrasound (TCD) waveforms from the middle cerebral artery (MCA) in microgravity. Volunteers were repeatedly subjected to 15-20 s intervals of microgravity ('near zero gravity') during flights on the KC-135 military aircraft. Continuous TCD recordings from the MCA were stored on magnetic tape. The paper describes the system that was developed to digitise the Doppler ultrasound data and markers that corresponded to the various levels of microgravity, obtain the maximum and mean Doppler waveforms, identify the waveforms and quantify them. The results demonstrate the feasibility of making TCD recordings in a microgravity environment and illustrate excellent performance of the system and its ease of operation. Quantitative waveform analysis of the recordings from the first subject studied in the supine position showed statistically significant changes in MCA velocity waveforms during microgravity.

Cerebral Arteries↗
PubMed1985

Contralateral gaze deviation after frontal lobe haemorrhage.

Contralateral deviation of the eyes was sustained for a week in a patient with discrete subcortical frontal lobe haematoma. When deviation recovered, ipsilateral saccades were hypo-metric and saccadic latencies were prolonged in both horizontal directions. Smooth pursuit was paretic during tracking toward the side of the haematoma. Pursuit gain was higher during tracking to the contralateral side. Smooth eye movement imbalance may explain the unusual finding of contralateral gaze deviation with frontal lobe damage.

Adolescent↗
PubMed1985

Canadian medical experiments on Shuttle flight 41-G.

During the 41-G mission, two payload specialist astronauts took part in six Canadian medical experiments designed to measure how the human nervous system adapts to weightlessness, and how this might contribute to space motion sickness. Similar tests conducted pre-flight provided base-line data, and post-flight experiments examined re-adaptation to the ground. No changes were detected in the vestibulo-ocular reflex during this 8-day mission. Pronounced proprioceptive illusions were experienced, especially immediately post-flight. Tactile acuity was normal in the fingers and toes, but the ability to judge limb position was degraded. Estimates of the locations of familiar targets were grossly distorted in the absence of vision. There were no differences in taste thresholds or olfaction. Despite pre-flight tests showing unusual susceptibility to motion sickness, the Canadian payload specialist turned out to be less susceptible than normal on-orbit. Re-adaptation to the normal gravity environment occurred within the first day after landing.

Adaptation, Physiological↗
PubMed1984

Rebound nystagmus in olivocerebellar atrophy: a clinicopathological correlation.

Rebound nystagmus was recorded in a patient with cerebellar dysfunction. Neuropathological examination showed degeneration of the inferior olivary nuclei and the cerebellar cortex. The basis pontis and the brainstem tegmentum were spared. Rebound nystagmus is attributed to a smooth eye movement bias that is generated within intact vestibuloocular pathways to oppose gaze-evoked centripetal drift of the eyes. The source of the rebound bias was not visual, because rebound nystagmus normally occurs in darkness, smooth pursuit was paretic, and the olivocerebellar visual relay pathway was degenerated. An extraretinal, efference copy signal of the eye position error must detect the ocular drift and generate the rebound bias. The neuropathological findings indicate that rebound nystagmus can be a sign of involvement confined to the olivocerebellar circuit and that nonvisual signals of eye position are monitored independently of this cerebellar system.

Aged↗
PubMed1984

Ischemic optic neuropathy associated with optic disc drusen.

Ischemic optic neuropathy developed in five eyes of four patients with optic nerve drusen. Two of the patients were in their 20s, a decade when idiopathic ischemic optic neuropathy is rare. This argues against a chance concurrence of drusen and idiopathic ischemic optic neuropathy. Infarction of the distal portion of the optic nerve in patients with drusen may result from mechanical distortion of blood vessels in the laminar and prelaminar regions.

Adult↗
PubMed1981

Mitral valve prolapse: a cause of stroke in children?

For a large proportion of children suffering a stroke, no specific cause can be found. Two cases with infantile hemiplegia are reported who subsequently were found to have mitral valve prolapse, which occurred as a familial trait in both cases. An association between stroke in childhood and mitral valve prolapse is suggested.

Adult↗
PubMed1977

Neurofibrillar changes in goldfish (Carassius auratus L.) brain in relation to environmental temperature.

Neurofibrillar changes occur in the brains of goldfish, Carassius auratus L., maintained at 5 degrees C for 177 days or more under a 12-hour photoperiod. In paraffin sections impregnated by the silver method of Holmes, the light microscopic appearance of the neurofibrillary change was evidenced by black rings 1 micrometer to 2 micrometer in outside diameter. A quantitative study showed the mean number of rings to be: optic tectum layer 3, 1.34 X 10(2)/mm(3), layer 5, 1.14 X 10(2)/MM(3), nucleus prerotundus 4.63 X 10(2)/mm(3), olfactory bulbs, 6.2 X 10(2)/mm3. In the brains of fish kept at 15 degrees C a few rings are found only in some olfactory bulbs and not in any other region of the brain. The brain wet weight also changes and was found to be significantly (p less than 0.01) less in 5 degrees C than in 15 degrees C fish, the mean values being 0.1588 g and 0.2091 g respectively. The significance of the observed changes is discussed. It is suggested that the smaller brain wet weight may reflect a change in the vasculature of the brain and be related to the acclimation process. It is hypothesized that the rings are a morphological expression of a physiological change caused by prolonged exposure to low temperatures; a neuronal response reflecting either early degeneration or a functional adaptation which may involve an alteration in axoplasmic transport. It is suggested that this system is a useful model for the study of relationships between neurofibrillar disturbances and neuronal function.

Animals↗
PubMed1977

Neurofilamentous changes in goldfish (Carassius auratus L.) brain in relation to environmental temperature.

The presence of neurofilaments in the synaptic boutons in the brains of goldfish maintained at 5 degrees C for 177 days or more is reported. Neurofilaments are not found in boutons of control fish kept at 15degreesC. It is suggested that the neurofilaments may be equated with neurofibrillary rings seen by light microscopy. Neurofilaments have been implicated in axoplasmic transport and, therefore, irregularities in the occurrence or appearance of these filaments may reflect alterations in their functions. The unusual occurrence of neurofilaments in the boutons of cold temperature goldfish may be an expression of early degenerative changes or may represent a modification of axoplasmic transport. The suitability of goldfish as a model for the study of the functional effects of neurofibrillary/neurofilamentous accumulations is discussed.

Animals↗