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Biomedical subjects

C H Markham

Publications and source records attributed to C H Markham.

At least 19 recordsLinked to original sources
PubMed1992

Ventral intermediate thalamotomy for posttraumatic hemiballismus.

An unusual case of hemiballismus following closed head injury is presented. The abnormal movement persisted for 16 years despite medical treatment. Preoperative studies did not reveal a specific lesion within the subthalamic nucleus or within the basal ganglia. A stereotactic ventral intermediate thalamotomy was performed producing a complete resolution of the ballistic movement which persisted for the length of our 12-month follow-up.

Adult↗
PubMed1992

Further evidence to support disconjugate eye torsion as a predictor of space motion sickness.

Disconjugate eye torsion in hypo- and hypergravity of parabolic flight was examined in four former astronauts and four previously tested ex-astronauts to replicate an earlier study and to further test the asymmetry hypothesis of otolith function. Results in the new subjects supported the asymmetry hypothesis and confirmed previous findings that those with low scores of torsional disconjugacy on the KC-135 did not suffer space motion sickness in their prior Shuttle missions while those with high scores did. Tilting subjects with high disconjugacy scores slightly to one side and the other failed to find a position that decreased disconjugacy in hypergravity, leading to the conclusion that a simple planar asymmetry about the y-axis was probably not the cause of the observed torsional differences in the two eyes. Disconjugacy increased at 0 G with increasing parabolas, much more so in subjects who had suffered SMS. Because of this, 10 to 20 parabolas were deemed to be a more certain discriminator than a fewer number.

Aerospace Medicine↗
PubMed1992

The dystonias.

The various dystonias have been found in at least five different hereditary backgrounds. The gene responsible for one of the dystonias, idiopathic torsion dystonia (ITD), lies on chromosome 9q32-34, with flanking markers now 1-2 cM apart. Magnetic resonance imaging and computerized tomography (CT) abnormalities in the basal ganglia, especially in the putamen, are found in many secondary dystonias. Botulinum toxin therapy is proving very useful in the treatment of focal dystonias.

Animals↗
PubMed1991

Prediction of space motion sickness susceptibility by disconjugate eye torsion in parabolic flight.

The hypothesis of asymmetric otolith function asserts that physiological or anatomical differences in the two sides of the bilateral gravity-sensing otolith apparatus of the inner ear may be well compensated on Earth, but when exposed to novel gravitational states, the prior compensatory stratagems may be ineffective, leading to unstable vestibular responses and causing the phenomenon of space motion sickness. To investigate this hypothesis, spontaneous eye torsion, a reflex governed by the otolith organs, was examined in the upright position during the hypo- and hypergravity of parabolic flight aboard NASA's KC-135 aircraft in nine former astronauts whose history of space motion sickness was revealed after data analysis had been completed. Results showed that astronauts who had been sick in space had significantly higher scores of disconjugate eye torsion in parabolic flight, and that their responses were consistently different in 1.8 G relative to 0 G compared to astronauts who had not been sick in space. In 1 G, there were no differences in disconjugate eye torsion between the subjects. The results support the asymmetry hypothesis and offer a possible predictive test of space motion sickness.

Disease Susceptibility↗
PubMed1979

Cat primary canal neurons: relation of conduction velocity to resting and dynamic firing characteristics.

Spontaneous discharge patterns of first-order canal afferents were analyzed in cats anethetized with pentobarbital sodium with particular emphasis on the relationship of regularity of resting discharge, sensitivity to angular acceleration and adaptation to the time delay between electrical labyrinthine stimulation and recording from afferents near Scarpa's ganglion. Regular units were found to have a high resting rate, low sensitivity to angular acceleration, were mostly nonadapting during prolonged acceleration and showed relatively long latency to electrical stimulation. Irregular units tended to have a low resting rate, high sensitivity, frequently showed adaptation and had short latencies. Intermediate neurons had mixed characteristics of regular and irregular units. In medulated nerve fibers, a direct relation exists between conduction velocity and fiber diameter. As latency is due primarily to conduction in the first-order axon, we may speculate that regular neurons have thin fibers which innervate the slope of the crista, irregular neurons have thick fibers which innervate the summit, and intermediate units have medium caliber fibers which innervate both the slope and summit of the crista ampullaris.

Animals↗
PubMed1978

A double-blind comparison of levodopa, Madopa, and Sinemet in Parkinson disease.

A sixteen-week study examined the effect of Madopa and Sinemet on patients with Parkinson disease disease suffering nausea or vomiting as side-effects of levodopa therapy and compared the efficacy of the three preparations in controlling the symptoms of Parkinson disease. Following a control period on levodopa, 20 patients underwent four consecutive four-week regimens as follows: (1) double-blind, in which a randomized half received levodopa and half received Madopa; (2) single-blind, in which all received Madopa; (3) double-blind, in which a re-randomized half received Madopa and half Sinemet; and (4) single-blind, in which all received Sinemet. Levodopa administration via Sinemet and Madopa was held to a fixed 20% of prior levodopa dosage. Almost all patients showed great reduction in nausea and vomiting with both Madopa and Sinemet. Seventy percent of the patients showed improvement in disability compared to their levodopa baseline levels. Group means showed no difference between the improvement seen on Madopa and that seen on Sinemet. However, examination of individual responses showed that the majority of patients fared distinctly better on either Sinemet or Madopa.

Adult↗
PubMed1977

The relationship of conduction velocity to other physiological properties of the cat's horizontal canal neurons.

The conduction velocity and other physiological characteristics of the first order horizontal canal afferents were studied in 24 anesthesized cats. From their spontaneous discharge patterns, neurons were classified into three groups: regular, intermediate and irregular; The irregular units tended to have a low resting rate, high sensitivity to angular acceleration, frequently exhibited adaptation during prolonged acceleration, and showed a short latency from the time of electric stimulation of the labyrinth to recording the action potential near Scarpa's ganglion. The regular units tended to have a high resting discharge rate, low sensitivity, were mostly non-adapting, and showed longer latency to electric stimulation. The intermediate neurons had a mixed character of regular and irregular units. Based on the very short conduction times (mean 0.34 msec) and the work of Moxon (1971), we conclude the locus of activation of electrical stimulation is neural rather than the receptor cells. Since the latency is due predominantly to conduction in the first order axon, and since there is a direct linear relation between conduction velocity and fiber diameter in the medullated nerve fibers, it is possible to speculate that the regular cells have thin fibers which innervate the slope of the crista, the irregular neurons have thick fibers which innervate the summit of the crista, and the intermediate units have medium caliber fibers which innervate both the slope and summit of the crista ampullaris.

Action Potentials↗
PubMed1977

The contribution of the contralateral labyrinth to second order vestibular neuronal activity in the cat.

Vestibular brain stem units of the horizontal canal in the awake C1 transected cat were examined in acute experiments before and after the contralateral vestibular nerve was cut. The latter procedure resulted in an immediate increase in mean resting rate from 19 to 45 spikes/sec and greater spontaneous fluctuations in firing rate. Mean sensitivity to constant accelerations from 2 to 16 degrees/sec2 was significantly reduced. In the 4-6 degrees/sec2 range, for example, mean sensitivity fell from 5.7 +/- 3.2 spike/sec/deg/sec2 (range 0.7-13.6, n = 107) to 2.8 +/- 1.4 (range 0.2-5.5, n = 29). Mean sensitivity to 4-6 degrees/sec2 deceleration was reduced from about 4.5 to 3.0. On the other hand, time constants and the ratio of adapting to non-adapting units was unchanged. Removal of the midline cerebellum, including the vermis and fastigial nuclei in a portion of the animals, did not materially alter the above results. It is concluded that the contralateral labyrinth, acting via the vestibular brain stem commissural pathway, not only exerts a powerful effect on the resting activity of brain stem canal vestibular neurons, but also on their response to acceleration.

Action Potentials↗
PubMed1977

Intraaxonal transport of Herpes simplex virus in the rat central nervous system.

Light and electron microscopic observation 3--4 days after microinjection of Herpes simplex virus (HSV) into the left neostriatum of rat demonstrated the following results. (1) Virus labeled nerve cells were found in the ipsilateral substantia nigra; a large number of infected neurons were in the zona compacta and some were in the zona reticulata. No virus infection was evident in the contralateral side. (2) Virus labeled neurons were found in the cortex, a greater number ipsilaterally than contralaterally, and in the dorsal raphé nuclei. Cortical microinjection of HSV led to infection of some cortical cells but no neostriatal cells. We conclude, therefore, that spread of the virus to the cortex, the substantia nigra and the dorsal raphé following neostriatal injection was by retrograde axonal transport. (3) The left neostriatum, where HSV was injected, showed a surprisingly small number of virus infected neurons. The infected neurons were mostly the large neurons; the majority of medium sized neurons were well preserved. There was massive degeneration of nerve terminals throughout the neuropil. Most of these degenerating nerve terminals are considered to be afferent fibers.

Animals↗
PubMed1977

Semicircular canal radii of curvature (R) in cat, guinea pig and man.

The radii of curvature (R) of the horizontal (Rh), anterior (Ra) and posterior (Rp) semicircular canals were measured by a new technique (called ROTA) for cat, guinea pig and man. For each canal, data points from the osseous canal were rotated and plotted by computer such that the plane of the sheet of computer plot corresponded to the plane best fitting that canal. The radius of each osseous canal was determined and where necessary, the radius of the arc of data points was corrected for thickness of the absent tissue. For cat, guinea pig and man there are differences in R between canals within a labyrinth suggesting that if other things are equal there could be differences in the average mechanical sensitivity of the canals, which is consistent with physiological recordings from primary vestibular neurons in the cat. The Rs determined by ROTA are compared with Rs determined by conventional histological means.

Action Potentials↗
PubMed1977

Semicircular duct and ampulla dimensions in cat, guinea pig and man.

Predictions from the classic theory of semicircular canal operation, the torsion pendulum model, depend upon labyrinthine dimensions and the physical properties of the endolymph. The dimensions of the semicircular canal, duct and ampulla in cat, guinea pig and man were determined from measurements of magnified sections of decalcified temporal bones. Estimates of the effect of shrinkage were obtained from measures in fresh material and it appears shrinkage is probably only a fairly small factor. The dimensions so obtained were used to provide new estimates of the short time constant and other mechanical parameters of the torsion pendulum model in the three species.

Animals↗
PubMed1977

Ocular accomodative changes in humans induced by positional changes with respect to gravity.

Ocular accomodation was measured in human subjects while they were rotated at 1 degree/sec about their naso-occipital axes. Sixteen normal subjects were tested with 45 complete and 27 partial revolutions. Naso-occipital rotations ipsilateral to the eye being observed caused accommodative, lens-thickening changes. This effect begin at about 14 degrees from head upright position, tended to reach a maximum by 45 degrees and usually stayed at this level until about 90 degrees. The values tended to return to control level by 180 degrees. With naso-occipital roll in the direction opposite to the eye being observed, there was little change until about 135 degrees at which point further roll was typically clear accomodation. This continued to a maximum at about 270 degrees rotation, and at about 350 degrees returned to control values. Arguments are presented relating this response to the utricles, which are approximately parallel to earth horizontal. The threshold of this response, between 3.7 and 77 cm/sec2, is similar to the threshold of linear acceleration when measured by other means.

Accommodation, Ocular↗
PubMed1976

Present morality in parkinson's disease: the ratio of observed to expected deaths with a method to calculate expected deaths.

Excess mortality, i.e. more deaths than expected in a similar normal population, has been reduced in Parkinson's disease by levodopa. A California series and a large collaborative study throughout the United States show the ratio of observed to expected deaths to be normal. In contrast, a New York study was similar patients and a Montreal group of much more severely disabled patients showed greater mortality. The reasons for these differences are unclear, but some variations in results may be attributed to different methods of calculating expected deaths to derive the ratio of observed to expected deaths.

Age Factors↗