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Biomedical subjects

B Conrad

Publications and source records attributed to B Conrad.

At least 127 records · Page 7Linked to original sources
PubMed1992

Imprecise excision of plasmid pE194 from the chromosomes of Bacillus subtilis pE194 insertion strains.

Plasmid pE194 has been shown to be rescued by integration after cultivation of infected Bacillus subtilis recE4 cells at a restrictive high temperature. The plasmid is also spontaneously excised from the chromosome at a low frequency by precise or imprecise excision (J. Hofemeister, M. Israeli-Reches, and D. Dubnau, Mol. Gen. Genet. 189:58-68, 1983). We have investigated nine excision plasmids, carrying insert DNA 1 to 6 kbp in length, either in a complete pE194 or in a partially deleted pE194 copy. Type 1 (additive) excision plasmids have the left- and right-junction DNAs preserved as 13-bp direct repeats (5'-GGGGAGAAAACAT-3') corresponding to the region between positions 864 and 876 in pE194. In type 2 (substitutive) excision plasmids, a conserved 13-bp sequence remains only at the right junction while the left junction has been deleted during the excision process. The type 3 excision plasmid carries at each junction the tetranucleotide 5'-TCCC-3', present in pE194 between positions 1995 and 1998. Although we isolated the excision plasmids from different integration mutants, the insert DNAs of eight independently isolated plasmids showed striking sequence homology, suggesting that they originated from one distinct region of the B. subtilis chromosome. Thus, we postulate that imprecise excision of pE194 occurs most frequently after its translocation from the original insertion site into a preferred excision site within the host chromosome. The imprecise excision from this site occurs at excision breakpoints outside the pE194-chromosome junctions in a chromosomal region which remains to be investigated further.

Bacillus subtilis↗
PubMed1992

Assessment of intracranial hemodynamics in sleep apnea syndrome.

BACKGROUND AND PURPOSE: Sleep apnea syndrome may lead to changes in cerebral hemodynamics due to altered alveolar ventilation. We investigated the dynamics of CO2- and blood pressure-regulated alterations of cerebral blood flow velocities during apneic episodes and evaluated CO2 reactivity during different sleep stages. METHODS: A computer-assisted pulsed Doppler system (2 MHz) was used for continuous overnight recordings of middle cerebral artery flow patterns together with simultaneous polysomnography, continuous blood pressure recordings, and measurements of end-expiratory CO2 in six patients with sleep apnea syndrome. RESULTS: Increases in mean flow velocity of 19-219% and in blood pressure of 12.5-83.1% could be observed during the apneic episodes, with maximum increases during rapid eye movement (REM) sleep. CO2 reactivity was in the normal range (4.4 +/- 1.2%) in the waking state and was markedly increased during sleep stages 1 and 2 (p less than 0.005 compared with awake). The greatest increase was found during REM sleep, with a rise of up to three times the waking value (p less than 0.0001 compared with sleep stage 2). CONCLUSIONS: The changes of mean flow velocity could be interpreted as reactive adaptation processes because of CO2 and blood pressure increases corresponding to apnea. The increased CO2 reactivity during sleep may indicate a "hypersensitivity" of intracranial vascular CO2 or pH receptors and a disturbance of central catecholaminergic and cholinergic systems. The pronounced velocity changes during apneic episodes and the concomitant alterations of vessel wall tension might lead to microangiopathies and macroangiopathies due to chronic strain on the brain vessels.

Adult↗
PubMed1992

Increased F-wave duration in patients with spasticity.

F-wave responses of the posterior tibial nerve have been studied in 22 patients with spasticity and in 18 normal control subjects with surface EMG. Mean amplitude and mean duration of the F-waves were significantly (p less than 0.001) longer in patients with spasticity than in healthy controls. These findings could be the result of an enhanced spinal excitability in spasticity. Based on the present results F-wave recording may be used as a simple and practical technique for detection and documentation of spasticity.

Adult↗
PubMed1991

Do brief bursts of spike and wave activity cause a cerebral hyper- or hypoperfusion in man?

The correlation between brain activity and cerebral blood flow velocities during brief bursts of generalized spike and wave activity was analysed by simultaneous registration of the EEG and the intracranial flow patterns. The flow patterns of the middle cerebral artery were continuously recorded by means of transcranial Doppler ultrasonography using a specially developed monitoring system. A total of 25 bursts was investigated in 3 patients with spontaneous occurrence of generalized 3 Hz spike and wave activity and normal background EEG. Characteristic changes of the flow patterns were found in all cases: 3.41 +/- 0.98 s (n = 25) after the beginning of generalized spike and wave patterns, the flow velocity decreased by 25.84 +/- 10.45% (n = 25) below the 'preictal' flow velocity level. The period of flow velocity changes lasted several times longer than the phase of spike and wave activity.

Adult↗
PubMed1991

Abnormal conduction in corticospinal pathways in Wilson's disease: investigation of nine cases with magnetic brain stimulation.

Electromyographic (EMG) responses evoked by transcranial magnetic brain stimulation were studied in nine patients with Wilson's disease (WD). Six of the nine patients had prolonged central motor latencies (CMLs), reduced amplitude, or absent responses in at least one of the examined muscles. In one patient, abnormal EMG responses normalized following treatment with penicillamine. Pathophysiologically abnormal EMG responses might result from a potentially reversible impairment of corticomotoneuronal pathways and/or a reduced excitability of motoneurons due to basal ganglia dysfunction. The possible pathophysiological mechanisms are discussed.

Adult↗
PubMed1991

Is there an age-dependent continuous increase in the duration of the motor unit action potential?

The duration of the motor unit potential plays an important role in the diagnosis of neuromuscular diseases, but is also subject to physiological variations. In order to evaluate the age-related changes the mean motor unit potential duration was studied in 4 proximal and distal muscles of the upper and lower extremities in 111 healthy subjects between 20 and 80 years. Contrary to the results of previous researches no marked increase of mean duration could be found in subjects younger than 55 years. Subjects older than 55 showed a slight tendency towards increased duration of the motor unit potential. These findings are interpreted as the result of changes in fiber density and are in accordance with single fiber EMG records.

Action Potentials↗
PubMed1991

Lack of hyperlipidemia in carpal tunnel syndrome.

115 females with a definitive diagnosis of a carpal tunnel syndrome (CTS) are compared with a corresponding age-matched group of healthy females with regard to their lipidemic parameters. The incidence of hyperlipoproteinemias in CTS patients was equal to that in the control group so that hyperlipoproteinemia is unlikely to be a probable cause of the entrapment syndrome. A statistically significant increase in the level of alpha-lipoprotein (high-density lipoprotein) was found which cannot be readily explained.

Adult↗
PubMed1991

Cerebral vasospasm evaluated by transcranial Doppler ultrasonography at different intracranial pressures.

The present study evaluates the interdependence of clinical stage, cerebral vasospasm, intracranial pressure (ICP), and transcranial Doppler ultrasonographic parameters. The mean flow velocity of blood in the middle cerebral artery and the index of cerebral circulatory resistance as a measure of the peripheral vascular flow resistance were determined in 76 patients with spontaneous subarachnoid hemorrhage. The ICP was measured using an epidural transducer in 41 patients. There was no case in which both high ICP and a high mean flow velocity were observed simultaneously. The investigations led to the following conclusions. 1) In patients with a resistance index of less than 0.5, changes in the mean flow velocity seem to reflect sufficiently the actual severity and time course of vasospasm. 2) During the time course of vasospasm, an increase in the resistance index above values of 0.6 with a simultaneously decreased mean flow velocity indicates a rise in ICP rather than a reduction in vasospasm. 3) With a pronounced increase in ICP, evaluation of the severity and time course of vasospasm by transcranial Doppler ultrasonography based solely upon the mean flow velocity can lead to false-negative results.

Adult↗
PubMed1990

A magnetic measurement device for the kinematic analysis of unrestrained human hand movements.

A magnetic measurement device is described which was constructed to study human hand- and finger-movements. The system overcomes some problems frequently arising in the study of finger grip movements. It allows the simultaneous recording of several positions which cannot be observed with optical devices because they are hidden by other parts of the limb. Trajectories are recorded using small receiver coils moving in an alternating magnetic field of 3 transmitter coils. The performance of subject's movements is not significantly disturbed. A high sampling rate and a lack of mechanical damping permit a high temporal resolution which can analyze rapid movements. Subjects are not exposed to any biological risk or discomfort. Thus, a recording session can be repeated numerous times. The results obtained from this type of apparatus may allow quantification of the course of progressing diseases and to study the effects of remediation.

Electromagnetic Fields↗
PubMed1990

[Extensive, continuous fasciculations of the lower leg as an isolated symptom--a clinical and electromyography follow-up].

10 patients suffering from a widespread continuous fasciculation of the lower extremities without any other neurological signs and symptoms are presented. A follow up study of 6 of these patients could be done. The fasciculation potentials were polyphasic with changing shape from discharge to discharge and appeared irregularly in most of the muscles of the legs. In 5 patients no change of clinical and neurophysiological signs could be detected over the period of observation, whereas in one patient a sensory polyneuropathy was evident in course of time. The findings illustrate that a state of widespread continuous fasciculations without other signs and symptoms is not predicative for the development of a amyotrophic lateral sclerosis.

Adult↗
PubMed1990

[Propofol infusion for sedation in regional anesthesia. A comparison with midazolam].

50 non-premedicated ASA class I or II patients were allocated randomly into two groups and received either a variable infusion of propofol or midazolam for sedation during orthopaedic surgery with regional blockade. To achieve a well-sedated patient with eyes closed and able to follow commands, the dose requirements for propofol were 1.25 mg/kg +/- 0.5 as a loading dose followed by a mean infusion rate of 3.17 mg kg-1 h-1 +/- 1.4 and for midazolam 0.073 mg/kg +/-0.02 and 0.074 mg kg-1 h-1 +/- 0.14. Steady-state plasma concentrations of propofol averaged 1.23 micrograms/kg +/- 0.75 and of midazolam 134 ng/ml +/- 62. Recovery was significantly shorter for propofol: 3.42 +/- 2.5 versus 8.05 min +/6.2 for midazolam. Perioperative cooperation was similar in both groups providing good or excellent conditions in 76% with propofol and in 52% with midazolam. 2h after discontinuation of the infusion 92% of the propofol patients were alert, while 36% of the midazolam were sleeping again. Cardiovascular effects of both drugs were minimal; however significant respiratory depression and/or airway obstruction developed in both groups (propofol 48%, midazolam 52%) requiring therapeutic intervention. Additional undesirable effects were: severe cough (propofol 40%, midazolam 20%), inadvertent movements (propofol 36%, midazolam 24%), confusion (propofol 24%, midazolam 20%), euphoria (propofol 44%), pain on injection (propofol 32%). The results of the study indicate that both drugs are useful and controllable sedative agents for surgery under regional anaesthesia, provided that measures for continuous monitoring of respiration and emergency care are guaranteed.

Anesthesia, Epidural↗
PubMed1989

Changes of transcranially evoked motor responses in man by midazolam, a short acting benzodiazepine.

The present study investigated the effects of midazolam, a short acting benzodiazepine, on muscle responses elicited by magnetic brain stimulation. During continuous midazolam infusion (0.3 mg/kg/h for up to 30 min) amplitudes and durations of transcranially elicited compound muscle action potentials decreased progressively while latencies remained unchanged. The results can be accounted for by midazolam enhancement of the inhibitory action of GABAergic cortical interneurons, which decreases the excitability of pyramidal cells and reduces the number of neurons available for generation of descending pyramidal tract activity.

Action Potentials↗
PubMed1989

Dynamics of regional cerebral blood flow for various visual stimuli.

Isotope tracer methods for measuring regional cerebral blood flow or metabolism do not provide data on the dynamics of the fast adjustment of local cerebral blood flow. Measuring intracranial flow patterns of the posterior cerebral artery by means or 2 MHz pulsed transcranial Doppler ultrasonography demonstrated that detailed dynamic effects of various visual patterns on local cerebral perfusion can be recorded, and that visual stimuli of different complexity as well as the strategy of stimulus perception cause distinct flow velocity changes in the occipital cortex involved in information processing. This type of on--line analysis may become a powerful tool for detecting fast autoregulatory mechanisms in relation to purely functional cerebral changes.

Adolescent↗
PubMed1989

Decay and recovery of the stapedial reflex by prolonged stimulation in the diagnosis of myasthenia gravis.

The decay and recovery of stapedial reflex amplitude was investigated in 19 patients with myasthenia gravis and 30 control subjects. In 9 untreated patients the amplitude was reduced to less than 10% of the initial amplitude following continuous stimulation for 120 s, whereas the maximum decay in the control subjects was only 50%. In the group of treated patients the reflex decay showed individual variations. The rate of recovery after prolonged stimulation (5 min) was slower in the patient group, especially within the first 30 s of recovery. With increasing age, the rate of decay rose in the patient group as well as in the control group. The technical parameters necessary for obtaining information of clear diagnostic value are indicated, with which it was shown that the continuous prolonged stimulation of the stapedial muscle is a practical and valid method for the evaluation of patients with myasthenia gravis.

Adolescent↗
PubMed1989

Effect of cannabinoids on spasticity and ataxia in multiple sclerosis.

The chronic motor handicaps of a 30-year-old multiple sclerosis patient acutely improved while he smoked a marihuana cigarette. This effect was quantitatively assessed by means of clinical rating, electromyographic investigation of the leg flexor reflexes and electromagnetic recording of the hand action tremor. It is concluded that cannabinoids may have powerful beneficial effects on both spasticity and ataxia that warrant further evaluation.

Adult↗