Percentage Of Amplitude Research Articles

Subcortical correlates of the auditory brain stem potentials in the monkey: bipolar EEG and multiple unit activity responses.

Bipolar EEG and multiple unit activity (MUA) responses correlated to the vertex auditory brain stem potentials (ABSP) were recorded in different brain stem and diencephalic primary auditory pathways and other anatomically related structures of large monkeys under barbiturate anesthesia. Bipolar EEG responses were recorded bilaterally to monaural stimulation and were formed by 3 or more of 6 consecutive components labeled A, B, C, D, E and F (peak latencies of 3.8, 4.2, 4.6, 5.0, 7.8 and 11.8 msec) correlated in latency with waves III, IV, V, VI, VII and SP3 of the ABSP, respectively. Component B was prominent and showed clearcut reverse polarity at the trapezoid body (TB) and superior olivary complex (SOC), while components C and F inverted and everted polarity at the mesencephalic reticular formation (MRF) and medial geniculate nucleus thalami (MG). Subcortical MUA peaks A, B, C, D and E time locked to the stimulus presentation correlated in latency to those of the bipolar EEG responses. In addition, a significant correlation was found between percentage amplitude of the subcortical EEG response components and MUA peaks in different structures contra- (r = 0.847) and ipsilateral (r = 0.973) to the stimulated ear. Although a single wave of the vertex ABSP correlated in latency with more than one response component in different subcortical loci, amplitude of component A was significantly larger (P less than or equal to 0.02) at TB ipsilateral, B at TB and SOC bilateral, and C and F at MRF, and D and E at MG contralateral to the stimulated ear.

Pentobarbitone interference with inhibitory synaptic transmission in crayfish stretch receptor neurones.

1. The effect of pentobarbitone (PB) on GABA-ergic inhibition was investigated in the isolated crayfish stretch receptor. The soma of the slowly adapting neurone was impaled with two micro-electrodes to give an accurate determination of membrane conductances. 2. Application of PB in concentrations from 10(-6) to 10(-3) M increased the rise time constant of the inhibitory post-synaptic potential (i.p.s.p.). The i.p.s.p. percentage amplitude and decay time constant were also increased in eight out of twelve neurones. On prolonged exposure, the percentage amplitude declined at a rate dependent upon the dose and the frequency of stimulation until the i.p.s.p. became undetectable. 3. The response to ionophoretically applied GABA remained essentially unaltered in the presence of PB, but the falling phase was prolonged by up to 8% in four of the ten neurones tested. Resting membrane conductance, i.p.s.p. driving force (i.p.s.p. reversal potential minus resting membrane potential), and parameters of the anti- and orthodromic action potential were not significantly affected. 4. Removal of PB after prolonged exposure usually caused an immediate increase in i.p.s.p. percentage amplitude but the i.p.s.p. rising phase remained slowed. 5. Application of excess extracellular GABA only affected the i.p.s.p. percentage amplitude after it had been reduced by PB. It transiently increased the attenuated i.p.s.p. percentage amplitude in the presence of PB, and after the removal of PB permanently increased the amplitude to its original value. 6. Nipecotic acid and cis-1,3-aminocyclohexane carboxylic acid, inhibitors of GABA re-uptake, slightly increased the i.p.s.p. percentage amplitude, and prolonged the falling phase but did not affect the rising phase. The percentage amplitude declined on prolonged exposure. 7. We conclude that PB has no electrophysiologically demonstrable post-synaptic action in the crayfish stretch receptor neurone, but it inhibits the presynaptic release and re-uptake of GABA.

Systolic and diastolic time intervals in young diabetics.

Systolic and diastolic time intervals were used to examine left ventricular performance in 22 young diabetic men (mean age 25 years) with no apparent clinical heart disease. Pre-ejection period index (PEPI), left ventricular ejection time index (LVETI), electromechanical systole index (QS2I), PEP to LVET ratio, the a wave percentage amplitude of the apexcardiogram (a/H5 ratio), the rapid filling wave (RFW), and the A2O interval were obtained in the conventional manner in 22 diabetics and 22 healthy men. The heart rate, diastolic pressure, PEP/LVET ratio, a/H per cent ratio, and A2O interval were significantly increased and LVET decreased in the diabetic group. QS2I, PEPI, and RFW did not differ from that in the normal group. Twenty-three per cent of patients had an abnormal systolic time interval, 54 percent an abnormal diastolic time interval, and 23 per cent had both abnormal intervals. Though these studies provide no difinite evidence of a cause, the abnormalities found may reflect a subclinical diabetic cardiopathy.

A neurological and biochemical study of early lead poisoning.

ABSTRACT Changes in nerve conduction velocity were found in 94 workers exposed to lead in a battery factory compared with 94 age-matched controls. There was no clinical evidence of nerve damage in the lead workers. The mean blood lead concentration in the 94 lead workers was 2·9 μmol/l (60 μg/100 ml) and their length of exposure to lead ranged from 6 months to 33 years. All mean maximum motor nerve conduction velocities (MMCV) measured were highly statistically significantly lower in the lead-exposed group when compared with their age-matched controls. Thus mean ulnar MMCV was 53·4 m/s in lead workers and 55·6 m/s in control subjects (p The amplitude of the muscle action potential produced by proximal stimulation of a nerve was expressed as a percentage of the amplitude of the muscle action potential produced by distal stimulation and the percentage amplitude thus obtained used as an indicator of the conduction velocity of slower fibres (SFCV). Peroneal nerve percentage amplitude of lead workers was statistically significantly lower (p There was no statistically significant correlation to indicate that progressive slowing of nerve conduction (MMCV and SFCV) was associated with increasing exposure to lead (as indicated by blood and urine lead concentrations) or with the commonly measured biochemical changes associated with disturbed haemopoiesis in lead exposure (δ-aminolaevulinic acid dehydrase; free erythrocytc protoporphyrin; haemoglobin and urinary δ-aminolaevulinic acid). MMCV of the ulnar nerve was the only conduction velocity statistically significantly correlated with length of exposure to lead. Increased length of exposure to lead was associated with a decrease in the ulnar MMCV. Only 13 of the subjects had been exposed to lead for two years or less and in none of them had the blood lead ever risen above 3·9 μmol/l (80 μg/100 ml) in three-monthly tests (mean blood lead concentration at time of testing: 2·8 μmol/l). In these subjects the MMCV of ulnar, radial, and peroneal nerves and the peroneal percentage amplitude were statistically significantly reduced. The results from this group suggest that the onset of nerve conduction changes occurs within two years and at concentrations of lead in blood of less than 3·9 μmol/l (80 μg/100 ml).

Use of apexcardiography in the assessment of myocardial function in aortic stenosis

Twenty-three patients with pure or predominant aortic stenosis were studied by simultaneous high-fidelity apexcardiographic and left ventricular pressure tracings as well as by cineangiographic measurements. Apex tracings were recorded additionally in 153 healthy subjects. The systolic upstroke time (SUT) of the apexcardiogram was significantly prolonged in the patients with decreased left ventricular function and separated these patients from those with normal function. Furthermore, SUT correlated significantly with angiographic ejection fraction as well as with contractile indexes derived from isovolumic pressure measurements, i.e., maximal value of left ventricular pressure rise and peak measured velocity of shortening of the contractile elements. Thus, the SUT is an indicator of the extent of interpatient differences in left ventricular function. In contrast, the time from the onset to the peak of the first derivative ( t-dA dt ) and the A wave percentage amplitude to total vertical height ( A H ) of the apexcardiogram were not sensitive in detecting impaired myocardial function, the former being, however, significantly correlated to the ejection fraction and the latter to the end-diastolic pressure of the left ventricle. These data demonstrate the superiority of the SUT as an index of myocardial function over the other apexcardiographic parameters. The usefulness of SUT is further enhanced by the simplicity of its measurement and its independence from the extent of chronic pressure overload as well as severity of the aortic stenosis. However, the validity of SUT for assessing changes in the contractile state of the left ventricle requires further investigation.

The Austin Flint murmur and the a wave of the apexcardiogram in aortic regurgitation.

Hemodynamic data from 45 patients with either aortic regurgitation (with and without the Austin Flint murmur) or aortic regurgitation and mitral stenosis were correlated with the a -wave percentage amplitude of the apexcardiogram. Changes in the a wave correlated well with corresponding changes in left heart pressures but not with variations in volume. Of 15 patients in whom the ratio of the a wave to the total excursion during systole ( a /H ratio) was [See Equation in PDF file]13%, 11 had left ventricular end-diastolic pressures (LVEDP) >20 mm Hg. All patients with a /H ratios >15% had abnormal LVEDP. The converse was not true; 13 patients had elevated LVEDP with normal a /H ratios. Patients with aortic regurgitation and mitral stenosis had a /H ratios similar to those of normal subjects. The Flint murmur showed a significant correlation with left ventricular volume changes. Its presence was valuable in prediction of a large regurgitant volume and a high left ventricular stroke volume. It was also present in association with elevated left atrial mean pressure and elevated LVEDP. Thus, two ancillary findings in aortic regurgitation, a high a wave in the apexcardiogram and the Austin Flint murmur, are of value in anticipating alterations in left ventricular hemodynamics as determined by left-sided catheterization and volume studies.

The Use of Apexcardiography in the Assessment of Left Ventricular Diastolic Pressure

A total of 58 observations of simultaneous left ventricular pressure and apex-cardiograms (ACG) was made on 18 patients. An a wave percentage amplitude (aWPA) of greater than 15% of the total deflection of the ACG indicated an increase in left ventricular end-diastolic pressure (LVEDP). In 12 observations on six patients, an aWPA of less than 15% was associated with a high LVEDP. Patients with high LVEDP and aWPA of less than 15% had a high early left ventricular diastolic pressure with further rise in pressure prior to atrial contraction. These patients had small LV a waves ("atrial kick"). The aWPA of the ACG correlated better with the magnitude of the LV a wave than the absolute level of LVEDP in all patients. Correlation was good between changes in aWPA and changes in LVEDP in individual patients; but the ACG as an indirect means of evaluating left ventricular function is limited by the fact that elevations in LVEDP can exist in the presence of a normal aWPA. The ACG is a complex tracing reflecting not only intracardiac pressures, but changes in left ventricular volume, compliance, position, and perhaps left atrial function as well.

A comparative study on pulsatile intracerebral impedance and rheoencephalography

Intracerebral pulsatile impedance was compared with the bipolar rheoencephalogram (REG) and extracranial subcutaneous tissue impedance. The investigations were carried out in man during stereotaxic surgery or through implanted steel wire electrodes. The following observations were made. 1. 1. The timing of the intracerebral impedance wave varied slightly in different parts of the brain, but it differed clearly from that of the REG wave: its descending phase started later than that of the REG and lasted almost twice as long. REG and extracranial impedance waves resembled each other in timing. 2. 2. The percentage amplitude of the intracerebral impedance wave was 20–50 times as large as that of the REG and extracranial impedance. 3. 3. The intracerebral base line impedance normally oscillated with a frequency of 2–3/min, while the base line impedance in REG and extracranial impedance was very constant. 4. 4. Intracranial hypertension was associated with a delayed, paradoxical, intracerebral impedance wave, whereas the REG and extracerebral impedance were normal in the same patients. All these findings constitute strong evidence that REG does not reflect intracerebral impedance and circulation.

Changing Structural Factors in Canada's Cyclical Sensitivity, 1903-54

An earlier paper examined changes in Canadian sensitivity to United States business fluctuations. The evidence suggested that this sensitivity may have declined from the ten years preceding the First World War to the twenties, and that it undoubtedly declined between the twenties, on the one hand, and the thirties and post-war period on the other. Changes in sensitivity were measured by changes in the average percentage amplitude of fluctuations in Canadian output indicators associated with given percentage fluctuations of the corresponding United States indicators. The changes in sensitivity observed in this way were very small, but the decline from the twenties to the thirties and the post-war period was statistically significant.The present paper attempts an explanation of these findings by examining changes in structural factors that can be assumed to have influenced Canada's cyclical sensitivity. Most of these factors have been frequently discussed by Canadian economists.Since exports are a major channel for the transmission of cyclical fluctuations (indeed, in the thinking of many economists they appear to be the only channel), and since United States business conditions influence, directly and indirectly, Canadian exports to all countries, the sensitivity of total Canadian exports to United States business fluctuations must be examined. Since the United Kingdom has been a major market for exports, the influence of its business fluctuations on the relation between United States and Canadian fluctuations is also relevant.