Computer aided data acquisition and analysis of acetlycholinesterase velocity sedimentation profiles.

Acetylcholinesterase (AChE) is an enzyme that appears in several molecular forms. Individual AChE molecular forms can be isolated and identified on the basis of their velocity sedimentation profiles. We have improved an existing method for analyzing AChE sedimentation profiles with a computer aided data acquisition and analysis system. The software facilitates measurements of AChE activity of individual molecular forms and comparison among AChE velocity sedimentation profiles. In practice, our program increased precision and reduced the time of AChE velocity sedimentation profile analysis. The software can also be applied to velocity sedimentation analysis of other proteins. We plan to upgrade the program by making it compatible with Microsoft Windows.

Pressure sensitivity of flow oscillations in postocclusive reactive skin hyperemia.

Skin blood flow was monitored using a laser-Doppler (LD) flowmeter in 21 healthy volunteers after an occlusion of the digital arteries. The peripheral vascular bed was exposed to occlusion ischemia of varying duration (1, 4, or 8 min) and to a change in digital arterial pressure produced by different positions of the arm above heart level to characterize the pattern of LD flow oscillations in postocclusive reactive hyperemia (PRH) and to elucidate the relevance of metabolic and myogenic mechanisms in governing its fundamental frequency. The descending part of the hyperemic flow was characterized by the appearance of conspicuous periodic oscillations with a mean fundamental frequency of 7.2 +/- 1.5 cycles/min (SD, n = 9), as assessed by a Fourier transform frequency analysis of 50-s sections of flow. The mean respiratory frequency during the periods of flow frequency analysis was 17.0 +/- 2.2 (SD, n = 9), and the PRH oscillations remained during apnea in all tested subjects. The area under the maximum flow curve increased significantly with prolongation of the occlusion (paired t test, P < 0.001; n = 9), but showed no dependence on the estimated blood pressure in the digital arteries, which suggests the predominant role of a metabolic component in this part of the PRH response. In contrast, the fundamental frequency of PRH oscillations exhibited a significant decrease with a reduction in the estimated digital arterial pressure (linear regression, b = 0.08, P < 0.001; n = 12), but did not change with the prolongation of arterial occlusion despite a significant increase in mean LD flow (paired t test, P < 0.001; n = 9).(ABSTRACT TRUNCATED AT 250 WORDS)

The voltage-clamp apparatus assisted by a 'current pump'.

A current pump is described, which is attached to the last stage of the 2-microelectrode voltage-clamp apparatus. Thus a voltage-to-current conversion independent of the impedance of the current microelectrode is obtained. In this way it is possible to pass relatively large currents through the current microelectrode and in the same time to have a stable negative feed-back system.

Dynamic characteristics of the thorax connected with the heart action.

We determined the indices of local vibrations (resonance frequency, damping coefficient, stiffness constant, extinction time) and transfer function H(s) . 10(-6) for three somatotypes and three respiratory positions on 88 points of the thorax. The examinees were males (age 21 years). We found the resonance frequencies of 36.86--54.75 cps, damping coefficient (delta) 0.121--0.217. This means the damping is less than critical (delta = 1). We applied shocks (a force of 2 N) with a reflex hammer on 88 points of the thorax. The force diminished from the exciting place (say ictus) to the recording place (accelerometer on the sternum) from 2 to 0.2 N. The athletic type has the highest resonance frequency and stiffness constant; the leptosomic type has the highest damping; the longest extinction time belongs to the pyknic type. The pyknic type has also the highest value of the transfer function. The respiratory position (quiet respiration, Valsalva and Müller experiment) influences the values of the indices of local vibrations and of the transfer function. The influence is evident especially on the intercostal points: the transfer of the oscillations is alleviated at a higher stiffness of the thorax (Valsalva; the value of H(S) . 10(-6) rises from 7.00 to 9.39 sec2), it deteriorates at a small stiffness of the thorax (in Müller's experiment falls to 2.78 sec2). With the fall in the intrathoracic pressure the damping in the intercostal points decreases. On the basis of experiments the conclusion was made that a short testing of the thorax of an examinee will give the dynamic characteristics of the thorax (indices of local vibrations and transfer functions) of the individual. This procedure will alleviate the quantitative use of noninvasive mechanical methods in the assessment of the cardiovascular function.

Further observations on modelling of the cardiovascular function in the electrical model.

In 1976 the fourth type of the electrical model of the cardiovascular function was constructed, showing formal and electronic changes: inverting system, hysteresis comparator (for the valve function), simulation of the insufficiency and the stenosis of the valves. The analog values were established but they are not yet definitive. The important values are: pressure 100 mm Hg = 100mV; flow 100 ml/sec = 137 microA. The action of the heart is given by changing capacity; the contractility is characterized by systolic capacity (CS). The diastolic capacity (CD) is not yet variable (CD = 4,000 microF) and consequently the diastolic pressure is always near to zero. The pressure curves of the left ventricle and of the aorta of cardiac patients with aortic valve disease were simulated. For comparison purposes only two clinical records and electrical model simulation records are given in this paper. In the patients (only aortic stenosis is given here) left heart catheterization was carried out. A case of coronary heart disease is also shown. The curves (simulated) are satisfactory and reflect the events in the compression chamber. The values of the parameters, which were used in the stimulation, represent the analysis of the clinical curves and a functional characterization of the situation. Besides these simulations the effect of valve changes on the pressure in the left ventricle, aorta and large arteries was also studied. With the aim of extending the integrative view of the use of the electrical model, an attempt of comparing the time course of capacity changes and the time course of inner surface changes of the left ventricle was made. The cinecardioangiographic data, obtained in an invasive way, were used for the purpose of obtaining the inner surface of the left ventricle. From pressure and surface data the cardiac forces (isometric, average and also total force per minute) were calculated and compared with the normal state, taken from the literature. The total force per minute includes the sum of systolic durations per minute and characterizes the energy expenses of the heart. Further data must be obtained by different cardiographic techniques in order to obtain a solid basis for the use of indirect methods, where the electrical model would be helpful as a noninvasive integrative tool in the assessment of the cardiovascular function.