Cardiac risk assessment: when and who? [Retrospectroscope].

Think about the above lines taken from the Old Testament: At 130 years of age, Adam begat a son and at 800 he kept going, quitting this earthly life at 930. These numbers surpass by far the limits our current experience teaches us, however, perhaps a life span into the hundreds of years is ? What if, in the future, science were to do away with disease? What then would cause people to die: accidents, killings, wars? How old would old age be? Aging has always been a hot topic for research (with considerable quackery, too). For example, animals with a slow metabolism tend to live longer than those with a fast metabolism. Compare the average life span of a mouse with that of a turtle. Apparently, meditators are able to slow their metabolism down [1].

The development of biomedical engineering.

This paper discussed how the bioengineering and medical engineering started in Argentina.

Arm EMG during abduction and adduction: hysteresis cycle.

The electromyographic study of the muscles involved in the complex movements of the shoulder, is usually one way to quantifying the static and dynamic joint's behavior. In particular, the deltoid medium EMG produced a phenomenon similar to a hysteresis cycle when its amplitude was plotted as a function of the lateral angular position during a static, step by step, sequential abduction-adduction of the arm. Such a cycle was consistently repeated in 16 subjects (12 males and 4 females). The paired Student t-test, after comparing the mean EMG values of the rectified wave for the same arm opening angle between abduction and adduction, produced a highly significant difference (alpha<0.001) in all subjects. In all likelihood, it manifests the participation of muscles other than the deltoid medium in the overall movement (as for example, the anterior and posterior deltoids), that is, they are collaborating muscles that are different in the opening or lifting of the arm from those involved in its closure or lowering. Thus, it is concluded that a quantifiable and significant deltoid medium EMG difference has been demonstrated when the muscle is either ready to abduction or ready to adduction. The effect is fully reproducible between 0 and 90 degrees of an arm in static position within the scapular plane.

Propagation velocity measurement: autocorrelation technique applied to the electromyogram.

Muscle fibre conduction velocity is an important measurement in electrophysiology, both in the research laboratory and in clinical practice. It is usually measured by placing electrodes spaced at known distances and estimating the transit time of the action potential. The problem, common to all methods, is the estimation of this time delay. Several measurement procedures, in the time and frequency domains, have been proposed. Time-domain strategies usually require two acquisition channels, whereas some frequency-domain methods can be implemented using a single one. The method described operates in the time domain, making use of the autocorrelation function of the difference signal obtained from two needle electrodes and only one acquisition channel. Experimental results were obtained from the electromyogram of two biceps muscles (two adult male subjects, nine records each) under voluntary contraction, yielding an average of 3.58 m s(-1) (SD=0.04 m s(-1)) and 3.37m s(-1) (SD=0.03 m s(-1)), respectively. Several tests showed that the proposed method works properly with electromyogram records as short as 0.3 s.

Medium and interface components in impedance microbiology.

Classic impedance microbiology (CIM) is based on the measurement of the impedance components that appear between a pair of electrodes submerged in a cell containing inoculated broth. Either a bipolar or a tetrapolar technique can be applied, requiring about 1 x 10(3) to 3 x 10(7) cells/ml to produce detectable changes in the impedance curves. Theoretical analysis of the electrode-electrolyte interface during bacterial growth is lacking, with no generally accepted measuring standards. Besides, there is considerable disagreement. We separated out the interface and medium components using the frequency variation technique (FVT) and also analyzed the interface reactance-resistance diagram, both before and after bacterial growth. Medium resistance Rm, interface reactance Xi, and interface resistance Ri, were quantified as time functions growth curves, from the complex bipolar impedance seen between two electrodes. We took into account the electrical current density, the temperature and the associated circuitry, also explaining the theoretical and experimental bases that justify the proposed dissecting procedure. It was found that, within the working frequency range, Rm, Ri, and Xi percental growth curves are frequency-independent, i.e., neither Rm(f), nor Xi(f) nor Ri(f) changed their slopes before, during and after bacterial growth. Besides, no alpha-dispersion effect in Rm curves was detected. It is concluded that impedance microbiology could become a fertile area for interdisciplinary knowledge; its development might offer new avenues for basic and applied research.

Parallel conductance determination in cardiac volumetry using dilution manoeuvres: theoretical analysis and practical implications.

Left ventricular volume calibration based on the conductance catheter depends on the correct determination of the parallel conductance (Gp). Baan's saline manoeuvre procedure leads to Gp by finding the end-systolic (Ges) and end-diastolic (Ged) conductances, for each beat of the dilution curve rising limb. After plotting such values in an xy-system, their linear regression is back-projected to intersect the identity line, so yielding an estimated Gp. The objective is to theoretically analyse all possible lines, Ges = aGed + b (Baan's line) and, based on experimental results, to establish their limitations. This was attained by calculating the regression lines using, first Ged = f1(Ges) and thereafter, Ges = f2(Ged), which led to two values, Gp2 and Gp1, for the parallel conductance. The morphology of the saline curve was also modified to assess its effect on the extrapolation. Multiple dilutions were recorded in eight experimental dogs injecting different concentrations. Each curve was classified according to the maximum change (VAR) reached by the total average conductance. Over 138 manoeuvres, 276 regressions were processed yielding correlations higher than 0.65. Of this total, 92.4% gave positive parallel conductances. The rest produced negative values and, thus, were neglected. If the two (Ged, Ges) statistical relationships were ideal, they should yield Gp = Gp1 = Gp2; however, there were differences which, when Gp1 was studied against Gp2, led to: Gp1 = 0.97 Gp2 + 0.055, with r = 0.9476, and n = 85. The remaining 53 were discarded because either some Gp values were negative, or the correlation of Ges which Ged (or vice versa) was < 0.85, and/or VAR < 15%; the two latter conditions were found necessary for reliable calibration. Baan's line high correlation is not a unique condition to ensure the accuracy and precision of Gp determination because the slope a depends on VAR and, thus, different intersections with the identity line may be obtained. Its recommended that manoeuvres be used with at least eight data points, with VAR > 15% and, finally, with (Ges, Ged) correlation better than 0.85. Theoretical analysis of Baan's line offers a reference frame, which contains only a limited number of practical possibilities.

Parallel conductance estimation by hypertonic dilution method with conductance catheter: effects of the bolus concentration and temperature.

The conductance catheter has gained momentum since its introduction in cardiovascular dynamics back in 1980. However, measuring errors are still blurring its clinical acceptance. The main objective here was to study the effects of the injected saline concentration and temperature on the evaluation of the parallel conductance, Gp, and thus, on the correction volume Vp. That conductance, Gp, and its associated volume, Vp, were computed using 167 saline dilution curves obtained with boluses at different concentrations and temperatures, injected in seven anesthetized closed-chest dogs. The excursion of the total conductance relative to the steady-state value during a saline maneuver showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive maneuvers, at 6-M concentration and at body temperature; therefore, the method acted as its own reference. The variation of Vp relative to the reference value was clearly dependent on the injected concentration and on its temperature; dispersion was greater at 22 degrees C than at 40 degrees C. The variability would recognize also other causes, such as uncertainty of the extrapolation procedure and the thoracic redistribution of electrical field lines. As conclusion, it is recommended to characterize each maneuver by its concentration and temperature. Body temperature and 6-M concentration appear as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the Vp estimation procedure in order to minimize errors. The variability of Vp, in different experimental conditions, demonstrated that both concentration and temperature are additional parameters that may modify the Gp estimate.

Impedance microbiology: quantification of bacterial content in milk by means of capacitance growth curves.

The impedancimetric method is a technique for the rapid evaluation of milk bacterial content and also of its subproducts. Several authors have made use of culture conductance changes during bacterial growth for quantitative and qualitative assessments of microbial growth. However, interface capacitance curves, Ci, have not been used. In this paper, we quantify bacteria in cow raw milk by following their growth as the above-mentioned capacitance change time course event. With it, bigger growth variations, shorter detection times and a better coefficient of correlation with the plate count method were obtained than those yielded by conductance curves. Calibration was performed by plotting initial known concentrations, IC (CFU/ml), as a function of the time detection theshold (TDT).

Automatic on-line analyser of microbial growth using simultaneous measurements of impedance and turbidity.

An apparatus for the measurement of bacterial growth is described. The instrument applies alternate adequate sequential currents of two different frequencies through a pair of electrodes immersed in a cultured medium. It monitors, detects and quantifies the growth of micro-organisms based on the measurement of the impedance across the two electrodes and, simultaneously, it measures the variation in the medium turbidity. The medium conductivity and the interface electrode impedance changes can be extracted from the measured impedance. The variations in turbidity can be calibrated in absorbance or optical density units. Moreover, all these parameters are also proportional to bacterial proliferation. The computer-controlled apparatus processes and displays the parameters on a monitor showing bulk resistance, electrode impedance and turbidity changes as time course events. The equipment can detect aerobic or anaerobic micro-organisms and permits the operator simultaneously to assess impedance and turbidity, or it can produce each parameter as a separate event. Time growth curves of different micro-organisms are presented in the results.

Codman's paradox of the arm rotations is not a paradox: mathematical validation.

Movement of a straight arm centred at the shoulder joint in three successive 90 degrees rotations, each around the respective orthogonal coordinate axis, leads to an apparently unrelated 90 degrees rotation around the longitudinal arm axis. This empirical fact is known as Codman's paradox, after a Bostonian surgeon who first reported it in 1934. However, by means of homogeneous coordinates, it is herein demonstrated that the phenomenon is just a mechanical property mathematically described by the equivalence between the matricial product of three orthogonal rotation matrices applied to a position vector and the matricial product of a single rotation matrix applied to the same vector. The latter rotation matrix corresponds to the middle one in the former group of three. When polar coordinates are used, the demonstration is even simpler, for the total shift vector clearly shows a single net effect on the longitudinal axis rotation. Thus, Codman's paradox is not a paradox. This property improves the muscle dynamics arm knowledge and might find applications in robotics.

Bioelectrical impedance techniques in medicine. Part I: Bioimpedance measurement. First section: general concepts.

After a brief historical overview, the concept of electrical impedance is introduced as a principle of transduction calling attention to the possible mechanisms by which a physiological event may change impedance, i.e., by geometric, resistivity, and/or permittivity changes. Thereafter, since impedance measurements usually require the injection of current, its biological effects are discussed in order to establish the safety criteria. Finally, the elements found in an impedancimetric circuit and their respective nature are presented and described. The particular behavior of the biological impedance and the electrode/electrolyte interface appear immediately as strikingly important. The section ends with a bird's-eye view of the basic circuitry to measure impedance. Each subsection is closed by partial conclusions to underline the relevant concepts.

Bioelectrical impedance techniques in medicine. Part II: Monitoring of physiological events by impedance.

The measurement of a physiological event caused by a change in dimension, conductivity, or permittivity can be easily carried out by the impedance technique, requiring only the application of two or more electrodes, which are easy to apply. In some cases, the impedance is transformed into its resistive and reactive components, in others the total impedance is measured. In certain cases only a change in impedance, with or without separation into its components, contains enough information to be correlated to the physiological event. Recent measurements of physiological data by impedance techniques have reemphasized the value of the painless and harmless acquisition from human and animal subjects in such diverse domains as manned spacecraft, nutrition, and electrical impedance imaging. This part attempts to present all the numerous experiments performed on humans to estimate changes in volume, orientation, and distribution of fluids and tissues accompanying physiological activity. The main sections concern the respiratory system, the cardiovascular system, the brain, the total body impedance, muscle and skin impedance, and bacteriometry.