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Biomedical subjects

M E Valentinuzzi

Publications and source records attributed to M E Valentinuzzi.

At least 37 records · Page 2Linked to original sources
PubMed1984

Ventricular fibrillation threshold in the three-toed sloth (Bradypus tridactylus).

The ventricular fibrillation threshold (VFT) can be defined as the minimum electrical value able to trigger fibrillation. The objective was to determine the threshold fibrillatory current in the three-toed sloth, animal which may show spontaneous defibrillation. Ten specimens were used (average weight 3.9 kg, SD 0.28). Two electrodes of the spoon type were laterally applied to the ventricles, stimulating with a nonsynchronized train of rectangular pulses, variable amplitude, until fibrillation was established. Applied voltage and current were displayed on a storage oscilloscope. The average VFT current was 2.3 mA/g of heart (SD 0.4). Each threshold was obtained as the mid-range value between the maximum current which did not fibrillate and the minimum one which did fibrillate. Out of 98 fibrillations, 40% showed spontaneous reversal before 60 sec of fibrillation were completed. Beyond that time, electrical defibrillation was instituted. Three puppies (average weight 5.2 kg, SD 1.4) yielded an average VFT of 0.59 mA/g of heart (SD 0.14) using the same procedure. When the two VFT were compared (unpaired "t"-test), a significant difference was found (t 6.35; p less than 0.001), concluding that sloths would appear as more difficult to fibrillate than dogs of comparable body size.

Animals↗
PubMed1983

High-sensitivity, high-linearity, low-leak, self-balanced impedance cardiograph.

An impedance cardiograph (so-called cardioimpedance meter) with the following characteristics is described: preadjustable current generator range of 0-4 mA rms at 100 kHz, crystal-controlled; sensitivity up to 50 V/omega with a resolution of 2 m omega; maximum nonlinearity of 2%; 0.7 microA arms of maximum leak current at 50 Hz; flat frequency response between 0 and 19 Hz. The instrument is self-balanced, using Arenson's bridge [1] with minor modifications, and is also able to operate as a plethysmograph, respirograph, and as an intracardiac Z-meter. Preliminary test as an impedance cardiograph yielded a correlation coefficient better than 0.8 when the stroke volume was evaluated by Kubicek's method and compared with values obtained using thermodilution.

Animals↗
PubMed1983

Stroke volume in the dog: measurements by the impedance technique and thermodilution.

The main objective of this paper was to assess the efficacy of a laboratory prototype cardio impedance meter, to determine stroke volume in experimental dogs, using Kubicek's classic model. A second objective, complementary to the first, was to evaluate the method itself, under the carefully controlled condition in which cardiac frequency was increased from the initial to the final value. Measurements were performed on ten mongrel dogs (average body weight = 15.2 kg, SD = 4.7), employing the standard thermodilution procedure as reference. Based on a total of 179 determinations (about 18 per animal), the following regression equation was obtained: SVd = (0.36 SVz + 3.94) ml where SVd = stroke volume by thermodilution, SVz = stroke volume by impedance, with a standard error of the estimate SEE = 4.26 ml, a coefficient of variation CV = 32.8%, and 0.84 as correlation r. Thus, the impedance technique overestimated consistently by an average factor in the order of 2. These conclusions were made: In the experimental dog, the impedancimetric method can measure non-invasively directional and relative changes in stroke volume; this permits the effect of several types of maneuvres to be followed on a beat-to-beat basis. The lack of accuracy would require the development of a more sophisticated mathematical model; however, a practical statistical expression for laboratory use is easily derivable, making the determination as if the measurement had been made with the thermodilution procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Electrical defibrillation thresholds with transventricular simple-capacitor discharge under conditions of ischemia by acute coronary occlusion.

The threshold for cardiac defibrillation is defined as that intensity of electrical stimulation that results in a 50% probability of success. Using transventricular simple-capacitor discharge, peak current defibrillatory thresholds were determined under conditions of relative normothermia with ligation of the left descending coronary artery. The average value over 151 successful shocks in 15 dogs was 81.1 mA/g of heart (SD = 29.3). This value was compared by means of the unpaired Student's t-test with the average obtained in a control series, without occlusion, but keeping the same general procedure and experimental conditions (89.5 mA/g, SD = 32.8, 346 defibrillations, 20 dogs). The difference (t = 2.82) was significant at a level P less than 1%. In many cases, there were spontaneous refibrillations after successful discharges, or cardiac arrests which called for mechanical pacing. The latter, in turn, easily led to a new fibrillation, especially when contractility was impaired. When the analysis of variance was applied (Snedecor f-test), we found that the threshold value was stable with respect to time (f = 0.35) during the average experimental period (124 min, SD = 55). We concluded that, on the average, peak current defibrillatory threshold decreased because of myocardial ischemia; however, during the recovery stage, the ventricles showed a high level of instability. Both phenomena (lower threshold and unstable recovery) were probably related to alterations in cellular excitability.

Analysis of Variance↗
PubMed1981

Saline and thermal dilution flow measurements: evaluation by means of an open hydraulic model.

A simple open hydraulic model was constructed with the main objective of making comparative evaluations of flow rate measurements, with saline and thermal dilution. In the range of 0.5 to 3.5 l/min, it was found that saline indicator gave a slight underestimation (in the order of 2%) while the thermal indicator showed a minor overestimation of approximately 1%. These values wee taken from the regression equations F (saline) = 0.945 F (real) + 0.0351 and F (thermo) = 1.020 F (real) - 0.0144, both in l/min. Correlations were higher than 0.99 in the two cases. Considering the overall error range, the thermodilution produced a value approximately twice that of saline (-21 to 25% versus -12 to +11%). However, this is not necessarily extendable to living organisms. The model was found useful for test and calibration of detecting cells and for teaching purposes.

Mathematics↗
PubMed1980

Effect of body hypothermia on transventricular simple-capacitor-discharge defibrillation thresholds.

In 260 successful transventricular simple capacitor-discharge defibrillations performed on 20 mongrel dogs under conditions of body hypothermia, an overall average peak current threshold of 69.5 mA/g of heart (SD 30.4) was found. This value, when compared by means of the unpaired t test with previous data obtained under conditions of relative normothermia (89.5 mA/g of heart, SD 32.8, 346 defibrillations, 20 dogs) yielded a highly significant difference (P less than 0.1%). When comparing the deviation of the regression equation (current vs. temperature) from the horizontal line, the Snedecor F test gave also a high level of significance (P less than 1%). These results led to the conclusion that body hypothermia significantly reduces transventricular defibrillation thresholds. After normalizing the regression equations, this reduction was found to be on the average equal to 4.1%/degrees C (SD 1.4) for current and to 5.9%/degrees C (SD 1.4) for energy over the 20 dogs. In all animals, the coefficient of variation was greater for energy than for current (about twice as much), suggesting that current is a better descriptor of what is needed for electrical defibrillation. The transventricular impedance was rather constant, yielding an overall average of 28.5 omega (SD 6.0).

Animals↗
PubMed1978

[Respirometry by bipolar electric transthoracic impendance].

In a population of ten young normal male subjects (average height of 174.2 cm +/- 3.8, average weight of 70.2 kg +/- 6.16), which was subjectively classified as mainly ectomorph (slightly biased towards the mesomorph type) a good correlation was found between the transthoracic impedance changes due to normal respiratory movements and tidal volume (average r of 0.963 +/- 0.034) and a mean coefficient b1 of 3.64 ohms/liter +/- 1.82. For equal volume, inspiratory and expiratory movements, on the average, produced impedance changes with no significant difference (p less than 0.55). Attempts to quantitatively correlate the coefficient b1 (ohms/liter) with the anthropometric parameters did not produce any consistent result.

Body Constitution↗
PubMed1977

[High linearity biologic impedancemeter (author's transl)].

A high linearity instrument for biological use which permits the measurement of impedance modulus and its variations in the range of 50 to 1,000 ohms is described. It has two outputs (Z and delta Z) which can be connected to an oscilloscope or to any conventional physiological recorder. The deviation from linearity is not greater than 0,06%, with a sensitivity of up to 100 mV/ohm, and an estimated average error better than 1% in absolute value with standard deviation better than 3% and an expected range smaller than +/- 10%. The instrument can stand changes of +/- 10% in the a.c. power supply without showing significant alterations in its behavior. Besides, it has good isolating characteristics in order to prevent undesirable leak currents which are potentially dangerous for the patient. The instrument was tested satisfactorily in human beings and in experimental dogs by recording respiratory movements and cardiac activity.

Adult↗