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Biomedical subjects

M R Armayor

Publications and source records attributed to M R Armayor.

6 recordsLinked to original sources
PubMed1988

Impedancimetric bacterial detection: theoretical and experimental aspects.

By means of the bipolar impedance technique, we detected bacterial growth in an inoculated broth as its time course absolute impedance. From it, the impedance change relative to sterile medium was obtained, calculating also its time derivative. The repeatability of the derivative curves (they overlapped within a band better than 3.3%) permitted the identification of a double-hump pattern which, in principle, could be accepted as an indicator of the type of bacteria (Escherichia coli). After six experimental series, the growth curves appeared as sensitive to the initial concentration of bacteria and to the culture time preceding inoculation; they were also dependent on the temperature and on the average basal impedance. Temperature showed a greater effect (one order of magnitude) on the lag-phase of the growth curve than on the stationary-phase. This effect occurs because the impedance growth curves tend to get away from the reference offered by the sterile medium. The best working conditions were obtained for an average basal impedance of 510 ohms under well controlled temperature conditions (variations smaller than or equal to 0.20 degrees C) with wire stainless steel electrodes vertically immersed in the culture broth. This impedance technique appears as inexpensive and easy to automatizing for large number of samples.

Electric Conductivity↗
PubMed1984

Transventricular simple-capacitor discharge defibrillation thresholds after coronary ligation and body hypothermia.

Peak current defibrillation thresholds (PCDT), i.e., values with 50% probability of success, were determined after ligation of the left anterior descending coronary artery (LADCA) while, simultaneously, body temperature was slowly decreased until central venous temperature reached an average minimum of 22.8 degrees C (s.d. 3.1). In 14 dogs with over 166 successful defibrillations, the average time elapsed between the moment of ligation and the last defibrillation was 179.1 min. (s.d. 31.9), with an average PCDT of 53.6 mA g-1 of heart (s.d. 20.5). This value was compared by means of the unpaired Student's t test with three previous values obtained, respectively, under hypothermia with no occlusion (HNO), normo-thermia with coronary occlusion (NCO), and normothermia with no occlusion (NNO), that is, HNO 69.5 (s.d. 30.4), NCO 81.1 (s.d. 29.3), and NNO 89.5 (s.d. 32.8), all expressed in mA g-1 of heart. All three differences even after Bonferroni's correction, were statistically significant (P less than 0.3%). We concluded that, (1) defibrillation thresholds were decreased by coronary occlusion and by hypothermia, (2) the decrease due to hypothermia was greater than that due to coronary occlusion, (3) both decrements appeared as additive.

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↗
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↗
PubMed1977

Properties and isolation of the diffusible factor involved in Bufo arenarum fertilization.

Earlier studies have shown that a substance(s) released from the egg jelly of the toad Bufo arenarum is required for fertilization. In this paper some properties of this diffusible factor were further examined, and a procedure was designed for its isolation from crude egg extracts. The active component is soluble in water and ethanol, and insoluble in chloroform, ether and n-butanol. The biological activity is stable to liophylization and to heat, and remains unaffected after trypsin treatment. In contrast, it is impaired after treatment with ethyl acetate, 0.1 N HCl or chloroform, and is completely destroyed after converting the diffusible factor into ash. Data are presented showing that the recovery of fertilizability of extracted eggs in the bioassay system as carried out under present conditions, cannot be ascribed to a pH alteration of the insemination medium. This lends further support to the view that diffusible factor activity is not mediated through a pH effect. The factor was purified by gel chromatography coupled with desalting and paper chromatography. The active molecule is of low molecular weight and appears associated with a high pH ninhydrin-positive fraction.

Animals↗