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Biomedical subjects

R Bernabei

Publications and source records attributed to R Bernabei.

At least 127 records · Page 7Linked to original sources
PubMed1986

On the mechanisms by which hypoxia eliminates digitalis-induced tachyarrhythmias.

The mechanism by which hypoxia abolishes the tachyarrhythmias induced by cardiac steroids was studied in cardiac Purkinje and ventricular muscle fibres. In muscle fibres, hypoxia reduces excitability markedly, reduces the size and increases the time to peak of the oscillatory potentials (Vos) and of the aftercontractions induced by cardiac steroids, thereby abolishing the tachyarrhythmias. In Purkinje fibres, hypoxia also decreases Vos and excitability but abolishes the tachyarrhythmias only if repeated or prolonged. In Purkinje-muscle preparations, hypoxia blocks impulse conduction from the fast discharging Purkinje fibres to the myocardial fibres when the latter are still little intoxicated. It is concluded that hypoxia affects promptly ventricular muscle fibres and (depending on the experimental conditions) Purkinje fibres also, and readily blocks impulse transmission to muscle fibres. Hypoxia abolishes arrhythmias by decreasing Vos size (probably through an impaired calcium uptake into the sarcoplasmic reticulum), by causing a conduction block at the Purkinje-muscle junction (probably through an increase in cytoplasmic calcium) and by reducing excitability.

Animals↗
PubMed1986

Strophanthidin inotropy in cardiac Purkinje fibers under conditions that vary cellular sodium or calcium.

The role of sodium and calcium on strophanthidin inotropy was studied in canine cardiac Purkinje fibers perfused in vitro under conditions that vary cellular sodium and calcium. With high concentrations of strophanthidin (greater than or equal to 10(-7) M), force increases more in the presence of low [Ca]0 or high [Na]0 and less in the presence of a low sodium-calcium concentration solution than in Tyrode solution. In a solution with a low concentration of sodium-calcium containing strophanthidin, restoring [Na]0 to normal decreases and then re-increases force: when [Na]0 is decreased again, the force transiently overshoots. These effects of strophanthidin are exaggerated by metabolic inhibitors. In a low [Ca] solution, low concentrations of strophanthidin (3 X 10(-8) or 5 X 10(-8) M) re-increase force a little or not at all. On recovery, the transient force increase is not exaggerated by low strophanthidin and is absent after manganese exposure. The inotropy of low concentrations of strophanthidin is potentiated by norepinephrine, high [Ca]0 (4 mM), or by lowering [Na]0. Thus, the present results suggest that the inotropic action of high strophanthidin concentrations depends primarily on sodium and secondarily on calcium, and that the inotropic action of low concentrations of strophanthidin involves a modification of the cell response to calcium.

Animals↗
PubMed1985

Age-related incidence of reperfusion- and reoxygenation-induced ventricular tachyarrhythmias in the isolated rat heart.

Reperfusion- and reoxygenation-induced ventricular tachyarrhythmias were studied on 6-month-old (adult) and 24-month-old (senescent) Langendorff perfused rat hearts. The incidence of arrhythmias was significantly higher in the group of senescent hearts. Furthermore, the reperfusion- and reoxygenation-induced contracture was also more frequent in the group of senescent hearts. The interrelation between contracture and arrhythmias might represent an indirect evidence to suggest that alterations in cell calcium homeostasis have an important role in the origin of both phenomena and, possibly, in their increased incidence in the senescent heart.

Age Factors↗
PubMed1984

The inotropic effects of strophanthidin in Purkinje fibers and the sodium pump.

The role of the inhibition of the Na pump in strophanthidin inotropy was studied in canine Purkinje fibers by correlating changes in contractile force with changes in maximum diastolic potential caused by conditions that enhance the electrogenic extrusion of Na. It was found that a brief exposure to a zero-K or to a zero-K, zero-Ca solution (but not to a zero-Ca solution) is followed by an increase in maximum diastolic potential. This hyperpolarization is reduced if NaCl is substituted by LiCl and in the presence of tetrodotoxin. In quiescent fibers exposed to tetrodotoxin, the hyperpolarization is abolished. A low concentration of strophanthidin (5 X 10(-8)M) increases contractile force but does not modify the hyperpolarization. Larger strophanthidin concentrations (5 X 10(-7)M to 10(-6)M) increase and then decrease contractile force and reduce or abolish the hyperpolarization. Metabolic inhibitors also reduce the hyperpolarization. We conclude that the positive inotropic effect of a low (therapeutic) concentration of strophanthidin is due to a mechanism other than Na pump inhibition.

Action Potentials↗
PubMed1980

Digoxin serum concentration measurement in patients with suspected digitalis-induced arrhythmias.

The serum digoxin concentration (SDC) was measured in 100 consecutive patients with suspected digitalis-induced arrhythmias. In 24 (toxic group) of these subjects arrhythmias disappeared after glycoside withdrawal. The mean (+/- SD) SDC was 2.88 +/- 1.89 ng/ml in the toxic group and 1.00 +/- 0.61 in the nontoxic group (p less than 0.0001). With respect to digitoxicity, the SDC showed a predictive accuracy rate of 88%, a specificity rate of 89%, and a sensitivity rate of 62%. Since our results were obtained from symptomatic patients, we observed a better predictive accuracy rate than other authors, who studied symptomatic and asymptomatic subjects. The high percentage of false-negatives makes it impossible to consider the SDC by itself a diagnostic test for digitoxicity. However, the SDC is a useful test since all other parameters are less sensitive and/or less rapid indicators of probable digitalis intoxication.

Aged↗
PubMedDate not supplied

Pain management in frail, community-living elderly patients.

BACKGROUND: Pain is a common problem among older people living in different community settings. As indicated by the World Health Organization (WHO), pain can be relieved using pharmacologic agents. However, pain continues to be addressed inadequately. OBJECTIVES: To describe the prevalence of pain in frail elderly people living in the community and to evaluate the adequacy of pain management. METHODS: We analyzed data from a large collaborative observational study group, the Italian Silver Network Home Care project, that collected data on patients admitted to home health care programs. Twelve home health care agencies participated in the project evaluating the implementation of the Minimum Data Set for Home Care instrument. We enrolled 3046 patients, 65 years and older, in the present study. The main outcome measures were the prevalence of daily pain and analgesic treatment. RESULTS: A total of 1341 individuals (39%, 49%, and 41% of those aged 65-74, 75-84, and > or = 85 years, respectively) reported daily pain. Of patients with daily pain, 25% received a WHO level 1 drug; 6%, a WHO level 2 drug; and 3%, a WHO level 3 drug (eg, morphine sulfate). Patients 85 years or older were less likely to receive analgesics compared with the younger patients (univariate odds ratio, 0.73; 95% confidence interval [CI], 0.60-0.89). Another independent predictor of failing to receive any analgesic was low cognitive performance (adjusted odds ratio, 0.80; 95% CI, 0.69-0.93). CONCLUSIONS: Daily pain is prevalent among frail elderly patients living in the community and is often untreated, particularly among older and demented patients.

Aged↗
PubMedDate not supplied

Age-related differences in isolated rat sinus node function.

In order to rule out age-related differences in the sinus node (SN) function, the effects of different substances were tested in SN isolated preparations from adult (4-5-month-old) and old (24-25-month-old) rats. No difference was seen in the in vivo heart rate between adult and old rats, whereas sinus node rate (SNR) was significantly lower in the old rather than in the adult preparations. The effects of acetylcholine (10(-9)-10(-5) M) were similar between the two groups of preparations. The response to adenosine (10(-9)-10(-4) M) was significantly higher in the adult than in the old preparations (p less than 0.05). No significant difference was noted in the response to isoproterenol (10(-10)-10(-6) M). High calcium (5.4-8.1 mM) caused an increase of the SNR that was significantly greater in the old than in the adult preparations (p less than 0.005). In conclusion, our results show an age-related decrease in the isolated SNR that does not seem to be mediated by different responses to neuromediators but is probably due to an alteration of the intrinsic activity of the SN cells.

Acetylcholine↗