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Results for “HEART BEAT AND RHYTHM”

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At least 19 recordsLinked to original sources
PubMed1988

Nicotinic and muscarinic responses of embryonic chick ventricular myocardium to acetylcholine: chronotropic and electrophysiological effects.

Sensitivity of 7-day-old chick embryo ventricular heart fragments to acetylcholine was investigated. Low doses mainly produced a positive chronotropic effect, whereas high doses of acetylcholine provoked a decrease in the heart beat rhythm. The positive chronotropic effect of acetylcholine was related to the presence of nicotinic receptors that were evidenced within ventricular myocardium by autoradiography. Membrane potential recording showed that acetylcholine hyperpolarizes the diastolic membrane potential when the drug had a negative chronotropic effect. This effect of acetylcholine on the membrane potential was not observed when the drug had a positive chronotropic effect. In many cases, the diastolic membrane potential exhibited spontaneous small depolarizing potentials. Their amplitude was low and their frequency was irregular. These potentials were suppressed by treatment with alpha-bungarotoxin, suggesting that they are triggered by nicotinic receptor activation.

Acetylcholine↗
PubMed1983

[Intracardiac neurogenic regulation of the rate of excitation conduction in the atrioventricular area of the heart. I. Dependence of the effect on the moment of stimulus application in spontaneous and artificially stabilized rhythms of the heart beat].

The influence of the intracardiac reflectory system on the atrioventricular propagation in the experiments on the isolated frog's heart has been investigated. The ability of the intracardiac reflectory cholinergic activation to accelerate or reduce the atrioventricular propagation was confirmed. Both effects remain on the background of the artificially stabilized heart rhythm. The dromotropic effect direction was shown not to be connected with the electrocardiogram (ECG) phase at which the stimulus has been given; the positive or negative dromotropic effect can appear giving the stimulus at the same phase of the ECG. But there is a strong correlation between the moment of the stimulation and the dromotropic effect intensity. The most high degree of the acceleration and inhibition appears when the stimulus is given near the P component of the ECG.

Action Potentials↗
PubMed2001

Single-pulse transcranial magnetic stimulation reset the rhythm of essential tremor but not heart beat.

BACKGROUND: Human oscillator is observed in and outside the nervous system. Cardiac rhythm is generated by heart itself but can be modulated by brain. Using the technique of transcranial magnetic stimulation (TMS) and resetting index, we studied if single-pulse TMS could reset the cardiac rhythm and help differentiate oscillator of neurogenic or non-neurogenic origin. METHODS: In addition to the study of 4 patients with essential tremor, cardiac rhythm was studied in 6 normal subjects. The magnetic intensity was initiated from motor threshold of hand muscle, and then with an increment of 10% up to the maximal output of magnetic stimulator. We used the resetting index (RI) to quantify the influence of the TMS. RESULTS: The resetting phenomenon was observed in essential tremor (RI = 0.92) but not in cardiac rhythm (RI = 0.02). CONCLUSIONS: Single-pulse TMS is able to reset the rhythm of essential tremor but not heart beat. The pacing mechanism is different between essential tremor and heart beat. The cardiac rhythm is regulated and modulated chiefly by heart itself. Essential tremor should not share the same mechanism with heart beat.

Adult↗
PubMedDate not supplied

[The reflex and direct actions of novocaine on the rhythm of the heart beats in rats in early postnatal ontogeny].

In experiments on newborn rats it was shown that heart beating frequency depended on the intensity of interoceptive afferentation. Partial shutdown of the afferentation by means of intraperitoneal injection of novocaine in the dose of 25 mg/kg of body weight caused the increase of heart beating and the more complete one at higher doses (100 mg/kg of body weight) led to its decrease. The injection of 2% novocaine (150-200 mg/kg of body weight) into the peritoneum of rat puppies on the first week of life caused the transition of bradycardia into temporary or permanent stop of heart beating. The same effect was observed for isolated atrium of rat puppies on the first week of life after the addition of 0.1% novocaine to feeding solution. This effect disappeared in older animals. It was concluded that resorptive effect of novocaine on heart structures causing the disturbance of heart automatism in newborn rats occurred along with the reflex one.

Aging↗
PubMed1986

Circadian rhythms of heart rate and premature ventricular beats in the aged.

The chronobiological analysis by means of the cosinor method on the dynamic electrocardiographic tracings of 30 subjects aged over 65 years with no clinical or instrumental signs of heart disease revealed a significant circadian rhythm of heart rate with acrophase in the early afternoon. When compared with a group of 30 young adult subjects, the elderly exhibited only a non-significant reduction of the rhythm amplitude. Elderly patients with heart disease exhibited a similar chronobiological pattern of heart rate. Premature ventricular beats (PVBs) were present in all subjects and occurred mostly during the day. A significant circadian rhythm was present only in elderly heart patients with 30-150 PVBs/h. The circadian distribution of PVBs showed significant interindividual differences with nocturnal acrophase in about one third of the patients. The chronobiological analysis can represent the basis for a more appropriate therapeutic approach to the elderly with PVBs.

Adult↗
PubMed1995

The role of proctolin in the antenna-heart beat acceleration of Periplaneta americana (L.).

So-called accessorial pulsatile circulatory organs in insects have developed during evolutionary reduction of the vascular system. As such a peripheral organ, the antenna-heart supplies the antennae with haemolymph. In the antenna-heart, the beat rhythm is generated by a myogenic automatism and is controlled neuronally. The electrical stimulation of the antenna-heart nerve produces an immediate heart beat inhibition brought about by octopamine release. Following this heart inhibition, an accelerating effect can be observed, which is based on a peptidergic mechanism. Proctolin-like material was found in both the dilator muscle and the antenna-heart nerve by means of immunocytochemistry. After HPLC-separation of antenna-heart tissue, proctolin was identified by sequencing the bioactive material and subsequent mass spectrometry. Proctolin proved to be extraordinarily effective producing stimulation of the antenna-heart beat rate up to 450%. The threshold concentration is 10(-10) mol.1(-1) and the value of the dissociation constant was fixed to KO = 1.3 x 10(-8) mol.1(-1). The chrono-trophic effect is caused by an increase in the steepness of the rising phase of pacemaker activity. The enhancement of the membrane resistance Rinput indicates a reduction of K(+)-conductance by proctolin. The PI-second messenger system is involved as well. Proctolin was identified and isolated from a real target organ. This fact and the physiological results furnished proof of peptidergic transmitter function of proctolin in the antenna-heart.

Animals↗
PubMed1994

Gender- and age-related differences in heart rate dynamics: are women more complex than men?

OBJECTIVES: This study aimed to quantify the complex dynamics of beat-to-beat sinus rhythm heart rate fluctuations and to determine their differences as a function of gender and age. BACKGROUND: Recently, measures of heart rate variability and the nonlinear "complexity" of heart rate dynamics have been used as indicators of cardiovascular health. Because women have lower cardiovascular risk and greater longevity than men, we postulated that there are important gender-related differences in beat-to-beat heart rate dynamics. METHODS: We analyzed heart rate dynamics during 8-min segments of continuous electrocardiographic recording in healthy young (20 to 39 years old), middle-aged (40 to 64 years old) and elderly (65 to 90 years old) men (n = 40) and women (n = 27) while they performed spontaneous and metronomic (15 breaths/min) breathing. Relatively high (0.15 to 0.40 Hz) and low (0.01 to 0.15 Hz) frequency components of heart rate variability were computed using spectral analysis. The overall "complexity" of each heart rate time series was quantified by its approximate entropy, a measure of regularity derived from nonlinear dynamics ("chaos" theory). RESULTS: Mean heart rate did not differ between the age groups or genders. High frequency heart rate power and the high/low frequency power ratio decreased with age in both men and women (p < 0.05). The high/low frequency power ratio during spontaneous and metronomic breathing was greater in women than men (p < 0.05). Heart rate approximate entropy decreased with age and was higher in women than men (p < 0.05). CONCLUSIONS: High frequency heart rate spectral power (associated with parasympathetic activity) and the overall complexity of heart rate dynamics are higher in women than men. These complementary findings indicate the need to account for gender-as well as age-related differences in heart rate dynamics. Whether these gender differences are related to lower cardiovascular disease risk and greater longevity in women requires further study.

Adult↗
PubMed1992

[Experience with the use of streptokinase in acute myocardial infarct at the prehospital stage].

The authors analyze the experience gained with the systemic thrombolytic therapy (STLT) at the prehospital stage of the treatment of acute myocardial infarction by specialized emergency cardiological teams. The screening of patients to be given STLT was performed via the remote diagnostic center. STLT was provided to 43 patients who were given intravenous injections of 500,000 PU streptokinase (Avalizin, GDR) for 15-30 minutes. The control group included 16 patients given standard therapy. After STLT 62.8% of the patients demonstrated moderate arterial hypotension, which could readily be corrected. Myocardial reperfusion after STLT manifested by rapid removal of the painful syndrome, characteristic dynamics of ECT, and by the appearance of specific reperfusion disorders of rhythm and conduction. The accelerated idioventricular rhythm, ventricular premature heart beat and A-V rhythm of the junction were recorded most frequently. The indicated rhythm disorders were removed readily enough. It is recommended that STLT may be carried out at the prehospital stage of AMI treatment by the cardiological emergency teams, which is likely to appreciably enhance the efficacy of the given therapy form.

Electrocardiography↗
PubMed1994

Beat-to-beat behavior of QT interval during conducted supraventricular rhythm in the normal heart.

To assess beat-to-beat behavior of QT interval under different conditions, high resolution recordings and computerized beat-to-beat analysis of the electrocardiogram were performed at rest, during recovery after short exercise, and during atrial pacing. Beat-to-beat variations of QT interval during sinus rhythm at rest and after short exercise were measured in ten healthy men. In an additional three patients with supraventricular tachycardia, beat-to-beat QT changes were studied after abrupt sustained acceleration and deceleration of heart rate by atrial pacing. Beat-to-beat changes in RR interval at rest are followed by minimal changes of the QT interval. The measured proportional change of the QT interval compared with the change in RR interval (delta QT/delta RR) was 0.02. This value represents 10% of the value expected for QT changes from Bazett's formula. Following short exercise QT interval did not change for 15 seconds and reached a maximal value 80 seconds later as compared to the RR interval (192 vs 115 secs, P < 0.001). The steady state of the QT interval during sustained atrial pacing was achieved after 132, 135, and 133 seconds for pacing intervals of 600, 500, and 600 msec, respectively. Our data indicate a relatively slow adaptation of the QT interval to changes in heart rate.

Adaptation, Physiological↗
PubMed1989

Coupling between cardiac and locomotor rhythms: the phase lag between heart beats and pedal thrusts.

During some rhythmic exercises, the heart and exercise rates may become coupled (be within 1% of each other). If the intraarterial and skeletal intramuscular pressure cycles were reciprocal, blood flow to exercising muscle should be maximized and cardiac load minimized. In this study the authors tested the hypothesis that, while coupling is present, the phase lag between the pedaling and cardiac contraction cycles is consistent and appropriate. Twenty-seven subjects pedaled, at a frequency natural to them, on an electronically braked bicycle ergometer that held the power output constant regardless of pedaling rate. To assess the phase lag between pedal thrust (two per revolution) and heart beat, pedal-gated plots of the electrocardiography signal were generated throughout the most coupled five-minute work load for each of the 9 subjects in whom the rates were within 1% of each other for at least two consecutive four-second samples taken every fifteen seconds. During this interval of thirty-seconds in which the rates were within 1% of each other, the phase lag of most subjects gradually lengthened and shortened and there was considerable variation among subjects, refuting the authors' hypothesis. The results of this study illustrate the importance of beat-by-beat analysis when studying coupling phenomena. The preliminary assumption, that the coupling between cardiac and locomotor rhythms during cycling was on the basis of a single ischemic muscle group, has apparently been disproven.

Adult↗