Heart Rate In Men Research Articles

A free-running endogenous rhythm of the resting heart rate in man.

A sine-wave oscillating rhythm of the heart rate is reported in 24 out of 31 resting healthy subjects. Identification of these free-running cycles was by spectral analysis of minute-by-minute recordings of electrocardiograms, and in a few cases by inspection of cardiotachometer records. The periodicity of this rhythm was circa 10 min and was intermediate in frequency between the rapid fluctuations with frequencies of 15, 30, and 60 s and those of a frequency recurrent every 90 min already described in the literature. Our cycles were independent of age and sex.

Arterial chemoreceptors, ventilation and heart rate in man.

1. Transient changes of heart rate (HR) and ventilation were recorded following step changes in alveolar gas composition in three healthy subjects. From a steady state of normo- or slightly hypercapnic hypoxia (PA,CO2 38-46 torr, PA,O2 50-60 torr) arterial chemoreceptor stimulation was transiently relieved by breathing a CO2-free mixture for two breaths, either pur O2 (causing a fall in PA,CO2 and a rise in PA,O2; O2 test) or a low O2 mixture (causing a fall in PA,CO2 without any change in PA, O2; CO2 test). For both test types ventilation was either allowed to change freely ('free-breathing' tests) or was consciously maintained at the pre-test level by the subjects ('controlled-breathing tests). The circulatory delay from the lungs to the ear was measured with a sensitive ear oximeter. 2. In all 'free-breathing' tests ventilation decreased significantly after a mean latency of 5.2 sec; the average lung-ear circulation time was 4.9 sec. HR increased slightly above pre-test levels in eighty-one of one hundred and four tests of all types, the changes being significant after a latency identical to that of the ventilatory changes. Except in the 'controlled-breathing' CO2 tests this early tachycardia was followed by a decrease in HR within the following 5-6 sec. 3. These findings indicate that the primary effect of withdrawal of arterial chemoreceptor stimulation in conscious man as in the anesthetized animal is tachycardia. The secondary development of bradycardia in 'free-breathing' CO2 tests is probably due to the operation of a lung reflex sensing changes in ventilation. The absence of bradycardia in 'controlled-breathing' CO2 tests and its presence in 'controlled-breathing' O2 tests, finally, suggest that relief of systemic hypoxia causes a slowing of the heart not due to lung reflexes but to some other mechanism which operates with a latency nearly twice as long as the arterial chemoreflex.

Halothane depresses baroreflex control of heart rate in man.

Baroreflex control of heart rate was determined during three awake control situations and during two depths of halothane anesthesia in man. Baroreflex function was quantiated by calculating the pressor test slope from the R-R interval change on the ECG produced by a pharmacologically induced pressor response. During the three awake control situations the subjects breathed room air or 100 per cent O2 spontaneously or 100 per cent O2 with ventilation controlled. Mean (+/- SD) slopes obtained were 15.1 +/- 4.5, 15.6 +/- 6.8 and 18.4 +/- 9.9, respectively. No significant difference in baroreflex function slope was observed. During light halothane anesthesia (0.7 per cent endtidal) baroreflex function was significantly depressed (mean slope = 2.5 +/- 1.5), and it was abolished at 1.1 per cent end-tidal halothane (mean slope = 0.03 +/- 0.04). It is concluded that halothane anesthesia produces depression of baroreflex control of heart rate in man.

Influence of acute changes in preload, afterload, contractile state and heart rate on ejection and isovolumic indices of myocardial contractility in man.

To determine the sensitivity of several isovolumic and ejection phase indices of myocardial contractility to loading, inotropic stimulation and heart rate in man, 14 patients (pts) were studied during cardiac catheterization with simultaneous recordings of left ventricular (LV) pressures and ultrasound dimensions. Measurements were made of instantaneous and mean circumferential fiber shortening velocity (VCF), maximal (max) rate of LV pressure rise (dP/dt), dPHdt divided by end-diastolic circumference [(dP/dt)/C], (DP/dt)/C divided by aortic valve opening pressure [(dP/dt/CP], PEAK CONTRACTILe element velocity (VCE) using total LV pressure, VCE extrapolated to zero total pressure (Vmax), VCE at a developed pressure of 10 mm Hg (VCEDP10) and dP/dt at a common isovolumic developed pressure of 40 mm Hg [(dP/dt)/DP40]. Resulta are expressed in per cent change of the mean for the group. Acute preload increase (8.6% increase in end-diastolic circumference) with volume expansion at constant heart rate in 7 pts produced insignificant changes in VSF, an 8.3% increase in max dP/dt, no change in (dP/dt)/C, a variable response in (dP/dt)/CP, 18% reduction in peak VCE, 16% reduction in Vmax, 14% increase in VCEDP10, and a 10% increase in (dP/dt)/DP40. An acute increase in afterload produced by angiotensin in 8 pts (44% increase in peak stress) led to a 38% decrease in VCF, a 2.5% increase in max dP/dt, no significant change in (dP/dt)/C, a 26% reduction in (dP/dt)/CP, variable responses in peak VCE and Vmax, an 11% increase in VCEDP10 and minor changes in (dP/dt)/DP40. All of the contractility indices were augmented significantly by isoproterenol and atrial pacing. In a given patient, max, dP/dt appears to be useful in the assessment of acute changes in inotropic state since the magnitude of its response to abrupt changes in preload is small and to afterload insignificant. Normalizing max dP/dt for end-diastolic circumference assures better stability during loading with good sensitivity to inotropic stimulation. VCF may be used whenever changes in afterload are minimal. The isovolumic measurements of VCE (regardless of whether total or developed pressure is used) lack sufficient stability during acute changes in loading conditions to warrant their use in the quantitative assessment of acute changes in inotropic state.

Modification by diluents of effects of intramuscular atropine on heart rate in man.

The effects of intramuscularly administered atropine on the human heart rate were significantly delayed when the atropine was mixed with pralidoxime chloride (300 mg/ml) or sodium chloride (8.5%). The time‐course of the atropine effects was unchanged when atropine was mixed with 180 mg/ml of pralidoxime chloride. These findings suggest that the delay is because absorption of atropine is slowed by solutions of higher osmolarity.

The effect of pancuronium on reflex regulation of heart rate in man

We have shown that the baroreflex is partially maintained in patients anaesthetized with methoxyflurane following the administration of pancuronium. Initially heart rate responses are counteracted by the vagolytic effect of pancuronium, which might be explained by a muscarinic and/or ganglionic blocking property of the drug.

SOME EFFECTS OF KÖ 1313 IN ANIMALS AND MAN

1 Kö 1313 competitively inhibited the increases in heart rate produced by isoprenaline in anaesthetized dogs. 2 Kö 1313 was 35 times more active than propranolol in blocking an isoprenaline induced tachycardia in anaesthetized dogs but only three times more active in blocking the increase in femoral blood flow produced by the injection of isoprenaline into the femoral artery. These observations suggest that Kö 1313 may have some cardio-selective activity. 3 When a series of doses of Kö 1313 was injected intravenously into anaesthetized dogs, the lower doses decreased heart rate while the larger doses increased heart rate. The same doses of propranolol reduced heart rate. 4 In lightly anaesthetized dogs, a series of doses of Kö 1313 progressively increased heart rate while propranolol produced little change. These observations indicate that Kö 1313 has slight intrinsic sympathomimetic activity. 5 The oral administration of Kö 1313 and propranolol had no effect on resting heart rate in man but reduced the increases produced by head-up tilt, standing and exercise.

Autonomic blockade and the resting heart rate in man

Neural control of resting pulse rate was studied in 12 subjects during high spinal anesthesia alone and during high spinal anesthesia plus intravenous atropine. Spinal anesthesia was used to produce complete preganglionic sympathetic block because of its freedom from pharmacologic side effects on heart rate. Sympathetic block slowed the resting heart rate; atropine elevated it to rates above basal control levels. The data confirm that the resting heart rate is influenced in man by both sympathetic and parasympathetic influences but that the latter predominate. Atropine elevates arterial blood pressure in the presence of complete sympathetic block.

The effects of exercise and changes in body temperature on the intrinsic heart rate in man

The intrisic heart rate (IHR) was measured after autonomic blockade by propranolol and atropine in normal human subjects during changes in central body temperature and at two levels of exercise. A direct linear relationship was found between the IHR and mixed venous blood temperature over the range from 35 to 40° C., with a mean slope of 7.1 beats per minute per degree Centigrade. The IHR increased during exercise, both at mild and near maximal levels, in each case by approximately one guarter of the rate increase during the same exercise before autonomic blockade. Neither rises in body temperature nor incomplete blockade of sympathetic stimuli appeared to account for these changes. By analogy with the effects of early hypoxia on cardiac function in dogs after autonomic blockade, it is suggested that increases in the IHR in exercise may represent a direct response of the myocardium to mild hypoxia. Although in 50-year-old normal subjects the IHR was lower than in young adults, and the maximum heart rate in exercise was correspondingly lower, the capacity to increase heart rate in exercise, above its intrinsic level was equal at different ages. Previous exercise increased the variability of serial measurements of the IHR in normal subjects. When exertion was avoided on the day of study, paired measurements one week apart showed a standard deviation of 1.6 beats per minute, or 1.7 per cent.

The normal range and determinants of the intrinsic heart rate in man.

Normal standards for the intrinsic heart rate (IHR) were measured in 432 healthy adult subjects aged 16 to 70 years. At rest, with normal body temperature, the IHR was highly reproducible. In different subjects, age was the only important determinant. Differences in IHR between individuals may correspond to differences in functional capacity of the myocardium, whether determined genetically, by age, or by disease.

Effects of anesthesia on baroreflex control of heart rate in man.

Effects of anesthesia on baroreflex control of heart rate in man.

The adrenergic system and electrical systole

Diverse results have been found when the effect of the adrenergic nervous system on the duration of electrical systole has been tested in various animals. The present study was designed to determine whether beta adrenergic stimulation shortened the Q-T interval at any given heart rate in man. Right atrial pacing at several rates was carried out before and during the administration of isoproterenol in six subjects. The Q-T interval shortened linearly as the R-R interval shortened. The administration of isoproterenol did not alter the Q-T interval at comparable heart rates as determined by rank sum analysis of Q-T intervals. The results were similar in a single study of a denervated heart, indicating that the results were not masked by rate-related release of endogenous catecholamine. These data demonstrate that beta adrenergic stimulation by the intravenous infusion of isoproterenol did not modify the duration of electrical systole in man independently of its effect on heart rate.

Support of myocardial performance after open cardiac operations by rate augmentation

Summary Cardiac pacing with intramyocardial electrodes was performed in 36 patients following open-heart surgery. Details of 24 hemodynamic studies in 19 patients are presented. Sixteen patients had atrioventricular conduction disturbance and 3 had sinus rhythm. Studies were performed in the following sequence: (a) ventricular pacing (mean 97 beats per minute), (b) non-pacing (mean 66 beats per minute), (c) ventricular pacing (mean 109 beats per minute), and (d) ventricular pacing at the identical rate of the preceding study plus isoproterenol administration. In patients with atrioventricular conduction disturbance, ventricular pacing was associated with a consistent and significant rise of cardiac index, averaging 23.7 per cent. Addition of isoprotenenol while the pacing rate remains relatively unchanged was found to cause a further slight rise in cardiac index. Pacing was also associated with significant reduction of left atrial pressure and left ventricular stroke work and volume. In 3 patients with normal atrioventricular conduction, ventricular pacing was not associated with a consistent hemodynamic change. The inotropic effect of increasing the heart rate in man is emphasized. Within the limits imposed by the study, a relationship of heart rate and cardiac output has been confirmed. Prophylactic implantation of myocardial electrodes at the time of open-heart surgery offers a simple and predictable means of controlling heart rate and overriding many of the cardiac arrhythmias observed in the postoperative period.

The Effect of Neostigmine, Atropine and Ephedrine on Heart Rate in Man

The effects of different doses of neostigmine methylsulfate, atropine sulfate and ephedrine on the heart rate in fit volunteers were studied. Neostigmine decreased heart rate equally in unmedicated subjects and in subjects premedicated with 25 mg. ephedrine, but decreased the rate much more in subjects premedicated with 0.6 to 1.5 mg. atropine sulfate. Under the experimental conditions, from sevenfold to twentyfold doses of atropine sulfate were required to block completely the effect of neostigmine methylsulfate on heart rate. About twice the weight of atropine sulfate was required to prevent neostigmine methylsulfate from lowering heart rates below base line. The effect of neostigmine on heart rate began within a minute after intravenous injection, reached a maximum in about 20 minutes, and lasted for more than an hour.

The Effect of Neostigmine, Atropine and Ephedrine on Heart Rate in Man

The Effect of Neostigmine, Atropine and Ephedrine on Heart Rate in Man

Effects of OXYGEN AND BELLADONNA DRUGS ON HEART RATE and FINGER VOLUME PULSATIONS IN MAN

Department of Anesthesiology, College of Medicine, University of Florida, Gainesville, Florida. This project was supported in part by National Institutes of Health Training Grant No. GM-427. Read at the 40th Congress of the International Anesthesia Research Society, February 27-March 3, 1966, Bal Harbour, Florida.

Effects of changing heart rate in man by electrical stimulation of the right atrium. studies at rest, during exercise, and with isoproterenol.

A technic is described for controlling the heart rate in patients with normal atrioventricular conduction by means of an electrical pacemaker catheter that stimulated the right atrium. When the heart rates of 17 patients in the resting state were elevated from an average of 80 to 121 beats/min., the cardiac indices remained virtually unchanged and averaged 3.67 and 3.72 L./min./M. 2 , respectively. Further increases in the heart rates resulted in small reductions in the cardiac indices to an average value of 3.21 L./min./M. 2 at 148 beats/min. The stroke volumes, ejection periods, and mean rates of ejection decreased as heart rate was increased. The role of heart rate in the circulatory response to exercise was examined in seven patients. When the heart rates were controlled by electrical stimulation at rates comparable to those previously achieved spontaneously during exercise, it was observed that cardiac output rose normally with exercise and that this rise was accomplished entirely through an increase in the stroke volume. In five patients the effects of isoproterenol infusion were also studied before and during control of the heart rate at the level reached spontaneously during isoproterenol administration. Again, when the heart rate was not permitted to rise, the increases in cardiac output with isoproterenol were mediated through increases in the stroke volume. These studies indicate that in the absence of augmented metabolic requirements, homeostatic mechanisms maintain cardiac output relatively constant despite large induced changes in the heart rate. However, when metabolic demands are increased by muscular exercise, or the circulation is stimulated by catecholamines, cardiac output can rise through an increase in stroke volume, even when alterations in the heart rate are prevented.

THE CONTINUOUS HEART RATE IN MEN EXHIBITING AN OVERT BEHAVIOR PATTERN ASSOCIATED WITH INCREASED INCIDENCE OF CLINICAL CORONARY ARTERY DISEASE.

The continuous heart rates of a group of subjects exhibiting behavior pattern A (associated with a high incidence of clinical coronary heart disease) were obtained by means of a specially designed instrument at various times of the total day and compared with that obtained from subjects exhibiting a converse pattern (behavior pattern B). In addition, the heart rates of patients suffering from functional cardiovascular disease and from clinical coronary heart disease were measured throughout the day. The average daily heart rates appeared to be about the same in subjects with pattern A and in subjects with pattern B. Moreover, their average heart rates were approximately the same as those in patients with functional cardiovascular disease. Patients suffering from coronary heart disease with or without a previous infarction, if essentially asymptomatic, showed about the same average daily heart rate as did the subjects of the other groups. However, the patients who had suffered from a previous infarction and who were experiencing symptoms exhibited a faster heart rate.

LEFT VENTRICULAR EJECTION TIME INDEX IN MAN.

The present studies were undertaken in an attempt to formulate an accurate expression of the relationship between the duration of left ventricular ejection and heart rate in man. On the basis of regression equations relating the duration of left ventricular ejection and heart rate in normal individuals, the index LVET + .0016 HR was derived and tested in normal adults and prepubertal children. The left ventricular ejection time index (ETI) remained constant and reproducible over the range of heart rate from 50 to 150 and yielded more consistent values in this range of heart rate than did previously derived equations. A slight but significantly higher value of the ETI was present in the adult females when compared to the adult males, while no significant difference according to sex was apparent in the children. A decrease in ETI was found when cardiac output was diminished in normal individuals during 60° head-up tilt and in patients with congestive heart failure. Of note was the finding of a significant correlation between the level of the ETI and the cardiac output in these situations. Submitted on December 13, 1962

On the nature of cardiac control.

Excerpt The survival and, in a sense, the supremacy of the mammalian class are dependent on biological control mechanisms that render the organism extraordinarily responsive to change. One such con...