Rapid Increase In Heart Rate Research Articles

The cardiac responses to shell opening and closure in the bivalve Arctica islandica (L.)

Shell closure in Arctica islandica is followed by an exponential decrease in the oxygen tension of the mantle cavity water and is accompanied by an initial increase in heart rate which is followed at lower oxygen tensions by a bradycardia. Prior to shell opening there is a slight increase in heart rate before any movement of the shell valves can be detected. However, once the shell opens and pumping activity recommences there is a rapid increase in heart rate, often to levels above normal. Perfusion of the mantle cavity with water of high and low oxygen tension resulted in the cardiac responses normally associated with shell opening and closure. Recordings of the PO2 of the blood in the ventricle, made simultaneously with cardiac recordings, showed that the changes in heart rate were recorded only after the PO2 of the blood had changed. These experiments suggest that changes in the PO2 of the mantle cavity water may be primarily responsible for the cardiac responses to shell closure in Arctica.

Autonomic origin of heart rate fluctuations at the onset of muscular exercise

The time courses of the heart rate (HR) changes were studied in six healthy male subjects who performed step changes from rest to light dynamic leg exercise (50 W) in the sitting position during a) control, b) parasympathetic blockade (atropine, 2-2.5 mg iv), c) beta-adrenergic blockade (propranolol, 10 mg iv), and d) during combined blockade with both drugs. During the control and beta-blockade experiments all subjects showed an immediate, rapid increase in HR, reaching a peak value after about 10 s, whereafter an equally rapid transient drop by 10-20 beats/min took place reaching the lowest values about 17 s after the onset of work. HR then again increased to reach a steady-state level within 60-90 s. In the atropine experiments this response pattern was not evident at all, whereas in the experiments with combined blockade it could be distinguished to a small, but significant degree. It is concluded that the observed fluctuations of HR at the onset of light dynamic exercise can be explained by a rapid vagal withdrawal, followed by a transient increase in vagal tone.

Site of central chemosensitivity in fetal sheep.

The heart rate, blood pressure, and respiratory response to topically applied cyanide on the ventrolateral medullary surface and upper spinal cord was studied on exteriorized sinaortic-denervated fetal lambs under pentobarbital anesthesia. On all sites tested cyanide produced a rapid increase in heart rate and blood pressure (P smaller than 0.05) which was most pronounced from the area adjacent to the nerve roots IX to XI (mean 32%). Respiratory efforts consisting of 1-8 gasps were induced in half the applications to the medulla but never when the pledgets were applied to the spinal cord. The mean delay to response was 43 s (range 13-102 s). After cautery of the chemosensitive areas, topical application of cyanide failed to stimulate gasping, whereas intravenous cyanide or cord clamping still produced a vigorous respiratory response. It is concluded that sympathetic stimulation of the heart and blood vessels can originate centrally in response to local histotoxic hypoxia of the ventral medulla and upper spinal cord. Furthermore, it is proposed that in the apneic fetus histotoxic hypoxia of the medulla initiates respiration possibly by stimulating a special gasping mechanism which is separate from the respiratory center responsible for rhythmic breathing after birth. The responsible neurons must be located at least 2 mm beneath the ventral medullary surface.

Effect of glucagon in hemorrhagic shock.

AbstractGlucagon has been shown to selectively increase renal blood flow in anesthetized dogs. This observation coupled with the known ability of the hormone to increase cardiac output suggested that this agent might be beneficial in the acute treatment of shock. The purpose of this study was to correlate changes in cardiac output and renal blood flow in response to intravenous infusions of glucagon during hemorrhagic shock in the dog. Cardiac output and renal blood flow were monitored simultaneously on a square‐wave electromagnetic flowmeter with probes placed around the ascending aorta and left renal artery. Shock was produced by bleeding to a constant systolic pressure of 70 mm Hg. After a 60‐min stabilization period, glucagon was infused, intravenously for 30 min at 0.5 or 1 μg/kg/min. The drug produced a rapid increase in heart rate, cardiac output, mean arterial pressure, and renal blood flow. Most responses dissipated within 30 min after discounting the infusion. Following reinfusion of the shed blood, glucagon increased heart rate but did not increase cardiac output. Renal blood flow was either increased or unchanged. In the normovolemic animals the effect of glucagon on the kidney was reflected as a marked fall in renal vascular resistance. Total peripheral resistance did not fall. It is concluded that glucagon has potential usefulness in clinical situations in which cardiac output and renal blood flow are compromised.

Antigravity effects of leg exercise.

AbstractRosenhamer, G. Antigravity effects of leg exercise. Acta physiol. scand. 1968. 72. 72–80,To investigate the effects of leg exercise on the overall tolerance to exaggerated gravitational stress, 8 subjects were exposed for 13 min to a threefold increase of the force of gravity in centrifuge experiments (+ 3 Gz) while in the sitting position, both during motionless resting and when exercising at 600 kpm/min on a bicycle ergometer. In all subjects, continuous leg exercise prevented the occurrence of circulatory collapse. which otherwise became imminent in 5 subjects after 5 to 12 min in the resting condition as evidenced by blackout or rapid increase in heart rate. Subjectively, exercise was experienced as less stressful than the resting condition. The improved circulatory stability with exercise was also reflected by uniformity of individual heart rate responses, the group mean value increasing from 152 to 160 beats/min during the 6th to 12th min.

Antigravity Effects of Leg Exercise

Rosenhamer, G. Antigravity effects of leg exercise. Acta physiol. scand. 1968. 72. 72–80, To investigate the effects of leg exercise on the overall tolerance to exaggerated gravitational stress, 8 subjects were exposed for 13 min to a threefold increase of the force of gravity in centrifuge experiments (+ 3 Gz) while in the sitting position, both during motionless resting and when exercising at 600 kpm/min on a bicycle ergometer. In all subjects, continuous leg exercise prevented the occurrence of circulatory collapse. which otherwise became imminent in 5 subjects after 5 to 12 min in the resting condition as evidenced by blackout or rapid increase in heart rate. Subjectively, exercise was experienced as less stressful than the resting condition. The improved circulatory stability with exercise was also reflected by uniformity of individual heart rate responses, the group mean value increasing from 152 to 160 beats/min during the 6th to 12th min.

Effects of Age and Diet on the Heart Rate of the Developing Cockerel

INTRODUCTIONA STUDY of the literature revealed a paucity of information on the heart rate pattern of chicks throughout normal development from hatch to maturity.One such study was reported by Ringer et al. (1957). These workers revealed there was a rapid increase in heart rate of restrained, unanesthetized White Leghorn chicks of mixed sexes in the first week posthatch and a gradual decrease in rate up to six months of age. They did not, however, give the composition of the ration fed in their studies.The purpose of this study, therefore, was to learn the normal heart rate pattern of the male chick from the first day posthatch to six months fed a diet of known composition. Three different basal rations were also fed in an attempt to learn if type of diet had an effect on the heart rate pattern within the first week posthatch. EXPERIMENTALS. C… .

Factors affecting the recovery from diving bradycardia in the frog.

ABSTRACT Recovery from diving bradycardia is not prevented by allowing a frog to surface into nitrogen or excess carbon dioxide. Artificial respiration performed during submersion causes an immediate increase in heart rate whether the lungs are filled with air or nitrogen. The initial rapid increase in heart rate is prevented by bilateral vagotomy but is unaffected by section of the sympathetic connexion to the heart. Spike activity in the pulmonary vagus increases as the lungs are filled. A burst of activity frequently occurs in the cardiac vagus during this period. The heart rate increases as the cardiac vagus becomes quiet. Activity continues in the pulmonary branch until deflation of the lungs. The suggestion is made that the initial rapid increase in heart rate following artificial respiration or on surfacing is due to a decrease in parasympathetic inhibitory activity, by an interaction from either proprioceptors in the lungs or presso-receptors in the walls of the atria or veins.

Effect of excitement on coronary and systemic energetics in unanesthetized dogs.

The effect of excitement on phasic aortic pressure and flow, phasic left coronary flow, and myocardial metabolism has been studied in dogs 1–8 weeks after implantation of appropriate flowmeters and other devices. The rapid increase in heart rate and mild increase in blood pressure in the first few seconds tend to maintain coronary flow per minute despite a decrease in stroke cardiac output and coronary flow throughout the cardiac cycle. The main response is a delayed rise in coronary flow per minute resulting from further elevation of heart rate and blood pressure, a moderate increase in stroke cardiac output and a sizeable increase in stroke coronary flow, the latter being divided fairly evenly between systole and diastole. From 60 to 90% of the increase in mean coronary flow arises from the increase in stroke coronary flow, and the remainder from the increased number of heartbeats per minute. Some of the possible mechanisms concerned are discussed.

INITIAL CARDIOVASCULAR ADJUSTMENT TO EXERCISE IN DOGS WITH CHRONIC CARDIAC DENERVATION.

In three normal dogs and in six dogs with cardiac denervation, there was a rapid increase in cardiac output (electromagnetic flowmeter) from the start of exercise. The denervated group showed an average delay of 25 sec in reaching plateau values of cardiac output and a deficit of 18% in the accumulated flow over the first minute of running; augmentation of output was due principally to a rapid increase in stroke volume since acceleration of heart rate was slow. In normal dogs, the augmentation of output came from a rapid increase in heart rate. The steady-state values for cardiac output and oxygen consumption were similar in the two groups as was the pattern of oxygen consumption in the first minutes of exercise and the manner in which the oxygen debt was repaid. This suggested that the denervated dogs extracted more oxygen from the circulating blood in the first moments of running. The changes with exercise in aortic blood pressure were similar in the two groups.