Selective autonomic blockade of conditioned and unconditioned heart rate changes in rabbits

1974 ◽  
Vol 2 (4) ◽  
pp. 493-501 ◽  
Author(s):  
Alice Fredericks ◽  
John W. Moore ◽  
Frederick U. Metcalf ◽  
James S. Schwaber ◽  
Neil Schneiderman
Keyword(s):  
Heart Rate ◽  
Autonomic Blockade

Baroreflex modulation of heart rate and initiation of atrial activation in dogs

1988 ◽  
Vol 255 (3) ◽  
pp. H503-H513 ◽  
Author(s):  
R. B. Schuessler ◽  
T. E. Canavan ◽  
J. P. Boineau ◽  
J. L. Cox
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Right Atrial ◽  
Autonomic Blockade ◽  
Left And Right ◽  
Atrial Activation ◽  
The Right ◽  
A Site ◽  
Induced Changes ◽  
Cardiac Nerves

In open-chest dogs, blood pressure was regulated by titrating doses of phenylephrine and nitroprusside to determine its effect on heart rate and pacemaker location. Changes in blood pressure correlated with changes in heart rate (r = 0.86). Activation time mapping demonstrated multicentric atrial activation, with a site of origin-rate relationship. The fastest pacemakers were located in the most cranial regions and slowest in the most caudal areas. In this chloralose-morphine anesthetized model, autonomic blockade with atropine and propranolol suggests that acute baroreflex-induced changes in heart rate were mediated exclusively by either increased sympathetic or parasympathetic tone and were not associated with inhibition of the opposite system. Division of right and left thoracic cardiac nerves indicated the left sympathetics participated in the baroreflex in 50% of the animals and the left parasympathetics in 90% of the animals. Both the right sympathetics and parasympathetics were active in the baroreflex in all animals. The data demonstrate that physiological heart rate response is regulated through an extensive system of right atrial pacemakers modulated by both left and right efferent cardiac nerves.

Effect of radiofrequency catheter ablation of accessory pathways on autonomic tone in children

1999 ◽  
Vol 9 (4) ◽  
pp. 377-383 ◽  
Author(s):  
Ruchir Sehra ◽  
Joyce E. Hubbard ◽  
Susan P. Straka ◽  
Naomi S. Fineberg ◽  
Douglas P. Zipes ◽  
...  
Keyword(s):  
Heart Rate ◽  
Catheter Ablation ◽  
Supraventricular Tachycardia ◽  
Radiofrequency Catheter Ablation ◽  
Autonomic Function ◽  
Accessory Pathways ◽  
Non Invasive ◽  
Autonomic Changes ◽  
Before And After ◽  
Autonomic Blockade

AbstractBackgroundRadiofrequency catheter ablation is standard treatment for children with re-entrant supraventricular tachycardias. Autonomic changes have been noted after such ablation for atrioventricular nodal re-entry tachycardia, but not as well documented with atrioventricular re-entry over an accessory pathway.Methods and resultsIn 10 normal paediatric volunteers and 12 children referred for electrophysiologic testing and radiofrequency ablation of supraventricular tachycardia, non-invasive autonomic function tests and tilt-table testing were performed, and the variability in 24-h heart rate was analysed. Patients with supraventricular tachycardia underwent these tests both 24–72 h before and 24 h after ablation. Patients with tachycardia underwent additional autonomic testing to assess the sensitivity of baroreceptors and the intrinsic heart rate with autonomic blockade immediately before and after ablation. One non-invasive autonomic function test, namely handgrip, demonstrated significant differences (p < 0.05) in diastolic blood pressure before and after ablation, though these values did not differ from controls. Significant decreases were noted in two indexes of the variability of heart rate before and after ablation (p < 0.05). Certain tilt test variables also demonstrated significant differences between controls and those with tachycardia subsequent to ablation. Intracardiac testing demonstrated changes (p < 0.05) in sinus cycle lengths, effective refractory periods and/or blood pressures at baseline and during testing of the sensitivity of baroreceptors before and after ablation. These changes were consistent with increased sympathetic or decreased parasympathetic tone. With autonomic blockade, these differences were abolished.ConclusionsCatheter ablation of accessory pathways in children was associated with changes consistent with increased sympathetic or decreased parasympathetic tone. These autonomic changes persisted 24 h after the ablation procedure.

Hypotension in Fetal and Newborn Lambs; Different Patterns of Reflex Heart Rate Control Revealed by Autonomic Blockade

Neonatology ◽  
1983 ◽  
Vol 44 (6) ◽  
pp. 358-365 ◽  
Author(s):  
Adrian M. Walker ◽  
J.P. Cannata ◽  
B.C. Ritchie ◽  
J.E. Maloney
Keyword(s):  
Heart Rate ◽  
Rate Control ◽  
Heart Rate Control ◽  
Autonomic Blockade

Baroreflex buffering of pressor response to vasopressin is mediated by V1, not V2, receptors in conscious rats

1993 ◽  
Vol 264 (2) ◽  
pp. R345-R349
Author(s):  
K. Shimizu ◽  
J. Schwartz ◽  
B. P. McGrath
Keyword(s):  
Heart Rate ◽  
Receptor Agonist ◽  
Pressor Response ◽  
Conscious Rat ◽  
Conscious Rats ◽  
Pressor Responses ◽  
Autonomic Blockade ◽  
V2 Receptor ◽  
Intact Rats

Arginine vasopressin (AVP) enhances reflex buffering of its own pressor response, thus attenuating its vasoconstrictor potential in vivo. To investigate the extent to which this effect of AVP is mediated by V1 or V2 receptors, mean arterial pressure (MAP) and heart rate (HR) changes were examined in response to graded injections of AVP or [Phe2,Orn8]oxytocin, a potent, selective V1-receptor agonist, in the absence and presence of infusion of [Val4,D-Arg8]VP, a selective V2-receptor agonist. Responses were compared in intact and autonomically blocked conscious rats. During autonomic blockade with methscopolamine and hexamethonium, the pressor sensitivities to AVP and [Phe2,Orn8]oxytocin were similarly increased. Infusion of the V2-receptor agonist had no effect by itself on MAP or HR in conscious intact rats. It also did not alter the pressor responses to the V1 agonist, in either intact or autonomically blocked rats. In the presence of the V2 agonist, the decrease in heart rate induced by the V1 agonist was enhanced. These results indicate that reflex buffering of the pressor response to AVP in the conscious rat is mediated by V1 and not V2 receptors. However, V2 receptors may be involved in modulating the heart rate response to AVP.

Afferent vascular resistance control during hemorrhage in normal and autonomically blocked rabbits

1991 ◽  
Vol 261 (2) ◽  
pp. H380-H391 ◽  
Author(s):  
C. A. Courneya ◽  
P. I. Korner ◽  
J. R. Oliver ◽  
R. L. Woods
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Afferent Input ◽  
Ang Ii ◽  
Local Response ◽  
Simple Addition ◽  
Autonomic Blockade ◽  
The Difference ◽  
Constrictor Response

We examined the role of the arterial and cardiac baroreceptors on the hindquarter conductance and heart rate responses of conscious rabbits bled at approximately 3% blood volume (BV)/min to 80% BV (i.e., 20% BV removed). We used rabbits with both sets of baroreceptors working and when only one or neither sets was working. Each animal was studied with normal effector function and during autonomic blockade (hormonal + local effectors), where release of arginine vasopressin (AVP) and renin (angiotensin II, ANG II) were enhanced. The local response (LR) to hemorrhage was determined in a separate group of neurohumorally blocked rabbits. The estimated constrictor response (ECR) was the difference between the LR and net conductance response. In normal rabbits, the ECR was 49 units, with the estimated arterial-to-cardiac barorecptor drive ratio approximately 2.8:1 and with the two receptor groups acting by simple addition. Both barorecptors contributed to the rise in heart rate, with the relative arterial-to-cardiac baroreceptor drive ratio approximately 4:1. When hemorrhage was performed during autonomic blockade, ECR was 84 units (compared with normal rabbits, P less than 0.01), but blood pressure was poorly maintained and the constrictor effect was not under baroreceptor control. Although the baroreceptors were critical for AVP release during autonomic blockade, they played no role in renin release (ANG II production); the latter was released in large amounts, producing near-maximum constriction, which was unrelated to the afferent input. Thus neurally mediated regulation during hemorrhage has substantial advantages over that mediated primarily through the pressor hormones.

Autonomic blockade and coronary catecholamines and cyclic AMP in exercising man

1977 ◽  
Vol 43 (6) ◽  
pp. 949-952 ◽  
Author(s):  
R. H. Robson ◽  
D. C. Fluck
Keyword(s):  
Heart Rate ◽  
Cyclic Amp ◽  
Coronary Sinus ◽  
Coronary Circulation ◽  
Dynamic Exercise ◽  
Catecholamine Release ◽  
Cycling Exercise ◽  
Autonomic Blockade

To assess in man the effects of autonomic blockade on the response of catecholamines in the coronary circulation to dynamic exercise, arterial and coronary sinus catecholamine concentrations were measured in six patients during supine cycling exercise, following atropine 1.8 mg and oxprenolol 0.2 mg/kg iv. Although arterial concentrations did not increase significantly, coronary sinus catecholamine concentrations increased from 2.54 +/- 0.59 nmol/1 at rest 4.44 +/- 1.3 nmol/1 during exercise (P less than 0.05; one-tailed test) and were associated with a small increase in heart rate and coronary sinus cyclic AMP concentrations from 9.4 +/- 0.7 nmol/1 (rest) to 11.6 +/- 1.1 nmol/1 (exercise) (0.05 greater than P greater than 0.01). Although autonomic blockade may have increased catecholamine release, this was not reflected in an increased efflux of catecholamines from the heart, because similar increases in coronary sinus catecholamine concentrations occurred in the absence of autonomic blockade.

Effect of ‘Autonomic Blockade’ on Cardiac β-Adrenergic Chronotropic Responsiveness in Healthy Young, Healthy Elderly and Endurance-Trained Elderly Subjects

1994 ◽  
Vol 87 (3) ◽  
pp. 297-302 ◽  
Author(s):  
G. A. Ford ◽  
O. F. W. James
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Geometric Mean ◽  
Cardiovascular Responses ◽  
The Elderly ◽  
Elderly Subjects ◽  
Healthy Elderly ◽  
Age Related ◽  
Autonomic Blockade ◽  
Young Subjects

1. Cardiac chronotropic responses to isoprenaline are reduced with ageing in man. It is unclear whether this is due to reduced cardiac β-adrenergic sensitivity or to age-associated differences in reflex cardiovascular responses to the vasodilatory effects of isoprenaline. Age-associated changes in physical activity are also reported to influence β-adrenergic sensitivity. 2. The aim of the present study was to determine the contribution of alterations in reflex changes in parasympathetic and sympathetic influences and physical fitness to the age-associated reduction in cardiac chronotropic responses to β-adrenergic agonists. 3. The effect of ‘autonomic blockade’ with atropine (40 μg/kg intravenously) and clonidine (4 μg/kg intravenously) on blood pressure, heart rate and chronotropic responses to intravenous bolus isoprenaline doses was determined in eight healthy young (mean age 21 years), nine healthy elderly (72 years) and 10 endurance-trained elderly (69 years) subjects. 4. Elderly subjects had a reduced increase in heart rate after atropine (young, 49 ± 9 beats/min; elderly, 36 ± 5 beats/min; endurance-trained elderly, 34 ± 12 beats/min; P < 0.01) and did not demonstrate the transient increase in systolic blood pressure after clonidine observed in young subjects (young, 11 ± 10 mmHg; elderly, −12 ± 16 mmHg; endurance-trained elderly, −18 ± 11 mmHg; P < 0.01). 5. Cardiac chronotropic sensitivity to isoprenaline after ‘autonomic blockade’ increased in the young but decreased in the elderly subjects. The isoprenaline dose that increased heart rate by 25 beats/min before and after autonomic blockade' was: young, before 1.6 μg, after 2.8 μg, P < 0.01 (geometric mean, paired test); elderly, before 6.9 μg, after 3.6 μg, P < 0.05; endurance-trained elderly, before 5.9 μg, after 4.0 μg, P < 0.05. Cardiac chronotropic sensitivity to isoprenaline was significantly reduced in elderly compared with young subjects before (P < 0.01) but was similar after (P = 0.09) ‘autonomic blockade’. Chronotropic sensitivity did not differ between healthy and endurance-trained elderly subjects before or after ‘autonomic blockade’. 6. The age-associated reduction in cardiac chronotropic responses to bolus isoprenaline is primarily due to an age-related reduction in the influence of reflex cardiovascular responses on heart rate and not to an age-related reduction in cardiac β-adrenergic sensitivity. Endurance training is not associated with altered β-adrenergic chronotropic sensitivity in the elderly. The transient pressor response to intravenously administered clonidine may be lost in ageing man.

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