Centers involved in the autonomic reflex reactions originating from stretching of the atria.

Abstract

Stretching the atria in anesthetized dogs produces reflex changes in heart rate, and in cardiac anTrenal sympathetic nerve activity. Anemic decerebration, cord transection at C4-C5, and severance of vagal or sympathetic cardiac nerves was done to identify the pathways and centers essential for these reflexes. Stretching the right atrium produced an acceleration of the heart and a definite increase in sympathetic nerve activity. Left atrial-stretch caused biphasic responses: an initial sympathetic nerve inhibition and slower heartbeat followed by sympathetic excitation and heart acceleration. The afferents responsible were carried mainly by the vagi; efferent neural control of the heart was mostly sympathetic. Since Bainbridge first discovered the phenomenon in 1915 (1), stretching the atria has been known to evoke reflex changes in heart rate, although reports of which reflex reactions are actually involved have been contradictory. In the last decade, cardiac reflexes have again attracted the attention of many physiologists and clinicians (2-5). Linden and his associates, using anesthetized dogs found that both left and right atrial stretch evoked acceleration of the heart, and that this acceleration is due solely to increased activity of cardiac sympathetic nerves (2). They also showed that the afferent pathways that evoke these reflexes are in the vagi, as originally stated by Bainbridge. Other investigators have reported that the heart rate is reduced by stretch of the left atrium (see refs. 3 and 6). It was also found that cardiac sympathetic nerves contained afferent tracts that could evoke reflex responses when the atria were stretched and it was claimed that the cardiac acceleration produced by stretching the atria was mainly mediated by sympathetic nerves and spinal reflex action (7). In a previous study (8), in which balloons were inserted and then inflated in the atria to cause stretching or in which sensitive areas were directly stretched, we found that stretching the right atrium produced only an acceleration of the heart and an increase in cardiac sympathetic nerve discharges. Stretching the left atrium, on the other hand, produced an early deceleration followed by a longer-lasting cardiac acceleration concurrent with a decrease and then an increase in cardiac sympathetic activity. Stretching the atria produced similar changes in activity of other sympathetic nerve trunks, such as the renal 2177 nerves. It was also found that somatosympathetic reflexes evoked by various somatic afferent nerves were affected by atrial stretch (8).Although there have been many morphological and physiological studies of atrial receptors and their afferent nerves (3, 9), the reflexes they evoke and the nerve centers involved have not been fully determined. The objective of the present study was to identify the centers, as well as the afferent and efferent pathways that are involved in reflex responses originating from the atria, and to analyze the individual roles of each. METHODS Twenty-four dogs of either sex ...

The Effects of Successful Percutaneous Mitral Balloon Valvuloplasty on Acute and Intermediate Term Aortic Stiffness

“…In addition, atrial stretch, that is, stretching of the right atrium, produces a definitive increase in sympathetic activity, 22 whereas left atrial stretch causes a biphasic responseinitial sympathetic nerve inhibition followed by sympathetic activation. 23,24 In the present study, systemic and pulmonary vascular resistance, which were both high before PMBV, decreased significantly following PMBV, which is in agreement with earlier reports. Ashino et al 20 reported that arterial and cardiopulmonary baroreflex mechanisms were impaired in MS patients, and that they returned to normal 7 days post-PMBV.…”

“…Low CO and increased pulmonary arterial resistance cause structural and functional changes in the cardiopulmonary system, the most important of which is an increase in central sympathetic outflow to the skeletal muscle that is primarily due to a reduction in CO that results in decreased afferent activity from the baroreceptors. In addition, atrial stretch, that is, stretching of the right atrium, produces a definitive increase in sympathetic activity, whereas left atrial stretch causes a biphasic response – initial sympathetic nerve inhibition followed by sympathetic activation . In the present study, systemic and pulmonary vascular resistance, which were both high before PMBV, decreased significantly following PMBV, which is in agreement with earlier reports.…”

The impact of arterial load on left ventricular performance: an invasive haemodynamic study in severe mitral stenosis

“…) and increased atrial stretch (Koizumi et al . ; Ashino et al . ), which in turn imply increased sympathetic tone and hence elevated contractility.…”

“…A plausible explanation for this disparity might lie in the discrepancy of haemodynamic findings between the two cohorts; in our study, MS subjects demonstrated lower CO (3.0 ± 1.0 vs. 3.7 ± 0.9 l min −1 ), higher LAP (26 ± 7 vs. 18 ± 7 mmHg) and higher PAP m (58 ± 24 vs. 41 ±13 mmHg). These haemodynamic discrepancies suggest lower baroreceptor sensitivity (Ferguson et al 1990) and increased atrial stretch (Koizumi et al 1977; Ashino et al…”

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“…Vagal activity, which was greatly augmented by sinus distension, was decreased by atrial stretch, while previously inhibited sympathetic activity due to sinus distension was augmented by stretch of the atrium. The effect of stretch on vagal activity seems to depend to a degree on the prestimulus level 22,23 . Therefore, chronic atrial stretch may explain the sympathetic overactivity in patients with mitral stenosis.…”