Responses of atrial mechano‐receptors to pulsation of atrial volume

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Abstract
Firing patterns of single atrial fibers were monitored in order to study their sensitivity to rate of change of atrial volume and their dependence on receptor location in the atria. To that effect, sinusoidal fluctuations of volume (.+-. 1 ml; 60/min) were superimposed on the natural pulsations of the heart of spontaneously breathing anesthetized cats. Stimulus-response histograms revealed that maximal firing frequency of B-impulses preceded maximal volume change by 10-80.degree. (average 48 .+-. 7.degree. (SE), 13 right and left atrial receptors) indicating that sensitivity to rate of change of atrial volume at least equaled volume sensitivity. The rate sensitive component of B-firing increased with respect to the volume sensitive component when atrial filling diminished and was larger for high threshold receptors than for low threshold receptors (P < 0.001). The A-bursts were not affected by atrial pulsing in 8 out of 9 anatomically localized receptors; inspiration prolonged the A-bursts of 3 receptors and advanced the timing of A-bursts with respect to the a-wave (10-50 ms) of all 9 receptors. About half of all anatomically localized receptors were traced to the interatrial septum; they differed from right and left atrial receptors. B-fibers were sensitive to both change and rate of change of atrial volume; their role as sensors of venous return is suggested strongly. Results further suggested that A- and B-firing are determined largely by the location of atrial stretch receptors.