Effects of Respiratory Center Activity on the Heart By Matthew

• Rhythmic variations in peak left ventricular pressure were often observed in recent studies upon innervated, isovolumetric, paced, left ventricle preparations.' The frequency of these pressure fluctuations coincided with that of the movements of the rib cage, although the lungs were collapsed, the hili were securely ligated, and the perfusion pressure for the coronary circulation and the cephalic portion of the animal was rigorously maintained at a constant level. Under such conditions, the rhythmic modulation of peak left ventricular pressure in an isovolumetric preparation must have represented phasic variations in cardiac autonomic activity, originating from neurons located in the respiratory centers or from neurons which discharge synchronously with those in the respiratory centers. This paper deals with a more detailed description of these respiratory fluctuations in left ventricular performance, and with the interrelationships between such "contractility waves" in the paced heart and the respiratory variations in heart rate in the xinpaced heart. Some of the data included in this paper were extracted from the previously conducted experiments.