Changes in Cardiac Output upon Stimulation of the Hypothalamic Defence Area and the Medullary Depressor Area in the Cat

Folkow, B., B. Lisander, K. S. Tuttle and S. C:. Wang. Changes in cardiac output upon stimulation of the hypothalamic defenca araa and the medullary depressor area in the. cat. Acta physiol. scand. 1968. 72. 220–233. The hypothalamic defence area and the bulbar depressor area, with related hypothalamic sympatho-inhibitory structures, were topically stimulated while changes in cardiac output (C. O.). heart rate, stroke volume, central venous pressure and peripheral blood flow were studied in anesthetized-curarized cats and dogs. Defence area stimulation induced up to two-fold increases in C. O. and up to threefold increases in calculated work load for the left ventricle. The major part of the C. O. increase was directed to the skeletal muscles, where active cholinergic vasodilatation increased flow up to fivefold. Gastrointestinal and renal blood flows were promptly reduced and since this neurogenic flow reduction slightly prereded muscle vasodilatation, the C. O. increase could be preceded by a very brief phase of C. O. decrease. β-adrenergic blockade could reduce the threefold increase in left ventricular work load by 50–60 per cent by eliminating the sympathetic drive on the heart. Depressor area stimulations produced an often profound reduction in C. O., sometimes prereded by a brief C. O. increase. Flow resistance fell, especially so in skeletal musrles, where an initial flow increase coincided with the transient C. O. increase; further, blood was pooled within the capacitance section. Blood loss or raised venous transmural pressure greatly potentiated these changes so that imminent cardiovascular collapse could be induced by this central depressor stimulation. The mechanisms involved in the mentioned, diametrically opposite cardiovascular patterns are. discussed.