Overview
Introduction: How Flow Falls
Blood pressure alone does not tell you whether the heart is delivering enough flow.
Blood pressure alone does not tell you whether the heart is delivering enough flow. A patient may be hypotensive because the ventricle cannot eject, because vascular tone has fallen, or because too little blood returns to the heart; those mechanisms call for different responses. The working model is CO = HR × SV. When output falls, trace the change through four levers: filling or preload, ejection resistance or afterload, myocardial force or contractility, and heart rate. Because body size changes expected flow, cardiac index is more useful than raw cardiac output when judging perfusion. The clinical task is to connect the number with congestion, perfusion, rhythm, and cause rather than chase an isolated measurement.