Cardiac output (CO) represents the total volume of blood the heart pumps into the systemic circulation each minute. This continuous flow is the mechanism by which oxygen and nutrients are delivered to every cell and tissue in the body. Decreased cardiac output (DCO) is a physiological state where the heart’s pumping ability is insufficient to meet the body’s metabolic demands for oxygen supply and waste removal. When this volume drops too low, it can lead to immediate organ dysfunction or chronic health issues.
Calculating Cardiac Output
Cardiac output is determined by two primary components, expressed by the formula: CO = Stroke Volume (SV) multiplied by Heart Rate (HR). The resulting figure is typically measured in liters per minute, with a healthy adult at rest normally circulating about five liters of blood every sixty seconds. Heart Rate (HR) is the number of times the heart contracts each minute. Stroke Volume (SV) is the amount of blood ejected with each beat, affected by three mechanical factors: preload (the volume filling the ventricles), contractility (the force of the muscle’s squeeze), and afterload (the resistance the heart must overcome to push blood into the arteries).
Conditions That Lead to Decreased Output
A reduction in cardiac output stems from conditions that impair either heart rate or stroke volume. Damage to the heart muscle, such as from a myocardial infarction or long-term high blood pressure, leads to cardiomyopathy, which weakens the force of contraction and reduces stroke volume. Severe valvular disorders, like aortic stenosis, also mechanically limit the amount of blood that can be effectively pumped forward. Conditions affecting the heart’s filling, such as pericardial tamponade, physically prevent the ventricles from fully expanding. Disruptions to the heart’s electrical rhythm impair the Heart Rate component; bradycardia (slow rate) may not circulate enough volume, while tachyarrhythmias (fast rate) prevent adequate ventricular filling.
How Decreased Output Affects the Body
When the heart fails to deliver sufficient blood, the body attempts to compensate by activating the sympathetic nervous system. This effort is seen as an initial increase in heart rate (tachycardia), but this compensation is often unsustainable. Reduced blood flow to the muscles and brain quickly manifests as chronic fatigue, weakness, and dizziness. The kidneys are highly sensitive to reduced perfusion, triggering fluid retention to increase circulating volume, which leads to peripheral edema (swelling in the legs, ankles, and feet). The body also prioritizes blood flow to the brain and heart, sacrificing circulation to the extremities, resulting in cool and pale skin.
General Management Strategies
The goal in managing decreased cardiac output is to restore the balance between the body’s metabolic demand and the heart’s pumping capacity. Treatment often begins with medications designed to improve mechanical function. Inotropic drugs enhance the force of contraction to increase stroke volume, while vasodilators reduce arterial resistance, lowering afterload. Fluid management is also addressed using diuretics to excrete excess fluid and relieve congestion and edema. For rhythm-related causes, procedural interventions like pacemaker implantation may be necessary. Alongside medical treatments, patients are advised to adopt lifestyle adjustments, including sodium-restricted diets and controlled exercise, to reduce strain on the heart.