What is the definition of cardiac output?

Choice A rationale

During physical exertion, the myocardial oxygen demand increases significantly to sustain an elevated heart rate and contractility. In coronary artery disease, atherosclerotic plaques narrow the arterial lumen, creating a fixed obstruction. This limitation prevents the coronary blood flow from increasing proportionally to the oxygen demand, leading to myocardial ischemia. The resulting anaerobic metabolism produces lactic acid, which stimulates pain receptors, manifesting as the clinical symptom of chest pain or angina.

Choice B rationale

While dehydration can lead to hemoconcentration and a potential increase in blood viscosity, it is not the primary physiological mechanism triggering angina during exercise in a patient with coronary artery disease. Angina is specifically a mismatch between oxygen supply and demand within the cardiac tissue itself. Systemic dehydration would more likely result in tachycardia or hypotension rather than the localized ischemic pain caused by obstructed coronary arteries failing to deliver enough oxygenated blood.

Choice C rationale

Angina is not caused by the heart being overloaded with excessive blood volume, which would typically describe a state of volume overload or congestive heart failure. Instead, angina is a supply-side issue where the blood vessels cannot deliver enough oxygen to meet the metabolic needs of the myocardium. While increased preload can increase the workload of the heart and exacerbate ischemia, the core issue in coronary artery disease is the inability to provide adequate flow.

Choice D rationale

Inflammation of the chest muscles, known as costochondritis or musculoskeletal strain, can cause chest pain that mimics angina, but it is not the cause of true angina pectoris. Angina is specifically cardiac in origin, resulting from ischemia of the heart muscle due to coronary artery narrowing. Chest wall inflammation is usually localized to the musculoskeletal structures and often changes with palpation or specific movements, unlike the deep, pressure-like pain associated with myocardial ischemia.

Choice A rationale

Fluid volume excess occurs when there is too much water and sodium in the extracellular space. Hyponatremia, or a low serum sodium level less than 135 mEq/L, can occur due to hemodilution. Pulmonary congestion happens when the heart cannot pump the excess volume, leading to fluid backing up into the lungs. This increases hydrostatic pressure in the pulmonary capillaries, causing fluid to leak into the alveoli, which results in crackles and shortness of breath.

Choice B rationale

Fluid volume deficit, or dehydration, involves a loss of body fluids. Weight loss is a very sensitive indicator of fluid loss, as acute changes in weight are usually due to water fluctuations. Weak or thready pulses occur because there is less circulating blood volume to create a strong pressure wave during cardiac contraction. Other signs include dry mucous membranes and decreased skin turgor. Monitoring intake and output is essential for managing patients with these manifestations.

Choice C rationale

Hypertension and peripheral edema are classic signs of fluid volume excess. As the total volume of circulating blood increases, the pressure against the arterial walls rises, leading to high blood pressure. Peripheral edema occurs because the increased capillary hydrostatic pressure forces fluid out of the vascular space and into the surrounding interstitial tissues, commonly seen in the ankles and feet. This indicates the body's inability to effectively clear or distribute the excess fluid load.

Choice D rationale

This choice is correct because it encompasses all the accurate clinical correlations mentioned in the previous sections. Fluid volume excess is consistently linked with hyponatremia, pulmonary congestion, hypertension, and edema due to overhydration and pressure changes. Conversely, fluid volume deficit is correctly linked with weight loss and weak pulses due to the reduction in total body water and circulating pressure. Understanding these patterns is fundamental for nurses and clinicians to properly assess and treat electrolyte imbalances.