Which factor stimulates breathing in a patient with COPD?

In patients with Chronic Obstructive Pulmonary Disease (COPD), breathing is primarily stimulated by hypoxemia, which is a deficiency of oxygen in the blood. In the context of COPD, the body may adapt to high levels of carbon dioxide (hypercapnia) and rely more on low oxygen levels as a trigger for the respiratory drive. This is due to the blunted response of the central chemoreceptors to carbon dioxide, which means that as carbon dioxide levels rise, the body's primary stimulus to breathe becomes the decrease in oxygen levels.

Hypoxemia leads to increased respiratory effort as the body attempts to increase the oxygen saturation and improve oxygen delivery to tissues. This physiological response is vital in managing daily activities and preventing respiratory failure in COPD patients.

While hypercapnia can affect the respiratory drive, particularly in severe cases, it is the combination of elevated carbon dioxide and reduced oxygen that characterizes the condition and the resultant stimulus for breathing. Other factors such as acidosis and asphyxia can occur in advanced stages but are typically consequences of hypoxemia rather than primary driving forces for breath stimulation in COPD patients.