How is hypercapnic respiratory failure primarily caused?

Hypercapnic respiratory failure occurs when there is an inability to effectively ventilate the lungs, leading to an accumulation of carbon dioxide (CO2) in the bloodstream. This condition can arise from several physiological issues, but the primary cause is inadequate respiration. When the respiratory system is unable to maintain normal gas exchange, particularly during periods of decreased respiratory effort or dysfunction, CO2 is not effectively removed from the body, resulting in elevated levels and respiratory acidosis.

This inadequate respiration could be due to a variety of factors, including muscle weakness (as seen in neuromuscular diseases), central nervous system disorders that affect the respiratory drive, or conditions that inhibit lung expansion. Thus, insufficient respiratory function is central to the pathology of hypercapnic respiratory failure, making this choice the most accurate answer.