A 65-year-old patient with a history of congestive heart failure (CHF) is being transported by air to a specialized cardiac center. During the ascent, the patient starts experiencing increased dyspnea and a marked decrease in oxygen saturation. Which physiologic factor related to altitude changes is most likely contributing to the patient's symptoms?
Increased noise levels
Enhanced vibration during flight
Reduced partial pressure of oxygen
Increased partial pressure of carbon dioxide