Final answer:
A fever would lead to an increase in oxygen demand because as the body's temperature rises, the metabolic rate increases and cells require more oxygen. Sleep and taking a narcotic usually lower oxygen demand, while factors like increased exercise result in heightened oxygen consumption.
Step-by-step explanation:
An increase in oxygen demand could be caused by a variety of physiological changes and activities. Among the options provided, A. A fever would lead to an increase in oxygen demand. When the body's temperature rises, metabolism increases, and cells consume more oxygen to sustain the increased activity. This situation necessitates the delivery of more oxygen to the tissues to meet the heightened metabolic demand.
Sleep and taking a narcotic typically decrease oxygen demand because the body's overall metabolic rate decreases during these states. Postural drainage, a technique used to clear the airways, does not directly affect oxygen demand. Factors like increased exercise, which intensifies metabolic activity, and increased carbon dioxide levels, which can trigger a rise in respiration rate to exhale excess CO2, are also known to increase oxygen demand.