Final answer:
During vigorous exercise, there is an acute decrease in PO₂ in the muscle capillary bed due to increased oxygen consumption by muscles and a decrease in pH due to the rise in carbon dioxide levels which lower the affinity of hemoglobin for oxygen and promote oxygen delivery (B).
Step-by-step explanation:
During vigorous exercise in a 30-year-old patient, one would expect to see an acute decrease in the partial pressure of oxygen (PO₂) in the muscle capillary bed. This decrease occurs because muscles are consuming oxygen at a higher rate for energy production.
Additionally, there is an increase in carbon dioxide (PCO₂) production and a subsequent decrease in pH, due to the accumulation of carbon dioxide which reacts with water to form carbonic acid, dissociating into bicarbonate (HCO₃) and hydrogen ions (H⁺). The increased levels of carbon dioxide and lower pH decrease the affinity of hemoglobin for oxygen, known as the Bohr effect, promoting the release of oxygen from hemoglobin to the muscle tissues to meet the high metabolic demand. In contrast, increased body temperature is another change associated with increased exercise intensity, which also reduces hemoglobin-oxygen affinity aiding in oxygen delivery to active muscles.