Final answer:
Hypoventilation results in increased PaCO₂ levels as the inadequate ventilation of the alveoli leads to reduced expulsion of carbon dioxide from the body. The correct answer from the given options is that the PaCO₂ exceeds 45 mmHg. It is different from hyperventilation, which leads to low CO₂ levels (hypocapnia).
Step-by-step explanation:
When hypoventilation occurs, it means that the ventilation of the alveoli in the lungs is insufficient, leading to an inadequate exchange of gases. This causes an increase in the partial pressure of carbon dioxide (PaCO₂), as carbon dioxide is not being expelled from the body effectively. Among the given options, the correct one is:
B. The PaCO₂ exceeds 45 mmHg.
Hypoventilation can be caused by disorders that affect the respiratory system such as pneumonia and congestive heart failure, or by depressant substances like morphine, barbiturates, or ethanol. It is important to differentiate between hypoventilation and hyperventilation, which is an increased ventilation rate leading to abnormally low blood carbon dioxide levels, or hypocapnia. High-altitude environments lead to hyperpnea rather than hypoventilation, due to the decreased oxygen availability, and this can contribute to the symptoms of altitude sickness if the body does not acclimate.