Final answer:
When holding your breath, arterial PCO₂ would increase due to the metabolic production of carbon dioxide, and ventilation would decrease as there is no air movement in and out of the lungs.
Step-by-step explanation:
If you hold your breath, the arterial partial pressure of carbon dioxide (PCO₂) would increase and ventilation would decrease. This is because when you are not inhaling fresh air and not exhaling carbon dioxide, the levels of carbon dioxide in the blood will rise due to continuous metabolic production in the body. Consequently, the lack of breaths being taken leads to a decrease in ventilation, as there is no movement of air in and out of the lungs.
Considering the physiology of the circulatory system, PCO₂ levels change as blood moves through the body. In the body tissues, the partial pressure of oxygen (PO₂) drops, and the PCO₂ increases because cells use oxygen for metabolism and produce carbon dioxide as a byproduct. If ventilation is not sufficient, the partial pressure of carbon dioxide in the affected alveolus increases, and the bronchioles dilate in response to the higher levels of carbon dioxide, as a way to increase the expulsion of this gas from the body. Thus, the accurate response is that PCO₂ would increase, and ventilation would decrease, which corresponds to option c: PCO₂ increases, ventilation decreases.