Final answer:
Increased PaCO2-etCO2 gradient is primarily due to dead space ventilation, where a portion of the breath doesn't participate in gas exchange, often exacerbated by lung diseases such as pulmonary embolism and emphysema.
Step-by-step explanation:
The increased PaCO2-etCO2 gradient is contributed by dead space ventilation. When there is an increase in dead space ventilation, there is less removal of carbon dioxide because a portion of each breath does not participate in gas exchange, as it occurs in areas of the lungs that are ventilated but not perfused. Examples of conditions that contribute to an increased dead space include lung diseases like pulmonary embolism or diseases affecting the pulmonary vessels and airways such as emphysema.
Breathing and gas exchange can be affected by changes in the compliance and resistance of the lung. If the compliance of the lung decreases, as in restrictive diseases like fibrosis, it leads to air trapping. Conversely, when resistance increases, as seen in obstructive diseases like asthma or emphysema, it also leads to difficulty in breathing and effective gas exchange. Therefore, the key factors that contribute to an increased PaCO2-etCO2 gradient include dead space ventilation and changes in lung compliance and resistance influencing the efficiency of pulmonary ventilation.