Final answer:
Gradual lowering of ETCO₂ can be caused by hyperventilation, metabolic acidosis, overfeeding leading to lipogenesis, and exercise. These processes alter the balance of CO₂ and byproducts of metabolism, which can impact ETCO₂ levels measured.
Step-by-step explanation:
The possible causes for a gradual lowering of end-tidal carbon dioxide (ETCO₂) include hyperventilation, metabolic acidosis, overfeeding leading to lipogenesis, and exercise. Hyperventilation can lead to respiratory alkalosis, reducing CO₂ levels.
Metabolic acidosis, where bicarbonate levels are lower than normal, initially keeps pCO₂ normal, but as the body compensates to restore the bicarbonate and carbonic acid/CO₂ ratio, pCO₂ may decrease. Exercise increases the body's metabolic rate, consuming oxygen and producing more CO₂ and hydrogen ions, which can lead to a transient decrease in blood pH and subsequently in ETCO₂. Also, the chloride shift facilitates the movement of bicarbonate out of the erythrocytes in exchange for chloride ions, affecting ETCO₂ readings.