Final answer:
Respiration affects blood oxygen levels, blood carbon dioxide levels, and venous return but does not directly affect blood K+ levels.
Step-by-step explanation:
The question asks which condition respiration does not affect, and the answer is blood K+ levels. Respiration affects blood levels of oxygen and carbon dioxide by exchanging these gases in the lungs and through the circulatory system. It also affects venous return of blood, which ties into the efficiency of gas exchange. However, respiration does not directly alter blood K+ levels; these are mainly regulated by the kidneys and endocrine system.