Two physiological variables affecting respiration
1. Lung Volume: The amount of air in the lungs affects the rate and depth of respiration. When the lungs are filled with more air, the body may slow down the rate of breathing. Conversely, when the lungs are not inflated to their full capacity, the body may increase the rate of breathing to bring in more oxygen.
2. Blood pH levels: The body tightly regulates blood pH levels to maintain internal balance. If the blood becomes too acidic (low pH), the body may increase respiration to blow off excess carbon dioxide and restore the pH balance. Conversely, if the blood becomes too alkaline (high pH), the body may decrease respiration to retain carbon dioxide and bring the pH back to normal levels.