Now, what exactly does that mean physiologically? Well, what that means is the lungs will not be able to pump as much oxygen into the blood. And if there's less oxygen circulating inside our blood, less oxygen will be delivered to the cells and tissues of our body. And that is a problem because the cells need oxygen to produce ATP molecules in an efficient way. And these ATP molecules are used as energy molecules to carry out all the different types of processes that take place inside the cells and inside our body. Now, what our body does immediately is it increases the rate at which we breathe, so it increases the ventilation rate.