It is possible to have multiple independent variables and/or multiple dependent variables. For instance, in multivariable calculus, one often encounters functions of the form, where z is a dependent variable and x and y are independent variables.
Gas exchange between the air within the alveoli and the pulmonary capillaries occurs by diffusion. The oxygen must first dissolve before passing through the respiratory epithelium. Gas moves from a region of high partial pressure to a region of low partial pressure, down a partial pressure gradient.
2. in respiratory physiology, the process of exchange of air between the lungs and the ambient air. Pulmonary ventilation (usually measured in liters per minute) refers to the total exchange, whereas alveolar ventilation refers to the effective ventilation of the alveoli, where gas exchange with the blood takes place.