The gradient, an indicator of V/Q status, is the difference between the arterial carbon dioxide partial pressure (PaCO2) and end-tidal carbon dioxide partial pressure (etCO2) values. It is a result of the relationship between ventilation (V), or airflow to the alveoli, and perfusion (Q), or blood flow to the pulmonary capillaries. This is referred to a ventilation-perfusion matching or V/Q ratio. We look at what mismatching can look like in this video. US-PM-2200559