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In respiratory physiology, the ventilation/perfusion ratio (V/Q ratio) is a ratio used to assess the efficiency and adequacy of the ventilation-perfusion coupling and thus the matching of two variables: V – ventilation – the air that reaches the alveoli; Q – perfusion – the blood that reaches the alveoli via the capillaries
The ventilation/perfusion ratio (V/Q ratio) is higher in zone #1 (the apex of lung) when a person is standing than it is in zone #3 (the base of lung) because perfusion is nearly absent. However, ventilation and perfusion are highest in base of the lung, resulting in a comparatively lower V/Q ratio.
Ventilation–perfusion coupling is the relationship between ventilation and perfusion processes, which take place in the respiratory system and the cardiovascular system. [1] Ventilation is the movement of gas during breathing, and perfusion is the process of pulmonary blood circulation , which delivers oxygen to body tissues. [ 2 ]
Integrated pulmonary index (IPI) is a patient pulmonary index which uses information from capnography and pulse oximetry to provide a single value that describes the patient's respiratory status. IPI is used by clinicians to quickly assess the patient's respiratory status to determine the need for additional clinical assessment or intervention.
Oxygenation and capnography, although related, remain distinct elements in the physiology of respiration. Ventilation refers to the mechanical process of which the lungs expand and exchange volumes of gasses, however respiration further describes the exchange of gasses (mainly CO 2 and O 2) at the level of the alveoli.
Cardiac index is a critical parameter in evaluating cardiac performance and the adequacy of tissue perfusion. In healthy adults, the normal range of cardiac index is generally between 2.6 to 4.2 L/min/m². Values below this range may indicate hypoperfusion and are often seen in conditions such as heart failure, hypovolemia, and cardiogenic shock.
By redirecting blood flow from poorly-ventilated lung regions to well-ventilated lung regions, HPV is thought to be the primary mechanism underlying ventilation/perfusion matching. [1] [2] The process might initially seem counterintuitive, as low oxygen levels might theoretically stimulate increased blood flow to the lungs to increase gas exchange.
The ratio of the AC component to the DC component, expressed as a percentage, is known as the (peripheral) perfusion index (Pi) for a pulse, and typically has a range of 0.02% to 20%. [43] An earlier measurement called the pulse oximetry plethysmographic (POP) only measures the "AC" component, and is derived manually from monitor pixels.