![]() The blood that cannot get to this area of lung by the embolism gets shunted to other parts of the lung, leading to low V/Q ratio in these parts of the lung. ![]() Not much blood gets through these alveoli, so the volume of the blood in this condition is very low or none. ![]() In patients with pulmonary embolism (PE), they have emboli that block the blood flow Changing V/Q ratio pathologically Extreme cases: Well oxygenated blood from the apex contribute the least because the volume is relatively small (low perfusion), and base of the lung will contribute a large effect in the mixture due to a high volume of blood. Hence, low V/Q ratio high CO2, low O2 Why is it significant?Īrterial blood gases measured from periphery are results of blood from all 3 areas of the lung mixing together. PaO2=100mmHg PaCO2 = blood flow, less ventilation This creates a V/Q mismatch, changing blood gas values of arterialised blood leaving each region of the less blood and relatively high ventilation More blood goes to the base of the lung than the apex due to gravity while standing. Thus, high V/Q refers to ventilation in excess of metabolic needs being met by perfusion, decrease CO2 level (PACO2 & PaCO2) and increase O2 (PAO2 & PaO2). More oxygen to the alveoli, blowing off more CO2 from the lungīlood takes away less oxygen, deliver less CO2 Alveolar CO2 (PACO2) level increases as we are not getting rid of CO2 as quickly, leading to an increase of arterial CO2 (PaCO2). Alveolar O2 decreases (PAO2), which leads to decreased arterial oxygen level (PaO2). Thus, low V/Q refers to ventilation not able to keep up with perfusion. More red blood cells (RBC) are present to remove O2 from the alveolus as they deliver more CO2 than being exhaled Not bringing enough oxygen to meet our metabolic need for O2 (consumption) as well as not blowing out enough CO2 to get rid of the CO2 we produce The ratio between ventilation and perfusion is one of the major factors affecting the alveolar (also arterial) level of oxygen (O2) and carbon dioxide (CO2) V/Q = alveolar ventilation/CO Why is it important? VQ ratio is literally the ratio between the amount of air getting into the alveoli (measured as alveolar ventilation in mL/min) and the amount of blood being sent to the lung (measured as cardiac output (CO) in mL/min). ![]()
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