The ratio of total lung alveolar ventilation to total pulmonary blood flow is called ventilation and blood flow ratio. Abnormal ventilation/blood flow (V/Q), whether elevated or decreased, is undoubtedly the main cause of hypoxia and decreased arterial oxygen partial pressure. V/Q less than 0.8 indicates a significant reduction in ventilation, seen in chronic bronchitis, obstructive emphysema, pulmonary edema and other diseases.

Basic Information

Specialist classification: Respiratory examination classification: pulmonary function test

Applicable gender: whether men and women apply fasting: not fasting

Tips: Check the eve of the night to eliminate tension and rest properly so as not to affect the inspection results. Normal value

Ventilation / blood flow = 4 / 5 (0.8).

Clinical significance

Abnormal ventilation/blood flow (V/Q), whether elevated or decreased, is undoubtedly the main cause of hypoxia and decreased arterial oxygen partial pressure. V/Q less than 0.8 indicates a significant reduction in ventilation, seen in chronic bronchitis, obstructive emphysema, pulmonary edema and other diseases.

V/Q greater than 0.8 indicates a significant reduction in pulmonary blood flow, seen in pulmonary infarction, right heart failure.

(1) Increase may be due to increased alveolar ventilation, and may also be reduced due to perfusion. The former forms ineffective ventilation, loss of breathing work in vain, no oxygenation effect, because oxyhemoglobin can not be supersaturated; the latter is seen in pulmonary vascular diseases such as pulmonary embolism, capillaries in high emphysema, etc., blood flow Reduce, can not carry enough oxygen, causing hypoxemia.

(2) Reduced due to decreased alveolar ventilation, seen in chronic obstructive pulmonary disease (especially chronic bronchitis and emphysema), neuromuscular disease (multiple spinal radiculitis), respiratory central inhibition (anaesthetic overdose, brain Diseases and other diseases. At this time, ventilatory dysfunction is present, which not only causes hypoxemia, but also causes carbon dioxide retention, causing hypercapnia.

(3) The ratio of zero is seen in atelectasis, the alveolar ventilation is completely stopped, the capillary blood is not exposed to oxygen, and the venous blood is injected into the left heart, which is mixed into the systemic circulation, which is actually venous blood doping, resulting in hypoxemia. disease. The percentage of venous blood mixed into the arterial system as a percentage of cardiac output is called the partial flow (Qs/Qt).

Precautions

Check the eve of the night to eliminate tension and rest properly so as not to affect the inspection results.

Inspection process

Pulmonary blood flow measurement requires cardiac catheterization or radionuclide methods, alveolar gas-arterial oxygen partial pressure difference [P (Aa) O2], P (Aa) O2 = PAO2-PaO2.

Not suitable for the crowd

Generally, there are no contraindications. If you have serious cardiopulmonary diseases, you should consult your doctor before doing this check.

Adverse reactions and risks

Generally no complications and harm.