Ventilation-Perfusion (V/Q) Mismatch

Ventilation-perfusion mismatch (V/Q mismatch) is when the ratio of air into your lungs versus the blood flow in your lungs doesn’t match. The “V” stands for ventilation, or airflow to your alveoli (the air sacs in your lungs). The “Q” stands for quantity of perfusion, or blood flow to the small blood vessels in your lungs.

For oxygen to get to your blood and out to your tissues, you need both the “V” and the “Q” — ideally, the same amount of each one. If you have too little of either, you could end up with plenty of oxygen in your lungs but too little blood flow to pick it up (high V/Q). Or you could have plenty of blood flow ready for oxygen, but none waiting in your alveoli (low V/Q).

Healthcare providers measure ventilation and perfusion in a ratio (ventilation over perfusion). As an example, if the ventilation in one area of your lungs is 5 L/min and its perfusion is 5 L/min, the V/Q ratio is 1, or 100% (5 divided by 5).

What is a normal V Q ratio?

Most people have a V/Q ratio around .8, or 80%. Ideally, it would be 1, which would mean all the oxygen coming into your lungs would make it into your bloodstream. But different areas of your lungs have different ratios (some areas have much more ventilation than perfusion and vice-versa). Overall, most of us have a ratio slightly less than 1.

Conditions that affect your blood flow cause a high V/Q ratio (above 1). Conditions that affect your lungs cause a low V/Q ratio (below 0.8). A pulmonary embolism can cause a high V/Q close to the blockage (where there’s no perfusion), but low V/Q values in other areas, where blood flood is redirected.

What are the symptoms of V/Q mismatch?

Symptoms of V/Q mismatch include:

• Shortness of breath
• Fatigue or getting tired easily
• Dizziness
• Headache
• Bluish, gray or white skin around your lips, eyes or nails (cyanosis)
• Confusion, disorientation or altered mental state

What causes V/Q mismatch?

Conditions that affect your blood flow or lungs can cause V/Q mismatch. These include:

• Blood clot in your lungs (pulmonary embolism)
• COPD (chronic obstructive pulmonary disease)
• Lung scarring (pulmonary fibrosis)
• High blood pressure in your lungs (pulmonary hypertension)
• Atelectasis
• Asthma
• Fluid in your lungs (pulmonary edema)
• Infections in your lungs (pneumonia)
• Congenital diaphragmatic hernia
• Acute respiratory distress syndrome (ARDS)

What are the complications of V/Q mismatch?

V/Q mismatch and the conditions that cause it can lead to:

• Lung infections
• Hypoxemia
• Hypercapnia
• Respiratory failure

How is V/Q mismatch diagnosed?

Healthcare providers diagnose V/Q mismatch with a V/Q scan. This measures your ventilation and profusion in two scans. Depending on your symptoms and the underlying cause, you may also need:

• Blood tests, including an arterial blood gas test
• Chest X-ray or CT scan
• Pulmonary (lung) function tests
• Echocardiogram

How do you treat V/Q mismatch?

Providers treat V/Q mismatch with supplemental oxygen. You’ll also need to treat or manage the condition that caused the mismatch. This could include:

• Blood thinners (anticoagulants) or surgery for blood clots
• Bronchodilators and/or corticosteroids for COPD and asthma
• Antibiotics if you have a bacterial infection in your lungs
• Pulmonary rehabilitation to strengthen your lungs
• Antifibrotic medications for pulmonary fibrosis
• Diuretic medications for fluid in your lungs

What can I expect if I have V/Q mismatch?

What to expect if you have V/Q mismatch depends on the underlying cause. Some causes are life-threatening and need to be treated right away. Others, like COPD, might get worse over time and need ongoing treatment to get enough oxygen to your tissues.

When should I see my healthcare provider?

Talk to your healthcare provider if you have increasing shortness of breath or feel more tired than usual with exertion. Serious conditions can cause symptoms of V/Q mismatch. It’s important to get to the bottom of your symptoms and get treatment if necessary.

When should I go to the ER?

Call 911 (or your local emergency service number) or go to the emergency room if you experience:

• Sudden or severe difficulty breathing
• Chest pain
• Severe headache
• Confusion or altered mental state
• Bluish, gray or white skin around your lips, eyes or nails

Can V/Q mismatch be prevented?

There’s no specific way to prevent V/Q mismatch. But keeping your heart and lungs healthy can reduce your risk of the conditions that cause it. Not smoking and avoiding secondhand smoke is especially important. Managing ongoing conditions, like COPD and asthma, can also help reduce your risk.