Breathing in causes a slight reduction in both the air pressure inside the chest and systolic blood pressure. Pulsus paradoxus (PP) is an exaggerated reduction in blood pressure that can occur during inhalation. The condition can occur as a result of an underlying issue with the heart or lungs.

Some people with asthma may experience PP, while others will not. As breathing difficulties can trigger PP, doctors may use the presence of PP to help determine the severity of asthma or the effectiveness of asthma treatments.

This article describes what PP is and how asthma may cause it. It also outlines how doctors diagnose PP and lists some other conditions that may cause this type of variation in blood pressure.

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PP is an exaggerated variation in blood pressure that occurs during the respiratory cycle.

Understanding blood pressure is key to understanding PP. Systolic blood pressure (SBP) measures the force the heart exerts on the artery walls each time it beats. This is different than diastolic blood pressure (DBP), which measures the force the heart exerts on the artery walls in between beats. Blood pressure monitors give both values, displaying SBP as the top number and DBP as the bottom number.

Inhalation causes a slight negative pressure in the lungs, which means that the pressure is higher outside the lungs than inside them. As the heart also sits in the chest, this difference in pressure causes a reduction in the amount of blood leaving the left ventricle of the heart. The result is a subtle temporary dip in SBP.

In PP, the negative pressure inside the lungs is more pronounced due to breathing difficulties. As a result, the drop in blood pressure during inhalation is also more significant. PP can cause a drop of 10 or more millimeters of mercury (mm Hg) in SBP.

PP can occur as a result of breathing difficulties, but it is not a feature of asthma. Although it can occur if asthma is severe or not well-managed, it does not affect all people with asthma.

In individuals with both asthma and PP, the drop in SBP may be as much as 40 mm Hg.

Asthma causes inflammation and constriction of the airways. These symptoms mean that a person has to work harder to breathe, especially during an asthma attack.

It is normal for pressure in the lungs to decrease slightly during inhalation. However, a person who has breathing difficulties due to severe obstruction will experience an exaggerated decrease in air pressure within the lungs when they inhale. This drop in air pressure then translates to a decrease in SBP.

PP tends to occur in people with an underlying heart or lung disease.

A doctor who suspects that a person has PP will need access to accurate blood pressure measurements while a person breathes in. Inaccurate testing can change blood pressure by 10 or more mm Hg.

A doctor or nurse will take certain steps to obtain an accurate blood pressure measurement. These include:

  • taking the reading when the person is relaxed and has not recently engaged in strenuous physical activity
  • asking the person to sit down in a chair with their back supported
  • ensuring that the person does not have their legs crossed
  • asking the person to remain quiet during the reading, as talking can elevate blood pressure
  • helping the person relax, since anxiety and stress can elevate blood pressure and cause inaccurate readings
  • starting to take the reading just before the person breathes in

An automatic blood pressure cuff cannot accurately diagnose PP. Instead, a doctor or nurse will use a manual cuff.

It is possible to have multiple conditions that can cause PP. Due to this, a doctor will take a complete medical history and may order additional tests of heart and lung function.

PP is a symptom, not a disease. Rather than treating PP, doctors view it as an indication of how severe a person’s asthma is and a measure of how well they are responding to asthma treatment.

If a person with asthma has PP, a doctor may recommend additional asthma treatments, such as:

  • Environmental control: This approach involves:
    • removing or avoiding allergens
    • treating underlying allergies
    • wearing a mask during allergy season
  • Lifestyle changes: The following lifestyle changes may help alleviate asthma in some cases:
    • losing weight if a person is overweight or has obesity
    • exercising according to a doctor’s recommendations
    • managing stress and anxiety, which can trigger asthma attacks
  • Emergency medication: People with asthma may need to carry an emergency inhaler to help stop an asthma attack.
  • Long-acting asthma medication: Medications such as inhaled corticosteroids and bronchodilators may reduce the severity of asthma symptoms and the frequency of asthma attacks. Some individuals may even require the use of biologic agents.

Pulsus paradoxus may occur as a result of other conditions besides asthma. These include:

  • Cardiac tamponade: This potentially life threatening condition occurs due to a buildup of fluid in the space around the heart, which puts pressure on the heart and prevents it from pumping effectively. It can occur as a complication of the following:
  • Cardiomyopathy: This stretching, thickening, or stiffening of the heart chamber walls makes it difficult for the heart to pump blood around the body effectively.
  • Heart attack: A sudden blockage in the blood supply to the heart can cause PP, particularly if the blockage affects the right ventricle.
  • Collapsed lung: This potentially life threatening condition involves air escaping from a lung and entering the space between the lung and the chest wall. The buildup of air puts pressure on the lung so that it cannot expand fully during inhalation. A collapsed lung can occur following a serious injury to the chest.
  • Pulmonary embolism (PE): A PE is a blockage in a pulmonary artery within the lungs. Most PEs result from a blood clot that has traveled to the lungs from elsewhere in the body.

Breathing in typically causes a slight dip in blood pressure. Pulsus paradoxus is an exaggerated fall in systolic blood pressure when a person inhales. It can occur as a result of breathing difficulties.

PP is not a disease but a symptom of an underlying heart or lung issue. Some people with asthma may experience PP, while others may not. It is more likely to occur in people whose asthma is severe or not well-controlled.

As PP is not a disease, it does not require treatment. However, a doctor may use PP to assess the severity of a person’s asthma or monitor the effectiveness of asthma treatments.