What Is Pulsus Paradoxus

When we are unwell, we experience symptoms - say a sore throat or a runny nose. They are the outward signs that we are not entirely healthy at this time and we might need to seek medical attention. When we have a physical examination the process can also lead to the discovery of clinical signs, that we might not know we have because we are not feeling any symptoms, but indicate a health issue. Pulsus paradoxus is one such clinical sign with a wide range of conditions linked to it. Here we will discuss what causes it, what conditions it is associated with and what clinicians may do if you are found to have pulsus paradoxus.

Introduction

Pulsus paradoxus is defined as a fall of more than 10 millimetres of mercury (or mmHg) in a person’s systolic blood pressure (the top number of the two in your blood pressure reading) whilst breathing in normally (inspiration).¹

Pulsus paradoxus was first recorded in a patient in the mid-1600s, before finally being named in 1873 by Adolf Kussmaul - a leading German physician of his time whose name is attached to many clinical signs, symptoms and diseases.²

Mechanism of pulsus paradoxus

To appreciate the implications of pulsus paradoxus, it is important to first understand blood pressure. Blood pressure is a measurement of the force the heart creates during contraction (systole) along with the pressure present in arteries during its relaxation (diastole). During systole the muscular heart ventricles contract, pushing blood out to the lungs and the rest of the body. In diastole the ventricles relax, allowing them to refill with blood from the atria above them.³ The left and right sides of the heart are synchronised during this cycle, with both ventricles contracting and relaxing at the same time. 

It is normal to have a small reduction in systolic blood pressure during the in-breath (inspiration), but this should normally be less than 10 mmHg.

This entirely normal drop is caused by decreased pressure in the chest whilst breathing in, which ‘sucks out’ the walls of the blood vessels to and from the lungs, increasing their capacity and thereby reducing the pressure within. Thus this momentary force on the blood vessels lessens the pressure of the blood being carried in them, causing a brief fall in the blood pressure reading.¹

Pulsus paradoxus is most commonly related to heart (cardiac) conditions, but can also be seen as a clinical sign in some lung (respiratory) diseases.¹

In cardiac disease, stiffness in the heart’s ventricles restricts the forceful pumping of blood around the body. This is either due to the heart not pumping efficiently or to less blood being available to be pumped. It can also be the case that pressure in the right ventricle can press on the ventricular septum, effectively limiting the capacity of the left ventricle and thus the volume of blood available to be pumped out of the ventricle.^1,5 The ventricles can also be weakened by damage, for instance following a heart attack; this would also reduce the flow of blood being sent around the body.⁶

In respiratory disease, pressure in the chest cavity (thorax) can exert force on the heart chambers, and reduce the heart’s ability to fill effectively with blood. This can be owing to leaked air in the membrane around the lungs (the pleura) raising the pressure in the chest, or swelling of the airways, related to breathing difficulties creating the same effect.^4,6

Significant reductions in blood volume, known as hypovolaemia, can also affect blood pressure. Less blood in the circulation system means there is less blood to fill the left ventricle and to be sent around the body. There are many causes of hypovolaemia, including diarrhoea, internal bleeding and vomiting.⁷

Clinical presentation

Pulsus paradoxus is a clinical sign rather than a symptom and so needs a medical professional to confirm its presence.⁴ Someone with pulsus paradoxus will not have any physical symptoms of this, but may have other symptoms relating to the condition causing it. 

Diagnostic tests

The simplest way to identify pulsus paradoxus is through blood pressure measurement using a manual blood pressure cuff (sphygmomanometer). Once the cuff is tightened, measurements of the systolic blood pressure are taken both whilst breathing in and breathing out normally. Pulsus paradoxus is confirmed if there is more than a 10 mmHg difference between the two readings.⁴

In severe cases of pulsus paradoxus, the drop in blood pressure can be felt in the arterial pulse at the wrist, again whilst breathing normally.⁵ It may feel like the pulse is weaker or even disappearing, and this is where the paradox part of the name comes from - because the pulse feels weak even though the heart is still pumping as usual.¹

Arterial lines and pulse oximetry waveform analysis can also be used to identify pulsus paradoxis.^1,5 Arterial lines are used in unwell patients in hospitals and the pressure waves can be read with normal breathing.⁵ Pulse oximetry measures in a similar way but by using a clip attached to a finger or an earlobe. Changes in the waves created by the oximeter can be compared between breathing in and breathing out.¹

Causes of pulsus paradoxus

Cardiac (heart) causes

• Pericardial Effusion - an increase in the usual amount of fluid that sits in a protective membrane sac around the heart (the pericardium). The increased fluid reduces the amount the heart can pump. This is the most common cause of pulsus paradoxus
• Cardiac Tamponade - a progression of pericardial effusion, where the amount of fluid in the pericardium puts so much pressure on the heart muscles that they cannot pump at all
• Pericarditis - like pericardial effusion, the ability for the heart to pump is reduced but caused by the pericardium membrane itself becoming thickened 
• Restrictive Cardiomyopathy - similar in mechanism to pericarditis, the ability of the heart to pump is reduced by a thickening of the muscles in the heart’s ventricles 
• Congestive Heart Failure - weakening of the ventricles causes a build-up of pressure in the blood vessels from the lungs^4,6,8

Respiratory causes

• Tension Pneumothorax - this is caused by air building up in the lung (pleural) membrane. This can cause increased pressure in the chest, which in turn puts external pressure on the heart⁶
• Acute Asthma - an asthma attack causes swelling and narrowing of the airways. This increases inflation of the lungs to compensate for the breathing difficulty, which in turn creates increased pressure on blood vessels and the heart⁵
• Chronic Obstructive Pulmonary Disease (COPD) - as with asthma, COPD can have acute symptoms - caused by a cold, or chest infection, and the lungs similarly overinflate causing the same pressure on the arteries to the heart
• Pleural Effusion - similar to pericardial effusion, pleural effusion is having too much fluid in the pleural membrane around the lungs
• Pulmonary embolism - if a very large blood clot from another part of the body travels to the lung (pulmonary) arteries and blocks them, this can also cause a drop in blood pressure^5,8

Other Underlying Conditions:

• Severe hypovolaemia - a reduction in blood volume, causing less blood to be pumped around the body^1,7

Management and treatment

Pulsus paradoxus is not a disease in itself, but is a clinical sign found associated with other conditions. The only way to eliminate pulsus paradoxus is to find and treat the underlying cause. 

Medical professionals will assess you by taking a medical history, and by carrying out a physical examination and investigations related to the potential cause. 

For both cardiac and lung cases, these tests may include blood tests and chest X-rays. Cardiac investigations also include echocardiograms, to look at the structure and muscles of the heart and electrocardiogram (ECG) to look at the electrical activity. Respiratory investigations include arterial blood gases, and CT Pulmonary Angiography (CTPA) to assess the structure of the lungs and assess for blood clots, along with ultrasound scans of the deep veins of the legs.

Significance in different medical conditions

Where pulsus paradoxus occurs in pericardial effusion, it is very likely that the effusion may progress into a cardiac tamponade. However, it is important to note that a lack of pulsus paradoxus does not exclude cardiac tamponade. People with suspected cardiac tamponade and pulsus paradoxus must be managed as an emergency.¹

In acute asthma, the presence of pulsus paradoxus relates directly to the severity of the asthma, with the drop in blood pressure increasing with greater airway obstruction.⁴

Prognosis

As pulsus paradoxus is a clinical sign of an underlying diagnosis it does not have a prognosis. Through investigations, clinical history, physical examination and subsequent diagnosis a treatment plan can be made to treat the condition causing it. 

Summary

Pulsus paradoxus, characterized by a drop of more than 10 millimeters of mercury (mmHg) in systolic blood pressure during inhalation, serves as a clinical indicator of an underlying condition. While a large pericardial effusion ranks among the most common causes, various heart and lung-related issues can also contribute, along with severely reduced blood volume. Typically asymptomatic, pulsus paradoxus is identified during blood pressure assessments, palpation of the pulse, or measurements using a pulse oximeter, particularly in hospital settings where arterial lines may be utilized for measurement.

Not a standalone medical condition, pulsus paradoxus warrants further investigation to pinpoint its root cause. Subsequent treatment hinges upon the specific diagnosis, tailored to address the underlying condition effectively.