Paroxysmal Nocturnal Dyspnea Causes

Paroxysmal nocturnal dyspnea, often called "PND" by doctors, is a particularly distressing symptom usually caused by heart failure. A person who has PND will suddenly awaken from a deep sleep with severe dyspnea (shortness of breath) and will find him-or-herself gasping for air, coughing, and feeling compelled to get out of bed and assume an upright posture. At the very least the victim will sit up at the edge of the bed, and often may feel a need to go to an open window for air.

The breathlessness generally improves over several minutes. Even after the symptoms go away, however, it still may be impossible to return to sleep after an episode of PND, due to the anxiety that this very distressing and dramatic symptom commonly produces.

Sometimes the PND does not resolve quickly and instead may persist. Because the symptoms are invariably too severe to ignore, a persistent episode of PND compels a call to 911 or a trip to the emergency room.

Whether or not it resolves on its own, PND is always a dangerous sign which usually indicates that a person’s heart failure is becoming substantially worse. So, anyone who experiences PND needs to contact their doctor right away, even if the symptoms resolve quickly.

Paroxysmal nocturnal dyspnea is usually caused by congestive heart failure, most commonly (but not always) in people who also have had episodes of dyspnea with exertion, or of orthopnea (shortness of breath when lying down).

People who experience PND also usually have at least some edema (swelling) in their feet and legs which, in heart failure, usually indicates fluid overload.

In people who have heart failure, lying down to go to sleep can cause significant fluid shifts in the body. For one thing, fluid tends to shift from the tissues into the plasma, which increases the plasma volume.

Further, some of the excess fluid, that gravity has “pooled” in the legs or the abdomen during the day is able to move from the lower parts of the body when the person lies down. This excess fluid then is able to redistribute to the lungs.​

Sometimes these fluid shifts will cause shortness of breath as soon as the person with heart failure lies down. This immediate fluid shift produces the symptom of orthopnea. People who have orthopnea quickly learn to elevate the head of their beds, which has the effect of keeping their chests elevated. This helps keep the fluid from moving up to their lungs. (This is also why doctors usually ask their patients with heart failure how many pillows they use at night — it’s a rough estimate of the degree of orthopnea that person is experiencing.)

But with PND the fluid shifts do not cause symptoms right away. Rather, a chain of events occurs that eventually (after the individual has had a chance to fall asleep) produces a delayed — and usually much more severe — onset of dyspnea. The reason for the delayed onset of symptoms in people with PND is not entirely clear. It is thought that perhaps the respiratory center in the brain may become depressed during sleep in people with heart failure, or that reduced levels of adrenaline during sleep may depress cardiac function, and gradually allows fluid to accumulate in the lungs.

The “right” way to use the term “PND” is not completely agreed upon by doctors. Cardiologists generally consider PND to be a term of art, and they tend to apply it exclusively to patients with congestive heart failure. This usage imparts a particular significance to “PND.” People with heart failure who develop PND are very likely to develop more severe, acute heart failure quite soon. This means that they ought to have aggressive therapy right away to prevent that severe, possibly life-threatening episode of heart failure from occurring.

So when cardiologists say “PND” they are making both a diagnostic and a prognostic statement.

However, strictly speaking, “paroxysmal nocturnal dyspnea” really just means “sudden-onset shortness of breath at night,” and as such it can be applied to any medical condition that may produce dyspnea during sleep. So, among the medical community at large, “PND” is just a description of a symptom. Thus, you will hear “PND” applied to several different medical conditions that can cause sudden dyspnea at night. These conditions are quite numerous and include sleep apnea, asthma, and pulmonary embolus. They also include cardiac conditions other than congestive heart failure, such as diastolic heart failure and acute cardiac ischemia (as with acute coronary syndrome).

It’s not up to you to figure out whether your acute dyspnea at night is due to heart failure or to some other cause. It’s up to your doctor. What you need to know is that PND always indicates that a serious medical problem is going on. Whatever the cause turns out to be, you need to get medical help right away if you experience this symptom.