Paroxysmal nocturnal dyspnea (PND) is a sensation of severe shortness of breath that typically awakens a person from sleep, often one or two hours after they have fallen asleep.
Here's a breakdown:
- Paroxysmal: Meaning sudden and intense.
- Nocturnal: Relating to or occurring in the night.
- Dyspnea: Shortness of breath or difficulty breathing.
Therefore, PND signifies sudden, severe shortness of breath at night that disrupts sleep. It's often relieved by sitting upright or standing.
Key characteristics of PND:
- Timing: It usually occurs 1-2 hours after falling asleep.
- Relief: The breathlessness improves when the individual sits upright, stands, or opens a window.
- Association: It is commonly associated with underlying heart conditions, particularly left ventricular heart failure.
Why does PND occur?
Several factors contribute to PND:
- Fluid redistribution: When lying down, fluid that has accumulated in the legs during the day redistributes to the central circulation. In individuals with heart failure, the heart may not be able to effectively pump this increased blood volume, leading to pulmonary congestion (fluid buildup in the lungs).
- Reduced adrenergic stimulation: During sleep, there is a decrease in sympathetic nervous system activity. This can further compromise heart function in individuals with underlying cardiac issues.
- Increased venous return: Lying down increases venous return to the heart, which the failing heart may not be able to handle effectively.
Differential Diagnosis:
It's important to differentiate PND from other causes of nocturnal breathlessness, such as:
- Orthopnea: Shortness of breath while lying flat, which is relieved by propping oneself up with pillows.
- Asthma: Nocturnal asthma can also cause breathlessness during the night, but it is usually associated with wheezing and chest tightness.
- Sleep Apnea: Characterized by pauses in breathing during sleep, often accompanied by loud snoring.
- Anxiety/Panic Attacks: Can sometimes manifest as sudden shortness of breath at night.
Clinical Significance:
PND is a significant symptom that warrants medical evaluation. It is often a sign of underlying heart disease or other medical conditions that require diagnosis and treatment.
