Shortness of breath – what are its causes?

Shortness of breath, also known as dyspnea, is an unpleasant, subjective feeling of not being able to breathe well enough and not getting enough air. In healthy persons, it usually occurs after intense physical activity. When it is a symptom of a disease, it may take the form of effort dyspnea (occurring during activities of varying intensity) or dyspnea at rest (occurring while being idle).

What is shortness of breath?

Dyspnea is defined as a feeling of being short of breath and having difficulty breathing. It can be a physiological symptom, that is, it can occur in healthy people during significant physical exertion and disappears after rest. If, on the other hand, shortness of breath is caused by negligible physical effort, daily activity, or even it occurs when a person is at rest - it can be a pathological symptom. 

Based on its duration, shortness of breath is divided into two categories: 

Acute dyspnea - it develops relatively quickly, although depending on its cause, "quickly" can mean anywhere from a few seconds to several days. It lasts until its causes are eliminated or effective treatment is applied.

Chronic dyspnea - lasts for an extended period of time, increases gradually, initially being a symptom of hard effort, and over time becoming also a resting symptom. 

Based on the circumstances of occurrence, dyspnea is divided into:

effort dyspnea - occurs during intense physical activity, 

dyspnea at rest - occurs even when the patient is lying idly in bed, without any physical activity. 

In addition, there are specific types of dyspnea that appear or worsen depending on the patient's body position. These include: 

orthopnoë – occurs when lying down and subsides when the patient sits or stands up, 

platypnoë – occurs when standing or sitting and is relieved after lying down. 

How dyspnea develops

The mechanisms of dyspnea’s development are very complex and not fully understood. Dyspnea is triggered based on interactions between neurological centers located in the cerebral cortex and the medulla, as well as signals received and transmitted by receptors located in the lungs, chest, and chemoreceptors responding to blood gas concentration. 

There are two basic mechanisms of dyspnea’s formation: 

The first of those is tissue hypoxia happening as a result of: 

respiratory insufficiency - a disturbance of proper gas exchange in the lungs, leading to a decrease in the concentration of oxygen in the arterial blood and an increase in the concentration of carbon dioxide contained in it, which causes a reduction in the amount of oxygen supplied to the tissues, 

a decrease in cardiac output – a reduction in the volume of blood supplied by the heart, resulting in a lowered blood supply and thus inadequate tissue oxygenation, 

anemia - a decrease in the concentration of hemoglobin, which is used to transport oxygen in the blood., 

poisoning with substances that reduce the body’s ability to bind hemoglobin with oxygen, e.g. carbon monoxide, 

The second factor causing dyspnea is hyperventilation, caused by excessive stimulation of the respiratory center resulting from: 

the reduced diameter of the airways caused by obstructive diseases such as asthma or COPD,

the reduction in the lungs’ functional surface, where gas exchange takes place, as a result of heart disease with pulmonary congestion, interstitial lung diseases, chest deformities, or pleural diseases,

weakened respiratory muscles in muscle and neuromuscular diseases,

the reduction of blood supply to the lungs in pulmonary embolism,

disturbances in the acid-base balance, particularly in metabolic acidosis,

the functioning of intrinsic (e.g. uremic toxins in renal failure) and extrinsic toxicants (e.g. salicylates),

the body’s reaction to strong emotional or physical stimuli,

intense exercise. 

Shortness of breath – causes 

The most important pathological causes of dyspnea include:

chronic obstructive pulmonary diseases,

bronchial asthma,

interstitial lung diseases,

bronchiectasis,

primary and metastatic lung cancer,

chronic and acute heart failure,

myocardial infarction,

infectious diseases of the respiratory system - pneumonia, bronchitis, tuberculosis,

pneumothorax,

anemia,

pulmonary embolism,

foreign body in the airways,

muscle and neuromuscular diseases,

metabolic acidosis,

poisoning. 

Shortness of breath - diagnosis and treatment 

Numerous laboratory, imaging, and functional tests can be used when diagnosing dyspnea, and which of those are necessary is decided based on the symptom's suspected cause. And so, in the diagnosis of obstructive pulmonary disease, spirometry will be necessary, when suspecting a neoplastic disease, computed tomography is used, and in heart failure - echocardiography. Laboratory tests can reveal acid-base disorders, possible increases in inflammatory parameters, or an increase in BNP indicating worsening of heart failure.   

Treatment is also usually tailored to the dyspnea's cause. In obstructive diseases, it is aimed at bronchodilation, in heart failure - diuretic treatment, and in infectious diseases - antimicrobial treatment.