What is shortness of breath and why does it occur?
Shortness of breath, or dyspnea, is the subjective sensation of air hunger, labored or rapid breathing. It is not an independent disease, but a symptom that can indicate a wide range of conditions, from mild fatigue to serious pathologies. While many associate shortness of breath with lung or heart diseases, there are less obvious causes that are often underestimated. Understanding these hidden factors is crucial for accurate diagnosis and effective treatment, improving the quality of life of patients.
When breathing is interrupted: the connection between shortness of breath and cardiovascular diseases
The cardiovascular system plays a key role in supplying the body with oxygen, and any disruptions in its work can manifest as shortness of breath. Some of these connections are not always obvious.
Obstructive sleep apnea (OSA)
Obstructive sleep apnea (OSA) is a condition in which repeated cessations of breathing or a significant decrease in its intensity occur during sleep due to the narrowing or complete closure of the upper airways. This leads to disrupted sleep, daytime sleepiness, and, more importantly, episodes of nocturnal hypoxemia (decreased blood oxygen levels). OSA is a widespread but often underestimated disorder, especially among patients with cardiovascular diseases [1].
Studies show that OSA is closely linked to coronary artery disease (CAD). Patients with CAD have a significantly higher prevalence of OSA [1]. Moreover, nocturnal hypoxemia, measured by the oxygen desaturation index (ODI), is associated with an increased risk of developing CAD [3]. OSA may also contribute to the development of the heart failure with preserved ejection fraction (HFpEF) phenotype, especially in patients with CAD. This phenotype is often associated with risk factors such as obesity, hypertension, and diabetes, which also frequently coexist with OSA [5].
Coronary artery disease (CAD) and heart failure
CAD, characterized by the narrowing of the coronary arteries, can cause shortness of breath during physical exertion due to insufficient blood supply to the myocardium. However, even in the absence of obstructive coronary artery disease (ANOCA), patients may experience angina and shortness of breath. In such cases, the cause may be coronary microvascular dysfunction and vasomotor dysfunction (CMVD) [4]. This is a condition where the small vessels of the heart do not function properly, limiting blood flow to the heart muscle, which can lead to symptoms similar to classic angina, including shortness of breath. Non-invasive methods, such as oxygen-sensitive cardiovascular magnetic resonance imaging (OS-CMR), are being developed to diagnose CMVD [4].
Heart failure with preserved ejection fraction (HFpEF)
As already mentioned, HFpEF is a form of heart failure in which the heart retains the ability to contract normally, but its ability to relax and fill with blood is impaired. This phenotype is closely linked to age and cardiometabolic risk factors and frequently coexists with OSA [5]. Patients with HFpEF experience shortness of breath, especially upon exertion, due to increased pressure in the left atrium and pulmonary veins.
Airways under threat: reflux and environmental exposure
In addition to direct heart problems, shortness of breath can be caused by conditions that, at first glance, have no direct relation to the respiratory system.
Gastroesophageal reflux disease (GERD)
Gastroesophageal reflux disease (GERD) is a condition in which stomach contents regularly flow back into the esophagus, causing symptoms or damage. In addition to typical manifestations such as heartburn and regurgitation, GERD can have extra-esophageal symptoms, including respiratory disorders [2]. The role of GERD in the pathogenesis of respiratory diseases is actively discussed. The prevalence of GERD among patients with bronchial asthma ranges from 30% to 90%, which is significantly higher than the average 24% in the control group. Patients with chronic obstructive pulmonary disease (COPD) also exhibit an increased prevalence of GERD [2]. Mechanisms linking GERD to shortness of breath may include microaspiration of gastric contents into the airways or reflex bronchoconstriction.
Exposure to ozone
The quality of the air we breathe has a direct impact on lung health. Ozone (O3) is a powerful oxidant that, when inhaled, causes irritation, airway hyperreactivity, inflammation, and damage to alveoli—the gas exchange zone of the lungs [6]. Even a single exposure to a high dose of ozone can lead to acute disruption of the bronchiolar epithelial barrier function, leakage of serum proteins into the bronchoalveolar space, destruction of tight junctions, and cell death. This is accompanied by the activation of reactive oxygen species (ROS), airway hyperreactivity, and inflammation [6]. Chronic exposure to ozone can lead to irreversible loss of alveolar cells and alveoli, a decrease in the gas exchange area, and the development of emphysema, which is one of the causes of chronic shortness of breath [6].
The importance of diagnostics and timely treatment
Shortness of breath, especially if it occurs regularly, intensifies, or is accompanied by other alarming symptoms (chest pain, dizziness, fainting), requires immediate medical attention. Self-diagnosis and self-treatment can be dangerous because the causes of shortness of breath can be diverse and serious.
A comprehensive examination, which may include:
- Medical history collection and physical examination.
- Pulmonary function tests (spirometry).
- Electrocardiography (ECG), echocardiography.
- Sleep studies (polysomnography or cardiorespiratory polygraphy) to detect OSA [1].
- Endoscopic examinations to diagnose GERD.
- Specialized studies, such as oxygen-sensitive cardiac MRI to detect microvascular dysfunction [4].
Early detection and adequate treatment of the underlying cause of shortness of breath not only alleviates symptoms but also prevents the progression of concomitant diseases, significantly improving the patient's prognosis and quality of life.
Sources
- Obstructive Sleep Apnea in Patients with Significant Coronary Artery Disease: An Underdiagnosed Condition. (Obstructive Sleep Apnea in Patients with Significant Coronary Artery Disease: An Underdiagnosed Condition.)
- Review article: gastro-oesophageal reflux disease in asthma and chronic obstructive pulmonary disease. (Review article: gastro-oesophageal reflux disease in asthma and chronic obstructive pulmonary disease.)
- Nocturnal Hypoxemia and Incident Coronary Artery Disease in Obstructive Sleep Apnea: Results from the Sleep Apnea Patients in Skaraborg Study. (Nocturnal Hypoxemia and Incident Coronary Artery Disease in Obstructive Sleep Apnea: Results from the Sleep Apnea Patients in Skaraborg Study.)
- Oxygenation-sensitive cardiovascular magnetic resonance imaging to identify coronary microvascular and vasomotor dysfunction in angina and no obstructive coronary artery disease. (Oxygenation-sensitive cardiovascular magnetic resonance imaging to identify coronary microvascular and vasomotor dysfunction in angina and no obstructive coronary artery disease.)
- Heart Failure With Preserved Ejection Fraction-Like Phenotype in Coronary Artery Disease and Obstructive Sleep Apnea: Insights From the RICCADSA Cohort. (Heart Failure With Preserved Ejection Fraction-Like Phenotype in Coronary Artery Disease and Obstructive Sleep Apnea: Insights From the RICCADSA Cohort.)
- Acute Respiratory Barrier Disruption by Ozone Exposure in Mice. (Acute Respiratory Barrier Disruption by Ozone Exposure in Mice.)
The information presented in this article is for informational purposes only and cannot replace professional medical consultation, diagnosis, or treatment. Always consult a qualified physician regarding any health-related questions.