Dyspnea on Exertion (Exertional Dyspnea): Causes and Treatment
Exertional dyspnea and its pathophysiology
Dyspnea on exertion is caused by various factors. However, low body oxygenation is the key parameter, which is always present in people with this symptom. Mouth breathing and chest breathing are among the main additional causes of exertional dyspnea since they reduce body and brain oxygenation and create the sensation of air hunger (shortage of air) like in people with heart disease and cancer. However, those who have diabetes or COPD (e.g., asthma or bronchitis) and many other chronic conditions are also most likely to experience this debilitating symptom, as many studies found.
What do we know about their body oxygenation and breathing at rest? Why do people with chronic diseases, but not healthy people, experience exertional dyspnea? What are the main problems with oxygen transport in the sick? Consider this evidence.
Chronic hyperventilation (or having an automatic deep-breathing pattern) leads to alveolar hypocapnia (lack of CO2), which causes low oxygen levels in body cells. Therefore, these people have more problems during physical exertion since any forms of exercise require additional oxygen, causing dyspnea on exertion.
Healthy or normal breathing is very small and slow. It is imperceptible or unperceivable (only about 500 ml for tidal volume, and 10-12 breaths/min with 6 L/min for minute ventilation at rest for a 70-kg person). Patients with dyspnea commonly have over 12 L/min (double the norm) for their ventilation rates at rest and over 18 breaths/min for respiratory frequency.
Overbreathing leads to greatly increased work of breathing due to large minute ventilation rates and causes many other adverse effects, apart from exertional dyspnea.
Exacerbating causes in the pathophysiology of exertional dyspnea are:
- oral breathing (due to reduction in NO or nitric oxide absorption and alveolar CO2)
- thoracic breathing (due to reduction in the arterial oxygenation causing hypoxemia)
- presence of chronic inflammation and sputum in airways, causing further narrowing or obstruction of air movement.
Physical exertion, due to anaerobic cell respiration at rest and elevated resting blood lactate, worsens gas exchange and causes further overbreathing and additional losses in alveolar CO2. This leads to acute exertional dyspnea. Acute dyspnea leads to even heavier and faster breathing due to a negative feedback in breathing control caused by a prominent O2 drive (hunger for air), instead of normal CO2-based control of respiration. Respiratory receptors located in the brain sense low brain oxygenation, creating the sensation of air hunger and trying to increase ventilation.
Treatment of dyspnea on exertion
This YouTube video clip "Dyspnea" explains causes and treatment of dyspnea in people with chronic diseases.
Significant reduction in exertional dyspnea has been found in numerous clinical trials after the application of various breathing techniques and respiratory devices that gradually change automatic (basal) breathing patterns at rest, reduce the degree of hyperventilation, and increase body-oxygen levels. Generally, patients with exertional dyspnea need to achieve more than 20 s for the body-oxygen test to prevent dyspnea at rest and on exertion.
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