Short of Breath (Dyspnea)
Dyspnea means difficulty breathing or shortness of breath. There
is a subjective component. The dyspnea patient is distressed
by sensations of difficulty and limited breathing ability. The respiratory system is designed
to maintain adequate oxygenation and acid-base status by adjusting the arterial tension of carbon dioxide [PaCO2] to maintain normal pH.
Derangements in oxygenation as well as acidemia lead to breathing discomfort.
Dyspnea may be
caused by inadequate delivery of oxygen to, or utilization by muscles.
Persona et al summarized the problem: ”Shortness of breath, or dyspnea, an
uncomfortable subjective breathing sensation that is distressful or unpleasant
in nature, causes anxiety because the shortness of breath feels out of
proportion to the degree of effort exerted. By contrast, an exercising athlete,
for example, will not complain of dyspnea because a degree of respiratory
difficulty is expected. Dyspnea prevalence increases with age from as low as
2.4% in the population aged 18 years and older to 32% in the population aged 70
years and older.”
The rate and depth of breathing is
regulated by a host of sensors and brain responses. The sympathetic nervous
system is the master controller that increases heart and breathing rates when
activated. Sympathetic dyspnea is often described as an anxiety attack. Breathing is regulated by signals from neural receptors in the lungs, large and
small airways, respiratory muscles and chest wall. Arterial sensors are found in
the carotid and aortic bodies and central chemoreceptors respond to the partial
pressure of oxygen (PO2), partial pressure of carbon dioxide (PCO2) and pH of
the blood and cerebrospinal fluid. The diagnosis of dyspnea begins with
assessing lung and heart function. Cardiac causes of dyspnea include congestive
heart failure, coronary artery disease, recent or remote myocardial infarction,
cardiomyopathy, valvular dysfunction, left ventricular hypertrophy with
resultant diastolic dysfunction, asymmetric septal hypertrophy, pericarditis and
arrhythmias. Pulmonary causes include obstructive and restrictive processes. The
most common obstructive causes are chronic obstructive pulmonary disease (COPD)
and asthma. Restrictive lung problems include extrapulmonary causes such as
obesity, spine or chest wall deformities, and intrinsic pulmonary pathology such
as interstitial fibrosis, pneumoconiosis, granulomatous disease or collagen
Other body systems may be the cause: metabolic conditions
such as anemia, diabetic ketoacidosis and other, less common causes of metabolic
acidosis, pain in the chest wall or elsewhere in the body, and neuromuscular
disorders such as multiple sclerosis and muscular dystrophy. Nasal obstruction
due to allergy, polyps or septal deviation, enlarged tonsils and supraglottic
or subglottic airway stricture may contribute to or cause dyspnea.
reactions are created by the release of cytokines, molecular signals that effect
breathing. This is most evident during asthma attacks caused by food, drugs and
airborne exposure to antigens. The cytokines may cause swelling at all levels of
the respiratory tract, obstructing airflow. Systemically released cytokines may
activate receptors that control breathing causing dyspnea. The anaphylaxis
victim may be hyperventilating as his or her body release adrenalin to
counteract the decreasing blood pressure associated with the allergic reaction.(Gene R. Pesola
et al. Screening for Shortness of Breath: Stretching the Screening Paradigm to Tertiary Prevention.
Am J Public Health. 2017;107(3):386-388.)
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