Parkinson’s Disease (PD) is a progressive neurological disorder characterized primarily by motor symptoms like tremor, rigidity, and slowed movement. Shortness of breath, or dyspnea, is a common and often distressing symptom affecting many individuals with PD. This feeling of being unable to get enough air can be a motor or non-motor manifestation of the disease. The causes are complex, stemming from the underlying degeneration in the brain that affects both movement and involuntary bodily functions.
Impairment of Respiratory Muscle Function
The hallmark motor symptoms of Parkinson’s Disease directly interfere with the physical mechanics of breathing. Rigidity, the muscle stiffness characterizing PD, affects the chest wall and diaphragm, restricting their ability to expand fully. This stiffness reduces the compliance of the ribcage, making the chest less elastic and requiring more effort to breathe.
Bradykinesia, the slowness and smallness of movement, further reduces the amplitude and efficiency of breathing movements. The muscles responsible for inhalation and exhalation, including the diaphragm and intercostals, move slowly and with reduced force. This muscular impairment often results in a restrictive lung pattern, meaning the total volume of air the lungs can hold is significantly reduced.
Uncoordinated respiratory muscle action can also lead to a paradoxical breathing pattern. In this scenario, the chest wall moves inward during inspiration instead of outward, indicating a lack of synchronized contraction. This mechanical failure makes deep breathing difficult and reduces the overall efficiency of gas exchange, contributing to the sensation of breathlessness.
Autonomic Regulation and Breathing Control
Breathing is controlled by the Autonomic Nervous System (ANS), which manages involuntary functions like heart rate and breathing rhythm. In PD, progressive neurological changes can damage ANS centers, particularly those in the brainstem, leading to dysautonomia. This condition disrupts the body’s ability to maintain a consistent and stable breathing pattern.
The dysregulation results in irregular breathing, including periods of shallow or rapid respiration that do not meet the body’s oxygen needs. Sleep-related breathing disorders, such as obstructive sleep apnea, are also common due to PD’s effect on upper airway muscle function. ANS dysfunction can also alter the sensitivity of chemoreceptors, the body’s sensors that monitor oxygen and carbon dioxide levels in the blood.
This altered sensitivity means the brain may not correctly sense when oxygen is low or carbon dioxide is high, leading to an inability to appropriately adjust the breathing rate or depth. This failure of the involuntary control system can cause difficulty adjusting breathing during physical exertion. Furthermore, changes in autonomic tone, such as increased parasympathetic activity, may increase airway resistance, further complicating airflow.
Secondary Physical and Infectious Complications
The progression of Parkinson’s Disease often leads to structural changes that limit lung capacity. A common consequence is the development of a forward stooping posture, known as kyphosis, which physically compresses the chest cavity. This persistent flexed posture restricts the full expansion of the lungs, reducing the total lung volume available for breathing.
Another serious complication is the increased risk of aspiration pneumonia, a leading cause of death in people with PD. PD frequently causes dysphagia, or difficulty swallowing, because the coordination between the pharyngeal and respiratory muscles is impaired. This swallowing dysfunction allows food, liquid, or saliva to accidentally enter the lungs, a process called aspiration.
Aspiration introduces foreign material and bacteria into the pulmonary system, causing inflammation and infection that manifests as pneumonia. The resulting infection in the lung tissue compromises the ability to exchange oxygen and carbon dioxide, leading to shortness of breath. The reduced strength of the cough reflex, also due to PD, makes it harder to clear the aspirated material, increasing the risk of infection.
Contribution of Parkinson’s Disease Medications
While treatments for PD are designed to improve motor function, they can sometimes have unintended effects on breathing. Levodopa and other dopamine agonists can lead to dyskinesia—involuntary, erratic movements. When these movements involve the muscles of the trunk, chest, and diaphragm, the condition is termed respiratory dyskinesia.
Respiratory dyskinesia causes irregular, rapid, and sometimes shallow breathing patterns that make breathing erratic and tiring. This effect often occurs when medication levels are at their peak, known as “peak-dose” dyskinesia. Conversely, some individuals experience dyspnea during “off” periods, when medication levels are low and underlying rigidity and bradykinesia return to restrict muscle movement.
In rare instances, certain older-generation dopamine agonists have been linked to pleuropulmonary fibrosis, a scarring of the lung tissue that causes breathing difficulty.