Polio survivors may have difficulties with breathing related to their polio. There are three groups of polio survivors with respiratory difficulties: 1) those who had respiratory failure during their acute illness and were never weaned from a ventilator, 2) those who develop breathing difficulties later in life and 3) those with sleep disordered breathing (sleep apnea). This article will deal primarily with the latter two groups of patients.
As polio survivors age, they may experience accelerated strength loss both in muscles that were initially affected by polio but seemed to recover fully and in muscles that did not seem to be affected by the acute illness. These muscles may include those necessary for breathing such as the diaphragm, chest wall (intercostal), abdominal and even neck (sternocleidomastoid and scalene) muscles. If these muscles lose enough strength, the ability to breathe is impaired. Early difficulties with breathing may not be recognized by the patient. In addition to muscle weakness, scoliosis (curvature of the spine) and other superimposed lung diseases, such as asthma or chronic obstructive pulmonary disease (COPD) caused by smoking, can contribute to breathing difficulties.
In patients with polio who have breathing difficulties because of muscle weakness and do not have an additional form of lung disease, the problem is purely mechanical, i.e. due to inability to completely fill the lungs with air. One can think of the lungs as balloons that need to be fully inflated in order to work optimally. Muscle weakness can make it impossible to fully inflate the lungs. Once the lungs are inflated, the body is able to extract oxygen from the air in them without difficulty. Forced vital capacity (FVC) is a measure of the adequacy with which an individual can inflate his lungs. FVC is normally expressed as a percentage of the predicted value for the patient’s height and age. Most patients with polio do not experience symptoms related to underventilation until their FVC is 50% of predicted or less.
An arterial blood gas (ABG) is sometimes performed to assess adequacy of ventilation. A sample of blood is taken from the radial artery, near the wrist, so that both oxygen and carbon dioxide levels can be assessed. Because polio patients do not have difficulty extracting oxygen from air, these levels are usually normal until the FVC falls well below 50% of predicted. With advanced respiratory failure, the oxygen level may fall below normal, and the carbon dioxide level becomes elevated. The ABG is not a sensitive screening test for polio related breathing difficulties, but it is useful in assessing polio patients who already use ventilators.
Symptoms that suggest difficulties with breathing often occur first during the night because patients with muscle weakness frequently have a lower FVC when lying down than when sitting up. These symptoms may include poor sleep quality with frequent awakening, early morning headaches, excessive daytime fatigue or sleepiness and frequent nightmares. Other signs of respiratory muscle weakness are inability to sleep lying down, frequent sighing and a weak cough with difficulty raising secretions. A sign of more advanced respiratory failure is shortness of breath with exertion or when eating or speaking. Of course, polio related muscle weakness is not the only cause of any of these symptoms, so other medical problems should be excluded. Heart disease is a common cause of shortness of breath.
Patients who had respiratory or bulbar (speech and swallowing muscles) weakness during their acute polio illness are most likely to develop problems with breathing years later, but all polio survivors are at risk. Thus, I recommend a baseline pulmonary function test for any patient who has had polio. If the test is normal, it does not need to be repeated unless symptoms suggesting a breathing problem subsequently develop.
Pulmonary function tests are performed by a respiratory therapist in a standard laboratory that is part of all acute care hospitals. The test involves performing several maneuvers that all involve breathing or blowing forcefully into a tube. The test itself is not uncomfortable. Patients are often given a medication called a bronchodilator as part of the test to assess whether or not they have abnormal narrowing of the airways such as occurs in asthma and COPD. When assessing patients with muscle weakness, the FVC measurement and maximum inspiratory and expiratory pressure (MIP and MEP) measurements are most important. The MIP and MEP assess the strength of the muscles used for inspiration (breathing in) and expiration (blowing out). Good inspiratory muscle strength is necessary to fully inflate the lungs, and good expiratory muscle strength is necessary to cough up secretions. It is useful to also measure the FVC with the patient lying down because it may be less than it is sitting up. If any of the measurements discussed above are less than 80% of predicted (considered normal), the pulmonary function tests should be repeated regularly, usually annually unless symptoms dictate otherwise, to detect progression of breathing muscle weakness that may require treatment. Patients with an FVC or MEP less than 50% of predicted often benefit from treatment to assist their breathing muscles. In addition, patients with values above 50% of predicted will benefit from treatment if they are symptomatic.
The treatment for a low FVC is to provide mechanical assistance with inflating the lungs. This is done with non-invasive positive pressure ventilation (NIPPV) using either a bilevel positive airway pressure (BiPAP) machine or a portable ventilator to help blow more air into the lungs. The patient can use a mask over the nose or the mouth through which the air is delivered. Most commonly, patients are advised to use the machines at night to assist with their breathing. Oxygen is not needed unless the patient has a disease other than polio that affects the breathing. In fact, oxygen can be harmful in patients with breathing difficulties due to muscle weakness because it suppresses the body’s natural drive to breathe. A respiratory therapist familiar with NIPPV techniques is very helpful for teaching patients to use NIPPV and recommending a mask and machine settings that are comfortable.
Methods of assisting breathing, other than using NIPPV, exist but are less commonly used. These include a technique called glossopharyngeal breathing (frog breathing) and the use of body ventilators, similar to the old iron lung in mechanism of action, such as the portalung, chest shell and poncho. A detailed discussion of these devices is beyond the scope of this article.
For patients with weak expiratory muscles (low MEP), a machine called an in-exsufflator, ‘coughing machine,’ or Cough Assist (J.H. Emerson Co., MA) is useful. The device has a vacuum cleaner type of motor and is used to suck deep secretions or mucus out of the lungs. It is especially useful when patients have an upper respiratory tract infection (common cold); good secretion clearance helps prevent the development of superimposed pneumonia, a potentially serious medical problem that may require hospitalization.
In the past, polio patients have experienced difficulty getting their insurers to cover NIPPV equipment and the in-exsufflator. In January 2002, a new Medicare and Medicaid ruling was passed that supported reimbursement for the in-exsufflator in those with a MEP less than 60 cm H20 (about 60% of predicted for most adults). Also, according to Medicare guidelines, NIPPV equipment should be reimbursed for any polio patient with an FVC less than 50% of predicted without the requirement that a sleep study be performed or a low oxygen saturation be documented.
Preventing infection is important in patients with breathing muscle weakness. A pneumococcal vaccination protects against one form of bacterial pneumonia and is only needed once. The influenza vaccination (flu shot) protects against common strains of the flu caused by influenza viruses. This should be received yearly.
There are no medications that can improve breathing difficulties primarily due to muscle weakness. Thus, inhalers and other medications commonly prescribed to treat asthma are not usually helpful to polio patients and may have adverse side effects.
Sleep apnea is a second type of breathing difficulty that may be experienced by polio survivors. Sleep apnea refers to brief episodes when one stops breathing during sleep. If the episodes are long enough, they usually wake the patient. Oxygen levels fall abnormally low during the episodes of apnea. Patients with sleep apnea often feel fatigued during the day and unrefreshed by their sleep. If sleep apnea is severe, serious medical complications such as heart rhythm disturbances, pulmonary hypertension and congestive heart failure can develop. There are 2 major causes of sleep apnea in polio patients. The first is weakness of the throat muscles that allows the airway to collapse when one lies down. The second cause is a direct effect of the polio virus on nerve cells in the brainstem that help control breathing.
Sleep apnea should be suspected if quality of sleep is poor or if excessive daytime sleepiness occurs in a patient with normal pulmonary function tests. Family members of patients with sleep apnea may report loud snoring or actually may observe brief periods where the patient appears to stop breathing in his or her sleep.
Sleep apnea is diagnosed by undergoing a sleep study. Sometimes, sleep studies also are useful for determining if a patient with respiratory muscle weakness would benefit from NIPPV and/or for assessing how well a patient using NIPPV is being ventilated. Sleep studies are performed in a special laboratory where the patient is required to spend the night. During sleep, brain wave signals (EEG), limb movements, heart rhythm and oxygen saturation are measured.
Once sleep apnea has been diagnosed, the treatment involves using a mask over the nose to blow air into the lungs with either a BiPAP or a continuous positive airway pressure (CPAP) machine. The airflow acts as a stent to prevent the airway from collapsing. CPAP is the standard treatment for patients with sleep apnea who do not have weakness of the breathing muscles. In polio patients who have both weakness of the breathing muscles and sleep apnea, a BiPAP machine is used to assist the weak muscles and prevent airway collapse.
Any polio survivor who feels excessively fatigued, sleeps poorly or exhibits other symptoms discussed above should discuss with his or her physician whether or not an evaluation for breathing dysfunction is indicated. The appropriate treatment of polio related breathing problems can greatly improve the polio survivor’s fatigue resistance, energy level and quality of life.
ABG: arterial blood gas
BiPAP: bilevel positive airway pressure
COPD: chronic obstructive pulmonary disease
CPAP: continuous positive airway pressure
FVC: forced vital capacity
MEP: maximum expiratory pressure
MIP: maximum inspiratory pressure
Lisa S. Krivickas, MD, is Assistant Professor of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, Boston, MA.
Dr. Krivckas kindly wrote this article at the request of the GBPPA. Reprint permission should be obtained from:
Lisa S. Krivickas, MD
Spaulding Rehabilitation Hospital
125 Nashua St.
Boston, MA 02114-1198