Post-Polio Health (ISSN 1066-5331)
Vol. 11, No. 4, Fall 1995
New Breathing Problems in Aging Polio Survivors: Respiratory Muscle Weakness
Ann Romaker, MD, Kansas City, Missouri
In my pulmonary practice over the past 15 years, I have seen individuals who have a history of polio and who have respiratory problems but are unaware of them. Only one required ventilatory support during acute polio, and one other had known bulbar polio. The others had isolated or extensive limb involvement, even quadriplegia. Most had involvement in just a single limb. When studied, all of them had measurable respiratory muscle weakness. Anyone with a prior history of a neuromuscular disease, such as polio, needs to be evaluated in depth before and around stressful, physiologic events such as surgery.
Function of the respiratory muscles ...
The diaphragm is the major muscle of breathing and its descent increases the length of the thorax and increases lung capacity. The external intercostal muscles pull the ribs up and out. The scalene muscles raise the rib cage and the sternum (or breastbone). Another muscle, the sternocleidomastoid, elevates and expands the rib cage. Negative pressure is created within the chest, and the increase in the dimension of the chest increases the volume of the lungs. Air then enters the lungs through the nose, and is inspired.
Expiration is a much less active process. The abdominal muscles pull the ribs down and push the diaphragm up. The internal intercostal muscles pull the ribs down and in and squeeze the air out. If either the inspiratory or expiratory muscle groups, or both, are not functioning properly, some type of respiratory assistance may be needed.
Representative case ... An individual with involvement (that she was aware of) only in her legs and who wears leg braces, works full time as a nurse. After routine gynecologic surgery, she developed pneumonia and had problems maintaining an adequate oxygen level. I was called in because the gynecologist and internist did not understand why the chest x-ray would not clear and why her oxygen level was so low. The first thing I ordered was a pulmonary function test to determine how strong her respiratory muscles actually were.
Pulmonary function tests ...
In my opinion, the most accurate is a specific test of muscle strength. Some call it maximum inspiratory pressure. We call it negative inspiratory force. Expiratory strength can be measured by blowing as hard as possible against a resistance. We measure how much force is generated when someone tries to take a breath against an occluded mouthpiece. How hard one struggles to take a breath reveals how strong the respiratory muscles are. These special tests are helpful, easy to do, and they can be done at the bedside. However, not all hospitals are properly equipped.
Standard respiratory testing involves having a clip placed over the nose while blowing as hard as possible. This measures actual lung volume and the ability to push air out in one second. Results of standard respiratory testing can give an indication of respiratory muscle weakness.
If any of the breathing muscles are weak, lung capacity and ability to expel air are reduced proportionally. It is important to note that with repeated effort most people have a learning curve and will get better results over the first three or four tries. On the contrary, someone with muscle weakness, who is asked to work harder and harder, will get worse with each try. A knowledgeable pulmonologist looking at that pattern will recommend tests to measure respiratory muscle strength.
Representative case ... The individual referred to earlier did have a significant decrease in respiratory muscle strength. The normal amount of pressure generated to breathe against an occlusion is about minus 60 to 70 centimeters of water pressure. She was generating about minus 20. As a matter of fact, no individual with prior neuromuscular disease who has been tested in my practice has done better than minus 26.
Stressors on the breathing system ...
There may be no consequences of respiratory muscle weakness at all for someone in the minus 30 to minus 40 category until the breathing system is stressed, and surgery is often the stressor that highlights the fact that one has weak breathing muscles.
Infections also can highlight weak breathing muscles. If some find it difficult to cough, which is another function of the respiratory muscles, and have severe pneumonia, they may have difficulty clearing secretions, trouble maintaining oxygenation and problems recovering from respiratory infection. Individuals with difficulty coughing due to weak muscles also may have a tendency toward bronchitis.
Medications also may unmask respiratory muscle weakness. Some post-polio individuals who believe they do not have respiratory weakness may take sleeping pills and then cannot cough, or take a deep breath. Others can react the same way to pain medications.
The respiratory weakness appears with the use of the medication.
Exercise can also be the trigger. Polio survivors who do not recognize their respiratory muscle weakness may live a fairly sedentary life noting that they are short of breath with exercise and then quit exercising. When they are forced into vigorous exercise, their respiratory weakness becomes apparent.
Others who are not aware of any particular breathing problem show problems during sleep when studied. Everyone's tidal volume drops when sleeping, as does the oxygen level. People with respiratory muscle weakness may present initially with problems just during sleep which is why sleep studies are recommended.
If one has weak respiratory muscles and is overweight, the muscles are required to do more work. People with borderline respiratory muscle function may do just fine at a normal weight but may not be able to tolerate an extra 30 pounds. People who are borderline live fairly normal lives. However, they do not handle physiologic stress too well and may develop chronic respiratory insufficiency resulting in exercise limitation, abnormal gax exchange (with low oxygen and a rise in carbon dioxide), and profound oxygen desaturaion during sleep which can cause strain on the right side of the heart and possibly cor pulmonale. One can develop acute respiratory failure from respiratory muscle w eakness in conjunction with a physiologic stressful event. This situation requires mechanical ventilation immediately.
Other conditions of concern are the ability of the esophagus to function, dysphagia (swallowing problems), and aspiration (taking in of fluid or particles of food in the lung).
Suggestions for management ...
Support for people who have weak respiratory muscles includes aggressively treating infections and regularly implementing chest physical therapy that can be done at home when someone has bronchitis. However, when someone has an infection and trouble coughing, more assistance may be needed. Many hospitals do not have the older IPPB (intermittent positive pressure breathing) machine, but the same principle can be employed with Intermittent CPAP (continuous positive airway pressure). It is generally prescribed 15 minutes four times a day resulting in considerable improvement in the movement of air in the lungs decreasing atelectasis (small mucus plugs in the lungs).
Another support for respiratory muscle weakness is rest. The breathing muscles can be rested at night by using one of the many types of ventilation assistance.