Options offered for respiratory care
This is the first of a two-part series on respiratory care, which concludes with "A Breath of Fresh Air."
When most of us think of breathing, we think first about our lungs, those spongy pink lobes where oxygen enters the blood and carbon dioxide leaves it. However, lungs can't do their job without the efforts of another, equally important group of structures, the muscles of ventilation.
For many people with neuromuscular disease, progressive weakness of these muscles significantly affects health, mobility and quality of life. In fact, for people with severe, generalized neuromuscular disease, complications from ventilatory muscle weakness are a major cause of death. As John Bach, co-director of the MDA clinic at the New Jersey Medical School in Newark, puts it, "Breathing in and coughing out are the two most important medical issues for a person with neuromuscular disease."
Advances in understanding of the special ventilatory issues in neuromuscular disease have led to a wide variety of options for many people needing ventilatory assistance. Perhaps even more important, strategies that keep the airways clear and the lungs free of infection can delay the need for "invasive" (tracheostomy tube) mechanical ventilation in most cases, and even avoid it in others.
Unfortunately, when we hear the phrase "mechanical ventilation," the only images most of us summon are of restriction and confinement — an iron lung or a maze of tubes and wires on a hospital bed. This may prevent some from seeking treatment at all until a crisis occurs, or from exploring the options that are available when the time comes.
Understanding those options, and exploring them early on, can make an important difference in both the length and the quality of life. In the words of one person with neuromuscular disease, effective mechanical ventilation "gave me back my life." And as John Paul McCoy, a 24-year-old ventilator user with Duchenne muscular dystrophy from Manhattan Beach, Calif., puts it, "It'll help your life a lot. You won't have to worry about breathing all the time, and you can have fun."
To understand the special ventilatory problems of neuromuscular disease, it's helpful to understand a bit about the workings of the respiratory system. Respiration includes both ventilation — moving air in and out of the lungs — and the exchange of gases (oxygen and carbon dioxide) between blood and air.
Taking a breath, called inspiration, requires contracting the diaphragm, a sheet of muscle below the lungs that separates the chest from the abdomen. As the diaphragm pulls downward, it causes the chest cavity to expand. Muscles in the rib cage pull the ribs outward, further expanding the chest. As the space inside the chest increases, outside air pushes in to fill the partial vacuum.
Air travels through the pharynx, or throat, into the trachea, the rigid tube you can feel at the front of your neck. The trachea divides into the left and right bronchi to enter the lungs. These main bronchi subdivide into smaller passages called bronchioles, and eventually end in blind sacs called alveoli, which are lined with blood capillaries. When air reaches the alveoli, oxygen passes into the blood, while carbon dioxide leaves the blood and enters the air.
One of the most important facts about respiration in neuromuscular disease is that there is nothing wrong with the gas exchange system. "Patients with neuromuscular disease have essentially normal lungs," says Robert Warren, director of Pediatric Pulmonology Services at Arkansas Children's Hospital in Little Rock. So, if a person can get air to the alveoli, he can get enough oxygen for all his needs. Weakness of the diaphragm and the rib cage muscles interferes with that, and is the reason mechanical ventilation may be needed.
This is quite different from other types of problems affecting the respiratory system, such as emphysema, cystic fibrosis, cancer or infection. In these conditions, muscle strength is usually normal, but gas exchange is impaired by obstruction or loss of exchange capacity. In such cases, it makes sense to provide extra oxygen, since less exchange surface is available in the lungs. But Bach believes that in neuromuscular conditions, "Perhaps the worst thing we can do for an otherwise healthy patient is to give them oxygen."
Unfortunately, says Greg Carter, co-director of the MDA clinic at Mary Bridge Hospital in Tacoma, Wash., some doctors, and even respiratory specialists, don't recognize these important differences when they treat people with neuromuscular disease. Carter notes that many physicians still use the confusing term "restrictive lung disease associated with neuromuscular disease," implying that the problem is in the lungs themselves. As a result, they may offer therapy designed for obstructive, but not neuromuscular, conditions.
The reason giving oxygen may do more harm than good stems from the way the body regulates breathing. High levels of oxygen in the blood suppress the natural drive to breathe, diminishing even further the already low rate of gas exchange. This allows carbon dioxide, or CO2, to build up in the blood to dangerously high levels. Supplemental oxygen temporarily hides the problem of underventilation, but does nothing to solve it. "It's like putting a Band-Aid on a cancer," Bach says.
|An Ambu bag, also known as a resuscitation bag, can be used to "stack breaths," which means taking a breath and holding it and then taking more breaths to put as much air into the lungs as possible.|
In addition, he says, bronchodilators — drugs that expand the airways — are also overused, since again, the problem isn't obstruction, but an inability to breathe deeply enough to fill and clear the lungs. Carter notes, however, that "some patients with very weak respiratory muscles do occasionally benefit from bronchodilators such as albuterol, because these agents not only dilate airways but help muscles contract more strongly."
Nonetheless, their possible benefits may not outweigh their risks even here, since bronchodilators can also affect the heart rate. Any drug affecting the heart must be used with caution where cardiomyopathy (heart muscle damage) may be a feature of the disease, as in Friedreich's ataxia, virtually all the muscular dystrophies and other generalized muscle diseases.
Deep breaths fulfill another important function besides supplying air to the lungs — they stretch out the lung tissue and chest wall. Just as the wrists and ankles will tighten without regular range of motion exercises to keep them loose, so will the lungs and chest wall stiffen without regular deep breaths, such as those taken during a yawn or a sigh. This stiffening can have serious consequences for the health of the lungs.
Breathing out and coughing
During normal expiration, or breathing out, the diaphragm relaxes while muscles in the rib cage contract. Air, now laden with CO2, reverses its course, passing out again through the bronchi and trachea. At the top of the trachea, it passes through the larynx, or "voice box," a group of muscular flaps that vibrate to produce sound.
When a more forceful expiration is required, such as for a cough, additional strength is provided by the abdominal muscles. Abdominal weakness can be more important than even diaphragm weakness, because of the crucial role played by coughing in maintaining healthy lungs.
The importance of coughing
Coughing may seem more like a small annoyance than a central mechanism of respiratory health. But, in fact, the forceful expulsion of air from the lungs during a cough is designed to remove mucus secretions, and removing secretions is the body's way of preventing infection.
Normally, the moist lining of the lungs produces small amounts of clear mucus, which traps dirt and bacteria from the air. The mucus is swept slowly up and out of the lungs by tiny hairs on the surface of the cells lining the airways. During infection, increased mucus levels may plug up some air passages.
|A spirometer can measure the vital capacity, the total volume of air that can be expelled after an unassisted breath. It can also be used to measure the maximum volume of air that the lungs can hold after using the "air stacking" procedure.|
This not only reduces the amount of lung tissue available for gas exchange, but greatly increases the likelihood of more serious infection, since the mucus plug prevents cleansing of the airways behind it. How do we clear it? We cough.
Unfortunately, weak abdominal muscles mean a weak cough. "Normal cough flows are between 6 and 20 liters per minute," Bach explains. "With advanced neuromuscular disease, this can be as low as 1 liter per minute." (A liter is about a quart.)
A second factor affecting the ability to cough is weakness of the bulbar, or throat, muscles. Coughing requires closing off the glottis, or top of the throat, in order to build up pressure inside the chest. Without good bulbar control, this may be impossible.
Finally, a good cough requires a deep breath. If the diaphragm is weak, if the chest wall has become stiff through underuse or if scoliosis (spinal curvature) interferes with expansion of the chest, a person may not be able to get enough air in to produce an effective cough. "None of us can cough with our lungs empty," Bach notes.
Signs of trouble
For many people with neuromuscular disease, the beginnings of ventilatory failure come on slowly and may be mistaken for other problems. Shortness of breath — the best-known symptom of too little oxygen — may not occur, especially when weakness prevents exertion. Instead, Warren says, the most common symptoms are fatigue, poor sleep, vivid dreams or nightmares, and headaches, especially right after waking. In fact, underventilation at night is often the first problem, both because the natural urge to breathe is lower during sleep, and because the abdomen pushes up against the diaphragm when a person lies down.
Lori Hinderer, 36, of Tucson, Ariz., had such symptoms, and only realized the cause in retrospect. "The worst part for me is that I had no idea I needed ventilatory assistance. For months, I had awakened with nausea and bad headaches in the morning. Over the course of the day, they would go away. I had no idea this was due to my muscular dystrophy."
Anxiety, confusion, loss of appetite and weight loss are also possible signs of impending respiratory failure, as is weakening of the voice and weak coughing that doesn't move mucus up toward the mouth.
Months of underventilation and inadequate coughing may go by without causing a respiratory emergency. A crisis can then appear, as if from nowhere, causing a life-threatening medical situation in which a major airway becomes clogged with mucus and the ventilatory muscles are too weak to cough it out.
A respiratory crisis is often set off by an infection of the respiratory tract, especially a chest infection.
Chris Arblaster of Washington, Pa., began with several bouts of pneumonia in the late fall of 1996. Chris, who has Becker muscular dystrophy, was 25 years old at the time and was using supplemental oxygen.
His mother, Barbara, recalls what happened the day after Christmas: "Chris woke up early that morning, but he was completely unaware of where he was, and he was talking nonsense. He went back to sleep, but I was really worried."
Chris woke up a couple of hours later, and remembers his mother saying, "I'm taking you to the hospital." Chris continues the story: "That's the last thing I remember from that period — I was unconscious for the next three days."
When he came to, he found himself in the emergency room with a breathing tube going from his mouth down his throat. He had a tracheostomy tube — a tube going directly into the trachea through a surgical incision — inserted a week later.
Preventing or postponing problems
Certainly not all people with neuromuscular disease will eventually need mechanical ventilation. In almost all cases of Duchenne muscular dystrophy, however, some form of mechanical ventilation is ultimately required; the same is true of amyotrophic lateral sclerosis (ALS). Other neuromuscular diseases differ in severity, and many people will never develop the diaphragm and abdominal weaknesses that put a person at risk. Nonetheless, such weakness is a possibility in the most advanced or severe cases of most of these conditions.
In cases of progressive ventilatory weakness, the need for mechanical ventilation may be delayed by a number of measures. The most important are effective coughing and regular deep breaths, discussed below. Warren lists a variety of measures you can take, including:
At the clinic
|People who are at risk for ventilatory problems may need to monitor their oxygen levels using a device called an oximeter.|
People with neuromuscular disease should have their ventilatory function monitored regularly. Bach says, "One of the most important aspects of evaluation for the neuromuscular patient is measuring the vital capacity," or the total volume of air that can be expelled after an unassisted deep breath. This is done with a simple instrument called a spirometer. He notes that it's important to measure vital capacity lying down, since it represents the sleeping position, and the first problems usually develop at night.
He goes on: "When vital capacity is less than 1.5 liters, we teach the patient how to 'stack breaths' using an Ambu bag (or a ventilator if one is already being used)." An Ambu bag has a mask that fits over the mouth and nose and a flexible bag that forces air into the lungs when it's squeezed. It's a sort of handheld ventilator.
"What air stacking involves is taking a breath and holding it, and taking a second breath on top of that and trying to hold that, and putting as much air into the lungs as possible. We then have the patient exhale that air into the spirometer, and that is the patient's maximum insufflation capacity," or the maximum volume of air that the lungs can hold. "The greater the maximum insufflation capacity, the greater the patient's ability to cough."
Whether the person has the strength to cough is a separate question, addressed by a different test.
"We use a peak cough flow meter and have our patient cough as hard as he can, and we measure the flow of air," Bach says. Peak flows above 6 liters per second are usually sufficient to prevent mucus plugging. When the flows are lower, manually or mechanically assisted coughing is usually needed during a respiratory infection.
The abdominal thrust is the most common type of manually assisted technique. Carter notes, "It's a technique we teach early on in the course of neuromuscular disease, and it can be quickly learned by any home caregiver."
In this simple technique, the caregiver places a hand on the person's abdomen while he's holding in a maximum inspiration. A thrust to the abdomen is applied at the same time as the person coughs. This supplies the extra expiratory force needed to produce good cough flows and productive coughs, providing the person can get enough volume into the lungs.
If the flows still aren't sufficient, Bach recommends using a cough machine, such as the In-Exsufflator distributed by Respironics of Pittsburgh. This machine first delivers a deep breath, and then rapidly reverses the pressure to produce the cough.
Hinderer hooks hers up to her tracheostomy tube, while Arblaster (who no longer has a "trach") uses his machine with a mask. Hinderer says, "The In-Exsufflator works real well to get up deep secretions." She notes, though, that the machine isn't battery-operated and is too heavy for her to move around, so when she's away from home, she uses a suction tube. She knows it's time to use one or the other, she says, "when I am coughing or can just hear crackling in my lungs."
Finally, Bach recommends that people with neuromuscular disease who are at risk for ventilatory problems use a portable measuring device called an oximeter to monitor the level of oxygen in the blood. In his clinic, they are lent out to patients for overnight monitoring, and he prescribes them for those needing them more often.
"Normal is 95 percent to 98 percent oxygen saturation," Bach says. "If it falls below that, you should be thinking one of two things: There's a mucus plug, or you are underventilating." If you neglect these problems, he cautions, you can end up with pneumonia or collapse of your alveoli and develop acute respiratory failure.