Tell Me About Bronchopulmonary Dysplasia (BPD)
This web page will tell you about lung anatomy and what BPD is, as well as what the common symptoms are.
What is BPD?
Bronchopulmonary Dysplasia (or BPD) is a chronic lung disease with persistent difficulty breathing and abnormal changes on the chest X-ray, that sometimes follows lung diseases that affect newborn infants. In most cases, BPD occurs in infants who are born prematurely and who have Respiratory Distress Syndrome (or RDS), a lung disease common in premature babies. In some cases, BPD may follow other lung conditions of the newborn, such as pneumonia. In most cases, BPD occurs after babies have required extra oxygen and/or a mechanical ventilator to treat their original lung problem. In many cases, the symptoms of BPD disappear quite rapidly. Some infants with BPD may have breathing difficulties for many months or years.
A little anatomy
The lungs consist of airways (also known as bronchial tubes, or bronchi), and air sacs (also known as alveoli). The purpose of the airways is to allow fresh air to travel into the air sacs, and to allow spent air to travel out of the lungs. Blood vessels move blood close to the alveoli, so that fresh oxygen inhaled from the atmosphere can move into the blood. In addition, waste gas (or carbon dioxide) travels from the blood into the alveoli, to be later exhaled into the atmosphere. Other blood vessels move the blood, newly-loaded with oxygen and relatively-free of waste gas away from the alveoli, to travel to the rest of the body.
The inner surface of the airsacks is covered by a thin layer of a soapy liquid (called surfactant). This acts as a lubricant, helping the airsacks open more easily. Surfactant also helps keeping the airsacks from collapsing.
The bronchial tubes have tiny bands of muscle, which encircle them. In the presence of irritants (such as smoke), these bands of muscles can contract, to try to keep the irritant(s) out of the lungs. This process is known as bronchospasm.
Breathing requires breathing muscles, such as the diaphragm, which enlarge the chest cavity toallow air to travel into the lungs. Other breathing muscles squeeze gas out of the lungs. The process is similar to the way air moves in and out of a bellows.
What's different about the lungs of a premature baby?
As babies mature before birth, their organs develop at different rates. The lungs are one of the last organs to develop, so they are one of the commonest areas to be under-developed when babies are born prematurely.
By 24 weeks after conception, all of the bronchial tubes have formed, but only the very first airsacks have developed and very little surfactant has been produced. Useful amounts of surfactant are not found in the lungs before 28-32 weeks after conception.
When a baby is born prematurely, a number of things may be wrong with his or her respiratory system. The lungs of premature babies have relatively fewer airsacks, so their may be difficulty absorbing enough oxygen into the blood to meet the body's needs. Because of both the lack of airsacks and smaller amount of surfactant, the lungs are abnormally stiff. This makes breathing much harder work than normal. The breathing muscles of the premature baby tire out easily, and as they get weaker, they move less and less air in and out of the lungs. Carbon dioxide (CO2) builds up in the lungs and the blood. Carbon dioxide in the blood turns into acid, which, along with low levels of oxygen in the blood, can cause damage. The combination of abnormally stiff lungs along with abnormal blood gases in the premature baby is known as Respiratory Distress Syndrome (or RDS).
What causes BPD?
A number of things "conspire" to cause BPD. Even though the lungs of a premature baby act "stiff" and don't move very easily, the tissues that make up the lungs are very soft and can be easily damaged. Occasionally, even vigorous attempts to breathe by a premature newborn seem to be able to result in lung problems. Newborns with RDS or other lung conditions (such as severe pneumonia) frequently need treatments in order to survive. These treatments are life-saving, but can also lead to lung damage.
The first such treatment is oxygen. Newborns with lung disease need extra oxygen, to make sure that the body gets enough oxygen. High levels of oxygen in the air breathed in by the infant can, however, cause harmful chemical reactions in the lungs.
Sicker newborns often require a mechanical ventilator. A ventilator helps move air into the lungs. A ventilator is vital for the newborn whose lungs are so stiff that his breathing muscles can't move them adequately. The lungs of many premature babies do not contain enough surfactant, so the airsacks can easily collapse. Ventilators help keep the airsacks open, allowing oxygen to reach the blood vessels in the lungs. Ventilators are also needed in premature babies who "forget" to breathe (a condition called apnea). Unfortunately, the pressures needed to get air into stiff lungs can also cause further damage.
"In many infants, RDS begins improving in a week or less. Other infants may need oxygen and treatment with a ventilator for longer periods. In this situation, BPD may result. Once BPD has occurred, other processes may cause further problems. Injured lungs tend to leak fluid. As the walls of the airsacks soak up fluid, they become stiffer, making breathing even more difficult. Tiny muscles in the bronchial tubes can become "irritated" and can go into spasm, which makes the bronchial tubes narrower. This is known as bronchospasm, and can makes it harder for air to get in and out of the lungs. When air has to travel through these narrowed bronchial tubes, you may hear wheezing. Once the lungs are damaged by BPD, the body sends cells into the lungs to help heal them. This process is called inflammation, and is a bit like the reactions you may see after you burn your skin. These cells, unfortunately, can release chemicals which cause further damage, swelling of the bronchial tubes, bronchospasm, mucous production by the bronchial tubes, and, sometimes, scarring.
The lungs of an infant with BPD usually contain areas where airsacks have been scarred, areas where airsacks are over-inflated because air has difficulty leaving the airsacks, and, in some cases, areas where the bronchial tubes are scarred or in bronchospasm.