What will happen during my pulmonary function tests?

DEAR DOCTOR K:

My doctor ordered breathing tests to see if I have asthma. He didn’t tell me what it’s like to go through this. Can you explain?

DEAR READER:

The tests your doctor almost surely is referring to are pulmonary function tests. The tests are painless. You breathe in and out through a tube that is connected to various machines.

One of the tests, called spirometry, measures how forcefully you can inhale and exhale while taking as large a breath as possible. Give this test your best effort. If you don’t, the test result can make it look like you have a problem. And then the doctor may order treatment you don’t need. So try hard.

A separate test will measure how much air your lungs can hold. It also measures how much air is left in your lungs when you breathe out as much as you can. This may be done in one of two ways. One way is to have you inhale a small amount of a specific gas (such as helium).

Another way to measure your lung volume is for you to sit inside an airtight cubicle. You breathe in and out through a pipe in the wall. Your breathing will cause the air pressure inside the box to change. This pressure change is measured and used to calculate the amount of air you are breathing.

Your doctor will also want to measure how efficiently your lungs deliver oxygen and other gases to your bloodstream. To measure this, you breathe in a small quantity of carbon monoxide (too little to do any harm). The amount of carbon dioxide you breathe back out is measured. Your ability to absorb carbon monoxide is representative of your ability to absorb other gases into your bloodstream.

Today, doctors can quite accurately measure the oxygen in your blood with a simple device that clips to your finger. The old way of doing it required sticking a needle into an artery; you should be glad it can be done so simply now.

What do doctors learn from pulmonary function testing? As in your case, they can learn whether you have signs of asthma. They also can determine if you have chronic obstructive pulmonary (or lung) disease, known as COPD or COLD. This condition is seen most often in long-term smokers. They also can measure the severity of a group of diseases that make the lung stiff, known collectively as chronic restrictive lung disease.

You should hear back about the test results within a week. If your doctor finds that you do have asthma, he or she may ask you to do your own simple pulmonary function testing at home. To do this, you use a peak flow meter. This is a small tube that you hold in your hand. You blow into it as hard as you can. With this home test, as with the spirometry test, it is really important that you try as hard as you can. Otherwise, it may indicate a problem that leads your doctor to prescribe treatment you don’t need.