Advances in technology, in particular miniaturization and computers, have made a powerful difference in the practice of medicine, especially with respect to medical appliances. But this progress can have very unhappy effects as PNS correspondent Mark O'Brien discovered on Thanksgiving Day. Author of two books of poetry and a forthcoming autobiography, "How I Became A Human Being" (Kadansha Press, 1998), he is the subject of the 1997 Oscar-winning documentary "Breathing Lessons" (Inscrutable Films in collaboration with Pacific News Service). A photo of Mr. O'Brien is available from PNS. Call George Gundrey at (415-438-4755).

My life support device, an old iron lung, was broken. Every three seconds it thumped loudly, reminding me that an important part was cracked, and that Respironics, the company that owns the iron lung, would not replace the part.

A Respironics mechanic had told me this iron lung would destroy itself in a month. Every three seconds, the thumping reminded me that I was afraid and angry at my need for a machine now considered obsolete.

I have been using iron lungs since 1955, when I was six years old. Caught in the last wave of polio to sweep the United States, my limbs were paralyzed and my lungs shriveled. Doctors put me into an iron lung so I could breathe.

At first, I used it all the time, but after a year, I became strong enough to use it only at night.

This allowed me to grow up -- to leave home and earn a B.A. at the University of California. But halfway through graduate school, I was boomeranged by post-polio syndrome. Weaker than ever, I was forced to spend my days and nights in the iron lung, forced to quit school.

During the 1980s and 1990s, I wrote poetry and journalism, went outside for brief journeys, and "starred" in a documentary which won an Academy Award.

That is personal history. There is also an institutional history.

Franklin D. Roosevelt created the National Foundation for Infantile Paralysis (the "March of Dimes") in the 1920s to combat polio, the disease that had crippled him. The Foundation bought iron lungs, distributed them and maintained them through the 1960s.

The success of vaccines made It difficult for the foundation to raise money for polio, so it started the "Lifecare Foundation" to own and maintain the iron lungs still in use.

Lifecare did a good job. Their mechanics were willing to make repairs on Saturday nights -- the iron lung always seemed to break down on Saturday night -- but they worried about spare parts as no one made them any more.

In 1997, I received a letter informing me that Respironics Corp. had taken over Lifecare and pledging continued support of iron lungs.

When the thumping began in October, a Respironics mechanic told me he could not fix it. Another Respironics employee said it could be repaired, but the company did not want employees to ask for spare parts.

Respironics suggested I try the "Porta-Lung," the 1990s version of the iron lung, made of gleaming fiberglass and with an external, programmable control box called "NEV."

The day before Thanksgiving, my attendants put me in the Porta-Lung. Respironics said it would take a day to get used to it, and I wanted to give it a shot for the holidays.

I found I could breathe. My heart felt normal. My attendants wheeled my 650 pound iron lung out to the porch.

That night, I had nightmares. I wanted to go back in the iron lung, but at 3 in the morning it seemed like too much to ask.

Early the next morning, my friend Susan came over and, seeing how groggy I was, adjusted the settings on the NEV, and asked if I wanted to watch the parades on TV as we always do on Thanksgiving, but I felt too tired for such a strenuous activity. She was worried about me, and massaged my head before going back to her place to cook the feast.

When my attendant arrived, we discussed putting me back in the iron lung, but I wanted to see if the Porta-Lung would work. Susan returned and tried to adjust the NEV again, but the readout kept changing. On the verge of tears, she telephoned Respironics.

The guests arrived. Everything was delicious, but I could not eat or drink much. Then the mechanic came and said the NEV was broken -- and that he was prohibited from fixing it by U.S. Food and Drug Administration rules. He said he would get me another one the next day, but meanwhile I should get back into the iron lung.

After much furniture moving, I did -- and shouted "Oh boy!" at the rush of air.

The NEV did not come until a week later. I tried the Porta-Lung again, but Respironics decided it would not work for me, so they gave me another iron lung.

I don't know why they were willing to replace the lung but unwilling to fix it. I don't know why Respironics insisted I use the Porta-Lung when they had another iron lung. I don't know why Respironics claims it will support iron lungs then tells its employees not to order spare parts.

But I suspect all this has something to do with money. Respironics, unlike Lifecare, is a for-profit corporation. Dropping old models and introducing new ones is a way to make more money.

Of course, I am grateful that Respironics still makes my health their basic concern. But how long will that concern last? I have learned, as many Americans have, that when we leave health policy to corporations they choose and we lose.