LOUISVILLE, Ky. (WHAS11) -- For Zack Barnum, life has always been an uphill battle.

"I was born with cystic fibrosis, so I have that. I was diagnosed at about seven days old," he said. "I was always skinny, underweight, so as a kid, I was constantly teased for that."

As a child, Barnum was told he would probably live until his teens. Now 41 years old, Barnum has proved those doctors wrong, getting married and having twin daughters along the way. But one year ago, things took a turn for the worse.

"I always joked my entire life I wanted to make it to 40. Well I made it to 40, but as it turns out, things started to get a lot worse at that point," he said.

Cystic fibrosis is a genetic disease that damages a person's lungs and digestive system. Barnum said around his 40th birthday, his lungs were only operating at about 17 percent and he was faced with the inevitable - he needed a transplant.

"I couldn't go anywhere without oxygen 24/7," he said. "I couldn't walk. Walking up a flight of stairs was grueling."

His doctors placed him on a donor list, which he stayed on for a little more than three months before receiving the call from the hospital - he would be getting a double lung transplant

"You have kids. You want to see them grow up," he said. "You want them to graduate high school, get married one day."

With his two daughters and wife by his side, Barnum underwent an 18-hour surgery in April last year, then spent another five weeks recovering in the hospital.

"We did celebrate [his daughters'] 8th birthdays in the hospital while I was still in recovery, so that was a unique experience, to say the least," he said.

One year later, his lungs are now working at 90 percent. While there are still some things he is not allowed to do and he still needs to maintain an exercise regimen, he said the surgery has changed his health - and his perspective - for the better.

"It's not necessarily the big things," he said. "It's being able to see them on a daily basis and be able to play frisbee in the yard with them or kick around a soccer ball with them. I have that chance now and I try to appreciate that a lot more now than I'm sure I did before."

Barnum has since also become an advocate for cystic fibrosis awareness and research as well as an advocate for organ donation. Barnum said he was a registered donor prior to his transplant and remains one still.