A handful of cameramen, a boom mike operator and a producer follow identical twin sisters Anabel Stenzel and Isabel Stenzel Byrnes as they walk a wide loop across the Stanford University campus.

They stop to reminisce at Roble Hall, where they shared a dorm room in the early 1990s, and the cafeteria where Isa met her future husband, Andrew Byrnes. They pass Stanford Stadium, where the twins graduated with matching degrees in human biology in 1994, then on to Memorial Church, where Isa and Andrew married.

Finally, they come to Stanford Medical Center, where both Ana and Isa nearly died but lived because of the double lung transplants they received there.

Today, Ana and Isa, 38, both live in Redwood City and are the stars of a documentary chronicling their lifelong battle with cystic fibrosis.

Doctors did not expect them to live past their 10th birthdays. But the twins are still thriving and have dedicated their lives to advocating for organ donation.

Three years ago, the Stenzel sisters published their memoir, "The Power of Two" (University of Missouri Press, 2007), in the United States and Japan, where their mother grew up. That book inspired Academy Award-nominated filmmaker Marc Smolowitz to pursue their story after he received a copy from an acquaintance, Isa's husband, Andrew.

"The title is symbolic not only of the two sisters, but of the two sets of lungs they've had and the two lung donors who gave them a second chance at life," said Smolowitz, who hopes to premiere the film at the 2011 Sundance Film Festival in January.

Transplants taboo

"Organ donation really struggles to meet the mainstream, especially in Japan, where the idea of transplanting organs has a cultural taboo," he said. "We hope to use the film to demystify the process and inspire people to become organ donors."

Next month the sisters will run, jump and swim in the Transplant Games - an Olympic-style competition that brings together 7,000 post-transplant athletes in Madison, Wis. It will be the fourth games for Isa and the fifth for Ana, who holds two gold medals in swimming.

Isa also has taken up the bagpipes - one of the most demanding wind instruments.

"We're flying high. We don't want to waste a minute," said Ana, who got married last month in Fremont.

Ana and Isa were born in Los Angeles in 1972 to immigrant parents. Their mother was from Japan, their father, Germany.

Every day, their parents lovingly - but forcefully - clapped their hands against the girls' chests for 30 minutes to help loosen mucus so they could breathe more easily.

"Cystic fibrosis isn't a very ladylike disease," Isa said. "But it helped to have my sister there, going through it with me."

Coughing contests

"And we had someone to compete with," Ana chimed in. "We actually used to compete to see who could handle the chest percussion longer and harder and who could cough up more. "

Together, the sisters continued to defy doctors' predictions. Their 10th birthdays came and went. They graduated from high school and then Stanford. Both eventually found careers in the health care world they knew so well: Ana as a genetic counselor at Stanford Medical Center and Isa as a social worker at Lucile Packard Children's Hospital at Stanford.

Yet, over time, Ana and Isa's lungs were deteriorating, and lung transplantation still seemed like a scary, maverick approach.

Ana was on the transplant waiting list for 16 months before suitable donor lungs became available. When she awoke in the recovery room on June 14, 2000, 10 years ago today, she could breathe deeply and clearly - for the first time in her life.

"I'm alive," she recalls thinking when she first opened her eyes. "I'm alive."

Unlike Ana, who had a slow respiratory decline, Isa landed on the lung transplant list after an emergency admission to the hospital in 2004. Just 2 1/2 weeks afterward, she received her transplant.

Despite their recoveries, the twins haven't been without setbacks. They've had to cope with other health problems brought on by cystic fibrosis, including diabetes, high blood pressure and osteoporosis.

In 2007, seven years after her transplant, Ana's body rejected her donor lungs, and Dr. Bruce Reitz performed a very rare - but successful - second lung transplant.

Years after transplantation, both Ana and Isa met the families of their organ donors.

"Donor families are incredible heroes," Isa said. "We carry parts of them inside us."

Ana agreed. "I want to encourage donor families to know that somebody out there is living and enjoying life and thinking of them on a moment-by-moment basis," she said. "I think of my donor family every single day."