Scientists have discovered the transplantation of bigger lungs is associated with higher survival rates in transplant patients, according to a study published in The Annals of Thoracic Surgery.

The research – from Johns Hopkins Medicine alongside other medical centers in the US – could improve the options available to people waiting for transplant operations. It reveals that although there has been concern in the past about matching the size of donor lungs to the size of the recipient, oversized donor lungs may be best.

The study involved analyzing data from 4,520 double lung transplants and 2,477 single lung transplants that were performed in the US between 2005 and 2010.

The researchers say that lung size can be estimated from the height and sex of the patient. The estimation is described as the “predicted total lung capacity.” They add that taller people have bigger lungs, as do men compared with women of the same height.

The size of the lungs used in each of the transplant patients was analyzed by using the ratio of the predicted lung capacity of the donor relative to the recipient.

For example, a ratio of 1.0 is a perfect size match, but a ratio of, say, 1.3 indicates that the transplanted lung is larger than the originally predicted capacity for the recipient.

The results of the research revealed that the double lung transplant recipients who received lungs of an average ratio of 1.3 had a 30% increased chance of surviving the first year.

Christian A. Merlo of the John Hopkins University School of Medicine says:

Despite what we thought, bigger lungs turn out to be better. The survival rates for lung transplant, unfortunately, are not as good as with other solid organ transplants like liver, kidney and heart.

But our study tells us that if we were to routinely transplant larger lungs into patients, we could potentially make a real impact on survival. And that’s the goal of research.”

According to the University of Michigan Transplant Center, around 1,500-1,700 people in the US undergo lung transplantation every year. There is an average 5-year survival rate of 50-60% following a lung transplant. The center says the biggest limiting factor in lung transplants is having enough suitable donors.

The study authors say that this research could be used to build a new calculation for predicted lung capacity, where larger lungs could be offered to patients in place of smaller lungs that may not function as well.

They add that present regulations mean children under the age of 12 cannot receive lungs from adult donors, and adults cannot accept lungs from child donors.

But they say that this research could remove this restriction from the equation when allocating lungs for transplantation. This could allow doctors to make decisions based on individual cases and the size of the donor organs available.

The study authors note that this discovery is particularly relevant after a lung transplant case of a 10-year-old girl caused national debate. Because of the regulations in place, the girl was required to wait for a suitable lung donor, meaning she was deteriorating rapidly.

Ashish Shah, surgical director of lung transplantation at the Johns Hopkins Hospital, says:

This study tells us that rather than looking at things like age or height, you have to look at each patient very carefully and determine what their lung capacity is.

There may be children who could take adult lungs that would be oversized for them with a good result. And there may be small adults who would do well with pediatric lungs.”

But the researchers warn that lungs can still be too large for transplantation. If the lungs are too large for the recipient, the surgeons may have complications closing the chest cavity, they could weigh too much on the heart causing low blood pressure, or the lungs could become too compressed and collapse.

Ashish Shah adds that although larger lungs could be the preferred option, this does not mean smaller lungs should be rejected – they are often better than no transplant at all.