Can Divers’ Potentially Fatal Heart Changes Really be Found?

Researchers in Pisa, Italy recently published results of tests they performed on scuba divers hearts. Using an underwater ultrasound scan, they discovered significant changes in cardiac function both during and after a dive. That test could be used to identify divers with undetected heart disease or cardiac abnormalities that might prove fatal during a dive, they wrote in Acta Physiologica.

They tested 18 scuba divers, 16 men and two women, who averaged 42 years old and had made at least 100 dives. None smoked or had hypertension, heart or lung disease. They conducted cardiac-ultrasound tests on land before and after diving, and underwater at two depths. The divers wore suits with access for an ultrasound probe and maintained a kneeling positions at a depth for specific time periods..

Among the heart changes recorded during and after the dive: The volume of the left ventricle, a lower heart chamber that pumps newly oxygenated blood to the body, increased significantly, while the flow of blood into the ventricles decreased. These changes may be due to a diving-related shift of blood from the lower extremities to the upper body, exerting a constrictive effect on the chest. Bradycardia, the term for a slow resting heart rate that can cause dizziness and weakness if it falls below 50 beats per minute, was documented after but not during the diving. The cardiovascular changes that occur during a dive may increase the risk of cardiac problems in divers who are unfit, overweight or have underlying heart disease.

Petar DeNoble, vice president of medical research at Divers Alert Network (DAN), says other studies have concurred with this one's findings, so the results are not unusual. But while the concerns for this study were about divers with pre-existing heart conditions, the study used 18 healthy divers. And the results of the recorded heart changes aren't that significant, because they're only temporary changes. "Other studies describe that the heart changes return to normal in less than an hour after a dive," DeNoble says. "There are no studies exploring how these temporary changes may acutely affect divers with pre-existing conditions or how long these changes may persist in such divers. So there may be negative effects or an increased risk of arrhythmia, but the way to establish that is to measure an outcome of interest during the study, and that is actual arrhythmia."

That's what DAN is trying to do in one of its new studies: identify people with heart conditions who could be vulnerable to changes underwater, then follow them during dives with continuous EKG monitoring to measure if there's any increased incidence of cardiac arrhythmia. DeNoble also wants to look at the cumulative effects of multi-day diving. "Are there any cumulative effects during three to five days of diving, and could this trigger dangerous arrhythmias?" He wants to enroll 120 people in the study to do five week-long trips on liveaboards. He is planning to book and announce those trips soon so he can have all the data for analysis by the end of 2014.

Other study subjects DAN is looking for: divers with pacemakers. DeNoble's other study is researching divers with implanted pacemakers or defibrillators choosing to dive. The study consists of a10-minute online survey, plus a possible follow-up interview if additional clarification is needed.

If you're interested in being a test subject in either study, contact DeNoble's team by e-mailing research@dan.org . Participation should be done with the goodness of your heart (no pun intended), as there's no payment for taking part in the studies.