Living with half a heart
Megan’s feet are resting on the pedals of the exercise bicycle. She has avoided what she is about to do all her life, out of concern for her heart, but in the coming minutes she will push herself to her physical limits. The 29-year-old is a Fontan patient – she was born with a complex heart defect, where the dividing wall between her two ventricles is incomplete. When she exerts herself, her heart is only able to supply her body with the vital oxygen it needs to a limited extent. “Please get started,” says Dr Julian Härtel of the University Hospital Bonn. Megan starts pedalling. Cables connect her body to measuring devices, and a breathing mask analyses the gases in the air that she exhales. A whole team of cardiologists and doctoral students is standing around her, measuring her blood pressure, drawing blood from her ear and monitoring all the readings on the electrocardiogram. Two days later she will repeat this stress test with reduced oxygen content in the ambient air.
Exertion under medical supervision
The Hypofon study (Hypoxia in Fontan patients), which is being conducted by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) in conjunction with the University Hospital Bonn and the Cologne Sports University at the DLR :envihab research facility in Cologne, aims to answer an important question. Can someone like Megan, who does not have two functioning ventricles, travel long distances in the reduced-oxygen environment on board an aeroplane, or sleep safely in a mountain hut 2500 metres above sea level? The search for Fontan patients was far from easy. There are several hundred people in Germany who were born with a complex heart defect that required surgery when they were still babies. Eventually, 18 Fontan patients aged between 16 and 40 were recruited from all over Germany for the study. The participants spent four days and three nights in the DLR test participant facility, where they carried out stress tests and other assessments under medical supervision.
Daily life with limitations
Just a few decades ago, children born with such a complex heart defect did not have a long life expectancy. However, now that several operations can be carried out in infancy and childhood, modern-day cardiology has made it possible to live with a ‘half a heart’ well beyond childhood. Nevertheless, those affected, and their families, remain concerned about what the heart can and should do. “This is a subject of great concern in many families,” says Professor Jens Tank, Head of the Department of Cardiovascular Aerospace Medicine at the DLR Institute of Aerospace Medicine. Megan’s grandparents live in England, so she has regularly taken short-haul flights to visit them. She has never experienced a long-haul flight. “My everyday life is actually pretty normal,” says the 29-year-old, “but I usually avoid situations where I would be able to feel my limitations.” She found out about the study from social media and her cardiologist also recommended that she take part. “This is a good opportunity for me to meet other people with similar heart defects and to have my body checked out.”
Cooperation for practical research
Jens Tank is jointly leading the study alongside Dr Nicole Müller and Dr Julian Härtel of the Paediatric Cardiology Department at Bonn University Hospital. The combination of research facility and clinic is beneficial for everyone involved. “Without Bonn University Hospital, we would not be able to see and care for such patients,” says Professor Tank. “And without the DLR team and the :envihab research facility, we would not have been able to carry out a study of this scale and duration,” says Dr Müller. The research is closely allied to the application, and the areas of expertise of the collaboration partners complement one another. This is resulting in data that have never been obtained in this form anywhere in the world.
High-altitude air in the bedroom
Meanwhile, Megan has been putting in immense effort for a quarter of an hour on the exercise bicycle. She is finding it increasingly difficult to breathe in and out. A staff member regularly holds out a board with a scale – how does Megan feel? Megan taps her finger firmly on the numbers on the scale. Every heartbeat and breath add to an important data set that will enhance understanding of her body’s reactions and performance. The four days and three nights that she spends as a patient in the Hypofon study are filled with experiments. During the day, there are jumping and standing tests, blood tests, heart pressure measurements and stress tests on the exercise bicycle. At night, when she is not consciously controlling her breathing, her heart, respiration and brainwaves are measured and recorded. To investigate the test participants’ reactions to a reduced oxygen supply under controlled conditions, the bedrooms and examination rooms are partially filled with nitrogen on the second day of the study. At this stage, the air in the :envihab is just 15.2 percent oxygen, instead of 21 percent on the remaining study days. This is comparable to the air at an altitude of 2500 metres or the pressurised interior of a passenger aircraft during cruising flight.
Testing the limits
The teams worked together to plan the protocols for the experiments, the daily routines and the entire logistics. Patients and scientists alike will benefit from the experiments and the data analysis. “In my work in paediatric cardiology, parents often ask me whether their child can go skiing or fly to Australia. Until now, there has been very little data that I can use as a basis for my decision,” says Dr Mueller, who works as a senior physician. “Children with a heart defect like this are often wrapped in cotton wool.” But that's not really desirable: “Children belong in sports clubs and have to test their limits every now and then.”
At 29, Megan is no longer a child. Like many of the other patients, she has a good sense of what she is capable of. But after she had endured the increasing stress on the exercise bicycle for more than 20 minutes, she had begun to ponder a bit. “More sport – that is definitely something I will tackle in future.”
Professor Jens Tank has been at the DLR Institute of Aerospace Medicine since 2017. He is expanding the institute’s cardiovascular research work as Head of the Cardiovascular Aerospace Medicine Department. Professor Tank specialises in internal medicine, clinical pharmacology and pathophysiology, and also works in sports medicine. He received his clinical training at the Charité university hospital in Berlin. From 2008 to 2016 he was Head of Clinical Research at the Institute of Clinical Pharmacology at Hannover Medical School (Medizinische Hochschule Hannover; MHH). Since 2011 he has held a W2 university professorship for cardiovascular clinical pharmacology at MHH. In addition to aerospace medicine, his research focuses on rare diseases of the autonomic nervous system, orthostatic hypotension, therapy-resistant arterial hypertension and heart failure.