By Anna Horner | News & Views

Astronauts become intolerant of being in an upright position after just a few days in flight. What does this have to do with a condition that primarily affects young women? The orthostatic intolerance, or the development of symptoms (such as rapid heart rate and dizziness, among others) when you stand upright, experienced by astronauts during space flight is a core component of cardiovascular deconditioning; and much of what is known about the impact of space flight on an astronaut's physiology has helped inform the treatment of POTS (postural orthostatic tachycardia syndrome), a condition in which patients experience an abnormal increase in heart rate, among other symptoms, in the upright posture.

POTS is a challenging disease that mostly affects young women and is fundamentally characterized in the chronic state by profound cardiovascular deconditioning, according to Benjamin D. Levine, MD, FACC, FAHA, FACSM, founder and director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Dallas and a professor of medicine and cardiology at the University of Texas Southwestern Medical Center. "We simulate space flight on earth by putting people to bed. And we've put people to bed for two weeks, five weeks, six weeks, 12 weeks to look at how the heart and circulation adapt to detraining," he says. "Universally, what that causes is a shrinkage and atrophy of the heart, a shrinkage of the blood volume, and a marked increase in upright heart rate and sympathetic activation, which at least in the chronic state, contributes to much of the disability in POTS." 

"It is important to emphasize," says Dr. Levine, "that this link to deconditioning doesn’t place the blame on the patient – they are not ‘lazy’ or ‘anxious,’ but rather experiencing a well-described consequence of bed rest and the physiological process of cardiovascular deconditioning.”

Another major influence in today's treatment of POTS patients is the 1966 Dallas Bed Rest and Training Study, which Dr. Levine says is probably the most important study in the field. The research involved putting five young men to bed for three weeks and then training them for two months. "Much of what we know about cardiac rehabilitation and the process of rehabilitation began with that study," he notes.

In his AACVPR live webinar on July 14, Dr. Levine discussed how space flight and gravity influence the deconditioning process, "and how that can cause quite profound disability, more than people might think, and more quickly than people might think." He also talked about the Dallas Bed Rest and Training Study and how it "was really the major impetus for a whole change in how we manage patients with heart disease." According to Dr. Levine, putting people with cardiac issues to bed once was the standard therapy, but the Dallas Bed Rest and Training Study showed the adverse consequences of bed rest. "Now we don't do that," he explains. "We try to get people upright as quickly as possible and get them into cardiac rehabilitation."

Dr. Levine asserts that exercise is the only therapy to have shown a sustained improvement in function and quality of life in POTS patients. He stresses the importance of understanding the physiology of cardiovascular deconditioning and bed-rest deconditioning, which is at the heart of POTS and many other diseases that CR professionals see, as well as how exercise training modifies and changes that underlying pathophysiology to make patients feel better.

Asked whether it can be difficult to ensure patients with POTS stick to their treatment program, Dr. Levine says that giving them a very clear and specific set of instructions is important. "We give them a calendar that tells them exactly what to do every single day for the next three months, and they're pretty good about keeping up with that," he notes. "For our POTS patients, about 75% of them were able to get through the program, and virtually all of those who do feel better. But there are some who don't, and particularly at the beginning, some people feel worse during exercise, and that is something that has to be overcome."

Recognizing that exercise training isn't easy, Dr. Levine explains that in the POTS world, "we have people start by exercising sitting down, so they're not suffering from the consequences of the upright posture." For patients with POTS, appropriate exercise programs can include rowing, recumbent cycling and even some swimming. "We don't let people stand up for the first month of training, so that they get used to exercise and can start the process of rehabilitation early on without suffering from the upright posture," he says.

AACVPR members can access the webinar recording, at no charge, here.