from Dysautonomia International FB group:
full paper here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4860548/Dysautonomia International on FB said:More proof that POTS is not caused by deconditioning! This is an important research paper POTS patients should share with their doctors. Harvard affiliated researchers studying exercise intolerance found that POTS patients had lower than normal right atrial pressure at rest and upon exertion, which differs from the higher than normal right atrial pressure found in deconditioned individuals.
They suggest that cardiac output (the amount of blood the heart can pump per minute) is reduced in POTS due to low ventricular filling pressure, which they suggest is due to impaired venoconstriction (in other words, your veins aren't constricting enough to get the blood flow back to your heart when you exercise, which makes your heart not work as efficiently, which makes exercise really hard).
They also found that providing 1 liter of saline increased cardiac output in POTS, but didn't increase V02max much. V02max is the maximum amount of oxygen that an individual can utilize during intense exercise. They suggest that this finding may be evidence that saline is diluting the red blood cells, which may make it harder for the body to use the oxygen carried by those cells. They suggest that treatments to increase blood volume (salt, oral fluids, florinef, saline) may be less effective than therapies directed at vascular tone (midodrine, pyridostigmine).
This study included several patients with exercise intolerance, 5 of whom had POTS. So we will need more research to know for sure if this applies to everyone with POTS, but it's a very interesting paper, and it's certainly nice to see additional confirmation that it's not simply decondtioning.
We do not recommend changing your treatments based on this study, but this is definitely something worth discussing with your doctors. Addressing the low blood volume that is common in POTS is still important. Exercise is still important to ward off deconditioning (which can happen in POTS because it's so hard to exercise). Exercise also increases red blood cell volume and it increases the efficiency of the muscle pumps in your legs, which help push blood back to your heart.
title said:Unexplained exertional dysapnea caused by low ventricular filling pressures: results from clinically invasive cardiopulmonary exercise testing.