May 24, 2011 (New York, New York) — Boldly going where few have gone before appears to have a positive effect on blood pressure, a new study shows. While investigators are not yet recommending relocating large swaths of the hypertensive population to space, data showing weightlessness lowers blood pressure, as well as a not-yet-understood increase in catecholamine levels, open up the possibility that different mechanisms might be involved in blood-pressure regulation.

Dr Peter Norsk

Studying astronauts at the International Space Station, Dr Peter Norsk (NASA Johnson Space Center, Houston, TX) and colleagues reported this week at the American Society of Hypertension (ASH) 2011 Scientific Meeting that systolic blood pressure decreases 10 mm Hg after spending three to six months in space. After a return to earth, blood pressure returned to normal within two months, and in fact, was approximately 1 to 2 mm Hg higher than preflight blood-pressure levels. Cardiac output increased approximately 33% during the months spent in space, while total peripheral resistance decreased.

Interestingly, in an attempt to understand the mechanism of vasodilation in the astronauts, Norsk told heartwire that they observed a significant increase in catecholamine levels. "The catecholamine levels were inappropriately high compared with the cardiovascular effects," said Norsk. "I don't understand this and would like to know why there is a mismatch between the level of sympathetic nervous system activity and the total peripheral vascular resistance. It doesn't fit."

Norsk speculates the chronic dilation of the heart, which would occur in patients with higher cardiac output during a space flight, might release natiuretic vasodilatory peptides that induce relaxation, meaning that the sympathetic nervous system activity increase would play a secondary role.

Commenting on the study during a morning press conference where the results were announced, Dr Robert Phillips (University of Massachusetts Medical School, Worcester) said the advantages of studying these astronauts, even though it might appear "somewhat esoteric," is that researchers are learning about mechanisms no longer functioning in the standard way as they would on earth. Understanding how these mechanisms are interrupted and the counterregulatory measures that develop might allow researchers to target some of these mechanisms with future interventions.

The authors report no conflicts of interest.