Does Orthostatic Hypotension Mean a Return to my G-Suit?
by Duane Graveline, MD MPH
During my tour of duty as a research scientist in the U.S. Air Force ( U.S.A.F.) much of my research was directed towards exploration of the effects of absence of gravity on the human body.
By keeping volunteers in a comfortable bed or floating them about in warm water I studied those mechanisms that enable us to adjust to gravity.
Knowing that soon we would be residing and even sleeping in zero gravity while orbiting about the Earth in spacecraft, we in space medicine research had a mandate to study every aspect of zero gravity using these analogs of the weightless state.
Blood pressure control was one of the targets for study. By placing our subjects in comfortable beds we soon learned that postural hypotension would soon be a major adversary. Just as hypertension means excess blood pressure, postural hypotension means insufficient blood pressure while standing upright.
By staying in bed for weeks on end we were allowing gravity compensation to go to sleep, in a sense. No longer did we encounter the almost constant feedback with every change in body position from the volume and pressure receptors lining our blood vessels.
When once more exposed to normal gravity we found profound changes - a blood pressure while standing of 124/80 before the test would plummet to 80/60 after the test with complaints of weakness, nausea, "grey-out", blindness, and shortness of breath. Our subjects were experiencing postural hypotension and several days might be required before normal blood pressure response ensued.
Using immersion in warm water for our studies gave a similar change in much less time. We found water immersion to be a much better analogue of zero gravity from the perspective of duration of time involved. When the first astronauts returned with their fainting tendency from several days in orbit, we were ready for them.
Now, in the International Space Station, 80% of occupants will have a marked tendency for postural hypotension on return to Earth after their six- month missions despite some 2.5 hours each day in self-maintenance exercises, intensive rehydration prior to de-orbit and the use of anti-G suits. Gradually they re-adjust to Earth's demands but many weeks are required before re-adaptation is complete.
Last year my blood pressure was beginning to attract the attention of my doctors. I am fast approaching 80 years of age and most of my doctors are just out of medical school and still oriented on 120/80 as the ideal blood pressure. Little do they know how subtly driven they are by the drug companies' self-satisfying recommendations for ideal blood pressure by inducing these doctors to accept 80 mm as a diastolic target rather than 90 yet every study intended to prove objectively a health benefit for 80 has failed.
This fact is thoroughly documented by numerous studies. Having been brought up on 100 plus your age for systolic, I talked my way out of pills for a while but inevitably I had to start the least compromising of the lot, a beta blocker with a small dose of thiazide.
It was about the same time that I began to be aware that gravity was tugging on me far more than it used to. Although I still did regular walking at first I was breathless and became disinclined to do tasks that required standing upright.
Standing before my workbench or rinsing off dishes at the kitchen sink caused sweating and a sense of weakness. The upright posture no longer was my friend. My regular sitting blood pressures during this time were 166-170/88-92, certainly nothing to suggest a blood pressure etiology for my weakness and shortness of breath on standing - or did it?
Standing at a podium longer than 10 minutes caused me a novel sensation of weakness and sweating. I am reluctant to admit how long it took me before I finally did tests of orthostatic tolerance but finally, in a "Eureka!" moment of awareness, it came to me abruptly.
They are easy enough to do. You simply take your blood pressure while recumbent and repeat after standing erect for a few moments. My findings at home were quite remarkable: Recumbent = 170/84; Erect = 108/96. They were similar the next day at my doctor's office with the working diagnosis of overdose of anti-hypertensive drugs.
However, two weeks later with the offending drugs out of my system and a far more liberal daily intake of salt, my orthostatic intolerance was just as great. If I was to function effectively while upright I needed some form of external compression.
I needed an anti-G suit, the same thing required of me in the past while flying high performance jet aircraft. While waiting for my anti-G-suit to arrive I have conceived the interim scheme of using compression stockings combined with a wide lumbo-sacral belt, both immediately available at a local medical supply store. This greatly improved my orthostatic tolerance, allowing me to get around reasonably well.
Needless to say, I still have 200/100 while sitting at my desk but my orthostatic values with stockings and belt are now 140/96. With my anti-G suit the blood pressure values will be identical to standing upright.
It was while studying zero gravity blood pressure control as an Air Force research scientist that I conceived the lower body negative pressure device. My shop foreman said it looked like half a casket to him, and it did. I was the only one who dared to get into it. It was with breathless anticipation that I pushed the button to evacuate the air from the box-like chamber into which the lower half of my body extended. It worked like a charm, my blood pressure was the same as if I was standing upright even though I was horizontal.
This would work the same way in zero gravity I promised - and it did. NASA put bells and whistles on it but it has been in use now for 40 years. Even the Soviets picked it up for use on the MIR space station. When my military style anti-G suit arrives I am going to convert it into a civilian model as I will be wearing it all the time.
The family doctor in me desperately wants to treat my 200/100 blood pressure but the practical research scientist in me reassures that I will have to bear in mind that 100 plus my age will soon be 180.
Duane Graveline MD MPH
Former USAF Flight Surgeon
Former NASA Astronaut
Retired Family Doctor