Case File: A Commercial Spaceflight Participant With Hypertension

Who decides whether he is medically fit to fly, and what should your letter say?

The operator decides, not you and not the government. U.S. rules under 14 CFR Part 460 do not set medical standards for spaceflight participants (SFPs). Instead, operators must give each participant written information about known and unknown hazards and train them for emergencies [1].

Your role is to optimize, document and communicate: control his blood pressure, summarize his history, medicines and test results, and send them to the operator’s flight surgeon. SMF’s spaceflight participant screening article suggests wording such as “no contraindication identified to the operator’s medical evaluation” rather than “cleared for spaceflight.”

What level of screening does the FAA’s 2006 guidance suggest for an orbital flight?

The Federal Aviation Administration (FAA) guidance (DOT/FAA/AM-06/1) is advisory. It describes two tiers [2]:

His orbital flight falls in tier 2. “Gz” means head-to-foot acceleration (G-load).

Is well-controlled hypertension likely to stop him from tolerating launch and landing G-forces?

Probably not, based on centrifuge data, but the evidence is limited. In a centrifuge study, 86 volunteers aged 20–78 with high blood pressure, heart disease, diabetes, lung disease or back problems rode simulated suborbital profiles (up to +6 Gx and +4 Gz). Heart rate peaked at 192 beats per minute and systolic blood pressure at 217 mmHg. Grayout (69%), nausea (20%) and chest discomfort (6%) were common, yet no subject had a significant adverse physiological response [3]. The authors concluded that most people with well-controlled conditions can tolerate these forces [3]. Note the selection: volunteers with severe or uncontrolled medical disease were disqualified before testing [3].

These were short centrifuge runs, not real flights, and they modeled suborbital rather than orbital profiles. The FAA guidance advises care with rapid-onset profiles of +3 Gz or more sustained for 5 seconds or longer in people with compromised cardiovascular function [2]. Uncontrolled high blood pressure is different: it needs treatment and a flight-surgeon review.

Escalate before writing any letter if you find: uncontrolled blood pressure; left ventricular hypertrophy or strain on the ECG; angina or evidence of ischemia; unexplained fainting; or a drop in blood pressure on standing at baseline. The IAA study group lists uncontrolled hypertension and autonomic neuropathy with hypotension among conditions that acceleration can make worse [4].

What else in his history deserves attention?

• Anxiety in confined spaces. In the centrifuge studies, three of the five volunteers who withdrew did so because of anxiety [3]. The screening authors wrote that better methods are needed to identify people prone to anxiety reactions [5]. Mention it to the operator’s flight surgeon.

• Motion sickness. Childhood car sickness does not reliably predict space motion sickness (SMS); a previous episode of space motion sickness does. Most first-time flyers get it in the first 2–3 days [6].

• Landing day and his blood pressure medicines. Even short orbital flights shift body fluids. Circulating blood volume falls by about 15% within about 2 days in weightlessness, which causes lightheadedness on standing after landing (orthostatic intolerance) [7]. Some drug classes make this worse:

  • Diuretics add to the volume loss. An International Academy of Astronautics (IAA) study group also lists diuretics among medicines that reduce heat tolerance [4].
  • Beta-blockers blunt the heart-rate rise that compensates on standing. In a meta-analysis of randomized trials they were the class most strongly associated with orthostatic hypotension (odds ratio 7.76 vs placebo) [8]. In an FAA-sponsored crossover trial, atenolol modestly impaired orthostatic tolerance under lower-body negative pressure [9].
  • Alpha-blockers carried a smaller increase in risk (up to about twofold) [8]. Medication review is the recommended first step for drug-related orthostatic hypotension [10].

  What to do: name each of his medicines and doses in your letter, and ask the operator’s flight surgeon whether any should be changed, held or re-timed around launch and landing. Do not stop a beta-blocker abruptly, and make any change well before flight so its effect can be checked. Always record lying and standing blood pressure and heart rate (orthostatic vitals).

• Knees. Ask about mobility for emergency exit training, which Part 460 requires [1].