Author: Hamzah Rahman
Year 3 student - Guy's, King's and St Thomas' School of Medicine & Space Enthusiast!
The General Practitioner (GP) medical professional has undoubtedly played a major role in providing a plethora of care packages and programmes for individuals seeking to travel; from immunisations and vaccinations to advice and even guidance for mothers in the late gestational stage. The advent of jet flight allowed the masses to venture to destinations that only aristocracy could once afford, which in turn generated a greater need for primary healthcare management. The GP is therefore the point of access to these healthcare packages and consequently plays a pivotal role in enabling tourists to travel safely. This responsibility is deeply intertwined with the historic increase in accessibility to affordable flight.
The first British commercial jetliner was the de Havilland Comet in 1949. This aircraft enabled more people to travel further, as well as reducing the price of tickets substantially. The GP during this age would have played an important role in ensuring that passengers were fit to fly, by managing their pre-flight healthcare requirements.
The Boeing 707 soon joined the aviation world in 1957 and dramatically changed the way we travelled; it opened flight corridors that were once untenable, and consequently, accessed a greater consumer market - the working classes. In 1969, Boeing unveiled the revolutionary 747, coined the “Jumbo Jet” due to its sheer size, which resulted in greater passenger capacity and far more affordable tickets.
With such quantum leaps forward in jet aviation, by the mid-70s the British GP was providing care and advice to thousands of travellers from all walks of life, different backgrounds and with all manner of pre-existing health conditions. The workload of the GP thus became much more diverse and they gained great responsibility in permitting the public to exercise their freedom to travel safely.
Just as jet flight was once an exclusive mode of transport for those from higher socio-economic backgrounds, spaceflight has now emerged onto the world market with exclusive and expensive tickets to fly. Undoubtedly, spaceflight will become more affordable in the coming years and decades, and as such will inevitably require a more established initial healthcare access point for travellers- a service that GPs could provide. As space tourism flights become more accessible through lower prices and increased provision, the remit of travel healthcare provided by general practice could evolve in the near future to encompass spaceflight health clearance.
Recently, on the 13th October 2021, Bezos’ Blue Origin New Shepherd craft took tourists such as Star Trek’s William Shatner on a flight to an altitude of 66.5 miles. Tourists such as these, from different age groups, with a myriad of pre-existing long-term health conditions and with no prior spaceflight experience has highlighted the need for a service that operates independently of space organisations to provide clearance and medical management for spaceflight.
As it stands currently, these tourist flights do not have a destination per se, other than low Earth orbit (expected altitude 65 to 200 miles) above the Kármán line, but not quite outside the absolute border of the earth’s exosphere. This means that passengers need not be screened and cleared as fastidiously as if they were travelling on long distance, extra-exospheric spaceflight to specific destinations such as the Moon or Mars- an exclusivity that only agencies such as NASA currently possess, with professional-only programmes such as the Artemis Lunar Mission.
Any underlying health issues that these space tourists may have can be exacerbated by the challenges and stresses posed by the unique microgravity environment of low Earth orbit. The task of medical clearance is therefore a task that a GP is most well equipped to accomplish, as they have access to, and experience with a patient’s entire past medical history and general state of health.
THE UNIQUE ENVIRONMENT OF LOW EARTH ORBIT AND ITS HEALTH CHALLENGE
The unique environment of low Earth orbit means that underlying medical conditions and contingency plans must be organised and managed in a way that is very different to that of terrestrial flight. Consequently, the GP must take a more particular approach to verifying the fit-to-fly status of potential spaceflight tourists.
One consideration is the exacerbation of anaemia during spaceflight. Research has recently shown that any duration in microgravity, ranging from a few hours to several months, increases the rate of haemolysis proportionally to the duration in space. Whilst space tourists in the next few decades will not be spending more than at most a few days in microgravity, there is still a risk that individuals with pernicious, iron-deficiency and anaemia of chronic disease (TB, malignancy, rheumatoid arthritis) could be at risk of low blood haemoglobin levels during spaceflight and possible medical complications upon return to Earth. A GP would be responsible for ensuring that these risk factors are screened for before declaring a patient fit-to-fly, with blood haemoglobin being measured several times prior to flight to ensure stability in vascular oxygen saturation (spO2).
Another issue is the effect of microgravity on patients with impaired left ventricular ejection fractions (LVEF) (for whatever underlying aetiology). Whilst acutely unwell patients would be denied fit to fly clearance, those who are well managed may still be eligible to fly based on cardiovascular review on Earth. This may become an issue in post-flight situations, due to an in-flight cephalad movement of fluid and removal of any hydrostatic pressure gradients leading to a greatly increased stroke volume. Heart rate and mean arterial pressure both decrease, ultimately in their aggregation leading to a greater cardiac output. Whilst this decrease in afterload can be seen to be an improvement in patients with heart failure and other cardiac conditions, upon re-entry to Earth, there is a risk for orthostatic intolerance due to cardiac deconditioning, where the duration of decreased afterload and stress upon the heart can lead to cardiac atrophy. This decrease in cardiac function would become more apparent in Earth’s gravity, with dizziness, syncope and possible a more reduced LVEF than before. This phenomenon is more pronounced the longer the duration of spaceflight (in the region of weeks to months), however, for patients who have underlying disease, this process could happen sooner, and is therefore paramount for a GP to assess this risk.
Tourists who have a history of glaucoma, wherein there is an elevated intraocular pressure due to insufficient drainage of aqueous humour, must be screened more carefully before being declared fit to fly. In the microgravity environment, due to an absence of gravity, there may be impaired orthostatic drainage of aqueous humour through the ocular trabecular meshwork, leading to even more excessive intraocular pressure increases. Experiments carried out on SkyLab showed a 114% increase in intraocular pressure for astronauts - data that suggests that those with glaucoma may be at risk of severe ocular complications if not managed appropriately pre-spaceflight. Another ocular related consideration for GPs, even for those without glaucoma, is the possibility of spaceflight associated neuro-ocular syndrome (SANS). SANS maybe related to the headward fluid shift of blood due to microgravity and leads to possible distensions of the optic nerve sheath, globe flattening, hyperoptic shifts and other ocular lesions. Whilst SANS tends to affect those in microgravity after several months, there is insufficient data to exclude short term spaceflight travellers from this condition, and as such, tourists should be risk stratified before making a decision for fit to fly.
One more consideration for GPs is the risk assessment of potential thrombotic events in microgravity. In stark contrast to the deep vein thrombosis risk of patients on long haul terrestrial flights, there is a risk of thrombosis in any part of the cardiovascular system due to blood stasis, particularly in the intracranial and jugular veins, where gravity (and not valves) is utilised to drain back into the heart. Those who require thrombolytic medication (antiplatelet and anticoagulant) must be managed accordingly before being declared fit to fly, especially so if they have additional cardiovascular disease that may predispose them to an even higher risk of a thrombotic event (both venous and arterial), such as those with arrythmias and hypertension.
HOW CAN GENERAL PRACTICE ESTABLISH ITSELF IN PRE-SPACEFLIGHT CLEARANCE?
One thing that becomes apparent from analysis of potential pre-spaceflight risks that a GP may manage is the lack of research and data in respective medical fields. Most data currently are from established space agencies, regarding usually male astronauts who have been selected after passing all the required medical and fitness assessments, and would therefore be very unlikely to have any underlying health conditions. Drawing parallels to jet flight, initially the only data available was from military aircrew, with data becoming more widely available as more civilians flew. As such, more data will become available as more tourists with underlying health conditions travel to space and their health is monitored. This is important for GPs as it allows national databases and organisations to publish guidance in a similar fashion to that of NICE CKS and the National Travel Health Network and Centre. This will allow GPs to provide spaceflight clearance services with centralised clinical guidance.
Whilst the longer term physiological effects of space travel, such as bone demineralisation and muscular atrophy, are not likely to impact on space tourists, there are a plethora of other conditions that may become more apparent in short-term spaceflight that have not yet been mentioned. Such examples include motion sickness, psychosocial illness in space and increased radiation exposure. Although the GP may be the central point of clearance for spaceflight, there must also be relevant correspondence with and referral to specific medical specialties that may be able to manage specific flight risks more appropriately.
To conclude, with the ever increasing demand for spaceflight tourism, in a commensurate manner to commercial flight’s infancy, there will be a greater need for fit-to-fly clearance. This service can be provided by general practice, with GPs’ long-term experience with patients’ entire past medical history enabling them to make informed decisions and management plans. Whilst the clinical infrastructure and organisation may not yet be established, it is only a matter of time before it forms, as more and more people seek to boldly go where few have gone before.
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