Jonathan B Clark

Baylor College of Medicine | BCM · Department of Neurology

The advent of commercial human spaceflight is now upon us, with tourist flights to suborbital and orbital space about to commence, and NASA aiming to return to the moon and eventually head to Mars. Such missions pose substantial risk to their crews and all those in their immediate vicinity, particularly during launch and reentry. Medical personnel...

The deep space environment far beyond low-Earth orbit (LEO) introduces multiple and simultaneous risks for the functioning and health of the central nervous system (CNS), which may impair astronauts’ performance and wellbeing. As future deep space missions to Mars, moons, or asteroids will also exceed current LEO stay durations and are estimated to...

Neuro-ocular changes during long-duration space flight are known as spaceflight-associated neuro-ocular syndrome (SANS). The ability to detect, monitor, and prevent SANS is a priority of current space medicine research efforts. Optic nerve sheath diameter (ONSD) measurement has been used both terrestrially and in microgravity as a proxy for measure...

Balloons have had in instrumental part in many aspects of human flight in both aviation and space. Humans first left the surface of the Earth in 1783 in balloons, and rapid advances in high-altitude physiology were made in the following century as well as recognition of the grave dangers associated with high-altitude exposure. Balloons have advance...

Spaceflight presents hazards and risks to crew health, performance, and safety. The hazards of spaceflight involve the space (natural) environment, spacecraft (vehicle) environment, and the space activities (mission operations) environment. The space environment hazards include reduced gravity, ionizing and electromagnetic radiation, neutral (non-i...

The Soviet Union (Russia) was the first country to launch humans into space with the launch of Yuri Gagarin on April 12, 1961. This chapter reviews of human spaceflight associated mishaps and incidents launched by Russia (former Soviet Union) and their human health threats involved with spaceflight. The mainstay Russian launch system is the Soyuz s...

This chapter is an overview of human spaceflight-associated mishaps and incidents and also describes human health threats involved with spaceflight. Humans flying is space have historically had a higher risk compared to comparable humans engaged in aviation operations, particularly fatal mishaps (loss of crew) per mission sortie (launch/landing). H...

Neurologic concerns associated with Human Spaceflight

Chapter in Encyclopedia of Bioastronautics

During long duration space missions, crewmembers are exposed to a variety of incessant noises and acoustic conditions, as well as brief, but very loud, sound levels during launch, descent, and possible abort scenarios. Some common sources of these sounds are payloads (science experiments), ventilation fans, thermal control systems, and equipment wi...

The physiological zone from sea level to 3048 m (10,000 ft.) encompasses the pressure to which humans are well adapted, although if appropriately acclimated, they can survive the summit of Earth’s highest mountain (Mt. Everest at 8850 m/29,028 ft.) without supplemental oxygen. At higher altitudes, artificial systems are required to supply needed ox...

Neurologic function is critical for astronauts to operate in the complex flight environment of space and during readaptation to gravity following return. The altered gravitoinertial environment of space flight can significantly affect neurologic function and sensorimotor performance. High-risk tasks requiring optimal neurologic function on orbit in...

Reaching new milestones in space, historically, has been achieved through the execution of a comprehensive developmental test program of increasing complexity, which validates engineering design models and provides operational experience. In this paper, the Red Bull Stratos program, which culminated with Felix Baumgartner's successful space dive on...

Background: There is a need to develop noninvasive methods to monitor intracranial pressure (ICP). Pupillary reactivity decreases in patients with elevated ICP with demonstrated cerebral edema. We sought to determine whether pupillary reactivity is affected when ICP is elevated in the absence of brain edema. Methods: Healthy subjects and individ...

Astronauts aboard the International Space Station (ISS) have exhibited hyperopic shifts, posterior eye globe flattening, dilated optic nerve sheaths, and even optic disc swelling from spaceflight. Elevated intracranial pressure (ICP) consequent to cephalad fluid shifts is commonly hypothesized as contributing to these ocular changes. Head-down tilt...

Introduction: Flights to high altitude can lead to exposure and unique pathology not seen in normal commercial aviation. Methods: This paper assesses the potential for point-of-care ultrasound to aid in management and disposition of injured crewmembers from a high altitude incident. This was accomplished through a systematic literature review re...

INTRODUCTION: The Stratex Project is a high altitude balloon flight that culminated in a freefall from 41,422 m (135,890 ft), breaking the record for the highest freefall to date. Crew recovery operations required an innovative approach due to the unique nature of the event as well as the equipment involved. The parachutist donned a custom space su...

The StratEx program used a self-contained space suit and balloon system to loft pilot Alan Eustace to a record-breaking altitude and skydive from 135,897 feet (41,422 m). After releasing from the balloon and a stabilized freefall, the pilot safely landed using a parachute system based on a modified tandem parachute rig. A custom spacesuit provided...

OBJECTIVES: The study goal was to determine whether a single Space Shuttle mission can induce decrements in astronaut hearing. STUDY DESIGN: We retrospectively compared audiogram information obtained from Space Shuttle astronauts at 10 days preflight, day of return (R + 0), 3 days after landing return (R + 3), and at a mean delayed postflight follo...

Introduction: Postflight postural ataxia reflects both the control strategies adopted for movement in microgravity and the direct effects of deconditioning. Computerized dynamic posturography (CDP) has been used during the first decade of the International Space Station (ISS) expeditions to quantify the initial postflight decrements and recovery o...

Background: Noninvasive intracranial pressure (ICP) measurement would represent a major advance for patients with neurological problems. The Vittamed ICP meter is an ultrasound-based device reported to have high agreement with lumbar puncture cerebrospinal fluid (CSF) pressure measurement. However, previous studies included mostly patients with no...

The current Ebola outbreak has been the largest in history. It has ravaged Guinea, Sierra Leone and Liberia with 11,120 deaths, including the deaths of over 500 healthcare professionals. This outbreak has escalated to a global health issue with many countries utilizing their resources and budgets to come up with measures to protect themselves again...

Space applications have evolved to play a significant role in disaster relief by providing services including remote sensing imagery for mitigation and disaster damage assessments; satellite communication to provide access to medical services; positioning, navigation, and timing services; and data sharing. Common issues identified in past disaster...

Introduction Red Bull Stratos was a commercial program that brought a test parachutist, protected by a full-pressure suit, in a stratospheric balloon with pressurized capsule to over 127,582 ft (38,969 m), from which he free fell and subsequently parachuted to the ground. Given that the major risks to the parachutist included ebullism, negative Gz...

Objectives: Recent studies suggest that elevated intracranial pressure (ICP), created by hydrocephalus, can alter the lower limit of cerebrovascular autoregulation (LLA). Our objective in the present study was to determine if ICP elevation from cerebral venous outflow obstruction would result in comparable alterations in the LLA. Methods: Anesth...

The Red Bull Stratos Project consisted of incremental high altitude parachute jumps [maximum altitude 127,852 ft (38,969 m)] from a pressurized capsule suspended from a stratospheric helium-filled balloon. A physiological monitoring system was worn by the parachutist to provide operational medical and acceleration data and to record a unique set of...

Ultrasound (U/S) and MRI measurements of the optic nerve sheath diameter (ONSD) have been proposed as intracranial pressure measurement surrogates, but these methods have not been fully evaluated or standardized. The purpose of this study was to develop an ex-vivo model for evaluating ONSD measurement techniques by comparing U/S and MRI measurement...

Nontraumatic, nonhydrocephalic increases in intracranial pressure (ICP) are often difficult to diagnose and may underlie spaceflight-related visual changes. This study looked at the utility of a porcine animal model of increasing cephalic venous pressure to mimic acute changes in ICP and optic nerve sheath diameter (ONSD) from cephalic venous fluid...

Red Bull Stratos was a commercial program that brought a test parachutist protected by a full pressure suit to 127,852 ft (38,964 m), via a stratospheric balloon with a pressurized capsule, from which he free fell and subsequently parachuted to the ground. In light of the uniqueness of the operation and the medical threats faced, medical protocols...

Komorowski M, Watkins SD, Lebuffe G, Clark JB. Potential anesthesia protocols for space exploration missions. Aviat Space Environ Med 2013; 84:226–33. In spaceflight beyond low Earth’s orbit, medical conditions requiring surgery are of a high level of concern because of their potential impact on crew health and mission success. Whereas surgical tec...

Red Bull Stratos was a commercial program designed to bring a test parachutist protected by a full-pressure suit via a stratospheric balloon with a pressurized capsule to 120,000 ft (36,576 m), from which he would freefall and subsequently parachute to the ground. On March 15, 2012, the Red Bull Stratos program successfully conducted a preliminary...

In 1998 Patel et al searched for Earth-Mars free-return trajectories that leave Earth, fly by Mars, and return to Earth without any deterministic maneuvers after Trans-Mars Injection. They found fast trajectory opportunities occurring two times every 15 years with a 1.4-year duration, significantly less than most Mars free return trajectories, whic...

Long duration spaceflight, permanent human presence on the Moon, and future human missions to Mars will require autonomous medical care to address both expected and unexpected risks. An integrated non-invasive visual field test & diagnosis system is presented for the identification, characterization, and automated classification of visual field def...

Ebullism is the spontaneous evolution of liquid water in tissues to water vapor at body temperature when the ambient pressure is 47 mmHg or less. While injuries secondary to ebullism are generally considered fatal, some reports have described recovery after exposure to near vacuum for several minutes. The objectives of this article are to review th...

As directed by the Council of the Aerospace Medical Association, the Commercial Spacefl ight Working Group has developed the following position paper concerning medical issues for commercial suborbital spacefl ight crewmembers. This position paper has been approved by the AsMA Council to become a policy of the AsMA.

Spacecraft mishaps involving loss of life are fortunately relatively rare. They always offer tremendous insight into improve- ments in vehicle design and operations. Aeromedical forensic analysis is a vital aspect of every aviation mishap, yet its application in spacecraft mishap investigation seems elusive. Due to the sensitive nature of fatal spa...

Orbiter landing data show decrements in pilot performance following spaceflight compared to preflight simulated landings. This study aimed to characterize pilot head-eye coordination during simulated orbiter landings, and relate findings to microgravity-related spatial disorientation. Orbiter landings were simulated in an A340-300 simulator flown b...

Executive Committee, Space Medicine Association. International Space Station life sciences research funding. Aviat Space Environ Med 2008; 79:440–1.

Among other functions, the neurological and neurovestibular systems serve to support positional awareness and motor control. Because gravitational cues and visual references play a role in this support, it is not surprising that the spaceflight environment profoundly influences static and dynamic positional sense and subsequent motor function. Huma...

The physiological zone from sea level to 3,048 m (10,000 ft) encompasses the pressure to which humans are well adapted, although if appropriately acclimated they can survive the summit of Earth's highest mountain (Mt. Everest at 4,448 m/29,028 ft) without supplemental oxygen. Continuing to altitudes above this, artificial systems are required to su...

Omnipresent with human habitation in artificial environments is background and operational noise. Inherent in almost any platform or craft that maintains a human crew in an enclosed cabin is the need for circulation of air to remove metabolic and other adverse waste products and to replenish consumed oxygen. Water and fluid coolants of thermal cont...

Hand and upper-extremity overuse and repetitive injuries in astronauts have been and continue to be a common problem in the space program. The demands on upper-extremity use in the astronaut training program, the zero-gravity environment, the extreme temperature conditions of space, the effects of space travel on human physiology/anatomy, and the c...

Hypoxia poses a documented threat to aerospace and diving operations in healthy people and is a component of many clinical conditions. Practical training for aircrew, and research on clinically relevant hypoxic conditions frequently rely exclusively on large, expensive hypobaric chambers. Here we describe and report the efficacy of a compact, econo...

Objectives: The study goal was to determine whether a single Space Shuttle mission can induce decrements in astronaut hearing. Study design We retrospectively compared audiogram information obtained from Space Shuttle astronauts at 10 days preflight, day of return (R + 0), 3 days after landing return (R + 3), and at a mean delayed postflight follo...

Summary form only given. Adaptive plasticity driven by gravity transitions associated with launch and return from space flight modifies the performance of sensory-motor control systems crucial to mission activities and activities of daily living (ADL). Data from pre- and post-flight balance control studies demonstrate the initial deficit and subseq...

A Note from the Editor: The previous article by Hendriksen and Elderson (Aviat Space Environ Med 2001; 72:1025-33) on the use of electroencephalography in the assessment of aircrew fitness will likely generate appropriate and well-considered viewpoints from readers. Owing to the nature of the subject matter and importance of neurological examinatio...

The purpose of Space Medicine is to ensure mission success by providing quality and comprehensive health care throughout all mission phases to optimize crew health and performance and to prevent negative long-term health consequences. Space flight presents additional hazards and associated risks to crew health, performance, and safety. With an exte...

The current training program for hypoxia familiarization requires a low-pressure chamber that places aviator trainees at risk for decompression sickness. A cost-effective reduced oxygen-breathing (ROB) paradigm that decreases oxygen (O2) concentration leading to normobaric hypoxia was assessed as an alternative to the hypobaric chamber. To help est...

Divers may be exposed to intense noise underwater. Two cases of neurologic disturbances during experimental exposures to 15 min of continuous underwater sound are described. Sound exposure in the first case consisted of a warble tone with center frequency of 240 Hz and a sound pressure level of 160 dB re 1 microPa. Symptoms during exposure consiste...

Navy divers may be exposed to active sonar transmissions while underwater. Previous manned experiments to determine safe levels of exposure have all been conducted in enclosed settings characterized by standing wave sound fields. The purpose of this experiment was to determine if plane wave (open water) acoustics alters the physiological or subject...

The authors present a case of an attack helicopter pilot with recurrent spatial disorientation (SD) flying with night vision goggles (NVG's), diagnosed as having visually triggered migraine headaches. Serial Dynamic Platform Posturography testing during an acute migraine attack demonstrated balance dysfunction under visual and somatosensory deficie...

This article presents a format of aeromedical decision-making used in neurology cases referred to a U.S. Navy Special Board of Flight Surgeons (SBFS) from 1988 to 1990. The format consists of a series of questions addressing aeromedical concerns, an aeromedical disposition flowchart, and a decision analysis tree. Decision Analysis is a tool used in...

Loss of spatial awareness has been implicated as a direct causal factor in 4-10% of serious aircraft mishaps and 10-20% of fatal aircraft mishaps (7). Spatial disorientation in flight usually results from misperception of visual, vestibular, or proprioceptive cues. Pathologic causes have rarely been implicated. A student naval aviator with recurren...

Victims of air embolism often recover rapidly on hyperbaric treatment then deteriorate again, even if hyperbaric treatment is continued. In previous animal experiments, lidocaine has been shown to improve recovery of somatosensory evoked response amplitude after air embolism. However, animals in these experiments rarely deteriorated. We have shown...

A Navy helicopter pilot was found to have a suprasellar mass during evaluation for primary infertility and mildly elevated prolactin level. Extensive evaluation revealed no other abnormalities. After 1 year of followup without radiographic tumor enlargement, he was returned to flying duties with continuing medical monitoring. Aeromedical considerat...

Injuries to the cervical region have been associated with high-G loads sustained during air combat maneuvering (ACM) in high performance fighter aircraft. The spectrum of injuries ranges from mild neck pain to musculoskeletal strain, injury to the nerve roots or spinal cord, and fracture of the cervical spine. A 36-year-old fighter pilot with 2,800...

This article reviews the available medical data that form the basis for the U.S. Navy's policy on aeromedical disposition of Human Immunodeficiency Virus (HIV) seropositive flyers. Following a brief review of military HIV antibody testing and clinical evaluation, this article addresses the main issue in the Navy's aeromedical disposition policy--th...

A 36-year-old man presented with episodic exertional dyspnea, fluctuating exercise intolerance, and myoglobinuria. He never experienced cramps or myalgias. Subsequent evaluation revealed carnitine palmitoyl transferase deficiency. The unusual features of this case suggested that carnitine palmitoyl transferase deficiency may have a more diverse cli...

This article has no abstract; the first 100 words appear below. Botulism is a neuroparalytic illness caused by the action of a heat-labile neurotoxin elaborated by Clostridium botulinum. Botulism in adults typically results from ingestion of preformed toxin in contaminated food, whereas in botulism in infants and in wound botulism, the neurotoxin i...

We describe a patient with a gunshot wound to the brain that traversed the left cerebellar hemisphere and terminated in the left lateral midpons. The clinical findings, operative course, neuroradiographic features, and evoked potential data are correlated with the functional anatomy of the pons. It is possible to demonstrate that a local lesion in...

The authors report a patient with an epidermoid tumor that eroded through the frontal sinus, causing an acute neurological deficit secondary to tension pneumocephalus. The historical perspective, radiographic features, and pathophysiological mechanisms are discussed.

A patient with a fusiform aneurysm of the cervical vertebral artery at C-1 presenting with posterior circulation infarctions is reported. Exposure via the posterolateral approach, resection of the aneurysm, and end-to-end anastomosis are described. The authors emphasize the importance of the surgical approach and ability to expose and mobilize a ge...

When a hearing conservation program (HCP) involves NASA's astronauts and their unique working environment, special acoustical concerns develop that are receiving heightened attention from medical, safety, and engineering teams. The presence of distinctive characteristics (like prolonged noise exposures in weightless environments) associated with th...

Interaction of the vestibular system with the other vision stabilizing visual vestibular interaction (VVI) systems is essential for retinal image stability during movement to optimize visual performance. Dynamic visual acuity (DVA) is the threshold of visual resolution achieved during relative motion, and is a performance measure of VVI. Dynamic vi...