Jonathan B. Clark

Botulism in an adult associated with food-borne intestinal infection with Clostridium botulinum.

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 ...

Effect of lidocaine on somatosensory evoked response and cerebral blood flow after canine cerebral air embolism.

Background and Purpose: 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 that the induction of air embolism and transient hypertension in canines produces deterioration despite hyperbaric treatment, and we decided to test the effect of lidocaine on somatosensory evoked potential recovery and cerebral blood flow in this model. Methods: Dogs were treated with repeated doses of lidocaine or equivalent volumes of saline during hyperbaric therapy after internal carotid air embolism and transient hypertension. The investigators were unaware of treatment group assignment during the experiments. The amplitude of the median nerve somatosensory evoked potential and cerebral blood flow measured with carbon‐14‐labeled iodoantipyrine autoradiography were used to assess effect of therapy. Results: Lidocaine‐treated dogs recovered 60±10% (mean±95% confidence limits) of the baseline somatosensory evoked potential amplitude 220 minutes after air embolism; saline‐treated dogs recovered 32±10% (a significant difference at p<0.01). Lidocaine‐treated dogs also had higher cerebral blood flow values than saline‐treated dogs 220 minutes after air embolism. Conclusions: Lidocaine ameliorated the delayed deterioration of evoked potential associated with air embolism and hypertension in this canine model. The improved cerebral blood flow may be a mechanism of action of lidocaine or an associated effect of improved neuronal survival. (Stroke 1992;23:1515‐1521)

Feasibility analysis for a manned mars free-return mission in 2018

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, which take up to 3.5 years. This paper investigates these fast trajectories. It also determines the launch and life support feasibility of flying such a mission using hardware expected to be available in time for an optimized fast trajectory opportunity in January, 2018.

Head-Eye Coordination During Simulated Orbiter Landing

BACKGROUND 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. METHODS Orbiter landings were simulated in an A340-300 simulator flown by six pilots. Turns about the Heading Alignment Circle (HAC) to align the orbiter with the runway were simulated by 45 degrees banking turns. Final approach was simulated with an 11 degrees glide slope from an altitude of 4267 m, with preflare at 610 m and touchdown at 200 kn. Orbiter landings were also performed in the Vertical Motion Simulator (VMS) at NASA Ames by a NASA test pilot. RESULTS A340: During the HAC maneuver the head and eyes rolled toward the visual horizon with a combined gain of 0.14 of bank angle. Pilots alternated fixation between the instruments and the runway during final approach, almost exclusively focusing on the runway after preflare. Optokinetic nystagmus was observed during rollout. VMS: Head and eye roll tilt when rounding the HAC were of similar magnitude to that observed in the A340. During final approach the Heads-Up Display (HUD) reduced pitch head and eye movement. CONCLUSIONS Roll tilt of the head and eyes during the HAC tended to align the retina with the visual horizon. Overlaying critical flight information and the approaching runway with the HUD reduced pitch head and eye movement during orbiter final approach in the VMS relative to the A340 (no HUD installed).

Potential anesthesia protocols for space exploration missions.

In spaceflight beyond low Earths 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 techniques have been thoroughly studied in spaceflight analogues, the research focusing on anesthesia is limited. To provide safe anesthesia during an exploration mission will be a highly challenging task. The research objective is thus to describe specific anesthesia procedures enabling treatment of pre-identified surgical conditions. Among the medical conditions considered by the NASA Human Research Program Exploration Medical Capability element, those potentially necessitating anesthesia techniques have been identified. The most appropriate procedure for each condition is thoroughly discussed. The substantial cost of training time necessary to implement regional anesthesia is pointed out. Within general anesthetics, ketamine combines the unique advantages of preservation of cardiovascular stability, the protective airway reflexes, and spontaneous ventilation. Ketamine side effects have for decades tempered enthusiasm for its use, but recent developments in mitigation means broadened its indications. The extensive experience gathered in remote environments, with minimal equipment and occasionally by insufficiently trained care providers, confirms its high degree of safety. Two ketamine-based anesthesia protocols are described with their corresponding indications. They have been designed taking into account the physiological changes occurring in microgravity and the specific constraints of exploration missions. This investigation could not only improve surgical care during long-duration spaceflights, but may find a number of terrestrial applications in isolated or austere environments.

Pathophysiology, prevention, and treatment of ebullism.

INTRODUCTION 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 the current literature on ebullism and to present prevention and treatment recommendations that can be used to enhance the safety of high altitude activities and space operations. METHODS A systematic review was conducted on currently available information and published literature of human and animal studies involving rapid decompression to vacuum and ebullism, with subsequent development of an applicable treatment protocol. RESULTS Available research on ebullism in human and animal subjects is extremely limited. Literature available identified key pathophysiologic processes and mitigation strategies that were used for treatment protocol design and outlining appropriate interventions using current best medical practices and technologies. DISCUSSION Available literature suggests that the pathophysiology of ebullism leads to predictable and often treatable injuries, and that many exposures may be survivable. With the growing number of high altitude and space-related activities, more individuals will be at risk for ebullism. An integrated medical protocol can provide guidance for the prevention and treatment of ebullism and help to mitigate this risk in the future.

Pharmacological Agents for the Prevention and Treatment of Toxic Radiation Exposure in Spaceflight

BACKGROUND Astronauts are exposed to toxic ionizing radiation sources, including galactic cosmic radiation and solar particle events (SPE). Exposure to these radiation sources can lead to cataracts, heritable genetic mutations, cancer, acute life-threatening physiological compromise, and death. Current countermeasures focus on spacecraft shielding and creation of heavily shielded safe havens. At issue is the extraordinarily high cost of launching these heavy structures into space and their inability to provide adequate shielding from heavy ions at a feasible shield thickness. Pharmacological enhancement of cellular radiation resistance, an alternative method to limiting radiation toxicity, has received less attention. METHODS We have conducted an extensive literature review and critical evaluation of the scientific data pertaining to this field of study. Publications for review were identified through a Medline search using relevant terms, including radiotherapeutics, galactic cosmic radiation, radiopharmacology, radioprotectants, radiation countermeasures, solar particles, solar flares, radiation toxicity, and radiotoxicity. RESULTS We identified 15 agents with significant radiation dose reduction factors, ranging from 1.1 to 2.4, in experimental models. Of these, only amifostine is FDA approved for use in treating radiation toxicity. CONCLUSIONS Current data do not support the use of radiopreventive agents in the treatment of low-level ionizing radiation exposures. However, pharmacological countermeasures should be instituted for life-threatening, high-level radiation exposures, as occur with SPE. Given the catastrophic effects of SPE, the risk of toxicity from radioprotective agents is warranted. The current data supports treatment with high-dose amifostine (at 910 mg m(-2)) 30 min prior to radiation exposure.

Assessing Sensorimotor Function Following ISS with Computerized Dynamic Posturography.

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 of postural stability. METHODS The CDP data were obtained on 37 crewmembers as part of their pre- and postflight medical examinations. Sensory organization tests evaluated the ability to make effective use of (or suppress inappropriate) visual, vestibular, and somatosensory information for balance control. This report focuses on eyes closed conditions with either a fixed or sway-referenced base of support, with the head erect or during pitch-head tilts (± 20° at 0.33 Hz). Equilibrium scores were derived from peak-to-peak anterior-posterior sway. Motor-control tests were also used to evaluate a crewmembers ability to automatically recover from unexpected support-surface perturbations. RESULTS The standard Romberg condition was the least sensitive. Dynamic head tilts led to increased incidence of falls and revealed significantly longer recovery than head-erect conditions. Improvements in postflight postural performance during the later expeditions may be attributable to higher preflight baselines and/or advanced exercise capabilities aboard the ISS. CONCLUSIONS The diagnostic assessment of postural instability is more pronounced during unstable-support conditions requiring active head movements. In addition to supporting return-to-duty decisions by flight surgeons, the CDP provides a standardized sensorimotor measure that can be used to evaluate the effectiveness of countermeasures designed to either minimize deconditioning on orbit or promote reconditioning upon return to Earth.

Alteration in the lower limit of autoregulation with elevations in cephalic venous pressure

Abstract 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: Anesthetized juvenile pigs were assigned to one of two groups: naïve ICP (n  =  15) or high ICP (>20 mmHg; n  =  20). To elevate ICP through venous obstruction, a modified 5F esophageal balloon catheter was inserted via the right external jugular vein into the superior vena cava (SVC) and inflated to maintain an ICP of >20 mmHg. To calculate the LLA, gradual hypotension was induced by continuous hemorrhage from a catheter in the femoral vein. The LLA was determined by monitoring cortical laser Doppler flux (LDF). Results: The naïve and high ICP groups had LLAs of 45 mmHg (95% CI: 41–49 mmHg) and 71 mmHg (95% CI: 66–77 mmHg) respectively by LDF. The LLA was significantly different between the two groups and correlated significantly with ICP. Discussion: Elevated ICP from cephalic venous engorgement leads to an increase in the LLA. These findings suggest that pathologic processes resulting in cephalic venous outflow obstruction and intracranial venous congestion can acutely elevate ICP and may place the brain at risk for impaired cerebrovascular autoregulation.

Suborbital commercial spacefl ight crewmember medical issues

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