SPACE-COT: Studying the Physiological and Anatomical Cerebral Effects of Carbon Dioxide and Tilt
Eric Bershad, M.D.
Baylor College of Medicine
The SPACE COT study was a landmark international collaboration led by investigators from Baylor College of Medicine and DLR (German Aerospace Institute) to simulate the conditions on International Space Station that may give rise to the visual impairment intracranial pressure (VIIP) syndrome. Healthy subjects were exposed to a combination of 12 degree head down tilt (HDT) with regular air versus HDT and elevated carbon dioxide (0.5% CO2). An integrated approach was applied to measure brain, ocular, and systemic physiology using gold standard and novel innovative methods. The results suggest that HDT and CO2 may have both detrimental and beneficial effects on various aspects of human performance. Based on the findings so far, it is likely that an individualized assessment of astronauts will be necessary to understand how they will respond to the fluid shifting and carbon dioxide exposure during space flight.
Video: Watch this overview of the SPACE COT project, an international space biomedical study that took place in Cologne, Germany in June 2015.
Six healthy male subjects were enrolled in a randomized double masked, crossover study at the “:envihab” facility in Cologne, Germany. Each subject underwent a baseline period in the upright/supine with ambient air condition, followed by 26 hours of 12 degree HDT and carbon dioxide or ambient air. This was followed by a 2 hour period of acutely elevated 3% CO2. The subject then had a one week washout period, followed by a second bedrest campaign with the other condition (i.e. HDT and ambient air or HDT and 0.5% CO2). Subjects had measurement of brain, ocular and systemic physiology in order to develop an integrated understanding of the individual response to the experimental conditions.
Measurements of brain physiology were made with: MRI (cerebral blood flow, volumetric analysis, CSF flow), transcranial Doppler (cerebral blood flow), Vittamed (intracranial pressure), cFLOW (CBF), near infrared spectroscopy [NIRS] (CBF and volume), Cerebrotech (intracranial fluid monitor), Olfactory threshold, and internal jugular vein volumes, Cognition battery, and psychological questionnaires. Ocular measurements including optical coherence tomography, visual acuity, and intraocular pressure measurements. Systemic measurements included: echocardiography, vascular function (flow mediated-dilation) plasma volume, orthostatic intolerance testing, pulmonary function (CO2 response, pulmonary function tests, arterial blood gases, end tidal CO2), hematological and systemic laboratory analysis.
Several novel and unexpected findings were revealed. First, the effect of 12 degree head down decreased cerebral blood flow regardless of 0.5% CO2 versus ambient air. This suggests that HDT may be detrimental to brain functioning due to decreased CBF and energy supply to the brain. This effect was partially reversed with higher levels of CO2 (3%) as measured by MRI. Cognitive performance was worse on several measures in the HDT alone condition, but improved when 0.5% of CO2 was present (HDT + 0.5% C02). The ICP did not significantly elevate from baseline, after HDT, regardless of the atmosphere (i.e. no differences between HDT alone vs HDT + 0.5% CO2). No major ocular changes were seen in this short duration exposure to the HDT +/- 0.5% CO2. Subjects did not have any major adverse events from 12 degree HDT +/- 0.5% CO2 or 3% CO2, although most had moderate back pain resolved with mild analgesics or mechanical methods. One subject developed significant urinary retention in the 12 degree HDT position and required urinary catheterization during campaign 1, and temporary interruption of the HDT position. Insights from this study will be instrumental for longer term HDT bedrest analogs which are planned at :envihab.
Video: Watch the next video of the SPACE COT project, an international space biomedical study that took place in Cologne, Germany in June 2015 here.
This study provides important insights into brain physiology in response to HDT and CO2 which are also applicable to conditions on earth. Additionally, the novel and innovative devices used for monitoring the brain and ocular physiology can also be implemented in setting on Earth including the neurological ICU, battlefield, high altitude, and remote environments. Most of the devices used are relatively easy to operate, do not require high energy, and are mobile, and thus have uses in multiple settings by basic medical personnel. Carbon dioxide is a key parameter to measure in brain injured patients, and several of the devices used in our study specifically measured the effects of CO2 on cerebral blood flow (NIRS, cFLOW, TCD) and thus can be applied in the neuro-ICU or other earth based settings to optimize brain functioning. The insights gained from HDT on the cerebral blood flow and cognitive function may be applicable to patients with brain injury to better understand the effects of body position including supine and head down tilt on brain health.