Effects of short-term mild hypercapnia during head-down tilt on intracranial pressure and ocular structures in healthy human subjects

Steven S. Laurie, Gianmarco Vizzeri, Giovanni Taibbi, Connor R. Ferguson, Xiao Hu, Stuart M.C. Lee, Robert Ploutz-Snyder, Scott M. Smith, Sara R. Zwart, Michael B. Stenger

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Many astronauts experience ocular structural and functional changes during long-duration spaceflight, including choroidal folds, optic disc edema, globe flattening, optic nerve sheath diameter (ONSD) distension, retinal nerve fiber layer thickening, and decreased visual acuity. The leading hypothesis suggests that weightlessness-induced cephalad fluid shifts increase intracranial pressure (ICP), which contributes to the ocular structural changes, but elevated ambient CO2 levels on the International Space Station may also be a factor. We used the spaceflight analog of 6° head-down tilt (HDT) to investigate possible mechanisms for ocular changes in eight male subjects during three 1-h conditions: Seated, HDT, and HDT with 1% inspired CO2 (HDT + CO2). Noninvasive ICP, intraocular pressure (IOP), translaminar pressure difference (TLPD = IOP-ICP), cerebral and ocular ultrasound, and optical coherence tomography (OCT) scans of the macula and the optic disc were obtained. Analysis of one-carbon pathway genetics previously associated with spaceflight-induced ocular changes was conducted. Relative to Seated, IOP and ICP increased and TLPD decreased during HDT. During HDT + CO2 IOP increased relative to HDT, but there was no significant difference in TLPD between the HDT conditions. ONSD and subfoveal choroidal thickness increased during HDT relative to Seated, but there was no difference between HDT and HDT + CO2. Visual acuity and ocular structures assessed with OCT imaging did not change across conditions. Genetic polymorphisms were associated with differences in IOP, ICP, and end-tidal PCO2. In conclusion, acute exposure to mild hypercapnia during HDT did not augment cardiovascular outcomes, ICP, or TLPD relative to the HDT condition.

Original languageEnglish (US)
Article numbere13302
JournalPhysiological Reports
Volume5
Issue number11
DOIs
StatePublished - Jun 1 2017

Fingerprint

Head-Down Tilt
Hypercapnia
Intracranial Pressure
Healthy Volunteers
Intraocular Pressure
Space Flight
Optical Coherence Tomography
Optic Nerve
Visual Acuity
Fluid Shifts
Astronauts
Weightlessness
Papilledema
Intracranial Hypertension
Optic Disk
Genetic Polymorphisms
Nerve Fibers

Keywords

  • Head-down tilt
  • hypercapnia
  • NASA
  • one-carbon metabolism
  • translaminar pressure difference

ASJC Scopus subject areas

  • Physiology (medical)
  • Physiology

Cite this

Effects of short-term mild hypercapnia during head-down tilt on intracranial pressure and ocular structures in healthy human subjects. / Laurie, Steven S.; Vizzeri, Gianmarco; Taibbi, Giovanni; Ferguson, Connor R.; Hu, Xiao; Lee, Stuart M.C.; Ploutz-Snyder, Robert; Smith, Scott M.; Zwart, Sara R.; Stenger, Michael B.

In: Physiological Reports, Vol. 5, No. 11, e13302, 01.06.2017.

Research output: Contribution to journalArticle

Laurie, SS, Vizzeri, G, Taibbi, G, Ferguson, CR, Hu, X, Lee, SMC, Ploutz-Snyder, R, Smith, SM, Zwart, SR & Stenger, MB 2017, 'Effects of short-term mild hypercapnia during head-down tilt on intracranial pressure and ocular structures in healthy human subjects', Physiological Reports, vol. 5, no. 11, e13302. https://doi.org/10.14814/phy2.13302
Laurie, Steven S. ; Vizzeri, Gianmarco ; Taibbi, Giovanni ; Ferguson, Connor R. ; Hu, Xiao ; Lee, Stuart M.C. ; Ploutz-Snyder, Robert ; Smith, Scott M. ; Zwart, Sara R. ; Stenger, Michael B. / Effects of short-term mild hypercapnia during head-down tilt on intracranial pressure and ocular structures in healthy human subjects. In: Physiological Reports. 2017 ; Vol. 5, No. 11.
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