Engineering topics

Meehan, Richard T.

Publications and source records attributed to Meehan, Richard T..

5 records

NASA NTRS1993

Cerebral blood velocity and other cardiovascular responses to 2 days of head-down tilt

Spaceflight induces a cephalad redistribution of fluid volume and blood flow within the human body, and space motion sickness, which is a problem during the first few days of space flight, could be related to these changes in fluid status and in blood flow of the cerebrum and vestibular system. To evaluate possible changes in cerebral blood flow during simulated weightlessness, we measured blood velocity in the middle cerebral artery (MCA) along with retinal vascular diameters, intraocular pressure, impedance cardiography, and sphygmomanometry on nine men (26.2 +/- 6.6 yr) morning and evening for 2 days during continuous 10 deg head-down tilt (HDT). When subjects went from seated to head-down bed rest, their heart rate and retinal diameters decreased, and intraocular pressures increased. After 48 h of HDT, blood flow velocity in the MCA was decreased and thoracic impedance was increased, indicating less fluid in the thorax. Percent changes in blood flow velocities in the MCA after 48 h of HDT were inversely correlated with percent changes in retinal vascular diameters. Blood flow velocities in the MCA were inversely correlated (intersubject) with arterial pressures and retinal vascular diameters. Heart rate, stroke volume, cardiac output, systolic arterial pressure, and at times pulse pressure and blood flow velocities in the MCA were greater in the evening. Total peripheral resistance was higher in the morning. Although cerebral blood velocity is reduced after subjects are head down for 2 days, the inverse relationship with retinal vessel diameters, which have control analogous to that of cerebral vessels, indicates cerebral blood flow is not reduced.

Frey, Mary A. B.↗

NASA NTRS1992

Portable dynamic fundus instrument

A portable diagnostic image analysis instrument is disclosed for retinal funduscopy in which an eye fundus image is optically processed by a lens system to a charge coupled device (CCD) which produces recordable and viewable output data and is simultaneously viewable on an electronic view finder. The fundus image is processed to develop a representation of the vessel or vessels from the output data.

Taylor, Gerald R.↗

NASA NTRS1992

Immune responsiveness and risk of illness in U.S. Air Force Academy cadets during basic cadet training

It has been proposed, but not confirmed, that environmental stressors alter immune function and increase the risk of viral infection among healthy individuals. This hypothesis was evaluated by examining the relationship among stress, immune function, and illness in 96 first-year U.S. Air Force Academy cadets during orientation and four weeks later during the stressful environment of basic cadet training (BCT). Perceived stress and well-being levels of cadets were assessed via questionnaire. Immune responsiveness was analyzed by PHA-stimulated thymidine uptake in mononuclear leucocytes and by serologic evidence of reactivation of the Epstein-Barr virus (EBV). Results showed significant declines in in vitro PHA-induced lymphocyte transformation (-35 percent)and subjective well-being (-19 percent) from orientation to BCT with corresponding, significant increases in perceived stress (+32 percent). Despite significantly altered in vitro immune responsiveness, there was no serologic evidence of EBV reactivation nor was there an association between these measures and risk of illness as determined by medical chart review and self-reported symptoms.

Lee, David J.↗

NASA NTRS1990

Immunology presentation at the 1990 NASA/NSF Antarctica Biomedical Science Working Group

An overview of methodology used for determining human in vitro lymphocyte activation, proliferation and effector cell function was presented and results of previous manned space flight immunology studies from Apollo through Shuttle were reviewed. Until the Shuttle era, lymphocyte assays were not very sensitive and had such large variations among normal subjects that it was difficult to define a consistent effect of space flight. More sensitive assay, however, even with Shuttle missions as brief as 6 days indicate depressed T-cell proliferative responses are routinely observed following space flight. Using a slight modification of the Shuttle assay, five different human stress-immunology models have been studied over the last 6 years in our lab. These have included: academic examinations of medical students having blood drawn during major test periods on three separate groups of first year students and two hypoxia studies (at 25,000 feet in a 6 week chamber ascent to the equivalent of Mount Everest and twice on Pikes Peak at 14,000 feet). These studies are particularly pertinent to Antarctica, since the altitude equivalent of 11,000 feet at the South Pole may affect some of the variables that are being measured in immunology, physiology or cognitive studies. An extravehicular study was performed drawing blood from 35 individuals before and immediately following a chamber exposure study. Preliminary results from 30 Shuttle astronauts investigated immunophenotype analysis and the role of a novel monocyte population in modulating the previously observed suppressed in vitro immune function. The results of the Air Force Academy cadet stress study were also presented.

Meehan, Richard T.↗

NASA NTRS1990

Intraocular pressure, retinal vascular, and visual acuity changes during 48 hours of 10-deg head-down tilt

Intraocular pressures, retinal vascular diameters, and visual acuities of nine men, were repeatedly measured while the subjects were tilted 10 deg head-down for 48 h and while they were seated before (baseline), and after the tilt. An immediate increase in intraocular pressure, measured by pneumatonometer was recorded when subjects assumed the head-down position, and diurnal variations in intraocular pressures were observed for the 48 h. The initial and final head-down intraocular pressures were not significantly different. However, when subjects resumed the sitting position, intraocular pressures fell below the initial sitting values. Computer image analysis of the retinal vasculature detected a 6 percent and 2 percent reduction in the caliber of arteries and veins, respectively, as compared with sitting baseline values. No changes in visual acuity were documented during the 48 h of head-down tilt. The data suggest that the choroidal blood reservoir increases in volume over 48 h at continuous head-down position with a compensatory decrease in aqueous volume. These findings may explain intraocular pressure changes noted in astronauts during previous space missions and in studies associated with change in body position.

Mader, Thomas H.↗