INTRODUCTION: Magnetic resonance imaging (MRI) brain scans of U.S. Air Force (USAF) altitude workers show increased white matter hyperintensities (WMH) that appear related to decompression stress. Relevant exposure thresholds are unknown. This MRI survey compares the white matter
status of UK participants (UKP) in altitude chamber research and training with USAF cohorts having background and increased WMH.METHODS: UKP (N = 20) comprised 13 research subjects and 7 military altitude chamber instructors ages 33 to 50 yr (16 men, 4 women), encompassing
1417 decompressions over a 15,000-ft (4572 m) pressure altitude (range 11–189; median 50). High resolution MRI reproduced USAF sequences and data were analyzed at the University of Maryland to validate comparison with age-matched USAF control (DOC; N = 85) and aerospace operational
physiologist (PHY; N = 55) cohorts.RESULTS: UKP data are dichotomous: 17 subjects (85%) had normal scans (total 19 WMH) and three outliers had excess (>15) WMH (total of 83 lesions). WMH were not associated with metrics of decompression history (total exposures, rapid
decompression, pressure breathing, hypoxia familiarization, decompression sickness, or exposure intensity). Ranked data indicate that UKP have fewer WMH than PHY but not DOC. UKP outliers’ excess WMH are attributable to past mild traumatic brain injury.CONCLUSIONS: WMH in
UKP are unrelated to subjects’ low intensity (brief, infrequent) experience of altitude chamber decompression, encompassing occasional hypobaric hypoxia and mild decompression sickness, even with cumulative experience over many years. Such low intensity hypobaric exposure appears ‘subthreshold’
for promotion of WMH.Connolly DM, Lee VM, Hodkinson PD. White matter status of participants in altitude chamber research and training. Aerosp Med Hum Perform. 2018; 89(9):777–786.
BACKGROUND: Artificial hypergravity has been proposed to prevent or treat various forms of physiological deconditioning experienced during spaceflight. We have previously reported that cerebral blood flow decreased at 15−21 min of +1.5-Gz centrifugation without
decreases in arterial pressure at heart level. We reanalyzed our previous data to clarify time-dependent changes in cerebral blood flow and arterial pressure during mild +Gz hypergravity.METHOD: We reanalyzed data for 0–20 min during +1.5-Gz centrifugation
on 13 male subjects for whom physiological data were steadily recorded. Mean cerebral blood flow velocity in the middle cerebral artery (MCBFVMCA), mean arterial pressure at heart level (MAPheart), and middle cerebral artery level (MAPMCA) during centrifugation
were averaged every 5 min and compared with prehypergravity data (+1.0 Gz, 5 min).RESULTS: MAPheart did not change significantly, but MAPMCA decreased significantly throughout centrifugation compared to prehypergravity data (−16.7% to −24.7%).
MCBFVMCA tended to be decreased at 0–5 min of +1.5-Gz centrifugation (−3.3%), but this was not statistically significant. MCBFVMCA was significantly decreased at 5–10 min (−5.5%). MCBFVMCA at 10–15 min and 15–20
min were also significantly decreased to almost the same level (−6.9% and −6.8%, respectively).DISCUSSION: No significant change in MAPheart was detected, whereas MAPMCA decreased significantly from the beginning of +1.5-Gz centrifugation.
On the other hand, MCBFVMCA gradually decreased and became roughly flat in the latter half of 20-min centrifugation. Understanding the different time-dependent changes in cerebral blood flow and arterial pressure under mild +Gz hypergravity might be important for implementation
of centrifuging as a countermeasure for spaceflight-induced deconditioning.Konishi T, Kurazumi T, Kato T, Takko C, Ogawa Y, Iwasaki K. Time-dependent changes in cerebral blood flow and arterial pressure during mild +Gz hypergravity. Aerosp
Med Hum Perform. 2018; 89(9):787–791.
Retrospective Evaluation of Clinical Symptoms Due to Mild Hypobaric Hypoxia Exposure in Microgravity
INTRODUCTION: A habitat atmosphere of 34% oxygen (O2) and 66% nitrogen (N2) at 8.2 psia (56.5 kPa) is proposed to minimize the risk of decompression sickness during extravehicular activity. The resulting inspired O2 partial pressure (PIo2)
of 128 mmHg is similar to that experienced during portions of 41 Space Shuttle missions that used a “staged” denitrogenation (prebreathe) protocol with an atmosphere of 26.5% O2 and 73.5% N2 at 10.2 psia (70.3 kPa). We evaluated symptoms possibly linked to
mild hypoxia in astronauts breathing a PIo2 of 127 mmHg.METHODS: Environmental data were used to determine time in the shuttle at 10.2 psia and time at 14.7 psia (101.3 kPa). A total of 14 possible hypoxia symptoms were compared with symptoms collected during
normoxic shuttle operations at 14.7 psia using logistic regression.RESULTS: There were 134.1 d (788.8 person days) under the 10.2 psia staged condition with a mean of 3.17 ± 2.2 SD d/mission. There were 258.81 d at 14.7 psia (2192.95 person days). An average of 4.31 potentially
hypoxia-related symptoms per mission day was documented under the staged condition compared with 4.08 per mission day during the normoxic condition. Logistic regression showed no symptoms were significantly associated with just the 10.2 psia condition.DISCUSSION: Chronic exposure
to a PIo2 of 127 mmHg is well-tolerated by healthy humans on Earth. A similar short-duration exposure on the shuttle resulted in no increased reporting of possible hypoxia-related symptoms. However, chronic mild hypoxia interactions with physiological changes due to microgravity
adaptations remain unclear.Wessel JH III, Schaefer CM, Thompson MS, Norcross JR, Bekdash OS. Retrospective evaluation of clinical symptoms due to mild hypobaric hypoxia exposure in microgravity. Aerosp Med Hum Perform. 2018; 89(9):792–797.
BACKGROUND: +Gz tolerance is traditionally determined in centrifuges with open-loop G control, i.e., the centrifuge is under operator control (open loop), and thus the test subject is unable to influence the Gz load. In modern centrifuges, however, the subject
is commonly able to continuously control the Gz load (closed loop). It is a widespread opinion among fighter pilots that +Gz tolerance is higher under closed- than open-loop G control. The aims were to investigate whether +Gz tolerance is higher in closed-
than open-loop G control, and whether it is possible to use closed-loop G control during precise determination of +Gz tolerance.METHODS: Relaxed +Gz tolerance was determined in eight men during rapid Gz-onset rate (ROR) under three conditions: 1)
OL-VFB, open loop with visual feedback; 2) OL-NFB, open loop with no visual feedback; and 3) CL, closed loop. Straining +Gz tolerance was determined in 10 men during ROR in OL and CL conditions.RESULTS: Relaxed +Gz tolerance did not differ between CL (3.66
Gz), OL-VFB (3.70 Gz) and OL-NFB (3.64 Gz). Straining +Gz tolerance was similar in the CL (8.5 Gz) and OL (8.6 Gz) conditions. In the CL condition, the Gz load varied substantially and was on average lower than in
the OL conditions, at any stipulated G-time profile.DISCUSSION: There is no systematic difference in relaxed or straining +Gz tolerance as determined in closed- vs. open-loop G-controlled systems. During closed-loop control, precision and reproducibility are too low to
recommend it for accurate determination of relaxed G tolerance.Grönkvist M, Levin B, Eiken O. G tolerance during open- vs. closed-loop G-time control. Aerosp Med Hum Perform. 2018; 89(9):798–804.
INTRODUCTION: The purpose of this study was to determine how short- and long-duration spaceflight affects astronauts’ performance on functional tests that challenge the balance control system (Seated Egress and Walk; Object Translation; Recovery from Fall/Stand; and Jump
Down) and on clinical tests of balance function (Computerized Dynamic Posturography and Tandem Walk). In addition, we examined how exercise affects functional performance after long-term axial body unloading during 70 d of bed rest at 6° head-down tilt.METHODS: Data were collected
twice during the 2-mo period before spaceflight or during the 2-wk period before bed rest, and four times after flight or bed rest: on the day of landing or the day bed rest ended, 1 d and 6 d later, and a final session 12 d after bed rest or 30 d after spaceflight.RESULTS: For
bed rest subjects, long-term axial unloading alone caused functional performance deficits immediately after bed rest. However, the addition of an exercise regimen did not significantly improve median functional performance immediately after this axial unloading. For spaceflight subjects, the
length of the space mission was directly related to the severity of functional performance deficits within 1 d of landing and during the subsequent recovery period after flight.DISCUSSION: The performance data suggest that an additional sensorimotor-based countermeasure may be necessary
to maintain functional performance at preflight levels immediately after spaceflight.Miller CA, Kofman IS, Brady RR, May-Phillips TR, Batson CD, Lawrence EL, Taylor LC, Peters BT, Mulavara AP, Feiveson AH, Reschke MF, Bloomberg JJ. Functional task and balance performance in bed rest
subjects and astronauts. Aerosp Med Hum Perform. 2018; 89(9):805–815.
INTRODUCTION: Because a significant association between training to perform emergency free ascent (EFA) and the occurrence of pulmonary barotrauma (PBT) was demonstrated in 2006, the Belgian Underwater Federation (BUF) decided to discontinue this procedure. An evaluation was
needed 10 yr after the implementation of this change.METHODS: All medical records with a diagnosis of PBT that occurred in Belgium from November 2006 to September 2016 were prospectively collected. Data on the proportion of in-water skills training dives were obtained from BUF.RESULTS:
A total of 5 cases of PBT were identified, significantly down from 34 cases in the previous 10-yr period. Of those cases, four occurred during training dives (two during ascent training). Analysis of the case files furthermore showed that two should have been medically disqualified from diving.
Compared with the retrospective cohort (1995–2005), incidences are significantly reduced from 0.83 to 0.078/10,000 training dives and from 3.33 to 0.11/10,000 ascent-training dives; concomitantly, the incidence of PBT in nontraining dives also was reduced (from 0.0042 to 0.0014×10−4/10,000
dives), possibly because less divers undertake the EFA procedure in case of a technical incident and have learned to solve the problem differently.DISCUSSION: Discontinuation of emergency free ascent training was associated with a reduction in the incidence of PBT in the 10-yr follow-up
period. We observed a significant decrease of PBT during training dives, confirming the hypothesis that EFA training in its previous form did not contribute significantly to diving safety.Lafère P, Germonpré P, Guerrero F, Marroni A, Balestra C. Decreased incidence
of pulmonary barotrauma after discontinuation of emergency free ascent training. Aerosp Med Hum Perform. 2018; 89(9):816–821.
INTRODUCTION: The advent of autonomous automobiles raises new challenges for maintaining passenger safety and comfort. The challenge addressed here is how to predict and mitigate motion sickness when passengers read in a moving vehicle.METHODS: We utilized a car equipped
with a commercial active suspension system developed for attenuating the transmission of road surface fluctuations to passengers. The system was used to reproduce, in a parked car, either the vibrations that would be experienced in a moving car equipped with a conventional suspension system
(unmitigated ride) or the attenuated vibrations that would occur on the road with the active cancellation system engaged (mitigated ride). We evaluated the consequences of these two simulated ride conditions for reading performance, comfort, and evocation of motion sickness.RESULTS:
Both ride conditions reduced the 0 to 0.8 Hz vibrations to below threshold for evoking motion sickness during passive exposure. Only the mitigated ride condition attenuated frequencies in the 0.8 to 8 Hz band where visual suppression of the vestibulo-ocular reflex is known to break down, and
this condition also reduced the motion sickness induced by reading and increased reading comprehension and comfort relative to the unmitigated ride.DISCUSSION: The palliative effects of 0.8 to 8 Hz attenuation are discussed in terms of the different mechanisms underlying motion
sickness evoked by reading in a vehicle versus mere exposure to vehicle motion without reading. Implications for ISO-2631 standards for human exposure to vibration are also discussed.DiZio P, Ekchian J, Kaplan J, Ventura J, Graves W, Giovanardi M, Anderson Z, Lackner JR. An active
suspension system for mitigating motion sickness and enabling reading in a car. Aerosp Med Hum Perform. 2018; 89(9):822–829.
INTRODUCTION: In the United States, between 1995 and 2013, night-time visual flight rules (VFR) Helicopter Emergency Medical Service (HEMS) fatal accidents mostly encountered adverse weather, and pilots with <6 yr of HEMS experience showed higher likelihood of a night operational
accident. One adverse weather indicator is cloud-ceiling likelihood indicated by temperature dew point spread (TDPS). This study investigated the relationship between TDPS and HEMS pilot years of experience. It was hypothesized pilots with <6 yr HEMS experience were associated with fatal
outcomes encountered at lower TDPS.METHODS: Between 1995 and 2013, 32 single pilot night VFR HEMS fatal accidents occurring in the United States, caused by controlled flight into terrain or loss of control, were analyzed. Using Federal Aviation Administration weather guidance, the
0–4°C TDPS was selected as an indicator of cloud ceiling. Each flight’s TDPS was analyzed with pilots’ HEMS domain task experience.RESULTS: There were 27 flights which entered the 0–4°C TDPS range; 20 (74%) were significantly associated with adverse
weather. A significant negative linear relationship was found between TDPS of each mission and years of pilot HEMS experience (r = −0.423, P = 0.028). Pilots with <6 yr of experience were significantly associated with fatal outcomes (P = 0.049).CONCLUSION:
Pilots’ incremental years of HEMS experience were associated with a TDPS decrement. Fatal outcomes were over nine times higher for pilots with <6 yr of HEMS experience in night VFR operational accidents in those conditions. Interventions for <6-yr pilots are recommended during
experience building to prevent likelihood of operational accidents.Aherne BB, Zhang C, Chen WS, Newman DG. Pilot decision making in weather-related night fatal helicopter emergency medical service accidents. Aerosp Med Hum Perform. 2018; 89(9):830–836.
INTRODUCTION: Inflight medical incapacitations are rare events that can result in the loss of lives and aircraft. The potential for an in-flight medical event deserves the attention of certification authorities. Cardiac emergencies are among the most common serious events. The
primary focus of this study was to examine whether the proportions of pilots with reported cardiac conditions could be used to identify those who had inflight medical incapacitations.METHODS: The Civil Aerospace Medical Institute Inflight Incapacitation Registry was searched to
identify airline pilots with a cardiac history and an inflight medical event between 1995 and 2015. The Federal Aviation Administration's Decision Support System was searched for airline pilots without an inflight medical event. The cardiovascular history of incapacitated pilots was then compared
to that of airline pilots without incapacitation events.RESULTS: Although a significantly greater proportion of airline pilots with cardiac events had pacemakers than a control group with the same cardiac history who did not have inflight events, no significant difference was found
in the proportions of other markers of cardiac health.CONCLUSION: The proportions of airline pilots with identified cardiac conditions could not be reliably used to identify which pilots had inflight incapacitations.DeJohn CA, Mills WD, Hathaway W, Larcher J. Cardiac inflight
incapacitations of U.S. airline pilots: 1995–2015. Aerosp Med Hum Perform 2018; 89(9):837–841.
BACKGROUND: Analysis of mishap data is an obvious measure of performance for those who wish to improve flight safety and affect aviation capability development within military forces.METHODS: This study examined rotary-wing accident information held by UK Ministry
of Defence authorities for the 16-yr (inclusive) period from January 2000 through December 2015 in order to ascertain incidence patterns. Serious accidents of military registered aircraft operated by Joint Helicopter Command, the Royal Navy, the Search and Rescue Force, and the Defence Helicopter
Flying School were included in the analysis. A secondary intent of the review was to examine the influence of broad-based organizational changes on the overall incidence of rotary-wing accidents across the U.K. Ministry of Defence that grew out of the report published by Charles Haddon-Cave,
QC, following his wide-ranging investigation into the catastrophic crash of Royal Air Force Nimrod XV230 that occurred during a routine mission in Southern Afghanistan.RESULTS: During the 16-yr period between January 2000 and December 2015, 53 rotary-wing accidents occurred. The
overall accident rate was 2.32 accident events per 100,000 flight hours. Spatial disorientation accidents remain a prevalent risk in this study, being acknowledged in 43% of accidents. Prior to the Haddon-Cave report, the accident rate was 2.81 events per 100,000 flight hours. Following the
report, the accident rate decreased to 1.24 events per 100,000 flight hours.DISCUSSION: The decrease in the accident rate between 2000 and 2015 shares a temporal association with the adoption and operationalization of the recommendations found in Haddon-Cave’s report.Bushby
AJR, Powell-Dunford N, Porter WD. UK military rotary-wing accidents: 2000–2015. Aerosp Med Hum Perform. 2018; 89(9):842–847.
BACKGROUND: Sopite syndrome is a poorly understood symptom complex characterized by drowsiness and lethargy relating to motion sickness. Though often occurring in conjunction with the classic symptomatology of motion sickness, the literature suggests that sopite syndrome is a
separate entity that may occur independently of the feelings of nausea characteristic of traditional motion sickness. Additionally, the syndrome can last long after symptoms of nausea have subsided and can be debilitating to some patients. Due to the frequent concomitance of sopite syndrome
and the classic symptoms of motion sickness, the syndrome may frequently go unidentified and there is a paucity of data recording its exact incidence in the available literature.CASE REPORT: In this study, we report a case of sopite syndrome identified in a 23-yr-old student naval
aviator who was ultimately unable to overcome his symptoms and adapt to the dynamic environment of flight.DISCUSSION: This process is particularly relevant to student aviators and others involved in transportation settings where the existence of even mild performance challenges
may create the potential for operational hazards. Because the training of aviators and flight officers is historically one of the most expensive investments undertaken by the Department of the Navy each year, documenting unique manifestations of this common problem and addressing them early
in the training pipeline may help reduce the time and financial burden associated with student naval aviator attrition in the later stages of training.Gemender MS, Sholes PC, Haight SP. Sopite syndrome identified in a student naval aviator. Aerosp Med Hum Perform. 2018; 89(9):848–850.
Netters TA Jr. You’re the flight surgeon: chest discomfort in a flyer. Aerosp Med Hum Perform. 2018; 89(9):851–853.
