Preliminary Study of the Effects of Sequential Hypoxic Exposures in a Simulated Flight Task.

BACKGROUND: Previous studies of acute hypoxia have largely examined different altitudes in isolation. Pilots, however, receive two exposures during in-flight hypoxic emergencies (IFHEs): the initial exposure at altitude, followed by a second mild exposure after descending and removing the breathing mask. Conventional wisdom holds that performance recovers with blood oxygen saturation and that exposure to mild hypoxia is safe. This study examined the possibility that the effects of moderate hypoxia may linger to overlap with the effects of mild hypoxia during sequential exposures such as those experienced by pilots during an IFHE.METHODS: Subjects performed a simulated flight task and secondary task while being exposed to normobaric hypoxia via the ROBD-2.RESULTS: Average error on the flight task during exposure to 3048 m (10,000 ft) was marginally worse when preceded by exposure to 7620 m (25,000 ft; 7.40 ± 3.32) than when experienced in isolation (6.42 ± 3.82). Performance on the secondary task was likewise worse when the mild exposure followed the moderate exposure (0.27 ± 0.30 lapses per minute) than when the mild exposure occurred by itself (0.19 ± 0.20 lapses per minute). Minimum Spo2 showed a similar pattern of results (84.87 ± 4.37 vs. 86.61 ± 2.47).DISCUSSION: We believe our results are most likely due to a failure to recover from the original moderate exposure rather than an additive effect between the exposures. Even so, our findings suggest that pilot impairment following an IFHE may be worse than previously believed.Robinson FE, Horning D, Phillips JB. Preliminary study of the effects of sequential hypoxic exposures in a simulated flight task. Aerosp Med Hum Perform. 2018; 89(12):1050-1059.

Exhaled isoprene for monitoring recovery from acute hypoxic stress.

Hypoxia-like incidents in-flight have increased over the past decade causing severe safety concerns across the aviation community. As a result, the need to monitor flight crews in real-time for the onset of hypoxic conditions is paramount for continued aeronautical safety. Here, hypoxic events were simulated in the laboratory via a reduced oxygen-breathing device to determine the effect of recovery gas oxygen concentration (21% and 100%) on exhaled breath volatile organic compound composition. Data from samples collected both serially (throughout the exposure), prior to, and following exposures yielded 326 statistically significant features, 203 of which were unique. Of those, 72 features were tentatively identified while 51 were verified with authentic standards. A comparison of samples collected serially between recovery and hypoxia time points shows a statistically significant reduction in exhaled breath isoprene (2-methyl-1,3-butadiene, log2 FC -0.399, p = 0.005, FDR = 0.034, q = 0.033), however no significant difference in isoprene abundance was observed when comparing recovery gases (21% or 100% O2, p = 0.152). Furthermore, examination of pre-/post-exposure 1 l bag breath samples illustrate an overall increase in exhaled isoprene abundance post-exposure (log2 FC 0.393, p = 0.005, FDR = 0.094, q = 0.033) but again no significant difference between recovery gas (21% and 100%, p = 0.798) was observed. A statistically significant difference in trend was observed between isoprene abundance and recovery gases O2 concentration when plotted against minimum oxygen saturation (p = 0.0419 100% O2, p = 0.7034 21% O2). Collectively, these results suggest exhaled isoprene is dynamic in the laboratory ROBD setup and additional experimentation will be required to fully understand the dynamics of isoprene in response to acute hypoxic stress.

The identification of hypoxia biomarkers from exhaled breath under normobaric conditions.

Pilots have reported experiencing in-flight hypoxic-like symptoms since the inception of high-altitude aviation. As a result, the need to monitor pilots, in-flight, for the onset of hypoxic conditions is of great interest to the aviation community. We propose that exhaled breath is an appropriate non-invasive medium for monitoring pilot hypoxic risk through volatile organic compound (VOC) analysis. To identify changes in the exhaled breath VOCs produced during periods of reduced O2 levels, volunteers were exposed to simulated flight profiles, i.e. sea level for 5 min, O2 levels found at elevated altitudes for 5 min or placebo and 5 min at 100% O2 recovery gas, using a modified flight mask interfaced with a reduced O2 breathing device. During the course of these test events, time series breath samples from the flight mask and pre/post bag samples were collected and analyzed by gas chromatography/mass spectrometry (GC/MS). Seven compounds (pentanal, 4-butyrolactone, 2-pentanone, 2-hexanone, 2-cyclopenten-1-one, 3-methylheptane and 2-heptanone) were found to significantly change in response to hypoxic conditions. Additionally, the isoprene, 2-methyl-1,3-butadiene, was found to increase following the overall exposure profile. This study establishes an experimental means for monitoring changes in VOCs in response to hypoxic conditions, a computational workflow for compound analysis via the Metabolite Differentiation and Discovery Lab and MatLab(©) software and identifies potential volatile organic compound biomarkers of hypoxia exposure.

Cognitive and perceptual deficits of normobaric hypoxia and the time course to performance recovery.

BACKGROUND: Many in-flight hypoxia-like incidents involve exposure to normobaric hypoxia following an oxygen delivery equipment failure. Studies have documented the effect of hypoxia on specific aspects of human performance. The goal of the present study was to establish the effects of acute hypoxia on cognitive, psychomotor, and perceptual abilities and to chronicle the time required for these capabilities to fully recover to pre-exposure levels. METHODS: Subjects were presented with a battery of tests designed to assess visual acuity, contrast sensitivity, color vision, executive control, and reaction time (simple reaction time, SRT, and choice reaction time, CRT) before, during, immediately following, 60 min, 120 min, and 24 h after hypoxic exposure. Oxygen saturation was continuously measured throughout the duration of the study using near-infrared spectroscopy measured on the forehead and finger pulse oximetry. RESULTS: During the course of six assessment periods, contrast sensitivity, color vision, and subjective workload were affected to varying degrees during hypoxic exposure, but returned to baseline levels soon after a return to normoxia. Conversely, reaction time values and regional cerebral oxygen saturation (MrSO2), while also affected during hypoxic exposure (MSRT = 362.17 ms, MCRT = 389.55 ms, MrSO2 = 79.36%), did not return to baseline levels (MSRT = 337.35 ms, MCRT = 372.75 ms, MrSO2 = 99.75%) until the assessment period 24 h following exposure (MSRT = 324.35 ms, MCRT = 366.22 ms, MrSO2 = 99.10%). DISCUSSION: Evidence from this study suggests an impairment of specific performance characteristics following hypoxic exposure - some for a considerable period of time. Mitigation efforts should focus more on the prevention of hypoxia exposure rather than relying exclusively on training operators to recognize and react earlier to hypoxic symptomology.

Evaluation of Bio-VOC Sampler for Analysis of Volatile Organic Compounds in Exhaled Breath.

Monitoring volatile organic compounds (VOCs) from exhaled breath has been used to determine exposures of humans to chemicals. Prior to analysis of VOCs, breath samples are often collected with canisters or bags and concentrated. The Bio-VOC breath sampler, a commercial sampling device, has been recently introduced to the market with growing use. The main advantage for this sampler is to collect the last portion of exhaled breath, which is more likely to represent the air deep in the lungs. However, information about the Bio-VOC sampler is somewhat limited. Therefore, we have thoroughly evaluated the sampler here. We determined the volume of the breath air collected in the sampler was approximately 88 mL. When sampling was repeated multiple times, with the succeeding exhalations applied to a single sorbent tube, we observed linear relationships between the normalized peak intensity and the number of repeated collections with the sampler in many of the breath VOCs detected. No moisture effect was observed on the Tenax sorbent tubes used. However, due to the limitation in the collection volume, the use of the Bio-VOC sampler is recommended only for detection of VOCs present at high concentrations unless repeated collections of breath samples on the sampler are conducted.

Predicting individual differences in response to sleep loss: application of current techniques.

BACKGROUND: Fatigue's negative impact on safety represents one of the top threats to military transportation. Biomathematical models have been developed to predict the response to fatigue; however, current models do not take into account stable individual differences in fatigue susceptibility. Readiness Screening Tools (RSTs) can capture individual differences in fatigue response, but cannot predict performance long-term. The objective of this study was to combine an existing biomathematical model of fatigue with existing RST-derived measures to determine current ability to predict individual differences in fatigue response. We hypothesized that the predictive ability of the biomathematical model could be significantly improved by incorporating cognitive and oculometric measures shown to be sensitive to individual differences in fatigue response. METHODS: Data on multiple cognitive and oculometric measures were collected at rested baseline and then every 3 h across 25 h of continual wakefulness. Results characterized actual fatigued performance at the group and individual levels. Actual performance was compared to predicted performance decrements over the same time period. The unique variance explained by each approach was then combined to determine if RST-derived individual difference measures added significant predictive power to the model. RESULTS: Addition of individual-difference sensitive RST measures to an existing fatigue model significantly increased the amount of variance in performance explained by the model from 13.8 to 35.7%. DISCUSSION: Simply leveraging RSTs' ability to capture individual differences in fatigue susceptibility can substantially improve biomathematical prediction of fatigued performance.

A single dose of armodafinil significantly promotes vigilance 11 hours post-dose.

OBJECTIVE: This study was conducted to test the ability of armodafinil to promote vigilance among air traffic control operators 8 to 11 hours post-dose. METHODS: Forty-eight U.S. Naval air traffic control students were assigned to one of two groups, 150 mg dose of armodafinil or placebo. At 8:00 a.m., participants were administered armodafinil or a placebo, after which they completed a standard work day. Participants returned at 3:45 p.m. to complete the 4-hour performance portion of the study, where they performed the psychomotor vigilance task. RESULTS: The analysis showed a significant difference in vigilance between the armodafinil group and placebo (p < 0.05). Psychomotor vigilance task data revealed that participants receiving a 150 mg dose of armodafinil experienced significantly fewer lapses of attention compared to the control group. CONCLUSIONS: These results justify additional investigation into the efficacy of armodafinil to promote sustained vigilance in military operational settings where fatigue-related performance decrements are especially problematic.

The efficacy of low-dose intranasal scopolamine for motion sickness.

INTRODUCTION: Scopolamine is an effective motion sickness prophylactic, but oral and transdermal formulations are slowly absorbed. To enhance absorption and potentially efficacy, an intranasal formulation of scopolamine (INSCOP) was tested. METHOD: There were 16 motion sickness susceptible subjects with an average age of 23.5 +/- 3.0 yr and an average score of 11.3 +/- 4.7 on the Modified Motion Sickness Susceptibility Questionnaire-Short Form who volunteered to participate in the study. Each subject was given 0.4 mg of INSCOP and a placebo in a randomized, double-blind crossover design and, at 40 min post-dose, experienced Coriolis cross-coupling in a staircase progression until moderate nausea. Efficacy data and cognitive, physiological, and alertness assessments were collected during baseline control and throughout experimental testing. RESULTS: Intranasal scopolamine significantly increased the mean number of head movements tolerated [INSCOP 275.9 +/- 120.5, Placebo 230.7 +/- 76.4; t (15) = 2.21]. Estimation of medication absorption via plasma concentration indicated the drug was absorbed relatively rapidly to measurable levels by 15 min post-administration. Diastolic blood pressures and heart rate were significantly lower after administration of INSCOP compared to placebo. No significant cognitive or medication side effects were reported. Subjects reported no significant decrease in alertness as indicated by the Karolinska Sleepiness Scale. CONCLUSIONS: Results of the current study strongly suggest that intranasal scopolamine is efficacious for the treatment of motion sickness in susceptible individuals with no significant cognitive or sedative effects. Intranasal delivery offers a promising alternative for use in dynamic operational environments without cognitive detriment or increased side effects.

What dot clusters and bar graphs reveal: subitizing is fast counting and subtraction.

In two studies, we found that dot enumeration tasks resulted in shallow-sloped response time (RT) functions for displays of 1-4 dots and steep-sloped functions for displays of 5-8 dots, replicating results implicating subitizing and counting processes for low and high ranges of dots, respectively. Extracting number from a specific type of bar graph within the same numerical range produced a shallow-sloped but scallop-shaped RT function. Factor analysis confirmed two independent subranges for dots, but all bar graph values defined a unitary factor. Significantly, factor scores and asymmetries both showed correlations of bar graph recognition to dot subitizing but not to dot counting, strongly suggesting that subitizing was used in both enumeration of low numbers of dots and bar graph recognition. According to these results, subitizing appears to be a nonverbal process operating flexibly in either additive or subtractive fashion on analog quantities having spatial extent, a conclusion consistent with a fast-counting model of subitizing but not with other models of the subitizing process.

Predicting dual-task performance with the Multiple Resources Questionnaire (MRQ).

OBJECTIVE: The objective was to assess the validity of the Multiple Resources Questionnaire (MRQ) in predicting dual-task interference. BACKGROUND: Subjective workload measures such as the Subjective Workload Assessment Technique (SWAT) and NASA Task Load Index are sensitive to single-task parameters and dual-task loads but have not attempted to measure workload in particular mental processes. An alternative is the MRQ. METHOD: In Experiment 1, participants completed simple laboratory tasks and the MRQ after each. Interference between tasks was then correlated to three different task similarity metrics: profile similarity, based on r(2) between ratings; overlap similarity, based on summed minima; and overall demand, based on summed ratings. Experiment 2 used similar methods but more complex computer-based games. RESULTS: In Experiment 1 the MRQ moderately predicted interference (r = +.37), with no significant difference between metrics. In Experiment 2 the metric effect was significant, with overlap similarity excelling in predicting interference (r = +.83). Mean ratings showed high diagnosticity in identifying specific mental processing bottlenecks. CONCLUSION: The MRQ shows considerable promise as a cognitive-process-sensitive workload measure. APPLICATION: Potential applications of the MRQ include the identification of dual-processing bottlenecks as well as process overloads in single tasks, preparatory to redesign in areas such as air traffic management, advanced flight displays, and medical imaging.