Combined Effects of Moderate Hypoxia and Sleep Restriction on Mental Workload

Abstract

Aircraft pilots face a high mental workload (MW) under environmental constraints induced by high altitude and sometimes sleep restriction (SR). Our aim was to assess the combined effects of hypoxia and sleep restriction on cognitive and physiological responses to different MW levels using the Multi-Attribute Test Battery (MATB)-II with an additional auditory Oddball-like task. Seventeen healthy subjects were subjected in random order to three 12-min periods of increased MW level (low, medium, and high): sleep restriction (SR, <3 h of total sleep time (TST)) vs. habitual sleep (HS, >6 h TST), hypoxia (HY, 2 h, F_IO₂ = 13.6%, ~3500 m vs. normoxia, NO, F_IO₂ = 21%). Following each MW level, participants completed the NASA-TLX subjective MW scale. Increasing MW decreases performance on the MATB-II Tracking task (p = 0.001, MW difficulty main effect) and increases NASA-TLX (p = 0.001). In the combined HY/SR condition, MATB-II performance was lower, and the NASA-TLX score was higher compared with the NO/HS condition, while no effect of hypoxia alone was observed. In the accuracy of the auditory task, there is a significant interaction between hypoxia and MW difficulty (F_(2-176) = 3.14, p = 0.04), with lower values at high MW under hypoxic conditions. Breathing rate, pupil size, and amplitude of pupil dilation response (PDR) to auditory stimuli are associated with increased MW. These parameters are the best predictors of increased MW, independently of physiological constraints. Adding ECG, SpO₂, or electrodermal conductance does not improve model performance. In conclusion, hypoxia and sleep restriction have an additive effect on MW. Physiological and electrophysiological responses must be taken into account when designing a MW predictive model and cross-validation.

Keywords: ECG; MATB-II; SpO2; auditory oddball; breathing rate; eye tracking; hypoxia; sleep restriction.

Figure 1

Performance to the MATB-II tracking task (A), NASA-TLX subjective scores (B), and accuracy (ACC) and reaction time (RT) to the auditory task ((C) and (D), respectively) in the four experimental conditions (Habitual sleep/Normoxia, Habitual sleep/Hypoxia, Sleep restriction/Normoxia, Sleep restriction/Hypoxia) and at the three MW difficulty levels (Low, Medium, High) * is a significant difference with the Habitual sleep/Normoxia condition, p < 0.05).

Figure 2

Changes in peripheral oxygen saturation (SpO₂), respiratory (breathing rate), and cardiac parameters (heart rate and heart rate variability parameters) in the four experimental conditions (Habitual sleep/Normoxia, Habitual sleep/Hypoxia, Sleep restriction/Normoxia, Sleep restriction/Hypoxia) and at the three MATB-II MW difficulty levels (Low, Medium, High) * is a significant difference with the Habitual sleep/Normoxia condition, p < 0.05).

Figure 3

Changes in physiological Eye tracking parameters in the four experimental conditions (Habitual sleep/Normoxia, Habitual sleep/Hypoxia, Sleep restriction/Normoxia, Sleep restriction/Hypoxia) and at the three MATB-II MW difficulty levels (Low, Medium, High). Pupil size in raw values (A), pupil size in Z-score (B), an example of the Pupil Dilatation Response (PDR) at the three MATB-II MW difficulty levels (C), amplitude and latency ((D) and (E), respectively) of PDR. * is a significant difference with the Habitual sleep/Normoxia condition, p < 0.05).

Figure 4

(A). Correlation analysis (with Pearson coefficient, R and P) between physiological parameters and MATB-II tracking performance in the four experimental conditions (Habitual sleep/Normoxia, Habitual sleep/Hypoxia, Sleep restriction/Normoxia, Sleep restriction/Hypoxia). Only parameters showing a significant correlation (corrected p < 0.05) with MATB-II tracking performance (RMSD value) in Habitual sleep/Normoxia were presented. p values take into account multiple comparison corrections [27] (B): examples of repeated-measures correlations between MATB-II tracking performance (RMSD values) and heart, breathing rate, and amplitude and Z-score of the PDR response in the four experimental conditions.

Figure 5

Illustration of the four subtasks of the Multi-Attribute Task Battery (MATB)-II and the auditory Oddball-like task: SYSTEM MONITORING (A) task in the upper left corner where participants had to respond as quickly as possible to scale fluctuations via keystrokes, TRACKING (B) task in the upper corner where participants had to keep a tracker as close to the center with a joystick, COMMUNICATIONS (D) task in the bottom left corner where participants had to only answer broadcast messages that matched their call signs and RESSOURCE MANAGEMENT (E) task in the bottom right corner that required participants to keep tanks’ levels as close to target level as possible (2500 for the left and 1000 for right) by managing eight pumps. AUDITORY ODDBALL-LIKE (F) task that requires ignoring frequent tone and detecting infrequent auditory stimulus. (C) A workload rating survey is not a task but an automatic evaluation of the temporal progression; no action is required.

Figure 6

The study protocol. The order of conditions is: Habitual sleep Normoxia (HSNO), Habitual sleep Hypoxia (HSHY), Sleep restriction Normoxia (SRNO), Sleep restriction Hypoxia (SRHY). The levels of MATB-II difficulty (low, medium, or high) are randomized. Black square: NASA-TLX test.