Many studies have reported method to detect car driver drowsiness by heartbeat interval signals, but it is hard to record stable signals while driving in a way that does not burden the drivers. We examined whether the driver’s drowsiness can be detected from respiration signal. In 9 healthy subjects (seven males and two females; age, 45 ± 9 y), respiration, electrocardiogram, and acceleration signals were recoded for a total of 2,359 min (137-468 min per subject) of driving with a smart shirt biometric sensor (Hexoskin). Minute-to-minute respiratory rate, heart rate, and their variability were analyzed by complex demodulation. The sleepiness of drivers was assessed by subjective reports and by a surrogate maker of Dip & Waves, which is known to be a characteristic R-R interval pattern associated with driver drowsiness. Although respiratory rate showed no significant changes associated with Dip & Wave, respiratory rate variability increased progressively from 4 min before, peaked at Dip & Waves, and decreased immediately thereafter. No such definite trend was observed in any time- or frequency domain indices of heart rate variability. The findings of this study not only show the possibility of smart-shirt sensor as a device to detect driver drowsiness but also suggest that respiration signals may provide useful clues to predict driver drowsiness, which is unique from those provided by heart rate variability.
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