Predicting performance and safety based on driver fatigue.

Fatigue causes decrements in vigilant attention and reaction time and is a major safety hazard in the trucking industry. There is a need to quantify the relationship between driver fatigue and safety in terms of operationally relevant measures. Hard-braking events are a suitable measure for this purpose as they are relatively easily observed and are correlated with collisions and near-crashes. We developed an analytic approach that predicts driver fatigue based on a biomathematical model and then estimates hard-braking events as a function of predicted fatigue, controlling for time of day to account for systematic variations in exposure (traffic density). The analysis used de-identified data from a previously published, naturalistic field study of 106 U.S. commercial motor vehicle (CMV) drivers. Data analyzed included drivers' official duty logs, sleep patterns measured around the clock using wrist actigraphy, and continuous recording of vehicle data to capture hard-braking events. The curve relating predicted fatigue to hard-braking events showed that the frequency of hard-braking events increased as predicted fatigue levels worsened. For each increment on the fatigue scale, the frequency of hard-braking events increased by 7.8%. The results provide proof of concept for a novel approach that predicts fatigue based on drivers' sleep patterns and estimates driving performance in terms of an operational metric related to safety. The approach can be translated to practice by CMV operators to achieve a fatigue risk profile specific to their own settings, in order to support data-driven decisions about fatigue countermeasures that cost-effectively deliver quantifiable operational benefits.

Rapid ventricular pacing for flow arrest during cerebrovascular surgery: revival of an old concept.

BACKGROUND: Intraoperative rupture of a cerebral aneurysm can be a devastating event that increases operative morbidity and mortality. Rapid ventricular pacing (RVP) is a technique used in interventional cardiology to obtain flow arrest for short periods of time. OBJECTIVE: To present our experience using RVP for flow arrest during cerebrovascular surgery. METHODS: We used RVP to produce flow arrest for periods of 40 seconds in 12 patients who underwent craniotomy for a cerebrovascular disorder (11 aneurysms and 1 arteriovenous malformation). RESULTS: During RVP, there was an immediate and significant reduction of blood pressure in each patient. The maximum degree of hypotension was obtained 3.2 ± 0.7 seconds (mean ± SD) after the start of RVP. When RVP was terminated, normal sinus rhythm returned instantaneously, along with recovery of indexes of hemodynamic function. Subjectively, the decrease in blood pressures facilitated dissection, and during clipping, the aneurysm sac felt softer and was easier to manipulate. No complications related to RVP occurred. CONCLUSION: Rapid ventricular pacing during cerebrovascular surgery is an effective method for lowering the arterial blood pressure in a controlled and directly reversible manner. Advances in cardiology now make RVP a promising and safe technique that can facilitate complex cerebrovascular surgery.

Continuous noninvasive blood pressure measurement by pulse transit time.

Blood pressure measurement is performed either invasively by an intra arterial catheter or noninvasively by cuff sphygmomanometry. The invasive method is continuous and accurate but has increased risk; the cuff is safe but less reliable and infrequent. A reliable continuous noninvasive blood pressure measurement is highly desirable. While the possibility of using pulse transit time to monitor blood pressure has previously been investigated, most studies were limited to calculating the correlation of the pulse transit time and blood pressure under rather static conditions. The relationship between the pulse transit time and blood pressure is yet to be clearly identified. This paper focuses on the modeling between the two values and presents results on cases where dramatic variation in blood pressure of the patient was induced by drug administration or surgical stimulation.