The characteristics of the drivers, crashes, and environment of the crash by sex are shown in . Male drivers had on average higher mean BMI than female drivers. A greater proportion of female drivers than male drivers were driving passenger cars, were wearing seatbelts, and were in vehicles in which an airbag deployed. Female drivers were also driving relatively newer cars. Male drivers were driving vehicles with a higher vehicle weight and ΔV during the crash and were more likely to be involved in crashes involving alcohol use, ejection, and rollover. Male drivers were also more likely to have single-vehicle collisions than were female drivers. More male drivers had MVCs on roads with speed limits of 80 to 105 km/h, whereas more female drivers had crashes on roads with speed limits of 48 to 80 km/h. In addition, male drivers were involved in MVCs more frequently at night than were female drivers.
Sample characteristics and injury outcomes, by sex.
Except for injuries to the head, face, and abdomen, the percentages of injury (injured versus not injured) to the thorax, spine, and upper and lower extremities were all higher for women than for men. However, the percentages of serious injury (seriously injured versus not seriously injured) to all body regions except for the thorax, abdomen, and upper extremity were greater for men than for women. Shown in are the coefficients derived from the logistic regression of BMI (BMI and BMI2) for each regional body injury measured by each of two outcomes, injured versus not injured (left) and seriously injured versus not seriously injured (right), in the all subjects model (upper) and in the ΔV model (lower). In the all subjects model, the sex difference was present only for injuries to the lower extremities for the injured versus not injured outcome. In the ΔV model, regional body injuries to the face, thorax, and abdomen differed significantly between male and female drivers for the injured versus not injured outcome and regional body injuries to the head, thorax, and spine differed significantly between male and female drivers for the seriously injured versus not seriously injured outcome.
Logistic regression coefficients of BMI for regional body injury severity, by sex.
The adjusted ORs derived from the logistic regression in the ΔV model of the BMI continuum for head, face, thorax, and spine injuries are shown in . The adjusted ORs for the abdomen, upper extremity, and lower extremity are shown in . Compared to nonobese male drivers, obese male drivers had a higher risk for injury and serious injury to the head, thorax, and spine. Male drivers had a higher risk of being injured in the head, thorax, and spine for both outcomes, injured versus not injured and seriously injured versus not seriously injured, than did female drivers. In addition, a U-shaped relation between BMI and serious injury in the abdominal region was found for both male and female drivers.
Adjusted OR for being injured or seriously injured by drivers' BMI and sex in upper body regions: head, face, thorax, and spine.
Adjusted OR for being injured or seriously injured by drivers' BMI and sex in the abdomen, upper extremity, and lower extremity.
Information was missing on ΔV for approximately 44% of drivers. Drivers' age, BMI, and proportions of race-ethnicities did not differ significantly between the groups for which ΔV was available or not. A higher proportion of subjects in the ΔV group were injured in the thorax, spine, and upper and lower extremities, and a lower proportion of subjects were seriously injured in the spine. The interaction terms between ΔV group and BMI (or BMI and BMI2) were not significant except for abdomen and upper extremity injuries for the injured versus not injured outcome and for face injury for the seriously injured versus not seriously injured outcome.
illustrates the standard and obese dummies used in the model simulations for male and female. All of the male dummies have the same height as 1.77 m. The weights of the male dummies are 78.4, 92.7, and 110.0 kg for the BMI 25, 30, and 35 models, respectively. The weight of torso subcutaneous adipose tissue was 9.4 kg for the BMI 30 model and 13.5 kg for BMI 35 model. All of the female dummies have the same height of 1.52 m. The weights of the female dummies are 49.3, 69.4, and 80.8 kg for the BMI 22, 30, and 35 models, respectively. The weight of torso subcutaneous adipose tissue was 14.3 kg for the BMI 30 model and 17.2 kg for BMI 35 model.
Standard and obese dummy models for male (top) and female (bottom).
shows the result of model validation study. The body kinematics of standard and obese dummies was consistent with that of PMHS subjects. Even though the body excursion of the obese dummy was predicted to be less than that of the PMHS subjects due to dummy's lighter weight (110 kg) than the subjects (mean weight 128 kg) used in the experiment, the decreased torso pitch induced by increased hip excursion of the obese subjects was well predicted in the model simulation. The ratios of shoulder excursion to hip excursion were 1.12 (simulation) and 1.23±0.37 (experiment) for obese subjects, and 1.82 (simulation) and 2.05±0.80 (experiment) for nonobese subjects.
Figure 4 Comparison of head, shoulder, hip, and knee excursions between model simulation and experiment . Videos S1
are the animated results of the model simulation to compare the kinematics of the standard and obese dummies (BMI 35) during a frontal crash (Case 1) for male and female, respectively. From the simulation outcomes, the regional body injuries (head injury criterion [HIC], neck injury criterion [Nij], thorax, and lower extremity criterion [LEC]), which are based on the mechanical responses (regional acceleration, force, moment, deflection) from the six different dummies shown in , were measured for each simulation case (total five cases). – show the variations of the injury measures as BMI increases, for head, neck, thorax (chest acceleration and deflection), and lower extremity, respectively. From the results, obese males have a much increased risk of injury (especially head, chest acceleration, chest deflection, and lower extremity) as compared to the standard male. Meanwhile, obese females have much increased (chest acceleration), slightly increased (head and lower extremity), or decreased (neck and chest deflection) risk of injury as compared to the standard female.
Computational investigation of the effect of obesity on the head injury criterion (HIC) for male (top) and female (bottom).
Computational investigation of the effect of obesity on the neck injury criterion (Nij) for male (top) and female (bottom).
Computational investigation of the effect of obesity on the thorax injury criterion (chest acceleration, g) for male (top) and female (bottom).
Computational investigation of the effect of obesity on the thorax injury criterion (chest deflection, mm) for male (top) and female (bottom).
Computational investigation of the effect of obesity on the lower extremity injury criterion (LEC) for male (top) and female (bottom).
According to the results of sensitivity analysis, no factors showed a significant impact on the models except for ΔV; however, crashes with ΔV available have been analyzed separately in our study. Results for belted and unbelted drivers were calculated separately and compared to the results for all drivers. Both belted and unbelted drivers showed very similar injury patterns with the results of both combined, especially for upper body regions, in all outcome models that could be estimated successfully (101 out of 112 models). In the other 11 cases (for example, serious facial injury in the all-subjects model for females, serious upper extremity injury in the ΔV models for both sexes), sample sizes in some covariate combinations were insufficient to estimate the models. Given this robust experience with sensitivity analysis, we have reported results for combined analyses that retain seat belt use as an indicator covariate in all models.