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Subcutaneous fat distribution in the human Torso
Abstract
With obesity becoming a major health issue in recent years and a topic of interest in vehicle occupant safety, there is a need for detailed descriptions of body fat distribution in order to develop accurate models of the human body. In this study subcutaneous fat measurements were obtained from over 17,000 CT scans using planar distance maps from skin surface locations to the fascial envelope. Measures were taken as a map registered by vertebral level (from T6 down to L5, extended to the sacrum) and body location around the body perimeter. Multivariate regression maps were calculated showing the individual effect of demographics on the subcutaneous layer thickness. Regression coefficients were statistically significant, with results showing the progression of 20 years of age producing a migration of 3mm of fat from mid-abdominal to lower-abdominal regions and female occupants having thicker subcutaneous regions compared to males by between 6 and 24mm with accumulation peaks near the buttocks and breasts. Each 20kg of added body weight produce regional fat increases between 2 and 14mm across the torso, with a primary peak near the hips and secondary peak near the lower abdomen.
... Depending on the result, person can be classified as an underweight, normal, overweight, and obese. [10] In this study, we have focused on the thickness of the hypodermis which considerable changes with the aforementioned BMI classification. The thickness values of hypodermis for different BMI classes are reported in the Table I. ...
... LAYER IN THE CHEST NEAR SHOULDER AREA OF PEOPLE WITH DIFFERENT BMI[10]. ...
... The PC76 standard stipulates that the thickness of the gel used for testing should not be less than 22 mm [24]. Since AIMDs are often implanted subcutaneously, the average thickness of subcutaneous fat in the human chest ranges from 15 to 25 mm, while the average thickness in the abdomen and lower back can range from 40 to 60 mm [35], [36]. Therefore, for AIMDs implanted in areas such as the subclavian pocket (e.g., cardiac pacemakers) or in the pelvis and lower back (e.g., sacral nerve stimulators), the corresponding thickness of human tissue varies. ...
The temperature rise effect caused by a time-varying magnetic field in an MRI scanner on active implantable medical devices is related to the safety of patients. A reasonable experimental design is an important step to objectively evaluate the temperature rise of the equipment. To clarify the influence of key parameters of the temperature rise experiment on the results, this work theoretically modeled the physical mechanism of the temperature increase and studied the temperature increase of the device by experiments under different initial system temperatures, gel thicknesses, and magnetic field waveforms. The results show that the initial temperature has no effect on the temperature increase of the device. A thicker gel thickness corresponds to a smaller temperature increase. Under identical effective magnetic field switching rates, the sine wave magnetic field has a significantly stronger temperature rise effect than the triangular wave magnetic field. In addition, the point where the device has the largest temperature increase is located near the battery. This result indicates that the influence of these factors on temperature increase must be thoroughly considered during all phases of the device’s design, development, testing, and evaluation.
... On the contrary to radiological methods that can irradiate directly through the skin and soft tissues to the internal skeletal structures of the body, surface topography methods determine the location of anatomical landmarks based on the surface morphology of the human body. Holcombe [50] et al. studied the distribution of subcutaneous fat in humans for each vertebral plane from T6 to the sacrum. They found that the average thickness of subcutaneous fat was greater in the areas on both sides of the lumbar spine (mainly in the L3-L5 vertebral plane) than in other areas of the back. ...
Background:
Surface topography (ST) is one of the methods in scoliosis assessment. This study aimed to systematically review the reliability and validity of the ST measurements for assessing scoliosis.
Methods:
A literature search of four databases was performed and is reported following PRISMA guidelines. The methodological quality was evaluated using Brink and Louw appraisal tool and data extraction was performed. The results were analyzed and synthesized qualitatively using the level of evidence method.
Results:
Eighteen studies were included and analyzed. Four were evaluated for reliability, six for validity, and eight for reliability and validity. The methodological quality of fourteen studies was high. Good to excellent intra-investigator reliability was shown on asymmetry, sagittal, horizontal, and most frontal ST measurements (evidence level: strong). Asymmetry and most frontal, sagittal, horizontal ST measurements showed good to excellent inter-investigator reliability (evidence level: moderate). When comparing corresponding ST and radiological measurements, good to strong validity was shown on most frontal, sagittal, and asymmetry measurements (evidence level: strong). Formetric measurements had good intra-investigator reliability and validity (evidence level: strong).
Conclusions:
Most asymmetry, sagittal, and frontal ST measurements showed satisfactory reliability and validity. Horizontal ST measurements showed good reliability and poor validity. The ST technique may have great potential in assessing scoliosis, especially in reducing radiation exposure and performing cosmetic assessments.
... The interface between the abdominal cavity and subcutaneous adipose tissue was modeled as a simplified abdominal wall, attached to the superior edge of the pelvic innominate bones and the inferior edge of the ribcage. The cutaneous surface of this abdominal wall was estimated by projecting the skin surface inwards using the thickness of the subcutaneous adipose tissue, predicted using a regression model (Holcombe and Wang, 2014). The pleural surface of the abdominal wall was estimated by offsetting the cutaneous surface inwards using the estimated thickness of the abdominal wall. ...
Finite element Human Body Models are increasingly becoming vital tools for injury assessment and are expected to play an important role in virtual vehicle safety testing. With the aim of realizing models to study sex-differences seen in the injury- and fatality-risks from epidemiology, we developed models that represent an average female and an average male. The models were developed with an objective to allow tissue-based skeletal injury assessment, and thus non-skeletal organs and joints were defined with simplified characterizations to enhance computational efficiency and robustness. The model lineup comprises female and male representations of (seated) vehicle occupants and (standing) vulnerable road users, enabling the safety assessment of broader segments of the road user population. In addition, a new workflow utilized in the model development is presented. In this workflow, one model (the seated female) served as the base model while all the other models were generated as closely-linked derivative models, differing only in terms of node coordinates and mass distribution. This approach opens new possibilities to develop and maintain further models as part of the model lineup, representing different types of road users to reflect the ongoing transitions in mobility patterns (like bicyclists and e-scooter users). In this paper, we evaluate the kinetic and kinematic responses of the occupant and standing models to blunt impacts, mainly on the torso, in different directions (front, lateral, and back). The front and lateral impacts to the thorax showed responses comparable to the experiments, while the back impact varied with the location of impact (T1 and T8). Abdomen bar impact showed a stiffer load-deflection response at higher intrusions beyond 40 mm, because of simplified representation of internal organs. The lateral shoulder impact responses were also slightly stiffer, presumably from the simplified shoulder joint definition. This paper is the first in a series describing the development and validation of the new Human Body Model lineup, VIVA+. With the inclusion of an average-sized female model as a standard model in the lineup, we seek to foster an equitable injury evaluation in future virtual safety assessments.
... Non-contrast scans CT image processing. After being transferred into a spatial database, CT images were processed using Analytic Morphomics, a semi-automated image analysis method that has been previously described 24,29,30 . A combination of automated and user-guided algorithms written in Matlab (The Mathworks Inc, Natick, MA) identified the vertebral bodies to serve as an anatomical coordinate reference system. ...
Measurements of visceral adipose tissue cross-sectional area and radiation attenuation from computed tomography (CT) scans provide useful information about risk and mortality. However, scan protocols vary, encompassing differing vertebra levels and utilizing differing phases of contrast enhancement. Furthermore, fat measurements have been extracted from CT using different Hounsfield Unit (HU) ranges. To our knowledge, there have been no large studies of healthy cohorts that reported reference values for visceral fat area and radiation attenuation at multiple vertebra levels, for different contrast phases, and using different fat HU ranges. Two-phase CT scans from 1,677 healthy, adult kidney donors (age 18–65) between 1999 and 2017, previously studied to determine healthy reference values for skeletal muscle measures, were utilized. Visceral adipose tissue crosssectional area (VFA) and radiation attenuation (VFRA) measures were quantified using axial slices at T10 through L4 vertebra levels. T-tests were used to compare males and females, while paired t-tests were conducted to determine the effect (magnitude and direction) of (a) contrast enhancement and (b) different fat HU ranges on each fat measure at each vertebra level. We report the means, standard deviations, and effect sizes of contrast enhancement and fat HU range. Male and female VFA and VFRA were significantly different at all vertebra levels in both contrast and non-contrast scans. Peak VFA was observed at L4 in females and L2 in males, while peak VFRA was observed at L1 in both females and males. In general, non-contrast scans showed significantly greater VFA and VFRA compared to contrast scans. The average paired difference due to contrast ranged from 1.6 to − 8% (VFA) and 3.2 to − 3.0% (VFRA) of the non-contrast value. HU range showed much greater differences in VFA and VFRA than contrast. The average paired differences due to HU range ranged from − 5.3 to 22.2% (VFA) and − 5.9 to 13.6% (VFRA) in non-contrast scans, and − 4.4 to 20.2% (VFA) and − 4.1 to 12.6% (VFRA) in contrast scans. The − 190 to − 30 HU range showed the largest differences in both VFA (10.8% to 22.2%) and VFRA (7.6% to 13.6%) compared to the reference range (− 205 to − 51 HU). Incidentally, we found that differences in lung inflation result in very large differences in visceral fat measures, particularly in the thoracic region. We assessed the independent effects of contrast presence and fat HU ranges on visceral fat cross-sectional area and mean radiation attenuation, finding significant differences particularly between different fat HU ranges. These results demonstrate that CT measurements of visceral fat area and radiation attenuation are strongly dependent upon contrast presence, fat HU range, sex, breath cycle, and vertebra level of measurement. We quantified contrast and non-contrast reference values separately for males and females, using different fat HU ranges, for lumbar and thoracic CT visceral fat measures at multiple vertebra levels in a healthy adult US population.
... To simplify the coding scheme, the sternum length is increased by about 3 cm, and the arc length of the first rib is also increased. The average thickness of subcutaneous fat tissue in the thorax model ranges from 0.5 to 2.5 cm for male and 1.5 to 4.0 cm for female [31]. It was reported that excessive heating could be induced in the subcutaneous fat which was thicker than 1.5-2 cm [9]. ...
An electroquasistatic (EQS) model of capacitive hyperthermia for treating lung tumors is proposed, based on which the finite element method is applied to compute the electrical potential in a human thorax model. The temperature distribution in the thorax model, which is surrounded by a bolus maintained at a constant temperature, is computed by numerically solving a bio-heat equation, which includes metabolic heat generated in the tissues, heat convection mechanism in tissues and bolus, as well as the heat delivered by the microwave field computed with the EQS model and finite element method. Temperature-dependent blood perfusion rates of blood and muscle, respectively, are adopted to account for the physiological reaction of tissues to temperature variation. By simulations, it is observed that adjusting the dielectric properties of adipose tissue via injection, the time evolution of temperature distribution can be controlled to some extent, providing more flexibility to customize a hyperthermia treatment plan for specific patient.
... This provided a wide range of combinations that allowed us to analyze the incremental energy absorption (i.e. with and without the implant) as a function of anatomical variations. This interval was chosen with respect to the subcutaneous fat distribution in the chest area as described in [7], [12]. Fig. 1 shows the general geometrical layout of the multilayer structure. ...
... Depending on the result, person can be classified as an underweight, normal, overweight, and obese. [8] In this study, we have focused on the thickness of the hypodermis which considerable changes with the aforementioned BMI classification. The thickness values of hypodermis for different BMI classes are reported in the Table 1. ...
The proposed paper deals with simulation and analysis of the
radiofrequency field (2.4 GHz) inside the human tissue using a multi-layered skin and pacemaker model. The research was carried out using electromagnetic modelling based on the Finite Integration method. The simulations were performed in terms of computing electric field distributions calculated for four different hypodermis layer thickness. The focus was on near-field exposure modelled by dipole antenna. The results have shown that higher hypodermis layer causes higher absorption of electromagnetic field which leads to lower values of electric field strength on the pacemaker casing.
This study provides insight into the advantages and disadvantages of using ferrite particles embedded in agar gel phantoms as MRI temperature indicators for low-magnetic field scanners. We compare the temperature-dependent intensity of MR images at low-field (0.2 T) to those at high-field (3.0 T). Due to a shorter T1 relaxation time at low-fields, MRI scanners operating at 0.2 T can use shorter repetition times and achieve a significant T2* weighting, resulting in strong temperature-dependent changes of MR image brightness in short acquisition times. Although the signal-to-noise ratio for MR images at 0.2 T MR is much lower than at 3.0 T, it is sufficient to achieve a temperature measurement uncertainty of about ±1.0 °C at 37 °C for a 90 μg/mL concentration of magnetic particles.
Background:
Sarcopenia is defined as the loss of skeletal muscle mass and function associated with aging. Muscle mass can be reliably and accurately quantified using clinical CT scans but reference measurements are lacking, particularly in healthy US populations.
Methods:
Two-phase CT scans from healthy kidney donors (age 18-40) at the University of Michigan between 1999-2010 were utilized. Muscle mass was quantified using two thoracic and two lumbar muscle cross-sectional area (CSA) measures. Indexed measurements were computed as area divided by height-squared. Paired analyses of non-contrast and contrast phases and different Hounsfield Unit (HU) ranges for muscle were conducted to determine their effect on CSA muscle measures. We report the means, standard deviations, and 2SD sarcopenia cutoffs from this population.
Results:
Healthy population CSA (cm2) cutoffs for N=604 males/females respectively were: 34.7/20.9 (T12 Dorsal Muscle), 91.5/55.9 (T12 Skeletal Muscle), 141.7/91.2 (L3 Skeletal Muscle), 23.5/14.3 (L4 Total Psoas Area), and 23.4/14.3 (L4 Psoas Muscle Area). Height-indexed CSA (cm2/m2) cutoffs for males/females respectively were: 10.9/7.8 (T12 Dorsal Muscle), 28.7/20.6 (T12 Skeletal Muscle), 44.6/34.0 (L3 Skeletal Muscle), 7.5/5.2 (L4 Total Psoas Area), and 7.4/5.2 (L4 Psoas Muscle Area). We confirmed that a mask of -29 to 150 HU is optimal and shows no significant difference between contrast-enhanced and non-contrast CT scan CSA measurements.
Conclusions:
We quantified reference values for lumbar and thoracic muscle CSA measures in a healthy US population. We defined the effect of IV contrast and different HU ranges for muscle. Combined, these results facilitate the extraction of clinically valuable data from the large numbers of existing scans performed for medical indications.
Objective: Human Body Models have the potential to better describe the human anatomy and variability than dummies. However, datasets available to verify the human response to impact are typically limited in numbers, and they are not size or gender specific. The objective of the study was to investigate the use of model morphing methodologies within that context.
Methods: In the current study, a simple human model scaling methodology was developed to morph two detailed human models (Global Human Body Model Consortium models 50th male, M50 and 5th female F05) to the dimensions of Post Mortem Human Surrogates (PMHS) used in published literature. The methodology was then successfully applied to 52 PMHS tested in 14 impact conditions loading the abdomen. The corresponding 104 simulations were compared to the responses of the PMHS and to the responses of the baseline models without scaling (28 simulations). The responses were analysed using the CORA method and peak values.
Results: The results suggest that model scaling leads to an improvement of the predicted force and deflection but has more marginal effects on the predicted abdominal compressions. M50 and F05 models scaled to the same PMHS were also found to have similar external responses but large differences were found between the two sets of models for the strain energy densities in the liver and the spleen for mid abdomen impact simulations. These differences, which were attributed to the anatomical differences in the abdomen of the baseline models, highlight the importance of the selection of the impact condition for simulation studies, especially if the organ location is not known in the test.
Conclusions: While the methodology could be further improved, it shows the feasibility of using model scaling methodologies to compare human models of different sizes and to evaluate scaling approaches within the context of human model validation.
Analytic morphomics is a novel methodology that uses high-throughput computed tomography (CT) processing techniques to generate reproducible body measurements (Supplementary Table).1, 2, 3, 4 Body mass index is widely used in clinical and public health studies to predict mortality risk.⁵ Indeed, we recently examined its impact in allogeneic hematopoietic cell transplantation (HCT) and found that obese patients were at significantly greater risk of mortality compared with normal weight individuals.⁶ Unfortunately, body mass index does not reliably distinguish adipose tissue mass from muscle mass.⁷ Therefore, we sought to index patient size using CT measurements.² The aim of the current study was to apply analytic morphomics in a cohort of allogeneic HCT patients and correlate with clinical outcomes.
Seated posture inside a vehicle influences driver performance and control of a vehicle. Many vehicles do not properly allow for a natural seated posture for all drivers. Some vehicles are difficult to drive due to the fact that the driver is inadequately accommodated in the driver seat. For people of extreme stature, tall or short, and for people of extreme width, obese or pregnant populations, it can be difficult to safely operate a vehicle if there is not enough room in the cab or if some controls cannot be reached. This paper employs digital human models to study the effect of obesity on seated posture inside a vehicle. Eight digital human models, four non-obese and four obese, are subjected to reach tests inside a virtual vehicle cab. These tests are used to determine how obesity affects the clearance between the steering wheel and driver body and whether additional factors contribute to discomfort associated with obese people seated inside a vehicle. In order to model the obese subjects, factors such as increased waist circumference and limited joint range of motion due to obesity are included in the simulations. Also given is an indication of discomfort level through the output values of the multi-objective function in the optimization formulation. The benefit of using this method is that the human aspect of design can be included early in the design process, reducing or eliminating prototypes. If adjustments to the layout of the vehicle cab are needed the resulting postural differences can be quickly observed.
Men tend to have more upper body mass and fat than women, a physical characteristic that may predispose them to severe motor vehicle crash (MVC) injuries, particularly in certain body regions. This study examined MVC-related regional body injury and its association with the presence of driver obesity using both real-world data and computer crash simulation.
Real-world data were from the 2001 to 2005 National Automotive Sampling System Crashworthiness Data System. A total of 10,941 drivers who were aged 18 years or older involved in frontal collision crashes were eligible for the study. Sex-specific logistic regression models were developed to analyze the associations between MVC injury and the presence of driver obesity. In order to confirm the findings from real-world data, computer models of obese subjects were constructed and crash simulations were performed. According to real-world data, obese men had a substantially higher risk of injury, especially serious injury, to the upper body regions including head, face, thorax, and spine than normal weight men (all p<0.05). A U-shaped relation was found between body mass index (BMI) and serious injury in the abdominal region for both men and women (p<0.05 for both BMI and BMI(2)). In the high-BMI range, men were more likely to be seriously injured than were women for all body regions except the extremities and abdominal region (all p<0.05 for interaction between BMI and sex). The findings from the computer simulation were generally consistent with the real-world results in the present study.
Obese men endured a much higher risk of injury to upper body regions during MVCs. This higher risk may be attributed to differences in body shape, fat distribution, and center of gravity between obese and normal-weight subjects, and between men and women. Please see later in the article for the Editors' Summary.
This report presents national anthropometric reference data for the U.S. population aged 3 months and older in 1988-1994.
Data in this report are from the Third National Health and Nutrition Examination Survey (NHANES III), which was conducted on a complex, stratified, multistage probability sample of the civilian, noninstitutionalized U.S. population. A total of 31,241 persons were examined. The anthropometric measurements taken included weight, height, recumbent length, circumferences, limb lengths, joint breadths, and skinfold thicknesses. Body mass index values were computed from measured height and weight values.
The tables in this report include weighted population means, standard errors of the means, and selected percentiles of body measurement values. Because measurements varied by sex and age (and by race and ethnicity in adults), results are reported by these subgroups.
These data add to the knowledge about trends in child growth and development and are useful in monitoring overweight and obesity in the U.S. population.
The purpose of the study was to investigate the relationship between obesity and mortality of drivers in severe motor vehicle crashes involving at least one fatality.
Fatalities were selected from 155,584 drivers included in the 2000-2005 Fatality Analysis Reporting System. Drivers were stratified by body mass index, confounders were adjusted for, and multiple logistic regression was used to determine the odds ratio (OR) of death in each body mass index class compared with normal weight.
The adjusted risk of death from lowest to highest, reported as the OR of death compared with normal weight with 95% confidence intervals, was as follows: (1) overweight (OR, 0.952; 0.911-0.995; P = .0293), (2) slightly obese (OR, 0.996; 0.966-1.026; P = .7758), (3) normal weight, (4) underweight (OR, 1.115; 1.035-1.201; P = .0043), (5) moderately obese (OR, 1.212; 1.128-1.302; P < .0001), and (6) morbidly obese (OR, 1.559; 1.402-1.734; P < .0001).
There is an increased risk of death for moderately obese, morbidly obese, and underweight drivers and a decreased risk in overweight drivers.
The objective of this study was to document the motion and potential injury mechanisms of obese occupants in frontal car crashes compared to a control group of nonobese occupants in controlled laboratory impacts. Eight cadavers were divided into obese (n = 3) and a nonobese (n = 5) groups and exposed to a 48 km/h impact. High speed digital video documented the motion of the belted subjects. Compared to the nonobese cohort, the obese exhibited a characteristically different set of motions. As expected, the obese (heavier) subjects experienced greater maximum forward displacement (excursion) before their motion was arrested by the restraint. In addition, the obese exhibited a different distribution of excursions among body segments. The primary difference between the cohorts was substantially larger hip excursion in the obese (452 +/- 83 mm vs. 203 +/- 42 mm, P < 0.01), which was the proximate cause of a tendency of the obese cadavers' torsos to pitch forward less during impact. Some of the published epidemiology can be elucidated by the results reported here. The increased hip excursion and concomitant decreased torso pitch may reduce the risk of the head striking some component of the vehicle interior. Furthermore, the reclined torso during belt loading may increase the risk of rib and pulmonary trauma because the load is concentrated on the compliant and vulnerable lower thorax and less on the stiff upper ribs and clavicle. The lower extremities also experience increased excursion as a result of this hip excursion, and thus an increased risk of a hard contact and resulting injury.
We sought to investigate the effect of increased body weight on the risk of death and serious injury to occupants in motor vehicle crashes. We employed a retrospective cohort study design utilizing data from the National Automotive Sampling System, Crashworthiness Data System (CDS), 1993-1996. Subjects in the study included occupants involved in tow-away crashes of passenger cars, light trucks, vans and sport utility vehicles. Two outcomes were analyzed: death within 30 days of the crash and injury severity score (ISS). Two exposures were considered: occupant body weight and body mass index (BMI; kg/m2). Occupant weight was available on 27263 subjects (76%) in the CDS database. Mortality was 0.67%. Increased body weight was associated with increased risk of mortality and increased risk of severe injury. The odds ratio for death was 1.013 (95% CI: 1.007, 1.018) for each kilogram increase in body weight. The odds ratio for sustaining an injury with ISS > or = 9 was 1.008 (95% CI: 1.004, 1.011) for each kilogram increase in body weight. After adjustment for potentially confounding variables (age, gender, seatbelt use, seat position and vehicle curbweight), the significant relationship between occupant weight and mortality persisted. After adjustment, the relationship between occupant weight and ISS was present, although less marked. Similar trends were found when BMI was analyzed as the exposure. In conclusion, increased occupant body weight is associated with increased mortality in automobile crashes. This is probably due in part to increased co-morbid factors in the more overweight occupants. However, it is possibly also due to an increased severity of injury in these occupants. These findings may have implications for vehicle safety design, as well as for transport safety policy.
In this review methods to measure the content and distribution of body fat or adipose tissue in humans are examined. The review particularly emphasizes methods to characterize regional fat distribution and ectopic fat (fat contained within other tissues) including specific applications and implications of region-specific or tissue-specific fat content.
Recent novel applications of body composition methods, including in-vivo imaging modalities, magnetic resonance spectroscopy techniques, and direct measurement of extracted tissue have advanced our understanding of many health related issues including obesity, type 2 diabetes mellitus, progressive muscle weakness in aging and lipodystrophy. In particular, the accumulation of lipid within muscle and liver has received increased attention because of its association with metabolic dysregulation or impaired muscle function.
Methods to quantify total body fat content in humans have provided considerable insight into obesity and related disorders, the aging process and its associated changes in function, and response to intervention. However, these methods have typically not been able to identify fat contained within specific regions of the body or within specific tissue. Direct quantification of fat distribution and fat within tissue in humans have been accomplished through in-vivo imaging techniques as well as invasive histological and biochemical approaches, and have advanced our understanding of many structure-function relationships. Further queries about human health and disease will undoubtedly lead to refinement of these methods and innovation of new body composition methodologies.
The automotive safety community is questioning the impact of obesity on the performance and assessment of occupant protection systems. This study investigates fatality and serious injury risks for front-seat occupants by body mass index (BMI) using a matched-pair analysis. It also develops a simple model for the change in injury risk with obesity.
A simple model was developed for the change in injury risk with obesity. It included the normal mass (m) and stiffness (k) of the body resisting compression during a blunt impact. Stiffness is assumed constant as weight is gained (Delta m). For a given impact severity, the risk of injury was assumed proportional to compression. Energy balance was used to determine injury risks with increasing mass. NASS-CDS field data were analyzed for calendar years 1993-2004. Occupant injury was divided into normal (18.5 kg/m2 < or = BMI < 25.0 kg/m2) and obese (BMI > o= 30 kg/m2) categories. A matched-pair analysis was carried out. Driver and front-right passenger fatalities or serious injuries (MAIS 3+) were analyzed in the same crash to determine the effect of obesity. This also allowed the determination of the relative risk of younger (age < or = 55 years), older (age >55 years), male, and female drivers that were obese compared to normal BMI. The family of Hybrid III crash test dummies was evaluated for BMI and the amount of ballast was determined so they could represent an obese or morbidly obese occupant.
Based on the simple model, the relative injury risk (r) for an increase in body mass is given by: r = (1 + Delta m / m)(0.5). For a given stature, an obese occupant (BMI = 30-35 kg/m2) has 54-61% higher risk of injury than a normal BMI occupant (22 kg/m2). Matched pairs showed that obese drivers have a 97% higher risk of fatality and 17% higher risk of serious injury (MAIS 3+) than normal BMI drivers. Obese passengers have a 32% higher fatality risk and a 40% higher MAIS 3+ risk than normal passengers. Obese female drivers have a 119% higher MAIS 3+ risk than normal BMI female drivers and young obese drivers have a 20% higher serious injury risk than young normal drivers. This range of increased risk is consistent but broader than predicted by the simple injury model. The smallest crash test dummies need proportionately more ballast to represent an obese or morbidly obese occupant in the evaluation of safety systems. The 5% female Hybrid III has a BMI = 20.4 kg/m2 and needs 22 kg of ballast to represent an obese and 44.8 kg to represent a morbidly obese female, while the 95% male needs only 1.7 and 36.5 kg, respectively.
Obesity influences the risk of serious and fatal injury in motor vehicle crashes. The effect is greatest on obese female drivers and young drivers. Since some of the risk difference is related to lower seatbelt wearing rates, the comfort and use of seatbelt extenders should be examined to improve wearing rates. Also, crash testing with ballasted dummies to represent obese and morbidly obese occupants may lead to refined safety systems for this growing segment of the population.