Thomas Seacrist

Chest Compression Quality Over Time in Pediatric Resuscitations

BACKGROUND: Chest compression (CC) quality deteriorates with time in adults, possibly because of rescuer fatigue. Little data exist on compression quality in children or on work done to perform compressions in general. We hypothesized that compression quality, work, and rescuer fatigue would differ in child versus adult manikin models. METHODS: This was a prospective randomized crossover study of 45 in-hospital rescuers performing 10 minutes of single-rescuer continuous compressions on each manikin. An accelerometer recorded compression quality measures over 30-second epochs. Work and power were calculated from recorded force data. A modified visual analogue scale measured fatigue. Data were analyzed by using linear mixed-effects models and Cox regression analysis. RESULTS: A total of 88 484 compression cycles were analyzed. Percent adequate CCs/epoch (rate ≥ 100/minute, depth ≥ 38 mm) fell over 10 minutes (child: from 85.1% to 24.6%, adult: from 86.3% to 35.3%; P = .15) and were <70% in both by 2 minutes. Peak work per compression cycle was 13.1 J in the child and 14.3 J in the adult (P = .06; difference, 1.2 J; 95% confidence interval, −0.05 to 2.5). Peak power output was 144.1 W in the child and 166.5 W in the adult (P < .001; difference, 22.4 W, 95% confidence interval, 9.8–35.0). CONCLUSIONS: CC quality deteriorates similarly in child and adult manikin models. Peak work per compression cycle is comparable in both. Peak power output is analogous to that generated during intense exercise such as running. CC providers should switch every 2 minutes as recommended by current guidelines.

Kinetics of the cervical spine in pediatric and adult volunteers during low speed frontal impacts

Previous research has quantified differences in head and spinal kinematics between children and adults restrained in an automotive-like configuration subjected to low speed dynamic loading. The forces and moments that the cervical spine imposes on the head contribute directly to these age-based kinematic variations. To provide further explanation of the kinematic results, this study compared the upper neck kinetics - including the relative contribution of shear and tension as well as flexion moment - between children (n=20, 6-14 yr) and adults (n=10, 18-30 yr) during low-speed (<4 g, 2.5 m/s) frontal sled tests. The subjects were restrained by a lap and shoulder belt and photo-reflective targets were attached to skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3D infrared tracking system quantified the position of the targets. Shear force (F(x)), axial force (F(z)), bending moment (M(y)), and head angular acceleration (θ(head)) were computed using inverse dynamics. The method was validated against ATD measured loads. Peak F(z) and θ(head) significantly decreased with increasing age while M(y) significantly increased with increasing age. F(x) significantly increased with age when age was considered as a univariate variable; however when variations in head-to-neck girth ratio and change in velocity were accounted for, this difference as a function of age was not significant. These results provide insight into the relationship between age-based differences in head kinematics and the kinetics of the cervical spine. Such information is valuable for pediatric cervical spine models and when scaling adult-based upper cervical spine tolerance and injury metrics to children.

Passive cervical spine flexion: The effect of age and gender

BACKGROUND Previous studies reported passive cervical range of motion under unknown loading conditions or with minimal detail of subject positioning. Additionally, such studies have not quantitatively ensured the absence of active muscle during passive measurements. For the purpose of validating biomechanical models the loading condition, initial position, and muscle activation must be clearly defined. A method is needed to quantify the passive range of motion properties of the cervical spine under controlled loading conditions, particularly in the pediatric population where normative clinical and model validation data is limited. METHODS Healthy female pediatric (6-12years; n=10), male pediatric (6-12years; n=9), female adult (21-40years; n=10), and male adult (20-36years; n=9) volunteers were enrolled. Subjects with restrained torsos and lower extremities were exposed to a maximum 1g inertial load in the posterior-anterior direction, such that the head-neck complex flexed when subjects relaxed their neck musculature. Surface electromyography monitored the level of muscle relaxation. A multi-camera 3-D target tracking system captured passive neck flexion angle of the head relative to the thoracic spine. General estimating equations detected statistical differences across age and gender. FINDINGS Passive cervical spine flexion equaled 111.0° (SD 8.0°) for pediatric females, 102.8° (SD 7.8°) for adult females, 103.8° (SD 12.7°) for pediatric males, and 93.7° (SD 9.9°) for adult males. Passive neck flexion significantly decreased with age in both genders (P<0.01). Females exhibited significantly greater flexion than males (P<0.01). INTERPRETATION This study contributes normative data for clinical use, biomechanical modeling, and injury prevention tool development.

Pediatric Head and Neck Dynamics in Frontal Impact: Analysis of Important Mechanical Factors and Proposed Neck Performance Corridors for 6- and 10-Year-Old ATDs

Objective: Traumatic injuries are the leading cause of death of children aged 1–19 in the United States and are principally caused by motor vehicle collisions, with the head being the primary region injured. The neck, though not commonly injured, governs head kinematics and thus influences head injury. Vehicle improvements necessary to reduce these injuries are evaluated using anthropomorphic testing devices (ATDs). Current pediatric ATD head and neck properties were established by scaling adult properties using the size differences between adults and children. Due to the limitations of pediatric biomechanical research, computational models are the only available methods that combine all existing data to produce injury-relevant biofidelity specifications for ATDs. The purpose of this study is to provide the first frontal impact biofidelity corridors for neck flexion response of 6- and 10-year-olds using validated computational models, which are compared to the Hybrid III (HIII) ATD neck responses and the Mertz flexion corridors. Methods: Our virtual 6- and 10-year-old head and neck multibody models incorporate pediatric biomechanical properties obtained from pediatric cadaveric and radiological studies, include the effect of passive and active musculature, and are validated with data including pediatric volunteer 3 g dynamic frontal impact responses. We simulate ATD pendulum tests—used to calibrate HIII neck bending stiffness—to compare the pediatric model and HIII ATD neck bending stiffness and to compare the model flexion bending responses with the Mertz scaled neck flexion corridors. Additionally, pediatric response corridors for pendulum calibration tests and high-speed (15 g) frontal impacts are estimated through uncertainty analyses on primary model variables, with response corridors calculated from the average ± SD response over 650 simulations. Results and Conclusions: The models are less stiff in dynamic anterioposterior bending than the ATDs; the secant stiffness of the 6- and 10-year-old models is 53 and 67 percent less than that of the HIII ATDs. The ATDs exhibit nonlinear stiffening and the models demonstrate nonlinear softening. Consequently, the models do not remain within the Mertz scaled flexion bending corridors. The more compliant model necks suggest an increased potential for head impact via larger head excursions. The pediatric anterioposterior bending corridors developed in this study are extensible to any frontal loading condition through calculation and sensitivity analysis. The corridors presented in this study are the first based on pediatric cadaveric data and provide the basis for future, more biofidelic, designs of 6- and 10-year-old ATD necks.

Evaluation of pediatric ATD biofidelity as compared to child volunteers in low-speed far-side oblique and lateral impacts.

Objective: Motor vehicle crashes are a leading cause of injury and mortality for children. Mitigation of these injuries requires biofidelic anthropomorphic test devices (ATDs) to design and evaluate automotive safety systems. Effective countermeasures exist for frontal and near-side impacts but are limited for far-side impacts. Consequently, far-side impacts represent increased injury and mortality rates compared to frontal impacts. Thus, the objective of this study was to evaluate the biofidelity of the Hybrid III and Q-series pediatric ATDs in low-speed far-side impacts, with and without shoulder belt pretightening. Methods: Low-speed (2 g) far-side oblique (60°) and lateral (90°) sled tests were conducted using the Hybrid III and Q-series 6- and 10-year-old ATDs. ATDs were restrained by a lap and shoulder belt equipped with a precrash belt pretightener. Photoreflective targets were attached to the head, spine, shoulders, and sternum. ATDs were exposed to 8 low-speed sled tests: 2 oblique nontightened, 2 oblique pretightened, 2 lateral nontightened, 2 lateral pretightened. ATDs were compared with previously collected 9- to 11-year-old (n = 10) volunteer data and newly collected 6- to 8-year-old volunteer data (n = 7) tested with similar methods. Kinematic data were collected from a 3D target tracking system. Metrics of comparison included excursion, seat belt and seat pan reaction loads, belt-to-torso angle, and shoulder belt slip-out. Results: The ATDs exhibited increased lateral excursion of the head top, C4, and T1 as well as increased downward excursion of the head top compared to the volunteers. Volunteers exhibited greater forward excursion than the ATDs in oblique nontightened impacts. These kinematics correspond to increased shoulder belt slip-out for the ATDs in oblique tests (ATDs = 90%; volunteers = 36%). Contrarily, similar shoulder belt slip-out was observed between ATDs and volunteers in lateral impacts (ATDs = 80%; volunteers = 78%). In pretightened impacts, the ATDs exhibited reduced lateral excursion and torso roll-out angle compared to the volunteers. Conclusions: In general, the ATDs overestimated lateral excursion in both impact directions, while underestimating forward excursion of the head and neck in oblique impacts compared to the pediatric volunteers. This was primarily due to pendulum-like lateral bending of the entire ATD torso compared to translation of the thorax relative to the abdomen prior to the lateral bending of the upper torso in the volunteers, likely due to the multisegmented spinal column in the volunteers. Additionally, the effect of belt pretightening on occupant kinematics was greater for the ATDs than the volunteers.

Electromyography responses of pediatric and young adult volunteers in low-speed frontal impacts

No electromyography (EMG) responses data exist of children exposed to dynamic impacts similar to automotive crashes, thereby, limiting active musculature representation in computational occupant biomechanics models. This study measured the surface EMG responses of three neck, one torso and one lower extremity muscles during low-speed frontal impact sled tests (average maximum acceleration: 3.8g; rise time: 58.2ms) performed on seated, restrained pediatric (n=11, 8-14years) and young adult (n=9, 18-30years) male subjects. The timing and magnitude of the EMG responses were compared between the two age groups. Two normalization techniques were separately implemented and evaluated: maximum voluntary EMG (MVE) and neck cross-sectional area (CSA). The MVE-normalized EMG data indicated a positive correlation with age in the rectus femoris for EMG latency; there was no correlation with age for peak EMG amplitudes for the evaluated muscles. The cervical paraspinous exhibited shorter latencies compared with the other muscles (2-143ms). Overall, the erector spinae and rectus femoris peak amplitudes were relatively small. Neck CSA-normalized peak EMG amplitudes negatively correlated with age for the cervical paraspinous and sternocleidomastoid. These data can be useful to incorporate active musculature in computational models, though it may not need to be age-specific in low-speed loading environments.

Simulated Driving Assessment (SDA) for teen drivers: results from a validation study

Background Driver error and inadequate skill are common critical reasons for novice teen driver crashes, yet few validated, standardised assessments of teen driving skills exist. The purpose of this study is to evaluate the construct and criterion validity of a newly developed Simulated Driving Assessment (SDA) for novice teen drivers. Methods The SDA’s 35 min simulated drive incorporates 22 variations of the most common teen driver crash configurations. Driving performance was compared for 21 inexperienced teens (age 16–17 years, provisional license ≤90 days) and 17 experienced adults (age 25–50 years, license ≥5 years, drove ≥100 miles per week, no collisions or moving violations ≤3 years). SDA driving performance (Error Score) was based on driving safety measures derived from simulator and eye-tracking data. Negative driving outcomes included simulated collisions or run-off-the-road incidents. A professional driving evaluator/instructor (DEI Score) reviewed videos of SDA performance. Results The SDA demonstrated construct validity: (1) teens had a higher Error Score than adults (30 vs 13, p=0.02); (2) For each additional error committed, the RR of a participants propensity for a simulated negative driving outcome increased by 8% (95% CI 1.05 to 1.10, p<0.01). The SDA-demonstrated criterion validity: Error Score was correlated with DEI Score (r=−0.66, p<0.001). Conclusions This study supports the concept of validated simulated driving tests like the SDA to assess novice driver skill in complex and hazardous driving scenarios. The SDA, as a standard protocol to evaluate teen driver performance, has the potential to facilitate screening and assessment of teen driving readiness and could be used to guide targeted skill training.

Evaluation of the Hybrid III and Q-Series Pediatric ATD Upper Neck Loads as Compared to Pediatric Volunteers in Low-Speed Frontal Crashes

Debate exists in the automotive community regarding the validity of the pediatric ATD neck response and corresponding neck loads. Previous research has shown that the pediatric ATDs exhibit hyper-flexion and chin-to-chest contact resulting in overestimations of neck loads and neck injury criteria. Our previous work comparing the kinematics of the Hybrid III and Q-series 6 and 10-year-old ATDs to pediatric volunteers in low-speed frontal sled tests revealed decreased ATD cervical and thoracic spine excursions. These kinematic differences may contribute to the overestimation of upper neck loads by the ATD. The current study compared upper neck loads of the Hybrid III and Q-series 6 and 10-year-old ATDs against size-matched male pediatric volunteers in low-speed frontal sled tests. A 3-D near-infrared target tracking system quantified the position of markers on the ATD and pediatric volunteers (head top, nasion, bilateral external auditory meatus). Shear force (Fx), axial force (Fz), bending moment (My), and head angular acceleration (

The Six Degrees of Freedom Motion of the Human Head, Spine, and Pelvis in a Frontal Impact

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