William A. Woods

Survival Risk Assessment for Primary Blast Exposures to the Head

Many soldiers returning from the current conflicts in Iraq and Afghanistan have had at least one exposure to an explosive event and a significant number have symptoms consistent with traumatic brain injury. Although blast injury risk functions have been determined and validated for pulmonary injury, there is little information on the blast levels necessary to cause blast brain injury. Anesthetized male New Zealand White rabbits were exposed to varying levels of shock tube blast exposure focused on the head, while their thoraces were protected. The specimens were euthanized and evaluated when the blast resulted in respiratory arrest that was non-responsive to resuscitation or at 4?h post-exposure. Injury was evaluated by gross examination and histological evaluation. The fatality data from brain injury were then analyzed using Fishers exact test to determine a brain fatality risk function. Greater blast intensity was associated with post-blast apnea and the need for mechanical ventilation. Gross examination revealed multifocal subdural hemorrhages, most often near the brainstem, at more intense levels of exposure. Histological evaluation revealed subdural and subarachnoid hemorrhages in the non-responsive respiratory-arrested specimens. A fatality risk function from blast exposure to the head was determined for the rabbit specimens with an LD(50) at a peak overpressure of 750?kPa. Scaling techniques were used to predict injury risk at other blast overpressure/duration combinations. The fatality risk function showed that the blast level needed to cause fatality from an overpressure wave exposure to the head was greater than the peak overpressure needed to cause fatality from pulmonary injury. This risk function can be used to guide future research for blast brain injury by providing a realistic fatality risk to guide the design of protection or to evaluate injury.

Comparison of Viral Load in Individuals with and without Asthma during Infections with Rhinovirus

RATIONALE Most virus-induced attacks of asthma are caused by rhinoviruses (RVs). OBJECTIVES To determine whether people with asthma are susceptible to an increased viral load during RV infection. METHODS Seventy-four children (4-18 yr old) were enrolled; 28 with wheezing, 32 with acute rhinitis, and 14 without respiratory tract symptoms. Nasal washes were evaluated using quantitative polymerase chain reaction for RV to judge viral load along with gene sequencing to identify strains of RV. Soluble intercellular adhesion molecule-1, IFN-λ1, and eosinophil cationic protein in nasal washes, along with blood eosinophil counts and total and allergen-specific IgE in sera, were also evaluated. Similar assessments were done in 24 young adults (16 with asthma, 8 without) who participated in an experimental challenge with RV (serotype 16). MEASUREMENTS AND MAIN RESULTS Fifty-seven percent of wheezing children and 56% with acute rhinitis had nasal washes testing positive for RV. The geometric mean of viral loads by quantitative polymerase chain reaction in washes from wheezing children was 2.8-fold lower, but did not differ significantly from children with rhinitis (7,718 and 21,612 copies of viral RNA per microliter nasal wash, respectively; P = 0.48). The odds for wheezing were increased if children who tested positive for RV were sensitized to one or more allergens (odds ratio, 3.9; P = 0.02). Similarly, neither peak nor cumulative viral loads differed significantly in washes from adults with asthma compared with those without asthma during the experimental RV challenge. CONCLUSIONS During acute symptoms, children infected with RV enrolled for wheezing or acute rhinitis had similar viral loads in their nasal washes, as did adults with and without asthma infected with RV-16 experimentally.

Brain Injury Risk from Primary Blast

BACKGROUND Military service members are often exposed to at least one explosive event, and many blast-exposed veterans present with symptoms of traumatic brain injury. However, there is little information on the intensity and duration of blast necessary to cause brain injury. METHODS Varying intensity shock tube blasts were focused on the head of anesthetized ferrets, whose thorax and abdomen were protected. Injury evaluations included physiologic consequences, gross necropsy, and histologic diagnosis. The resulting apnea, meningeal bleeding, and fatality were analyzed using logistic regressions to determine injury risk functions. RESULTS Increasing severity of blast exposure demonstrated increasing apnea immediately after the blast. Gross necropsy revealed hemorrhages, frequently near the brain stem, at the highest blast intensities. Apnea, bleeding, and fatality risk functions from blast exposure to the head were determined for peak overpressure and positive-phase duration. The 50% risk of apnea and moderate hemorrhage were similar, whereas the 50% risk of mild hemorrhage was independent of duration and required lower overpressures (144 kPa). Another fatality risk function was determined with existing data for scaled positive-phase durations from 1 millisecond to 20 milliseconds. CONCLUSION The first primary blast brain injury risk assessments for mild and moderate/severe injuries in a gyrencephalic animal model were determined. The blast level needed to cause a mild/moderate brain injury may be similar to or less than that needed for pulmonary injury. The risk functions can be used in future research for blast brain injury by providing realistic injury risks to guide the design of protection or evaluate injury. (J Trauma Acute Care Surg. 2012;73: 895–901. Copyright

MUSCLE TETANUS AND LOADING CONDITION EFFECTS ON THE ELASTIC AND VISCOUS CHARACTERISTICS OF THE THORAX

Thoracic deformation under an applied load is an established indicator of injury risk, but the force required to achieve an injurious level of deformation currently is not understood adequately. This article evaluates how two potentially important factors, loading condition and muscle tensing, affect the structural response of the dynamically loaded thorax. Structural models of two human cadaver thoraxes and two porcine thoraxes were used to quantify the effects. The human cadavers, which represent anthropometric extremes, were subjected to anterior loading from (1) a 5.1-cm-wide belt oriented diagonally (i.e., seatbelt-like loading), (2) a 15.2-cm-diameter rigid hub, and (3) a 20.3-cm-wide belt oriented laterally (i.e., a distributed load). A structural model having the mathematical formulation of a quasilinear viscoelastic material model was used to model the elastic and viscous response, with ramp-hold tests used to determine the model coefficients. The effect of thoracic musculature was assessed using similar ramp-hold tests on the porcine subjects, each with and without forced muscle contraction. Even maximally contracted thoracic musculature is shown to have a minimal effect on the response, with similar elastic and viscous characteristics exhibited by each subject regardless of muscle tone. The elastic response is shown to be approximately a factor of three stiffer for diagonal belt loading and for this distributed loading condition than for the hub loading, indicating that the response is influenced most by the particular anatomical structures that are engaged and, secondarily, by the area of load application. Specifically, shoulder involvement is shown to have a strong influence. The force relaxation is found to be pronounced, but insensitive to the loading condition, with long-time force relaxation coefficients (G∞) in the range of 0.1 to 0.3. The findings of this study provide restraint-specific guidelines for the force-deflection characteristics of both physical and computational thoracic models.

The Role of Muscle Tensing on the Force-Deflection Response of the Thorax and a Reassessment of Frontal Impact Thoracic Biofidelity Corridors

Abstract This paper evaluates how muscle tensing changes the structural response of the dynamically loaded thorax. Nine porcine thoraces with both ventral (supine) and dorsal (prone) loading were used to quantify the effect. Muscle tensing was assessed using repeated tests on a subject with and without forced muscle contraction. Dynamic (53.9 ± 2.9 cm/s) and quasistatic tests were performed with a potentiometer and load cells to calculate effective thoracic stiffness. The results show that the effect of muscle tensing decreases with increasing chest deflection, a fact which is supported by the limited human data available. The peak force increases with muscle tensing for chest deflection levels up to about 20 per cent, after which the peak force changes negligibly when the muscles are tensed. The shape of the force-deflection curve and therefore the work done by the deforming thorax do, however, depend upon muscle tensing regardless of the peak deflection level attained. A simplified finite element model is used to elucidate the mechanisms for the experimental findings. This model shows that the changes in force-deflection response of the thorax that occur with muscle tensing are due primarily to the increased modulus of the muscle tissue itself, rather than to any stiffening effect from pretensioning the muscle membrane around the bony structure. The findings are discussed relative to current thoracic biofidelity corridors, which include an adjustment to account for muscle tensing.

Flexion-extension cervical spine radiography in pediatric blunt trauma

Ligamentous cervical injury may not be apparent when viewed with static cervical spine radiography (CSR). Dynamic (flexion-extension) views of the cervical spine may aid in the identification of such injury. A retrospective descriptive study was carried out between July 1, 1990, and June 30, 1994, in an academic emergency department averaging 60,000 patient visits (of which 20% are pediatric) per year. The subjects were pediatric blunt trauma patients, 0–18 years of age. CSR was performed in the static (lateral, anteroposterior, odontoid) and dynamic (flexion and extension) views.One hundred thirty-seven patients (53% male; mean age, 12.9 years) met entry criteria. Mechanisms of injury included motor vehicle accident (57 patients, 43%), fall from a height (56 patients, 42%), and direct trauma (20 patients, 15%). Indications for CSR included a traumatic mechanism, the complaint of neck pain, and posterior midline neck tenderness on examination in all cases; abnormal static CSR was also an indication in 40 cases (30%). Results of static CSRs were normal in 93 patients (70%), all of whom had a normal dynamic CSR. Static CSRs were abnormal in 40 patients (30%), of whom 33 had a normal dynamic CSR. The 7 patients (5%) with an abnormal dynamic CSR had disruption of the lines of cervical contour (6), and/or reversal of lordotic curve (2) noted on the static CSR. No patient required invasive spine surgery, and all were discharged with a satisfactory neurologic outcome after hospital admission. No complications of dynamic CSR use occurred. Among patients who are alert and communicative, dynamic CSR is safe and assists in the evaluation of pediatric blunt neck trauma when patients present with pain, midline tenderness, and abnormal static CSR.

The transient relationship between pressure and volume in the pediatric pulmonary system

An accurate understanding of the relationship between pulmonary pressure and volume is required for modeling pulmonary mechanics in a variety of clinical applications. In this study the experimental techniques and mathematical formulations used to characterize viscoelastic materials are applied to characterize transient pulmonary compliance in juvenile swine. Fixed volumes of air were insufflated into 5 swine and held constant for 45 s while the transient decay in tracheal pressure was measured. An analytical model was developed using an optimization scheme that maximized the model fit to the experimental data over the entire time convolution. The initial injected volume was varied to assess the spatial and temporal linearity of the behavior. Model performance was assessed by comparing measured and predicted pressure during insufflations of erratic volume waveforms. It is concluded that the pulmonary impedance of healthy juveniles can be adequately described over a wide volume and frequency range using a relatively simple 5-parameter model that is linear both spatially and temporally.

Pediatric Resuscitation and Cardiac Arrest

Cardiac arrest in children is, fortunately, a relatively infrequent event. Mortality rate after cardiac arrest is greater than 50%. This article discusses strategies to increase the chance of survival to discharge. These strategies focus on suggestions for organizing a system prepared to care for critically ill children, incorporating the 2010 American Heart Association resuscitation guidelines into clinical practice, and encouraging physicians to become advocates of decreasing the occurrence of pediatric cardiac arrest. Providing the best-prepared system available to care for critically ill children will, it is hoped, decrease the number of preventable deaths in children.

Care of children who have had surgery for congenital heart disease

Children who have had surgical correction for congenital heart disease can present to the ED with an acute illness that could be associated with their cardiac lesion. There is no data available to summarize complications that could be associated with surgically corrected congenital heart disease. This work was undertaken to describe the common procedures used, list known complications of these procedures, and review general management principles in caring for the acutely ill child who has had heart surgery.

Care of the acutely ill pediatric heart transplant recipient.

Young children may present to the emergency department after undergoing orthotopic heart transplantation. Emergency department care of pediatric heart transplant recipients with an acute illness is not clearly defined. To assist the emergency physician with treating these children, 2 cases are detailed to demonstrate the variation in outcome of young children presenting to the emergency department with acute illness months after their transplant. The cases typify the varied outcomes possible after emergency department presentation. After the cases, a review of the medical conditions common in transplant recipients precedes a description of management suggestions.