Margulies, Susan S

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Now showing 1 - 10 of 31
  • Publication
    Neurocritical Care Monitoring Correlates with Neuropathology in a Swine Model of Pediatric Traumatic Brain Injury
    (2011-11-01) Friess, Stuart H; Ralston, Jill; Eucker, Stephanie A; Helfaer, Mark A; Margulies, Susan S; Smith, Colin
    BACKGROUND—Small animal models have been used in traumatic brain injury (TBI) research to investigate the basic mechanisms and pathology of TBI. Unfortunately, successful TBI investigations in small animal models have not resulted in marked improvements in clinical outcomes of TBI patients. OBJECTIVE—To develop a clinically relevant immature large animal model of pediatric neurocritical care following TBI. METHODS—Eleven 4 week old piglets were randomized to either rapid axial head rotation without impact (N=6) or instrumented sham (N=5). All animals had an intracranial pressure monitor, brain tissue oxygen (PbtO2) probe, and cerebral microdialysis probe placed in the frontal lobe and data collected for 6 h following injury. RESULTS—Injured animals had sustained elevations in intracranial pressure and lactatepyruvate ratio (LPR), and decreased PbtO2 compared to sham. PbtO2 and LPR from separate frontal lobes had strong linear correlation in both sham and injured animals. Neuropathologic examination demonstrated significant axonal injury and infarct volumes in injured animals compared to sham at 6 hours post-injury. Averaged over time, PbtO2 in both injured and sham animals had a strong inverse correlation with total injury volume. Average LPR had a strong correlation with total injury volume. CONCLUSION—LPR and PbtO2 can be utilized as serial non-terminal secondary markers in our injury model for neuropathology, and as evaluation metrics for novel interventions and therapeutics in the acute post-injury period. This translational model bridges a vital gap in knowledge between TBI studies in small animal models and clinical trials in the pediatric TBI population.
  • Publication
    The Shaken Baby Syndrome: A Clinical, Pathological, and Biomechanical Study
    (1987-03-01) Duhaime, Ann-Christine; Gennarelli, Thomas A; Thibault, Lawrence E; Bruce, Derek A; Margulies, Susan S; Wiser, Randall
    Because a history of shaking is often lacking in the so-called “shaken baby syndrome,” diagnosis is usually based on a constellation of clinical and radiographic findings. Forty-eight cases of infants and young children with this diagnosis seen between 1978 and 1985 at the Children's Hospital of Philadelphia were reviewed. All patients had a presenting history thought to be suspicious for child abuse, and either retinal hemorrhages with subdural or subarachnoid hemorrhages or a computerized tomography scan showing subdural or subarachnoid hemorrhages with interhemispheric blood. The physical examination and presence of associated trauma were analyzed; autopsy findings for the 13 fatalities were reviewed. All fatal cases had signs of blunt impact to the head, although in more than half of them these findings were noted only at autopsy. All deaths were associated with uncontrollably increased intracranial pressure. Models of 1-month-old infants with various neck and skull parameters were instrumented with accelerometers and shaken and impacted against padded or unpadded surfaces. Angular accelerations for shakes were smaller than those for impacts by a factor of 50. All shakes fell below injury thresholds established for subhuman primates scaled for the same brain mass, while impacts spanned concussion, subdural hematoma, and diffuse axonal injury ranges. It was concluded that severe head injuries commonly diagnosed as shaking injuries require impact to occur and that shaking alone in an otherwise normal baby is unlikely to cause the shaken baby syndrome.
  • Publication
    Stretch Magnitude and Frequency-Dependent Actin Cytoskeleton Remodeling in Alveolar Epithelia
    (2010-07-01) DiPaolo, Brian Christopher; Lenormand,, Guillaume; Margulies, Susan S; Fredberg, Jeffrey J
    Alveolar epithelial cells (AEC) maintain integrity of the blood-gas barrier with gasket-like intercellular tight junctions (TJ) that are anchored internally to the actin cytoskeleton. We hypothesize that stretch rapidly reorganizes actin (<10 >min) into a perijunctional actin ring (PJAR) in a manner that is dependent on magnitude and frequency of the stretch, accompanied by spontaneous movement of actin-anchored receptors at the plasma membrane. Primary AEC monolayers were stretched biaxially to create a change in surface area (ΔSA) of 12%, 25%, or 37% in a cyclic manner at 0.25 Hz for up to 60 min, or held tonic at 25% ΔSA for up to 60 min, or left unstretched. By 10 min of stretch PJARs were evident in 25% and 37% ΔSA at 0.25 Hz, but not for 12% ΔSA at 0.25 Hz, or at tonic 25% ΔSA, or with no stretch. Treatment with 1 μM jasplakinolide abolished stretch-induced PJAR formation, however. As a rough index of remodeling rate, we measured spontaneous motions of 5-μm microbeads bound to actin focal adhesion complexes on the apical membrane surfaces; within 1 min of exposure to ΔSA of 25% and 37%, these motions increased substantially, increased with increasing stretch frequency, and were consistent with our mechanistic hypothesis. With a tonic stretch, however, the spontaneous motion of microbeads attenuated back to unstretched levels, whereas PJAR remained unchanged. Stretch did not increase spontaneous microbead motion in human alveolar epithelial adenocarcinoma A549 monolayers, confirming that this actin remodeling response to stretch was a cell-type specific response. In summary, stretch of primary rat AEC monolayers forms PJARs and rapidly reorganized actin binding sites at the plasma membrane in a manner dependent on stretch magnitude and frequency.
  • Publication
    Uses of Remnant Human Lung Tissue for Mechanical Stretch Studies
    (2012-12-11) Davidovich, Nurit; Chhour, Peter; Margulies, Susan S
    Human lung tissue donated for research purposes is a precious resource which can enhance the exploration of mechanisms involved in ventilator-induced lung injury (VILI). The goal of this work was to establish methods and demonstrate the feasibility of obtaining viable primary human type I-like alveolar epithelial cells (AECs) from remnant tissue, even after a significant lapse in post-mortem time, as well as human precision-cut lung slices (PCLSs), and stretch them at magnitudes correlated with mechanical ventilation volumes. Although after 3 days in culture many of the isolated cells stained for the type II AEC marker pro-surfactant Protein C (pro-SPC), after 6 days in culture the monolayer stained only weakly and non-specifically for pro-SPC, and stained brightly for the type I AEC marker aquaporin-5. A strong zona-occludin 1 stain demonstrated the formation of tight junctions between the cells in the epithelial monolayer after only 3 days in culture. To demonstrate the utility of the preparations for the study of lung injury, we stretched the cells and the PCLSs cyclically, uniformly, and equibiaxially and quantified their viability. Our data show that the described methods allow the utilization of human tissue in in vitro stretch studies investigating VILI.
  • Publication
    Maturation-Dependent Response of the Piglet Brain to Scaled Cortical Impact
    (2000-09-01) Duhaime, Ann-Christine; Margulies, Susan S; Durham, Susan R; O'Rourke, Maureen M; Golden, Jeffrey A; Marwaha, Sunil; Raghupathi, Ramesh
    Object. The goal of this study was to investigate the relationship between maturational stage and the brain's response to mechanical trauma in a gyrencephalic model of focal brain injury. Age-dependent differences in injury response might explain certain unique clinical syndromes seen in infants and young children and would determine whether specific therapies might be particularly effective or even counterproductive at different ages. Methods. To deliver proportionally identical injury inputs to animals of different ages, the authors have developed a piglet model of focal contusion injury by using specific volumes of rapid cortical displacement that are precisely scaled to changes in size and dimensions of the growing brain. Using this model, the histological response to a scaled focal cortical impact was compared at 7 days after injury in piglets that were 5 days, 1 month, and 4 months of age at the time of trauma. Despite comparable injury inputs and stable physiological parameters, the percentage of hemisphere injured differed significantly among ages, with the youngest animals sustaining the smallest lesions (0.8%, 8.4%, and 21.5%, for 5-day-, 1-month-, and 4-month-old animals, respectively, p = 0.0018). Conclusions. These results demonstrate that, for this particular focal injury type and severity, vulnerability to mechanical trauma increases progressively during maturation. Because of its developmental and morphological similarity to the human brain, the piglet brain provides distinct advantages in modeling age-specific responses to mechanical trauma. Differences in pathways leading to cell death or repair may be relevant to designing therapies appropriate for patients of different ages.
  • Publication
    Biomechanics of the Toddler Head During Low-height Falls: An Anthropomorphic Dummy Analysis Laboratory Investigation
    (2010-07-01) Ibrahim, Nicole G; Margulies, Susan S
    OBJECT Falls are the most common environmental setting for closed head injuries in children between 2 and 4 years of age. The authors previously found that toddlers had fewer skull fractures and scalp/facial soft-tissue injuries, and more frequent altered mental status than infants for the same low-height falls (≤3 ft). METHODS To identify potential age-dependent mechanical load factors that may be responsible for these clinical findings, the authors created an instrumented dummy representing an 18-month-old child using published toddler anthropometry and mechanical properties of the skull and neck, and they measured peak angular acceleration during low-height falls (1, 2, and 3 ft) onto carpet pad and concrete. They compared these results from occiput-first impacts to previously obtained values measured in a 6-week-old infant dummy. RESULTS Peak angular acceleration of the toddler dummy head was largest in the sagittal and horizontal directions and increased significantly (around 2-fold) with fall height between 1 and 2 ft. Impacts onto concrete produced larger peak angular accelerations and smaller impact durations than those onto carpet pad. When compared with previously measured infant drops, toddler head accelerations were more than double those of the infant from the same height onto the same surface, likely contributing to the higher incidence of loss of consciousness reported in toddlers. Furthermore, the toddler impact forces were larger than those in the infant, but because of the thicker toddler skull, the risk of skull fracture from low-height falls is likely lower in toddlers compared with infants. CONCLUSIONS If similar fracture limits and brain tissue injury thresholds between infants and toddlers are assumed, it is expected that for impact events, the toddler is likely less vulnerable to skull fracture but more vulnerable to neurological impairment compared with the infant.
  • Publication
    Persistently Altered Brain Mitochondrial Bioenergetics After Apparently Successful Resuscitation From Cardiac Arrest
    (2015-09-14) Kilbaugh, Todd; Sutton, Robert M; Karlsson, Michael; Hansson, Magnus J; Nadkarni, Vinay; Naim, Maryam Y; Becker, Lance; Morgan, Ryan W; Margulies, Susan S; Bratinov, George; Lampe, Joshua Willard; Berg, Robert A
    Background Although advances in cardiopulmonary resuscitation have improved survival from cardiac arrest (CA), neurologic injury persists and impaired mitochondrial bioenergetics may be critical for targeted neuroresuscitation. The authors sought to determine if excellent cardiopulmonary resuscitation and postresuscitation care and good traditional survival rates result in persistently disordered cerebral mitochondrial bioenergetics in a porcine pediatric model of asphyxia‐associated ventricular fibrillation CA. Methods and Results After 7 minutes of asphyxia, followed by ventricular fibrillation, 5 female 1‐month‐old swine (4 sham) received blood pressure–targeted care: titration of compression depth to systolic blood pressure of 90 mm Hg and vasopressor administration to a coronary perfusion pressure >20 mm Hg. All animals received protocol‐based vasopressor support after return of spontaneous circulation for 4 hours before they were killed. The primary outcome was integrated mitochondrial electron transport system (ETS) function. CA animals displayed significantly decreased maximal, coupled oxidative phosphorylating respiration (OXPHOSCI+CII) in cortex (PPPPCI PCII PCIPCII PCI+CII), as well as a 30% reduction in citrate synthase activity (P<0.04). Conclusions Mitochondria in both the cortex and hippocampus displayed significant alterations in respiratory function after CA despite excellent cardiopulmonary resuscitation and postresuscitation care in asphyxia‐associated ventricular fibrillation CA. Analysis of integrated ETS function identifies mitochondrial bioenergetic failure as a target for goal‐directed neuroresuscitation after CA. IACUC Protocol: IAC 13‐001023.
  • Publication
    Rho Kinase Signaling Pathways During Stretch in Primary Alveolar Epithelia
    (2012-05-15) DiPaolo, Brian Christopher; Margulies, Susan S
    Alveolar epithelial cells (AECs) maintain integrity of the blood-gas barrier with actin-anchored intercellular tight junctions. Stretched type I-like AECs undergo magnitude- and frequency-dependent actin cytoskeletal remodeling into perijunctional actin rings. On the basis of published studies in human pulmonary artery endothelial cells (HPAECs), we hypothesize that RhoA activity, Rho kinase (ROCK) activity, and phosphorylation of myosin light chain II (MLC2) increase in stretched type I-like AECs in a manner that is dependent on stretch magnitude, and that RhoA, ROCK, or MLC2 activity inhibition will attenuate stretch-induced actin remodeling and preserve barrier properties. Primary type I-like AEC monolayers were stretched biaxially to create a change in surface area (ΔSA) of 12%, 25%, or 37% in a cyclic manner at 0.25 Hz for up to 60 min or left unstretched. Type I-like AECs were also treated with Rho pathway inhibitors (ML-7, Y-27632, or blebbistatin) and stained for F-actin or treated with the myosin phosphatase inhibitor calyculin-A and quantified for monolayer permeability. Counter to our hypothesis, ROCK activity and MLC2 phosphorylation decreased in type I-like AECs stretched to 25% and 37% ΔSA and did not change in monolayers stretched to 12% ΔSA. Furthermore, RhoA activity decreased in type I-like AECs stretched to 37% ΔSA. In contrast, MLC2 phosphorylation in HPAECs increased when HPAECs were stretched to 12% ΔSA but then decreased when they were stretched to 37% ΔSA, similar to type I-like AECs. Perijunctional actin rings were observed in unstretched type I-like AECs treated with the Rho pathway inhibitor blebbistatin. Myosin phosphatase inhibition increased MLC2 phosphorylation in stretched type I-like AECs but had no effect on monolayer permeability. In summary, stretch alters RhoA activity, ROCK activity, and MLC2 phosphorylation in a manner dependent on stretch magnitude and cell type.
  • Publication
    Stretch Increases Alveolar Epithelial Permeability to Uncharged Micromolecules
    (2006-04-01) Cavanaugh, Kenneth Joseph; Cohen, Taylor Sitarik; Margulies, Susan S
    We measured stretch-induced changes in transepithelial permeability in vitro to uncharged tracers 1.5–5.5 Å in radius to identify a critical stretch threshold associated with failure of the alveolar epithelial transport barrier. Cultured alveolar epithelial cells were subjected to a uniform cyclic (0.25 Hz) biaxial 12, 25, or 37% change in surface area (ΔSA) for 1 h. Additional cells served as unstretched controls. Only 37% ΔSA (100% total lung capacity) produced a significant increase in transepithelial tracer permeability, with the largest increases for bigger tracers. Using the permeability data, we modeled the epithelial permeability in each group as a population of small pores punctuated by occasional large pores. After 37% ΔSA, increases in paracellular transport were correlated with increases in the radii of both pore populations. Inhibition of protein kinase C and tyrosine kinase activity during stretch did not affect the permeability of stretched cells. In contrast, chelating intracellular calcium and/or stabilizing F-actin during 37% ΔSA stretch reduced but did not eliminate the stretch-induced increase in paracellular permeability. These results provide the first in vitro evidence that large magnitudes of stretch increase paracellular transport of micromolecules across the alveolar epithelium, partially mediated by intracellular signaling pathways. Our monolayer data are supported by whole lung permeability results, which also show an increase in alveolar permeability at high inflation volumes (20 ml/kg) at the same rate for both healthy and septic lungs.
  • Publication
    Anthropomorphic Simulations of Falls, Shakes, and Inflicted Impacts in Infants
    (2003-07-01) Coats, Brittany; Prange, Michael Thomas; Margulies, Susan S; Duhaime, Ann-Christine
    Object: Rotational loading conditions have been shown to produce subdural hemorrhage and diffuse axonal injury. No experimental data are available with which to compare the rotational response of the head of an infant during accidental and inflicted head injuries. The authors sought to compare rotational deceleration sustained by the head among free falls, from different heights onto different surfaces, with those sustained during shaking and inflicted impact. Methods: An anthropomorphic surrogate of a 1.5-month-old human infant was constructed and used to simulate falls from 0.3 m (1 ft), 0.9 m (3 ft), and 1.5 m (5 ft), as well as vigorous shaking and inflicted head impact. During falls, the surrogate experienced occipital contact against a concrete surface, carpet pad, or foam mattress. For shakes, investigators repeatedly shook the surrogate in an anteroposterior plane; inflicted impact was defined as the terminal portion of a vigorous shake, in which the surrogate’s occiput made contact with a rigid or padded surface. Rotational velocity was recorded directly and the maximum (peak–peak) change in angular velocity ( max) and the peak angular acceleration ( max) were calculated. Analysis of variance revealed significant increases in the max and max associated with falls onto harder surfaces and from higher heights. During inflicted impacts against rigid surfaces, the max and max were significantly greater than those measured under all other conditions. Conclusions: Vigorous shakes of this infant model produced rotational responses similar to those resulting from minor falls, but inflicted impacts produced responses that were significantly higher than even a 1.5-m fall onto concrete. Because larger accelerations are associated with an increasing likelihood of injury, the findings indicate that inflicted impacts against hard surfaces are more likely to be associated with inertial brain injuries than falls from a height less than 1.5 m or from shaking.