Prognostic Risk Factors for the Development of Compartment Syndrome in Acute Lower Limb Ischemia Patients Treated With Catheter-Directed Thrombolysis.

BACKGROUND: To determine predisposing factors that may lead to the development of compartment syndrome (CS) in patients with acute lower limb ischemia (ALLI) managed with intra-arterial catheter-directed thrombolysis (CDT). METHODS: This is a retrospective study of patients admitted between 01/2002 and 12/2015 to three university hospitals in Tampere, Turku, and Oulu, Finland, with acute or acute-on-chronic lower limb ischemia (Rutherford I-IIb). Patients managed with CDT and aspiration thrombectomies (AT) as an adjunct to CDT were included in the study. Multivariable binary logistic regression models were used to detect possible risk factors for the development of CS and its impact on the limb salvage and survival. Amputation-free survival (AFS) rates of CS and non-CS patients were compared using Kaplan-Meier survival analysis. The length of hospitalization was calculated and compared between the CS and non-CS groups. RESULTS: A total of 292 CDTs with or without ATs were performed on patients with a mean age of 71 years (standard deviation 13 years), 151 (51.7%) being male. Altogether, 12/292 (4.1%) treatment-related CS cases were registered. Renal insufficiency (odds ratio [OR] 4.27, P = 0.07) was associated with an increased risk of CS. All CS cases were managed with fasciotomies. Treatment with fasciotomy was associated with a prolonged hospitalization of a median of 7 days versus the 4 days for non-CS patients, P < 0.001. During the median follow-up of 51 months (interquartile range 72 months), 152/292 (52.1%) patients died and 51/292 (17.5%) underwent major amputations. CS was not associated with an increased risk of mortality, but it was associated with a higher risk of major amputation (OR 3.87, P = 0.027). The AFS rates of patients with or without CS did not significantly differ from each other in the long term. CONCLUSIONS: CS after CDT for the treatment of ALLI is uncommon. Renal insufficiency is associated with an increased risk of CS. Fasciotomy prolongs the hospitalization. Patients with CS are exposed to an increased risk of major amputation.

Continuous improvement of safety in the Intensive Care and Surgical environment according to UNE 179003:2013 standard: 8 years experience. / Mejora continua de la seguridad en el ámbito de un Servicio de Anestesiología y Cuidados Intensivos a través de la certificación según la norma de UNE 179003:2013: 8 años de experiencia.

INTRODUCTION: The UNE 179003:2013 standard requires compliance with protocols to reduce the risks of patients from adverse events. METHODS: A description is presented of the procedure used in the Hospital Povisa to achieve UNE 179003:2010 certification for the intensive care unit, surgical division, and post-anaesthesia recovery unit (PARU). This was based on a risk management system, focusing on pro-active analysis using failure modes and effects analysis (FMEA) with the description of causes, consequences, risk weighting, and specific risk-minimising measures. A description is also presented of the analysis of reported adverse events (reactive analysis) in the Safety in Anesthesia and Resuscitation (SENSAR) notification system and the measures implemented over an eight-year period. RESULTS: The UNE 179003:2010 certification was obtained in July 2012, and the re-certification was achieved in July 2015. A total of 66 potential risks were established, which were weighted using a risk probability index (RPI), and measures were implemented that reduced this RPI by half. It also reflects the analysis of 1114 events declared in the SENSAR system over the past eight years, allowing for the introduction of 2681 measures, of which 98.4% are fully implemented. CONCLUSION: The application of the risk management methodology allowed (a) to improve safety in the area of action by reducing the risk to which the patients are subject, and (b) to gain certification in the UNE 179003 standard.

Diffusion Monte Carlo simulations of gas phase and adsorbed D2-(H2)n clusters.

We have computed ground state energies and analyzed radial distributions for several gas phase and adsorbed D2(H2)n and HD(H2)n clusters. An external model potential designed to mimic ionic adsorption sites inside porous materials is used [M. Mella and E. Curotto, J. Phys. Chem. A 121, 5005 (2017)]. The isotopic substitution lowers the ground state energies by the expected amount based on the mass differences when these are compared with the energies of the pure clusters in the gas phase. A similar impact is found for adsorbed aggregates. The dissociation energy of D2 from the adsorbed clusters is always much higher than that of H2 from both pure and doped aggregates. Radial distributions of D2 and H2 are compared for both the gas phase and adsorbed species. For the gas phase clusters, two types of hydrogen-hydrogen interactions are considered: one based on the assumption that rotations and translations are adiabatically decoupled and the other based on nonisotropic four-dimensional potential. In the gas phase clusters of sufficiently large size, we find the heavier isotopomer more likely to be near the center of mass. However, there is a considerable overlap among the radial distributions of the two species. For the adsorbed clusters, we invariably find the heavy isotope located closer to the attractive interaction source than H2, and at the periphery of the aggregate, H2 molecules being substantially excluded from the interaction with the source. This finding rationalizes the dissociation energy results. For D2-(H2)n clusters with n≥12, such preference leads to the desorption of D2 from the aggregate, a phenomenon driven by the minimization of the total energy that can be obtained by reducing the confinement of (H2)12. The same happens for (H2)13, indicating that such an effect may be quite general and impact on the absorption of quantum species inside porous materials.

"Leaching or not leaching": an alternative approach to antimicrobial materials via copolymers containing crown ethers as active groups.

In this work, new copolymers containing either MMA and 18C6 crown-ether pendants, or PEG, MMA and 18C6 crown-ether pendants were synthesized to test the idea that sequestering structural alkali-earth ions from the bacterial outer membrane (OM) may lead to bacterial death. The copolymers were obtained either via uncontrolled radical polymerization or ATRP; the latter approached allowed us to produce not only linear copolymers but also branched Y-like structures. After checking for the capability of complexing magnesium and calcium ions, the antimicrobial activity of all copolymers was tested placing their casted plaques in contact with pure water E. coli suspensions. All plaques adsorbed alkali-earth ions and killed bacteria, albeit with different antimicrobial efficiencies. Differences in the latter characteristic were attributed to different plaque roughness. The role of the 18C6 crown-ether pendants was elucidated by pre-saturating plaques with Mg/Ca ions, the marked reduction in antimicrobial efficiency indicating that losing the latter from OM due to surface complexation does play an important role in killing bacteria at short (<5 h) contact times. At longer times, the mode of action is instead related to the poly-cationic nature acquired by the plaques due to ion sequestering.

Are the intertidal fish highly resistant to UV-B radiation? A study based on oxidative stress in Girella laevifrons (Kyphosidae).

Sea chub, Girella laevifrons, is a coastal fish that inhabits high intertidal rockpools along the coast of Chile. The intertidal pools where the juveniles live, are an extreme environment with high levels of ultraviolet (UV) radiation, becoming harmful to the organisms, due to oxidative stress generated by reactive oxygen species. For this reason organisms develop adaptations that allow them to survive in this complex environment. The search of biomonitor species, sensitive to UV radiation is very important in aquatic ecosystems, mainly in the southern hemisphere where depletion of the ozone layer and the consequent increase of UV radiation, have become an environmental problem. The aim of this study was to evaluate the effect of ultraviolet radiation in G. laevifrons and its possible use as UV-B radiation biomonitor specie in intertidal systems, which are very important for the Chilean fisheries. The effect of UV radiation exposure on juvenile G. laevifrons was measured through oxidative stress parameters. Catalase's activity increased with the time of exposure, unlike superoxide dismutase's activity which peaked at 2h, decreasing towards the 5th hour of irradiation. The superoxide dismutase activity in muscle tissue did not show significant differences. The lipid peroxidation and DNA damage increased in relation to exposition times. Tissue muscle's DNA damage was shown only at 5h of exposure. Significant differences between the two organs in the antioxidant capacity were observed, the liver of G. laevifrons exhibited the higher antioxidant capacity. It can be concluded that this specie exhibits effective protection mechanisms against UV radiation exposure and it is not appropriate specie as a biomonitor in intertidal systems.

[Antimicrobial susceptibility, capsular serotypes and clonal relationship of invasive streptococcus pneumoniae isolates in adult population of the Bio-Bio region, Chile. 2005-2006]. / Susceptibilidad antimicrobiana, serotipos capsulares y relación clonal entre cepas invasoras de streptococcus pneumoniae aisladas de pacientes adultos de la Región del Bío-Bío, Chile. Periodo 2005-2006.

Streptococcus pneumoniae infections constitute a public health problem. In our country there is scarce information regarding isolates from bacteraemic episodes in adult population. The antibiotic susceptibility, serotypes and clonal relationship of 56 isolates of S. pneumoniae from adult patients with bacteraemic infections in Concepcion-Talcahuano, Bio-Bio Region, Chile, were studied. Resistance to tetracycline (21.4%), trimethoprim/ sulfamethoxazole (18%), erythromycin (18%), chloramphenicol (7%) and 1 penicillin resistant isolate from a meningeal focus (2%) was found. Also, all the isolates were susceptible to cefotaxime, levofloxacin, moxifloxacin and vancomycin. A wide variety of capsular serotypes was demonstrated, with predominance of serotypes 1, 5, 23F, 7F and 3. The macrorestriction analysis by pulse field electrophoresis revealed 31 electrophoretic patterns and 12 clonal groups, discarding a predominant clone. According to the results, at least, 80% of the S. pneumoniae serotypes isolated from bacteraemic adult patients are included in the available commercial vaccine.

Susceptibilidad antimicrobiana, serotipos capsulares y relación clonal entre cepas invasoras de Streptococcus pneumoniae aisladas de pacientes adultos de la Región del Bío-Bío, Chile: Período 2005-2006 / Antimicrobial susceptibility, capsular serotypes and clonal relationship of invasive Streptococcus pneumoniae isolates in adult population of the Bio-Bio Region, Chile: 2005-2006

Las infecciones ocasionadas por Streptococcus pneumoniae constituyen un problema de salud pública. En nuestro país existe escasa información sobre aislados de procesos bacteriémicos en población adulta. Se estudió la susceptibilidad, serotipos y relación clonal de 56 aislados de S. pneumoniae desde hemocultivos, entre enero 2005 y agosto 2006, de pacientes adultos de la intercomuna Concepción-Talcahuano, Región del Bío-Bío, Chile. Se encontró resistencia a tetraciclina (21,4 por ciento), cotrimoxazol (18 por ciento), eritromicina (18 por ciento), cloranfenicol (7 por ciento) y a penicilina en un solo aislado procedente de un foco meníngeo (2 por ciento). La totalidad mostró susceptibilidad a cefotaxima, levofloxacina, moxifloxacina y vancomicina. Se demostró una amplia variedad de serotipos capsulares, con predominio de los serotipos 1, 5, 23F, 7F y 3. El análisis de macrorestricción y electroforesis en campo pulsado reveló 31 patrones electroforéticos con 12 grupos clona-les, descartando un clon predominante. De acuerdo a los resultados, al menos 80 por ciento de los serotipos de aislados de S. pneumoniae de procesos bacteriémicos están incluidos en la vacuna comercial disponible.

Streptococcus pneumoniae infections constitute a public health problem. In our country there is scarce information regarding isolates from bacteraemic episodes in adult population. The antibiotic susceptibility, sero-types and clonal relationship of 56 isolates of S. pneumoniae from adult patients with bacteraemic infections in Concepcion-Talcahuano, Bio-Bio Region, Chile, were studied. Resistance to tetracycline (21.4 percent), trimethoprim/ sulfamethoxazole (18 percent), erythromycin (18 percent), chloramphenicol (7 percent) and 1 penicillin resistant isolate from a meningeal focus (2 percent) was found. Also, all the isolates were susceptible to cefotaxime, levofloxacin, moxifloxacin and vancomycin. A wide variety of capsular serotypes was demonstrated, with predominance of serotypes 1, 5, 23F, 7F and 3. The macrorestriction analysis by pulse field electrophoresis revealed 31 electrophoretic patterns and 12 clonal groups, discarding a predominant clone. According to the results, at least, 80 percent of the S. pneumoniae serotypes isolated from bacteraemic adult patients are included in the available commercial vaccine.

Bombas de expulsión multidrogas en Acinetobacter baumannii y resistencia a antimicrobianos / Multi-drug efflux pumps and antibiotic resistance in Acinetobacter baumannii

Los sistemas multidrogas bacterianos contribuyen al desarrollo del fenotipo de multi-resistencia presentado por cepas de Acinetobacter baumannü, patógeno intrahospi-talario, que durante los últimos años ha incrementado su importancia por la creciente resistencia a carbapenémicos. El fenotipo de multi-resistencia está otorgado por la combinación de varios mecanismos de resistencia entre los cuales se encuentran estos sistemas de bombas de expulsión. El sistema multidroga AdeABC se ha detectado en muchas de estas cepas multi-resistentes de A. baumannü y, se ha relacionado con resistencia a diversos grupos de antimicrobianos, incluidos tigeciclina y meropenem. La inhibición de dichos sistemas multidrogas permitiría aumentar la eficacia de la terapia antimicrobiana. La siguiente revisión se enfoca en las bombas de expulsión multidrogas presentes en A. baumannü, con particular énfasis en el sistema AdeABC.

Bacterial multi-drugs systems contribute to the development of multi-resistance patterns of Acinetobacter baumannii, a nosocomial pathogen of increasing importance due to its emerging resistance to carbapenems. The multi-resistance phenomena is generated by a combination of mechanisms, one of which the efflux pump system. Many of these multiresistant isolates of A. baumannii harbor genes for the AdeABC multi-drug efflux system, related with resistance to various groups of antibacterial agents, including tygecicline and meropenem. Inhibition of these systems would allow to increase the efficacy of this antimicrobial. This review focuses on the multi-drug efflux pump system oí A. baumanni with special emphasis in the AdeABC system.

Hermansky Pudlak syndrome: an unusual form of procto-colitis

Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder consisting of oculocutaneous albinism, platelet dysfunction and systemic complications associated with lipofuscin deposition in the reticuloendothelial system. HPS has been associated with a granulomatous enterocolitis with pathologic features suggestive of Crohn's disease. It remains uncertain if HPS represents a truly distinct form of granulomatous enterocolitis. We report a series of two patients with HPS treated in Puerto Rico, and the results from medical and surgical intervention for gastrointestinal disease. Our experience with HPS patients has shown the difficult management of perineal disease similar in the management of Crohn's. However, complications from the bleeding diathesis necessitate caution during surgery and potential anesthesia complications. Furthermore, avoidance of a perineal wound is preferred, and when possible, ileostomies have fewer complications than colostomies as they do not involve the small bowel.

Puerto Rico experience with plugs in the treatment of anal fistulas

BACKGROUND: Anorectal fistula is a common problem that affects quality of life. Main objective of therapy has been to eradicate the fistula tract while preserving fecal continence. Latest good results for anal fistula treatment have been an anal fistula plug. This study was undertaken to determine if these results could be reproduced in Puerto Rico. METHOD: From January 2003 to January 2008, two experienced colorectal surgeons performed this new operation in 23 consecutive patients. A multivariable analysis was undertaken including age, sex, location of the fistula, previous surgeries, Seton placement before the insertion of the plug, continence pre and post operation, as well as close follow up. No patient with inflammatory bowel disease was included. RESULTS: We had a good result or healing of the fistula in 14 of 23 patients for a success rate of 60%. We had a subgroup of patients who did slightly better and had a healing rate of 66% compared to the 60% of the whole group. It appears to be a trend in favor of the Seton group but is not statically significant. We had 9 failures of 23 patients or 39%. Suppuration was noticed in three patients and all three had failures of the plug with recurrences. CONCLUSIONS: This new operation is another alternative to add to our armamentarium but we need to search for an operation that decreases the incidence of recurrences we had in our study while maintaining function of the sphincters.

[Mutations in gyrA and gyrB genes among strains of Gram-negative bacilli isolated from Chilean hospitals and their relation with resistance to fluoroquinolones]. / Mutaciones en genes gyrA y gyrB en cepas de bacilos Gram negativos aisladas en hospitales chilenos y su relación con la resistencia a fluoroquinolonas.

BACKGROUND: A progressive frequency of resistance to fluoroquinolones is observed among Gram-negative bacilli. AIM: To investigate the mechanism of resistance to fluoroquinolones mediated by mutations affecting gyrA and gyrB genes in strains of Gram negative bacüli isolated from CMean hospitals. MATERIAL AND METHOD: Minimal inhibitory concentration of fluoroquinolones was determined in 91 randomly selected nalidixic acid-resistant strains of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa, isolated from hospitals of 12 Chilean cities. Quinolone resistance determining region (QRDR) was amplified by PCR and mutations were determined by restriction fragment length polymorphism (RFLP) and DNA sequencing. RESULTS: Strains with mutation in codon 83 of gyrA showed decreased susceptibility to ciprofloxacin with MICs ranging from 0.25 to 1024 fig/ml. The sequencing of PCR products for gyrA indicated amino acid changes in the QRDR region. One strain ofE. coli presented a double mutation, in codon 83 Ser to Leu as well as in codon 87 Asp to Asn. In strains ofK. pneumoniae, however, the change of codon 83 was Ser to Tyr, in A. baumannii was Ser to Leu and in P. aeruginosa was Thr to He. No strains with mutations affecting gyrB were found. CONCLUSIONS: Mutations in codon 83 of gyrA is a frequent genetic event involved in the mechanism leading to decreased susceptibility to fluoroquinolone in strains of Gram-negative bacilli.

Mutaciones en genes gyrA y gyrB en cepas de bacilos Gram negativos aisladas en hospitales chilenos y su relación con la resistencia a fluoroquinolonas / Mutations in gyrA and gyrB genes among strains of Gram-negative bacilli isolated from Chilean hospitals and their relation with resistance to fluoroquinolones

Background: A progressive frequency of resistance to fluorquinolones is observed among Gram-negative bacilli. Aim: To investigate the mechanism of resistance to fluoroquinolones mediated by mutations affecting gyrA and gyrB genes in strains of Gram negative bacüli isolated from CMean hospitals. Material and method: Minimal inhibitory concentration of fluoroquinolones was determined in 91 randomly selected nalidixic acid-resistant strains of Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa, isolated from hospitals of 12 Chilean cities. Quinolone resistance determining region (QRDR) was amplified by PCR and mutations were determined by restriction fragment length polymorphism (RFLP) and DNA sequencing. Results: Strains with mutation in codon 83 of gyrA showed decreased susceptibility to ciprofloxacin with MICs ranging from 0.25 to 1024 fig/ml. The sequencing of PCR products for gyrA indicated amino acid changes in the QRDR region. One strain ofE. coli presented a double mutation, in codon 83 Ser to Leu as well as in codon 87 Asp to Asn. In strains ofK. pneumoniae, however, the change of codon 83 was Ser to Tyr, in A. baumannii was Ser to Leu and in P. aeruginosa was Thr to He. No strains with mutations affecting gyrB were found. Conclusions: Mutations in codon 83 of gyrA is a frequent genetic event involved in the mechanism leading to decreased susceptibility to fluoroquinolone in strains of Gram-negative bacilli.

[Impact of infectious diseases specialist evaluation on the rational use of antibiotics in patients with Streptococcus pneumoniae bacteremia]. / Impacto de la evaluación infectológica en el uso racional de antimicrobianos en pacientes con bacteriemia por Streptococcus pneumoniae.

The increasing reporting of Streptococcus pneumoniae resistance to penicillin has lead to the recommendation of third generation cephalospirins for the treatment of serious pneumococcal infections. As a consequence, clinicians usually do not prescribe first line antibiotics despiste the availability of susceptibility studies. Whit the aim to evaluate the impact of the infectious diseases specialist evaluation in the apropriate use oh the susceptibility studies, two series were compared: a historic control one (1998-2002, n = 50) and a prospectuve group that had the advisement of one infectious diseases specialist (2003-2006, n = 60). In both series, pneumonia stood out as the source of the bacteremia, and -alcoholism/hepatic insufficiency as associated factor. In the first series, 48 isolates resulted susceptible to penicillin by agar diffusion, and 1 out of 36 patients with pneumonia had a change in the antibiotic therapy to penicillin. In the prospective series, we found 56 susceptible isolates, and the remaining four were classified as intermediate susceptibility according to the MIC value. Antibiotics were changed in 36 out of 50 patients with bacteremic pneumococcal pneumonia (p < 0.05). The infectious diseases specialist evaluation had a positive impact on the use of the microbiological information for therapeutics purposes.

Impacto de la evaluación infectológica en el uso racional de antimicrobianos en pacientes con bacteriemia por Streptococcus pneumoniae / Impact of infectious diseases specialist evaluation on the rational use of antibiotics in patients with Streptococcus pneumoniae bacteremia

The increasing reporting of Streptococcus pneumoniae resistance to penicillin has lead to the recommendation of third generation cephalospirins for the treatment of serious pneumococcal infections. As a consequence, clinicians usually do not prescribe first line antibiotics despiste the availability of susceptibility studies. Whit the aim to evaluate the impact of the infectious diseases specialist evaluation in the apropriate use oh the susceptibility studies, two series were compared: a historic control one (1998-2002, n = 50) and a prospectuve group that had the advisement of one infectious diseases specialist (2003-2006, n = 60). In both series, pneumonia stood out as the source of the bacteremia, and -alcoholism/hepatic insufficiency as associated factor. In the first series, 48 isolates resulted susceptible to penicillin by agar diffusion, and 1 out of 36 patients with pneumonia had a change in the antibiotic therapy to penicillin. In the prospective series, we found 56 susceptible isolates, and the remaining four were classified as intermediate susceptibility according to the MIC value. Antibiotics were changed in 36 out of 50 patients with bacteremic pneumococcal pneumonia (p < 0.05). The infectious diseases specialist evaluation had a positive impact on the use of the microbiological information for therapeutics purposes.

La descripción creciente de Streptococcus pneu-moniae resistente a penicilina, ha llevado a la recomendación de emplear cefalosporinas de tercera generación para el tratamiento de las infecciones neumo-cócicas graves. Como consecuencia, los médicos clínicos no prescriben, usualmente, antimicrobianos de primera línea, a pesar de disponer de estudios de susceptibilidad in vitro. Con el propósito de evaluar el impacto de la asesoría del infectólogo para el uso adecuado de los estudios de susceptibilidad, se compararon dos series: un control histórico (1998-2002, n = 50) y un grupo prospectivo en que sí hubo asesoría infectológica (2003-2006, n = 60). En ambas series, la neumonía fue el foco principal de bacteriemia y alcoholismo/falla hepática los factores asociados más frecuentes. En el primer grupo, 48 aislados resultaron susceptibles a penicilina por prueba de difusión en agar y en uno de 36 pacientes con neumonía, se efectuó cambio en la terapia antimicrobiana a bencilpeni-cilina. En el grupo prospectivo, hubo 56 cepas susceptibles y las cuatro restantes fueron clasificadas como de susceptibilidad intermedia, de acuerdo con los valores de CIM. Se cambió de antimicrobiano en 36 de 50 pacientes con neumonía neumocóccica bacteriémica (p < 0,05). La evaluación hecha por el infectólogo tuvo un impacto positivo en el uso de información micro-biológica con fines terapéuticos.

Enhancement of viability of muscle precursor cells on 3D scaffold in a perfusion bioreactor.

The aim of this study was to develop a methodology for the in vitro expansion of skeletal-muscle precursor cells (SMPC) in a three-dimensional (3D) environment in order to fabricate a cellularized artificial graft characterized by high density of viable cells and uniform cell distribution over the entire 3D domain. Cell seeding and culture within 3D porous scaffolds by conventional static techniques can lead to a uniform cell distribution only on the scaffold surface, whereas dynamic culture systems have the potential of allowing a uniform growth of SMPCs within the entire scaffold structure. In this work, we designed and developed a perfusion bioreactor able to ensure long-term culture conditions and uniform flow of medium through 3D collagen sponges. A mathematical model to assist the design of the experimental setup and of the operative conditions was developed. The effects of dynamic vs static culture in terms of cell viability and spatial distribution within 3D collagen scaffolds were evaluated at 1, 4 and 7 days and for different flow rates of 1, 2, 3.5 and 4.5 ml/min using C2C12 muscle cell line and SMPCs derived from satellite cells. C2C12 cells, after 7 days of culture in our bioreactor, perfused applying a 3.5 ml/min flow rate, showed a higher viability resulting in a three-fold increase when compared with the same parameter evaluated for cultures kept under static conditions. In addition, dynamic culture resulted in a more uniform 3D cell distribution. The 3.5 ml/min flow rate in the bioreactor was also applied to satellite cell-derived SMPCs cultured on 3D collagen scaffolds. The dynamic culture conditions improved cell viability leading to higher cell density and uniform distribution throughout the entire 3D collagen sponge for both C2C12 and satellite cells.