argon

Summary

Summary: A noble gas with the atomic symbol Ar, atomic number 18, and atomic weight 39.948. It is used in fluorescent tubes and wherever an inert atmosphere is desired and nitrogen cannot be used.

Top Publications

  1. Galliero G, Boned C, Fernández J. Scaling of the viscosity of the Lennard-Jones chain fluid model, argon, and some normal alkanes. J Chem Phys. 2011;134:064505 pubmed publisher
    ..fluid, the flexible Lennard-Jones chain fluid (from the monomer to the hexadecamer), then to real fluids, such as argon and normal alkanes...
  2. Dot C, Parier V, Behar Cohen F, BenEzra D, Jonet L, Goldenberg B, et al. Influence of age on retinochoroidal healing processes after argon photocoagulation in C57bl/6j mice. Mol Vis. 2009;15:670-84 pubmed
    To analyze the influence of age on retinochoroidal wound healing processes and on glial growth factor and cytokine mRNA expression profiles observed after argon laser photocoagulation.
  3. Herrera S, Bordas J, Llach J, Gines A, Pellise M, Fernandez Esparrach G, et al. The beneficial effects of argon plasma coagulation in the management of different types of gastric vascular ectasia lesions in patients admitted for GI hemorrhage. Gastrointest Endosc. 2008;68:440-6 pubmed publisher
    ..There is also little knowledge on the efficacy of argon plasma coagulation (APC) in different subgroups of GVE lesions.
  4. Hosseinzadeh Colagar A, Memariani H, Sohbatzadeh F, Valinataj Omran A. Nonthermal atmospheric argon plasma jet effects on Escherichia coli biomacromolecules. Appl Biochem Biotechnol. 2013;171:1617-29 pubmed publisher
    ..In this study, Escherichia coli cells and their macromolecules were exposed to the nonthermal atmospheric argon plasma jet for different time durations. Total protein, genomic DNA, and malondialdehyde (MDA) levels of E...
  5. Song S, Kim Y, I H, Cho J, Lee J. Videothoracoscopic parietal pleurectomy with argon pneumodissection. Ann Thorac Surg. 2010;90:e64-5 pubmed publisher
    Pleural dissection in pleurectomy under videothoracoscopy in patients with pneumothorax is easily and safely performed using argon gas.
  6. Nezhat C, Kho K, Morozov V. Use of neutral argon plasma in the laparoscopic treatment of endometriosis. JSLS. 2009;13:479-83 pubmed publisher
    To report the feasibility and safety of the use of a novel energy source that uses an electrically neutral beam of pure argon plasma for the laparoscopic management of endometriosis.
  7. Jawad N, Rizvi M, Gu J, Adeyi O, Tao G, Maze M, et al. Neuroprotection (and lack of neuroprotection) afforded by a series of noble gases in an in vitro model of neuronal injury. Neurosci Lett. 2009;460:232-6 pubmed publisher
    ..In this study, the neuroprotective properties of the other noble gases, namely, krypton, argon, neon and helium, were explored in an in vitro model of neuronal injury...
  8. Cummings J, Smith R, Heck R. Argon beam coagulation as adjuvant treatment after curettage of aneurysmal bone cysts: a preliminary study. Clin Orthop Relat Res. 2010;468:231-7 pubmed publisher
    ..Curettage, with or without adjuvant therapy, has been advocated for tumors in most locations. To evaluate argon beam coagulation as adjuvant therapy to curettage, we retrospectively analyzed the complication and recurrence ..
  9. Yang Y, Wang C, Lu Y, Bai W, An L, Qu J, et al. Outcomes of ultrasound-guided percutaneous argon-helium cryoablation of hepatocellular carcinoma. J Hepatobiliary Pancreat Sci. 2012;19:674-84 pubmed publisher
    To evaluate the efficacy and safety of ultrasound (US)-guided percutaneous argon-helium cryoablation for hepatocellular carcinoma (HCC) and determine appropriate indications.

Scientific Experts

More Information

Publications62

  1. Lee C, Lee S, Park J, Lee T, Chung I, Park S, et al. Prophylactic argon plasma coagulation ablation does not decrease delayed postpolypectomy bleeding. Gastrointest Endosc. 2009;70:353-61 pubmed publisher
    ..However, there are no established guidelines for the prevention of delayed PPB. It is possible that submucosal vessels of an artificial ulcer are a potential source of delayed bleeding that occurs several days after polypectomy...
  2. Fuccio L, Zagari R, Serrani M, Eusebi L, Grilli D, Cennamo V, et al. Endoscopic argon plasma coagulation for the treatment of gastric antral vascular ectasia-related bleeding in patients with liver cirrhosis. Digestion. 2009;79:143-50 pubmed publisher
    Gastric antral vascular ectasia (GAVE) is a cause of bleeding in patients with liver cirrhosis. Argon plasma coagulation (APC) is the most used endoscopic treatment for GAVE-related bleeding...
  3. Coelho P, Giro G, Teixeira H, Marin C, Witek L, Thompson V, et al. Argon-based atmospheric pressure plasma enhances early bone response to rough titanium surfaces. J Biomed Mater Res A. 2012;100:1901-6 pubmed publisher
    This study investigated the effect of an Argon-based atmospheric pressure plasma (APP) surface treatment operated chairside at atmospheric pressure conditions applied immediately prior to dental implant placement in a canine model...
  4. Manner H, Plum N, Pech O, Ell C, Enderle M. Colon explosion during argon plasma coagulation. Gastrointest Endosc. 2008;67:1123-7 pubmed publisher
  5. Rayatpisheh S, Li P, Chan Park M. Argon-plasma-induced ultrathin thermal grafting of thermoresponsive pNIPAm coating for contractile patterned human SMC sheet engineering. Macromol Biosci. 2012;12:937-45 pubmed publisher
    ..Given its simplicity and low cost, this thermoresponsive grafting method can be utilized for engineering patterned cell sheets for future bottom-up tissue engineering techniques...
  6. Formentini A, Schwarz A, Straeter J, Stanescu A, Henne Bruns D. Treatment of Barrett's esophagus with argon plasma coagulation and antireflux surgery. A retrospective analysis. Hepatogastroenterology. 2007;54:1991-6 pubmed
    The aim of this study was to assess the efficacy and the results of ablation of Barrett'esophagus by endoscopic argon plasma coagulation (APC) followed by fundoplication.
  7. Zhuang L, Yang T, Zhao H, Fidalgo A, Vizcaychipi M, Sanders R, et al. The protective profile of argon, helium, and xenon in a model of neonatal asphyxia in rats. Crit Care Med. 2012;40:1724-30 pubmed publisher
    Xenon provides neuroprotection in multiple animal models; however, little is known about the other noble gases. The aim of the current study was to compare xenon, argon, and helium neuroprotection in a neonatal asphyxia model in rats.
  8. Giro G, Tovar N, Witek L, Marin C, Silva N, Bonfante E, et al. Osseointegration assessment of chairside argon-based nonthermal plasma-treated Ca-P coated dental implants. J Biomed Mater Res A. 2013;101:98-103 pubmed publisher
    This study investigated the effect of an Argon-based nonthermal plasma (NTP) surface treatment-operated chairside at atmospheric pressure conditions applied immediately prior to dental implant placement in a canine model...
  9. Bich C, Havelund R, Moellers R, Touboul D, Kollmer F, Niehuis E, et al. Argon cluster ion source evaluation on lipid standards and rat brain tissue samples. Anal Chem. 2013;85:7745-52 pubmed publisher
    b>Argon cluster ion sources for sputtering and secondary ion mass spectrometry use projectiles consisting of several hundreds of atoms, accelerated to 10-20 keV, and deposit their kinetic energy within the top few nanometers of the surface...
  10. Koban I, Holtfreter B, Hübner N, Matthes R, Sietmann R, Kindel E, et al. Antimicrobial efficacy of non-thermal plasma in comparison to chlorhexidine against dental biofilms on titanium discs in vitro - proof of principle experiment. J Clin Periodontol. 2011;38:956-65 pubmed publisher
    ..In this study, we evaluated the effect of three different plasma devices on the reduction of Streptococcus mutans (S. mutans) and multispecies human saliva biofilms...
  11. Ryang Y, Fahlenkamp A, Rossaint R, Wesp D, Loetscher P, Beyer C, et al. Neuroprotective effects of argon in an in vivo model of transient middle cerebral artery occlusion in rats. Crit Care Med. 2011;39:1448-53 pubmed publisher
    The neuroprotective effects of the noble gas xenon are well known. Argon, in contrast to xenon, is abundant, inexpensive, and therefore widely applicable...
  12. Fischinger S, Schulze J. The argon-induced decline in nitrogenase activity commences before the beginning of a decline in nodule oxygen uptake. J Plant Physiol. 2010;167:1112-5 pubmed publisher
    Replacement of N(2) by argon in the air around nodules directs nitrogenase electron flow in its total onto H(+) resulting in increased nodule H(2) evolution (total nitrogenase activity (TNA))...
  13. García J, Asadinezhad A, Pachernik J, Lehocký M, Junkar I, Humpolícek P, et al. Cell proliferation of HaCaT keratinocytes on collagen films modified by argon plasma treatment. Molecules. 2010;15:2845-56 pubmed publisher
    b>Argon plasma treatment was used to modify the surface of atelocollagen films using a plasmochemical reactor...
  14. Isbary G, Morfill G, Schmidt H, Georgi M, Ramrath K, Heinlin J, et al. A first prospective randomized controlled trial to decrease bacterial load using cold atmospheric argon plasma on chronic wounds in patients. Br J Dermatol. 2010;163:78-82 pubmed publisher
    ..Objectives To examine the safety and efficiency of cold atmospheric argon plasma to decrease bacterial load as a new medical treatment for chronic wounds.
  15. Li M, Zhang S, Zhou Y, Guo Y, Jiang X, Miao L. Argon-helium cryosurgery for treatment of C6 gliomas in rats and its effect on cellular immunity. Technol Cancer Res Treat. 2010;9:87-94 pubmed
    b>Argon-helium cryosurgery has shown encouraging therapeutic effects on some solid tumors, but its application in the treatment of gliomas remains poorly documented...
  16. Wang C, Lu Y, Chen Y, Feng Y, An L, Wang X, et al. Prognostic factors and recurrence of hepatitis B-related hepatocellular carcinoma after argon-helium cryoablation: a prospective study. Clin Exp Metastasis. 2009;26:839-48 pubmed publisher
    To determine the long-term prognosis of hepatocellular carcinoma (HCC) after argon-helium cryoablation and identify the risk factors that predict metastasis and recurrence...
  17. García Alcantara E, López Callejas R, Morales Ramírez P, Peña Eguiluz R, Fajardo Muñoz R, Mercado Cabrera A, et al. Accelerated mice skin acute wound healing in vivo by combined treatment of argon and helium plasma needle. Arch Med Res. 2013;44:169-77 pubmed publisher
    ..In the development of the present study, an argon plasma needle was chosen for coagulation purposes, whereas for healing purposes, a helium plasma needle was used.
  18. Weng C, Wu Y, Liao J, Kao C, Chao C, Chang J, et al. Inactivation of bacteria by a mixed argon and oxygen micro-plasma as a function of exposure time. Int J Radiat Biol. 2009;85:362-8 pubmed publisher
    ..A radio-frequency dielectric barrier discharge (DBD) was applied as a micro-plasma device for the inactivation of bacteria, e.g., Escherichia coli...
  19. Teixeira H, Marin C, Witek L, Freitas A, Silva N, Lilin T, et al. Assessment of a chair-side argon-based non-thermal plasma treatment on the surface characteristics and integration of dental implants with textured surfaces. J Mech Behav Biomed Mater. 2012;9:45-9 pubmed publisher
    ..001). Result indicated that the NTP treatment increased the surface energy and the biomechanical fixation of textured-surface dental implants at early times in vivo...
  20. Ermolaeva S, Sysolyatina E, Kolkova N, Bortsov P, Tuhvatulin A, Vasiliev M, et al. Non-thermal argon plasma is bactericidal for the intracellular bacterial pathogen Chlamydia trachomatis. J Med Microbiol. 2012;61:793-9 pubmed publisher
    Non-thermal plasma (NTP) is a flow of partially ionized argon gas at an ambient macroscopic temperature and is microbicidal for bacteria, viruses and fungi...
  21. Hirano T, Kazama Y, Ohbu S, Shirakawa Y, Liu Y, Kambara T, et al. Molecular nature of mutations induced by high-LET irradiation with argon and carbon ions in Arabidopsis thaliana. Mutat Res. 2012;735:19-31 pubmed publisher
    ..Therefore, the 290keV?m(-1) heavy-ion beams can effectively induce large deletions and will prove useful as novel mutagens for plant breeding and analysis of gene functions, particularly tandemly arrayed genes...
  22. Rabbani S, Barber A, Fletcher J, Lockyer N, Vickerman J. TOF-SIMS with argon gas cluster ion beams: a comparison with C60+. Anal Chem. 2011;83:3793-800 pubmed publisher
    ..It is therefore important to explore the potential of other candidates. A systematic study of the suitability of argon gas cluster ion beams (Ar-GCIBs) of general composition Ar(n)(+), where n = 60-3000, as primary particles in TOF-..
  23. Gagos M, Gruszecki W. Organization of polyene antibiotic amphotericin B at the argon-water interface. Biophys Chem. 2008;137:110-5 pubmed publisher
    ..Organization of AmB was studied in monocomponent monomolecular layers formed at the argon-water interface, by means of polarized and non-polarized electronic absorption spectroscopy and analyzed in terms ..
  24. Spaggiari S, Kepp O, Rello Varona S, Chaba K, Adjemian S, Pype J, et al. Antiapoptotic activity of argon and xenon. Cell Cycle. 2013;12:2636-42 pubmed publisher
    ..with gas combinations, including the same amount of oxygen (20%) and carbon dioxide (5%) but 75% helium, neon, argon, krypton, or xenon instead of nitrogen...
  25. David H, Haelewyn B, Degoulet M, Colomb D, Risso J, Abraini J. Ex vivo and in vivo neuroprotection induced by argon when given after an excitotoxic or ischemic insult. PLoS ONE. 2012;7:e30934 pubmed publisher
    In vitro studies have well established the neuroprotective action of the noble gas argon. However, only limited data from in vivo models are available, and particularly whether postexcitotoxic or postischemic argon can provide ..
  26. Pauzat F, Ellinger Y, Pilme J, Mousis O. H3(+) as a trap for noble gases-3: multiple trapping of neon, argon, and krypton in X(n)H3(+) (n = 1-3). J Chem Phys. 2009;130:174313 pubmed publisher
    ..X reaction energy, increases slightly with n varying from 1 to 3 in the neon series, while it decreases in the argon series and shows a minimum for n = 2 in the krypton series...
  27. David H, Haelewyn B, Risso J, Abraini J. Modulation by the noble gas argon of the catalytic and thrombolytic efficiency of tissue plasminogen activator. Naunyn Schmiedebergs Arch Pharmacol. 2013;386:91-5 pubmed publisher
    b>Argon has been shown to provide cortical as well as, under certain conditions, subcortical neuroprotection in all models so far (middle cerebral artery occlusion, trauma, neonatal asphyxia, etc.)...
  28. Brücken A, Cizen A, Fera C, Meinhardt A, Weis J, Nolte K, et al. Argon reduces neurohistopathological damage and preserves functional recovery after cardiac arrest in rats. Br J Anaesth. 2013;110 Suppl 1:i106-12 pubmed publisher
    ..However, xenon is very costly, which might preclude its widespread use. We hypothesized argon, which is more available, might also protect central nervous tissues and allow better functional recovery in a ..
  29. Muqit M, Wakely L, Stanga P, Henson D, Ghanchi F. Effects of conventional argon panretinal laser photocoagulation on retinal nerve fibre layer and driving visual fields in diabetic retinopathy. Eye (Lond). 2010;24:1136-42 pubmed publisher
    To determine the effects of argon green panretinal laser photocoagulation on retinal nerve fibre layer thickness, threshold visual fields, and Estermann full-binocular visual fields over time in diabetic retinopathy.
  30. Loetscher P, Rossaint J, Rossaint R, Weis J, Fries M, Fahlenkamp A, et al. Argon: neuroprotection in in vitro models of cerebral ischemia and traumatic brain injury. Crit Care. 2009;13:R206 pubmed publisher
    ..In this study we tested the hypothesis that the noble gas argon has a neuroprotective potential as well...
  31. Fahlenkamp A, Rossaint R, Haase H, Al Kassam H, Ryang Y, Beyer C, et al. The noble gas argon modifies extracellular signal-regulated kinase 1/2 signaling in neurons and glial cells. Eur J Pharmacol. 2012;674:104-11 pubmed publisher
    Recently, the noble gas argon has been identified as a potent neuroprotective agent, but little is known about its cellular effects...
  32. Ristagno G, Fumagalli F, Russo I, Tantillo S, Zani D, Locatelli V, et al. Postresuscitation treatment with argon improves early neurological recovery in a porcine model of cardiac arrest. Shock. 2014;41:72-8 pubmed publisher
    Effects of postresuscitation treatment with argon on neurologic recovery were investigated in a porcine model of cardiac arrest (CA) with an underlying acute myocardial infarction.
  33. Canullo L, Cassinelli C, Gotz W, Tarnow D. Plasma of argon accelerates murine fibroblast adhesion in early stages of titanium disk colonization. Int J Oral Maxillofac Implants. 2013;28:957-62 pubmed publisher
    This study was conducted to analyze how a cleaning treatment using plasma of argon would affect fibroblast growth on titanium disks at different time points to determine whether this treatment could enhance soft tissue healing around ..
  34. Harris K, Armstrong S, Campos Pires R, Kiru L, Franks N, Dickinson R. Neuroprotection against traumatic brain injury by xenon, but not argon, is mediated by inhibition at the N-methyl-D-aspartate receptor glycine site. Anesthesiology. 2013;119:1137-48 pubmed publisher
    ..The authors investigate the neuroprotective mechanisms of the inert gases such as xenon, argon, krypton, neon, and helium in an in vitro model of traumatic brain injury.
  35. Wang H, Hsu P, Lo G, Chen T, Cheng L, Chen W, et al. Comparison of hemostatic efficacy for argon plasma coagulation and distilled water injection in treating high-risk bleeding ulcers. J Clin Gastroenterol. 2009;43:941-5 pubmed publisher
    ..Many endoscopic devices have been demonstrated to be effective in the hemostasis of bleeding ulcers. However, the hemostatic efficacy of argon plasma coagulation (APC) has not been widely investigated.
  36. Hameed H, Kalim S, Khan Y. Closure of a nonhealing gastrocutanous fistula using argon plasma coagulation and endoscopic hemoclips. Can J Gastroenterol. 2009;23:217-9 pubmed
    ..The fistula was first managed conservatively, then was closed by argon plasma coagulation and hemoclip placement...
  37. Ikegami T, Shimada M, Imura S, Nakamura T, Kawahito S, Morine Y, et al. Argon gas embolism in the application of laparoscopic microwave coagulation therapy. J Hepatobiliary Pancreat Surg. 2009;16:394-8 pubmed publisher
    A major concern in the use of the argon beam coagulator system is the potential risk of argon gas embolism.
  38. Manner H. Argon plasma coagulation therapy. Curr Opin Gastroenterol. 2008;24:612-6 pubmed publisher
    To give a summary of recent advances in argon plasma coagulation (APC) therapy in gastroenterology.
  39. Clément Ziza M, Munnich A, Lyonnet S, Jaubert F, Besmond C. Stabilization of RNA during laser capture microdissection by performing experiments under argon atmosphere or using ethanol as a solvent in staining solutions. RNA. 2008;14:2698-704 pubmed publisher
    ..The first one consists of performing LCM under an argon atmosphere, thus preventing tissue rehydration; it is compliant with all existing microdissection protocols...
  40. Ermolaeva S, Varfolomeev A, Chernukha M, Yurov D, Vasiliev M, Kaminskaya A, et al. Bactericidal effects of non-thermal argon plasma in vitro, in biofilms and in the animal model of infected wounds. J Med Microbiol. 2011;60:75-83 pubmed publisher
    ..The purpose of this study was to test the individual susceptibility of pathogenic bacteria to non-thermal argon plasma and to measure the effectiveness of plasma treatments against bacteria in biofilms and on wound surfaces...
  41. Min S, Kim J, Lee S. Carbon dioxide and argon gas embolism during laparoscopic hepatic resection. Acta Anaesthesiol Scand. 2007;51:949-53 pubmed
    ..9 mmHg) associated with near cardiac arrest occurred concomitantly with hepatic vein laceration and the use of an argon beam coagulator system...
  42. Rabenstein T, May A, Michel J, Manner H, Pech O, Gossner L, et al. Argon plasma coagulation for flexible endoscopic Zenker's diverticulotomy. Endoscopy. 2007;39:141-5 pubmed
    ..This retrospective study reports the mid-term results of argon plasma coagulation (APC) for flexible endoscopic therapy of Zenker's diverticulum.
  43. Henry C, Dyer B, Wagner M, Judy M, Matthews J. Phototoxicity of argon laser irradiation on biofilms of Porphyromonas and Prevotella species. J Photochem Photobiol B. 1996;34:123-8 pubmed
    ..and other microorganisms were cultivated as biofilms on agar medium and examined for their susceptibility to argon laser irradiation (continuous mode; wavelengths, 488-514 nm; fluences, 20-200 J cm(-2))...
  44. Khan K, Schwarzenberg S, Sharp H, Weisdorf Schindele S. Argon plasma coagulation: Clinical experience in pediatric patients. Gastrointest Endosc. 2003;57:110-2 pubmed
    b>Argon plasma coagulation has potential advantages in pediatric endoscopy.
  45. Nomura Y. Argon laser irradiation of the semicircular canal in two patients with benign paroxysmal positional vertigo. J Laryngol Otol. 2002;116:723-5 pubmed
    ..b>Argon laser irradiation of the blue-lined posterior and lateral semicircular canals in one patient, and of only the ..
  46. Sun Z. [Photodynamic therapy of nasopharyngeal carcinoma by argon or dye laser--an analysis of 137 cases]. Zhonghua Zhong Liu Za Zhi. 1992;14:290-2 pubmed
    ..Forty-eight and 72 hours after iv administration of 3-5 mg/kg HpD, laser treatment with either argon or dye laser was given...
  47. Van Laethem J, Jagodzinski R, Peny M, Cremer M, Deviere J. Argon plasma coagulation in the treatment of Barrett's high-grade dysplasia and in situ adenocarcinoma. Endoscopy. 2001;33:257-61 pubmed
    ..b>Argon plasma coagulation (APC) appears to be effective in the eradication of nondysplastic Barrett's mucosa, but no ..
  48. Ghafar M, Johnson C, de la Taille A, Benson M, Bagiella E, Fatal M, et al. Salvage cryotherapy using an argon based system for locally recurrent prostate cancer after radiation therapy: the Columbia experience. J Urol. 2001;166:1333-7; discussion 1337-8 pubmed
    ..We report our experience with the safety and efficacy of salvage cryosurgery using the argon based CRYOCare system (Endocare, Inc, Irvine, California).
  49. Bergler W, Sadick H, Hammerschmitt N, Oulmi J, Hormann K. Long-term results of inferior turbinate reduction with argon plasma coagulation. Laryngoscope. 2001;111:1593-8 pubmed
    ..Current surgical methods have disadvantages (e.g., necessity of nasal packing, extended postoperative swelling, and high costs). Theoretical considerations render argon plasma coagulation (APC) a promising new therapeutic approach.
  50. Becker D, BRYANT FRIEDRICH A, Trzasko C, Sevilla M. Electron spin resonance study of DNA irradiated with an argon-ion beam: evidence for formation of sugar phosphate backbone radicals. Radiat Res. 2003;160:174-85 pubmed
    ..Hydrated DNA samples at 77 K were irradiated with argon-ion beams ((36)Ar or (40)Ar beam at energies between 60 and 100 MeV/nucleon)...
  51. Rifai N, Sfeir R, Rakza T, Alameh J, Besson R, Lequien P, et al. Successful management of severe chylothorax with argon plasma fulguration and fibrin glue in a premature infant. Eur J Pediatr Surg. 2003;13:324-6 pubmed
    ..The chylothorax was treated successfully by a combination of argon beam coagulation of the mediastinum and fibrin glue application...
  52. Rotondano G, Bianco M, Marmo R, Piscopo R, Cipolletta L. Long-term outcome of argon plasma coagulation therapy for bleeding caused by chronic radiation proctopathy. Dig Liver Dis. 2003;35:806-10 pubmed
    ..Radiation-induced proctopathy is a serious complication of radiation therapy for pelvic malignancy...
  53. Gemmel C, Weickert U, Eickhoff A, Schilling D, Riemann J. Successful treatment of gallstone ileus (Bouveret's syndrome) by using extracorporal shock wave lithotripsy and argon plasma coagulation. Gastrointest Endosc. 2007;65:173-5 pubmed