Bio

Clinical Focus


  • Anesthesia

Academic Appointments


Professional Education


  • Residency:University Hospital Erlangen Dept of Anesthesia (2008) Germany
  • Internship:University Hospital Erlangen Dept of Anesthesia (2002) Germany
  • Medical Education:Friedrich-Alexander University Erlangen-Nuernberg School of Medicine (2001) Germany

Publications

Journal Articles


  • Correction: shaped magnetic field pulses by multi-coil repetitive transcranial magnetic stimulation (rTMS) differentially modulate anterior cingulate cortex responses and pain in volunteers and fibromyalgia patients. Molecular pain Tzabazis, A., Aparici, C. M., Rowbotham, M. C., Schneider, M. B., Etkin, A., Yeomans, D. C. 2014; 10: 16-?

    View details for DOI 10.1186/1744-8069-10-16

    View details for PubMedID 24594349

  • Postictal agitation after electroconvulsive therapy: incidence, severity, and propofol as a treatment option. journal of ECT Tzabazis, A., Schmitt, H. J., Ihmsen, H., Schmidtlein, M., Zimmermann, R., Wielopolski, J., Münster, T. 2013; 29 (3): 189-195

    Abstract

    Postictal agitation (PIA) after electroconvulsive therapy (ECT) is a major medical problem. This observational study investigated the incidence and severity of PIA and evaluated propofol as a treatment option in a patient population.The study included 14 patients that underwent a series of ECTs performed either with or without an approximately 0.5-mg/kg propofol bolus after the end of an electroencephalography (EEG) seizure. Among other values, we documented PIA incidence and severity as rated by a simple score; orientation to person, time, place, and situation; transfer times to the postanesthesia care (PACU) and inpatient unit; nurses' and patients' rating of recovery period, and others and tested for significant differences.Five minutes after the end of ECT, the patients showed moderate to severe PIA in 8 of 37 ECT sessions. Incidence was significantly lower when patients had received propofol (3/37). Transfer time to the PACU was longer, but transfer time to the inpatient unit was shorter after administration of propofol. The recovery period was rated significantly better after propofol administration by nurses and patients.A single bolus of propofol administered after the end of the seizure reduced the incidence of post-ECT PIA. The PACU staff and patients rated the emergence period significantly better when propofol was administered.

    View details for DOI 10.1097/YCT.0b013e3182887b5b

    View details for PubMedID 23792779

  • Shaped magnetic field pulses by multi-coil repetitive transcranial magnetic stimulation (rTMS) differentially modulate anterior cingulate cortex responses and pain in volunteers and fibromyalgia patients MOLECULAR PAIN Tzabazis, A., Aparici, C. M., Rowbotham, M. C., Schneider, M. B., Etkin, A., Yeomans, D. C. 2013; 9
  • High-dose remifentanil prevents development of thermal hyperalgesia in a neuropathic pain model BRITISH JOURNAL OF ANAESTHESIA Manering, N. A., Reuter, T., Ihmsen, H., Yeomans, D. C., Tzabazis, A. 2013; 110 (2): 287-292

    Abstract

    Intraoperative nerve lesions can lead to chronic postoperative pain. There are conflicting data as to whether or not anaesthetics administered intraoperatively are beneficial. We investigated if remifentanil administered at the time of nerve injury was able to attenuate neuropathic hypersensitivity.Rats were anaesthetized with isoflurane, endotracheally intubated, and a tail vein catheter was inserted. Rats received an i.v. infusion of either saline or low- or high-dose remifentanil (2 or 20 ?g kg(-1) min(-1), respectively) for 20 min. During this time, rats received a spinal nerve L5 transection to induce neuropathic pain or a sham procedure. Behavioural tests to assess mechanical and cold allodynia and heat hyperalgesia were performed on postoperative days 1, 3, 7, 14, 21, and 28.Sham-operated animals exhibited no hypersensitivity regardless of the intraoperative remifentanil dose. In rats which received spinal nerve L5 transection, mechanical and cold allodynia developed with no significant differences between treatment groups. However, thermal hyperalgesia was reduced in rats given high-dose remifentanil: mean (standard deviation) area under the curve 426 (53) compared with 363 (34) and 342 (24) in saline or low-dose remifentanil treated rats, respectively (P<0.05).High-dose remifentanil administered at the time of transection of the spinal nerve at L5 prevents subsequent thermal hyperalgesia.

    View details for DOI 10.1093/bja/aes360

    View details for Web of Science ID 000313826500018

    View details for PubMedID 23045364

  • The Orofacial Formalin Test in Mice Revisited-Effects of Formalin Concentration, Age, Morphine and Analysis Method JOURNAL OF PAIN Bornhof, M., Ihmsen, H., Schwilden, H., Yeomans, D. C., Tzabazis, A. 2011; 12 (6): 633-639

    Abstract

    The orofacial formalin test is established in rats and was recently transferred to mice. The aim of this study was to determine the ideal formalin concentration for testing analgesic drugs, to examine alternatives for the assessment of nociceptive and non-nociceptive behavior as well as the effects of morphine and age on formalin-induced nociception. Formalin (.5, 1, 2.5, 5, 7.5, 10, and 15%) was injected into the vibrissa of mice. The cumulative nociceptive behavior was measured as well as nociceptive and non-nociceptive behavior based on a score that was recorded over a 5-second observation period once per minute. We also examined the effects of morphine on the nociceptive response induced by 2.5% formalin. Age-dependent differences were tested in the third part of the experiment. NONMEM was used to model the pharmacodynamic effects of formalin and morphine. Injection of formalin lead to a concentration-dependent increase in cumulative nociceptive behavior ratings as well as the specific nociceptive behavior 3 of scratching injection site with hindpaw (score 3). The formalin concentrations that lead to 50% of the maximum effect were 2.6 and 3.3%, respectively, for the continuous rating method and the scoring method. Morphine dose dependently suppressed the nociceptive behavior and the number of score 3 ratings of the nociceptive behavior. Age differences in behavior could not be detected by either analytic method.To improve the existing behavioral nociceptive assay for pain processed by the trigeminal system, we determined an ideal formalin concentration for the orofacial formalin test in mice, evaluated alternative timesaving analysis approaches, and investigated effects of morphine and age on formalin-induced nociception.

    View details for DOI 10.1016/j.jpain.2010.11.009

    View details for Web of Science ID 000291959100003

    View details for PubMedID 21481645

  • Selective nociceptor activation in volunteers by infrared diode laser MOLECULAR PAIN Tzabazis, A. Z., Klukinov, M., Crottaz-Herbette, S., Nemenov, M. I., Angst, M. S., Yeomans, D. C. 2011; 7

    Abstract

    Two main classes of peripheral sensory neurons contribute to thermal pain sensitivity: the unmyelinated C fibers and thinly myelinated A? fibers. These two fiber types may differentially underlie different clinical pain states and distinctions in the efficacy of analgesic treatments. Methods of differentially testing C and A? thermal pain are widely used in animal experimentation, but these methods are not optimal for human volunteer and patient use. Thus, this project aimed to provide psychophysical and electrophysiological evidence that whether different protocols of infrared diode laser stimulation, which allows for direct activation of nociceptive terminals deep in the skin, could differentially activate A? or C fiber thermonociceptors in volunteers.Short (60 ms), high intensity laser pulses (SP) evoked monomodal "pricking" pain which was not enhanced by topical capsaicin, whereas longer, lower power pulses (LP) evoked monomodal "burning" pain which was enhanced by topical capsaicin. SP also produced cortical evoked EEG potentials consistent with A? mediation, the amplitude of which was directly correlated with pain intensity but was not affected by topical capsaicin. LP also produced a distinct evoked potential pattern the amplitude of which was also correlated with pain intensity, which was enhanced by topical capsaicin, and the latency of which could be used to estimate the conduction velocity of the mediating nociceptive fibers.Psychophysical and electrophysiological data were consistent with the ability of short high intensity infrared laser pulses to selectively produce A? mediated pain and of longer pulses to selectively produce C fiber mediated thermal pain. Thus, the use of these or similar protocols may be useful in developing and testing novel therapeutics based on the differential molecular mechanisms underlying activation of the two fiber types (e.g., TRPV1, TRPV2, etc). In addition, these protocol may be useful in determining the fiber mediation of different clinical pain types which may, in turn be useful in treatment choice.

    View details for DOI 10.1186/1744-8069-7-18

    View details for Web of Science ID 000289115700001

    View details for PubMedID 21426575

  • Trigeminal antihyperalgesic effect of intranasal carbon dioxide LIFE SCIENCES Tzabazis, A. Z., Niv, S. H., Manering, N. A., Klyukinov, M., Cuellar, J. M., Bhatnagar, A., Yeomans, D. C. 2010; 87 (1-2): 36-41

    Abstract

    Clinical studies demonstrate attenuation of trigeminal-related pain states such as migraine by intranasal CO(2) application. This study investigated the underlying mechanisms of this observation and its potential use to reverse trigeminal pain and hypersensitivity.We used a behavioral rat model of capsaicin-induced trigeminal thermal hyperalgesia, intranasal CO2 application and several pharmacologic agents such as carbonic anhydrase, acid-sensing ion channels (ASICs), and TRPV1 blocker as well as acidic buffer solutions to investigate and mimic the underlying mechanism.Intranasal CO(2) application produced a robust dose-dependent antihyperalgesic effect in rats that lasted at least one hour. Blockade of nasal carbonic anhydrase with a dorzolamide solution (Trusopt ophthalmic solution) showed only a non-significant decrease of the antihyperalgesic effect of intranasal CO(2) application. Pharmacologic blockade of ASICs or TRPV(1) receptor significantly attenuated the antihyperalgesic effect of CO(2) application. The effect of intranasal CO(2) application could be mimicked by application of pH 4, but not pH 5, buffer solution to the nasal mucosa. As with CO(2) application, the antihyperalgesic effect of intranasal pH 4 buffer was blocked by nasal application of antagonists to ASICs and TRPV(1) receptors.Our results indicate that intranasal CO(2) application results in a subsequent attenuation of trigeminal nociception, mediated by protonic activation of TRPV(1) and ASIC channels. A potential central mechanism for this attenuation is discussed. The antihyperalgesic effects of intranasal CO(2) application might be useful for the treatment of trigeminal pain states.

    View details for DOI 10.1016/j.lfs.2010.05.013

    View details for Web of Science ID 000279499000005

    View details for PubMedID 20561904

  • Antihyperalgesic effect of a recombinant herpes virus encoding antisense for calcitonin gene-related peptide ANESTHESIOLOGY Tzabazis, A. Z., Pirc, G., Votta-Velis, E., Wilson, S. P., Laurito, C. E., Yeomans, D. C. 2007; 106 (6): 1196-1203

    Abstract

    Calcitonin gene-related peptide (CGRP) is contained in and released by small-diameter, nociceptive primary afferent sensory neurons. Upon spinal release, one of the effects of CGRP seems to be to sensitize dorsal horn neurons to subsequent input from nociceptive afferents and, consequently, to induce a behavioral hyperalgesia. Therefore, attenuating evoked release of CGRP from central terminals of nociceptors should have an antihyperalgesic effect.The authors applied a recombinant herpes vector, encoding an antisense sequence to the whole CGRP gene, to the dorsal surface of the hind paw of mice to knock down expression of the peptide selectively in primary afferents innervating this tissue.Herpes virus-based vector encoding an antisense sequence for the whole CGRP clearly reduced CGRP immunoreactivity in the infected spinal dorsal horn levels as well as in cultured dorsal root ganglia neurons. Selective knockdown of CGRP in primary afferents significantly attenuated the thermal, C-fiber hyperalgesia normally observed after topical application of capsaicin. The effect of viral vector-mediated knockdown of CGRP was comparable to the effect of intrathecal application of the CGRP antagonist CGRP8-37, but lasted for 14 weeks after one single application.Viral vector-mediated knockdown of CGRP in primary afferent neurons provides a promising tool for treatment of chronic pain states as well as for studies investigating the pathophysiology underlying these conditions.

    View details for Web of Science ID 000246797500019

    View details for PubMedID 17525595

  • Differential activation of trigeminal C or A delta nociceptors by infrared diode laser in rats: Behavioral evidence BRAIN RESEARCH Tzabazis, A., Klyukinov, M., Manering, N., Nemenov, M. I., Shafer, S. L., Yeomans, D. C. 2005; 1037 (1-2): 148-156

    Abstract

    Radiant heat is often used for studying thermal nociception, although inherent characteristics such as the broad spectrum of applied wavelengths of typical light sources limit control over and repeatability of stimuli. To overcome these problems, we used a diode infrared laser-based stimulator (wavelength: 980 nm) for selectively stimulating trigeminal Adelta or C thermonociceptors in rats. To provide indirect evidence for nociceptor-selective stimulation, we tested the effects of capsaicin, dimethylsulfoxide (DMSO), and morphine on withdrawal latencies for long pulses with a low current (hypothesized to selectively stimulate C nociceptors) and for threshold currents of short pulses with high current (hypothesized to selectively stimulate Adelta nociceptors) in lightly anesthetized rats. Nonmem analysis was used to perform pharmacodynamic modeling. The measured baseline withdrawal latency for long pulses was 12.5 +/- 0.3 s which was changed significantly to 6.7 +/- 0.4 s after applying topical capsaicin which selectively sensitizes C nociceptors and to 16.5 +/- 1.3 s after 1.0 mg/kg morphine which preferentially attenuates C fiber nociception. Topical DMSO which appears to selectively sensitize Adelta afferents did not significantly alter withdrawal latencies to the long pulses. Fitted threshold currents for short pulses after DMSO were however significantly lower (974 +/- 53 mA vs. 1113 +/- 12 mA for baseline) indicating Adelta sensitization. Capsaicin and morphine did not significantly change threshold currents. Best Nonmem fits for the long pulse were obtained using a model assuming no DMSO effect, but a different inter-individual variability after applying this substance. For the short pulse, a model assuming no capsaicin or morphine effect, but again allowing different inter-individual variabilities after applying these drugs, best described the data. We conclude that different settings of the stimulator used in this study were capable of selectively activating trigeminal Adelta or C thermonociceptors.

    View details for DOI 10.1016/j.brainres.2005.01.019

    View details for Web of Science ID 000228251400018

    View details for PubMedID 15777763

  • Decrease in inflammatory hyperalgesia by herpes vector-mediated knockdown of Na(v)1.7 sodium channels in primary afferents HUMAN GENE THERAPY Yeomans, D. C., Levinson, S. R., Peters, M. C., Koszowski, A. G., Tzabazis, A. Z., Gilly, W. F., Wilson, S. P. 2005; 16 (2): 271-277

    Abstract

    Induction of peripheral inflammation increases the expression of the Nav1.7 sodium channel in sensory neurons, potentially increasing their excitability. Peripheral inflammation also produces hyperalgesia in humans and an increase in nociceptive responsiveness in animals. To test the relationship between these two phenomena we applied a recombinant herpes simplex-based vector to the hindpaw skin of mice, which encoded both green fluorescent protein (GFP) as well as an antisense sequence to the Nav1.7 gene. The hindpaw was subsequently injected with complete Freund's adjuvant to induce robust inflammation. Application of the vector, but not a control vector encoding only GFP, prevented an increase in Nav1.7 expression in GFP-positive neurons and prevented development of hyperalgesia in both C and Adelta thermonociceptive tests. These results provide clear evidence of the involvement of an increased expression of the Nav1.7 channel in nociceptive neurons in the development of inflammatory hyperalgesia.

    View details for Web of Science ID 000227543900012

    View details for PubMedID 15761266

  • Ameroid rings for gradual chronic constriction of the sciatic nerve in rats: contribution of different nerves to neuropathic pain BRAIN RESEARCH BULLETIN Tzabazis, A., Kim, P. H., Sweitzer, S. M., Yeomans, D. C. 2004; 64 (2): 127-132

    Abstract

    Mononeuropathy was induced by placing an ameroid ring around the sciatic nerve and was compared with chronic constriction injury (CCI) of the sciatic nerve [Pain 33 (1988) 87] in rats. Mechanical allodynia was assessed and the role of sciatic and saphenous afferents (Adelta and C) in thermal hyperalgesia investigated. A shorter duration of mechanical allodynia in ameroid rats as compared to CCI rats was observed. Thermal hyperalgesia was observed in the saphenous innervated skin of the hindpaw for Adelta and C nociceptors in ameroid and for Adelta nociceptors only in CCI rats, respectively. The sciatic innervated skin showed a thermal hypoalgesia with a fast onset for Adelta afferents and a slower onset for C afferents in CCI and ameroid rats. The duration of both thermal hypo- and hyperalgesia was longer in ameroid rats. We conclude that ameroid rings are a useful tool for the investigation of long-duration hyperalgesic effects of nerve injury, as the effects were more stable and seen for a longer time (>8 weeks) as compared to the CCI model. The uninjured saphenous afferents, in particular C fibers, mediate thermal hyperalgesia after chronic constriction of the sciatic nerve using an ameroid ring.

    View details for DOI 10.1016/j.brainresbull.2004.05.006

    View details for Web of Science ID 000224035600004

    View details for PubMedID 15342099

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