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Biomedical subjects

Hakan Ay

Publications and source records attributed to Hakan Ay.

At least 19 recordsLinked to original sources
PubMed2006

The real estate factor: quantifying the impact of infarct location on stroke severity.

BACKGROUND AND PURPOSE: The severity of the neurological deficit after ischemic stroke is moderately correlated with infarct volume. In the current study, we sought to quantify the impact of location on neurological deficit severity and to delineate this impact from that of volume. METHODS: We developed atlases consisting of location-weighted values indicating the relative importance in terms of neurological deficit severity for every voxel of the brain. These atlases were applied to 80 first-ever ischemic stroke patients to produce estimates of clinical deficit severity. Each patient had an MRI and National Institutes of Health Stroke Scale (NIHSS) examination just before or soon after hospital discharge. The correlation between the location-based deficit predictions and measured neurological deficit (NIHSS) scores were compared with the correlation obtained using volume alone to predict the neurological deficit. RESULTS: Volume-based estimates of neurological deficit severity were only moderately correlated with measured NIHSS scores (r=0.62). The combination of volume and location resulted in a significantly better correlation with clinical deficit severity (r=0.79, P=0.032). CONCLUSIONS: The atlas methodology is a feasible way of integrating infarct size and location to predict stroke severity. It can estimate stroke severity better than volume alone.

Aged↗
PubMed2006

Effect of using local arterial input functions on cerebral blood flow estimation.

PURPOSE: To investigate a previously developed method for perfusion-weighted MRI (PWI) cerebral blood flow (CBF) estimation that uses local arterial input functions (AIFs) in stroke patients, and determine its ability to correct delay and/or dispersion (D/D) errors. MATERIALS AND METHODS: Analysis was performed on dynamic susceptibility contrast data from 36 stroke patients, and CBF maps were calculated with global- and local-AIF techniques using standard SVP based methods. The ratios of these maps were calculated and the mean ratios were calculated for voxels with both normal and abnormal time to peak or width. The locations of the voxels with high locally-defined to globally-defined CBF ratios were also mapped and the average underlying concentration-time curves for these voxels were calculated. RESULTS: The ratio of CBF estimates based on local AIFs to global AIFs was on average increased for D/D voxels. The voxels in which this ratio was high were commonly concentrated in the ipsilateral hemisphere, and these voxels also displayed underlying concentration-time curves that showed delay or dispersion. Conversely, there were no such findings based on high globally-defined to locally-defined CBF ratios. CONCLUSION: The local-AIF technique results in an increase in the calculated CBF values for tissues with D/D, consistent with a reduction in the errors associated with D/D.

Adult↗
PubMed2006

Automated perfusion-weighted MRI using localized arterial input functions.

PURPOSE: To investigate the utility of an automated perfusion-weighted MRI (PWI) method for estimating cerebral blood flow (CBF) based on localized arterial input functions (AIFs) as compared to the standard method of manual global AIF selection, which is prone to deconvolution errors due to the effects of delay and dispersion of the contrast bolus. MATERIALS AND METHODS: Analysis was performed on spin- and gradient-echo EPI images from 36 stroke patients. A local AIF algorithm created an AIF for every voxel in the brain by searching out voxels with the lowest delay and dispersion, and then interpolating and spatially smoothing them for continuity. A generalized linear model (GLM) for predicting tissue outcome, and MTT lesion volumes were used to quantify the performance of the localized AIF method in comparison with global methods using ipsilateral and contralateral AIFs. RESULTS: The algorithm found local AIFs in each case without error and generated a higher area under the receiver operating characteristic (ROC) curve compared to both global-AIF methods. Similarly, the local MTT lesion volumes had the least mean squared error (MSE). CONCLUSION: Automated CBF calculation using local AIFs is feasible and appears to produce more useful CBF maps.

Adult↗
PubMed2006

Transient ischemic attack: are there different types or classes? Risk of stroke and treatment options.

Recent advances in neuroimaging have revolutionized the evaluation of the clinical syndrome of transient ischemic attack (TIA). Diffusion-weighted imaging demonstrates microinfarctions (< 1 cm(3)) in approximately 50% of patients with TIA, establishing that not all clinically transient spells are transient at the tissue level. The clinical syndrome of TIA that is associated with ischemic brain injury is called "transient symptoms with infarction" (TSI). TSI appears to be a different subset because it harbors higher risk of imminent stroke than "TIA with no infarction." Armed with the evidence of ischemia as the cause of transient spell, clinicians can pursue the most appropriate therapy for stroke prevention by targeting the underlying etiology of brain ischemia.

Journal Article↗
PubMed2005

Carotid artery stenting and endarterectomy have different effects on heart rate variability.

OBJECTIVE: Due to their close proximity to the carotid sinus baroreceptor region, carotid endarterectomy (CEA) and carotid angioplasty/stenting (CAS) carry an inherent risk of affecting baroreflex-mediated regulation of the heart rate. Variations in the heart rate can be studied by measuring heart rate variability (HRV), in which distinct frequency bands in the power spectrum represent sympathetic and parasympathetic modulations on sinus node pacemaker activity. We aimed to investigate the influence of CEA and CAS on HRV. METHODS: One-hour recordings of R-R intervals on ECG were obtained before and after CEA (10 patients) or CAS (12 patients). The power spectrum of the R-R time series was estimated using the FFT technique. The power in low frequency (LF) and high frequency (HF) bands were computed and normalized to their total power (TP). The LF/HF ratio, an index of sympathovagal balance, was calculated. RESULTS: Compared to preoperative levels, LF/HF exhibited 85%, 96%, and 70% increase on the second, third, and fourth days after CEA, respectively. In contrast, LF/HF decreased by 26%, 32%, and 26% on the respective days following CAS; the difference between groups was significant (p=0.0069). Normalized LF increased after CEA and decreased after CAS, while the opposite was observed for normalized HF (p=0.0217). There was no significant change in TP. CONCLUSIONS: CEA and CAS have differential effects on the sympathovagal balance on the heart. The relative increase in sympathetic modulation after CEA and parasympathetic modulation after CAS are likely mediated by alterations in the sensitivity of carotid sinus baroreceptors. Altered cardiac autonomic modulation may play a role in the occurrence of cardiac disturbances following carotid interventions.

Adult↗
PubMed2005

Conversion of ischemic brain tissue into infarction increases with age.

BACKGROUND AND PURPOSE: Brain regions normal on diffusion-weighted imaging (DWI) but abnormal on mean transit time (MTT) maps represent tissue at risk of infarction, yet the fate of these regions is quite variable. The imperfect correlation between tissue outcome and initial imaging parameters suggests that each patient's brain may have different susceptibility to ischemic stress. We hypothesize that age is a marker for tissue susceptibility to ischemia and thus plays a role in determining tissue outcome in human stroke. METHODS: Sixty patients with acute ischemic stroke and a region of DWI/MTT mismatch that was >20% of the DWI volume were included. All patients were scanned twice, within 12 hours of symptom onset and on day 5 or later. The percentage mismatch lost (PML) was calculated as percentage of initial DWI/MTT mismatch volume that was infarcted on the follow-up MRI. The statistical analysis explored relationships among the covariates age, Trial of Org 10172 in Acute Stroke Treatment (TOAST) subtypes, time-to-MRI, and initial DWI, MTT volume, mean arterial blood pressure and blood glucose level at admission, and previous history of hypertension and diabetes mellitus. RESULTS: Univariate comparisons showed that age (P=0.003), hypertension (P=0.009), and diabetes mellitus (P=0.0002) were significantly associated with PML. Regression analyses showed age to be a significant covariate (P=0.02). The regression model predicted a change in PML of approximately 0.65% per year. The adjusted proportion of variance (R2) in PML that could be explained by age alone was 14%. CONCLUSIONS: Age-dependent increase in conversion of ischemic tissue into infarction suggests that age is a biological marker for the variability in tissue outcome in acute human stroke.

Adult↗
PubMed2005

Transient ischemic attack with infarction: a unique syndrome?

It is debated whether transient symptoms associated with infarction (TSI) are best considered a minor ischemic stroke, a subtype of transient ischemic attack (TIA), or a separate ischemic brain syndrome. We studied clinical and imaging features to establish similarities and differences among ischemic stroke, TIA without infarction, and TSI. Eighty-seven consecutive patients with TIA and 74 patients with ischemic stroke were studied. All underwent diffusion-weighted imaging on admission. Symptom duration and infarct volume were determined in each group. Thirty-six patients (41.3%) with TIA had acute infarct(s). Although TIA-related infarcts were smaller than those associated with ischemic stroke (mean, 0.7 vs 27.3 ml; p < 0.001), there was no lesion size threshold that distinguished ischemic stroke from TSI. In contrast, the symptom duration probability density curve was not broad, but instead peaked early with only a few patients having symptoms for longer than 200 minutes. The probability density function for symptom duration was similar between TIA with or without infarction. The in-hospital recurrent ischemic stroke and TIA rate was 19.4% in patients with TSI and 1.3% in those with ischemic stroke. TIA with infarction appears to have unique features separate from TIA without infarction and ischemic stroke. We propose identifying TSI as a separate clinical syndrome with distinct prognostic features.

Aged↗
PubMed2005

An evidence-based causative classification system for acute ischemic stroke.

Regular, evidence-based assignment of patients to etiologic stroke categories is essential to enable valid comparison among studies. We designed an algorithm (SSS-TOAST) that incorporated recent advances in stroke imaging and epidemiology to identify the most probable TOAST category in the presence of evidence for multiple mechanisms. Based on the weight of evidence, each TOAST subtype was subdivided into 3 subcategories as "evident", "probable", or "possible". Classification into the subcategories was determined via predefined specific clinical and imaging criteria. These criteria included published risks of ischemic stroke from various mechanisms and published reports of the strength of associations between clinical and imaging features and particular stroke mechanisms. Two neurologists independently assessed 50 consecutively admitted patients with acute ischemic stroke through reviews of abstracted data from medical records. The number of patients classified as "undetermined-unclassified" per the original TOAST system decreased from 38-40% to 4% using the SSS-TOAST system. The kappa value for inter-examiner reliability was 0.78 and 0.90 for the original TOAST and SSS-TOAST respectively. The SSS-TOAST system successfully classifies patients with acute ischemic stroke into determined etiologic categories without sacrificing reliability. The SSS-TOAST is a dynamic algorithm that can accommodate modifications as new epidemiological data accumulate and diagnostic techniques advance.

Adult↗
PubMed2005

Echocardiographic predictors of left atrial appendage spontaneous echocontrast in patients with stroke and atrial fibrillation.

OBJECTIVE: The presence of spontaneous echocontrast (SEC) in the left atrium (LA) or LA appendage (LAA) has been associated with a higher risk of thromboembolism and cerebrovascular accidents. The purpose of this study was to define the new transesophageal echocardiographic predictors of SEC for patients with stroke and atrial fibrillation. METHODS: We studied 47 patients with stroke and atrial fibrillation who were undergoing transesophageal echocardiography for the evaluation of source of cardiac emboli. Patients were divided into two groups based on the absence (group 1) or presence (group 2) of SEC in the LAA. RESULTS: Compared with group 1, group 2 had larger LA, larger LAA minimum and maximum areas, and decreased LAA flow velocity, LAA wall velocity, LAA tissue intensity, and intensity ratio. In the stepwise discriminate analysis tissue intensity of LAA, minimum LAA area, LAA flow velocity, and LAA wall velocity were found as independent predictors of LAA SEC. LAA wall velocity had the greatest area under the receiver operating characteristic curve, indicating that the most powerful parameter for SEC is LAA wall velocity. CONCLUSION: Decreased LAA flow velocity and LA wall velocity, increased LAA size, and less negative LAA tissue intensity are associated with SEC in patients with nonvalvular atrial fibrillation. Strain and strain measurements of LAA give no more benefit.

Aged↗
PubMed2005

Aural barotrauma in submarine escape: is mastoid pneumatization of significance?

OBJECTIVE: Submarine escape training is carried out by preselected, healthy young men under strictly controlled conditions regarding exposure to pressure and the rate of pressure change. This provides a unique opportunity to investigate the relations between middle ear characteristics and susceptibility to barotrauma while avoiding possible confounding parameters. We examined a possible association between mastoid pneumatization and middle ear barotrauma (MEB) in submarine escape trainees. STUDY DESIGN: Cross-sectional, parallel-group design. METHODS: Sixty-six subjects aged 19 to 28 participated in the study. The escape simulation included pressurization to 30 or 60 feet followed by a buoyant ascent to the surface. Subjects were evaluated for MEB after each ascent. A Schuller's mastoid radiograph was taken for the evaluation of mastoid pneumatization. RESULTS: Fifteen (23%) of the subjects suffered from MEB, and 6 (40%) of them had bilateral involvement. Repeated impedance audiometry after the completion of a successful ascent revealed a significant increase in middle ear compliance. Schuller's radiographs were obtained from 49 (74%) of the subjects. Of these radiographs, 16 (16%) were of ears that had suffered MEB. Mastoid pneumatization for all ears approached a normal Gaussian distribution, with a mean area of 9.58 cm. The mastoid areas and the proportion of ears with mastoid pneumatization at the extremes of the study population did not differ between barotrauma and no-barotrauma ears. CONCLUSION: In a population with no history of recurrent or chronic otitis media and normal tympanic membrane morphology and compliance, the amount of mastoid pneumatization probably represents merely the normal distribution of variation in organ size and is not related to the ability to equalize pressure in the middle ear.

Acoustic Impedance Tests↗
PubMed2005

Protective effects of exogenously administered or endogenously produced melatonin on hyperbaric oxygen-induced oxidative stress in the rat brain.

1. Hyperbaric oxygen (HBO) is a widely used treatment modality in many diseases. A known side-effect of HBO is the production of reactive oxygen species (ROS). Many anti-oxidants, such as vitamins C and E, riboflavin and selenium, have been used successfully to scavenge the ROS produced by HBO administration. 2. The aim of the present study was to determine whether melatonin, a newly discovered anti-oxidant, has a protective effect against the overproduction of ROS produced by HBO in rat brain tissue. 3. Seventy male Sprague-Dawley rats were divided into seven groups as follows: 1, daytime control; 2, daytime HBO; 3, melatonin; 4, daytime HBO plus melatonin; 5, night-time control; 6, night-time HBO; and 7, night-time HBO under light exposure. 4. Hyperbaric oxygen was administered at 303 kPa for 120 min. Melatonin was injected at a dose of 10 mg/kg, i.p. Brain malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels were measured to elucidate oxidant status. 4. The MDA and SOD levels of groups 2 and 7 increased significantly. Exogenous (group 4) and endogenous (group 6) melatonin protected against HBO-induced lipid peroxidation. Exogenously administered melatonin (groups 3 and 4) had increased levels of the anti-oxidant enzymes SOD and GPx. 5. In conclusion, HBO caused oxidative stress and melatonin exhibited protective effects. Both endogenously produced and exogenously administered melatonin were found to be effective.

Animals↗
PubMed2004

Visual loss as a late complication of carbon monoxide poisoning and its successful treatment with hyperbaric oxygen therapy.

PURPOSE: To present recovery from vision loss due to CO poisoning with Hyperbaric Oxygen (HBO) therapy in two patients. METHODS: Two female patients developed visual deterioration after carbon monoxide (CO) poisoning and were treated with hyperbaric oxygen therapy (HBO). Clinical examination, including visual acuity assessment, visual field examination and visual evoked potentials (VEPs) before and after the HBO therapy were performed. RESULTS: In Case 1 the visual loss started on the third day with visual acuity at the level of perception of hand movements at 10 cm in the right eye and finger count at 10 cm in the left eye. The visual evoked potentials (VEPs) had low amplitudes and prolonged (128 msec bilaterally) latencies (implicit times). After 48 sessions and 52 days of HBO therapy, the visual acuity became 0.2 in the right eye and 0.15 in the left eye. Visual field examination revealed homonymous right lower quadrant anopsia. The VEPs also improved. In Case 2 the visual acuity was 0.2 in the right eye and 0.1 in the left eye on the 6th day following the accident when the patient was admitted for treatment. The VEP latencies were within normal limits. After 36 days and 35 sessions of HBO therapy, the visual acuity became 0.7 on both eyes. The visual fields completely normalised. The VEP latencies in this case also became shorter. CONCLUSION: It appears that the adverse effects of CO poisoning continue to progress during the late period and we believe that HBO treatment in this period may still be effective and will prevent some of the neurological sequelae such as visual loss from becoming permanent. Clinical, neurological, neuropsychological, visual outcome seems to be favourable even if HBO treatment started as late as 6 or 8 days after the exposure to CO.

Adult↗
PubMed2004

Diffusion-weighted MRI for the "small stuff": the details of acute cerebral ischaemia.

Diffusion-weighted MRI (DWI) has already had a substantial effect on the diagnosis of patients with ischaemic stroke. It provides in vivo pathological information and allows the differentiation of acute stroke from chronic stroke and from non-specific white-matter lesions. The high contrast of the acute DWI lesion against the dark background facilitates the detection of lesions even when they are 1 mm or less in diameter. Small lesions, which are undetectable by other means, include small lacunar infarcts, punctate cortical infarcts, and DWI bright dots in patients with transient ischaemic attacks (TIA). The latter constitute remnants or "footprints" of recent ischaemia and confirm the clinical TIA syndrome as ischaemic. Because of these attributes, DWI not only confirms the clinical diagnosis, but also facilitates the recognition of certain patterns of ischaemia, thereby providing clues to the underlying aetiology. DWI is becoming an important technique for optimum management of patients.

Brain↗
PubMed2004

Submarine escape from depths of 30 and 60 feet: 41,183 training ascents without serious injury.

INTRODUCTION: In the case of a submerged, disabled submarine, survivors may be forced to escape by entering the water and ascending rapidly to the surface. The large pressure changes involved may produce pulmonary barotrauma, arterial gas embolism, or barotrauma. To assess the likelihood of such injuries, we retrospectively evaluated medical problems due to submarine escape training among military personnel. METHODS: We evaluated 41,183 controlled ascents performed over the past 21 yr in the escape training tank at Gölcük-Kocaeli, Turkey. Each trainee performed two free ascents from 30 ft and two hooded ascents from 60 ft. Before participating, candidates were screened by physical examination, spirometry, and chest X-rays; ear examinations for barotrauma were made after ascents. If a trainee failed to exhale properly during ascent, an instructor aborted the ascent and took him to a bell or side recess of the tank. RESULTS: No record of pulmonary barotrauma or other major complications were found. Middle-ear barotrauma was observed following 1,643 of the ascents (4.1%), with rupture of the tympanic membrane in 35 cases. DISCUSSION: Submarine escape ascents can be safely performed provided that subjects are medically screened and well trained.

Adult↗
PubMed2004

Seizure incidence in 80,000 patient treatments with hyperbaric oxygen.

INTRODUCTION: Hyperbaric oxygen treatment (HBOT) involves some risk of central nervous system (CNS) oxygen toxicity, which may be revealed by various signs and symptoms including seizures in patients breathing O2 at pressures of 2 ATA or higher. The aim of this study was to determine the incidence of such seizures in the Underwater and Hyperbaric Medicine Departments of two university hospitals. METHODS: We retrospectively evaluated 80,679 patient-treatments for 9 clinical indications to determine the incidence of seizures attributable to CNS O2 toxicity. Because different protocols were used for HBOT, the treatments were studied in four groups according to the chamber type used and the medical facility at which it was located. RESULTS: Only 2 seizures were documented, yielding an incidence of 2.4 per 100,000 patient-treatments. Both cases occurred in a multiplace chamber pressurized to 2.4 ATA with O2 delivered by mask for three x 30 min with 5-min air breaks. DISCUSSION: The seizure incidence reported here is lower than other studies published in the literature. The delivery of O2 by mask rather than hood may be a factor. Nevertheless, it appears that the risk of seizures due to CNS O2 toxicity during HBOT is very low as long as appropriate exclusion criteria and treatment profiles are used.

Adolescent↗
PubMed2003

Hyperhomocysteinemia is associated with the presence of left atrial thrombus in stroke patients with nonvalvular atrial fibrillation.

BACKGROUND AND PURPOSE: Blood stasis is the fundamental mechanism leading to thrombus formation in the venous system. Homocysteine also poses a significant risk for venous thrombosis through its endothelial toxic and prothrombotic properties. In the present study, we hypothesized that high homocysteine might be associated with thrombus formation in another stasis-related condition, atrial fibrillation. METHODS: Forty-two consecutive patients with ischemic stroke caused by nonvalvular atrial fibrillation and admitted within the first day of symptom onset were included. Total fasting plasma homocysteine, serum folic acid, and vitamin B12 levels were measured. All patients were evaluated by transesophageal echocardiography for the presence of a left atrial (LA) thrombus. Homocysteine and vitamin levels were compared between groups with or without LA thrombus. RESULTS: Transesophageal echocardiography revealed LA thrombus in 20 patients. Mean homocysteine levels were significantly higher in patients with LA thrombus (20.75 versus 13.34 micromol/L, P<0.001). Multivariate logistic regression analysis showed that the effect of high homocysteine was independent of other clinical or echocardiographic variables known to increase LA thrombus (P=0.017). There was no difference in vitamin B12 levels between groups (P=0.118), whereas the mean folic acid level was significantly lower in patients with LA thrombus (P=0.004). CONCLUSIONS: High plasma homocysteine conveys an independent risk for LA thrombus formation in patients with stroke caused by nonvalvular atrial fibrillation. This finding further supports the thrombogenic role of high homocysteine in conditions associated with blood stasis.

Aged↗
PubMed2003

The role of Austrian physicians and Prof. Joseph Hyrtl (1810-1894) on modernization of Ottoman-Turkish medicine.

Medical schools have a long history in Ottoman-Turkish medical education. At Ottoman medical schools (medreses), education has been given to students regularly. But because of social dogma and oppression of religion on the science of human anatomy they could not get a chance to improve for centuries. Traditionally, Ottoman-Turkish medical education was shaped under the influence of Galenos (129-200) and Avicenna (980-1037). These influences continued until the beginning of the 19th century. In this period, Avicenna's most famous medical book "Kanun-i fit-tip" was a main anatomy textbook in medical education of the eleventh century. Modernization of educational systems in the Ottoman Empire started during the reign of Sultan Selim the 3rd (1789-1807) and modern anatomy in Ottoman-Turkish Medicine has flourished following the Austrian physicians. Today's Department of Anatomy at Istanbul Medical School of the Istanbul University is a continuation of Galatasaray Medical School which was the first medical school achieving the western educational level.

Anatomy↗