Search PubMed⌕ Search

Biomedical subjects

A Antoniadis

Publications and source records attributed to A Antoniadis.

At least 55 records · Page 3Linked to original sources
PubMed1999

Wavelet transform to quantify heart rate variability and to assess its instantaneous changes.

Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information.

Adrenergic beta-Antagonists↗
PubMed1998

Data compression for diffraction patterns.

Efficient coding (lossless) and compression (lossy) of diffraction patterns is important in protein crystallography experiments because of storage and transmission limitations. The goal is to reduce the bit-rate significantly while keeping diffraction peak intensity distortion at an acceptable level. This paper presents an overview of coding and compression techniques more or less adapted to such problems. A large part of this study is dedicated to time-frequency-transform based compression algorithms and some of their extensions. Wavelet based software has been developed and tested. Results are compared with the discrete cosine transform (DCT) and other classical algorithms. These tools seem attractive and very promising for analyzing and compressing signals with singularities and transient phenomena such as diffraction peaks. Tests were performed on a standard protein crystallography data set coming from the CCD detector of D2AM beamline at the European Synchrotron Radiation Facility at Grenoble. These were compressed with DCT and wavelet-based algorithms. It appears that alterations of the result of the processing of restored images remain very weak for compression rates up to 10. These preliminary results indicate that the proposed wavelet method is a good standard technique for efficient compression of diffraction patterns.

Algorithms↗
PubMed1998

Retrospective serological and genetic study of the distribution of hantaviruses in Greece.

A retrospective serological and genetic study of hantaviruses responsible for hemorrhagic fever with renal syndrome (HFRS) in Greece during the last 17 years is presented. Fifty-one serum samples taken from 30 HFRS cases previously diagnosed by immunofluorescence assay were tested by ELISA for IgG (Hantaan, Dobrava, and Puumala) and IgM antibodies (Hantaan and Puumala). Results were compatible with the majority of infections being related to hantaviruses carried by rodents of the subfamily Murinae. RNA was extracted from 26 selected samples and reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using primers specifically designed for the detection of hanta-viruses associated with murine (MS-N-specific, MM-G1-specific primers) or arvicoline rodents (PPT-N-specific primers). In addition, primers previously designed for the detection of the G2 coding region of the Murine-associated hanta-viruses were also used. Sequencing of the PCR products was then performed, followed by phylogenetic analysis of nucleotide sequence differences. Eleven out of the 26 serum samples tested were found to be positive by PCR with the MS-N primers, whereas four were positive with the MM-G1 primers, and only two with the G2 primers. None of the samples was found positive with the PPT primers. The sequence analysis showed that the virus that was responsible for these 11 HFRS cases was the Dobrava virus, which is endemic throughout the Balkans.

Adult↗
PubMed1998

Atrial natriuretic peptide augments coronary collateral blood flow: a study during coronary angioplasty.

BACKGROUND AND HYPOTHESIS: In vitro studies have shown that atrial natriuretic peptide (ANP) causes relaxation of preconstricted blood vessel strips and inhibits the contraction of isolated vessels in response to norepinephrine and angiotensin II. The present study examined the effects of exogenous ANP on the coronary collateral blood flow during angioplasty. METHODS: We studied 15 patients undergoing elective balloon angioplasty during the second and third balloon inflations. A Doppler flow guidewire was advanced distal to the lesion and used for the estimation of coronary blood flow velocity. After the second balloon inflation, 25 ng/kg/min of ANP were administered intracoronarily for 8 min. Electrocardiogram, pressure, and flow velocity were recorded immediately before each balloon deflation. Fourteen other patients served as controls and received normal saline infusion. RESULTS: Velocity time integral increased from 65 +/- 40 to 79 +/- 46 mm (p < 0.05) during the third balloon inflation, whereas ST deviation decreased from 1.3 +/- 0.9 to 0.7 +/- 1.0 mV (p < 0.05). These variables did not change in the control group during the two tested balloon inflations. CONCLUSION: Exogenous ANP augments coronary collateral blood flow and ameliorates myocardial ischemia during angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed1998

Effect of rotational coronary atherectomy on peripheral endothelin-1, atrial natriuretic peptide, and cyclic adenosine monophosphate plasma levels.

We investigated the effects of coronary rotational atherectomy (PTCRA) on plasma levels of endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and cyclic adenosine monophosphate (cAMP). We studied 14 patients undergoing PTCRA and compared them with 14 patients undergoing plain balloon angioplasty. Blood samples were taken from the femoral vein at baseline, after the end of the atherectomy, after the first balloon inflation, after the end of the procedure, and 4 hours later. ET-1 increased in the angioplasty group from 6.3 +/- 3.2 pmol/L at baseline to 8.5 +/- 3.9 pmol/L at the end of the procedure (F = 3.83, P = .02), whereas it did not change in the PTCRA group. ANP increased in the PTCRA group from 78.1 +/- 15.7 pmol/L at baseline to 89.7 +/- 24.0 pmol/L at the end of the procedure (F = 6.75, P = .0001), whereas it did not change in the angioplasty group. cAMP decreased in the PTCRA group, whereas it did not change in the angioplasty group. In conclusion, ET-1 increases less, ANP increases more, and cAMP decreases more during atherectomy than during plain balloon angioplasty.

Aged↗
PubMed1998

Beta-adrenergic blockade decreases coronary collateral blood flow in patients with coronary artery disease.

The effect of beta-adrenergic blockade on coronary collateral blood flow has not been clarified. We examined the acute effects of beta-adrenergic blockade on coronary collateral blood flow. Fifteen patients (Part A) with stable angina were studied while undergoing coronary angioplasty. According to the protocol, all patients underwent a minimum of three balloon inflations. Collateral flow velocity was determined during balloon inflations using the Doppler flow guidewire positioned distally to the lesion. The two tested balloon inflations, the second and third, were maintained for the same length of time. Between the second and third balloon inflations, 1 mg of propranolol was administered IC into the treated artery. Ten controls were studied following saline infusion. In 10 other patients (Part B), the effect of 1 mg IC propranolol on the coronary artery area distal to the lesion was studied, and five patients served as controls. In the treated group, in Part A blood pressure remained stable during the balloon inflations tested. Heart rate decreased from 79 +/- 11 to 73 +/- 12 beats/min (P < .05), velocity time integral from 9.6 +/- 8.2 to 6.6 +/- 4.1 cm (P < .05), and ST elevation from 1.3 +/- .9 to .9 +/- 1.0 mV (P < .05) between the second and third balloon inflations. In the controls the variables examined did not change during the balloon inflations tested. In Part B, neither propranolol nor normal saline had any significant effect on coronary artery lumen area. Thus, IC administration of beta-adrenergic blockade decreases coronary collateral blood flow, and this potentially worsens the ischemic zone. However, beta-adrenergic blockade ameliorates myocardial ischemia during coronary angioplasty.

Adrenergic beta-Antagonists↗
PubMed1998

Short-term atrioventricular sequential pacing does not adversely affect collateral blood flow: a study during angioplasty.

Altered sequence of ventricular activation sequence results in marked derangements in mechanical events. In the present study, we investigated the comparative effects of atrial and AV sequential pacing on collateral blood flow during angioplasty. Twenty-eight patients with stable angina and left anterior descending artery disease undergoing balloon angioplasty were studied. Collateral flow was determined during balloon inflation from the distal flow velocity of the ipsilateral artery (17 patients) or from the increase of the maximal diastolic blood flow velocity (Vc) of the contralateral artery (11 patients). Flow measurements were made using the Doppler flow guidewire. The relative resistance in the collateral vascular bed (RR) also was estimated in the latter group of patients. After the first balloon inflation, two similar consecutive balloon inflations were done under atrial and AV sequential pacing, at a rate of 15 beats/min higher than the sinus rate, in the absence of vasoactive medication. One minute after the initiation of pacing, the second and third balloon inflations were begun and the pacing continued until the balloon inflations were completed. In the ipsilateral group, average peak velocity was 84.6 +/- 24.2 mm/2 during atrial pacing and 82.7 +/- 29.7 mm/s during AV sequential pacing (P = NS). In the contralateral group, Vc was 18% +/- 12% during atrial pacing and 17% +/- 14% during AV sequential pacing, and the RR was 4.5 +/- 4.7 and 4.9 +/- 6.4, respectively (both P = NS). The coronary wedge/mean blood pressure was similar during the two tested balloon inflations. Short-term AV sequential pacing at rest does not adversely affect collateral blood flow and resistance in patients with left anterior descending artery disease.

Angioplasty, Balloon, Coronary↗
PubMed1998

Coronary flow reserve in the contralateral artery increases after successful coronary angioplasty in patients with spontaneously visible collateral vessels.

OBJECTIVE: To test the hypothesis that coronary flow reserve could increase in the angiographically normal contralateral artery after successful coronary angioplasty of an ipsilateral coronary artery. DESIGN: Coronary flow reserve was estimated using a Doppler flow guide wire, by giving intracoronary adenosine in the contralateral artery, before and 15 minutes after the end of angioplasty. SETTING: Tertiary referral centre. PATIENTS: 31 patients, mean (SD) age 56 (11) years, with stable angina and single vessel disease, undergoing angioplasty of the right coronary or the left anterior descending artery. RESULTS: In the contralateral artery baseline average peak velocity was 21 (9) cm/s before angioplasty and decreased to 12 (6) cm/s after (p < 0.005), while hyperaemic average peak velocity was 47 (19) cm/s before and decreased to 34 (15) cm/s after (p < 0.005). However, coronary flow reserve in the contralateral artery was 2.4 (0.7) before angioplasty and increased to 2.9 (0.6) after (p < 0.05). The contralateral coronary flow reserve after angioplasty increased by 0.8 (0.4) in 11 patients with visible collaterals before angioplasty and by 0.3 (0.6) in the remaining patients without visible collaterals (p < 0.05). Blood pressure and heart rate were unchanged after the procedure. CONCLUSIONS: Coronary flow reserve in an angiographically normal contralateral artery increases after successful coronary angioplasty of the ipsilateral artery in patients with spontaneously visible collateral vessels before the procedure.

Adenosine↗
PubMed1998

Antibiotic resistance of Salmonella spp. and Listeria spp. isolates from traditionally made fresh sausages in Greece.

Sixty-five samples of traditionally made fresh sausages obtained from retail shops and butcher shops in northern Greece were screened for the presence of Salmonella spp. and Listeria spp. Salmonella spp. were found in 20% of the samples tested (54% Salmonella typhimurium and 46% Salmonella enteritidis). The prevalence of Listeria spp. in the samples was 26% (12% Listeria monocytogenes, 76% Listeria innocua, and 12% Listeria welshimeri). Nine of 13 Salmonella isolates were found to be resistant to ampicillin and 4 of 13 showed intermediate sensitivity; 1 of 13 was found to be resistant to chloramphenicol and 1 of 13 to tetracycline. Two strains of Salmonella typhimurum were multiresistant (resistant to ampicillin, chloramphenicol, and norfloxacin). All Listeria isolates were sensitive to the antibacterial agents tested that are commonly used for the treatment of human listeriosis.

Animals↗
PubMed1997

Acute hemodynamic effects of estrogen administration in postmenopausal women.

The hemodynamic effects of estrogens in replacement doses have not been fully clarified; therefore, we studied the acute hemodynamic changes after 0.625 and 1.25 mg of conjugated estrogens, administered intravenously, using a thermodilution catheter, in postmenopausal women without structural heart disease. Pulmonary and systemic pressures and resistances and stroke volume did not change compared with baseline, but heart rate and cardiac output decreased significantly, which may be associated with estrogen's previously described calcium-blocking effect or with a more recently contemplated beta-blocking action.

Aged↗
PubMed1997

Anteriorly displaced transverse fractures of the sacrum in adolescents: report of two cases.

A fracture of the sacrum at the level of the first and second segments, with forward displacement of the first segment, is a very rare injury in adolescents. The cases of two patients, who both suffered a displaced transverse fracture of the sacrum with resulting neural disturbance, are reported here. We consider that these unstable fractures may be treated surgically, by extensive laminectomies of the lumbosacral area and posterolateral fusion. Stabilization of the displaced fracture is possibly preferable, because it provides the prerequisites for early mobilization and reduces pain.

Adolescent↗
PubMed1996

Maximal blood lactate level acts as a major discriminant variable in exercise testing for coronary artery disease detection in men.

BACKGROUND: The interpretation of exercise stress testing for coronary artery disease detection is affected by the many differences in chosen variables and mathematical methods. We conducted a prospective trial to evaluate a global muscle fatigue parameter--the blood lactate level achieved at maximal exercise--as a method of distinguishing between diseased and nondiseased coronary status. METHODS AND RESULTS: We evaluated 236 consecutive male patients without previous myocardial infarction who had been referred for the diagnosis of coronary artery disease. None of the patients had cardiomyopathy, severe cardiac heart failure, or valvular heart disease. Blood lactate concentration at maximal exercise was measured as well as other classic variables. Correlations between variables and coronary status as assessed by coronary arteriography were described using receiver operating characteristic (ROC) curves and logistic regression analysis. The first four most powerful variables (lactate level, maximal power output, exercise duration, and percentage of maximal predicted heart rate), which are directly representative of the global functional capacity, showed values of 0.777, 0.775, 0.760, and 0.740, respectively, by ROC curve analysis. Mean +/- SD blood lactate level at peak exercise reached 7.68 +/- 2.70 mmol/L in the 153 diseased and 10.56 +/- 2.75 mmol/L in the 83 nondiseased patients (P < .0001). After adjustment for other variables, blood lactate level remained a significant predictor of coronary artery disease by logistic regression analysis (adjusted odds ratio, 1.2; confidence interval, 1.04 to 1.4). CONCLUSIONS: Global muscle fatigue as assessed by lactate levels in the blood at maximal exercise appears to be a powerful distinguisher of diseased and nondiseased coronary status.

Adult↗
PubMed1996

Direct genetic detection of Dobrava virus in Greek and Albanian patients with hemorrhagic fever with renal syndrome.

Blood samples were collected from an Albanian and a Greek patient with hemorrhagic fever with renal syndrome and tested by reverse transcriptase-polymerase chain reaction. The genetic detection assay amplified hantavirus-specific DNA fragments from RNA extracted from the blood of the patients; nucleotide sequence analysis revealed that the causative agent of the disease was Dobrava virus. These findings suggest that Dobrava virus (which was originally isolated from the lungs of an Apodenws flavicollis mouse in Slovenia) is endemic throughout the Balkan States and causes overt human disease.

Adult↗