Biomedical subjects

Andreas Voss

Publications and source records attributed to Andreas Voss.

At least 19 recordsLinked to original sources

PubMed2007

Extension of the Jones matrix formalism to higher-order transverse modes.

The well-known Jones matrix formalism, which can be directly applied to the propagation of the polarization of fundamental (TEM(00)) laser resonator modes, has to be modified for higher-order transverse modes. It is shown that this can be done in straightforward manner by using N x N matrices instead of the 2 x 2 Jones matrices, where N denotes the number of orthogonal polarization states of the transverse mode under consideration. The most common case of TEM(01) Hermite-Gaussian modes, where N is four, is discussed in detail.

Journal Article↗

PubMed2006

Scaling characteristics of heart rate time series before the onset of ventricular tachycardia.

Ventricular tachycardia (VT) provokes sudden cardiac death (SCD), which is a major cause of mortality in developed countries. Implantable cardioverter-defibrillators (ICDs) are an efficient therapy for SCD prevention. In this study we analyze heart rate variability (HRV) in data stored by ICDs. In 29 patients exhibiting VT episodes, the last 1000 normal beat-to-beat intervals are analyzed and compared to an individually acquired control time series (CON). HRV analysis is performed with standard parameters of time and frequency domain as suggested by the HRV Task Force. For scaling analyses of heart rate time series, the fractal dimension is analysed, applying Higuchi's algorithm (HFD). Furthermore, detrended fluctuation analysis (DFA) is performed. None of the standard HRV parameters shows significant differences between CON and VT. Before the onset of VT, the scaling characteristics by means of HFD and DFA are significantly changed. In conclusion, scaling analysis reveals changes in autonomic heart rate modulation preceding VT.

Algorithms↗

PubMed2006

Decreased baroreflex sensitivity in acute schizophrenia.

Decreased vagal activity has been described in acute schizophrenia and might be associated with altered cardiovascular regulation and increased cardiac mortality. The aim of this study was to assess baroreflex sensitivity in the context of psychopathology. Twenty-one acute, psychotic, unmedicated patients with a diagnosis of paranoid schizophrenia were investigated after admission to the hospital. Results were compared with 21 healthy volunteers matched with respect to age and sex. Cardiovascular parameters obtained included measures for heart rate variability, baroreflex sensitivity, as well as cardiac output, left ventricular work index, and total peripheral resistance. All parameters investigated were analyzed using linear and novel nonlinear techniques. Positive and negative symptoms were assessed to estimate the impact of psychopathology on autonomic parameters. Subjects with acute schizophrenia showed reduction of baroreflex sensitivity accompanied by tachycardia and greatly increased left ventricular work index. Nonlinear parameters of baroreflex sensitivity correlated with positive symptoms. For heart rate variability, mainly parameters indicating parasympathetic modulation were decreased. Vascular pathology could be excluded as a confounding factor. These results reflect a dysfunctional cardiovascular regulation in acute schizophrenic patients at rest. The changes are similar to adaptational regulatory processes following stressful mental or physical tasks in healthy subjects. This study suggests that hyperarousal in acute schizophrenia is accompanied by decreased efferent vagal activity, thus increasing the risk for cardiovascular mortality. Future studies are warranted to examine the role of the sympathetic system and possible autonomic differences in hyperarousal induced by anxiety and/or external stressful events.

Adult↗

PubMed2006

Community-acquired MRSA and pig-farming.

BACKGROUND: Sporadic cases of CA-MRSA in persons without risk-factors for MRSA carriage are increasing. CASE PRESENTATION: We report a MRSA cluster among family members of a pig-farmer, his co-workers and his pigs. Initially a young mother was seen with mastitis due to MRSA. Six months later her baby daughter was admitted to the hospital with pneumococcal otitis. After staying five days in hospital, the baby was found to be MRSA positive. At that point it was decided to look for a possible source, such as other family members and house-hold animals, including pigs on the farm, since those were reported as a possible source of MRSA earlier. Swabs were taken from the throat and nares of family members and co-workers. A veterinarian obtained swabs from the nares, throat and perineum of 10 pigs. Swabs were cultured following a national protocol to detect MRSA that included the use of an enrichment broth. Animal and human strains were characterized by PFGE, spa-typing, MLST analysis, SSCmec, AGR typing, and the detection for PVL, LukM, and TSST toxin genes. Three family members, three co-workers, and 8 of the 10 pigs were MRSA positive. With the exception of the initial case (the mother) all persons were solely colonized, with no signs of clinical infections. After digestion with SmaI, none of the strains showed any bands using PFGE. All isolates belonged to spa type t108 and ST398. CONCLUSION: 1. This report clearly shows clonal spread and transmission between humans and pigs in the Netherlands. 2. MLST sequence type 398 might be of international importance as pig-MRSA, since this type was shown earlier to be present in epidemiologically unrelated French pigs and pig-farmers. 3. Research is needed to evaluate whether this is a local problem or a new source of MRSA, that puts the until now successful Search and Destroy policy of the Netherlands at risk.

Adult↗

PubMed2006

Hand hygiene among laboratory workers.

We performed a study to measure the compliance of laboratory personnel with different components of hand hygiene. The level of compliance at the end of duty was 100%; however, 36.7% of subjects wore a ring, 46.9% wore a watch, and 6.1% wore a bracelet. Pathogenic microorganisms were exclusively found on hands of laboratory personnel who wore jewelry. After interventions, the level of compliance with the no-jewelry policy among laboratory personnel showed sustained improvement. Efforts to improve hand hygiene should be directed not only at healthcare workers but also at laboratory personnel.

Female↗

PubMed2006

Scaling graphs of heart rate time series in athletes demonstrating the VLF, LF and HF regions.

Scaling analysis of heart rate time series has emerged as a useful tool for the assessment of autonomic cardiac control. We investigate the heart rate time series of ten athletes (five males and five females), by applying detrended fluctuation analysis (DFA). High resolution ECGs are recorded under standardized resting conditions over 30 min and subsequently heart rate time series are extracted and artifacts filtered. We find three distinct regions of scale invariance, which correspond to the well-known VLF, LF and HF bands in the power spectra of heart rate variability. The scaling exponents alpha are alpha(HF): 1.15 [0.96-1.22], alpha(LF): 0.68 [0.57-0.84], alpha(VLF): 0.83[0.82-0.99], p < 10(-5)). In conclusion, DFA scaling exponents of heart rate time series should be fitted to the VLF, LF and HF ranges, respectively.

Adult↗

PubMed2006

Reduced baroreflex sensitivity in acute alcohol withdrawal syndrome and in abstained alcoholics.

Acute alcohol withdrawal is often associated with increased sympathetic activity, and a decreased baroreflex sensitivity (BRS) can be assumed. Parameters of heart rate variability (HRV), blood pressure variability (BPV), BRS as well as cardiac index (CI), left ventricular work index (LVWI) and total peripheral resistance (TPR) were investigated in 20 patients undergoing acute alcohol withdrawal and matched controls. Measures were obtained during the peak of withdrawal symptomatology prior to treatment as well as 2 and 24h under continuous clomethiazole treatment. Alcohol withdrawal scores were obtained and correlated with autonomic measures. In addition, parameters were assessed in 15 subjects who abstained from alcohol after long-term intake. We found a severe down-regulation of BRS during acute alcohol withdrawal and to a milder extent in abstained alcoholics. Furthermore, HRV and BPV did not unequivocally reveal signs of elevated sympathetic activity. Non-linear parameters of HRV and parameters of BRS correlated with the severity of AWS. The distinct decrease of BRS in AWS and in long-term abstained subjects described here is of importance since similar alterations have been identified as independent prognostic factors for cardiac mortality in other diseases.

Acute Disease↗

PubMed2006

Ventilator associated pneumonia and infection control.

Ventilator associated pneumonia (VAP) is the leading cause of morbidity and mortality in intensive care units. The incidence of VAP varies from 7% to 70% in different studies and the mortality rates are 20-75% according to the study population. Aspiration of colonized pathogenic microorganisms on the oropharynx and gastrointestinal tract is the main route for the development of VAP. On the other hand, the major risk factor for VAP is intubation and the duration of mechanical ventilation. Diagnosis remains difficult, and studies showed the importance of early initiation of appropriate antibiotic for prognosis. VAP causes extra length of stay in hospital and intensive care units and increases hospital cost. Consequently, infection control policies are more rational and will save money.

Bacterial Infections↗

PubMed2006

Autonomic cardiovascular control in pregnancies with abnormal uterine perfusion.

BACKGROUND: Abnormal uterine perfusion is associated with the development of hypertensive pregnancy disorders. However, its impact on maternal autonomic cardiovascular control is poorly understood. The aim of our study was to investigate the adaptation of autonomic control during pregnancy with abnormal uterine perfusion with normal and pathologic outcome in comparison to normal pregnancies. based on blood pressure variability (BPV), baroreflex sensitivity (BRS), and heart rate variability (HRV) analyses. METHODS: A total of 32 healthy pregnant women (CON, age 28 years, range 24 to 31 years); 16 women with abnormal uterine perfusion and normal outcome (AP-NO, age 29 years, range 28 to 33 years); and 19 women with abnormal uterine perfusion and pathologic outcome (AP-PO, age 26 years, range 25 to 30 years), were recruited for this longitudinal study. Beginning in the 20th week of pregnancy, the women were monitored every fourth week until delivery. For the analysis of BPV, BRS, and HRV, high-resolution ECG, and noninvasive continuous blood pressure (BP) recordings were taken simultaneously for 30 minutes. RESULTS: CON showed pregnancy-induced adaptation of cardiovascular control; in the course of gestation BPV was increased while parameters of HRV and BRS were reduced. On the contrary, no changes during the second half of pregnancy could be observed in pregnancies with abnormal perfusion. Variability parameters were significantly altered in women with abnormal perfusion compared with CON, whereas these changes were more pronounced in AP-PO compared with AP-NO. CONCLUSIONS: Abnormal uterine perfusion, independently of the pregnancy outcome, has a significant impact on maternal cardiovascular control. Measures of BPV, BRS and HRV might be used for improved risk stratification.

Adult↗

PubMed2006

A diffusion model analysis of adult age differences in episodic and semantic long-term memory retrieval.

Two experiments investigated adult age differences in episodic and semantic long-term memory tasks, as a test of the hypothesis of specific age-related decline in context memory. Older adults were slower and exhibited lower episodic accuracy than younger adults. Fits of the diffusion model (R. Ratcliff, 1978) revealed age-related increases in non-decisional reaction time for both episodic and semantic retrieval. In Experiment 2, an age difference in boundary separation also indicated an age-related increase in conservative criterion setting. For episodic old-new recognition (Experiment 1) and source memory (Experiment 2), there was an age-related decrease in the quality of decision-driving information (drift rate). As predicted by the context-memory deficit hypothesis, there was no corresponding age-related decline in semantic drift rate.

Adolescent↗

PubMed2006

Genotypic analysis of Acinetobacter bloodstream infection isolates in a Turkish university hospital.

Acinetobacter baumannii is a significant pathogen of bloodstream infections in hospital patients that frequently causes single clone outbreaks. We aimed to evaluate the genetic relatedness and antimicrobial susceptibility of Acinetobacter spp. bloodstream isolates, in order to obtain insight into their cross-transmission. This prospective study was conducted at the Erciyes University Hospital. During a 1-y period, all patients with nosocomial BSI caused by Acinetobacter spp. were included in the study. All data with regard to the patients, underlying diseases and risk factors for BSI and the severity of disease were collected. Blood culture isolates of Acinetobacter spp. were identified according to their morphology and biochemical reactions. The antimicrobial susceptibility was determined using the Kirby-Bauer disk diffusion test according to the NCCLS; the genetic relatedness of isolates was determined by RAPD-PCR analysis and pulsed-field gel electrophoresis (PFGE). 41 patients acquired a nosocomial bloodstream infection caused by A. baumanii during this period. 88% of these infections (36 of 41) occurred while the patients were treated in the intensive care unit. Nearly 80% of the isolates belonged to 3 genotypes, suggesting cross-transmission in ICU settings where infection control practices are poor. All Acinetobacter isolates were multidrug-resistant and the crude mortality of patients infected with A. baumanii was 80.5%. We concluded that the genetic relatedness of Acinetobacter spp. causing BSI was very high, indicating cross-transmission within the ICU setting. Essential components of an infection control programme to prevent nosocomial transmission of A. baumannii are early detection of colonized patients, followed by strict attention to standard precautions and contact isolation.

APACHE↗

PubMed2006

A combined technique for predicting pre-eclampsia: concurrent measurement of uterine perfusion and analysis of heart rate and blood pressure variability.

OBJECTIVE: Pre-eclampsia is a serious complication of pregnancy with high morbidity and mortality and an incidence of 3-5% in all pregnancies. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients have pathological uterine perfusion in the second trimester, perfusion disturbance has a positive predictive accuracy (PPA) only of approximately 30%. METHODS: Non-invasive continuous blood pressure recordings were taken simultaneously via a finger cuff for 30 min. Time series of systolic as well as diastolic beat-to-beat pressure values were extracted to analyse heart rate and blood pressure variability and baroreflex sensitivity in 102 second-trimester pregnancies, to assess predictability for pre-eclampsia (n = 16). All women underwent Doppler investigations of the uterine arteries. RESULTS: We identified a combination of three variability and baroreflex parameters to best predict pre-eclampsia several weeks before clinical manifestation. The discriminant function of these three parameters classified patients with later pre-eclampsia with a sensitivity of 87.5%, a specificity of 83.7%, and a PPA of 50.0%. Combined with Doppler investigations of uterine arteries, PPA increased to 71.4%. CONCLUSIONS: This technique of incorporating one-stop clinical assessment of uterine perfusion and variability parameters in the second trimester produces the most effective prediction of pre-eclampsia to date.

Adult↗

PubMed2006

Heart rate variability, blood pressure variability, and baroreflex sensitivity in overtrained athletes.

OBJECTIVE: To assess the effects of abruptly intensified physical training on cardiovascular control. DESIGN: Retrospective longitudinal study. SETTING: Research laboratory. PARTICIPANTS: Ten healthy athletes (5 men and 5 women) from track and field as well as triathlon. INTERVENTIONS: A 2-week training camp, including daily stepwise increasing cycling tests, running of 40 minutes, and additional cycling of 60 minutes. MAIN OUTCOME MEASUREMENTS: Time and frequency domain parameters of resting heart rate and blood pressure variability (HRV and BPV) and baroreflex sensitivity (BRS), before, during, and after the training camp. RESULTS: We found significantly reduced HRV during the training camp (mean beat-to-beat interval: 1042 [937 to 1194] ms vs. 933 [832 to 1103] ms vs. 1055 [947 to 1183] ms, P < 0.01; root-mean-square of beat-to-beat interval differences: 68 [52 to 95] ms vs. 52 [38 to 71] ms vs. 61 [48 to 78] ms, P < 0.05). Further, BRS was significantly reduced: 25.2 (20.4 to 40.4) ms/mmHg vs. 17.0 (12.9 to 25.7) ms/mmHg vs. 25.7 (18.8 to 29.1) ms/mmHg, P < 0.05. These effects disappeared at a large degree after 3 to 4 days of recovery. CONCLUSION: Abruptly intensified physical training results in an altered autonomic cardiovascular activity towards parasympathetic inhibition and sympathetic activation that can be monitored by means of HRV and BRS analyses and might provide useful markers to avoid the overtraining syndrome.

Adult↗

PubMed2006

Heart rate variability and sympathetic skin response in male patients suffering from acute alcohol withdrawal syndrome.

BACKGROUND: Many symptoms of alcohol withdrawal (AW) such as tachycardia or elevated blood pressure might be explained by increased peripheral and central adrenergic activity. In contrast to many neurochemical studies of sympathetic activation during AW, only very few studies investigated autonomic balance using neurophysiological methods. METHODS: We investigated heart rate variability (HRV) and sympathetic skin response (SSR) in male patients suffering from mild AW syndrome (n = 20, no treatment required) and in patients with moderate to severe AW syndrome (n = 20, clomethiazole treatment) in the acute stage. Sympathovagal influence was quantified using measures of time and frequency domain of HRV as well as modern nonlinear parameters (compression entropy). Furthermore, we obtained latencies and amplitudes of SSR to quantify isolated sympathetic influence. Measures were obtained during the climax of withdrawal symptomatology before treatment, 1 day after climax, and shortly before discharge from hospital. Alcohol withdrawal scores were obtained and correlated to autonomic measures. RESULTS: Ambulatory blood pressure and AW scores revealed characteristic withdrawal symptoms in both patient groups. Apart from the nonlinear parameter compression entropy, Hc, measures of HRV revealed no sign of autonomic dysfunction in contrast to the significantly increased heart rates at the time of admission. Latencies and amplitudes of SSR did not indicate any increase of sympathetic activity. A negative correlation was found between Hc and mental withdrawal symptoms. CONCLUSIONS: We show here that classical measures for autonomic nervous system activity such as HRV and SSR are not suitable for describing the autonomic changes seen in acute AW, although a major role for the sympathetic nervous system has been proposed. This might be due to multiple dysregulation of metabolites in AWS or to subtle alcohol-induced damage to neuronal structures, issues that should be addressed in future studies.

Adult↗

PubMed2006

Altered autonomic cardiac control predicts restenosis after percutaneous coronary intervention.

BACKGROUND: Early and late restenosis in up to 30% remains a major problem for long-term success after percutaneous coronary intervention (PCI). Compared to bare metal stents, the use of drug-eluting stents reduces restenosis below 10%, but implant coasts have to be considered. In restenosis noninvasive testing lacks diagnostic power. We applied a new approach to identify patients with a high risk for restenosis after PCI by combining heart rate (HR) and blood pressure variability (BPV) analyses. METHODS: In 52 patients with clinical suspicion of restenosis and history of PCI, we investigated patterns of cardiovagal autonomic regulation prior to cardiac catheterization. The patients were separated in (i) patients with restenosis (CAD+R) and (ii) patients without restenosis (CAD-R), where restenosis is defined as a stenosis greater than 75% of luminal diameter in at least one main vessel. The following parameters/methods were evaluated: Canadian Cardiovascular Society grade (CCS-grade), vessel disease score (CAD-level), left ventricular ejection fraction (LVEF), heart rate variability (HRV), BPV, baroreflex sensitivity (BRS), as well as HR turbulence and blood pressure (BP) potentiation caused by premature ventricular complexes. RESULTS: Whereas age, LVEF, CAD-level, CCS-grade, and mean BP did not differ between CAD+R and CAD-R, significant differences were found in (i) BPV: diastolic LF/P, systolic, and diastolic UVLF, (ii) in BRS: slope of tachycardic sequences, and (iii) in extrasystolic parameters: heart rate turbulence onset (HRTO) and potentiation of systolic BP (SBPP). Standard HRV parameters did not show significant differences between the groups. Using the two parameters diastolic LF/P (threshold >0.2) and HRTO (threshold >0) restenosis were predicted in 83.4%. CONCLUSIONS: These results demonstrate that indicators of sympathetic activation or vagal depression identify restenosis in patients after PCI, thus opening a perspective for a new noninvasive monitoring.

Angioplasty, Balloon, Coronary↗

PubMed2006

Presence of a novel DNA methylation enzyme in methicillin-resistant Staphylococcus aureus isolates associated with pig farming leads to uninterpretable results in standard pulsed-field gel electrophoresis analysis.

Genomic DNA from methicillin-resistant Staphylococcus aureus isolates recovered from pigs and their caretakers proved resistant to SmaI digestion, leading to uninterpretable results in standard pulsed-field gel electrophoresis. This is the result of a yet unknown restriction/methylation system in the genus Staphylococcus with the recognition sequence CCNGG.

5-Methylcytosine↗

PubMed2006

Compression entropy contributes to risk stratification in patients with cardiomyopathy.

Sudden cardiac death (SCD) is a leading cause of mortality with an incidence of 3 million cases per year worldwide. Therapies for patients who have survived an SCD episode or have a high risk of developing lethal ventricular arrhythmia are well established and depend mainly on risk stratification. In this study we investigated the suitability of the non-linear measure compression entropy (Hc) for improved risk prediction in cardiac patients. We recorded 24-h Holter ECG for 300 patients with congestive heart failure (CHF). During a mean follow-up period of 12 months, 32 patients died due to a cardiac event. Hc depends on the compression parameters window length w and buffer length b, which were optimised by analysing a subgroup of patients. Compression entropies based on the beat-to-beat interval (BBI) were subsequently calculated and compared with standard heartrate variability parameters. Statistical analysis revealed significant differences between high- and low-risk CHF patients in standard HRV measures, as well as compression entropy based on the BBI (cardiac death, p = 0.005; SCD, p = 0.02). In conclusion, the implementation of non-linear compression entropy analysis in multivariate analysis seems to be useful for enhanced risk stratification of cardiac death, especially SCD, in ischaemic cardiomyopathy patients.

Aged↗

PubMed2006

Multivariate and multidimensional analysis of cardiovascular oscillations in patients with heart failure.

Within 5 years of first diagnosis, nearly 60% of patients with heart failure (HF) suffer from cardiac death. Early diagnosis of HF and reliable risk prediction are still required. Therefore, the objective of this study was to develop a parameter set for enhanced risk stratification in HF patients. In 43 patients suffering from HF (NYHA class > or =II, ejection fraction <45%) and 10 healthy subjects (REF), heart rate and blood pressure variability (HRV and BPV), interactions between heart rate and blood pressure (joint symbolic dynamics, JSD) and blood pressure morphology (BPM) were analysed. BPV, BPM and JSD measures revealed high significance (p<0.0001) in discriminating REF and HF. A set of three parameters from BPV, JSD and BPM was developed for risk stratification (sensitivity 76.5%, specificity 84.2%, area under the receiver operating characteristic curve 81.4%) in patients with HF.

Biological Clocks↗