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Biomedical subjects

K Schwab

Publications and source records attributed to K Schwab.

At least 19 recordsLinked to original sources
PubMed2007

Fetal body weight and the development of the control of the cardiovascular system in fetal sheep.

Reduced birth weight predisposes to cardiovascular diseases in later life. We examined in fetal sheep at 0.76 (n = 18) and 0.87 (n = 17) gestation whether spontaneously occurring variations in fetal weight affect maturation of autonomic control of cardiovascular function. Fetal weights at both gestational ages were grouped statistically in low (LW) and normal weights (NW) (P < 0.01). LW fetuses were within the normal weight span showing minor growth dysproportionality at 0.76 gestation favouring heart and brain, with a primary growth of carcass between 0.76 and 0.87 gestation (P < 0.05). While twins largely contributed to LW fetuses, weight differences between singletons and twins were absent at 0.76 and modest at 0.87 gestation, underscoring the fact that twins belong to normality in fetal sheep not constituting a major malnutritive condition. Mean fetal blood pressure (FBP) of all fetuses was negatively correlated to fetal weight at 0.76 but not 0.87 gestation (P < 0.05). At this age, FBP and baroreceptor reflex sensitivity were increased in LW fetuses (P < 0.05), suggesting increased sympathetic activity and immaturity of circulatory control. Development of vagal modulation of fetal heart rate depended on fetal weight (P < 0.01). These functional associations were largely independent of twin pregnancies. We conclude, low fetal weight within the normal weight span is accompanied by a different trajectory of development of sympathetic blood pressure and vagal heart rate control. This may contribute to the development of elevated blood pressure in later life. Examination of the underlying mechanisms and consequences may contribute to the understanding of programming of cardiovascular diseases.

Animals↗
PubMed2006

Time-variant parametric estimation of transient quadratic phase couplings between heart rate components in healthy neonates.

The heart rate variability (HRV) can be taken as an indicator of the coordination of the cardio-respiratory rhythms. Bispectral analysis using a direct (fast Fourier transform based) and time-invariant approach has shown the occurrence of a quadratic phase coupling (QPC) between a low-frequency (LF: 0.1 Hz) and a high-frequency (HF: 0.4-0.6 Hz) component of the HRV during quiet sleep in healthy neonates. The low-frequency component corresponds to the Mayer-Traube-Hering waves in blood pressure and the high-frequency component to the respiratory sinus arrhythmia (RSA). Time-variant, parametric estimation of the bispectrum provides the possibility of quantifying QPC in the time course. Therefore, the aim of this work was a parametric, time-variant bispectral analysis of the neonatal HRV in the same neonates used in the direct, time-invariant approach. For the first time rhythms in the time course of QPC between the HF component and the LF component could be shown in the neonatal HRV.

Arrhythmia, Sinus↗
PubMed2005

Time-variant parametric estimation of transient quadratic phase couplings during electroencephalographic burst activity.

OBJECTIVES: Electroencephalographic burst activity characteristic of burst-suppression pattern (BSP) in sedated patients and of burst-interburst pattern (BIP) in the quiet sleep of healthy neonates have similar linear and non-linear signal properties. Strong interrelations between a slow frequency component and rhythmic, spindle-like activities with higher frequencies have been identified in previous studies. Time-varying characteristics of BSP and BIP prevent a definite patternrelated analysis. A continuous estimation of the bispectrum is essential to analyze these patterns. Parametric bispectral approaches provide this opportunity. METHODS: The adaptation of an AR model leads to a parametric bispectrum by using the transfer function of the estimated AR filter. Time-variant parametric bispectral approaches require an estimation of AR parameters which consider higher order moments to preserve phase information. Accordingly, a time-variant parametric estimation of the bispectrum was introduced. Data driven simulations were performed to provide optimal parameters. BSP (12 patients) and BIP (6 neonates) were analyzed using this novel approach. RESULTS: Significant differences in the time course of burst pattern during BSP and burst-like pattern before the onset of BSP could be shown. A rhythmic quadratic phase coupling (period 10 sec) was identified during BIP in all neonates. CONCLUSION: Quadratic phase couplings during BSP increases in the time course depending on depth of sedation. The visually detected burst activity in BIP is only the temporarily observable EEG correlate of a hidden neural process. Time-variant bispectral approaches offer the possibility of a better characterization of underlying neural processes leading to improved diagnostic tools used in clinical routine.

Algorithms↗
PubMed2004

On the spatio-temporal organisation of quadratic phase-couplings in 'tracé alternant' EEG pattern in full-term newborns.

OBJECTIVE: The time courses of quadratic phase-coupling (QPC) of electroencephalographic burst and interburst patterns of the 'trace alternant' (TA) in full-term newborns have been quantified. METHODS: Using the Gabor expansion, a fast Fourier transformation based method, biamplitude, bicoherence and phase-bicoherence time courses of both burst and interburst patterns have been determined (common average reference EEG recordings). With a frequency resolution of 0.25 Hz and a frequency grid of 1-1.5 <==> 3.5-4.5 Hz (region-of-interest), a number of 15 frequency pairs result. These pairs have been investigated. RESULTS: The burst and the interburst patterns are characterized by temporally and topographically different QPC profiles. All differences are dominant at the electrode Fp1 followed by Fp2. There is a significant difference (combined multiple and global test strategy) in the QPC characteristics between both patterns within the time period from 0.75 to 1.5 s after the pattern onset at electrode Fp1. The maximal QPC in burst patterns (especially at Fp1) can be observed during this time period. In contrast to this finding, maximal QPC in interburst patterns (at Fp1) are reached immediately after the onset and at 3 s. Summarising all findings, a QPC-rhythm of 0.1 Hz during TA can be assumed. CONCLUSIONS: It can be assumed that the QPC rhythm of the TA is generated by a pattern-spanning time-variant phase-locking process and there are indications for a possible correspondence between the QPC rhythm and vegetative rhythms. SIGNIFICANCE: This study showed that advanced, time-variant analysis methods quantifying QPC rhythms are able to add new scientific information to the understanding of nature, characteristics and significance of TA in the neonatal EEG.

Algorithms↗
PubMed2000

Cognitive rehabilitation for traumatic brain injury: A randomized trial. Defense and Veterans Head Injury Program (DVHIP) Study Group.

CONTEXT: Traumatic brain injury (TBI) is a principal cause of death and disability in young adults. Rehabilitation for TBI has not received the same level of scientific scrutiny for efficacy and cost-efficiency that is expected in other medical fields. OBJECTIVE: To evaluate the efficacy of inpatient cognitive rehabilitation for patients with TBI. DESIGN AND SETTING: Single-center, parallel-group, randomized trial conducted from January 1992 through February 1997 at a US military medical referral center. PATIENTS: One hundred twenty active-duty military personnel who had sustained a moderate-to-severe closed head injury, manifested by a Glasgow Coma Scale score of 13 or less, or posttraumatic amnesia lasting at least 24 hours, or focal cerebral contusion or hemorrhage on computed tomography or magnetic resonance imaging. INTERVENTIONS: Patients were randomly assigned to an intensive, standardized, 8-week, in-hospital cognitive rehabilitation program (n=67) or a limited home rehabilitation program with weekly telephone support from a psychiatric nurse (n=53). MAIN OUTCOME MEASURES: Return to gainful employment and fitness for military duty at 1-year follow-up, compared by intervention group. RESULTS: At 1-year follow-up, there was no significant difference between patients who had received the intensive in-hospital cognitive rehabilitation program vs the limited home rehabilitation program in return to employment (90% vs 94%, respectively; P=.51; difference, 4% [95% confidence interval ¿CI¿, -5% to 14%]) or fitness for duty (73% vs 66%, respectively; P=. 43; difference, 7% [95% CI, -10% to 24%]). There also were no significant differences in cognitive, behavioral, or quality-of-life measures. In a post-hoc subset analysis of patients who were unconscious for more than 1 hour (n = 75) following TBI, the in-hospital group had a greater return-to-duty rate (80% vs 58%; P=. 05). CONCLUSIONS: In this study, the overall benefit of in-hospital cognitive rehabilitation for patients with moderate-to-severe TBI was similar to that of home rehabilitation. These findings emphasize the importance of conducting randomized trials to evaluate TBI rehabilitation interventions. JAMA. 2000;283:3075-3081

Absenteeism↗
PubMed2000

Measurement of the quantum of thermal conductance

The physics of mesoscopic electronic systems has been explored for more than 15 years. Mesoscopic phenomena in transport processes occur when the wavelength or the coherence length of the carriers becomes comparable to, or larger than, the sample dimensions. One striking result in this domain is the quantization of electrical conduction, observed in a quasi-one-dimensional constriction formed between reservoirs of two-dimensional electron gas. The conductance of this system is determined by the number of participating quantum states or 'channels' within the constriction; in the ideal case, each spin-degenerate channel contributes a quantized unit of 2e(2)/h to the electrical conductance. It has been speculated that similar behaviour should be observable for thermal transport in mesoscopic phonon systems. But experiments attempted in this regime have so far yielded inconclusive results. Here we report the observation of a quantized limiting value for the thermal conductance, Gth, in suspended insulating nanostructures at very low temperatures. The behaviour we observe is consistent with predictions for phonon transport in a ballistic, one-dimensional channel: at low temperatures, Gth approaches a maximum value of g0 = pi2kB2T/3h, the universal quantum of thermal conductance.

Journal Article↗
PubMed1999

A novel Ggamma isolated from Drosophila constitutes a visual G protein gamma subunit of the fly compound eye.

Visual transduction in the compound eye of flies is a well established model system for the study of G protein-coupled transduction pathways. To characterize key components of the phototransduction cascade we performed substractive hybridization screening. We cloned the cDNA coding for the visual Ggamma (Ggamma(e)) subunit from Drosophila which had so far eluded identification at the molecular level. Northern blot analysis revealed the presence of a major, 1.4-kilobase(kb) Ggamma(e) transcript and two minor transcripts of 1.8 and 6 kb in size. The major 1.4-kb mRNA is expressed preferentially in the eye. The spatial expression pattern determined for Ggamma(e) as well as co-immunoprecipitation experiments demonstrated that Ggamma(e) dimerizes with Gbeta(e) to form the heterodimeric Gbetagamma subunit which functions in visual transduction in the Drosophila compound eye. Ggamma(e) shares common characteristics with the visual Ggamma subunits of human rod and cone photoreceptors although different classes of Galpha subunits are employed in vertebrate and invertebrate phototransduction. By the molecular cloning and characterization of the visual gamma subunit of Drosophila one of the few missing links in the well studied Drosophila phototransduction cascade has been characterized to complete our knowledge about the Drosophila visual transduction pathway.

Amino Acid Sequence↗
PubMed1999

Patterning of the R7 and R8 photoreceptor cells of Drosophila: evidence for induced and default cell-fate specification.

Opsin gene expression in the R7 and R8 photoreceptor cells of the Drosophila compound eye is highly coordinated. We have found that the R8 cell specific Rh5 and Rh6 opsins are expressed in non-overlapping sets of R8 cells, in a precise pairwise fashion with Rh3 and Rh4 in the R7 cells of individual ommatidia. Removal of the R7 cells in sevenless, boss or sina mutants, disrupts Rh5 expression and dramatically increases the number of Rh6-expressing R8 cells. This suggests that the expression of Rh5 may be induced by an Rh3-expressing R7 cell, whereas Rh6 expression is most likely a default state of the R8 cell. We found that the paired expression of opsin genes in the R7 and R8 cells occurs in a sevenless and boss independent manner. Furthermore, we found that the generation of both Rh3- and Rh4-expressing R7 cells can occur in the absence of an R8 cell. These results suggest that the specification of opsin expression in the R7 cells may occur autonomously, whereas the R7 photoreceptor cell may be responsible for regulating a binary developmental switch between induced and default cell-fates in the R8 cell.

Amino Acid Sequence↗
PubMed1998

Motivation for traumatic brain injury rehabilitation questionnaire (MOT-Q): reliability, factor analysis, and relationship to MMPI-2 variables.

A Likert scale questionnaire was developed to assess motivation for postacute rehabilitation by traumatic brain injury patients. Items were designed to reflect head-injured individuals' statements about their attitudes toward head injury rehabilitation. Factors such as denial of illness, anger, compliance with treatment, and medical information seeking behavior were used to assess unfavorable and favorable components of motivation. Reliability was assessed using Cronbach's Alpha, which was found to be 0.91 for the total scale. Four factor analysis derived subscales were identified: Lack of Denial, Interest in Rehabilitation, Lack of Anger, and Reliance on Professional Help. Correlation and multiple regression analyses demonstrated moderate relationships between MOT-Q and several MMPI-2 variables largely related to indicators of somatic distress, depression and capacity for self-sufficiency. Lack of Denial subscale showed the strongest relationship to MMPI-2 of all MOT-Q variables, while Interest in Rehabilitation showed the best correlation to the MOT-Q total.

Journal Article↗
PubMed1997

Site-directed mutagenesis of highly conserved amino acids in the first cytoplasmic loop of Drosophila Rh1 opsin blocks rhodopsin synthesis in the nascent state.

The cytoplasmic surface of Drosophila melanogaster Rh1 rhodopsin (ninaE) harbours amino acids which are highly conserved among G-protein-coupled receptors. Site-directed mutations which cause Leu81Gln or Asn86Ile amino acid substitutions in the first cytoplasmic loop of the Rh1 opsin protein, are shown to block rhodopsin synthesis in the nascent, glycosylated state from which the mutant opsin is degraded rapidly. In mutants Leu81Gln and Asn86Ile, only 20-30% and <2% respectively, of functional rhodopsins are synthesized and transported to the photoreceptive membrane. Thus, conserved amino acids in opsin's cytoplasmic surface are a critical factor in the interaction of opsin with proteins of the rhodopsin processing machinery. Photoreceptor cells expressing mutant rhodopsins undergo age-dependent degeneration in a recessive manner.

Amino Acid Sequence↗
PubMed1996

Outcome after traumatic brain injury in the U.S. military medical system.

Personality and behavioral change after traumatic brain injury (TBI) are often the most significant concerns for the families of TBI patients. This report examines discharge from military service after TBI for medical and behavioral criteria. When compared with the total discharge population (n = 1,879,724), the relative risk for behavioral discharge was 1.8 times greater for those with mild TBI (n = 1,778), and no difference for those with moderate (n = 174) or severe TBI (n = 274). Discharge for alcoholism or drug use was 2.6 times for mild TBI, 5.4 times for moderate TBI, and no difference for severe TBI compared with the total discharge population. Discharge for criminal conviction was 2.7 times for those with mild head injury, and no difference for those with moderate or severe TBI when compared with the total discharge population. Discharge for medical disability ranged from 7.5 times to 40.4 times, and mortality ranged from 11.6 to 142.4 times the total discharge population. Total sick days defined as the time from admission to return to duty or separation from service increased with head injury severity. Mean Injury Severity Score for mild TBI was 5.5, and 20.9 for severe TBI. Patients who sustain TBI should be monitored after injury for development of behavioral problems. The most effective way to reduce the cost of TBI is primary prevention of these injuries and examining military practices to reduce exposure to risk of TBI. Secondary and tertiary prevention measures such as evaluation and rehabilitation, where indicated, should be undertaken on a routine basis after TBI.

Adult↗
PubMed1996

Frontal lobe injuries, violence, and aggression: a report of the Vietnam Head Injury Study.

Knowledge stored in the human prefrontal cortex may exert control over more primitive behavioral reactions to environmental provocation. Therefore, following frontal lobe lesions, patients are more likely to use physical intimidation or verbal threats in potential or actual confrontational situations. To test this hypothesis, we examined the relationship between frontal lobe lesions and the presence of aggressive and violent behavior. Fifty-seven normal controls and 279 veterans, matched for age, education, and time in Vietnam, who had suffered penetrating head injuries during their service in Vietnam, were studied. Family observations and self-reports were collected using scales and questionnaires that assessed a range of aggressive and violent attitudes and behavior. Two Aggression/Violence Scale scores, based on observer ratings, were constructed. The results indicated that patients with frontal ventromedial lesions consistently demonstrated Aggression/Violence Scale scores significantly higher than controls and patients with lesions in other brain areas. Higher Aggression/Violence Scale scores were generally associated with verbal confrontations rather than physical assaults, which were less frequently reported. The presence of aggressive and violent behaviors was not associated with the total size of the lesion nor whether the patient had seizures, but was associated with a disruption of family activities. These findings support the hypothesis that ventromedial frontal lobe lesions increase the risk of aggressive and violent behavior.

Adult↗
PubMed1996

Long-term treatment of malignant gliomas with intramuscularly administered polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose: an open pilot study.

Polyinosinic-polycytidylic acid stabilized with polylysine and carboxymethylcellulose (poly-ICLC) (10-50 mcg/kg, administered intramuscularly one to three times weekly) was given for < or = 56 months to 38 patients with malignant gliomas. There was minimal or no toxicity. Twenty of 30 patients (66%) receiving at least twice weekly poly-ICLC showed regression or stabilization of gadolinium-enhancing tumor, as revealed by magnetic resonance imaging (median = 65% volume decrease). All but one patient with anaplastic astrocytomas who received continuous poly-ICLC remain alive, with a median progression-free survival of 54 months from diagnosis. Median Kaplan-Meier survival is 19 months for patients with glioblastomas who receive at least twice weekly poly-ICLC treatments. Tumor response was associated with 2',5' -oligoadenylate synthetase activation (P = 0.03) but not with serum interferon. We hypothesize clinical activation by poly-ICLC of a basic host tumor suppressor system. Prolonged, quality survival with tumor stabilization or regression confirmed by magnetic resonance imaging for most patients with anaplastic astrocytomas and glioblastomas suggests that more extensive laboratory and controlled clinical studies are warranted. The concept of long-term, broad spectrum stimulation of host defenses with nontoxic, inexpensive double-stranded ribonucleic acids, such as low-dose poly-ICLC, may be applicable to the treatment of other malignancies.

Adult↗
PubMed1995

Penetrating injuries in the Vietnam war. Traumatic unconsciousness, epilepsy, and psychosocial outcome.

The WF Caveness Vietnam Head Injury Study includes over a thousand men who survived penetrating head injuries during the Vietnam War and on whom detailed medical and follow-up data are available. This population offers unique opportunities for the study of recovery from brain injury and of brain structure-function relationships. The authors briefly review long-term outcome in this cohort with respect to traumatic unconsciousness, post-traumatic epilepsy, and elements of psychologic and psychosocial function, including returning to work.

Affect↗