Biomedical subjects

Peter C Chen

Publications and source records attributed to Peter C Chen.

13 recordsLinked to original sources

PubMed2007

Lower low-density lipoprotein cholesterol levels are associated with Parkinson's disease.

The apolipoprotein E (APOE) epsilon2 allele has been associated with both Parkinson's disease (PD) and lower low-density lipoprotein cholesterol (LDL-C). We tested the hypothesis that lower LDL-C may be associated with PD. This case-control study used fasting lipid profiles obtained from 124 PD cases and 112 controls. The PD cases were recruited from consecutive cases presenting at our tertiary Movement Disorder Clinic, and the controls were recruited from the spouse populations of the same clinic. Multivariate odds ratios (ORs) and 95% confidence intervals (CIs) were calculated from unconditional logistic regressions, adjusting for age, gender, smoking status, and use of cholesterol-lowering agents. Lower LDL-C concentrations were associated with a higher occurrence of PD. Compared with participants with the highest LDL-C (> or =138 mg/dL), the OR was 2.2 (95% CI = 0.9-5.1) for participants with LDL-C of 115 to 137, 3.5 (95% CI = 1.6-8.1) for LDL-C of 93 to 114, and 2.6 (95% CI = 1.1-5.9) for LDL-C of < or = 92. Interestingly, use of either cholesterol-lowering drugs, or statins alone, was related to lower PD occurrence. Thus, our data provide preliminary evidence that low LDL-C may be associated with higher occurrence of PD, and/or that statin use may lower PD occurrence, either of which finding warrants further investigation.

Aged↗

PubMed2006

Vibrational and vibronic processes in coherent 2D resonance Raman spectroscopy.

Coherent 2D resonance Raman spectroscopy is a multidimensional technique that is capable of separating and sorting peaks that appear heavily congested and disordered in conventional 1D spectra. It can sort rovibrational peaks according to rotational and vibrational quantum number, vibrational sequence, and rotational selection rule. New results suggest that pattern recognition methods can also be used to determine whether the highly detailed rovibrational information is coming from the ground electronic state or the excited electronic state. This capability is demonstrated using experimental results from I(2) and C(2).

Carbon↗

PubMed2006

Systemic function, oxygenation and microvascular correlation during treatment of hemorrhagic shock with blood substitutes.

Systemic function and oxygenation changes during hemorrhagic shock treatment were continuously monitored and correlated with real-time microvascular changes. After splenectomy, each dog (n = 12) was hemorrhaged (MAP = approximately 50 mmHg; approximately 40% blood loss = 32-36 ml/kg) and randomly assigned to 4 resuscitation groups: autologous/shed blood, hemoglobin-based oxygen-carrier/Oxyglobin, crystalloid/saline, and colloid/Hespan. Systemic function and oxygenation changes were continuously monitored and measured using standard operating room protocols. Computer-assisted intravital microscopy was used to non-invasively videotape and objectively analyze and quantify real-time microvascular changes in the conjunctival microcirculation. All measurements were made during pre-hemorrhagic (baseline), post-hemorrhagic and post-resuscitation phases of the study. Pre-hemorrhagic microvascular changes were similar in all 12 dogs (venular diameter = 43 +/- 12 microm; red-cell velocity = 0.6 +/- 0.2 mm/s). All dogs showed similar significant (P<0.01) post-hemorrhagic microvascular changes: approximately 20% decrease in venular diameter; approximately 80% increase in red-cell velocity. These microvascular changes correlated with post-hemorrhagic systemic function and oxygenation changes. The resuscitations restored microvascular changes to pre-hemorrhagic values; the microvascular reversals also correlated with post-resuscitation systemic function changes in all groups. However, only shed blood resuscitation restored oxygenation level close to pre-hemorrhagic values. All 12 dogs survived resuscitation treatments despite differences in oxygen-carrying capability between groups.

Animals↗

PubMed2005

Peak separation and sorting by coherent 2D resonance Raman spectroscopy.

The ability to separate and sort peaks is explored using a new coherent two-dimensional form of resonance Raman spectroscopy. This experimental technique distributes normally congested rotational-vibrational peaks along a series of curved lines according to vibrational sequence, rotational quantum number, and selection rule. Each line consists of rotational-vibrational peaks that have the same vibrational sequence and the same value for DeltaJ, distributed in order by rotational quantum number. For diatomic molecules, these lines originate from points where they initially travel in opposite or orthogonal directions in two-dimensional space, which helps facilitate the separation between lines. Simulations and experimental results on C2 in a flame confirm the ability to separate and sort these normally congested rotational-vibrational peaks. This method appears to provide a solution to the long-standing problems of spectral congestion and disorder in gas-phase electronic spectra.

Computer Simulation↗

PubMed2005

Variants of the tissue-sensor array window chamber.

Sensors are being developed that can be implanted in tissues for continuous monitoring of oxygen, glucose, and other metabolites. However, there have been difficulties in inferring metabolite concentrations in blood from the signals of tissue sensors due to the properties of tissues at the implant site and local physiological phenomena that can affect sensor responses. A multisensor array has been previously developed for implantation in a hamster skinfold window chamber preparation to study these effects. The preparation allows recording of concentration-dependent signals from multiple sensors while nondestructively visualizing the adjacent tissue and microvascular function. Variants of the tissue-sensor array window chamber described here have respective advantages over the original chamber design, including improved tissue visualization and reduced surgical intervention, and allow exposure of the sensor to different tissues. Results indicate that mass transfer within tissues is heterogeneous, and sensor signals are affected by variable perfusion of local microvasculature in addition to vascular metabolite concentration. These observations suggest new strategies for sensor design and operation. Window chamber variants are important tools for validation of implanted sensors.

Animals↗

PubMed2005

High-speed gas chromatography-multiplex coherent Raman analysis of BTEX.

Gas chromatography-multiplex coherent Raman (GC-MCR) is a new tandem technique that can be used for the high-speed analysis of volatile mixtures. BTEX serves as a useful and challenging test sample because of the similarity in boiling point and spectroscopic properties of its constituents. The ability to spectroscopically resolve isomers (e.g., m-xylene and p-xylene) allows GC-MCR to sacrifice chromatographic resolution for speed. The result is the analysis of BTEX in less than 5 min, which is relatively fast compared with other tandem GC techniques.

Chromatography, Gas↗

PubMed2004

APOE-[epsilon]2 allele associated with higher prevalence of sporadic Parkinson disease.

BACKGROUND: The link of the apolipoprotein (APOE) -epsilon4 allele to Alzheimer disease (AD) has led to studies investigating the role of apoE polymorphisms in Parkinson disease (PD). The authors hypothesized that any association between PD and APOE alleles and genotypes would be too small to be detected or precisely estimated by an individual case-controlled study. METHOD: The hypothesis was tested by systematic review and meta-analysis of results from case-control studies that provided clear clinical or pathologic criteria for PD and that reported APOE genotype frequencies. Published reports were obtained from MEDLINE, Biosis Previews, and ISI Web of Science searches, supplemented by citation analysis from retrieved articles. The authors estimated and compared prevalence odds ratios (OR) for PD in relation to each allele and genotype. RESULTS: Twenty-two eligible studies were identified. There was no evidence of heterogeneity (p > 0.4) or publication bias (p > 0.2) for any allele or genotype. The estimated summary OR for one or more copies of each APOE allele was 1.20 for APOE-epsilon2 (95% CI, 1.02 to 1.42), 0.83 for APOE-epsilon3 (95% CI, 0.63 to 1.09), and 0.99 for APOE-epsilon4 (95% CI, 0.87 to 1.14). CONCLUSIONS: Unlike Alzheimer disease, for which the APOE-epsilon4 allele increases the prevalence and the APOE-epsilon2 allele is protective, the authors' analysis shows the APOE-epsilon2 allele, but not the APOE-epsilon4 allele, to be positively associated with sporadic Parkinson disease.

Alleles↗

PubMed2003

Gas chromatography-multiplex coherent Raman spectroscopy.

A new detector for gas chromatography has been developed that is based upon nonlinear Raman spectroscopy. The resulting hyphenated instrument uses a simple windowless cell as the interface between the chromatograph and the spectroscopic detector. The eluents are detected using a unique spectrometer equipped with a broadband OPO. This spectrometer is capable of generating high-resolution coherent Raman signals that are suitable for rapid multichannel detection.

Chromatography, Gas↗

PubMed2003

Tissue window chamber system for validation of implanted oxygen sensors.

An experimental system is described for validating electrochemical oxygen sensors implanted in tissues. The system is a modified hamster window chamber in which a thin layer of vascularized tissue is held between two plates, one plate having an observation window and the other plate having an array of oxygen sensors. This arrangement permits simultaneous recording of oxygen sensor signals and nondestructive visualization of the tissue adjacent to the sensors over periods of 1 mo or more, without the inhibitory effects of anesthesia. The system provides a means for study of the effects of spatial and temporal oxygen distributions on the sensor signals and adaptation of the tissue structure over time. Examples are given of sensor recordings and images of tissues with implanted oxygen sensor arrays.

Animals↗

PubMed2003

Polyethylene cross-linking by two different methods reduces acetabular liner wear in a hip joint wear simulator.

Advances in cross-linking have led to the development of wear resistant ultrahigh molecular weight polyethylene for total joint replacement. This study compared wear reduction by two different cross-linking methods as measured in a hip wear simulator. One highly cross-linked polyethylene was treated with 7.5 Mrad gamma irradiation with post-irradiation annealing and a sterilization dose of 2.5 Mrad (10 Gamma), while the other used 9.5 Mrad warm irradiation with 10 MeV electron-beam (9.5 EB). Liners of the same design, made from nominally cross-linked (gamma sterilized) polyethylene were also tested. Gravimetric wear analysis was performed every 500,000 cycles for 5,000,000 cycles. After correcting for weight gain due to water absorption, the nominally cross-linked liners demonstrated mean wear rates of 15.7 (+/-1.7) and 12.5 (+/-1.0) mg/million cycles. Both highly cross-linked polyethylene liners demonstrated significantly less wear than their respective controls (with mean wear rates of 1.5 (+/-1.2) and -1.4 (+/-1.5) mg/million cycles). The 9.5 EB liners gained weight presumably due to increased fluid absorption, in addition to that measured in loaded-soaked control implants. Any wear occurring was therefore assumed to have been more than offset by weight gain. Highly cross-linked polyethylene was significantly more wear resistant than non- or nominally cross-linked polyethylene. The differences in wear rates between the two highly cross-linked polyethylene designs (9.5 EB or 10 Gamma) are probably too small to be clinically significant.

Acetabulum↗

PubMed2003

Polyethylene wear and acetabular component orientation.

BACKGROUND: Polyethylene wear contributes substantially to both periprosthetic osteolysis and aseptic loosening after total hip arthroplasty. Acetabular component orientation has been shown to affect the range of motion of the hip as well as contact stresses. A series of studies was designed to test the hypothesis that acetabular component orientation can affect the magnitude and direction of polyethylene wear. METHODS: A finite-element model was used to compute contact stresses during a normal gait cycle. Wear at the end of each gait cycle was calculated with use of the sliding-distance-coupled finite-element formulation. The wear that was calculated with use of finite-element analysis was validated by comparison with the findings of hip wear simulator studies with the acetabular liner oriented to simulate 45 degrees and 55 degrees of abduction. In a clinical study, fifty-six patients who underwent sixty hip arthroplasties with use of a single prosthetic design were followed for as long as five years. Radiographs were analyzed to measure the abduction angle of the acetabular component and polyethylene wear. RESULTS: The finite-element analysis predicted increased peak contact stresses with an increased abduction angle and reduced peak contact stresses with an increased anteversion angle. Linear wear rates ranging from 0.036 to 0.045 mm/million cycles were also predicted, and increased acetabular abduction angles were predicted to be associated with higher linear wear rates. In the hip wear simulator studies, significantly different wear rates were found between the cups with acetabular abduction angles of 45 degrees and 55 degrees (mean, 17.2 compared with 21.7 mg/million cycles; p < 0.01). In the clinical study, radiographic analysis revealed significant correlation between the acetabular abduction angle and the linear polyethylene wear rate. A 40% increase in mean linear polyethylene wear was seen in cups with an abduction angle of >or=45 degrees. The direction of wear was more medial (by 9.4 degrees ) in cups with an abduction angle of <45 degrees. CONCLUSION: All three studies presented here underlined the importance of optimizing the position of the acetabular component. Careful attention to acetabular position may help to minimize wear.

Aged↗

PubMed2003

Impact of patellofemoral design on patellofemoral forces and polyethylene stresses.

BACKGROUND: The patellofemoral joint is a complex articulation because it relies mainly on soft-tissue constraints for stable tracking. The presence of a functioning posterior cruciate ligament and the design parameters of a total knee arthroplasty, such as trochlear groove alignment and cam-post configuration, can have a major effect on patellar biomechanics. METHODS: A finite element model of a knee implanted with femoral, tibial, and patellar components was generated. The model was validated by experimental testing of three cadaver knees implanted with a total knee prosthesis and a patellar force transducer. Two femoral component designs with different valgus angles of the trochlear groove (0 degrees and 7 degrees ) were studied. The effects of femoral rollback, rotation of the femoral component, medialization of the patellar implant, and alignment of the trochlear groove on patellar forces were then analyzed. RESULTS: A consistent reduction of up to 7% in patellofemoral forces was seen with progressive magnitudes of femoral rollback. The 0 degrees -aligned trochlear groove generated some lateral patellofemoral shear force throughout knee flexion. The 7 degrees -aligned trochlear groove generated medial shear force at flexion angles of <20 degrees and lateral shear force at flexion angles of >20 degrees. A more medial patellar component position reduced peak lateral shear forces by up to 10 to 15 N. However, a corresponding increase in medial shear forces was seen. CONCLUSIONS: This model predicted substantial reduction in patellofemoral lateral shear forces with a medialized patellar component or with external rotation of the femur. The model supported the hypothesis that femoral rollback reduces patellofemoral forces by improving the efficiency of the extensor mechanism. CLINICAL RELEVANCE: Patellofemoral complications after total knee arthroplasty include anterior knee pain, patellar subluxation and dislocation, abnormal polyethylene wear and damage, and loosening. There is a wide variation in the design features of current total knee prostheses, such as the sagittal radius, depth, and orientation of the trochlear groove of the femur and the geometry of the patellar component surface. The finite element model used in the present study can provide insight into the effects of design parameters on patellofemoral forces and on local contact stresses.

Arthroplasty, Replacement, Knee↗

PubMed2002

High-speed high-resolution gas-phase Raman spectroscopy.

A new Raman spectrometer has been developed that can produce a complete high-resolution gas-phase vibrational spectrum during the time period of a single laser pulse. Conventional gas-phase Raman spectroscopy uses a single narrow-band laser to produce signals that are weak, requiring relatively long collection times. This spectrometer uses a degenerate OPO as a broad-band source that covers a continuous range of >3000 cm(-1). When a beam from this broad-band source is added to a narrow-band laser beam, the intensity of the Raman signal is amplified by the nonlinear optical effect. The resulting instrument can generate spectra with high-spectral (<1 cm(-1)), spatial (<0.05 mm2), and temporal resolution (<1 s).

Fourier Analysis↗