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Biomedical subjects

D Garcia

Publications and source records attributed to D Garcia.

At least 37 records · Page 2Linked to original sources
PubMed2000

Assessment of aortic valve stenosis severity: A new index based on the energy loss concept.

BACKGROUND: Fluid energy loss across stenotic aortic valves is influenced by factors other than the valve effective orifice area (EOA). We propose a new index that will provide a more accurate estimate of this energy loss. METHODS AND RESULTS: An experimental model was designed to measure EOA and energy loss in 2 fixed stenoses and 7 bioprosthetic valves for different flow rates and 2 different aortic sizes (25 and 38 mm). The results showed that the relationship between EOA and energy loss is influenced by both flow rate and aortic cross-sectional area (A(A)) and that the energy loss is systematically higher (15+/-2%) in the large aorta. The coefficient (EOAxA(A))/(A(A)-EOA) accurately predicted the energy loss in all situations (r(2)=0.98). This coefficient is more closely related to the increase in left ventricular workload than EOA. To account for varying flow rates, the coefficient was indexed for body surface area in a retrospective study of 138 patients with moderate or severe aortic stenosis. The energy loss index measured by Doppler echocardiography was superior to the EOA in predicting the end points, which were defined as death or aortic valve replacement. An energy loss index </=0.52 cm(2)/m(2) was the best predictor of adverse outcomes (positive predictive value of 67%). CONCLUSIONS: This new energy loss index has the potential to reflect the severity of aortic stenosis better than EOA. Further prospective studies are necessary to establish the relevance of this index in terms of clinical outcomes.

Adult↗
PubMed2000

Assessment of arterial stenosis in a flow model with power Doppler angiography: accuracy and observations on blood echogenicity.

The objective of the project was to study the influence of various hemodynamic and rheologic factors on the accuracy of 3-D power Doppler angiography (PDA) for quantifying the percentage of area reduction of a stenotic artery along its longitudinal axis. The study was performed with a 3-D power Doppler ultrasound (US) imaging system and an in vitro mock flow model containing a simulated artery with a stenosis of 80% area reduction. Measurements were performed under steady and pulsatile flow conditions by circulating, at different flow rates, four types of fluid (porcine whole blood, porcine whole blood with a US contrast agent, porcine blood cell suspension and porcine blood cell suspension with a US contrast agent). A total of 120 measurements were performed. Computational simulations of the fluid dynamics in the vicinity of the axisymmetrical stenosis were performed with finite-element modeling (FEM) to locate and identify the PDA signal loss due to the wall filter of the US instrument. The performance of three segmentation algorithms used to delineate the vessel lumen on the PDA images was assessed and compared. It is shown that the type of fluid flowing in the phantom affects the echoicity of PDA images and the accuracy of the segmentation algorithms. The type of flow (steady or pulsatile) and the flow rate can also influence the PDA image accuracy, whereas the use of US contrast agent has no significant effect. For the conditions that would correspond to a US scan of a common femoral artery (whole blood flowing at a mean pulsatile flow rate of 450 mL min(-1)), the errors in the percentages of area reduction were 4.3 +/- 1.2% before the stenosis, -2.0 +/- 1.0% in the stenosis, 11.5 +/- 3.1% in the recirculation zone, and 2.8 +/- 1.7% after the stenosis, respectively. Based on the simulated blood flow patterns obtained with FEM, the lower accuracy in the recirculation zone can be attributed to the effect of the wall filter that removes low flow velocities. In conclusion, the small errors reported in vitro may support the clinical use of this technique.

Algorithms↗
PubMed2000

Vertical partial laryngectomy versus supracricoid partial laryngectomy for selected carcinomas of the true vocal cord classified as T2N0.

From an inception cohort of 204 patients with squamous cell carcinoma of the true vocal cord classified as T2N0 and a minimum of 3 years of follow-up, the authors compare the oncological and functional outcomes following vertical partial laryngectomy (group 1; 85 patients) and supracricoid partial laryngectomy (group 2; 119 patients). The 10-year actuarial survival estimate was 46.2% for group 1 and 66.4% for group 2. Survival was statistically more likely to be reduced (p = .019) in group 1 than in group 2. The 10-year actuarial local control estimate was 69.3% for group 1 and 94.6% for group 2. Local recurrence was statistically more likely to occur (p < .0001) in group 1 than in group 2. Salvage treatment resulted in an overall 94.1% local control rate and a 78.1% laryngeal preservation rate for group 1 and an overall 99.2% local control rate and a 94.9% laryngeal preservation rate for group 2. The 10-year actuarial nodal control estimate was 81.7% for group 1 and 93.7% for group 2. Nodal recurrence was statistically more likely to occur (p = .028) in group 1 than in group 2. The 10-year actuarial estimate for patients without distant metastasis was 84.6% for group 1 and 95.1% for group 2. Distant metastasis was statistically more likely to occur (p = .05) in group 1 than in group 2. The hospital mortality rate was 1.2% for group 1 and 0.8% for group 2. The incidence of permanent gastrostomy was 0% for group 1 and 2.4% for group 2. The incidence of permanent tracheostomy was 1.2% for group 1 and 2.4% for group 2. The incidence of completion laryngectomy due to functional problems was 1.2% for group 1 and 0.8% for group 2.

Actuarial Analysis↗
PubMed2000

Laryngeal stenosis after supracricoid partial laryngectomy.

The purpose of this study was to review the incidence, risks, management, and outcomes of nontumoral laryngeal stenosis after supracricoid partial laryngectomy (SCPL) in a case series of 376 consecutive SCPLs performed at 1 institution from 1975 to 1995 with a minimum of 3 years of follow-up. Post-SCPL nontumoral symptomatic laryngeal stenosis was defined as an inability to decannulate patients before the 60th postoperative day (group 1) or the development of dyspnea (in patients without local recurrence) after an initial period of prolonged, successful decannulation (group 2). Of 376 SCPLs performed, nontumoral symptomatic laryngeal stenosis developed in 14 (3.7%). There were 7 patients (1.85%) in group 1 and 7 patients (1.85%) in group 2. In univariate analysis, none of the following variables appeared to be statistically related to the risk of immediate stenosis (group 1): age, gender, comorbidity, diabetes mellitus, symptomatic gastroesophageal reflux, arteritis, preoperative radiotherapy, arytenoid cartilage disarticulation, type of reconstruction performed, and postoperative radiotherapy. A delayed laryngeal stenosis (group 2) was statistically more likely to occur if the reconstruction performed at the time of SCPL was a cricohyoidopexy (p = .01). Successful management of the laryngeal stenosis without permanent tracheostomy was achieved in 5 group 1 patients and 3 group 2 patients. We believe that stenosis in group I patients arose through technical error, whereas group 2 patients seemed to suffer from problems of healing, mainly cicatricial narrowing of the airway at the site of the cricohyoidal impaction, or pexis. As a result, whereas laryngeal stenosis in group 1 patients was usually more easily correctable through dilation, laser incision, or resection of redundant tissue or revision of the impaction, laryngeal stenosis in group 2 patients presented a more difficult and frustrating complication. The management and outcomes of these patients are presented.

Adult↗
PubMed1999

Local recurrence after vertical partial laryngectomy, a conservative modality of treatment for patients with Stage I-II squamous cell carcinoma of the glottis.

BACKGROUND: Based on an inception cohort of 103 patients who had local recurrence (Group I) and a witness group of 311 patients who achieved local control (Group II) after vertical partial laryngectomy for Stage I-II glottic carcinoma, the current retrospective study documented the consequences and management of local recurrence. METHODS: Three hundred two patients (97.1%) in Group II and all 103 patients (100%) in Group I were followed until death or for a minimum of 10 years. Statistical analysis of survival, lymph node control, and distant metastasis was based on the Kaplan-Meier product limit method. RESULTS: The 10-year actuarial survival estimate was 30.8% for Group I patients and 63.1% for Group II patients. Survival was statistically more likely to be reduced in Group I patients (P < 0.0001) than in Group II patients. The percentage of patients who died of their initial disease was 44.6% in Group I and 6.3% in Group II. The 10-year actuarial lymph node control estimate was 70.2% for Group I and 96.1% for Group II. Lymph node recurrence was statistically more likely to occur in Group I patients than in Group II patients (P < 0.0001). The 10-year actuarial estimate for patients without distant metastasis was 80.2% for Group I and 96.7% for Group II. Distant metastasis was statistically more likely to occur in Group I patients than in Group II patients (P < 0.0001). Salvage treatment was unsuitable for 4.7% of patients with local recurrence; for other patients, it yielded a 86.7% local control rate, a 21.4% laryngeal preservation rate, a 4.5% death rate, and an 11.2% rate of incidence of severe complications. CONCLUSIONS: Among patients with Stage I-II glottic carcinoma managed with vertical partial laryngectomy, local recurrence results in a reduced rate of survival as well as a high rate of necessity for salvage total laryngectomy.

Adult↗
PubMed1999

Maturational changes in cerebral lactate and acid clearance following ischemia measured in vivo using magnetic resonance spectroscopy and microdialysis.

Intraischemic hyperglycemia has different effects on neurologic outcome in mature vs. immature brain, and may reflect differences in the extent or duration of cerebral lactic acidosis. We examined the hypotheses that post-ischemic lactate and acid clearance rates depend on the severity of intraischemic cerebral acidosis, and that rates of clearance change as a function of brain maturation. In vivo 31P and 1H magnetic resonance spectroscopy (MRS) was used to compare intracellular acid and lactate clearance rates in newborn and 1-month old swine following a 14-min episode of transient near-complete global ischemia. In the same animals, in vivo microdialysis was used to determine if extracellular lactate clearance changed as a function of cerebral lactic acidosis or differed between age groups following ischemia. Plasma glucose concentration was altered in individual animals to study a range of intraischemic cerebral lactic acidosis. For both age-groups, maximal brain acidosis and lactosis occurred in the post-ischemia interval, indicating a delay in the re-establishment of oxidative metabolism following ischemia. Clearance half-lives of both cerebral acidosis and lactosis increase as a function of increased intraischemic cerebral acidosis. For either age group, the clearance half-life for acidosis was faster than the half-life for lactate. However, the subgroup of 1-month old swine who experienced severe cerebral acidosis (i.e., pH<6.1) had a longer cerebral lactate clearance half-life as compared to the subgroup of newborn animals with a similar severity of acidosis. In both age groups, there were comparable maximal increases in extracellular lactate concentrations in the post-ischemic period and similar rates of decline from the maximum. These results demonstrate that post-ischemic lactate and acid clearance are altered by the extent of intraischemic acidosis, and the extent of post-ischemic uncoupling between brain acid and lactate clearance increases with advancing age. The transmembrane clearance of lactate was not a prominent mechanism that differentiated lactate clearance rates between newborn and 1-month old swine.

Acidosis, Lactic↗
PubMed1999

A multimodal strategy for the treatment of patients with T2 invasive squamous cell carcinoma of the glottis.

BACKGROUND: The current conservative standard of care for T2 squamous cell carcinoma of the glottis is either partial laryngectomy or radiation therapy. METHODS: Based on an inception cohort of 100 patients with T2 squamous cell carcinoma of the glottis and a minimum of 3 years of follow-up, the present study documented the results achieved with a multimodal strategy using platinum-based induction chemotherapy and partial laryngeal surgery. Statistical analysis of survival and local control was based on the Kaplan-Meier actuarial life table method. Univariate analysis was performed to determine whether there was a correlation among various factors and toxicity, clinical response, histologic regression, local control, and survival. RESULTS: A complete clinical response and a partial response after induction chemotherapy was achieved in 24% and 58% of patients, respectively. Complete histologic regression was noted in 31%. A significant statistical relation (P < 0.0001) was noted between a complete clinical response after induction chemotherapy and a complete histologic regression. The 5-year actuarial survival estimate was 85.8%. The 5-year actuarial local control estimate was 95.7% (97.7% if the vocal cord was mobile and 93.8% if the motion of the vocal cord was impaired). Salvage treatment resulted in an overall 99% rate of local control and a 95% rate of laryngeal preservation. CONCLUSIONS: Because this represents a nonrandomized retrospective study, no definitive conclusions can be derived. However, when compared with the data reported in a large series using radiation therapy or partial laryngectomy alone, this 10-year experience suggests that, in patients with "early" invasive squamous cell carcinoma of the glottis, the use of platinum-based induction chemotherapy prior to a conventional conservative treatment modality should be investigated further.

Adult↗
PubMed1999

Recurrent gustatory sweating (Frey syndrome) after intracutaneous injection of botulinum toxin type A: incidence, management, and outcome.

OBJECTIVE: To evaluate the duration of effectiveness of intracutaneous injection of botulinum toxin type A for gustatory sweating as well as the incidence, severity, management, and outcome of recurrent gustatory sweating. DESIGN: An inception cohort with a minimum of 18 months of follow-up. SETTING: A tertiary care center and university teaching hospital. PATIENTS: Thirty-three patients with severe gustatory sweating. INTERVENTION: Intracutaneous injection of 25 to 175 IU (mean, 86 IU) of botulinum toxin type A. MAIN OUTCOME MEASURES: Analysis of the effectiveness of the intracutaneous injection of botulinum toxin type A using the Kaplan-Meier actuarial life-table method; completion of the Minor starch-iodine test in patients without symptomatic recurrent gustatory sweating; and the patients' self-assessment of the severity of the recurrent gustatory sweating. RESULTS: The 1-, 2-, and 3-year actuarial estimate for symptomatic recurrent gustatory sweating was 27%, 63%, and 92%, respectively. In the 7 patients without symptomatic recurrent gustatory sweating, the Minor starch-iodine test revealed persistent gustatory sweating in 6, resulting in an overall 97% rate (32 of 33 patients) for recurrent gustatory sweating. No statistical relationship could be demonstrated between the duration of effectiveness, the incidence of recurrent gustatory sweating, the severity of recurrent gustatory sweating, and the following variables: age, sex, cause of gustatory sweating, skin surface involved, and dose of botulinum toxin type A injection. Within the group of 26 patients with symptomatic recurrent gustatory sweating, (1) the severity of the recurrent gustatory sweating was always reduced when compared with the severity of the initial gustatory sweating, and (2) the recurrent gustatory sweating always remained amenable to reinjection of botulinum toxin type A. CONCLUSIONS: The present series demonstrated a linear regression in the effectiveness of the intracutaneous injection of botulinum toxin type A in patients with gustatory sweating, while no factors appeared to be statistically related to the duration of effectiveness and/or the incidence of recurrent gustatory sweating. However, because the severity of recurrent gustatory sweating is reduced when compared with the severity of the initial gustatory sweating and because recurrent gustatory sweating remains amenable to reinjection of botulinum toxin type A, we believe that the intracutaneous injection of botulinum toxin type A should become the first-line treatment option in patients with gustatory sweating.

Adolescent↗
PubMed1999

Age-dependent differences in the relationship between plasma and brain extracellular fluid concentrations of magnesium after MgSO4 infusions in miniswine.

Magnesium is a potential neuroprotective agent in the treatment of head injury and ischemia whose efficacy is likely determined by increases in brain extracellular fluid (ECF) magnesium, which in turn depends on its concentration in plasma. The objectives of this study were to: 1) examine the effects of increasing plasma magnesium concentration ([Mg]plasma) to 4-6 mM on brain ECF magnesium concentration ([Mg]ECF) and 2) determine whether maturational changes occur in the transfer of magnesium into brain ECF for newborn and more mature (approximately 1 month old) miniswine. Increases in [Mg]plasma by systemic administration of MgSO4 resulted in similar maximal elevations in brain [Mg]ECF for both age groups (193+/-76% versus 253+/-106% of control for newborn and 1-month-old miniswine, respectively). Calculations of half-lives (t1/2) for the increase and decrease in magnesium concentration (t1/2 uptake and t1/2 clearance) were used to characterize magnesium kinetics in plasma and brain ECF. Plasma magnesium uptake was shorter in 1-month-old (t1/2 = 11.1+/-0.9 min) compared with newborns (12.9+/-1.7 min, p < 0.05). The faster increase in [Mg]plasma probably contributed to a faster uptake of brain [Mg]ECF in 1-month-old compared with newborn swine (t1/2 uptake = 27.9+/-12.8 versus 46.0+/-20.9 min, respectively, p < 0.05). Although plasma magnesium clearance was shorter in 1-month-old swine compared with newborn (t1/2 = 34.3+/-7.0 versus 74.7+/-33.7 min, respectively, p < 0.05), the clearance of magnesium from the brain ECF was similar for each age group. Reductions in blood pressure and heart rate occurred during hypermagnesemia and were similar in each age group. This study shows that acute elevations in [Mg]plasma to 4-6 mM result in similar relative increases in brain [Mg]ECF for both newborn and 1-month-old miniswine. However, there are maturational differences, as demonstrated by the faster rate of magnesium uptake into the ECF observed in the older miniswine.

Animals↗
PubMed1999

Structure-functional effects of ethanol on Drosophila melanogaster acetylcholinesterase probed by kinetic studies with substrate and inhibitors.

Ethanol is commonly used to extract and dissolve insecticides acting as inhibitors of acetylcholinesterase (EC 3.1.1.7). Here, experiments were undertaken to investigate the influence of solvent on the reaction and inhibition of the enzyme from Drosophila melanogaster. Ethanol (up to 20% by volume) is shown to induce a dramatic reduction of the affinity of acetylcholinesterase for the acetylthiocholine iodide substrate and all the edrophonium chloride, paraoxon ethyl and propidium diiodide inhibitors, with little influence on the rate constants. Taken together, these results point to a main perturbation of active-center related components involved in the formation and/or stability of Michaelis complexes. Inactivation and ligand-stabilization studies of acetylcholinesterase activity further indicate the occurrence of specific "conformational scrambling" at catalytic and regulatory sites. It is proposed that ethanol affects the enzyme reactivity by modifying the conformation of the aromatic gorge containing the active centre and hence, interactions involved in the molecular recognition of substrates and ligands.

Acetylcholinesterase↗
PubMed1999

A new flow model for Doppler ultrasound study of prosthetic heart valves.

BACKGROUND AND AIM OF THE STUDY: Steady and pulsatile flow models used to assess the hydrodynamic aspects of prosthetic heart valves are generally made of Plexiglas and Lucite tubing. They often allow continuous-wave and pulsed-wave Doppler ultrasound velocity measurements to be made parallel to the flow, but cannot be used as such for ultrasound scanning of valve inflow and outflow velocities because of ultrasonic reverberation and refraction by the tubing. The aim of the study was to develop a new flow model which allowed ultrasonic scanning of the prosthetic valve flow for three-dimensional (3D) reconstruction of color Doppler flow distributions. METHODS: The flow model, designed with left ventricular and aortic chambers composed of agar gel which mimics the ultrasound characteristics of biological tissues, was developed and tested for comparative in vitro hydrodynamic and Doppler ultrasonic studies of aortic prosthetic valves. An electromagnetic flowmeter and a pressure monitor provided the flow and pressure signals for the hydrodynamic tests. The Doppler ultrasonic evaluation was performed with an Ultramark 9 HDI ultrasound system and a 3D ultrasound imaging system. The model was designed to enable assessment of prosthetic valve performance by pulsed-wave and continuous-wave Doppler velocity measurements, as well as by 3D color Doppler velocity measurements obtained by ultrasonic scanning of the left ventricle or aortic chamber with an ultrasound probe mounted on a motorized translation assembly. RESULTS: The study results showed that this new flow model can provide 3D color Doppler velocity distributions as well as accurate comparisons of hydrodynamic parameters of mechanical and bioprosthetic heart valves derived from Doppler and catheter measurements, both under steady and pulsatile flow conditions. CONCLUSION: This new flow model can be used to evaluate the usefulness of hydrodynamic parameters for the assessment of prosthetic heart valves using both conventional Doppler echocardiography, as currently used in patients, and 3D color Doppler ultrasonic imaging.

Blood Flow Velocity↗
PubMed1999

Ethnic variation in the health burden of self-reported diabetes in adults aged 75 and older.

OBJECTIVE: The health burden of self-reported diabetes was compared across three ethnic groups of older adults. METHODS: Analysis of variance and logistic regression were used to compare ethnic differences in the rates of co-morbid chronic health conditions, complications, and disability for older diabetics vs non-diabetics, in a sample of 173 Mexican Americans, 201 African Americans, and 181 non-Hispanic whites, all aged 75 and older. RESULTS: The prevalence of self-reported diabetes was significantly higher in older Mexican Americans (17.6%) and African Americans (16.4%) than in non-Hispanic whites (8.5%). In all three ethnic groups, and after controlling for sociodemographic characteristics, diabetics were found to be generally at higher risk for chronic conditions such as heart disease, stroke, and hypertension, circulation and foot problems, obesity, and impaired vision and activities of daily living. Multivariate analyses indicated that the burden of diabetes appeared to be greatest among non-Hispanic white diabetics. We suggest that this is the result of higher diabetes-mortality rates among minority diabetics at earlier ages. CONCLUSIONS: Diabetes is known to be increasing in prevalence and incidence, particularly among the elderly, the fastest growing segment of the population. Our findings indicate that regardless of ethnicity, diabetes carries an increased burden that affects both the functioning and the quality of life of older adults.

Activities of Daily Living↗
PubMed1998

Whither neurosurgery?

Although trends in the marketplace demand for neurosurgeons should be of interest to neurosurgeons and prospective neurosurgeons, little data are available that accurately document these trends. A recent report published in the general medical journal Journal of the American Medical Association (JAMA) used the Conference Board help-wanted index to evaluate trends in physician marketplace demand. The authors of the JAMA study concluded that over the past 5 years there has been a significant fall in demand for specialist physicians. Because the discipline of neurosurgery was not included in the JAMA study, the authors of the present report attempt to evaluate the trend in the marketplace demand for neurosurgeons, using the same methodology of the JAMA study. The authors' data suggest that the conclusion of the JAMA study of steep declines in the demand for specialist physicians does not accurately reflect the job market for neurosurgeons, which in fact appears to be relatively stable. The present study attempts to document the stability of the neurosurgery market and outline the steps necessary to protect this market from existing threats.

Journal Article↗
PubMed1998

Age-related differences in the effect of dichloroacetate on postischemic lactate and acid clearance measured in vivo using magnetic resonance spectroscopy and microdialysis.

Numerous studies using adult animal models suggest that dichloroacetate (DCA) may have neuroprotective properties by virtue of its ability to increase rates of metabolism and, therefore, clearance of brain lactic acidosis, which may accumulate during cerebral ischemia. We tested the hypothesis that postischemic DCA administration affects lactate and acid clearance to different extents in immature versus mature brain. 31P and 1H magnetic resonance spectroscopy were used to measure intracellular acid and lactate clearance rates in vivo in newborn and 1-month-old swine after a 14-min episode of transient near-complete global ischemia. Simultaneous monitoring of extracellular lactate efflux and clearance was measured in the same animals by in vivo microdialysis. Plasma glucose concentrations were elevated in order to study animals with severe cerebral lactic acidosis. Maximal levels of brain lactosis (16-20 micromol/g) and acidosis (PHintracellular 5.8-6.0) were reached during the first 10 min of recovery and were the same in age groups and in subgroups either acting as controls or treated with DCA (200 mg/kg) given from the last minute of ischemia to 5-7 min after ischemia. For newborns, DCA administration improved the postischemic clearance rate of cerebral acidosis and cerebral phosphocreatine, with similar trends for the clearance of lactosis and increased rates of recovery of nucleotide triphosphates, compared with controls. In contrast, DCA administration in 1-month-olds resulted in a modest trend for improvement of cerebral lactate clearance, but did not affect acid clearance or the recovery rate of phosphocreatine or nucleotide triphosphates. Extracellular brain lactate concentrations had similar relative increases and rates of decline for subgroups of either age treated with DCA versus controls. The results of this study indicate that postischemic DCA administration helps to resolve cerebral acidosis to a greater degree in immature than more mature brain, suggesting that DCA may have cerebroprotective properties for neonatal hypoxic-ischemic encephalopathy.

Acids↗
PubMed1997

Characterization of the reaction center bound tetraheme cytochrome of Rhodocyclus tenuis.

Properties of the tetrahemic reaction center bound cytochrome have been investigated by different techniques. The mid-point potentials of the four hemes were determined by redox titration. The best fit of the data was obtained with a (n = 1) Nernst curve by using the following values of the redox parameters: Em = +420 mV for the two high-potential hemes and Em = +110 and +60 mV for the two low-potential hemes. The mid-point potentials of the two high-potential hemes are the highest reported so far. The spectral properties of the four hemes in the alpha-band have been determined by absorption spectroscopy and measurements of light-induced difference spectra in membranes of Rhodocyclus tenuis. The two high potential hemes present very similar spectra centered at 557 nm. The absorption spectra of the two low-potential hemes are very similar, and their alpha-band centered around 551 nm. Spectral properties at 100 K and the linear dichroism of optical transitions allow the determination of the relative orientations of the hemes with respect to the membrane plane. The orientation patterns thus obtained corresponds to none of the arrangements described so far for reaction center bound cytochromes.

Bacterial Proteins↗
PubMed1997

A risk profile of street youth in northern California: implications for gender-specific human immunodeficiency virus prevention.

PURPOSE: To assess human immunodeficiency virus (HIV) risk behaviors of street youth and to determine whether risk behaviors differ by gender or housing status. METHODS: Using systematic street-based sampling in four Northern California cities, we recruited 429 street youth (mean age = 19.2 years). Participants completed a structured interview which was used to assess sexual and drug HIV risk behaviors. RESULTS: The majority of youth were heterosexual (85%), white (77%), male (68%), and currently without any type of stable housing (75%). Although 60% of the sample had had vaginal sex in the past 30 days, only 44% used a condom the last time they had sex. About one-third (32%) of the sample reported ever injecting drugs, and almost all reported lifetime use of multiple drugs including D-lysergic acid diethylamide (96%), marijuana (90%), alcohol (81%), cocaine (70%), and speed (70%). Compared to males, females were equally likely to use injection and noninjection drugs, but were more likely to be sexually active (P < .001), were more likely to have been diagnosed with a sexually transmitted disease (P = .005), and were less likely to report consistent condom use (P = .003) or intent to use condoms consistently in the future (P = .005). Compared with those with stable housing, youth who were currently without such housing reported higher rates of injection, and other drug use; females without stable housing were less likely to have used condoms the last time they had vaginal intercourse. CONCLUSION: The high level of HIV risk behavior in this street-based sample of youth, particularly females and youth without stable housing, suggests an urgent need for gender-specific prevention efforts and an increased range of housing options.

Adolescent↗
PubMed1997

Modest hypothermia provides partial neuroprotection when used for immediate resuscitation after brain ischemia.

Intraischemic reduction in temperature of 2-3 degrees C (modest hypothermia) has been demonstrated to provide partial neuroprotection in neonatal animals. This investigation determined if modest hypothermia initiated immediately after brain ischemia provides neuroprotection. Piglets were studied with rectal temperature maintained during the 1st h after 15 min of brain ischemia at either 38.3 +/- 0.3 degrees C (normothermia, n = 11) or at 35.8 +/- 0.5 degrees C (modest hypothermia, n = 11). The severity of brain ischemia was similar between groups as indicated by equivalent reduction in mean blood pressure (90 +/- 15 to 24 +/- 3 versus 92 +/- 13 to 26 +/- 3 mm Hg), and changes in cerebral metabolites and intracellular pH (pH(i)) measured by magnetic resonance spectroscopy (beta-nucleoside triphosphate = 44 +/- 9 versus 42 +/- 18% of control, control = 100%, pH(i): 6.25+/- .15 versus 6.24 +/- 0.22 for normothermic and modestly hypothermic groups, respectively). In the first 90 min after ischemia, there were no differences between groups in the duration and extent of brain acidosis, and relative concentrations of phosphorylated metabolites. Categorical assessment of neurobehavior was evaluated at 72 h postischemia (n = 16), or earlier if an animal's condition deteriorated (n = 6). Postischemic hypothermia was associated with less severe stages of encephalopathy compared with normothermia (p = 0.05). Histologic neuronal injury was assessed categorically in 16 brain regions, and postischemic hypothermia resulted in less neuronal injury in temporal (p = 0.024) and occipital (p = 0.044) cortex at 10 mm beneath the cortical surface, and in the basal ganglia (p = 0.038) compared with that in normothermia. Modest hypothermia for 1 h immediately after brain ischemia provides partial neuroprotection and may represent an adjunct to resuscitative strategies.

Animals↗