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Biomedical subjects

H Lai

Publications and source records attributed to H Lai.

At least 55 records · Page 3Linked to original sources
PubMed1998

Influence of percentage of osseointegration on stress distribution around dental implants.

OBJECTIVE: Stress around implants may lead to bone resorption and loss of the implant. The present study examined the influence of percentage of osseointegration at the implant-bone interface on the transmission of occlusal forces for endosseous dental implants. METHODS: The three-dimensional finite element method used in the study was built from data obtained from slices of dental computed tomography scans. The study modeled a 3.75 x 10-mm cylindric implant placed in an edentulous mandible. Varying the elastic parameters assigned to the implant-bone interface, a load of 35 N was applied at the occlusal surface of the restoration at the vertical axis of the implant. Maximum principal stress, minimum principal stress and Von Mises stress were calculated. RESULTS AND CONCLUSIONS: The most extreme stresses in the bone were always located around the neck of the implant. Those stresses in the implant-tissue interface decreased in inverse proportion to the increase in percentage of osseointegration. These results indicate the value of osseointegration in the aspect of mechanics.

Alveolar Process↗
PubMed1998

Risk Factors for HTLV-I Mother to Child Transmission: Influence of Genetic Markers.

This study was designed to evaluate the influence of genetic markers on the seropositivity of offspring of HTLV-I positive mothers in Tumaco, Colombia, an endemic area for HTLV-I infection and a site where there exists a racially mixed population of Black and Caucasian ancestors. 33 HTLV-I seropositive women with at least one offspring were studied. A total of 111 offspring were tested using hemaglutination-inhibition for testing sera for the allotypic markers G1m (1, 2, 3, 17) and G3m (5, 6, 13, 21). Potential risk factors such as mother s age at child's birth, mother's age at the time of the study, breastfeeding months, TSP vs. asymptomatic HTLV-I carrier, sibship's size, children's age and sex, were not found to be associated with mother to child transmission. Mother's Negroid genetic marker genotype (1, 17, 5, 13/1, 17, 5, +/- 13) was marginally associated with mother to child transmission of HTLV-I (P=0.0057; OR=11.97; CI=0.92-155.96)

Journal Article↗
PubMed1998

Hospitalization, inpatient physical therapy and institutionalization after hospital discharge of prostate cancer patients in south Florida.

PURPOSE: Explaining survival variation in prostate cancer requires the identification of new predictive factors, of which physical function is attractive hypothetically. To understand physical dysfunction in prostate cancer better, we examined medical claims. Our aims were to describe the consumption of inpatient resources, examine the association of physical therapy with institutionalization after hospital discharge and determine the association of disease stage with frequency of hospitalization, inpatient physical therapy and discharge to a skilled nursing facility. MATERIALS AND METHODS: We used 1994 Medicare claims for patients in South Florida who had prostate cancer. To examine the association of disease stage with use of health services, we inferred disease stage from stage specific treatment. Multiple linear regression was used to examine the interaction of inferred disease stage with health services while adjusting for age. RESULTS: A total of 22,279 residents of South Florida a mean of 78.3 years old with prostate cancer billed Medicare in 1994. Of these patients 2,507 were admitted to a hospital 4,606 times, resulting in total charges of $70 million. Many claims indicated physical dysfunction, including 1,896 charges for physical therapy, which was associated with more institutionalization after hospital discharge. Disease stage and patient age were individually associated with the frequency of hospitalization, inpatient physical therapy and discharge to a skilled nursing facility. CONCLUSIONS: Inpatients with prostate cancer have substantial stage dependent physical dysfunction. If the hypothesized interaction of physical dysfunction with mortality is confirmed in prospective studies and outpatient settings, theoretically the door will have been opened to new interventions for prolonging survival in patients with prostate cancer.

Aged↗
PubMed1998

Acute exposure to a 60 Hz magnetic field affects rats' water-maze performance.

Rats were trained in six sessions to locate a submerged platform in a circular water-maze. They were exposed to a 1 mT, 60 Hz magnetic field for one hour in a Helmholtz coil system immediately before each training session. In addition, one hour after the last training session, they were tested in a probe trial during which the platform was removed and the time spent in the quadrant of the maze in which the platform was located during the training sessions was scored. Control animals were sham-exposed using the exposure system operating with the coils activated in an anti-parallel direction to cancel the fields. A group of "non-exposed" control animals was also included in the study. There was no significant difference between the magnetic field-exposed and control animals in learning to locate the platform. However, swim speed of the magnetic field-exposed rats was significantly slower than that of the controls. During the probe trial, magnetic field-exposed animals spent significantly less time in the quadrant that contained the platform, and their swim patterns were different from those of the controls. These results indicate that magnetic field exposure causes a deficit in spatial "reference" memory in the rat. Rats subjected to magnetic field exposure probably used a different behavioral strategy in learning the maze.

Animals↗
PubMed1998

Intracerebroventricular injection of mu- and delta-opiate receptor antagonists block 60 Hz magnetic field-induced decreases in cholinergic activity in the frontal cortex and hippocampus of the rat.

In previous research, we have found that acute exposure to a 60 Hz magnetic field decreased cholinergic activity in the frontal cortex and hippocampus of the rat as measured by sodium-dependent high-affinity choline uptake activity. We concluded that the effect was mediated by endogenous opioids inside the brain because it could be blocked by pretreatment of rats before magnetic field exposure with the opiate antagonist naltrexone, but not by the peripheral antagonist naloxone methiodide. In the present study, the involvement of opiate receptor subtypes was investigated. Rats were pretreated by intracerebroventricular injection of the mu-opiate receptor antagonist, beta-funaltrexamine, or the delta-opiate receptor antagonist, naltrindole, before exposure to a 60 Hz magnetic field (2 mT, 1 hour). It was found that the effects of magnetic field on high-affinity choline uptake in the frontal cortex and hippocampus were blocked by the drug treatments. These data indicate that both mu- and delta-opiate receptors in the brain are involved in the magnetic field-induced decreases in cholinergic activity in the frontal cortex and hippocampus of the rat.

Animals↗
PubMed1997

HIV-1 infection in women is associated with severe nutritional deficiencies.

Nutritional deficiencies may contribute to immune dysregulation, and have been shown to be sensitive markers of HIV-1 disease progression. Only limited information exists, however, regarding the nutritional profile of HIV-1-seropositive drug abusers. Immune and nutritional measurements were obtained in a subsample of 125 subjects from a larger cohort of drug users being followed for HIV-1 infection and cofactors of disease progression. Nutritional deficiencies, particularly vitamins A, E, and zinc, were widespread with up to 86% of the drug users exhibiting at least one nutritional alteration. Although immune parameters (CD4 count, CD8 count, beta2-microglobulin) were similar in the HIV-1-infected men and women, women had significantly poorer overall nutritional status, as measured by plasma proteins, which are considered to be sensitive markers of malnutrition. A comparison of individuals with advanced disease (CD4 count <200/mm3) revealed significantly lower levels of plasma prealbumin (p < .01), selenium, (p < .05), and greater deficiency of vitamins A (p < .01) and E (p < .05) in women than in men. The greater severity of nutritional deficiencies noted in HIV-1-infected women may be an important determinant of disease progression and survival.

Adult↗
PubMed1997

High risk of HIV-related mortality is associated with selenium deficiency.

To determine the independent contribution of specific immunologic and nutritional factors on survival in HIV-1 disease, CD4 cell count, antiretroviral treatment, plasma levels of vitamins A, E, B6, and B12 and minerals selenium and zinc were considered in relation to relative risk for HIV-related mortality. Immune parameters and nutrients known to affect immune function were evaluated at 6-month intervals in 125 HIV-1-seropositive drug-using men and women in Miami, FL, over 3.5 years. A total of 21 of the HIV-1-infected participants died of HIV-related causes during the 3.5-year longitudinal study. Subclinical malnutrition (i.e., overly low levels of prealbumin, relative risk [RR] = 4.01, p < 0.007), deficiency of vitamin A (RR = 3.23, p < 0.03), vitamin B12 deficiency (RR = 8.33, p < 0.009), zinc deficiency (RR = 2.29.1, p < 0.04), and selenium deficiency (RR = 19.9, p < 0.0001) over time, but not zidovudine treatment, were shown to each be associated with HIV-1-related mortality independent of CD4 cell counts <200/mm3 at baseline, and CD4 counts over time. When all factors that could affect survival, including CD4 counts <200/mm3 at baseline, CD4 levels over time, and nutrient deficiencies were considered jointly, only CD4 counts over time (RR = 0.69, p < 0.04) and selenium deficiency (RR = 10.8, p < 0.002) were significantly associated with mortality. These results indicate that selenium deficiency is an independent predictor of survival for those with HIV-1 infection.

Adult↗
PubMed1997

Survival after radical prostatectomy.

CONTEXT: The generalizability of currently available estimates of survival after radical prostatectomy is theoretically limited. OBJECTIVE: To obtain generalizable estimates of survival after radical prostatectomy. DESIGN: A population-based retrospective cohort study. SETTING: Nine regions of the United States. PATIENTS: Patients who were diagnosed with prostate cancer between 1983 and 1987 and underwent radical prostatectomy and lymph node dissection. MAIN OUTCOME MEASURES: Proportional hazards models incorporating geographical region, age, race, pathological stage, lymph node involvement, and tumor grade to identify independent correlates of disease-specific and overall survival and life table analyses to estimate 10-year survival distributions. RESULTS: A total of 3626 patients with a mean age of 65 years were included in the study; 92.6% were white, 54.2% had moderate-grade cancer, 60.4% had no extension beyond the prostate, and 91.2% had no lymph node involvement. Using San Francisco-Oakland, Calif, as a reference region, no other region was significantly associated with a risk of disease-specific or overall mortality. Older age and black race were independently associated with worse overall but not disease-specific survival. Higher grade, extension beyond the prostate, and lymph node involvement were independently associated with worse disease-specific and overall survival. Estimates of 10-year disease-specific survival ranged from 75% to 97% for patients with well-differentiated and moderately differentiated cancers and from 60% to 86% for patients with poorly differentiated cancers. CONCLUSIONS: Neither disease-specific nor overall survival varied by region, suggesting geographically uniform assessments of risk in patient selection for radical prostatectomy. Across regions, overall survival varied by patient and prostate cancer characteristics while disease-specific survival varied substantially by prostate cancer but not patient characteristics. The present analyses provide the most generalizable current estimates of survival after radical prostatectomy.

Aged↗
PubMed1997

Melatonin and a spin-trap compound block radiofrequency electromagnetic radiation-induced DNA strand breaks in rat brain cells.

Effects of in vivo microwave exposure on DNA strand breaks, a form of DNA damage, were investigated in rat brain cells. In previous research, we have found that acute (2 hours) exposure to pulsed (2 microseconds pulses, 500 pps) 2450-MHz radiofrequency electromagnetic radiation (RFR) (power density 2 mW/cm2, average whole body specific absorption rate 1.2 W/kg) caused an increase in DNA single- and double-strand breaks in brain cells of the rat when assayed 4 hours post exposure using a microgel electrophoresis assay. In the present study, we found that treatment of rats immediately before and after RFR exposure with either melatonin (1 mg/kg/injection, SC) or the spin-trap compound N-tert-butyl-alpha-phenylnitrone (PBN) (100 mg/kg/injection, i.p.) blocks this effects of RFR. Since both melatonin and PBN are efficient free radical scavengers it is hypothesized that free radicals are involved in RFR-induced DNA damage in the brain cells of rats. Since cumulated DNA strand breaks in brain cells can lead to neurodegenerative diseases and cancer and an excess of free radicals in cells has been suggested to be the cause of various human diseases, data from this study could have important implications for the health effects of RFR exposure.

Animals↗
PubMed1997

Competing risks of mortality in prostate cancer.

PURPOSE: We have observed that in prostate cancer older age, black race, high stage and no treatment are independently associated with higher disease specific and overall mortality. Because disease nonspecific mortality was not examined one cannot reasonably infer that higher overall mortality is largely due to higher disease specific mortality. To understand better the interactions of independent prognostic variables with overall mortality we jointly evaluated their effects on type of death and time to death. MATERIALS AND METHODS: Using the prostate cancer patients of the 1973 to 1990 public use tape of the Surveillance, Epidemiology and End Results program, we performed competing risks analysis with multivariate accelerated failure time model to examine if the prognostic factors were associated with type of death and time to death. RESULTS: Older age, black race and no treatment were independently associated with higher relative risk of disease specific and nonspecific mortality. Localized stage was associated with lower and higher disease specific and nonspecific mortality than regional stage, respectively. The relative risks of disease specific and nonspecific mortality were significantly different from each other for all prognostic factors. CONCLUSIONS: To our knowledge, a competing risks analysis in prostate cancer has not been done previously. While all prognostic factors were associated with disease specific and nonspecific mortality, the relative contribution of disease specific and nonspecific mortality to overall mortality varied by prognostic factor, with some prognostic factors associated with relatively high disease specific mortality while others were associated with relatively high disease nonspecific mortality. The similarity of the associations of age, race and treatment with disease specific and nonspecific mortality suggests that they mark an unidentified factor(s) that affects patient health nonspecifically. Such a factor(s) may partly or completely explain the association of treatment with lower disease specific mortality.

Aged↗
PubMed1997

Vasodepressor syncope due to subclinical myocardial ischemia.

INTRODUCTION: Vasodepressor syncope is a common cause of syncope, but the initiating event that triggers the vasodepressor response remains incompletely understood. Although ischemia due to acute right coronary occlusion may precipitate hypotension and bradycardia through the Bezold-Jarisch reflex, an ischemic precipitant for the common vasodepressor faint has not been previously identified. In the present study, we present evidence for a causal relationship between myocardial ischemia and vasodepressor syncope. METHODS AND RESULTS: Two patients referred for evaluation of syncope underwent upright tilt table testing with either ST segment monitoring, sestamibi scintigraphy and echocardiography during the tilt test, or coronary angiography. Both patients had positive tilt table tests during the control study. Patient 1 was documented to have reproducible ischemic ECG changes during atypical chest pressure induced by upright tilt, despite a normal coronary angiogram with ergonovine provocation. Subsequent tilt testing with simultaneous sestamibi perfusion imaging and echocardiography revealed reversible anterolateral hypoperfusion corresponding with anterolateral hypokinesis during upright tilt that preceded syncope. Ischemic ECG changes during incremental rapid atrial pacing further suggested ischemia on the basis of microvascular disease. Follow-up tilt testing on verapamil was negative. Patient 2 developed ischemic ECG changes during the recovery phase of an exercise stress test, which was followed by a vasodepressor response and frank syncope. Coronary angiography revealed a 90% distal right coronary artery stenosis that was successfully dilated, after which follow-up tilt table testing off all other medication was negative. CONCLUSIONS: These two cases illustrate a previously unrecognized causality between myocardial ischemia and clinical vasodepressor syncope, and demonstrate that subtle manifestations of myocardial ischemia, associated with either atypical angina or silent ischemia, can provoke syncope.

Cardiac Pacing, Artificial↗
PubMed1997

Melatonin and N-tert-butyl-alpha-phenylnitrone block 60-Hz magnetic field-induced DNA single and double strand breaks in rat brain cells.

In previous research, we have found an increase in DNA single- and double-strand breaks in brain cells of rats after acute exposure (two hours) to a sinusoidal 60-Hz magnetic field. The present experiment was carried out to investigate whether treatment with melatonin and the spin-trap compound N-tert-butyl-alpha-phenylnitrone (PBN) could block the effect of magnetic fields on brain cell DNA. Rats were injected with melatonin (1 mg/kg, sc) or PBN (100 mg/kg, ip) immediately before and after two hours of exposure to a 60-Hz magnetic field at an intensity of 0.5 mT. We found that both drug treatments blocked the magnetic field-induced DNA single- and double-strand breaks in brain cells, as assayed by a microgel electrophoresis method. Since melatonin and PBN are efficient free radical scavengers, these data suggest that free radicals may play a role in magnetic field-induced DNA damage.

Animals↗
PubMed1997

Acute exposure to a 60 Hz magnetic field increases DNA strand breaks in rat brain cells.

Acute (2 h) exposure of rats to a 60 Hz magnetic field (flux densities 0.1, 0.25, and 0.5 mT) caused a dose-dependent increase in DNA strand breaks in brain cells of the animals (assayed by a microgel electrophoresis method at 4 h postexposure). An increase in single-strand DNA breaks was observed after exposure to magnetic fields of 0.1, 0.25, and 0.5 mT, whereas an increase in double-strand DNA breaks was observed at 0.25 and 0.5 mT. Because DNA strand breaks may affect cellular functions, lead to carcinogenesis and cell death, and be related to onset of neurodegenerative diseases, our data may have important implications for the possible health effects of exposure to 60 Hz magnetic fields.

Analysis of Variance↗
PubMed1997

Reliability of Spanish translations of select urological quality of life instruments.

PURPOSE: Many patients with urological disease do not speak English. In medical studies restricting patients to those who speak only English undermines efforts to understand disease because restrictions decrease efficiency of patient recruitment, and because language and culture are associated with variable outcomes. In Spanish speaking locations, such as South Florida, studies would suffer severe selection bias if patients were required to speak English. To allow grouping in future studies of English and Spanish speaking patients we examined the English-Spanish reliability of select instruments that measure health related quality of life in patients with urological disease. MATERIALS AND METHODS: We assembled available Spanish versions and translated English versions of questions regarding satisfaction, the American Urological Association symptom index, the University of California, Los Angeles Prostate Cancer Index and a pain inventory. We then examined English-Spanish reliability by asking bilingual men 50 years old or older to complete English and Spanish versions at the same sitting. A convenience sample was recruited from outpatients and volunteers at the Miami Veterans Affairs Medical Center and population based subjects living in largely Hispanic Hialeah, Florida. Reliability estimates were calculated with kappa coefficients for categorical data and intraclass correlation coefficients for quantitative data. RESULTS: A total of 100 subjects a median of 59 years old completed the questionnaire, including 55 born in Puerto Rico or Cuba, while the remainder were born at various sites throughout the Americas and Spain. Reliability estimates showed that kappa = > 0.81 for almost all items. For 2 items relating to health and social interactions reliability was poor, and stratification showed that poor reliability was primarily a feature of subjects in good health who are theoretically socially active. CONCLUSIONS: Almost all items tested have excellent English-Spanish reliability in a mixed sample of bilingual men. Nonreliability of 2 items relating to health and social interactions probably originates from the effect of language on perception, and invalidates English and Spanish grouping of these items. Because the sample represents many dialects of Spanish, the translations tested may be transported to other cities. In studies that use these instruments investigators can reasonably group answers from English and Spanish speaking study subjects or study the effects of acculturation on quality of life.

Hispanic or Latino↗
PubMed1997

Variation in prostate cancer survival explained by significant prognostic factors.

PURPOSE: Traditional survival analytical tools do not reveal the ability of significant prognostic factors to predict (that is, explain variation in) survival. We used survival data in patients with prostate cancer to illustrate how the association of factors with survival diverges from their ability to explain variation in survival; bladder cancer was included as a point of general comparison. MATERIALS AND METHODS: We used the 1973 to 1990 records of the Surveillance Epidemiology and End Results program. Multivariate proportional hazards models were used to identify factors that significantly associated with survival. The proportion of variation explained by these factors was estimated with the Schemper method. RESULTS: The dataset included 10,636 patients with prostate cancer and 1,070 with bladder cancer. Median survival was significantly longer in prostate than bladder cancer; other characteristics were similarly distributed. Age, stage and marital status were associated with survival in both cancers (p value range 0.0001 to 0.0009). The total proportion of variation explained was 7.1% and 32.1% for prostate and bladder cancer, respectively. In prostate cancer, age, stage and marital status explained 0.6, 5.5 and 0.4%, of the adjusted proportion of variation explained, respectively, and in bladder cancer, they explained 14.7, 8.9 and 0.6%, respectively. CONCLUSIONS: Proportional hazards models identified but did not reveal the ability of significant prognostic factors to explain variations in survival. The proportion of variation explained analyses illustrate why predicting survival is so difficult, especially in prostate cancer. The prognostic factors used do not possess the ability to explain variation in survival; new prognostic factors must be identified.

Aged↗
PubMed1996

Spatial learning deficit in the rat after exposure to a 60 Hz magnetic field.

Rats were trained in ten daily sessions to perform in a 12-arm radial maze, which is a behavioral test for spatial memory functions. Exposure to a 60 Hz magnetic field (45 min, 0.75 mT) immediately before each training session retarded learning significantly. Pretreatment with the cholinergic agonist physostigmine before magnetic field exposure reversed the field's effect on spatial learning. Data from this experiment indicate that magnetic field-induced spatial learning deficit is caused by the effect of the field on cholinergic systems.

Analysis of Variance↗