Search PubMed⌕ Search

Biomedical subjects

D Brooks

Publications and source records attributed to D Brooks.

At least 55 records · Page 3Linked to original sources
PubMed1999

Acute and chronic effects of airway obstruction on canine left ventricular performance.

We used a canine model of chronic obstructive sleep apnea (OSA) to examine the effects of intermittent airway occlusion during sleep on left ventricular (LV) performance. Studies were performed in four dogs. The effects of acute airway occlusion on LV pressure and volume (on a background of chronic OSA) were determined with an impedance catheter and a high fidelity manometer. In conscious animals (n = 3), experiencing spontaneous episodes of sleep, acute airway occlusion caused significant increases in LV transmural systolic pressure that were associated with increased end-systolic volume and reduced stroke volume. To determine the effects of chronic OSA on baseline LV function, two-dimensional echocardiograms were performed in conscious animals (n = 4) during unobstructed breathing before and after a 1- to 3-mo period of OSA. During chronic OSA, there was a significant decrease in LV ejection fraction as a result of increases in end-systolic volume. We conclude that in chronic OSA acute airway occlusion during sleep is associated with increases in LV afterload and decreases in fractional shortening. Chronic OSA also leads to sustained decreases in LV systolic performance that could be caused by the development of systemic hypertension and/or transient increases in LV afterload during episodes of airway obstruction.

Airway Obstruction↗
PubMed1999

Trends in the epidemiology of COPD in Canada, 1980 to 1995. COPD and Rehabilitation Committee of the Canadian Thoracic Society.

PURPOSE: To describe trends in the epidemiology of COPD in Canada from 1980 to 1995, in terms of perceived prevalence, mortality, and hospital morbidity. DATA SOURCES: We limited the analysis to data related to chronic bronchitis, emphysema, or chronic airway obstruction not classified elsewhere, and excluded asthma (Ninth International Classification of Diseases, codes 490 to 492 and 496). The perceived prevalence rate of COPD was derived from the 1994-1995 National Health Survey. Mortality and hospital morbidity data (from 1980 to 1995) were obtained from the Health Statistics Division of Statistics Canada. RESULTS: From the National Health Survey, it was estimated that 750,000 Canadians had chronic bronchitis or emphysema diagnosed by a health professional. Prevalence rates were the following: ages 55 to 64 years, 4.6%; ages 65 to 74 years, 5.0%; > or =75 years, 6.8%. From 1980 to 1995, the total number of deaths from COPD increased from 4,438 to 8,583. Although the age-standardized mortality rate remained stable throughout this period in men (around 45/100,000 population), it doubled in women (8.3/100,000 in 1980 to 17.3/100,000 in 1995). There were 55,782 hospital separations in 1993-1994 with COPD as the primary discharge diagnosis (compared to 42,102 in 1981-1982). In people aged > or =65 years, the age-specific hospital separation rate increased over this period, especially in women > or =75 years (from 504/100,000 to 1,033/100,000). The average in-hospital length of stay was 9.6 days in 1981-1982 and 8.3 days in 1993-1994. CONCLUSION: COPD represents a major health issue in Canada and will likely remain so for decades. Physician and non-physician health professionals who provide health care, as well as those who fund it must actively encourage approaches for primary and secondary prevention of this condition as well as approaches shown to be effective in addressing its associated impairment, disability, and handicap.

Aged↗
PubMed1998

Sleep architecture in a canine model of obstructive sleep apnea.

Obstructive sleep apnea (OSA) causes recurrent sleep disruption that is thought to contribute to excessive daytime sleepiness in patients with this disorder. The purpose of this study was to determine the specific effects of OSA on overall sleep architecture in a canine model of OSA. The advantage of this model is that sleep during long-term OSA can be compared to both normal sleep before OSA and recovery sleep after OSA. Studies were performed in four dogs in which sleep-wake state was monitored continuously by a computer that received telemetered EEG and EMG signals. Whenever sleep was detected, the computer sent a signal to close a valve through which the dog breathed; when the dog awoke the occlusion was released. In each dog, data were analyzed from 4 consecutive nights in three phases: a control phase before induction of OSA, a phase during long-term OSA (mean = 85 days, apnea index = 59/hour), and a recovery phase after cessation of OSA. During recovery there was a significant increase in the amount of rapid-eye-movement (REM) sleep compared to the OSA phase (p < 0.01), as well as significant increases in sleep efficiency and decreases in wakefulness (p < 0.01), similar to that reported in OSA patients. The REM rebound during recovery, however, could not be attributed to overall REM deprivation since the amount of REM sleep during the OSA phase was not different from the control phase (p = 0.708). This finding suggests that REM rebound during recovery from OSA is not the result of an overall REM sleep deficit per se. Rather, repeated sleep disruption due to the effects of repetitive apneas and hypoxia may lead to an increased REM sleep drive that manifests itself as a REM sleep rebound during recovery sleep after OSA.

Animals↗
PubMed1998

Tissue restricted expression of two human Frzbs in preadipocytes and pancreas.

Frzb is a newly discovered family of secreted glycoproteins that function to modulate signaling activity of Wnt. Frzb proteins share sequence homology with the extracellular domain of the Wnt receptor (frizzled) and are capable of binding to Wnt. Thus, Frzb functions to antagonize Wnt activity by sequestering Wnt and preventing its binding to the frizzled receptor. Since the initial identification of bovine and human Frzb, several related members of this family have been isolated from rodent and human. In this paper, we describe the cloning and expression of two human frzb homologues termed hFRP-1b and hFRP-2. These human FRPs share significant homology to mouse sFRP-1 and sFRP-2 (55 and 98% identity at amino acid level, respectively). Northern blot experiments revealed that these Frzb homologues have highly restricted tissue distribution. hFRP-1b is exclusively expressed in pancreatic tissue while high levels of hFRP-2 were found in adipose tissue. In addition, low levels of hFRP-2 were also observed in other tissues including heart, pancreas and muscle. Remarkably, FRP-2 is predominantly expressed in un-differentiated preadipocytes in both rodent and man. The expression of FRP-2 is also significantly reduced in fat pads from obese mice. Taken together, these data indicate that distinctive members of the Frzb family exhibit different expression patterns in vivo, suggesting their ability to modulate diverse aspects of Wnt signaling. The expression and dysregulation of sFRP-2 in fat and obesity also suggest a potential roles on the Wnt signaling pathway in the pathology of obesity and related metabolic diseases. Molecular cloning and expression of these Frzbs will allow detailed molecular and biochemical analysis of Wnt-Frzb interaction and their impact on Wnt-Frizzled receptor signal transduction.

3T3 Cells↗
PubMed1998

Dopamine agonists and neuroprotection in Parkinson's disease.

There is increasing interest in the potential of dopamine agonists to provide a neuroprotective effect and to alter the natural course of levodopa-treated Parkinson's disease (PD). Theoretically, such a protective effect might derive from (a) a levodopa sparing effect, (b) stimulation dopamine autoreceptors resulting in decreased dopamine synthesis, release, and turnover, (c) direct anti-oxidant effects, and (d) restoration of dopaminergic tone to the dopamine-denervated brain so as to restore inhibition to the subthalamic nucleus and thereby diminish STN-mediated excitotoxicity. Preclinical studies have demonstrated that dopamine agonists reduce dopamine formation in comparison to levodopa, protect cultured dopaminergic neurons from a variety of toxins including levodopa, and protect dopaminergic neurons from toxins and age-related degeneration in some rodent models of parkinsonism. Based on these findings, several clinical trials have been initiated in patients with early PD to test the effect of dopamine agonists on clinical and neuroimaging markers of disease progression.

Animals↗
PubMed1998

Role of endoscopic retrograde cholangiopancreatography for suspected choledocholithiasis in patients undergoing laparoscopic cholecystectomy.

BACKGROUND: We report our experience of selective cholangiography in a series of laparoscopic cholecystectomies and evaluate the strategy of using "stricter criteria" to select preoperative endoscopic retrograde cholangiopancreatography (ERCPs). METHODS: A total of 1847 consecutive laparoscopic cholecystectomies were analyzed for use of cholangiography. A high risk of common bile duct stones (bilirubin level more than 2 mg/dL, jaundice, alkaline phosphatase level more than 150 U/L, pancreatitis, or dilated bile duct and/or stone on ultrasound or CT) was an indication for preoperative ERCP. Selective intraoperative cholangiography was performed for intermediate risk of bile duct stones. The strategy of using "stricter criteria" (jaundice and/or demonstrated bile duct stones on ultrasound or CT) for selecting preoperative ERCP was evaluated retrospectively. RESULTS: Preoperative ERCP was performed in 135 patients (7.3%) and demonstrated bile duct stones in 43 (32%). Of 36 patients with mild gallstone pancreatitis alone, stones were found only in 6 patients (17%). Selective intraoperative cholangiography was performed in 87 (5%), and stones were found in 2 (2%); 67 (3.6%) postoperative ERCPs were performed for suspected choledocholithiasis, and stones were found in 21 (32%). Applying "stricter criteria" to select preoperative ERCP would predict ductal stones in 56%, whereas 3% of patients with stones would be missed, resulting in a 50% reduction in preoperative ERCPs. CONCLUSIONS: Even in selected patients considered likely to have choledocholithiasis, the diagnostic yield of preoperative ERCP is low. Using "stricter criteria" to select patients for preoperative ERCP can avoid unnecessary ERCPs.

Cholangiography↗
PubMed1998

Factors associated with smoking among children and adolescents in Connecticut.

INTRODUCTION: The age of smoking initiation has dropped over the past four decades. Since behaviors and attitudes adopted in late childhood or early adolescence predict future smoking, it is important to understand the smoking and other risk-taking behaviors and attitudes of children aged 12 and younger. The goal of the analyses presented here was to describe behavioral and attitudinal factors associated with smoking among elementary school (grades 4-6), middle school (grade 7-8), and high school (grades 9-12) students in Connecticut. METHODS: We have used data from 8 years (1988-1996) of an anonymous, self-administered health risk appraisal survey given to children and adolescents in self-selected public and private schools. We compared the proportion of smokers and nonsmokers who reported various behaviors and attitudes and compared them with the chi-square test. RESULTS: Fifteen percent (n = 4,884) of the total population (n = 31, 861) were current smokers. At all grade levels, current smokers were more likely than nonsmokers to engage in risk-taking behaviors, and to report more stress and depression. Indicators of risk-taking and stress were also associated with the intent to smoke among children in grades 4-6. CONCLUSIONS: Smoking occurs within the context of other risk-taking behavior and psychological distress, among both children and older adolescents. Our data provide support for the idea of early identification and targeting of children at high risk of smoking in elementary school, possibly as early as grade four.

Adolescent↗
PubMed1998

Chronic follicular conjunctivitis associated with Chlamydia psittaci or Chlamydia pneumoniae.

We determined whether patients with chronic conjunctivitis in whom direct fluorescent antibody (DFA) tests revealed genus-specific chlamydial antigens (but not species-specific Chlamydia trachomatis antigens) were infected with Chlamydia psittaci or Chlamydia pneumoniae. Patients were divided into a case group of possible non-trachomatis chlamydial conjunctivitis and a control group of nonchlamydial conjunctivitis on the basis of examination and DFA testing. Species-specific primers were used to amplify C. trachomatis, C. psittaci, and C. pneumoniae DNA with polymerase chain reaction (PCR). Four (27%) of 15 samples from the case group were positive for C. psittaci or C. pneumoniae DNA, whereas none of 24 control samples were positive. Sequencing revealed a C. pneumoniae, an avian C. psittaci, and two mammalian C. psittaci strains. A short course of oral antibiotic treatment appears to be inadequate for patients with non-trachomatis chlamydial conjunctivitis. Ocular infections due to C. pneumoniae and C. psittaci may be more common than previously recognized and can be identified by DFA and PCR.

Adult↗
PubMed1998

Requirement for CD4(+) T cells in the Friend murine retrovirus neutralizing antibody response: evidence for functional T cells in genetic low-recovery mice.

Recovery from infection with the Friend murine leukemia retrovirus complex (FV) requires T-helper cells and cytotoxic T cells as well as neutralizing antibodies. Several host genes, including genes of the major histocompatibility complex (H-2) and an H-2-unlinked gene, Rfv-3, influence these FV-specific immune responses. (B10.A x A/Wy)F1 mice, which have the H-2(a/a) Rfv-3(r/s) genotype, fail to mount a detectable FV-specific T-cell proliferative response but nevertheless produce FV-specific neutralizing immunoglobulin M (IgM) antibodies and can eliminate FV viremia. Thus, this IgM response, primarily influenced by the Rfv-3 gene, may be T-cell independent. To test this idea, mice were depleted of either CD4(+) or CD8(+) T-cell populations in vivo and were monitored for the effect on the neutralizing antibody response following FV infection. Surprisingly, mice in which CD4(+) cells were depleted showed undetectable FV-neutralizing antibody responses and high viremia levels compared to nondepleted or CD8-depleted animals. In addition to knocking out the FV antibody response, CD4(+) T-cell depletion reduced survival time significantly, further indicating the importance of CD4(+) T cells. These studies revealed the first evidence for a functional T-cell response following FV infection in these low-recovery mice and showed that CD4(+) T-helper cells are required for the Rfv-3-controlled FV antibody response.

Animals↗
PubMed1998

The influence of 6 months of oral anabolic steroids on body mass and respiratory muscles in undernourished COPD patients.

STUDY OBJECTIVE: To evaluate the influence of oral anabolic steroids on body mass index (BMI), lean body mass, anthropometric measures, respiratory muscle strength, and functional exercise capacity among subjects with COPD. DESIGN: Prospective, randomized, controlled, double-blind study. SETTING: Pulmonary rehabilitation program. PARTICIPANTS: Twenty-three undernourished male COPD patients in whom BMI was below 20 kg/m2 and the maximal inspiratory pressure (PImax) was below 60% of the predicted value. INTERVENTION: The study group received 250 mg of testosterone i.m. at baseline and 12 mg of oral stanozolol a day for 27 weeks, during which time the control group received placebo. Both groups participated in inspiratory muscle exercises during weeks 9 to 27 and cycle ergometer exercises during weeks 18 to 27. MEASUREMENTS AND RESULTS: Seventeen of 23 subjects completed the study. Weight increased in nine of 10 subjects who received anabolic steroids (mean, +1.8+/-0.5 kg; p<0.05), whereas the control group lost weight (-0.4+/-0.2 kg). The study group's increase in BMI differed significantly from that of the control group from weeks 3 to 27 (p<0.05). Lean body mass increased in the study group at weeks 9 and 18 (p<0.05). Arm muscle circumference and thigh circumference also differed between groups (p<0.05). Changes in PImax (study group, 41%; control group, 20%) were not statistically significant. No changes in the 6-min walk distance or in maximal exercise capacity were identified in either group. CONCLUSION: The administration of oral anabolic steroids for 27 weeks to malnourished male subjects with COPD was free of clinical or biochemical side effects. It was associated with increases in BMI, lean body mass, and anthropometric measures of arm and thigh circumference, with no significant changes in endurance exercise capacity.

Administration, Oral↗
PubMed1997

Obstructive sleep apnea as a cause of systemic hypertension. Evidence from a canine model.

Several epidemiological studies have identified obstructive sleep apnea (OSA) as a risk factor for systemic hypertension, but a direct etiologic link between the two disorders has not been established definitively. Furthermore, the specific physiological mechanisms underlying the association between OSA and systemic hypertension have not been identified. The purpose of this study was to systematically examine the effects of OSA on daytime and nighttime blood pressure (BP). We induced OSA in four dogs by intermittent airway occlusion during nocturnal sleep. Daytime and nighttime BP were measured before, during, and after a 1-3-mo long period of OSA. OSA resulted in acute transient increases in nighttime BP to a maximum of 13.0+/-2.0 mmHg (mean+/-SEM), and eventually produced sustained daytime hypertension to a maximum of 15.7+/-4.3 mmHg. In a subsequent protocol, recurrent arousal from sleep without airway occlusion did not result in daytime hypertension. The demonstration that OSA can lead to the development of sustained hypertension has considerable importance, given the high prevalence of both disorders in the population.

Animals↗
PubMed1997

Evaluation of the Ultraviolet Index: media reactions and public response.

BACKGROUND: In response to the increasing rate of skin cancer, particularly melanoma in the United States, the Environmental Protection Agency, the National Weather Service, the Centers for Disease Control and Prevention, National Association of Physicians for the Environment, and the American Academy of Dermatology, developed the Ultraviolet Index (UVI) to inform the public of the strength of the sun's rays and advise on methods for sun protection. OBJECTIVE: Our purpose was to evaluate the extent to which television stations and newspapers reported the UVI and assess the public's response to it. METHODS: To evaluate the effect of this effort, we surveyed television weather forecasters at 185 stations and examined weather pages in 54 newspapers in 58 cities that received the UVI reports. We also conducted a population probability telephone survey of 700 white adults (18 years of age and older) in these 58 cities. RESULTS: Seventy-one percent of the 169 stations that provided survey data for both 1994 and 1995 broadcast the UVI; 61% of newspapers reported the UVI. Nearly 64% of the 700 respondents (n = 445) had heard of the UVI. Of these respondents, 38% (n = 170) stated that they or their family changed their sun protection practices as a result of the UVI. CONCLUSION: The majority of television weather forecasters and newspapers reported the UVI. Most of the public was aware of the UVI, causing some to change sun protection practices. Further evaluation is required to maximize the effect of the UVI on sun protection practices.

Adult↗
PubMed1997

Transdermal fentanyl versus sustained-release oral morphine in cancer pain: preference, efficacy, and quality of life. The TTS-Fentanyl Comparative Trial Group.

Cancer patients requiring strong opioid analgesia (n = 202; mean age, 61.5 years; range, 18-89 years; 55% men) were recruited from 38 United Kingdom palliative care centers into a randomized, open, two-period, crossover study comparing transdermal fentanyl with sustained-release oral morphine. Patients received one treatment for 15 days followed immediately by the other for 15 days. Daily diaries were completed. Both treatments appeared equally effective in terms of pain control, as assessed by the Memorial Pain Assessment Card and European Organization for Research and Treatment of Cancer (EORTC) pain scores. Fentanyl was associated with significantly less constipation (p < 0.001) and less daytime drowsiness (p = 0.015) but greater sleep disturbance (p = 0.004) and shorter sleep duration (p = 0.008) than morphine. The World Health Organization (WHO) performance status and EORTC global quality of life scores showed no significant difference between treatment groups. Of those patients who were able to express a preference (n = 136), significantly more preferred the fentanyl patches (p = 0.037). We conclude that, in this study, transdermal fentanyl provided pain relief that was acceptable to cancer patients and was associated with less constipation and sedation than morphine. These reduced side effects may contribute to patients preference for the patches.

Administration, Cutaneous↗
PubMed1997

The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres.

PURPOSE: The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained. METHODS: rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C. RESULTS: rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH. CONCLUSIONS: rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.

Chromatography, Gel↗
PubMed1997

Evaluation of the Vidas Chlamydia test to detect and verify Chlamydia trachomatis in urogenital specimens.

The Vidas Chlamydia test (CHL) is an automated enzyme-linked immunofluorescence assay for the detection of Chlamydia trachomatis. Positive and equivocal results are confirmed with a blocking assay. A mouse monoclonal antibody directed against the chlamydial lipopolysaccharides was used for the test. The CHL assay is widely used in Europe, but U.S. experience with it is limited. Three clinical test sites (The Arlington Hospital, Arlington, Va., Indiana University, Indianapolis, and the University of California, San Francisco) compared CHL with tissue culture (TC) for the identification of chlamydia in urogenital specimens (2,453 females and 850 males). True positives (TP) were defined as either TC positive or TC negative and CHL positive by a positive direct fluorescent-antibody assay or PCR test. Overall prevalence was 5.5% for females, 10.3% for male urethral swabs, and 10.7% for combined male TC urethral swabs and CHL with first catch urine (FCU) specimens. Compared to TP, CHL and TC had sensitivities of 89.6 and 94.1% with female cervical swabs and 90.9 and 86.4% with male urethral swabs, respectively. CHL sensitivity was 81.2 for male FCU specimens and 77.7% for matching male TC swabs. There were relatively few false-positive results, with all specificities being >99.4%. With the blocking assay, Vidas CHL specificity was >99.7%. However, male FCU specimen sensitivity was compromised because 9.2% (7 of 76) of the TP were initially positive but were not confirmed. An improvement in the Vidas blocking assay is needed before we can recommend its use with male urine. Alternatively, one could argue that the specificity of the test is so high that a confirmatory assay is not needed. For male and female swabs, the Vidas CHL assay has a performance that is similar to that of TC.

Bacteriological Techniques↗
PubMed1997

Effect of obstructive sleep apnea versus sleep fragmentation on responses to airway occlusion.

Although the acute physiologic responses to apnea in patients with obstructive sleep apnea (OSA) have been well documented, the changes in these responses over the course of the disease have not been investigated. The purpose of this study was to use a canine model of OSA to examine the long-term effects of sleep apnea on the acute responses to airway occlusion during sleep. Four dogs were studied during a control period before induction of OSA, during a period of OSA (83-133 d), and following cessation of OSA. At least 6 mo after completion of the OSA protocol, the dogs were re-studied on a sleep fragmentation protocol (30-60 d) to determine the impact of a similar degree of sleep disruption, without OSA, on the acute responses to airway occlusion. OSA and sleep fragmentation both resulted in lengthening of the time to arousal in response to acute airway occlusion (p < 0.02) and in greater arterial oxygen desaturation (p < 0.05), peak inspiratory pressures (p < 0.003), and surges in maximum systolic and diastolic blood pressure during airway occlusion (p < 0.01). There were no differences between the changes observed during OSA and during sleep fragmentation. We conclude that the changes in the acute responses to airway occlusion resulting from OSA are primarily the result of the associated sleep fragmentation.

Airway Obstruction↗