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Biomedical subjects

P P Tan

Publications and source records attributed to P P Tan.

At least 19 recordsLinked to original sources
PubMed2003

The Internet as a source of health information among Singaporeans: prevalence, patterns of health surfing and impact on health behaviour.

OBJECTIVE: The Internet is an increasingly popular source of healthcare information. This study describes the prevalence of health surfers in Singapore and their health-surfing patterns. It also assesses their confidence in online health information and the impact the Internet has on health-seeking behaviour. MATERIALS AND METHODS: A cross-sectional survey using a standardised questionnaire was carried out among residents aged 13 to 55 years in 1852 units in Bishan North. These units were selected by single-stage simple random cluster sampling method. RESULTS: The household response rate was 51% (n = 950) and the individual response rate was 69% (n = 1646). Responding and non-responding households were similar in terms of ethnicity and housing type. Of the responders, 62.9% surfed the Internet and 37.7% have surfed for health information. Health surfers tended to be younger (20 to 39 years) and have higher education status. Indians were also more likely than other ethnic groups to surf for health. Professional health-related sites comprised the majority (68%) of sites visited, and the most common search keywords concern chronic degenerative diseases, e.g. hypertension. The top preferred sources of health information were doctors (25.9%), the Internet (25.3%) and the traditional mass media (20.5%). Almost half (45.1%) considered online health information trustworthy if it was from a professional source or if the website displayed the source, while 10.6% trusted the information if it concurred with the doctors' advice. The vast majority (91.7%) had taken some action in response to the information. CONCLUSION: The Internet is being used as an accessible source of health information by a substantial proportion of the lay public. While this can facilitate greater partnership in healthcare, it underlines the need for doctors to be pro-active in the practice of evidence-based medicine, and for guidelines to enable patients to use this tool in a discerning manner.

Adolescent↗
PubMed2001

Neurotensin excitation of serotonergic neurons in the rat nucleus raphe magnus: ionic and molecular mechanisms.

To understand the cellular and molecular mechanisms by which neurotensin (NT) induces an analgesic effect in the nucleus raphe magnus (NRM), whole-cell patch-clamp recordings were performed to investigate the electrophysiological effects of NT on acutely dissociated NRM neurons. Two subtypes of neurons, primary serotonergic and secondary non-serotonergic cells, were identified from acutely isolated NRM neurons. During current-clamp recordings, NT depolarized NRM serotonergic neurons and evoked action potentials. Voltage-clamp recordings showed that NT excited serotonergic neurons by enhancing a voltage-insensitive and non-selective cationic conductance. Both SR48692, a selective antagonist of subtype 1 neurotensin receptor (NTR-1), and SR 142948A, a non-selective antagonist of NTR-1 and subtype 2 neurotensin receptor (NTR-2), failed to prevent neurotensin from exciting NRM serotonergic neurons. NT-evoked cationic current was inhibited by the intracellular administration of GDP-beta-S. NT failed to induce cationic currents after dialyzing serotonergic neurons with the anti-G(alphaq/11) antibody. Cellular Ca(2+) imaging study using fura-2 showed that NT induced the calcium release from the intracellular store. NT-evoked current was blocked after the internal perfusion of heparin, an IP(3) receptor antagonist, or BAPTA, a fast Ca(2+) chelator. It is concluded that neurotensin enhancement of the cationic conductance of NRM serotonergic neurons is mediated by a novel subtype of neurotensin receptors. The coupling mechanism via G(alphaq/11) proteins is likely to involve the generation of IP(3), and subsequent IP(3)-evoked Ca(2+) release from intracellular stores results in activating the non-selective cationic conductance.

Adamantane↗
PubMed2001

Modulations of spinal serotonin activity affect the development of morphine tolerance.

To test whether modulations of spinal serotonin (5-HT) levels would affect the development of morphine tolerance, we treated rats with either intrathecal 5-HT or 5,7-dihydroxytryptamine (5,7-DHT; a 5-HT neurotoxin) in addition to systemic infusion with morphine (2 mg x kg(-1) x h(-1)). Continuous infusion of 5-HT (10 microg x 6 microL(-1) x h(-1)) into the lumbar subarachnoid space of rats for 9 h accelerated the development of morphine tolerance. The area under the curve for the tail-flick latency test was 454.1 +/- 35.1 in the Sham Control group vs 327.6 +/- 41.0 in the 5-HT-Infused group. mu-opioid receptor binding in the lumbar spinal cord showed a decrease in the Bmax (maximal binding -46.5%), but not the binding affinity (Kd), in 5-HT-infused rats. However, intrathecal injection of 5,7-DHT (50 microg), which resulted in a 48% reduction in 5-HT and 51% reduction in 5-hydroxyindoleacetic acid concentrations, led to an attenuation of morphine tolerance (the area under the curve was 613.0 +/- 24.7 in the 5,7-DHT-Lesioned group). The binding study indicated that the affinity of lumbar micro-opioid receptors decreased 196% in 5-HT-depleted rats, whereas there was no effect on apparent binding. The infusion of 5-HT (10 microg x 6 microL(-1) x h(-1)) was not analgesic and the 5,7-DHT-induced lesion did not affect acute morphine-induced analgesia. We conclude that activity of spinal 5-HT-containing neurons plays a crucial role during the development of morphine tolerance.

5,7-Dihydroxytryptamine↗
PubMed2001

Neurotensin excites periaqueductal gray neurons projecting to the rostral ventromedial medulla.

Microinjection of neurotensin into the midbrain periaqueductal gray (PAG) produces a potent and naloxone-insensitive analgesic effect. To test the hypothesis that neurotensin induces the analgesic effect by activating the PAG-rostral ventromedial medulla (RVM) descending antinociceptive pathway, PAG neurons that project to RVM (PAG-RVM) were identified by microinjecting DiI(C18), a retrograde tracing dye, into the rat RVM. Subsequently, fluorescently labeled PAG-RVM projection neurons were acutely dissociated and selected for whole cell patch-clamp recordings. During current-clamp recordings, neurotensin depolarized retrogradely labeled PAG-RVM neurons and evoked action potentials. Voltage-clamp recordings indicated that neurotensin excited PAG-RVM neurons by opening the voltage-insensitive and nonselective cation channels. Both SR 48692, a selective NTR-1 antagonist, and SR 142948A, a nonselective antagonist of NTR-1 and NTR-2, failed to prevent neurotensin from exciting PAG-RVM neurons. Neurotensin failed to evoke cationic currents after internally perfusing PAG-RVM projection neurons with GDP-beta-S or anti-G(alpha q/11) antiserum. Cellular Ca(2+) fluorescence measurement using fura-2 indicated that neurotensin rapidly induced Ca(2+) release from intracellular stores of PAG-RVM neurons. Neurotensin-evoked cationic currents were blocked by heparin, an IP(3) receptor antagonist, and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a fast chelator of Ca(2+). These results suggest that by activating a novel subtype of neurotensin receptors, neurotensin depolarizes and excites PAG-RVM projection neurons through enhancing Ca(2+)-dependent nonselective cationic conductance. The coupling mechanism via G(alpha q/11) proteins is likely to involve the production of IP(3), and subsequent IP(3)-evoked Ca(2+) release leads to the opening of nonselective cation channels.

Animals↗
PubMed2001

[Observation on eggs of Oncomelania hupensis hupensis with scanning electron microscope].

OBJECTIVE: To observe the structure of the mud hull packed Oncomelania eggs and the surface structure of colloid membrane called the third grade membrane of eggs. METHODS: Scanning electron microscopy was used to observe Oncomelania snail eggs with integral mud hull collected from eastern Dongting Lake. RESULTS AND CONCLUSION: The mud hull of eggs was made of unshapen small humification combined with earth granules with a diameter of 2.6-9.2 microns. The mud hull in 60 um thickness was honeycomb-like in shape with many small holes and small folds on the wall. There were many round or irregularly round hollownesses on the inner layer of mud hull that contacts colloid membrane but no hole through mud hull. There were some protein fiber networks covering on the colloid membrane and apophysis. The structure of the mud hull showed that the exchange of matter was maintained between eggs and outside, and the mud hull is of great importance to regulating temperature and moisture for the growth of eggs by preventing hydrosoluble substances from penetrating into eggs. The protein fiber networks act on gluing mud hull and buffering outside power. The dense glue membrane might be a main barricade to prevent pharmaceutical molecules from penetrating into eggs.

Animals↗
PubMed2000

The cardiovascular effects of PFRFamide and PFR(Tic)amide, a possible agonist and antagonist of neuropeptide FF (NPFF).

Neuropeptide FF (NPFF), an endogenous opioid-related neuromodulater, has been reported to show significant effects on the cardiovascular system, namely elevation of arterial blood pressure (BP) and heart rate (HR) in rats. In the present study, we synthesized two novel NPFF analogs, PFRFamide (putative NPFF agonist) and PFR(Tic)amide (putative NPFF antagonist), and examined their cardiovascular effect on BP and HR in anesthetized rats. The arterial mean BP and HR were measured by way of direct femoral artery catheterization. The data showed that PFRFamide increased BP in a dose-dependent manner, while PFR(Tic)amide decreased BP dose-dependently. These results revealed the possibility of PFRFamide and PFR(Tic)amide to be NPFF agonist and antagonist (or inverse agonist), respectively. These two NPFF analogs may possess potential in new drug design, and the NPFF system could be very important in mammalian cardiovascular function.

Amides↗
PubMed2000

Effects of fenoterol and ipratropium on respiratory resistance of asthmatics after tracheal intubation.

We have studied the effects of a beta-agonist, fenoterol, and a cholinergic antagonist, ipratropium, on post-intubation total respiratory system resistance (Rrs) in asthmatics who developed increased Rrs after tracheal intubation. Sixteen stable asthmatics in whom Rrs increased after intubation were allocated randomly to receive either 10 puffs of fenoterol (group F) or 10 puffs of ipratropium (group IB) via a metered dose inhaler 5 min after intubation. Anaesthesia was induced and maintained with propofol i.v. Rrs was recorded before treatment and again 5, 15 and 30 min after treatment. Rrs decreased significantly from pretreatment values by mean 53 (SD 8)%, 53 (7)% and 58 (6)% at 5, 15 and 30 min, respectively, in group F, but declined by only 12 (6)%, 15 (4)% and 17 (5)% in group IB. At all times after treatment, patients in the fenoterol group had significantly lower Rrs values than those in the ipratropium group. We conclude that increased Rrs after tracheal intubation in asthmatics can be reduced effectively by treatment with fenoterol. A secondary finding of our study was that even after induction of anaesthesia with propofol, patients with a history of asthma may develop high Rrs.

Adrenergic beta-Agonists↗
PubMed2000

The factor structure of the Minnesota Satisfaction Questionnaire and participants of vocational rehabilitation.

This study investigated the factor structure of the Minnesota Satisfaction Questionnaire when used by individuals with psychiatric disabilities who are participating in vocational rehabilitation. The sample consisted of 87 respondents recruited from Columbus, Ohio, in 1996 who worked in noncompetitive employment. Factor analyses with varimax rotation conducted on the short-form of the questionnaire indicated three factors, an intrinsic factor and an extrinsic factor (as proposed by the Herzberg two-factor theory) as well as another pertaining to satisfaction derived from participating in vocational rehabilitation.

Adult↗
PubMed2000

Anesthesia with deep hypothermic circulatory arrest for giant basilar aneurysm surgery.

The application of deep hypothermic circulatory arrest (DHCA) as an adjutant technique in anesthetic management for surgery of giant and complex cerebral aneurysm has been clinically recognized with piling up experience in many institutes. DHCA provides the advantages such as a bloodless surgical field and protection of the brain, all of which make a precise clipping of the aneurysm possible and thus it lowers the mortality rate which could be extremely high without it. Nevertheless, in application, the disadvantages of this technique includes comparatively inefficient and uneven cooling or rewarming, severe physiological change, cardiac distension and arrhythmia during cardiopulmonary bypass (CPB), hemorrhage from systemic heparinization and brain damage due to inadequate protection, none of which has ever been stressed. Since many giant aneurysms are found inoperable during exploration with application of DHCA, it would change the fate of the patients, and the clinical value of DHCA in such an instance becomes contradictive and disputable. We would like to present our experience in a case who, because of a giant basilar aneurysm, underwent surgical correction under DHCA retrograde cerebral perfusion (RCP) with cerebral function monitoring including electroencephalography (EEG), brainstem auditory evoked potentials (BAEP), thermal diffusion cerebral blood flowmetry, study of the change of extracellular concentration of excitatory amino acid, glutamate and aspartate, and off-line neurochemical analysis with cerebral microdialysis technique.

Adult↗
PubMed2000

Anesthesia of CO2 laser surgery in a patient with Hunter syndrome: case report.

Hunter syndrome (mucopolysaccharidosis, type II; MPS II) is one of a heterogeneous group of recessively inherited mucopolysaccharide storage diseases. Patients with mucopolysaccharidosis show progressive involvement and derangement of many organs, especially upper airway anomalies, which are the major cause of perioperative death. In recent years, a CO2 laser is often applied to upper airway lesions. A 16-year-old patient suffering from Hunter syndrome was scheduled for CO2 laser surgery because of sleep apnea and respiratory stridor. Otolaryngological examination revealed bulging of the bilateral false cord with stenosis of the glottis. We adopted sevoflurane mask induction and high-frequency jet ventilation to overcome the perioperative airway problems. The anesthetic course was uneventful, and the patient was discharged 2 days after the operation.

Adolescent↗
PubMed1999

The use of multiplane transesophageal echocardiography to evaluate residual patent ductus arteriosus during video-assisted thoracoscopy in adults.

BACKGROUND: Video-assisted thoracoscopic surgery (VATS) has emerged as an innovative and popular procedure for interruption of patent ductus arteriosus (PDA), while intraoperative transesophageal echocardiography (TEE) has proven to be an effective monitor in the evaluation of residual patency. Previous reports on the adequacy of surgical interruption of PDA under VATS and TEE are available for pediatric patients, but only limited information is available for adults with PDA. MATEIALS AND METHODS: Between August 1995 and October 1997, we monitored 35 adult patients undergoing PDA interruption via VATS with Hewlett-Packard color Doppler multiplane TEE throughout the procedure. The average PDA diameter was 10.2 +/- 1.8 mm. All the PDA were completely ligated. RESULTS: Thirty-two patients showed no ductal flow after double ligation. In the other three patients, residual flow was detected intraoperatively after double ligation, but it was quickly abolished by the third ligation. One patient showed faint ductal flow by transthoracic echocardiography at postoperative follow-up, but no reintervention was needed. CONCLUSIONS: Our study showed that, with the refinement of adult PDA interruption via VATS, intraoperative multiplane TEE provides higher resolution for direct evaluation of the entire course of PDA ligation without interrupting the surgical procedure and minimizes the incidence of complications.

Adult↗
PubMed1999

"I" ministernotomy for aortic valve replacement.

BACKGROUND: Minimally invasive surgical approaches have been applied recently in the management of valvular heart disease. In this report, we reviewed our preliminary experience of minimally invasive aortic valve replacement. METHODS: Eighteen patients were operated on by means of an "I" ministernotomy, and 16 patients were operated on by means of a full median sternotomy during the same period. There was no difference between these two groups in term of age, sex, and preoperative left ventricular ejection fraction. In patients of the ministernotomy group, the operations were approached through an "I" median sternal split, from the second to the fifth intercostal space, 8 to 10 cm in length, with transverse division. Cardiopulmonary bypass was established through aorto-right atrial cannulation with aortic cross-clamping and antegrade or retrograde delivery of blood cardioplegia. RESULTS: Under direct vision, aortic valve replacement was performed successfully in patients of both groups. The duration of cardiopulmonary bypass time and aortic cross-clamp time was significantly longer in the ministernotomy group than in the full sternotomy group. However, the length of incision, duration of endotracheal intubation, intensive care unit stay, pain score, postoperative length of stay, and return to normal activity interval were significantly shorter and lower in patients of the ministernotomy group than in those of the full sternotomy group. All patients recovered from the operation rapidly. Follow-up was complete in all patients with no late complications. Echocardiographic examination showed good function of aortic prostheses. CONCLUSIONS: Our experience demonstrates that the "I" ministernotomy provides good exposure, reduced wound pain, enhanced recovery, shortened hospital stay, and good cosmetic healing. It may be a good alternative for surgical correction of aortic valve lesions.

Adult↗
PubMed1999

Morphine tolerance in arthritic rats and serotonergic system.

To understand whether chronic inflammation alters the development of morphine tolerance, the tail-flick test was used to evaluate the analgesic effect of morphine (75 mg tablet, s.c.) in the arthritic rats at the day 9-12 after the inoculation with Freund's adjuvant. Spinal cord monoamines and amino acid neurotransmitters were concomitantly measured. Chronic inflammation attenuated the antinociceptive effect of morphine as tolerance developed faster in the arthritic rats compared to the vehicle-treated controls. In addition, ratio of 5-hydroxyindole-3-acetic acid/5-hydroxytryptamine (5-HIAA/5-HT) increased in the lumbar spinal cord of arthritic rats without any change in the concentrations of norepinephrine, glutamate, aspartate or GABA. Interestingly, increased serotonin turnover in the spinal cord was observed in both control and arthritic rats 24 hours after morphine treatment. Overall, the results suggest a significant role of serotonin up-regulation in the spinal cord during chronic pain and the development of morphine tolerance.

Analgesics, Opioid↗
PubMed1999

Modulation of naloxone-precipitated morphine withdrawal syndromes in rats by neuropeptide FF analogs.

Neuropeptide FF (NPFF) has been reported to be an endogenous anti-opioid peptide that has significant effects on morphine tolerance and dependence. In the present study, we examined the chronic effects of NPFF and its synthetic analogs: the putative agonist, PFRFamide, and the putative antagonists, dansyl-PQRamide and PFR(Tic)amide on naloxone-precipitated morphine withdrawal syndromes in rats. After a 5-day co-administration with morphine [5 mg/kg, intraperitoneally (i.p.), twice per day (b.i.d.)] and the tested peptide [intracerebroventricularly (i.c.v.) or i.p., b.i.d.], naloxone (4 mg/kg, i.p.) was given systemically to evaluate the severity of the morphine withdrawal syndromes. Our results revealed that NPFF significantly potentiated the overall morphine withdrawal syndromes and, on the contrary, dansyl-PQRamide attenuated these syndromes. These results clearly indicate that modulation of the NPFF system in the mammalian central nervous system has significant effects on opiate dependence. In addition, morphine withdrawal syndromes could be practically applied as a valid parameter to functionally characterize the putative NPFF agonists and antagonists.

Animals↗
PubMed1999

Mechanisms underlying the inhibitory effect of propofol on the contraction of canine airway smooth muscle.

BACKGROUND: Propofol has been shown to produce relaxation of preconstricted airway smooth muscle. Although the inhibition of calcium mobilization is supposed to be the major mechanism of action, the whole picture of the mechanisms is not completely clear. METHODS: Contractile response was performed using canine tracheal rings. The effects of propofol on carbachol-induced mobilization of intracellular Ca2+ and phosphoinositide hydrolysis were measured using cultured canine tracheal smooth muscle cells by monitoring fura-2 signal and assessing the accumulation of [3H]-inositol phosphates. To detect the effect of propofol on muscarinic receptor density and affinity, [3H]N-methyl-scopolamine was used as a radioligand for receptor binding assay. RESULTS: Pretreatment with propofol shifts the concentration-response curves of carbachol-induced smooth muscle contraction to the right in a concentration-dependent manner without changing the maximal response. Propofol not only decreased the release of Ca2+ from internal stores but also inhibited the calcium influx induced by carbachol. In addition, carbachol-induced inositol phosphate accumulation was attenuated by propofol; the inhibitory pattern was similar to the contractile response. Moreover, propofol did not alter the density of muscarinic receptors. The dissociation constant value was not altered by pretreatment with 100 microM propofol but was significantly increased by 300 microM (propofol, 952+/-229 pM; control, 588+/-98 pM; P<0.05). CONCLUSIONS: Propofol attenuates the muscarinic receptor-mediated airway muscle contraction. The mechanism underlying these effects was attenuation of inositol phosphate generation and inhibition of Ca2+ mobilization through the inhibition of the receptor-coupled signal-transduction pathway.

Anesthetics, Intravenous↗