Biomedical subjects

P H Nguyen

Publications and source records attributed to P H Nguyen.

13 recordsLinked to original sources

PubMed2004

Adsorption of water vapor by poly(styrenesulfonic acid), sodium salt: isothermal and isobaric adsorption equilibria.

Air conditioning and dehumidifying systems based on sorption on solids are of great interest, especially in humid climates, because they allow reduction of thermal loads and use of chlorofluorocarbons. Previous studies have shown that hydrophilic polymers such as sulfonic polymers can have very high performance in water adsorption from air. The aim of this study was to characterize the water vapor adsorption properties of fully sulfonated and monosulfonated poly(styrenesulfonic acid), sodium salt, and to elucidate the mechanism of adsorption on these materials. Adsorption isotherms have been determined by TGA between 298 and 317 K for pressures ranging from 0.1 to 45 hPa. They have type II of the IUPAC classification and a small hysteresis loop between adsorption and desorption processes was observed only for the monosulfonated sample. Water content is up to 80% weight at 80% relative humidity. Adsorption isotherms have been well fitted with the FHH model. Adsorption-desorption isobars have been determined by TGA under 37 hPa in the temperature range 298-373 K. They show that these polymers can be completely regenerated by heating at 313 K under humidified air. No degradation of the adsorption properties has been observed after several regenerations. Adsorption enthalpies and entropies have been deduced from the Clapeyron equation and from DSC measurements. A good agreement was found. A mechanism of adsorption is proposed considering two kinds of adsorbate: bounded water in electrostatic interaction with functional groups and free water resulting from condensation.

Journal Article↗

PubMed2004

Challenges of assuring crew safety in space shuttle missions with international cargoes.

The top priority in America's manned space flight program is the assurance of crew and vehicle safety. This priority gained greater focus during and after the Space Shuttle return-to-flight mission (STS-26). One of the interesting challenges has been to assure crew safety and adequate protection of the Space Shuttle, as a national resource, from increasingly diverse cargoes and operations. The control of hazards associated with the deployment of complex payloads and cargoes has involved many international participants. These challenges are examined in some detail along with examples of how crew safety has evolved in the manned space program and how the international partners have addressed various scenarios involving control and mitigation of potential hazards to crew and vehicle safety.

Accidents, Aviation↗

PubMed2001

Elevation of internal auditory canal pressure by vestibular schwannomas.

OBJECTIVE: The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test whether increased pressure in the internal auditory canal from tumor growth is responsible for this clinical finding, the intracanalicular pressure in patients harboring these tumors was measured. STUDY DESIGN: Prospective study. SETTING: Tertiary referral hospital. PATIENTS: Fifteen consecutive patients undergoing a retrosigmoid approach for resection of vestibular schwannomas were included in the study. INTERVENTION: The intracanalicular pressure in every patient was measured by introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then correlated with tumor size and respective preoperative hearing status. RESULTS: Placement of the pressure monitor into the internal auditory canal revealed a biphasic waveform in every patient. Whereas the mean intracanalicular pressure was 20 mm Hg, there was significant variability among patients (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.012) but not with the total tumor size (r </= 0.40, p > 0.075). Furthermore, eight patients with class A preoperative hearing (American Academy of Otolaryngology-Head and Neck Surgery classification) had lower intracanalicular pressures than did five patients with class B hearing (16 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse correlation between the intracanalicular pressure and hearing function, the difference between the two groups was not statistically significant (p = 0.14). CONCLUSION: Pressure on the cochlear nerve as a result of tumor growth in the internal auditory canal may be responsible for hearing loss in patients with vestibular schwannomas. Modification of surgical techniques to address the elevated intracanalicular pressure may be beneficial in improving hearing preservation in these patients.

Cochlear Nerve↗

PubMed2000

Influence of muscle fibre type and fitness on the oxygen uptake/power output slope during incremental exercise in humans.

We recently reported that a higher percentage of type I fibres in vastus lateralis and a greater peak oxygen uptake (O2) were associated with a greater initial rise in O2 (O2 /W, where W is work rate) following the onset of heavy constant power output exercise (above the lactate threshold, LT). It was unclear if these results were true only for heavy exercise, or if the association between fibre type and/or fitness and O2 /W would also be seen for moderate (< LT) exercise. The purpose of the present study was to compare the relationships between fibre type or peak O2 and O2 /W determined for moderate (< LT) and heavy (> LT) exercise intensities during incremental exercise. Nine healthy subjects performed an incremental ramp test on a cycle ergometer. The O2 /Wslope was calculated for the domain of power outputs up to the LT (S1), from the LT towards peak O2 (S2), and over the entire linear portion of the O2 /W response (ST), and compared to fibre type distribution determined from biopsy of the vastus lateralis, and to peak O2 (as ml kg-1 min-1). Significant correlations between O2 /W and the proportion of type I fibres were found for each exercise domain (r is 0.69, 0.71 and 0.84 for S1, S2 and ST, respectively, P < 0.05). S1 ranged between about 9 ml min-1 W-1 for a low proportion of type I fibres and 11 ml min-1 W-1 for a high proportion of type I fibres. Similar correlations were also found between S2 (r = 0.70) and ST (r = 0.76) and peak O2. These results are consistent with our previous findings during > LT constant power output exercise, and suggest that the proportion of type I fibres, and possibly fitness as indicated by peak O2, is associated with greater O2 /W during the initial adjustment to < LT as well as > LT exercise. These results do not appear to be explained by classical descriptions of the kinetics of adjustment of O2 following the onset of ramp or constant power output exercise. They might reflect enhanced motor unit recruitment in subjects with a greater percentage of type I fibres, and/or who are more aerobically fit. However, the underlying mechanism for these findings must await further study.

Adult↗

PubMed1998

Expression of the apoptosis-related genes, caspase-1, caspase-3, DNA fragmentation factor, and apoptotic protease activating factor-1, in human granulosa cells.

OBJECTIVE: To investigate protein and messenger RNA expression products for a subset of apoptosis-related genes in human granulosa cells. DESIGN: In vitro experiment. SETTING: Department of Obstetrics, Gynecology, and Reproductive Biology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts. PATIENT(S): Women undergoing oocyte retrieval for IVF after ovulation induction with gonadotropins. INTERVENTION(S): Granulosa cells were isolated from follicular aspirates after oocyte removal. MAIN OUTCOME MEASURE(S): Reverse transcription polymerase chain reaction and Western blotting for apoptosis-related gene products. RESULT(S): The expression of caspase-1, caspase-3, DNA fragmentation factor, and apoptotic protease activating factor-1, which are intermediate molecules in phylogenetically conserved apoptotic pathways, was demonstrated in granulosa cells from patients undergoing IVF. Moreover, proforms, but not activated enzymes, for both caspase-1 and caspase-3 were observed. CONCLUSION(S): Granulosa cells from patients undergoing IVF have intrinsic apoptotic machinery that could be activated for tissue remodeling.

Apoptosis↗

PubMed1998

A role for Groucho tetramerization in transcriptional repression.

The Drosophila Groucho (Gro) protein is a corepressor required by a number of DNA-binding transcriptional repressors. Comparison of Gro with its homologues in other eukaryotic organisms reveals that Gro contains, in addition to a conserved C-terminal WD repeat domain, a conserved N-terminal domain, which has previously been implicated in transcriptional repression. We determined, via a variety of hydrodynamic measurements as well as protein cross-linking, that native Gro is a tetramer in solution and that tetramerization is mediated by two putative amphipathic alpha-helices (termed leucine zipper-like motifs) found in the N-terminal region. Point mutations in the leucine zipper-like motifs that block tetramerization also block repression by Gro, as assayed in cultured Drosophila cells with Gal4-Gro fusion proteins. Furthermore, the heterologous tetramerization domain from p53 fully substitutes for the Gro tetramerization domain in transcriptional repression. These findings suggest that oligomerization is essential for Gro-mediated repression and that the primary function of the conserved N-terminal domain is to mediate this oligomerization.

Amino Acid Sequence↗

PubMed1997

Nitric oxide production during exercise in chronic heart failure.

In chronic heart failure (CHF), the ventilatory response is increased compared with normal. This response is, in part, caused by reduced perfusion to ventilated lung. Nitric oxide (NO) is a potent vasodilator and may have an important role in pulmonary vasodilatation during exercise. NO is present in exhaled air. The amount of NO in exhaled air, when breathing NO-free compressed air, is known to increase in normal subjects during exercise. In this study, we quantified NO output in exhaled air in patients with CHF during exercise. Six patients with CHF (New York Heart Association Class II and III; two with dilated cardiomyopathy, three with ischemic heart disease, and one with hypertensive heart disease) and six normal subjects were studied with a symptom-limited incremental exercise test on a cycle ergometer. Oxygen uptake (VO2), carbon dioxide output (VCO2), and minute ventilation (VE) were measured breath by breath with a mass spectrometer, flow meter, and computer. The NO concentration was continuously measured in mixed expired air by chemiluminescence. Peak exercise work rate was lower in patients with CHF than in normal subjects (71.3 +/- 41.6 W vs 257.0 +/- 49.7 W; p < 0.01). Patients with CHF showed a higher VE/VCO2 level at peak exercise than normal subjects (CHF, 47.0 +/- 10.7; normal subjects, 35.6 +/- 5.2; p < 0.01). NO concentration of exhaled air at rest was lower in CHF patients than in normal subjects (4.0 +/- 2.2 ppb vs 10.5 +/- 6.2 ppb, respectively; p < 0.05). NO output from the respiratory tract (VNO) was significantly lower in patients with CHF compared with normal subjects at rest (45.3 +/- 24.3 nl/min, 117.5 +/- 60.1 nl/min, respectively, p < 0.05), and although it increased during exercise, it did not increase in patients with CHF as much as in normal subjects (75.3 +/- 43.4 nl/min vs 512.9 +/- 253.6 nl/min, respectively; p < 0.01). The increase above rest (exercise/rest) was smaller in patients with CHF than in normal subjects (2.10 +/- 1.92 vs 4.81 +/- 2.67, p < 0.05). These data support the concept that the smaller increase in NO production (VNO) during exercise may be responsible for a blunted vasodilation in patients with CHF, resulting in a smaller reduction in dead space/tidal volume and VE/VCO2 at the lactic acidosis threshold than normal. This finding may play a role in the abnormally high ventilatory response to exercise in patients with CHF.

Adult↗

PubMed1997

CADIAG-2 and MYCIN-like systems.

CADIAG-2 and MYCIN-like systems are expert systems with numerous applications in medicine. CADIAG-2 is a fuzzy expert system based on max-min inference, while MYCIN-like systems use combining functions to calculate the global weights (degrees) of suggested diagnoses. This paper brings a comparison of CADIAG-2 and MYCIN-like systems. It studies relations between them and shows how CADIAG-2 can be embedded into MYCIN-like systems. An approach of inclusion of negative knowledge into CADIAG-2 is proposed. Some remarks regarding the acquisition of weights of rules are given as well.

Expert Systems↗

PubMed1997

Modulation of Igf2 genomic imprinting in mice induced by 5-azacytidine, an inhibitor of DNA methylation.

The adjacent genes, insulin-like growth factor 2 (Igf2) and H19, are imprinted in both mouse and human. While Igf2 is expressed from the paternal allele, H19 is transcribed exclusively from the maternal allele. To explore the underlying mechanism of Igf2 and H19 imprinting, we studied the effect of DNA demethylation on allelic expression by injecting mice with the demethylating agent 5-azacytidine (5-aza-C). We observed a > or = 2-fold increase in the abundance of Igf2 mRNA in liver from treated mice compared with that of control mice. There was no significant change in Igf2 or H19 expression in brain. In the 5-aza-C-treated mice, there was dramatic modulation of Igf2 imprinting. In some tissues, Igf2 was expressed biallelically, while in other tissues, the paternal allele was silenced and the normally imprinted maternal allele was expressed, an example of allelic switching. There was no change in the normal biallelic pattern of Igf2 expression in brain. H19, on the other hand, remained imprinted in all tissues in mice treated with 5-aza-C. These results provide the first example of a pharmacological manipulation of genomic imprinting of an endogenous gene in vivo and further implicate DNA methylation as an important factor in maintaining the differential allelic expression of the Igf2 gene.

Animals↗

PubMed1996

Influence of muscle fiber type and pedal frequency on oxygen uptake kinetics of heavy exercise.

We tested the hypothesis that the amplitude of the additional slow component of O2 uptake (VO2) during heavy exercise is correlated with the percentage of type II (fast-twitch) fibers in the contracting muscles. Ten subjects performed transitions to a work rate calculated to require a VO2 equal to 50% between the estimated lactate (Lac) threshold and maximal VO2 (50% delta). Nine subjects consented to a muscle biopsy of the vastus lateralis. To enhance the influence of differences in fiber type among subjects, transitions were made while subjects were pedaling at 45, 60, 75, and 90 rpm in different trials. Baseline VO2 was designed to be similar at the different pedal rates by adjusting baseline work rate while the absolute increase in work rate above the baseline was the same. The VO2 response after the onset of exercise was described by a three-exponential model. The relative magnitude of the slow component at the end of 8-min exercise was significantly negatively correlated with % type I fibers at every pedal rate (r = 0.64 to 0.83, P < 0.05-0.01). Furthermore, the gain of the fast component for VO2 (as ml.min-1.W-1) was positively correlated with the % type I fibers across pedal rates (r = 0.69-0.83). Increase in pedal rate was associated with decreased relative stress of the exercise but did not affect the relationships between % fiber type and VO2 parameters. The relative contribution of the slow component was also significantly negatively correlated with maximal VO2 (r = -0.65), whereas the gain for the fast component was positively associated (r = 0.68-0.71 across rpm). The amplitude of the slow component was significantly correlated with net end-exercise Lac at all four pedal rates (r = 0.64-0.84), but Lac was not correlated with % type I (P > 0.05). We conclude that fiber type distribution significantly affects both the fast and slow components of VO2 during heavy exercise and that fiber type and fitness may have both codependent and independent influences on the metabolic and gas-exchange responses to heavy exercise.

Adult↗

PubMed1995

Effects of cocaine and corticotropin-releasing factor on pulsatile ACTH and cortisol release in ovariectomized rhesus monkeys.

Cocaine stimulates ACTH secretion by a corticotropin-releasing factor (CRF)-dependent mechanism in male rats, rhesus monkeys, and humans. To determine the generality of this effect, we examined the effects of acute cocaine administration on the pulsatile release of ACTH and cortisol in three ovariectomized (OVX) rhesus monkeys and compared its effects to stimulation with CRF. Venous blood samples were collected at 2-min intervals for 60 min before and after iv administration of cocaine (0.4 and 0.8 mg/kg) and CRF (1.0 and 10 micrograms/kg). Cluster analysis procedures were used to evaluate the pulsatile characteristics of ACTH and cortisol release. After placebo administration, an ACTH pulse frequency of 3 peaks/h was detected. After cocaine administration, plasma cocaine levels peaked at 92 +/- 3.0 and 201 +/- 60 ng/mL within 2 min. However, in contrast to normal intact males, cocaine did not stimulate the pulsatile release of ACTH in OVX females. Cocaine (0.4 mg/kg) decreased ACTH incremental peak height and valley levels compared with pre-cocaine values, and a higher dose of cocaine produced no changes in ACTH release. Bolus injection of a low dose of CRF (1.0 micrograms/kg, iv) significantly increased ACTH incremental peak height (P < 0.05), and a higher dose of CRF (10 micrograms/kg) increased ACTH peak amplitude, percentage increase in peak amplitude, area under the peaks, and incremental peak heights as well as ACTH valley level and nadir (10 micrograms/kg, iv) (P < 0.05). ACTH pulse frequency did not change after CRF or cocaine administration. Pulsatile release of cortisol was 2.7 peaks/h under placebo conditions and did not change after cocaine or CRF administration. Cortisol pulse amplitude was increased after low and high doses of CRF. High doses of CRF (10 micrograms/kg) also increased the mean level of cortisol valleys. In summary, we found that CRF but not cocaine stimulated pulsatile ACTH and cortisol release in OVX rhesus monkeys. The profound ACTH response to CRF challenge suggests that the CRF sensitivity and the ACTH release capacity of the anterior pituitary corticotroph cells were intact. The lack of stimulatory effects of cocaine on the hypothalamic-pituitary-adrenal axis in OVX monkeys, in contrast to normal male monkeys, may reflect the absence of gonadal steroids.

Adrenocorticotropic Hormone↗

PubMed1995

Protective effect of a 21-aminosteroid against hemorrhage-induced ischemia-reperfusion injury in the rat stomach: role of lipid peroxidation.

We investigated the role that lipid peroxidation plays in a hemorrhage-induced ischemia-reperfusion model of gastric injury. Rats were pretreated with an inhibitor of this process, a 21-aminosteroid (U-74389G, 10 mg/kg), or an appropriate control solution intravenously 15 min prior to 20 min of ischemia, followed by 20 min of reperfusion. Results indicated that U-74389G pretreatment significantly attenuated gastric damage compared with corresponding control animals (19.8 vs. 176.8 mm2, p < .001). Enaldehyde levels (picomoles/mg protein), a biochemical index of lipid peroxidation, paralleled these injury findings (12 vs 960, p < .001). Histologically, U-74389G pretreatment almost completely prevented gastric injury compared to control stomachs. Additional studies revealed that lipid peroxidation preceded the formation of gastric damage, and injury occurred predominantly during reperfusion, because animals subjected to ischemia alone without reperfusion failed to develop appreciable injury or enhanced enaldehyde formation. Further, if U-74389G was given intravenously after ischemia, but prior to reperfusion, gastric injury and enaldehyde formation were similarly attenuated. Our findings are consistent with the hypothesis that lipid peroxidation likely plays an important role in hemorrhage-induced ischemia-reperfusion injury to the stomach.

Animals↗

PubMedDate not supplied

Intraleucocytic malaria pigment and prognosis in severe malaria.

The quantity of malaria pigment liberated into the circulation at schizogony reflects the pathogenic sequestered parasite burden in Plasmodium falciparum malaria, and may therefore be a measure of disease severity. Among 300 consecutive adult patients with severe falciparum malaria, the 40 who died had significantly higher proportions of malaria pigment-containing neutrophils on admission (mean = 7.7%, standard deviation (SD) = 5.9%) and pigment-containing monocytes (mean = 8.6%, SD = 5.9%) than did survivors (mean 3.2%, SD = 4.1% and mean 4.8%, SD = 4.6%, respectively) (P < 0.0001). This proved a better indicator of prognosis than the peripheral parasite count. A count of peripheral neutrophils containing visible pigment > or = 5% predicted a fatal outcome with 73% sensitivity and 77% specificity (relative risk 6.2, 95% confidence interval (CI) 3.2-11.8) compared to 60% sensitivity and 57% specificity for parasitaemia > 100,000/microL (relative risk 1.8, 95% CI 1.0-3.3). The peripheral blood count of pigment-containing neutrophils in severe malaria is a rapid, simple, and practical prognostic test.

Adipose Tissue↗