Search PubMed⌕ Search

Biomedical subjects

S Yan

Publications and source records attributed to S Yan.

At least 91 records · Page 5Linked to original sources
PubMed1997

Kallikreins and kinins in inflammatory-like events in the reproductive tract.

The normal reproductive events of proliferation of the endometrial lining of the uterus during the menstrual cycle and ovulation have been likened to inflammatory-like events. The kallikrein-kinin system is involved in inflammatory processes in many tissues. In this review, we identify which components of the kallikrein-kinin system--the enzyme, tissue kallikrein; the substrate, low molecular weight kininogen and the effector receptor for the generated bradykinin peptide, the B2 receptor--have been identified in the uterus and ovary and their known involvement in the function of these organs. All three components have been localized to the glandular epithelial cells of the human endometrium. Tissue kallikrein gene expression is elevated midcycle when estrogens levels are also rising. This is also a time of extensive endometrial proliferation and tissue remodelling in preparation for embryo implantation, an event which is likened to other inflammatory processes. Similarly, tissue kallikrein gene expression was elevated following the estrogen surge at proestrous in the rat uterus, suggesting tissue kallikrein gene expression may be regulated by estrogens. Tissue kallikrein enzyme activity and gene expression has been demonstrated in the rat ovary and shown to be variously altered at the time of ovulation. Bradykinin has also been implicated in the expulsion of the ovum at the time of ovulation. These findings show that various components of the kallikrein-kinin system are present in the uterus and ovary. Further studies are required to more fully delineate their role in reproductive function.

Animals↗
PubMed1997

Evidence of linkage between the serotonin transporter and autistic disorder.

The serotonin transporter gene (HTT) is a primary candidate in autistic disorder based on efficacy of potent serotonin transporter inhibitors in reducing rituals and routines. We initiated a candidate gene study of HTT in trios consisting of probands with autistic disorder and both parents. Preliminary transmission/disequilibrium test (TDT) analysis with 86 families revealed no evidence for linkage or linkage disequilibrium between autistic disorder and a polymorphism in the second intron of HTT. However, preferential transmission of a short variant of the HTT promoter was found in the same 86 trios (TDT chi 2 = 4.69, 1 d.f., P = 0.030). In further analyses, we considered haplotypes of the HTT promoter variant and second intron locus as alleles in a multiallelic TDT. Results confirmed the significance of the effect of this region (TDT chi 2 = 11.85, 4 d.f., P = 0.018). This provides preliminary evidence of linkage and association between HTT and autistic disorder.

Adolescent↗
PubMed1997

Respiratory effort sensation during exercise with induced expiratory-flow limitation in healthy humans.

Nine healthy subjects (age 31 +/- 4 yr) exercised with and without expiratory-flow limitation (maximal flow approximately 1 l/s). We monitored flow, end-tidal PCO2, esophageal (Pes) and gastric pressures, changes in end-expiratory lung volume, and perception (sensation) of difficulty in breathing. Subjects cycled at increasing intensity (+25 W/30 s) until symptom limitation. During the flow-limited run, exercise performance was limited in all subjects by maximum sensation. Sensation was equally determined by inspiratory and expiratory pressure changes. In both runs, 90% of the variance in sensation could be explained by the Pes swings (difference between peak inspiratory and peak expiratory Pes). End-tidal PCO2 did not explain any variance in sensation in the control run and added only 3% to the explained variance in the flow-limited run. We conclude that in healthy subjects, during normal as well as expiratory flow-limited exercise, the pleural pressure generation of the expiratory muscles is equally related to the perception of difficulty in breathing as that of the inspiratory muscles.

Adult↗
PubMed1997

Rib cage mechanics during quiet breathing and exercise in humans.

During exercise, large pleural, abdominal, and transdiaphragmatic pressure swings might produce substantial rib cage (RC) distortions. We used a three-compartment chest wall model (J. Appl. Physiol. 72: 1338-1347, 1992) to measure distortions of lung- and diaphragm-apposed RC compartments (RCp and RCa) along with pleural and abdominal pressures in five normal men. RCp and RCa volumes were calculated from three-dimensional locations of 86 markers on the chest wall, and the undistorted (relaxation) RC configuration was measured. Compliances of RCp and RCa measured during phrenic stimulation against a closed airway were 20 and 0%, respectively, of their values during relaxation. There was marked RC distortion. Thus nonuniform distribution of pressures distorts the RC and markedly stiffens it. However, during steady-state ergometer exercise at 0, 30, 50, and 70% of maximum workload, RC distortions were small because of a coordinated action of respiratory muscles, so that net pressures acting on RCp and RCa were nearly the same throughout the respiratory cycle. This maximizes RC compliance and minimizes the work of RC displacement. During quiet breathing, plots of RCa volume vs. abdominal pressure were to the right of the relaxation curve, indicating an expiratory action on RCa. We attribute this to passive stretching of abdominal muscles, which more than counterbalances the insertional component of transdiaphragmatic pressure.

Abdomen↗
PubMed1997

Human respiratory muscle actions and control during exercise.

We measured pressures and power of diaphragm, rib cage, and abdominal muscles during quiet breathing (QB) and exercise at 0, 30, 50, and 70% maximum workload (Wmax) in five men. By three-dimensional tracking of 86 chest wall markers, we calculated the volumes of lung- and diaphragm-apposed rib cage compartments (Vrc,p and Vrc,a, respectively) and the abdomen (Vab). End-inspiratory lung volume increased with percentage of Wmax as a result of an increase in Vrc,p and Vrc,a. End-expiratory lung volume decreased as a result of a decrease in Vab. DeltaVrc,a/DeltaVab was constant and independent of Wmax. Thus we used DeltaVab/time as an index of diaphragm velocity of shortening. From QB to 70% Wmax, diaphragmatic pressure (Pdi) increased approximately 2-fold, diaphragm velocity of shortening 6.5-fold, and diaphragm workload 13-fold. Abdominal muscle pressure was approximately 0 during QB but was equal to and 180 degrees out of phase with rib cage muscle pressure at all percent Wmax. Rib cage muscle pressure and abdominal muscle pressure were greater than Pdi, but the ratios of these pressures were constant. There was a gradual inspiratory relaxation of abdominal muscles, causing abdominal pressure to fall, which minimized Pdi and decreased the expiratory action of the abdominal muscles on Vrc,a gradually, minimizing rib cage distortions. We conclude that from QB to 0% Wmax there is a switch in respiratory muscle control, with immediate recruitment of rib cage and abdominal muscles. Thereafter, a simple mechanism that increases drive equally to all three muscle groups, with drive to abdominal and rib cage muscles 180 degrees out of phase, allows the diaphragm to contract quasi-isotonically and act as a flow generator, while rib cage and abdominal muscles develop the pressures to displace the rib cage and abdomen, respectively. This acts to equalize the pressures acting on both rib cage compartments, minimizing rib cage distortion.

Abdominal Muscles↗
PubMed1997

Reliability of inspiratory capacity for estimating end-expiratory lung volume changes during exercise in patients with chronic obstructive pulmonary disease.

The inspiratory capacity (IC) maneuver is increasingly used to monitor exercise-induced dynamic hyperinflation in patients with COPD. However, the reliability of this method in patients with COPD exercising to symptom limitation has not been systematically studied and presented. The purpose of the present study was therefore to evaluate the reliability of the IC maneuver in assessing changes in end-expiratory lung volume (EELV) by assessing the pressure developed during IC maneuvers, in patients with COPD during incremental bicycle exercise to exhaustion. Fifteen patients with stable COPD performed bicycle exercise to symptom limitation. During the experiment, the patients performed IC efforts during resting breathing and at the end of each exercise work load. Esophageal pressure (Pes) measured at peak inspired volume plateau (zero flow) was -13.5 +/- 1.9 and -13.4 +/- 1.9 cm H2O (p = 0.79) during IC maneuvers at resting breathing and during the final exercise work load, respectively. When the Pes values at the peak inspired volume plateau during IC efforts at each exercise level were expressed as a percentage of those during resting breathing, the great majority of the ratios were above 90% with the lowest at 84%, and these ratios were independent of exercise intensity. Despite a constant Pes during IC, there was a progressive decrease in IC with increasing exercise work load in most patients, suggesting an increase in EELV. At the highest exercise work load achieved, delta EELV calculated as the decrease in IC was 0.26 +/- 0.06 L (p < 0.001). We conclude that repeated IC maneuver is a simple and reliable method for estimating EELV changes during exercise to exhaustion in patients with COPD.

Exercise↗
PubMed1997

Differential inspiratory muscle pressure contributions to breathing during dynamic hyperinflation.

During dynamic hyperinflation, the ventilatory pump is facing increased demand because it must overcome the intrinsic positive end-expiratory pressure (PEEPi) and decreased capacity since it must operate at a dynamically increased end-expiratory lung volume (EELV). The aim of this study was to evaluate the relative pressure contribution by the diaphragm and inspiratory rib cage muscles (RCMs) during dynamic hyperinflation. In six healthy subjects, dynamic hyperinflation was induced by limiting expiratory flow. The global inspiratory muscle pressure (delta Pmus,i) and transdiaphragmatic pressure (delta Pdi) were partitioned into the portion used to overcome PEEPi and the portion used to inflate the respiratory system. The delta Pdi/delta Pmus,i ratio was used to estimate the pressure contribution of RCMs relative to that of the diaphragm. Our results suggest that (1) with increasing severity of dynamic hyperinflation, there is a significant increase in the inspiratory pressure contribution of RCMs relative to that of the diaphragm for inflating the respiratory system; (2) during dynamic hyperinflation, especially at high EELV, the major pressure contribution of the diaphragm is to overcome the PEEPi-imposed inspiratory threshold load, whereas the inspiratory pressure needed for the subsequent task of inflating the respiratory system is largely contributed by RCMs. This arrangement is consistent with the change in mechanical advantages of RCMs and the diaphragm during the development of dynamic hyperinflation.

Humans↗
PubMed1997

Inspiratory muscle mechanics of patients with chronic obstructive pulmonary disease during incremental exercise.

Inspiratory muscles are weak and contribute to exercise limitation in chronic obstructive pulmonary disease (COPD). Differential inspiratory pressure contributions from the diaphragm and inspiratory rib cage muscles (RCMs) during exercise in patients with COPD patients are insufficiently described. We measured, in 16 patients with COPD, the global inspiratory muscle pressure (delta Pmus) and transdiaphragmatic pressure (delta Pdi) during an incremental bicycle exercise to exhaustion. The pressures needed to overcome the elastic load were further partitioned into portions for overcoming the PEEPi-imposed inspiratory threshold load (before the beginning of inspiratory flow) and for inflating the respiratory system (between the beginning and end of inspiratory flow). The delta Pdi/delta Pmus ratio was used to quantify the pressure contribution from RCMs relative to that from the diaphragm for a given inspiratory effort. We observed that in patients with COPD during exercise (1) there is a progressive increase in total inspiratory pressure contribution from RCMs relative to that of the diaphragm, and the magnitude of this increase appears to depend on the RCMs reserves during resting breathing; (2) most of the diaphragmatic pressure contribution occurs before the beginning of inspiratory flow, to overcome the PEEPi-imposed inspiratory threshold load; (3) RCMs pressure contribution predominates during the period of inspiratory flow once PEEPi is neutralized, not only for overcoming the elastic load caused by increased tidal volume, but also for compensating for the diaphragmatic pressure contribution during this interval that was gradually lost with increasing exercise work load.

Exercise Test↗
PubMed1997

[The synergistic effect of tetrandrine and rotundine on the action potential of rabbit sinus node dominant pacemaker cell and calcium currents of ventricular myocytes from guinea-pig].

Standard microelectrode technique and the whole-cell clamp technique were used to investigate the effects of tetrandrine and rotundine on the action potential of rabbit sinus node dominant pacemaker cell and calcium currents of ventricular myocytes from guinea-pig. The results indicate that: tetrandrine 1-200 mumol.L-1 and rotundine 3-300 mumol.L-1 decreased the action potential amplitude(APA), the maximal upstroke velocity (Vmax), spontaneous depolarizing velocity of phase 4(SP4) and prolonged the sinus circle length(SCL) in a dose-dependent manner. Tetrandrine 0.1 mumol.L-1 in combination with rotundine 0.3 mumol.L-1 was shown to effectively reduce the ICa of ventricular myotytes from guinea-pig, the rate of inhibition is 19.6%. The results suggest that the two drugs have a good synergistic effect on inhibiting calcium current. These results might also put forward a valuable theoretic base for using the two drugs together in treating patients.

Action Potentials↗
PubMed1997

[Studies on the chemical constituents of the alga Sargassum carpophyllum J. Agardh].

The alga Sargassum carpophyllum J. Agardh collected from the South China Sea was immersed in 95% ethyl alcohol. The combined extract was partitioned between ethyl acetate and water. The ethyl acetate phase was subjected to pressure-reduced chromatography over Silica H, eluted with a step gradient of EtOAc in petroleum ether. Two main fractions of sterols (I) and fatty acids (II) were obtained. The composition of I and II were identified by GC/MS. The fraction Ia was obtained, as a main composition of I, by repeated flash chromatography. On the basis of spectroscopic analysis, Ia was identified to be fucosterol.

Fatty Acids↗
PubMed1997

[Determination of trace rare earth in fossil of dinosaurian egg by laser thermal lens spectrometry].

Determination of trace rare earth in fossil of dinosaurian egg by LTLS (Laser thermal lens spectrometry) is presented in this paper. The trace rare earth in fossil of dinosaurian egg was separated and concentrated with ion exchange method. The measure conditions and effect factors are discussedian. The LTLS was applied to the determination of trace rare earth in fossil of dinosaurian egg with satisfactory results. It provides the reference data for the studies on the fossil of dinosaurian egg and an analytical method for the determination of rare earth in geochemical sample.

Animals↗
PubMed1997

Effects of thrombolytic therapy on recanalization in different starting time of treatment after acute myocardial infarction.

OBJECTIVE: To investigate the effects of thrombolytic therapy on recanalization in different starting time of treatment after acute myocardial infarction. METHODS: 172 cases with intravenous thrombolytic agents were divided into 4 groups: < or = 2 hours, > 2-4 hours, > 4-6 hours and > 6-12 hours, according to the different starting time of therapy after onset of symptoms. RESULTS: The recanalization rates were 78.6%, 74%, 39. 6% and 14.3% in < or = 2 hours, > 2-4 hours, > 4-6 hours and > 6-12 hours, respectively. The recanalization rate within 4 hours was significantly higher than those in the groups of > 4-6 hours AND > 6-12 hours. The time interval from the initiation of thrombolytic therapy to reperfusion was increased as the starting time of thrombolysis after onset of symptoms was delayed. CONCLUSIONS: Starting time of thrombolysis within 4 hours after onset of acute myocardial infarction is of the best effect on recanalization.

Aged↗
PubMed1996

Differential regulation of p27 and cyclin D1 by TGF-beta and EGF in C3H 10T1/2 mouse fibroblasts.

Previously, we found that stimulation of C3H 10T1/2 mouse fibroblasts with TGF-beta leads to the striking and rapid down-regulation of p27kip1 expression during G1 phase. Here, we demonstrate that TGF-beta treatment of C3H 10T1/2 cells does not alter the steady-state level of Kip1 message sufficiently to account for the observed down-regulation of p27. This demonstrates that TGF-beta-induced down regulation of p27kip1 occurs at a post-transcriptional level, consistent with a degradative mechanism of p27kip1 down-regulation. Epidermal growth factor (EGF) does not lead to the rapid down-regulation of p27 observed following treatment of cells with TGF-beta. Also in contrast with TGF-beta, EGF causes a strong upregulation of cyclin D1, while neither growth factor affects cdk4 protein levels. These results imply that in this cell type TGF-beta overcomes an inhibitory threshold to cdk activation by cyclin-dependent kinase inhibitors primarily through down-regulation of p27, while EGF overcomes this threshold predominantly through upregulation of cyclin D1 levels. This divergence in pathways may explain why TGF-beta-induced cell cycle kinetics are slower than those of EGF in these cells, and the ability of TGF-beta to delay EGF-induced cell cycle kinetics to its own, slower kinetics. In support of this hypothesis, TGF-beta prevents EGF-induced upregulation of cyclin D1 levels, while TGF-beta is still able to induce p27 down-regulation even in the presence of EGF. In contrast to the case with p27 degredation, neither TGF-beta nor EGF have an observable effect on the steady-state levels of p21 in this cell type.

Animals↗
PubMed1996

Specific induction of fibronectin binding activity by hemoglobin in Candida albicans grown in defined media.

Fibronectin (FN) is a major component of host extracellular matrix that may play an important role in the initiation and dissemination of Candida albicans infections. Expression of FN binding requires growth of C albicans blastoconidia in complex medium, and the regulation of FN receptor expression is poorly understood. We now demonstrate that hemoglobin is a potent and specific inducer of FN receptor expression and describe a defined medium supplemented with hemoglobin that greatly and stably enhances the binding activity of C. albicans for soluble FN. Enhancement of FN binding by hemoglobin in strain 44807 was concentration dependent and was maximal at 0.1% hemoglobin with 20- to 80-fold enhancement. The hemoglobin-induced FN binding to C. albicans was saturable, with a Kd of 2.7 X 10(-8) M. Enhancement required growth of C. albicans in hemoglobin-containing medium, since simply exposing blastoconidia to hemoglobin in a nongrowing status did not enhance binding. Induction was reversible following removal of hemoglobin from the growth medium and not associated with germination. Inorganic or protein-bound iron was not sufficient for the induction, since other iron-containing proteins or inorganic iron salts were inactive. Growth in the simple medium yeast nitrogen base supplemented with hemoglobin increased cell adhesion to immobilized FN and to cultured monolayers of bovine corneal endothelial cells. These data suggest that hemoglobin may be an important regulator of FN binding activity in C. albicans and thus may play a role in its pathogenesis.

Animals↗
PubMed1996

Influence of global inspiratory muscle fatigue on breathing during exercise.

We evaluated the effect of global inspiratory muscle fatigue (GF) on respiratory muscle control during exercise at 30, 60, and 90% of maximal power output in normal subjects. Fatigue was induced by breathing against a high inspiratory resistance until exhaustion. Esophageal and gastric pressures, anteroposterior displacement of the rib cage and abdomen, breathing pattern, and perceived breathlessness were measured. Induction of GF had no effect on the ventilatory parameters during mild and moderate exercise. It altered, however, ventilatory response to heavy exercise by increasing breathing frequency and minute ventilation, with minor changes in tidal volume. This was accompanied by an increase in perceived breathlessness. GF significantly increased both the tonic and phasic activities of abdominal muscles that allowed 1) the diaphragm to maintain its function while developing less pressure, 2) the same tidal volume with lesser shortening of the rib cage inspiratory muscles, and 3) relaxation of the abdominal muscles to contribute to lung inflation. The increased work performed by the abdominal muscles may, however, lead to a reduction in their strength. GF may impair exercise performance in some healthy subjects that is probably not related to excessive breathlessness or other ventilatory factors. We conclude that the respiratory system is remarkably adaptable in maintaining ventilation during exercise even with impaired inspiratory muscle contractility.

Adult↗
PubMed1996

Association of chest wall motion and tidal volume responses during CO2 rebreathing.

The purpose of this study is to investigate the effect of chest wall configuration at end expiration on tidal volume (VT) response during CO2 rebreathing. In a group of 11 healthy male subjects, the changes in end-expiratory and end-inspiratory volume of the rib cage (delta Vrc,E and delta Vrc,I, respectively) and abdomen (delta Vab,E and delta Vab,I, respectively) measured by linearized magnetometers were expressed as a function of end-tidal PCO2 (PETCO2. The changes in end-expiratory and end-inspiratory volumes of the chest wall (delta Vcw,E and delta Vcw,I, respectively) were calculated as the sum of the respective rib cage and abdominal volumes. The magnetometer coils were placed at the level of the nipples and 1-2 cm above the umbilicus and calibrated during quiet breathing against the VT measured from a pneumotachograph. The delta Vrc,E/delta PETCO2 slope was quite variable among subjects. It was significantly positive (P < 0.05) in five subjects, significantly negative in four subjects (P < 0.05), and not different from zero in the remaining two subjects. The delta Vab,E/delta PETCO2 slope was significantly negative in all subjects (P < 0.05) with a much smaller intersubject variation, probably suggesting a relatively more uniform recruitment of abdominal expiratory muscles and a variable recruitment of rib cage muscles during CO2 rebreathing in different subjects. As a group, the mean delta Vrc,E/delta PETCO2, delta Vab,E/delta PETCO2, and delta Vcw,E/delta PETCO2, slopes were 0.010 +/- 0.034, -0.030 +/- 0.007, and -0.020 +/- 0.032 1/Torr, respectively; only the delta Vab,E/delta PETCO2, slope was significantly different from zero. More interestingly, the individual delta VT/delta PETCO2 slope was negatively associated with the delta Vcr,E/delta PETCO2 (r = 0.68, P = 0.021) and delta Vcw,E/delta PETCO2 slopes (r = 0.63, P = 0.037) but was not associated with the delta Vab,E/delta PETCO2 slope (r = 0.40, P = 0.223). There was no correlation of the delta Vrc,E/delta PETCO2 and delta Vcw,E/delta PETCO2 slopes with age, body size, forced expiratory volume in 1 s, or expiratory time. The group delta Vab,I/delta PETCO2 slope (0.004 +/- 0.014 1/Torr) was not significantly different from zero despite the VT nearly being tripled at the end of CO2 rebreathing. In conclusion, the individual VT response to CO2, although independent of delta Vab,E, is a function of delta Vrc,E to the extent that as the delta Vrc,E/delta PETCO2 slope increases (more positive) among subjects, the VT response to CO2 decreases. These results may be explained on the basis of the respiratory muscle actions and interactions on the rib cage.

Abdominal Muscles↗
PubMed1996

Comparison of static and dynamic intrinsic positive end-expiratory pressure using the Campbell diagram.

Intrinsic positive end-expiratory pressure (PEEPi) due to dynamic hyperinflation has been measured as a plateau airway opening pressure during airway occlusion (PEEPi,stat). PEEPi has also been dynamically determined as a fall in esophageal pressure (Pes) before the inspiratory flow starts (PEEPi,dyn). The aims of the current study were to systematically compare PEEPi,stat and PEEPi,dyn and to explain the underlying mechanisms of their difference. The study was performed in healthy subjects with dynamic hyperinflation induced by expiration through a Starling resistor. The Campbell diagram was constructed for each subject by determining the static pressure-volume curves of the lung (Pst,[l]) and chest wall (Pst,[w]). For a given end-expiratory volume, PEEPi,stat was measured on the Campbell diagram as the pressure difference between Pst(w) and -Pst(l). PEEPi,dyn was measured as mentioned above. The effects of respiratory muscle recruitment on PEEPi,dyn were estimated by the Pes values when Pes started to fall relative to Pst(w). We found that: (1) there was a great variability of the PEEPi,dyn/PEEPi,stat ratio among and within subjects; (2) expiratory muscle recruitment was evident on most occasions; (3) persistent inspiratory muscle activity during expiration was present in some subjects; (4) the Pes values at the start of inspiratory flow were frequently on the left of -Pst(l), which contributed to the difference between PEEPi,stat and PEEPi,dyn and implied a greater dynamic than static elastance presumably due to viscoelastic properties; (5) chest wall distortions characterized by inflation of the abdomen with deflation of the rib cage during the initial inspiratory efforts were observed in three subjects. In conclusion, interpretation of PEEPi,dyn needs to be cautious because both expiratory and tonic inspiratory muscle activities that lead to significant over- or underestimation of PEEPi by PEEPi,dyn, respectively, are associated with acute dynamic hyperinflation. In addition, the effects of viscoelastic properties and chest wall distortions on PEEPi,dyn need to be further investigated.

Adult↗