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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 1,423 records · Page 79Linked to original sources
PubMed1989

Mechanical factors do not influence blood flow distribution in atelectasis.

The contribution of mechanical factors to the vascular resistance of the atelectatic lung has been studied in vivo in the anesthetized open-chest dog. When the left lung was ventilated with an hypoxic gas mixture (while the right lung was ventilated with 100% O2), left lung blood flow decreased from 0.99 +/- 0.11 1.min-1 to 0.40 +/- 0.08 1.min-1 due to hypoxic pulmonary vasoconstriction (hypoxic stimulus PSO2 = 36.1 +/- 0.8 mmHg). When the left lung was made atelectatic, blood flow decreased to 0.65 +/- 0.11 1.min-1, consistent with a weaker hypoxic stimulus (PSO2 = 54.0 +/- 3.2 mmHg). With the addition of sodium nitroprusside infused intravenously, left lung blood flow increased to 1.05 +/- 0.14 1.min-1 during atelectasis, and to 0.61 +/- 0.09 1.min-1 during hypoxic ventilation, while flow remained at 0.94 +/- 0.18 1.min-1 during hyperoxic ventilation. When the results were plotted on pressure-flow diagrams, the hyperoxic, hypoxic, and atelectatic lung points fell on the same pressure-flow line in the presence of nitroprusside. It is concluded that hypoxic pulmonary vasoconstriction is the major (but not necessarily only) determinant of increased vascular resistance in the atelectatic lung, and that passive mechanical factors do not measurably affect blood flow distribution during open-chest atelectasis.

Animals↗
PubMed1989

Clutter interference and the integration time of echoes in the echolocating bat, Eptesicus fuscus.

The ability of the echolocating bat, Eptesicus fuscus, to detect a sonar target is affected by the presence of other targets along the same axis at slightly different ranges. If echoes from one target arrive at about the same delay as echoes from another target, clutter interference occurs and one set of echoes masks the other. Although the bat's sonar emissions and the echoes themselves are 2 to 5 ms long, echoes (of approximately equal sensation levels--around 15 dB SL) only interfere with each other if they arrive within 200 to 400 microseconds of the same arrival time. This figure is an estimate of the integration time of the bat's sonar receiver for echoes. The fine structure of the clutter-interference data reflects the reinforcement and cancellation of echoes according to their time separation. When clutter interference first occurs, the waveforms of test and cluttering echoes already overlap for much of their duration. The masking effect underlying clutter interference appears specifically due to overlap, not between raw echo waveforms, but between the patterns of mechanical excitation created when echoes pass through bandpass filters equivalent to auditory-nerve tuning curves. While the time scale of clutter interference is substantially shorter than the duration of echo waveforms, it still is much longer than the eventual width of a target's range-axis image expressed in terms of echo delay.

Animals↗
PubMed1989

The acoustic basis for target discrimination by FM echolocating bats.

Past experiments show that echolocating bats of the species Myotis lucifugus and Eptesicus fuscus can discriminate among airborne sonar targets presented in the context of pursuit maneuvers for the interception of prey. These bats distinguish between edible mealworms and inedible spheres of various sizes. Myotis can distinguish between disks and mealworms similar enough in size that the bat's performance requires the ability to perceive the acoustic equivalent of target shape. Previously observed small differences in the spectrum of echoes from mealworms and disks appear insufficient to distinguish these targets at the performance levels achieved by bats. We measured the acoustic properties of the targets by broadcasting ultrasonic impulses at mealworms, spheres, and disks and recording their echoes, displaying the results in terms of impulse echo waveforms and the frequency response of targets derived from the target transfer function. The echoes from disks and mealworms at various orientations convey the range-axis profile of the target (number and spacing of reflecting points or glints distributed at different ranges) in terms of the impulse structure of their waveforms and in terms of the locations and spacing of notches or nulls in their spectra. For targets that bats can discriminate and that reflect echoes which do not clearly differ in overall amplitude, the targets appear distinguishable from the acoustic representation of their range profile, which is a feature of targets that bats can perceive with great acuity.

Animals↗
PubMed1989

Cardiac gap junctions and gap junction-associated vesicles: ultrastructural comparison of in situ negative staining with conventional positive staining.

By comparing in situ negative staining of mammalian heart muscle using La(NO3)3 with conventional positive staining by uranium and lead salts, we showed that 1) the membrane area of rat cardiac gap junctions (GJs) at the intercalated disks is threefold to fourfold greater than previously thought; 2) connexon arrays of cardiac GJ are subdivided into microdomains by connexon-free aisles; 3) profiles of GJ-associated vesicles (GJAVs) of plasmalemmal origin (which are present extracellularly and sharply localized at three extracellular sites) are paired to form GJs with each other and with myocyte plasmalemma; 4) some GJAVs contain arrays of assembled connexons; and 5) myocytes contain intracytoplasmic complexes lying within cylindrical or cigar-shaped membranes and consisting of GJs and multiple vesicles apparently dissociating from these GJs.

Animals↗
PubMed1989

Effects of hypoglycemia and prolonged fasting on insulin and glucagon gene expression. Studies with in situ hybridization.

In situ hybridization of proinsulin and proglucagon mRNA was performed in rat pancreas to assess prohormone gene expression during various glucopenic conditions. During a 4-d fast mean blood glucose declined by 48 mg/dl; proinsulin mRNA signal density remained normal while proglucagon mRNA signal density more than doubled. At the end of a continuous 12-d insulin infusion blood glucose averaged 53 +/- 12 mg/dl; proinsulin mRNA signal density declined to 30% of controls while proglucagon mRNA signal density more than doubled. In insulinoma-bearing NEDH rats blood glucose averaged 34 +/- 3.5 mg/dl; the proinsulin mRNA signal was virtually undetectable and proglucagon mRNA signal density was more than twice the controls. There was no detectable change in either beta-cell area or islet number in rats subjected to fasting or insulin infusion, but in insulinoma-bearing rats beta cell area was markedly reduced. Thus compensation during 4 d of starvation involves an increase in glucagon gene expression without change in insulin gene expression or beta cell mass. In moderate insulin-induced hypoglycemia glucagon gene expression is increased and insulin gene expression decreased. In more profound insulinoma-induced hypoglycemia, in addition to the foregoing changes in hormone gene expression, there is a profound reduction in the number of insulin-expressing cells.

Animals↗
PubMed1989

[Effects of ipratropium bromide (IPB) and its combination with salbutamol sulfate (SAS) in acute asthmatic attack].

34 patients with acute asthmatic attack were studied in double-blind, randomized and crossover manner. Each of them was treated with following two protocols during two sequential days: 0.5 mg of ipratropium bromide (IPB), followed by 5 mg of salbutamol sulfate (SAS) 75 minutes later; or 5 mg of SAS, followed by another dose 35 minutes late. The drugs were delivered via a jet nebulizer. The effects and side-effects of the treatment were evaluated immediately before the first inhalation and at peak of bronchodilatation (60-75 minutes after IPB or 20-35 minutes after SAS). Compared with inhaled SAS, IPB produced considerable improvement in central airway parameters such as forced expiratory volume in one second (FEV1) peak expiratory flow (PEF) and respiratory resistance (Rrs) (P greater than 0.05), but less improvement in peripheral airway parameters such as forced vital capacity (FVC) and maximal mid-expiratory flow (MMEF) (P less than 0.01). The sequential inhaled SAS after IPB improved all five parameters (P less than 0.01), but the repeated dose of SAS increased only MMEF (P less than 0.01). Compared with double-dose SAS, the sequential treatment with IPB and SAS 1 ed to considerable improvement in FVC and MMEF (P greater than 0.05), but greater improvement in FEV1, PEF and Rrs (P less than 0.01). Heart (rate and tremor scores after two doses of SAS increased significantly (P less than 0.01). It is concluded that IPB alone is less effective than beta-adrenoceptor agonist, but its combination with SAS would be an effective and safe treatment in acute asthmatic attack.

Adult↗
PubMed1989

[Effects of kappa-opiate receptor antagonist MR-2266-BS on ACTH and prolactin release].

The effect of intravenous injection of different doses of MR-2266-BS, a selective antagonist of kappa-opiate receptor, on plasma adrenocorticotropin (ACTH) and prolactin (PRL) in conscious male rats bearing an intrajugular cannulae was assessed. The results revealed that the MR-2266-BS of 3 mg/kg completely blocked the restraint stress-induced increase in plasma ACTH levels, and further elevated plasma PRL levels in these animals, while there were no effects on the resting levels of ACTH and PRL. MR-2266-BS of 6 mg/kg significantly increased the resting levels of plasma ACTH and also further elevated the restraint stress-induced increase of plasma ACTH and PRL. The present data suggest that kappa-opiate receptor and its endogenous ligand may be involved in the regulation of the resting and restraint stress-induced release of ACTH, and their action appears to be both stimulatory and inhibitory. Furthermore, kappa-opiate receptor and its endogenous ligand may only inhibit the stress-induced release of PRL.

Adrenocorticotropic Hormone↗
PubMed1989

[Indications of cesarean section for severe heart diseases in pregnancy--an analysis of 61 cases].

Sixty-one cases of severe heart diseases were treated between Jan. 1977 and Dec. 1986, accounting for 18.37% of the heart diseases in pregnancy. Of these 61 cases, 39 (63.93%) underwent cesarean section under continuous lumbar epidural anesthesia. The systolic/diastolic blood pressure and mean arterial pressure (MAP) values decreased from the beginning of anesthesia to the end of delivery, and then the values gradually went up to the preoperative level. During the operation, no heart failure occurred. In 22 cases (36.07%), when labor began, the systolic/diastolic pressure and MAP increased and attained the peak value during parturition. After the fetus was delivered, the blood pressure decreased immediately. In 10 cases, heart failure occurred during labor. The adjusted mortality was 4.92%. Two patients died after vaginal delivery. Of these, one had heart failure during labor and underwent cesarean section, but she died after the operation. It was noted that hemodynamic change during cesarean section was smaller than that during vaginal delivery. If an appropriate time is selected for termination of pregnancy or cesarean section is only performed in the early stage of labor, heart failure and fatal outcome may be avoided.

Adult↗
PubMed1989

Solubilization of immobilized protein substrates by metastatic tumor cells.

A new, sensitive automated assay based on the enzyme-linked immunosorbent assay was developed for measuring proteolytic enzyme activity produced by metastatic tumor cells. In this assay, a suitable protein substrate is adsorbed onto the surface of microplates and incubated with dilutions of standard proteinases, viable tumor cells, or tumor-cell-conditioned medium. The loss of immobilized protein due to proteolysis is then detected by means of antibodies directed against the target protein, and is measured by a microplate reader. Both casein and fibronectin were useful as substrates for the assay of various well-defined proteinases. The assay was successfully used to detect degradative activity elaborated by the mouse B16-BL6 melanoma and the human HT1080 fibrosarcoma cell lines. Both cell lines extensively removed immobilized protein substrates when the cells were seeded directly on the protein films. In addition, substrate removal could also be detected in the serum-free culture medium conditioned by the tumor cells. The results indicate that soluble proteinases secreted by tumor cells may be important during tissue invasion.

Animals↗
PubMed1989

[Observation on the efficacy of combined use of some new antimalarials for the treatment of falciparum malaria in Hainan Province].

Field trials were carried out to assess the therapeutic effects including the combined use of piperaquine (PQ) with nitroquine (NQ) and pyronaridine (PYR) with NQ against falciparum malaria in regions of Hainan Province with chloroquine-resistance in 3 successive autumns from 1985 to 1987. In an evaluation of PQ 750 mg with NQ 25 mg therapy in 33 falciparum malaria patients, the average fever subsidence time and parasite clearance time were 39 hours and 49 hours respectively, but within 28 days after medication, the recrudescence rates were 0-47% in different regions. In evaluations of PYR 600 mg with NQ 25 mg in 11 cases, PYR 800 mg with NQ 40 mg in 43 cases, PYR 800 mg with NQ 80 mg in 31 cases, the fever subsidence time were 31-35 hours, the parasite clearance time were 46-53 hours and the 28 days recrudescence rates were 13-18%. In the control, the use of PYR 1,200 mg alone in 42 cases, the average fever subsidence time and parasite clearance time were 33 hours and 48 hours respectively, the 28 days recrudescence rate was 12%. There was no statistically significant difference among them in their effects. The side-effects of all groups were mild.

Adolescent↗
PubMed1989

[Continuous ambulatory peritoneal dialysis treatment and blood glucose control in diabetics with end-stage diabetic nephropathy].

6 patients with end-stage diabetic nephropathy were treated with continuous ambulatory peritoneal dialysis (CAPD). The results showed that CAPD is a safe and effective therapeutic method for elderly uremic diabetics even with congestive heart failure or acute myocardial infarction. We also compared the insulin dosages and blood glucose levels in these patients treated with three routes of insulin administration. Good control of blood glucose was obtained by giving insulin subcutaneously or through dialysis tubes.

Adult↗
PubMed1989

Antagonism of serum of mice infected with chloroquine-resistant 'NS' line to the antimalarial action of chloroquine.

Chloroquine (CQ) solution was separately mixed with the serum of mice infected with chloroquine-resistant 'NS' line (SMNS), the serum of mice infected with chloroquine-sensitive Plasmodium berghei ANKA strain (SMCS), and the serum of normal mice (SM). These mixtures were then used in treating mice inoculated with P. berghei ANKA strain. The results obtained on d 5 after drug-serum administration showed that the erythrocyte infection rates in the SMNS + CQ, SMCS + CQ, and SM + CQ groups were 32, 16, and 14% respectively. There were significant differences with respect to parasitemia between the SMNS + CQ group and the SMCS + CQ or SM + CQ group (P less than 0.05), suggesting that SMNS may be antagonistic to the antimalarial action of chloroquine. Further study showed that when the 'NS' line lost resistance to chloroquine, the antagonism of SMNS to chloroquine disappeared. The antagonism rates of SMNS to chloroquine, piperaquine, hydroxypiperaquine and pyronaridine were 75, 56, -5, and -17% respectively, a trend similar to that of the results from cross-resistance tests on chloroquine-resistant P. berghei ANKA strain. The results indicate that drug-resistant malaria parasites may produce and release a certain 'specific anti-drug substance'.

Animals↗
PubMed1989

[Research on the dose-response relationship of hand transmitted vibration and its hygienic standard].

According to ISO 5349-1986, the akw(4) was 9.04-41.47m/s2 which was measured and calculated in 5 types of instruments: chain saw, cleaner, rock driller, riveter & emery wheel. There were 170 cases with white finger through epidemiologic investigation on 5 types of workers in 1,675 persons. Based on the work mentioned above, a formula, which represented worker cumulative exposure to vibration was deduced: D = [(a2kw(4).T)1/2.Y.d]2 Furthermore, the dose-response relationship of hand transmitted vibration and prevalence of white finger was computed, the regression equation was: P = 1.0904X - 6.214 2 Under precondition of exposure to vibration for 20 years with 90% of workers having no white fingers, the limit of hygienic standard of hand transmitted vibration in china should be set at 4 hours and as akw(4) less than or equal to 5 m/s2 based on the regression equation.

Fingers↗
PubMed1989

[Cross correlation function of BAEP for objective assessment of hearing threshold].

Brainstem auditory evoked potentials (BAEP) recorded were equally divided into two subensembles and a cross correlation function R (lambda) was calculated for them. The average amplitude of R (lambda) around lambda = 0 was chosen as the criterion for hearing threshold measurement. A linear regression equation which represented the relationship between the criterion and stimulus intensity above threshold was obtained on 21 normal and abnormal ears and thus a equation for assessment of hearing threshold was derived. When the equation was applied to ears to be evaluated, the criteria obtained at three different stimulus intensities above threshold were put into the equation and the mean value was calculated for assessment of hearing threshold. The results from 8 ears with different degrees of hearing loss demonstrated that the differences between estimated thresholds and corresponding subjective thresholds are 4.6 dB on the average.

Auditory Threshold↗
PubMed1989

[The Balint syndrome].

This paper reports a case of complete form of Bálint syndrome. A 56-year-old male suffered form psychic paralysis of gaze, impaired visual attention and optic ataxia of sudden onset in the basis of sequlae of cerebral vascular disease. CT scans of the present case demonstrated low densities in the left frontal, parietal lobe and right basal ganglia, right parito-occipital lobe. As for possible anatomical substrate of the Balint syndrome. according to Damasio's atlas, the authors inferred that despit the multiplicity of lesions in the present case, prefrontal area, lobulus paritalis inferior gyrus angularis and the associated fibers between the prefrontal area and 18, 19 area of occipital lobe were considered to be most responsible for the production of the Balint syndrome.

Brain↗