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Biomedical subjects

L F Zhang

Publications and source records attributed to L F Zhang.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Counter-effect of intermittent +Gz exposures on vasoreactivity in decline in hind body arteries of rats under simulated weightlessness].

Objective. To investigate the counter-effect of intermittent artificial gravity, the present study examined vasoreactivity changes of femoral and mesenteric arteries in rats subjected to simulated weightlessness plus standing or centrifugation. Method. Forty male Sprague-Dawley rats were divided into simultaneous control (CON), simulated weightlessness (SUS), simulated weightlessness plus 1 h standing (STD1), simulated weightlessness plus 1.5 G centrifugation (1.5 G), and simulated weightlessness plus 2.6 G centrifugation (2.6 G) groups. Responses of arteries to vasoconstrictor were examined in vitro using isolated femoral and mesenteric arterial rings. Result. The contractile responsiveness to KCl or PE of femoral and mesenteric arterial rings isolated from SUS significantly decreased as compared with CON. And those of STD1 and the two centrifuged groups significantly enhanced as compared with that of SUS. Whereas there was no difference among STD1, 1.5 G, 2.6 G and CON. Conclusion. Simulated weightlessness may result in decreased contractile responses to KCl and PE of rat femoral and mesenteric arteries. Both STD1, 1.5 G, and 2.6 G prevented the decrease of contractile response to KCl and PE of femoral arteries.

Animals↗
PubMed2001

[Daily 1 h standing can prevent depression of myocardial contractility in simulated weightless rats].

Objective. To observe and compare the effect of daily standing of rats for different durations in alleviating the depression of myocardial contractility induced by simulated weightlessness. Method. Fifty male Sprague-Dawley rats were randomly assigned to five groups: simultaneous control (CON), four-week tail-suspension (SUS), SUS plus daily 1 h standing (STD1), SUS plus daily 2 h standing (STD2) and SUS plus daily 4 h standing (STD4). Four weeks later, wet weights of the left soleus, testis and adrenal gland were measured, and the isometric contractile tension and its time parameters of isolated perfused papillary muscles from rats of various groups were examined. Result. Compared with CON, the wet weights of testis in different treatment groups decreased significantly (P<0.05). The wet weight of soleus in SUS decreased by 58.9% (P<0.01); but in STD1, STD2 and STD4, decreased by 38.5%, 24.0% and 11.0% (P<0.01, or P<0.05) respectively. The relative protections were 34.7%, 59.2% and 81.4% (P<0.01) respectively. In SUS group, developed tension (DT), peak rate of tension rise (+dT/dtmax) and peak rate of tension fall (-dT/dtmax) decreased by 32.2%, 29.2% and 30.7% (P<0.05), and time to peak rate of tension rise (TPP) and time to peak tension (TPT) prolonged by 21.2% and 11.0% (P<0.05), respectively. Whereas in STD1, STD2 and STD4, all the parameters reflecting myocardial contractility (like DT, + dT/dtmax, -dT/dtmax and TPP), did not show any significant change as compared with those of CON. However, being an exception, TPT still showed obvious prolongation (P<0.05) in STD1. Conclusion. Daily 1 h standing could prevent depression of myocardial contractility in rat induced by medium-term simulated weightlessness. However, with respect to prevention of atrophic changes in soleus muscle and testis, daily standing for 1 h, 2 h, or 4 h was only partially effective and even totally devoid of any effect, respectively.

Animals↗
PubMed2001

[Transition of soleus troponin I isoforms and atrophy of testis in tail-suspended rats].

Objective. To observe the transition time of soleus I (TnI) isoforms and to elucidate the relationship between soleus TnI transition and atrophy; and to analyze the time course between testis atrophy and soleus atrophy. Method. Eight groups of male rats were suspended for 3, 4, 5, 7, 14, 21, 28 and 42 d, respectively. Besides, three groups of female rats were suspended for 3, 4 and 5 d respectively. Wet and relative weights (wet weight/body weight) of testis and soleus were measured. The expression of TnI was observed by Western blot. Result. The relative weight of soleus of tail-suspended male rats decreased significantly after 4 d of suspension as compared with control. The degree of rats soleus atrophy in the first 14 d of suspension was greater than that after 14 d. The relative weight of testis showed the same change as that of soleus. There was no significant change in the relative weight of soleus in 4 d of tail-suspended female rats. The significant decrease in the relative weight of tail-suspended female rats began on the 5th day. The Western blot showed that the transition from slow skeletal TnI (ssTnI) to fast skeletal TnI (fsTnI) in the soleus occurred in 14 d of tail-suspension. Conclusion. The overt atrophy of tail-suspended male rats occurs on the 4th day. The soleus TnI transition from ssTnI to fsTnI is on the 14th day. It is suggested that the TnI is not the sensitive protein to gravity. The overt atrophy of female tail-suspended rats occurs at the 5th day. This indicated that the decrease in testosterone level may accelerate the atrophy of the soleus.

Animals↗
PubMed2001

[Estimating cardiovascular age of civil flying personnel by means of heart rate and blood pressure variability analysis].

Objective. To estimate the cardiovascular age of civil flying personnel by means of heart rate and blood pressure variability analysis and to evaluate its significance in aviation medicine. Method. First, heart rate variability (HRV), blood pressure variability (BPV) and spontaneous baroreflex sensitivity (BRS) were analyzed among 89 healthy civil flying personnel by using conventional AR spectral analysis and sequence method respectively. Then, principal component analysis was conducted over original and derived variables of HRV and BPV spectral and BRS data. Finally, by the use of multiple regression in which the chronological age acted as the dependent variable and the components significantly related to age were used as the regressors, the equation for estimating the cardiovascular age was established. Result. Only seven principal components can exactly reflect the same information of autonomic regulatory function which was embodied in the 17 variables of HRV and BPV spectral and BRS parameters. Among the seven principal components, the PC2orig, PC4orig and PC2deri were negatively correlated with chronological age (P<0.05), whereas the PC3orig was positively correlated with the chronological age (P<0.01). The cardiovascular age derived from the equation was significantly correlated with the chronological age of the civil flying personnel (r= 0.73, P<0.01). Conclusion. The cardiovascular age estimated by means of a multi-variate analysis of HRV, BPV and BRS can be treated as a comprehensive indicator reflecting the age dependency of autonomic regulatory function of cardiovascular system in healthy civil flying personnel, and its interpretation and significance in application are surely worthy of further and fully dedicated efforts.

Adult↗
PubMed2001

[Peripheral effector mechanism hypothesis on cardiovascular dysfunction after spaceflight].

In the years of 1990's, we systematically studied the adaptational changes in structure and function of both the heart and the vessels during simulated weightlessness. In our serial work, the tail-suspension rat model was used to simulate the microgravity-induced cephalad shift and redistribution of blood. On the basis of the facts we observed and the more recent advances in space and ground-based studies in 1990's, we put forward a hypothesis to offer a possible explanation for the frequent occurrence of postflight cardiovascular dysfunction. It states that, in addition to the factor of hypovolemia, the microgravity-induced adaptational changes in the structure and function of the two main effectors of the cardiovascular system, i.e., the arterial smooth muscle and the cardiac muscle might be one of the most important mechanisms accounting for postflight cardiovascular dysfunction.

Cardiovascular System↗
PubMed2001

Effects of depressed myocardial contractility induced by microgravity on cardiovascular response to orthostatic stress: a computer simulation.

The aim of present study is to investigate the role played by the depression of myocardial contractility in the mechanism of cardiovascular deconditioning and orthostatic intolerance (OI) induced by space weightlessness. Based on our previous model, which was used to simulate cardiovascular response to lower body negative pressure (LBNP), we incorporated the factor of changes of myocardial contractility into the model by multiplying a coefficient to the time-varying elastance that represents the changes of cardiac contractility. By decreasing the coefficient progressively, we simulated the changes of heart rate (HR), blood pressure (BP), and cardiac output (CO) during LBNP after 0-30% of myocardial contractility depression combined with 12% decrease of the total blood volume. Simulation results indicate that depressed myocardial contractility induces more augment of HR, and more decrement of BP and CO during LBNP and suggest that the depression of myocardial contractility degenerate cardiovascular response to orthostatic stress.

Blood Pressure↗
PubMed2000

HPV6b virus like particles are potent immunogens without adjuvant in man.

Subjects with genital warts were immunized three times or more with HPV6b VLPs without adjuvant. All immunized subjects had DTH to HPV6b L1 protein. Of 32 subjects, nine had HPV6b specific antibody prior to immunization and 22 acquired antibody with immunization. VLP specific antibody increased following a single immunization in 6 of 8 subjects with low level antibody at recruitment. Complete regression of genital warts was observed in 25 of 33 evaluable subjects over the 20-week observation period. We conclude that immunization with HPV6b L1 VLPs without adjuvant induces immunity to the L1 protein epitopes recognised during natural infection, and may accelerate regression of warts.

Adolescent↗
PubMed2000

Are learning approaches and thinking styles related? A study in two Chinese populations.

This article presents the results of an investigation of the construct validity of J. B. Biggs's (1987) theory of learning approaches and of R. J. Sternberg's (1988) theory of thinking styles in two Chinese populations. The study is also an examination of the nature of the relations between the two theories. University students from Hong Kong (n = 854) and from Nanjing, mainland China (n = 215), completed the Study Process Questionnaire (J. B. Biggs, 1992) and the Thinking Styles Inventory (R. J. Sternberg & R. K. Wagner, 1992). Results indicated that both inventories were reliable and valid for assessing the constructs underlying their respective theories among both Hong Kong and Nanjing university students. Results also showed that the learning approaches and thinking styles are related in the hypothesized ways: The surface approach was hypothesized to be positively and significantly correlated with styles associated with less complexity, and negatively and significantly correlated with the legislative, judicial, liberal, and hierarchical styles. The deep approach was hypothesized to be positively and significantly correlated with styles associated with more complexity, and negatively and significantly correlated with the executive, conservative, local, and monarchic styles. Implications of these relations are discussed.

Adult↗
PubMed2000

University students' learning approaches in three cultures: an investigation of Biggs's 3P model.

The relationship of various learning approaches to students' academic achievement, abilities, and other characteristics was examined in a sample of university students in Hong Kong, mainland China, and the United States. The theoretical framework for this project was J. B. Biggs's (1987) theory of student learning approaches. The participants completed the Study Process Questionnaire (based on Biggs's theory) and provided a variety of demographic information. The participants' achievement scores and self-rated scores on analytical, creative, and practical abilities were also obtained. Results indicated that scores on certain subscales of the Study Process Questionnaire statistically predicted participants' achievement beyond their self-rated abilities. In addition, certain learning approaches were significantly related to the participants' ages, gender, parents' education levels, and their travel and work experiences. Implications of these findings are discussed as they relate to teaching and learning.

Achievement↗
PubMed2000

Validity of the Learning Process Questionnaire with students of lower academic attainment.

The Learning Process Questionnaire was administered to 692 secondary school students (308 boys, 380 girls, and 4 unspecified) in the Philippines. The ages of the participants ranged from 14 to 22 years, with an average of 15 yr. An exploratory factor-analysis procedure was conducted for the entire sample, for the lower achievers (n = 333), and for higher achievers (n = 359). The factor structure of the Learning Process Questionnaire was uninterpretable with data obtained from students of lower academic achievement.

Adolescent↗
PubMed2000

[Counteracting effects of intermittent head-up tilt on simulated-weightlessness induced atrophy of anti-gravity muscles].

Objective. To study the efficacy of intermittent + Gz (45 degrees head-up tilt, HUT) exposures in preventing or alleviating atrophic changes in hind limb muscles induced by simulated weightlessness. Method. Male Sprague-Dawley (SD) rats were assigned randomly to one of three groups: simultaneous control (CON), simulated weightlessness (SUS), and SUS plus 6 h/d HUT (SUS + HUT). Muscles examined included soleus (SOL), medial gastrocnemius (correction from grastrocnemius) (MG), lateral gastrocnemius (LG) and extensor digitorum longus (EDL). Sections were treated with an adenosinetriphosphatase (ATPase) stain or alkaline phosphatase stain. The cross-sectional areas (CSA) of fibers, the relative proportion of type I fiber and the ratio of capillaries/fibers (C/F) were measured using Leica image analysis system. Result. Compared with CON, the wet weight of hind limb muscles in SUS were significantly reduced. The changes of wet weight in different groups were various. The C/F ratios of all muscles were significantly reduced. SUS + HUT rats showed significant increases in SOL and MG wet weight, and the relative counter-effects of intermittent HUT were 93.4% and 34.8%, respectively. In SUS + HUT group, the CSA of both type I and II fibers and relative proportion of type I fibers were completely recovered in SOL, and partially recovered in MG, while the counter-effects were much less obvious in the fibers of LG and EDL. However, HUT resulted in a significant recovery of the C/F ratios in all muscles. Conclusion. The present study demonstrated that intermittent HUT is effective in counteracting the atrophy induced by simulated weightlessness. The result that reactivity to HUT varied among different muscles suggests that the intermittent artificial gravity should be complemented with other countermeasures.

Animals↗
PubMed2000

[A simulated study of effects of simulated hypovolemia on cardiovascular response to orthostatic stress].

Objective. To study the effects of hypovolemia on cardiovascular response to orthostatic stress, and to investigate the role of hypovolemia in the mechanism of cardiovascular deconditioning and orthostatic intolerance induced by space weightlessness. Method. The effects of loss of blood volume had been incorporated in the sub-model of blood redistribution in the model developed for simulating the cardiovascular response to lower body negative pressure (LBNP). With the help of the model, we simulated the changes of heart rate (HR) and blood pressure (BP) during LBNP after 0-25% loss of blood volume. Result. When the amount of decrease of blood volume was less than 5% of the total blood volume, HR and BP could be maintained in normal range during LBNP through baroreflex regulation. When the amount of the decrease of blood volume was more than 15% of the total blood volume, HR and BP could be kept in normal range when the subject was supine and at rest. But BP fell sharply and the cardiovascular system almost collapsed during orthostatic exposure. Conclusion. Decrease of blood volume causes significant degradations of cardiovascular response to orthostatic stress.

Aerospace Medicine↗
PubMed2000

[Age dependency of heart rate variability, blood pressure variability and baroreflex sensitivity].

Objective. To compare the cardiovascular autonomic regulatory function between young and middle-aged male subjects and to assess the effects of aging. Method. Spectral indices of short term heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreflex sensitivity (BRS) in both supine and upright positions were obtained by AR spectral analysis and the sequential method, respectively, for both groups. Result. HRV spectral indices in both supine and upright, and the BRS in supine were lower in the middle-aged subjects than in the young subjects (P< 0.05, or P< 0.01). From supine to upright position total power (TP), low frequency power (LF) and high frequency power (HF) of HRV spectrum did not show any significant changes in the middle-aged subjects, whereas in the young subjects typical changes were observed. SBPV spectral indices did not show significant differences between the two groups in both supine and upright positions. However, SBPV HF was an exception, being lower in supine position in the middle-aged than in the young subjects (P< 0.01). For the young subjects, in supine position, BRS was correlated with LF and HF of HRV, respectively, and the spectral indices of HRV in supine position were also correlated with their corresponding indices in upright position. For the middle-aged subjects these correlations did not exist. Conclusion. In the middle-aged, both HRV and BRS are reduced and the correlations between HRV indices and BRS are not existent. However, the short-term blood pressure variability seems to be not age-dependent. It suggests that different regulatory mechanisms might account for it and that under resting condition the feed forward regulation from HRV to SBPV might be unimportant.

Adolescent↗
PubMed2000

[Effects of intermittent +45 degrees head-up-tilt on mechanical parameters of femoral (correction of femural) bone in tail-suspended rats].

Objective. To study the effects of different intermittent +45 degrees head-up-tilt (IHUT) on tail-suspended rats. Method. 28 male SD rats were randomly and equally divided into: control group (C), tail-suspended group (S), IHUT 2 h group (H2), and IHUT 4 h group (H4). On the basis of tail-suspension to simulate weightlessness, H rats were given 2 h or 4 h IHUT each day. The effects of 3 wk IHUT on tail-suspended rats were evaluated by measuring physical and mechanical parameters of the femur. Result. Femoral mass (fresh, dry and ash), diameter, and density (fresh, except H2 group) in S, H2 and H4 rats were declined significantly compared to C rats (P<0.01 or P<0.05). Diameter (P<0.05) and density of femur (P<0.01) in H2 rats were significantly improved compared to S rats. Compared to C rats, the strength and stiffness of femora were obviously weakened (P<0.01) in S rats. Elastic load in H2 rats improved markedly (P<0.05) than those in S group; in H4 group, elastic load, maximum load, and bending toughness coefficient improved significantly (P< 0.01 or P<0.05). Conclusion. Using IHUT, mechanical parameters of weight bearing bones of tail-suspended rats can be improved apparently, by extending the exposure time, mechanical parameters can be improved.

Animals↗
PubMed2000

Fos protein expression in the medulla oblongata and changes in size of spinal lateral horn neurons after 4-wk simulated weightlessness in rats.

Responses of the neurons in medulla oblongata and C8-T1 spinal cord lateral horn of rats induced by simulated weightlessness were investigated using anti-Fos protein and anti-tyrosine hydroxylase (TH) double staining immunohistochemical methods, and Nissl-staining technique respectively. After four weeks of tail-suspension, many Fos-like positive neurons were localized in the medullary visceral zone (MVZ), predominantly in the nucleus of tractus solitarii and ventrolateral medulla, and some of them showed TH-like immunoreactivity. Sizes of the cell bodies of the lateral horn neurons in C8-T1 segment were significantly increased in 4-wk tail-suspended rats (P<0.05) as compared with that in controls. The results suggest that the neurons in MVZ and the spinal lateral horn may be involved in the adaptation of central cardiovascular regulation during weightlessness.

Animals↗
PubMed2000

Changes in myocardial contractility and contractile proteins after four weeks of simulated [correction of simulate] weightlessness in rats.

The interaction between the gravitational field, the position of the body, and the functional characteristics of the blood vessels determines the distribution of intravascular volume. In turn, this distribution determines cardiac pump function. One of the most profound circulatory changes that occurs in man during exposure to weightlessness is a cephalad redistribution of fluid caused by the lack of hydrostatic pressure in this microgravitative environment. The cephalad redistribution of fluid results in a loss of blood volume and then induces a decrease in preload. Recently, a decrease in sensitivity of arteriole to catecholamine has reported in rats of simulated weightlessness. This change in arteriole may reduce afterload. As a result, cardiovascular system may be shifted to a hypokinetic state during weightlessness condition for long-term. Echocardiographic data from astronauts during space flight showed an increase in heart rate, a 12 % decrease in stroke volume, and a 16 % decrease in left end diastolic volume. Electron-microscopic studies have shown changes in cardiac morphology in rats after exposure to microgravity for 7-12.5 days. After the COSMOS 2044 flight for 14 days, the light-microscopic studies have shown an atrophy of papillary muscles in rats left cardiac ventricle. It is not clear whether the function of atrophic myocardium is impaired. The data in three aspects as mentioned above suggest that weightlessness or simulated weightlessness may decrease the myocardial function. However, definite changes in cardiac performance have been hard to prove due to many limits. This studies were to answer two questions: Is the myocardial contractility depressed in rats subjected to simulated weightlessness for four weeks? What are the underlying mechanisms of the changing contractility?

Animals↗
PubMed2000

Age dependency and correlation of heart rate variability, blood pressure variability and baroreflex sensitivity.

Simultaneous analysis of heart rate variability (HRV), blood pressure variability (BPV) and baroreflex sensitivity (BRS) with different types of measures may provide non-duplicative information about autonomic cardiovascular regulation. Therefore, a multiple signal analysis of cardiovascular time series will enhance the physiological understanding of neuro cardiovascular regulation with deconditioning in bedrest or related gravitational physiological studies. It has been shown that age is an important determinant of HRV and BRS in healthy subjects. Whereas in the case of BPV, the effect of aging seems to depend upon the activity status of the subjects. In view of the facts that most of the previous works were dealing with only the variability of one kind of cardiovascular parameters in one study with conventional time-domain and/or frequency-domain analysis, we therefore designed the present work to compare the HRV, BPV and BRS between young and middle-aged male healthy subjects in one study with the same subjects using various techniques, including the approximate entropy (ApEn) measurement, a statistic quantifying HRV "complexity" derived from non-linear dynamics.

Adolescent↗