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Biomedical subjects

J R Meng

Publications and source records attributed to J R Meng.

10 recordsLinked to original sources
PubMed2001

[Changes of cardiovascular indices during head up tilt plus lower body negative pressure].

OBJECTIVE: To understand the change of the cardiovascular function and to evaluate the usefulness of sphygmography and heart rate variability (HRV) spectrum techniques on estimating cardiovascular function during HUP + LBNP. METHOD: Blood pressure, ECG, cerebral oxygen saturation and sphygmogram of 16 subjects were studied during 75 degrees head up tilt plus lower body negative pressure (HUP + LBNP). RESULT: (1) During HUP + LBNP, heart rate, blood pressure, normalized low frequency component (LFn), LFn/HFn increased significantly, the cerebral blood oxygen saturation, T wave (ECG), HFn decreased significantly; (2) Blood pressure, heart rate and cerebral blood oxygen saturation decreased significantly in presyncopal state; (3) The heart rate in low tolerance group was higher than that in high tolerance group during the initial stage of HUT + LBNP; (4) The shape of pulse wave changed enormously during HUP + LBNP, so that no analysis could be made. CONCLUSION: HUP + LBNP was an effective approach to examine the regulatory function of cardiovascular system, and the sphygmogram could not be used in studying the regulatory function of cardiovascular system during HUP + LBNP.

Adult↗
PubMed2001

[Application of degree of complexity in heart rate variability analysis during orthostatic (correction of orthosatic) standing].

Objective. To introduce the degree of complexity in characterizing heart rate variability (HRV), and to discuss the changes in complexity of the cardiovascular system during orthostatic standing posture. Method. ECG of 8 subjects were recorded during supine and orthostatic standing postures. Degree of complexity was used to analyze the HRV. Result. Compared to supine before orthostatic standing posture, R-R intervals and its standard deviation at 0-5 min, 5-10 min, 10-15 min and 15-20 min during orthostatic standing posture were decreased significantly; the degree of complexity of HRV at 0-5 min and 15-20 min during orthostatic standing posture were decreased significantly; the approximate entropy of 0-5 min and 15-20 min were decreased significantly. Conclusion. The results showed that HRV and complexity of cardiovascular system was decreased during orthostatic standing. It was feasible that the degree of complexity can be used to analyze HRV.

Adolescent↗
PubMed2000

[Approximate entropy and its application in heart rate variability analysis].

Objective. To introduce approximate entropy in the analysis of heart rate variability, and to discuss the changes of the complexity of cardiovascular system during orthostatic standing posture. Method. ECG of 8 subjects were recorded during supine and orthostatic standing postures. Approximate entropy was used to analyze HRV. Result. Compared to supine before orthostatic standing posture, R-R intervals at 0-5 min, 5-10 min, 10-15 min and 15-20 min during orthostatic standing posture were decreased significantly, while approximate entropy at 0-5 min and 15-20 min decreased significantly. It showed that the complexity of cardiovascular system was decreased and the modulation of cardiovascular system changed. Conclusion. It is feasible that approximate entropy be used for heart rate variability analysis.

Adolescent↗
PubMed1999

[Effects of 7 d head down tilt on cardiopulmonary circulation during orthostasis].

Objective. To accumulate data for further studies on the mechanisms of the decrease of cardiovascular function after weightlessness. Method. Cardiopulmonary circulatory function under supine position and head up tilting (HUT) for 20 min before and after exposure to 7 d 6 degrees head down tilt (HDT) in 6 healthy adults who aged 19-21 were measured with a XXH-2000 lesser (pulmonary) circulation and cardiac function instrument. Result. The 7 d HDT resulted in orthostatic intolerance of the subjects; the reduction of RVET (j-z) and the elevation of RPEP [RVET(Q-j)/(j - z)] indicated a decrease of the right heart function. An obvious decrease of the right heart reserves was also observed under HUT after HDT. Conclusion. hc and hc/hz were demonstrated to be useful parameters to evaluate orthostatic tolerance or to forecast orthostatic syncope. The lesser (pulmonary) circulation and cardiac function testing methods are valuable in evaluating the cardiopulmonary circulatory function during HUT.

Adult↗
PubMed1995

The study on the mechanism of G intolerance of rabbits after simulated weightlessness.

The direct consequence of cardiovascular adaptation to weightlessness (WL) is the decrease of G tolerance. In studying the mechanism of G intolerance after WL, respiration, heart rate, electrocardiogram, temporal arterial flow, loss of vision were usually used as the indices for evaluation of G tolerance. However the changes of microcirculation and blood rheological indices were seldom observed. Considering that the changes of status of blood circulation after WL may be one of the important factors causing decrease of G tolerance, the purpose of this paper is to observe the changes of microcirculation, blood rheological and the structure and circulatory status of four organs in rabbits during -4Gx after exposure to simulated weightlessness (SWL), in order to understand the cause of G intolerance after WL.

Animals↗
PubMed1992

Effects of exogenous gamma-aminobutyric acid on experimental arrhythmias.

The effects of exogenous gamma-aminobutyric acid (GABA) 10 mg.kg-1 iv in preventing arrhythmias induced by drugs and ischemia were studied in mice, rats, and guinea pigs. It was found that the threshold dose of aconitine inducing arrhythmia in mice and the recovery rate to normal sinus rhythm increased significantly, ED50 of GABA was 5.4-5.8 mg.kg-1. The duration of ventricular tachycardia (VT) induced by aconitine in rats was shortened (P < 0.01). The incidence and the mortality of ventricular fibrillation (VF) in GABA group were decreased to 0/10 vs 6/10 and 5/10 in control, respectively (P < 0.05). The doses of ouabain to induce ectopic beats (EB), VT, VF, and cardiac arrest (CA) in guinea pigs were increased (P < 0.01). The incidence of VF induced by coronary artery ligation in rats was decreased to 0/5 in GABA group vs 4/5 in control group (P < 0.01). The total amount of EB, total time of VT, and VF were 66%, 41%, and 0% of the control group, respectively. The anti-arrhythmic effects of GABA were dose-dependent and as potent as procainamide (10 or 5 mg.kg-1, iv). The results suggest GABA (10 mg.kg-1, iv) may be useful for the prevention of VT and VF.

Aconitine↗
PubMed1992

[Influence of neural regulation on anti-arrhythmic effects of GABA in rats].

In anesthetized rats, GABA 10 mg.kg-1 iv delayed the onset of ventricular premature (VP) (P less than 0.01) and ventricular tachycardia (VT) (P less than 0.01) and reduced the incidence of ventricular fibrillation (VF) (P less than 0.05). The anti-arrhythmic effects of GABA remained after cervical vagotomy, iv hexamethonium 10 mg.kg-1 or destruction of CNS. It was also seen on pithed rats. In Langendorff heart, GABA 100 mg.L-1 elevated the threshold doses of aconitine required to induce VT (P less than 0.01), VF (P less than 0.01), and heart stop (HS) (P less than 0.01). These results suggest that iv GABA counteracts aconitine-induced arrhythmia directly on the heart, not related to the neural regulation.

Aconitine↗
PubMed1989

[Studies of the active constituents of the Chinese drug "duhuo" Angelica pubescents].

Eight coumarins isolated from the alcohol extract of the Chinese drug "Duhuo", the root of Angelica pubescents Maxim. f. biserrata Shan et Yuan (Umbelliferae) were elucidated to be columbianetin (I), columbianetin acetate (II), columbiadin (III), osthol (IV), isoimperatorin (V), bergapten (VI), xanthotoxin (VII), and columbianetin-beta-D-glucopyranoside (VIII), by chemical and spectral analysis, compound VIII was isolated from plant for the first time. All these coumarins were tested on platelet aggregation induced by 2 microns ADP. I, II, III, IV and VIII showed strong inhibiting activity against platelet aggregation.

Animals↗