Biomedical subjects

J K Li

Publications and source records attributed to J K Li.

131 records · Page 8Linked to original sources

PubMedDate not supplied

Monitoring cell concentration and activity by multiple excitation fluorometry.

Four key cellular metabolic fluorophores--tryptophan, pyridoxine, NAD(P)H, and riboflavin--were monitored on-line by a multiple excitation fluorometric system (MEFS) and a modified SLM 8000C scanning spectrofluorometer in three model yeast fermentation systems--bakers' yeast growing on glucose, Candida utilis growing on ethanol, and Saccharomyces cerevisiae RTY110/pRB58 growing on glucose. The measured fluorescence signals were compared with cell concentration, protein concentration, and cellular activity. The results indicate that the behavior and fluorescence intensity of various fluorophores differ in the various fermentation systems. Tryptophan fluorescence is the best signal for the monitoring of cell concentration in bakers' yeast and C. utilis fermentations. Pyridoxine fluoresce is the best signal for the monitoring of cell concentration in the S. cerevisiae RTY110/pRB58 fermentation. In bakers' yeast fermentations the pyridoxine fluorescence signal can be used to monitor cellular activity. The NAD(P)H fluorescence signal is a good indicator of cellular activity in the C. utilis fermentation. For this fermentation NAD(P)H fluorescence can be used to control ethanol feeding in a fed-batch process.

Candida↗

PubMedDate not supplied

Gelatin nanoencapsulation of protein/peptide drugs using an emulsifier-free emulsion method.

The nanoencapsulation of a model protein drug, bovine serum albumin (BSA), using gelatin as the matrix material is reported. Nanoencapsulation was conducted using a modified water-in-oil (w/o) emulsion method, which is emulsifier-free and simple. The nanoencapsulation product, BSA-containing gelatin nanoparticles, is characterized in terms of nanoparticle morphology, size and size distribution, water content, and in vitro protein release. The BSA-containing gelatin nanoparticles obtained from this nanoencapsulation process are nearly spherical and have a log-normal size distribution. The average diameter of the BSA-containing gelatin nanoparticles is approximately 840 nm. They can absorb 51-72% of water. In vitro release experiments demonstrate that BSA has been successfully encapsulated in, and can be released from the gelatin nanoparticles. The release of BSA from the gelatin nanoparticulate matrix follows a diffusion-controlled release mechanism. It is found that temperature affects both the water content and the BSA release rate of the gelatin nanoparticles.

Chemistry, Pharmaceutical↗

PubMedDate not supplied

A novel mechanical cardiac assist device for reversing left ventricular failure.

Diastolic augmentation of aortic pressure is an efficacious means of improving coronary perfusion in heart failure. A novel mechanical cardiac assist device (MCAD), that has advantages over a conventional intraaortic balloon pump and left ventricular assist devices, has been developed. It consists of a high efficiency rotary solenoid, coupled to a pair of actuator plates that clamp on a shunt aortic graft section, and operates in a diastolic counterpulsation mode. The system has been evaluated in six anesthetized, thoracotomized dogs with myocardial ischemia. The MCAD was activated 30-40 min after coronary artery occlusion and synchronized with the R-wave. As illustrated by a representative sample of the data obtained from one of several trials, the preliminary experimental results demonstrated that the MCAD worked effectively to fulfill the primary functions of a counterpulsation assist device, i.e., augmentation of coronary perfusion and reduction in the vascular impedance to ventricular ejection.

Animals↗

PubMedDate not supplied

Effect of beta-adrenoceptor stimulation or blockade on regional myocardial function and regional O2 consumption during myocardial ischemia.

The purpose of this study was to determine the effect of beta-adrenoceptor activation and blockade on the relationship between regional myocardial function and regional O2 consumption in ischemic and nonischemic myocardium. Myocardial regional segmental function was assessed in 28 open chest, anesthetized dogs using subepicardial dimension gauges. Ten min after LAD (left anterior descending coronary artery) occlusion, dogs were given i.v. saline, 2 mg/kg propranolol, 0.2 mg/kg pindolol, or 1 microgram/kg/min isoproterenol. Coronary blood flow was determined using radioactive microspheres before LAD occlusion, 10 min after occlusion, and 2 hr after LAD occlusion. Regional O2 consumption was determined using microspectrophotometry. LAD occlusion did not alter any index of myocardial function measured in the nonischemic region, but in the ischemic region, end systolic length (ESL) was increased 20% while shortening was converted to systolic bulging. No agent resulted in an improved ischemic regional function or an altered O2 consumption during LAD occlusion. In the nonischemic region the per cent shortening was increased 60% with isoproterenol compared to control. Propranolol and pindolol both increased the non-schemic regional ratio of per cent shortening vs O2 consumption significantly, suggesting an improved efficiency while isoproterenol lowered this ratio. When per cent shortening was plotted vs regional O2 consumption for all treatments, a significant linear relationship was observed in the nonischemic region. Thus, no drug treatment used in this study significantly improved central ischemic regional function, or O2 consumption, but both beta-adrenoceptor blockers seemed to result in an improved relationship between segmental shortening and O2 consumption in the nonischemic region.

Adrenergic beta-Agonists↗

PubMedDate not supplied

Novel design of a regional myocardial force transducer.

A novel force transducer was designed to measure the circumferential regional force developed in the ventricular myocardium in vivo. The transducer is composed of a frame, a carrier bar, and a cantilever spring. Two resistance strain gauges embedded on the spring serve as force-sensing elements. The output of a Wheatstone-bridge circuit, containing these two gauges and a temperature compensation resistor, is connected to a preamplifier. The main advantages of this prototype include the initial stretch-adjustment ability (physiologic 0) low temperature drift, high linearity (r = 0.99) with loads ranging from 0 to 100 g, and moderate sensitivity of 0.232 mV/V/g at room temperature. The transducer was validated with in-vivo canine experiments. The experimental results showed that this transducer can be used to reliably measure the myocardial force development during altered cardiac conditions, such as myocardial stunning and myocardial ischemia.

Animals↗