Beat Response Research Articles

Involvement of cyclic nucleotides in the beating response of rat heart cells in culture

The relationships of cyclic adenosine 3′,5′-monophosphate (cyclic AMP) concentration and cyclic guanosine 3′,5′-monophosphate (cyclic GMP) concentration to beating behaviour of cultured rat heart cells are reported. Cyclic AMP has a positive chronotropic effect and cyclic GMP has a negative inotropic effect on the beating of cultured rat heart cells. Rate and intensity of beating were measured using an automatic light sensitive monitor. Cultured cells were treated with cardioactive drugs until a physiological response was observed and recorded on the monitor at which time the cells were analyzed for cyclic AMP and cyclic GMP concentrations. Direct addition of dibutyryl cyclic AMP and cyclic GMP resulted in an increase in the rate of beating and a decrease in beating intensity, respectively. Both cyclic nucleotides affected rate and intensity of beating but significant relationships could be obtained only between cyclic AMP vs rate and cyclic GMP vs intensity.

Halothane and the beating response and ATP turnover rate of heart cells in tissue culture.

The effects of halothane on the beating response of rat heart cells in tissue culture were studied using an optical-electronic monitoring device. A dose-response curve was obtained over a concentration range to as much as 5 vol per cent halothane. The clinical dosage of 1 vol per cent halothane decreased the inotropic response of 4-10-day-old cells to 59 plus or minus 10 per cent of the original beating strength; no significant decrease in beating strength was seen in 25-30-day-old cells. One volume per cent halothane caused no significant change in the chronotropic response of the heart cells. Higher concentrations of halothane caused significant negative chronotropic and negative inotropic responses in a dose-related manner. When glycolysis was inhibited by 2-deoxyglucose in the growth medium, the cells became dependent on fatty-acid oxidation and oxidative phorphorylation for energy and showed increased sensitivity to halothane; for example, the chronotropic response to 5-8-day old cells treated with 2-deoxyglucose was decreased approximately 70 per cent by exposure to 3 vol per cent halothane, whereas 4-10-day-old cells maintained on a complete growth medium showed only a 40 per cent decrease. Increasing concentrations of halothane decreased the rate of ATP turnover. This supports evidence suggesting that halothane blocks electron transport in the NADH-coenzyme Q reductase level. The model described provides a means for determining anesthetic potency in a mammalian system in terms of functional as well as metabolic responses. It also provides a means for study of metabolic effects of anesthetics and other drugs.

Posicast Controllers using Switching Techniques

In a lightly damped control system rise time is small but large overshoot and prolonged oscillations present in the output are unwanted. If such a system is required to produce dead beat response, input is to be modified suitably by a prefilter or controller which is generally called possicast controller. Posicast control technique first proposed by O. J. M. Smith in 1957 for producing dead response with the help of delay lines was found satisfactory for second order systems. Zaborszky in 1958 on the same lines proposed a simple nonlinearized system using relays. This too was suitable for second order systems only. By changing system dynamics suitably it is possible to get dead beat response for third order and higher order systems also. A detailed study of posicast control system by N. G. Nath and A. K. Choudhury (1969) have shown that it is possible to apply posicast principle to higher order systems also. For even order systems a positive casting of the system input is required, while for odd order sys...

Posicast and negicast control systems†

A possibility of obtaining dead beat response of a class of high-order control systems by adopting the technique of a single step control of the input step command is described in this paper. For achieving the desired response by such input processing techniques, the possibility demands that configurations of high-order systems be of suitable forms and the method of control necessitates positive casting of the system input like the posicast control technique in ease of oven-order systems and negative casting of the input in case of odd–order systems. The system configurations and the forms of the processed input signals in those cases have separately been investigated. The speed of the response avoiding saturated operation of such compensated systems has been studied. The effect of an improper switching operation in casting the system input has also been investigated. The results of the above studios made on the simulated systems have been given.

Dead beat response of higher-order servo systems by single switching operation

Dead beat response of higher-order servo systems by single switching operation