Effects of volatile anesthetics on force interval relationships in guinea-pig atrial preparations
Saka, Y.; Oshita, S.; Hiraoka, I.; Sakabe, T.; Ban, T.
Masui. Japanese Journal of Anesthesiology 43(12): 1832-1841
1994
ISSN/ISBN: 0021-4892 PMID: 7837400 Document Number: 426640
Depressant effects of halothane, enflurane and isoflurane on isolated guinea-pig left atrial muscles bathed in Tyrode's solution at 30 degree C were examined. Contractions were elicited by stimulation through external field electrodes while tension was recorded continuously. Frequency-force relationships at stimulation rates of 0.1, 0.2, 0.5 and 1 Hz were studied. The pD-2 values of these volatile anesthetics at each stimulation rates were not different significantly, suggesting the frequency-independent depressions of these anesthetics. Interval-strength relationships at time intervals of 0.3 apprx 20 sec during 1 Hz-stimulation were also studied. Mechanical restitution curves after converting to logistic function reached a peak at 8 apprx 20 sec and were fitted well to double exponential functions with time constants of 200 apprx 600 msec (k-1) and 2 apprx 6 sec (k-2). All volatile anesthetics depressed the magnitude constants for fast response in a dose dependent manner. Accordingly, at high concentrations, mechanical resuscitation curves tended to fit single exponential function. Halothane and enflurane did not alter time constants k-1, k-2 significantly, while isoflurane increased k-2 significantly. These results suggest that the mechanisms of myocardial depressant effects are different between these anesthetics.