New developments in the isolated working heart: a comparison of neonatal, immature, and adult rabbits after sixty minutes of ischemia in respect to hemodynamic and biochemical parameters.

Hemodynamic and biochemical changes were studied on 36 white ELCO-rabbits, seven adult older than 150 days, seven immatures between 21 and 27 days, and seven neonatals between 7 and 14 days. Five supplementary hearts of each age group served for preischemic biochemical values. Protection during 60 min of global ischemia was provided by topical cooling and selective coronary perfusion with Bretschneider cardioplegia (8 degrees C). A comparison between pre- and postischemic results showed decreases in coronary flow in the adult (p < 0.004), aortic flow (p < 0.04), cardiac output (p < 0.02), and stroke volume (p < 0.02) in the neonate. The preservation of ATP and CP was sufficient in the adult and immature myocardium, whereas a significant decrease in neonatal ATP was found (p < 0.01). According to these findings we consider immature myocardium to be more resistant against ischemia than the two other age groups. The apparatus used is a development of the conventional working heart, but combines a physiological flow-pressure relation, with instruments guaranteeing high accuracy, devices for drug application, and fits for different sizes of hearts. Therefore, this new approach promises to be of clinical relevance for investigations on the improvement of myocardial protection in both adults and children.

A constant current peripheral nerve stimulator (Neurostim T4). Description, and evaluation in volunteers.

A pocket-size, battery-powered peripheral nerve stimulator featuring a calibrated constant current floating output (max. 80 mA) was evaluated in unanaesthetized volunteers. Modes of stimulation included continuous 1 Hz, continuous train-of-four every 15 s, and on-demand tetanus (50 Hz per 5 s). Within the limits of 0-250 V, voltage adjusted automatically for 0.2-ms monophasic square pulses. Between 20 and 80 mA, the dial error of current intensity was less than +/- 5%. Maximum allowable resistance for the generation of 40-mA pulses was 5 k omega--that is five times the average tissue impedance as measured in 15 volunteers. With surface electrodes, the current intensity required for maximal indirect muscle stimulation in another 50 individuals was 38 +/- 23 mA (mean +/- SD). With up to 80 mA stimulus current, supramaximal nerve stimulation was obtained in 94% of the volunteers.