Observation of the pre-systole of the toad heart and the compensatory interval experiment can be used for: observed that the pre-systole of the toad heart also has its own effective period of inactivity, so immediately after the pre-systole of a sinus node excitation to the ventricle, often fall right in the effective period of inactivity, so can not cause ventricular excitation, to wait until the excitation of the sinus node again when the contraction occurs. After a pre-systole, there is often a long period of cardiac diastole called the compensatory gap.
Operation method
Experiments on the observation of preterm contractions and compensatory intervals in the toad heart
Principle
After myocardial excitation, the excitability (excitation) will undergo periodic changes, and its effective refractory period (effective refractory period) is particularly long, equivalent to the entire systole and early diastole. Therefore, in the systole and early diastole of the heart, any stimulus can not cause myocardial excitation and contraction, but after the early diastole, the ventricle is given a suprathreshold stimulation, so that the ventricular muscle in the normal sinus node impulse before the arrival of additional stimulation to cause an early contraction, i.e., the preperiodic contraction (premature systole) or extraperiodic contraction (extrasystole). The prephase systole or extrasystole. Pre-periodic contraction also has its own effective period of inactivity, if the subsequent normal sinus node impulse arrives at the ventricle, falls within the effective period of inactivity of the ventricular myocardial pre-periodic systole, and therefore can not cause ventricular excitation and contraction, and need to wait until the normal sinus node impulse to arrive, the ventricle can produce contraction. The long diastolic period that occurs in the ventricle after the pre-systole is called the compensatory pause. In this experiment, the contractile activity of the isolated frog heart was used as an index, and strong electrical stimulation was given to the ventricle during different periods of the cardiac cycle to observe the time phases of the ventricular pre-systole and the compensatory pause, and to analyze the basic conditions required for the emergence of the ventricular pre-systole and compensatory pause, as well as their principles of generation.
Materials and Instruments
Isolated frog heart specimen Move Caveat 1. Do not injure the venous sinus when preparing isolated frog heart specimens. The head of the frog heart clip should be smooth and flat to avoid damage to the heart tissue. 2. good electrode contact. Common Problems Stimulation of the frog heart during its absolute period of inappropriateness produced no response; stimulation of the heart during its relative period of inappropriateness and hypernormalization produced preperiodic excitation. For more product details, please visit Aladdin Scientific website.
Ren's solution
Bio-signal Recording and Analysis System Tension Transducer Surgical Instruments Frog Plate Frog Heart Cannula Frog Heart Clamps Test Tube Clamps Iron Stent Bi-Concave Clamps Beaker Dropper Tube
I. Experimental preparation
1. Preparation of isolated frog heart specimens
2. Clamp the apical part of the frog heart with a wire during the diastolic phase, clamp the glass cannula with a test-tube clamp, and fix it on the iron support with a double concave clamp. The wire is connected to the strain beam of the tension transducer underneath it, and the biconcave clamp is moved to tighten the wire slightly.
3. Two wires are connected from the stimulation lead, one is placed inside the cannula and in contact with Ren's fluid, the other is connected to the frog heart clip, and the plug of the stimulation lead is inserted into the stimulation output socket of the BioSignal Recording and Analyzing System to stimulate the heart with single square-wave pulses in different phases of the ventricular contractile activity (commercial stimulation electrodes can be used in place of the wire electrodes).
4. Insert the wire plug of the tension transducer into the first channel signal input socket of the biosignal recording and analyzing system. Turn on the power supply of the host computer and monitor, start the computer, click on the icon of "Pre-phase contraction and compensatory interval" to enter the experimental program, and then click on the animal experiment (or set the stimulation parameters according to your own needs).
Observation Items
1. Prepare isolated frog heart specimen (refer to Chapter 9, Section 10).
2. Use a frog heart clip with a wire to hold the apical portion of the heart during the diastolic phase, use a test tube clamp to hold the glass cannula, and use a biconcave clamp to secure it to the iron support. The wire is connected to the strain beam of the tension transducer below it, and the biconcave clamp is moved to tighten the wire slightly.
3. Two wires are connected from the stimulation lead, one is placed inside the cannula and in contact with Ren's fluid, the other is connected to the frog heart clip, and the plug of the stimulation lead is inserted into the stimulation output socket of the BioSignal Recording and Analyzing System to stimulate the heart with single square-wave pulses in different phases of the ventricular contractile activity (commercial stimulation electrodes can be used in place of the wire electrodes).
4. Insert the wire plug of the tension transducer into the first channel signal input socket of the biosignal recording and analyzing system. Turn on the power supply of the host computer and monitor, start the computer, click on the icon of "Pre-phase contraction and compensatory interval" to enter the experimental program, and then click on the animal experiment (or set the stimulation parameters according to your own needs).
5. Print the results of the experiment.