Frog electrocardiogram and the conduction law of volume conductor

Frog electrocardiogram and the conduction law of volume conductor

Demonstration of the existence of volume conductors in the body will help to understand the conduction laws of organs or tissues guided by the body surface.
[Experimental principle]
Because all tissues and organs of the body are surrounded by tissue fluid, tissue fluid, as a volume conductor with good electrical conductivity, can transmit the bioelectric changes produced by tissues and organs to the body surface. Therefore, the electrical changes of an organ or tissue activity can be recorded in the remote part of the body surface or volume conductor. For example, the bioelectric changes caused by the heart activity can be recorded by guiding electrodes on different parts of the body surface. Electrocardiogram.
[test subject]
Frog or toad
[Experimental drugs]
Ren’s solution
[Apparatus and Apparatus]
ECG machine or computer biological signal acquisition and processing system (or two-channel physiological recorder), frog surgical instruments, petri dishes, alligator clips, dissecting needles, frog nails (or tack), frog board.
[Experimental methods and procedures]
1. Experiment preparation:
After the frog or toad destroys the brain and spinal cord, use a frog nail (or tack) to fix it on the frog board. Cut off the breast skin from under the xiphoid process, cut off the breastbone, and expose the heart.
2. Connect the experimental device
Simulate the connection method of standard ECG lead Ⅱ, fix the alligator clips with wires to the frog nails (tack) of the right foreleg and the hind limbs of the frog or toad respectively. Connect with the ground wire, and connect the output wire to the electrocardiograph or computer biological signal acquisition and processing system (or two-channel physiological recorder). To ensure good electrical conductivity, absorbent cotton soaked with Ren’s solution can be placed between the alligator clip and the frog nail.
3. Experimental project
(1) Record the electrocardiogram of the frog or toad in the regular lead.
(2) Place the guide electrodes randomly on various parts of the body of the frog or toad, and observe whether the electrocardiogram can be recorded? What are the changes in the waveform?
(3) Clamp the aorta with tweezers, quickly cut the heart together with the venous sinuses, and put the frog’s heart into a petri dish filled with Ren’s solution, and then start the electrocardiograph or computer biological signal acquisition and processing system ( Or two-channel physiological recorder) What is the change in the electrocardiogram?
(4) Put the heart in the sterile petri dish back to the original position of the chest cavity of the frog’s heart, and observe the changes on the recording paper or the monitor.
(5) Put the heart upside down (that is, the apex of the heart is facing upwards), what will happen to this waveform?
(6) Remove the lead wire from the frog’s leg, clamp it on the edge of the petri dish and contact with Ren’s liquid in the petri dish, then place the heart in the middle of the petri dish, and observe whether the ECG waveform is displayed on the recording paper or the monitor .
(7) After placing the heart in a petri dish arbitrarily, what happens to the waveform of the electrocardiogram?
[Precautions]
1. Do not injure the sinuses when cutting the heart.
2. The temperature of Ren’s solution in the petri dish is best kept at about 30°C.
3. The instrument must be well grounded to overcome interference. If it is connected according to the standard lead, when interference occurs, the left forelimb can also be connected with the left forelimb lead of the instrument to overcome the interference.
[Experiment Results]
Clip and record the curve, and summarize the conduction law of the volume conductor according to the experimental results.