Respiratory Control Mechanisms (Ex. 20)

Procedure:

Rabbits will be anesthetized one hour prior to lab using the anesthetic urethane. Gloves will be provided to the group member who does the surgery. The rabbit should be placed ventral side up on the board provided with its nose pointed towards the anterior end to ensure that the trachea is not obscured. Test the animal's pedal and corneal reflexes to ensure that it is in the stage of surgical anesthesia before beging surgery. Like last week Channel 1 will be the EKG and will be used to measure heart rate. The EKG is attached to the machine using a High Gain Coupler (special equipment). To hook it up, place the needle electrodes subcutaneously in an area where there is slight respiratory movement, low on the rib cage. Be sure that the electrodes are just under the skin and exterior to the ribcage, also place a pin electrode in the thigh for the ground. Channel 2 will be the Impedence Pneumograph. This is not a transducer because it only measures the amount of electrical impedence between the electrodes. You will connect this to the coupler in channel one using a silver cord, to allow you to read impedence through the same electrodes as EKG.

Surgery:

1. Apply soapy water to fur on the rabbits neck, where the surgical cut will be made, to keep the fur matted.

2. Make a midline incision in the neck and expose the trachea. Be sure to stay exactly midline as the vagi and carotids run along the sides of the trachea within the muscle layer that surrounds the trachea. Once it is isolated, loop suture under the trachea using your cruved forceps or hemostats. Make an incision in the trachea and quickly insert the trach tube and tie it in place.

3. Isolate the vagus nerves on both the right and left side, and place ligature and sleeve electrodes around each of them. Be very gentle when handling the nerves or you may damage them. Also be careful not to damage the carotid artery which lies next to the nerve or bleeding will occur.

4. You are now ready to hook up the Physiograph machine and the stimulator to your animal.

5. After you have done the first two records (A: Control record, and B: Asphyxia) you will need to cannulate the illiac vien for drug administration. Don’t forget to soap before cutting, and don't forget to use a three-way stopcock filled with mammalian saline (no air bubbles!).

For part B you will do two records. The first record is asphyxia. Then you need to cannulate the illiac for drug administration in the second record.

1. Run a 1/4 page control record with both channels on. Place the plastic bag over the end of the trach tube and hit the event marker. Leave the bag on for about 1/4 a page. Remove the bag, hit the event marker, and record 1/4 page of return to normal.

2. For the "Effect of NaH₂PO₄ on Respiration" record, record 1/4 page of control, then quickly inject 1.0 ml of NaH₂PO₄ via the illiac cannula. The effect should be immidiate and will last only for a few breaths (one or two deep breaths). Be sure to hit the event marker when you inject the drug.

Recording Criteria:

Title: Effects of Asphyxia on Respiration (1st record)

Title: Effects of Sodium Phosphate on Respiration (2nd record)

Transducer: ESG

Paper Speed: 0.5 cm/sec

Timer: 10 sec.

Special Equipment: ESG coupler, Impedence pneumograph

Drug Administered: NaH₂PO₄ (10%)

Drug Dosage: 1.0 ml, or dosage recommended by the TA

Label heart rate in beats per minute, label respiratory rate in breaths per minute and label respiratory depth in cm of pen deflection before during and after bag asphyxia, and before NaH₂PO₄ is administered and during the period where the effects are visible after the drug was administered.

Discussion: Effect of asphyxia on blood pCO₂ and pH. Where does the CO₂ go in the brain? What effect does the resulting stimulus have on respiratory rate? Effect of NaH₂PO₄ on respiration. Which chemoreceptors are being stimulated (and by what)? Why is the effect so short lived, i.e. how is the acid quickly delt with in the blood?

With both EKG and Impedence Pneumograph running, record 1/4 page of control, inject 0.1 ml of epinepherine (0.5 ug/ml), record 1/4 page after the effects are visible. Be sure to hit the event marker when you inject the drug.

Title: Effects of Epinepherine on Respiration

Transducer: ESG

Paper Speed: 0.5 cm/sec

Timer: 10 sec.

Special Equipment: ESG coupler, Impedence pneumograph

Drug Administered: Epinepherine (0.5 ug/ml)

Drug Dosage: 0.1 ml

Label average respiratory depth (cm of pen deflection), respiratory rate (respiration per min), and heart rate (beats per minute) before epinepherine injection and during a section after injection when the effects are obvious (i.e. there is a change in respiratory rate).

Discussion: Describe how epinepherine effects total peripheral resistance, how that effects the VMC (Vasomotor Center) of the brain, and how this effects the DRG (Dorsal Respiratory Group) which causes the observed change in respiratory rate.

1st record (Hering Breuer):

Run 1/4 page of control, stimulate the vagi (7 Volts, 2 msec, 25 stimuli per sec) on continuous for about 5 seconds (until a decrease in respirations are seen), then stop the record. Two group members should prepare to cut the vagi posterior to the sleeve electrodes, simultaneously. When the scissors are in place, so that the cuts can be done with a quick snip, turn the record on and cut the vagi and hit the event marker, record for 1/4 page, stimulate the vagi again and record the effects.

Recording Criteria:

Title: Hering Breuer Reflex

Transducer: ESG

Paper Speed: 0.5 cm/sec

Timer: 60 sec.

Stimulus: Electrical

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