Neurobiology (Mammalian Dive Reflex)

Goals:

1.To become familiar with reflex circuitry in the nervous system

2.To understand the effect of sensory stimuli on efferent output

Background:

The autonomic nervous system (ANS) is part of the peripheral nervous system. Its goal is to maintain homeostasis of the visceral organs. In this lab we will examine the mammalian diving reflex, which involves the ANS. In mammals, submerging the face in water initiates several physiological responses that maximize the time that can be spent under water. This includes a reduction of heart rate (bradycardia) and peripheral vasoconstriction. The reflex arc is as follows: the trigeminal nerve (CN5) of your face, nose, and mouth senses the cold temperature of the water, relays this information to the brainstem, which then sends parasympathetic efferent instructions to the heart via vagus nerve (CN10) and sympathetic output to peripheral blood vessels. This mix of sympathetic and parasympathetic responses is unique to diving. In humans, mild bradycardia is also caused by breath-holding without submersion. The physiological goals of the diving reflex are to reduce the energetically costly aerobic activity of the heart, to shunt blood to the vital organs, and to conserve core body heat.

Experiment:

Set up experiment for 2 divers. Fill two 20 gallon containers almost to the top with room temp water. Fill two containers with 35ºC water. This can be done in the lab stockroom faucet. Then fill two containers with 10ºC water. This can be done by filling the containers with room temperature water and adding 1 five gallon bag of ice. You will need to use a thermometer to determine the temperature before the experiment begins. Two students need to volunteer to be data handlers, i.e, they should be able to take B.P. with a manual sphygmomanometer confidently. Two other students need to document the data on the data sheets provided in Table 1. Two divers should be selected who are able to perform a breath hold and head dunk without a significant increase in anxiety. The divers should not have had any stimulants in the hour prior to class (eg. caffeine). The diversneed to keep his/her finger in the pulse oximeter for the duration of the experiment and the BP cuff should remain attached to one arm. The instructor will provide snorkel and mask, although divers are welcome to bring their own if they prefer.The vitals measured in this experiment are B.P, heart rate and %02. The subjects will need to hyperventilate before each breath hold. Hyperventilation is defined as 4 deep shallow breaths done prior to the breath hold. All students will need to write a formal lab report for this experiment. Please see Guide to Writing a Lab report located on the instructor’s website.

Equipment:

Pulse Oximeter Sphygmomanometer and stethoscope Mask & Snorkel

Experiment 1: Effect of breath-holding

Trial one: Baseline: Record resting heart rate. Keep finger in pulse oximeter.

Trial 2: Breath-holding: Subject should hold his/her breath for 45 seconds. Record heart rate at that time.

Experiment 2: Effect of breathing through a snorkel

Wait for subject’s heart rate to return to normal.

Trial 3: Snorkel: Subject should breathe through a snorkel. Record data at 45 seconds.

Experiment 3: Effect of limited v. full facial submersion with breathing

Wait for subject’s heart rate to return to normal.

Trial 4: Limited facial submersion with breathing: Subject should put on both snorkel and face mask and immerse face in water. Record data at 45 seconds of immersion.

Wait for subject’s heart rate to return to normal.

Trial 5: Full facial submersion with breathing: Subject should immerse his/her face in water (no face mask) while breathing through the snorkel. Record data at 45 seconds of immersion.

Experiment 4: Effects of limited v. full facial submersion with breath-holding

Wait for subject’s heart rate to return to normal. Place finger in pulse oximeter.

Trial 6: Limited facial submersion with breath-holding: Subject should put on a face mask and submerse face in water while holding breath. Take heart rate measurement at 45 seconds of submersion.

Wait for subject’s heart rate to return to normal.

Trial 7: Full facial submersion with breath holding: Subject should hold his/her breath and immerse the face in water (without face mask). Take heart rate measurement at 45 seconds of submersion.

Experiment 5: Effect of water temperature on the diving reflex

Wait for subject’s heart rate to return to normal. Place finger in pulse oximeter.

Trial 8: 35ºC: Immerse the subject’s face without face mask or snorkel in a water bath of approximately 35ºC. Record the results at 45 seconds. Also record the temperature of the bath.

Allow several minutes between tests for recovery.

Trial 9: 10 ºC: Repeat with ice water (not lower than 10 ºC). Record the heart rate at 45 seconds, and the temperature of the ice bath.

Record all temperature data on board (10ºC, 23ºC, and 35ºC). You don’t have to copy other group data into your lab notebook.

Table 1. Mammalian Dive Reflex Experiment. Immersion in water with or without snorkel gear and various temperature trials.

Trial (water immersion) / %O2 / Heart rate bpm / B.P. mmHg
Sub 1 / Sub 2 / Sub 1 / Sub 2 / Sub 1 / Sub 2
1. No immersion (at rest)
2. No immersion (breath hold)
3. No immersion (breath through snorkel)
4. Mask and snorkel (breathing)
5. Snorkel only (breathing)
6. With face mask (breath hold)
7. Without face mask (breath hold)
8. Face only 35oC (breath hold)
9. Face only 10o C (breath hold)