HUMAN DIVING RESPONSE

INTRODUCTION

In this lab we will examine the human physiological response to conditions that simulate underwater diving. This constellation of responses has been termed the diving reflex and can be observed in many vertebrates. It is most pronounced in marine and aquatic mammals such as cetaceans (whales and dolphins), sirenians (manatees), some carnivores (seals, walrus and otters) and rodents (beaver). The most dramatic components of the diving reflex are paradoxical: reduced heart rate (bradycardia) is mediated by the parasympathetic nervous system. Also there is increased blood pressure due to peripheral vasoconstriction mediated by the sympathetic nervous system. Since the increased blood pressure would be counteracted by the lower heart rate, the blood pressure is much more variable. The adaptive value of the diving reflex centers on the conservation of both oxygen and energy by reducing the energetically costly aerobic activity of the heart and periphery. Moreover, peripheral vasoconstriction shunts blood away from the extremities to the body's core, thereby conserving core temperature.

The diving reflex in mammals is mediated, in part, by receptors of the trigeminal nerve (cranial nerve V) in the face, nose and mouth, which respond to the temperature of the water. Your text's coverage is weak, but I refer you to table 9-1 on p. 298 for a list of the cranial nerves and their functions. In diving mammals and humans as well, the stimulation of the trigeminal cold receptors in the nasal and pharyngeal passages results in powerful reflex apnea (cessation of breathing). In fact, approximately 30% of human drowning victims do not have water in their lungs because this powerful laryngeal reflex prevents breathing.

In this lab we will monitor heart rate, peripheral blood flow and blood pressure during a simulated dive. A number of parameters associated with underwater submersion will be varied in an attempt to identify the features of submersion that are important for the diving reflex.

W. Michael Panneton in SLU's Pharmacology Physiology Department studies the diving response in animals. His site has a nice movie of a rat that has been trained to swim a maze under water. Also, he shows a big decrease in heart rate.

RECORDING PROCEDURE

Use the BioAmp & PowerLab to record the peripheral pulse and electrocardiogram (EKG). Blood pressure will be monitored using a blood pressure cuff. Heart rate, blood pressure and peripheral pulse will be recorded for each condition and during recovery from each condition.

I. Record peripheral pulse using the peripheral pulse transducer. Attach the transducer to the right thumb of the experimental subject.

II. EKG. In this exercise we will use the PowerLab as an electrocardiograph to measure cardiac function and provide a record of heart rate for comparison.

III. Blood Pressure. NOTE: DO NOT use the same arm for peripheral pulse and blood pressure.

Record blood pressure using a sphygmomanometer. First locate the position of the brachial artery by feeling for the pulse on the inner surface of the forearm around the bend of the elbow. That is where you will place the stethoscope diaphragm. Wrap the deflated cuff of the sphygmomanometer just above the stethoscope diaphragm and inflate the cuff until the pressure exceeds 180 mm Hg (no higher!). At this pressure, there are no audible sounds of blood flow due to the compression of the arterial walls. While observing the pressure gauge and with the stethoscope diaphragm placed firmly over the brachial artery, slowly release the cuff pressure using the valve located on the bulb. Listen carefully and note the pressure when you hear a loud thump sound as the blood rushes past the cuff. The pressure at the first detectable sound is called the systolic pressure reading. Continue monitoring the pressure until the rhythmic thumping sounds are no longer audible. The point at which the sound is no longer discernible is known as the diastolic pressure reading. Repeat this procedure several times until you are confident that you can measure the blood pressure quickly and accurately before you begin the experiment.

EKG and peripheral pulse in the PowerLab

EKG:

The EKG will be recorded during this lab as a means of monitoring heart rate changes in response to diving. "Lead 1" (consult earlier cardio lab) will probably work best, but, if you got a nicer tracing with lead II or lead III, use your favorite. Peripheral pulse will be recorded on channel 2 as a means of assessing the state of peripheral vasoconstriction in response to diving. The EKG will be on channel 3. I've made channel 1 a push button event marker you can use to indicate what you are doing. When you start the chart program, turn off Channel 4 (5-8 are already off). Drag the strip borders to divide most of the screen to channels 2 and 3.

Electrode Placement and Connections
(same as in Cardio Lab):

The EKG will be sent via a special wire into an input to Channels 3/4 (BioAmp) on the right side of the PowerLab. There are 3 wires plugged into the other end or this special wire, one to "earth, common" (most people call this "ground"). If the other two wires are plugged into POS and NEG of Ch1, then this record will actually show up on Channel 3 of the record. Three BioTac ECG conductive adhesive electrodes will be attached: one to each wrist and a third to the left ankle.

Connect Lead 1 (left arm POS, right arm NEG, left leg EARTH). Under the BioAmp, select "no calculation." Remember high-pass and low-pass filters from the electrophysiology lab? Well, here we apply that. We determined that the low pass filter should be set at 50 Hz or even 20 Hz in order to get rid of fast noise without interfering too much with the fast QRS. Set the high-pass at 1. (NOTE: During EKG recording, if the big QRS spike goes in the down direction, you should select "Invert" in the BioAmp.) Chart Settings: Time - 100/s (200 ms/div), Range 2 mV; you can increase or decrease, if necessary.

Click "start" and sit still until you get a nice recording, then you can stop. Note that you can scroll back and forth and that you can compress and re-expand the time scale with those little buttons on the bottom right that look like mountains.

Peripheral pulse transducer (same as for Cardio lab):

The peripheral pulse BNC connector will be sent directly into channel 2 on the front of the PowerLab. Set the range around 100 mV, maybe higher or lower to give a big response that does not go off scale. Velcro the white recording surface to the fingerprint side of the thumb.

EXPERIMENTAL PROCEDURE

Note:
It will be important to have a member of the lab group tabulate data on a spreadsheet on a nearby computer.

Part I. Effects of Anoxia and Facial Wetting.

The prep TA, Andrea, and I found that the only position for the subject (where the wires will reach and an arm is available for blood pressure) is sitting ready for a face dip in a dish pan on a stool in front of the subject.

1. Record from each subject heart rate, blood pressure and peripheral pulse while at rest sitting near the dish pan.

2. To examine the effect of apnea (breath-holding) on heart rate, BP and peripheral pulse, the subject should hold his/her breath for 45 seconds to one minute with readings/recordings taken during the last 15 seconds. A few trial runs should be used to determine the average time the subject can hold his/her breath. After the subject's heart rate has returned to normal proceed to the next step.

3. Immerse the subject's face in water at room temperature (20oC) Take EKG, BP and pulse readings during the last part of apnea while the subject is still immersed. After taking these measurements, remove the subject's face from the water, wait 30 seconds then repeat the measurements. Repeat the procedure two or three times to determine the average time the subject can comfortably hold his/her breath. Remember - this is not an endurance test!!!

4. After data from several successful trials has been obtained, determine the average percent change in peripheral pulse amplitude, mean heart rate and mean arterial pressure: M.A.P. = diastolic pressure + 1/3 pulse pressure (systolic minus diastolic pressure) for pre-dive period (resting), apnea in air, apnea during immersion and recovery following a simulated dive.

5. In this series of tests we will use a snorkel and facemask to compare the effects of apnea and facial wetting on the diving response. Determine the mean peripheral pulse changes heart rate and M.A.P. values for each of the following tests. On the basis of these results, you should be able to assess the importance of each factor to the onset and depth of the cardiovascular responses and the development of the reflex.

a. Using the same approach as above, take the same measurements while the subject breaths through the snorkel (no immersion). Compare these observations to the control values.
b. Obtain measurements for non-apneic immersion without facial wetting by having the subject immerse their face while using both snorkel and face mask. Record data after 30 seconds of immersion.
c. Remove the snorkel and repeat the immersion with facemask in place. Record data for apneic immersion without facial wetting after 30 seconds of immersion.
d. Repeat the immersion while breathing through the snorkel, but without the face mask to obtain readings for non-apneic immersion with facial wetting (a nose pinch may be necessary here). Record your data after 30 seconds.
e. Repeat the procedure without mask and snorkel to record the effects of apneic immersion with facial wetting.

Part II. Effects of Water Temperature on the Diving Reflex.

Record the effects of water temperature on EKG, BP and peripheral pulse pressure as above and
calculate changes in the mean peripheral pulse, heart rate and M.A.P. for each experimental
condition.

1. Obtain a control recording while the subject is at rest prior to immersion.

2. Immerse the subjects face in a water bath of 35oC (warm tap water) and record the results after 30 seconds. Repeat with water at 15oC, 5o C and 0oC. Empty the water bath after the 35oC immersion. Refill with cold tap water; mix crushed ice with the water for the colder temperatures. Wait for the temperature of the water bath to stabilize before testing. Allow the subject several minutes between tests for recovery.

Home work. Using the group data, each student should perpare a separate write-up (due at the beginning of the diving lab, i.e. this week) consisting of results and discussion, i.e. a partial lab report.

Your TA, Nishant Kumar, worked up averages for last semester's group data:

Subjects breathing normally in air
Diastolic pressure 79.29
Systolic pressure 128.00
Pulse 74.57

Subjects put face in 20 .3 (average) degree C water, holding breath
Diastolic pressure 96.43
Systolic pressure 138.86
Pulse 58.14

Subjects wear face mask covering eyes and nose and breathe with snorkel in in 20.3 (average) degree C water
Diastolic pressure 84.29
Systolic pressure 126.43
Pulse 75.86

Subjects wear mask but hold breath in 20.3 (average) degree C water
Diastolic pressure 90.71
Systolic pressure 130.14
Pulse 57.43

Subjects wear nose clip (since eyes and nose are in water) but breathe through snorkel in 20.3 (average) degree C water
Diastolic pressure 89.86
Systolic pressure 133.00
Pulse 67.86

Subjects put face in 36.7 (average) degree C water, holding breath
Diastolic pressure 87.71
Systolic pressure 126.14
Pulse 68.43

Subjects put face in 9.3 (average) degree C water, holding breath
Diastolic pressure 104.86
Systolic pressure 142.57
Pulse 64.86

Last semester, I gave a quiz, and here are the answers:
BL A347 - General Physiology Laboratory Spring semester, 2004
Prof. Stark - 4th quiz - March 18

What is the "official" physiology word for the cessation of breathing induced by diving?

apnea

Which is the nerve that reports sensations from the face that mediate the diving reflex?

trigeminal, 5th cranial nerve

Suppose that you or a classmate show a decreased magnitude of reading from the peripheral pulse monitor while holding your breath (like the figure hyperlinked to last week's cardio lab outline). This is most likely mediated by smooth muscle in what type of blood vessel?

arteriole

What is so unusual about the combination of pulse and pressure changes in diving?

b.p. going up while pulse goes down -- these two would usually go up or down together

Express MAP (mean arterial pressure) in terms of diastolic and systolic pressures.

diastolic + 1/3(systolic-diastolic)

Suppose the resting pulse is 72, typical for most people. You have a strip of 10 seconds from the power lab during a cold face dip where there are 6 heart beats. How was the pulse changed?

duh? ([6beats/10s]x[60s/1min]=36beats/min, goes to half resting)

If you used just a little too much low pass filtering on the EKG, which component(s) would be most inaccurately plotted out?

the fast QRS components would be clippec

What is the "official" physiology word for a low heart rate?

bradycardia

Why do you use one thumb for the pulse and the other arm for the pressure?

duh? (cuff closes off peripheral pulse)

What does breathing through a snorkel without a face mask during a dive control for?

Two possible answers.
(1) apnea (if you interpreted it as breathing vs. not breathing)
(2) trigeminal stimulation in eye-nose-area (if you interpreted it as with vs without a face mask)


This page was last updated 9/10/04

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