Laboratory 4

ENTC 4350

Measurement of Respiratory Rate and Volume

Purpose

In this lab the student will learn to measure respiratory rates and volumes, thereby, gaining a better understanding of respiratory physiology.

Objectives

The student will be able to:

1) measure the resting breathing rate. Use Table 1.

2) measure tidal volume by exhaling into a balloon. Use Table 2.

3) calculate the amount of air inhaled per minute. Use Table 3.

Materials (for each team of 2)

 string (1 meter)

 metric ruler

 clock or watch with second hand

Safety

Each student should have their own balloon to prevent the spread of disease.

Procedure

Resting Breathing Rate (Table 1)

1. Have your partner count the number of times you inhale in 30 seconds.

2. Repeat Step 1 two more times.

3. Calculate the average number of breaths.

4. Multiply the average number of breaths by two to get the average resting breathing rate (breaths per minute).

Table 1: Resting Breathing Rate

Trial / Inhalations in 30 s.
#1
#2
#3
Average
Inhalations per minute

Tidal Volume (Table 2)

1. Take a regular breath and exhale normally into the balloon. (Note: New balloons are often difficult to blow up. Stretch out and blow the balloon up a couple of times to reduce the resistance.) Pinch the balloon closed.

2. Have a partner fit the string around the balloon at the widest part.

3. Measure the length of the string in centimeters, around the circumference of the balloon and record the measurement.

4. Repeat steps 2-4 four more times.

5. Calculate the average circumference of the five measurements.

6. Calculate the average radius of the balloon by dividing the average circumference

by 6.28 (2 x ).

7. Tidal volume is the amount of air expelled during a normal breath. Tidal volume can be determined by using the balloon radius and the formula for determining the volume of a sphere:

Volume = where r = radius and  = 3.14.

Calculate the average tidal volume using the average balloon radius.

8. Your calculated volume will be in cubic centimeters; 1 cm3 = 1 mL.

Table 2: Tidal Volume

Trial / String measurement
#1
#2
#3
#4
#5
Average circumference
Average radius
Average tidal volume

Table 3: Amount of Air Inhaled

1. Multiply the average tidal volume by the average number of breaths per minute to calculate the amount of air you inhale per minute.

2. Divide the number of milliliters of air by 1000 to get the number of liters of air you inhale per minute. [Adapted from (1)]

Table 3: Amount of Air Inhaled

mL/min
L/min

Where to Go From Here

1. Students can calculate their tidal volume after exercising and compare this with their at-rest tidal volumes. An easy exercise for use in the classroom to accomplish this would be a simple step up/step down maneuver for 5-10 minutes.

2. If some students will voluntarily identify themselves as smokers, you could compare their results to the results of nonsmokers.

3. You might also compare the results of males to females, athletes to more sedentary students, or compare on the basis of height.

Fun Facts

1. Asthma is a condition in which the bronchi suddenly constrict due to spasms of the smooth muscles that line the walls of the smaller bronchi. The patient has trouble exhaling. Many asthma attacks are caused by allergies to edible or airborne substances as common as dust or pollen.(1)

2. The amount of air that can still be forced from the lungs at the end of a normal exhalation is called the expiratory reserve volume(ERV). The ERV is greatly reduced in people who have a chronic obstructive pulmonary disease such as emphysema. This means that the residual air that must always remain in the lungs to keep them from collapsing is larger than normal. In order for those individuals to pull enough air and therefore enough oxygen into their lungs, they must work harder to inhale than people with normal lung function. Since additional energy must be used to inflate the lungs in such conditions, the simple act of breathing is physically exhausting for these individuals.(3)

3. The physical act of breathing is controlled by the part of your brain called the medulla oblongata as it reacts to levels of carbon dioxide in your blood. When carbon dioxide levels increase, signals are sent that cause rib muscles and diaphragm to contract causing you to inhale. Death will occur if the medulla’s control is completely suppressed. This is what happens in the case of an overdose of sleeping pills or gross overindulgence in alcohol, also known as alcohol poisoning, resulting in the cessation of respiration. (1,3)

4. Can a small child cause himself any actual harm by holding his breath during a temper tantrum? No, because, the buildup of carbon dioxide in the blood will cause the medulla oblongata to trigger the muscles that will force the child to inhale. By extension, one cannot commit suicide by holding ones breath. (1)

5. Have a group of students secretly observe andcount the resting breathing rate of other students before beginning the actual experiment. Then compare these figures to the count as the experiment from Table 1. You should note a marked difference, indicating that even though the resting breathing rate is supposed to be at a natural level the rate will change due to the subject being more conscious of their own breathing.

6. Use a pair of glass microscope slides with a drop of water between them to illustrate the idea of surface tension. Then point out that this same surface tension is what holds the lungs to the walls of the body cavity. If there is a puncture wound, such as a knife wound or gunshot wound, air can enter the body cavity causing or allowing the lung to collapse. First aid in such a situation would be to cover the opening with a material, such as plastic, that would seal the opening. Even a driver’s license or credit card could be used. Then, if possible, place the victim with the wounded side downward to decrease the amount of collapse of the lung.

References

1. Biggs, A., D. Blaustein, C. Kapicka, A. Kaskel, and L. Lundgren, Biology: The Dynamics of Life, New York, Glencoe/McGraw-Hill, 1998.

2. Marieb, Elaine N., Human Anatomy and Physiology, Redwood City, CA, Benjamin/Cummings, 1992.

3. Marieb, Elaine N., Human Anatomy and Physiology Laboratory Manual, Redwood City, CA, Benjamin/Cummings, 1989.

Figure 1


Figure 2