Respiratory System and Spirometry

Objective:

To explain in a short essay or diagram the mechanical events responsible for movement of air into and out of the lungs and to relate these mechanical events to respiratory volumes and capacities, at the level of 85% proficiency for each student.

 

In order to achieve this objective, you will need to be able to:

  1. Explain the role of muscles and volume changes in the mechanical process of breathing
  2. Define VC, TV, IRV, and ERV and provide volume figures if applicable.
  3. Measure movement of air out of the lungs by way of a non-recording spirometer.

Materials:

Lab Materials:

Model lung (bell jar demonstrator)

Tape measure

Disposable mouthpieces

Group Materials

Spirometer

Mechanics of Respiration

Methods:

Observe the model lung, which demonstrates the principles involved in gas flows into and out of the lungs. It is a simple apparatus with a bottle "thorax," a rubber membrane "diaphragm," and "balloon lungs."

  1. Move the rubber membrane "diaphragm." Notice the changes in balloon (lung) size as the volume of the thoracic cavity is alternately increased and decreased.
  2. After observing the operation of the model lung, conduct the following tests on your lab partner. Use the tape measure to determine his or her chest circumference by placing the tape around the chest as high up under the armpits as possible.

 

Record the measurements in inches in the appropriate space for each of the conditions below.

Results and Discussion:

Chest circumference Quiet breathing:

inspiration _______________________ expiration ________________________

Chest circumference Forced breathing:

inspiration ______________________ expiration _________________________

Do the results coincide with what you expected based on what you have learned thus far?

Respiratory Volumes and Capacities – Spirometry

 

 

VC = TV + IRV + ERV

 

Methods:

Respiratory volumes will be measured with an apparatus called a spirometer. In nonrecording spirometers, an indicator moves as air is exhaled, and only expired air volumes can be measured directly. By contrast, recording spirometers allow both inspired and expired gas volumes to be measured. Directions for using a nonrecording spirometer are provided below.

  1. Without using the spirometer, count and record the subject's normal respiratory rate.

    Respirations per minute _______
  2. Identify the parts of the spirometer- you will be using by comparing it to the illustration. Examine the spirometer volume indicator before beginning to make sure you know how to read the scale.
  3. Conduct the test three times for each required measurement. Record the data in the table Respiratory Volumes, and then find the average volume figure for that respiratory measurement. After you have completed the trials and computed the averages, enter the average values on the table prepared on the chalkboard for tabulation of class data.

    4.
  4. Tidal volume (TV). The volume of air inhaled and exhaled with each normal respiration is approximately 500 mL. To conduct the test, inhale a normal breath, and then exhale a normal breath of air into the spirometer mouthpiece. (Do not force the expiration!) Record the volume and repeat the test twice.

5.      Compute the subject's minute respiratory volume (MRV) using the following formula:

MRV = TV x respirations/min

6.      Expiratory reserve volume (ERV). The volume of air that can be forcibly exhaled after a normal expiration ranges between 1000 and 1200 mL.

Inhale and exhale normally two or three times, then insert the spirometer mouthpiece and exhale forcibly as much of the additional air as you can. Record your results, and repeat the test twice again.
The ERV is dramatically reduced in conditions in which the elasticity of the lungs is decreased by a chronic obstructive pulmonary disease (COPD) such as emphysema. Since energy must be used to deflate the lungs in such conditions, expiration is physically exhausting to individuals suffering from COPD.

  1. Vital capacity (VC). The total exchangeable air of the lungs (the sum of TV + IRV + ERV) is normally 4500 mi to 4800 mi. Breathe in and out normally two or three times, and then bend over and exhale all the air possible. Then, as you raise yourself to the upright position, inhale as fully as possible. (It is very important to strain to inhale the maximum amount of air that you can.) Quickly insert the mouthpiece, and exhale as forcibly as you can. Record your results and repeat the test twice again.
  2. Inspiratory reserve volume (IRV). The IRV, or volume of air that can be forcibly inhaled following a normal inspiration, can now be computed using the average values obtained for TV, ERV, and VC and plugging them into the equation:

IRV = VC - (TV + ERV)

  1. Recording is finished for this subject. Before continuing with the next member of your group:

Dispose of used cardboard mouthpieces in the autoclave bag.

Put a fresh mouthpiece into the valve assembly (or on the stem of the hand-held spirometer) and continue recording all members of your group using the procedures outlined above.

 

Results and Discussion:

Respiratory Volumes

volume

trial 1

trial 2

trial 3

Average

Tidal Volume

 

 

 

 

Minute Respiratory Volume

 

 

 

 

Expiratory Reserve Volume

 

 

 

 

Vital Capacity

 

 

 

 

Inspiratory Reserve Volume

 

 

 

 

 

  1. The normal IRV is substantial, ranging from 2100 to 3100 mL. How does your computed value compare?

    ___________________________________________________________
  2. Figure out how closely your measured average vital capacity volume compares with the predicted values for someone your age, sex, and height. The equations for the predicted values are determined by multivariate regression analysis of a large pool of subject data. For these equations, age is expressed in years, and height is expressed in centimeters (cm). This is easily done by multiplying your height in inches by 2.54.

    Computed height: _____________ cm

    Predicted VC male = Age*(-19.6) + Height*(22.9) + 788

    Predicted VC female = Age*(-16.5) + Height*(17.7) + 788


    Predicted VC value: ________________ mL


Use the following equation to compute your VC as a percentage of the predicted VC value:

 

averaged measured VC

 

% of predicted VC =

——————————————

x 100

 

predicted value

 

3.     

% predicted VC value: ________________ %

 

  1. A respiratory volume that cannot be experimentally demonstrated here is the residual volume (RV), which is the amount of air remaining in the lungs after a maximal expiratory effort. The presence of residual air (usually about 1200 mL) that cannot be voluntarily hushed from the lungs is important because it allows gas exchange to go on continuously — even between breaths and prevents the lungs from collapsing.

Although the residual volume cannot be measured directly, it can be approximated by using one of the following factors.

For ages 16 — 34 Factor = 0.250

For ages 35 — 49 Factor = 0.305

For ages 50 — 69 Factor = 0.445

Compute your predicted RV using the following equation:

RV = VC x factor = ____________

 

© David G. Ward, Ph.D.  Last modified by wardd 23 May, 2006