Student Investigation 2.5

Background
The exchange of gases at the cellular level depends mainly on the integrated functioning of the cardiovascular and respiratory systems. Proper delivery of fresh air to the circulating blood and control of this delivery are examined in assessing respiratory functions.

The special tests to examine the volume of air in the lung during various respiratory maneuvers and to determine the rates of air flow are known as pulmonary function tests. Applying these tests to a subject and comparing his or her individual measurements with known standards allows certain patterns of impaired (improper functioning) lung function to be revealed. In the case of space flight, changes in lung function detected through inflight experimentation are not expected to suggest an impairment of function, but should be indicative of a readaptation of the system to its environment. We expect this to be the case because each astronaut has participated in preflight baseline control studies to characterize his or her respiratory profile (documentation of the astronaut's personal respiratory behavior), and has been found to be normal. (If the astronaut had exhibited impaired respiratory function in these preflight studies, he or she would have been removed from flight status.) Then, on theoretical grounds, it is expected that space flight will improve, not degrade, the respiratory profile.

Pulmonary function tests can examine either the static (volumes or capacities) or the dynamic (rates of change or volumes per minute) characteristics of the pulmonary system. The volume of air that moves in and out of the lungs during breathing is measured with an apparatus called a spirometer. You will be using a spirometer to measure and characterize your own respiratory profile. You will be plotting the results of this investigation on graph paper to produce a curve that is similar to the graph that you worked on in the previous exercise.

Not all the graphs generated by the students in your class will be exactly the same. It is important to note that the individual variability of the respiratory measurement, and, consequently, each student's graph is a result of many factors, including differences in the level of aerobic fitness, age, sex, height, and weight of each individual student in the class. The average values for the respiratory measurements shown in Table 2 serve only as general estimates for the normal volume determinations.

Materials
Spirometer with disposable mouthpieces
70% alcohol and cotton balls
Graph paper

Procedure
1. Students should work in pairs. All students should carefully follow the protocol described below for using the spirometer.

2. To obtain data for the graphing exercise, three measurements will be made: tidal volume (TV), expiratory reserve volume (ERV), and vital capacity (VC). The inspiratory reserve volume (IRV) will be calculated using the known relationship between VC, TV, ERV, and IRV. (It is left up to the student to determine the equation for obtaining IRV.) In addition, total lung capacity (TLC) will be calculated using the known relationship between VC and residual volume (RV). The RV value to be used in this calculat ion and in the graphing exercise should be the accepted general value of 1200 ml.

Protocol for Using a Spirometer

1. Each student should use his/her own sterile mouthpiece. Always sterilize the stem of the spirometer with a cotton ball dipped in alcohol before attaching a new mouthpiece.
2. The amount of air that moves in and out of your lungs during normal breathing is called your tidal volume (TV).
   To determine your TV:
   1. Set the spirometer dial to 0.
   2. Breathe normally for 30 seconds.
   3. Put the spirometer mouthpiece attached to the spirometer into your mouth.
   4. Inhale through your nose and exhale through the spirometer three times, breathing normally.
   5. The spirometer reading shows the total volume of air in your three breaths. Divide by 3 to obtain the value for your TV. Record that value.

3. Take a normal breath in and out (TV) and hold it for two seconds. Now continue to breathe out and expel as much air as possible. This is your ERV. It is the amount of air you can continue to expire a her the tidal volume.
   To determine your ERV:
   1. Set the spirometer dial to 1000 ml.
   2. Breathe normally for 30 seconds.
   3. after exhaling normally, put the spirometer mouthpiece, which is attached to the spirometer, into your mouth and continue to exhale, forcing all the air possible out of your lungs.
   4. Take the spirometer out of your mouth and breathe normally.
   5. Subtract 1000 from the spirometer reading to obtain the value for your ERV.
   6. Repeat steps (a) through (e) two more times; the highest number is your ERV.

4. The VC is the total amount of air that can move in and out of your lungs. It can be calculated by using the following equation: VC = TV + ERV + IRV. For this investigation, you will measure this value.
   To determine your VC:
   1. Set the spirometer dial to 0.
   2. Take two deep breaths and exhale completely.
   3. Put the spirometer mouthpiece, which is attached to the spirometer, into your mouth.
   4. Inhale as deeply as possible through your nose and exhale as completely as possible through the spirometer at a slow, even pace.
   5. Record the spirometer reading and take a minute or two to recover your normal breathing.
   6. Repeat steps (a) through (e) two more times; the highest value is your VC.

Data Collection, Analysis, and Interpretation
Do not write in your book. Your teacher will provide a copy of Table 5 to record your pulmonary measurements.

Table 5. Personal respiratory profile data sheet.

PERSONAL RESPIRATORY PROFILE DATA SHEET

	1. Record the spirometer values for the following respiratory measurements:
	TV =
	ERV =
	VC =
	2. Do the necessary calculations to obtain the following values [RV = 1200 ml]:
	Inspiratory Reserve Volume =
	Total Lung Capacity =

Questions

1. In comparing your graph with the graph in Figure 17, let's imagine that there are tremendous differences in relative values for the various respiratory volumes. How would you explain these differences

2. In the Background section of this Student Investigation, it was stated that "...on theoretical grounds, it is expected that space flight will improve, not degrade, the respiratory profile." Explain why you think this statement is reasonable or unreasonable.