Lab 11 Respiratory Physiology—Spirometry It is important to understand how our lungs work; knowledge of the mechanics of breathing, but also nervous system controls, etc., are essential for health care professionals treating patients with breathing disorders such as asthma or chronic obstructive pulmonary disorder (COPD). In addition to understanding these things, it is also helpful to have a measure of how efficient we are at moving air in and out of the lungs. This lab will give you an introduction to spirometry, which is the most common pulmonary function test measuring lung function.
While several different types of measurements can be taken in spirometry, the most common types are shown on the spirogram in Figure 1. You’ll see that there are both respiratory volumes and respiratory capacities; the differences between these are explained below.
Figure 1. Spirogram showing both respiratory volumes and capacities.
On the graph above, you’ll see that most of the breathing here is normal, quiet breathing, in which a small amount of air is being moved in and out of the lungs. This volume of air is called the tidal volume(TV) and averages about 500 ml in normal, healthy adults. However, you’ll also see on the graph—and you know from your own personal experience—that you can inhale much more air than you do during normal breathing. The amount of air you can inhale above and beyond a normal breath is called the inspiratory reserve volume(IRV). Similarly, the amount of air you can exhale beyond a normal breath is called the expiratory reserve volume(ERV). In normal, healthy adults, the IRV averages about 2000 ml and the ERV averages about 900 ml.
There is one more respiratory volume, the residual volume (RV), which represents the air left in the lungs even after a full exhalation. The average RV is 1150 ml, and represents the amount of air in the alveoli (which cannot collapse because of surfactants), and the bronchi and trachea, which are held open (patent) by C-shaped cartilage rings. Unless something really bad happened to you, you cannot void these spaces of air voluntarily.
You’ll see from Figure 1 that the respiratory volumes can be added together to produce respiratory capacities. For instance:
TV + IRV = inspiratory capacity (IC) Capacities like the IC, or expiratory capacity (EC) can tell us a lot about the ability of a patient to move air in and out of the lungs. Table 1 summarizes the important volumes, capacities, the average value of each in normal, healthy adults, and the derivation of the respiratory capacities.
Table 1. Respiratory volumes and capacities, their average values in men and women, and derivation of respiratory capacities (reproduced from Ganong, William. "Fig. 34-7". Review of Medical Physiology (21st ed.)).
Average value (ml)
Inspiratory Reserve Volume (IRV)
Tidal Volume (TV)
Expiratory Reserve Volume (ERV)
Residual Volume (RV)
Vital Capacity (VC)
IRV + TV + ERV
Inspiratory Capacity (IC)
IRV + TV
Expiratory Capacity (EC)
ERV + TV
Total Lung Capacity (TLC)
IRV + TV + ERV + RV
In lab today, you are going to measure several of these parameters on yourself, and compare your values to averages. To measure these respiratory volumes and capacities, you’ll be using a spirometer, which your lab instructor will show you how to use. After receiving instructions on how to use the spirometer, follow the instructions below to make your measurements.
In this lab, you will directly measure, or calculate, the following according to these directions:
Tidal Volume –
Set the spirometer at “0” (zero)
Breathing normally, first inhale (do not take a forceful or maximal breath), then place the spirometer’s mouthpiece in your mouth, pinch your nostrils closed, and breath a normal, relaxed breath into the spirometer.
Repeat step “b” twice more; do not re-set the dial at zero.
Divide the resultant volume displayed on the dial by three (3) to obtain your TV.
Expiratory Reserve Volume –
Set the spirometer at 1000ml
Breath in normally, then breath out relaxed tidal volume, then close your mouth around the mouthpiece, plug your nose, and forcibly breath out all of your remaining air into the spirometer for as long as you are able (without taking another breath).
Subtract 1,000 from the measured volume to obtain your first ERV.
Repeat steps a-c twice, add the three results, and divide the sum by three. The result is your average ERV.
Vital Capacity is normally a calculated value, but must be measured directly with our spirometers as follows –
Set the spirometer at “0” (zero).
Take the deepest breath you can, close your mouth around the mouthpiece and plug your nose, then breath into the spirometer for as long as you can until you run out of air.
Repeat steps a & b once or twice then average the results to determine your average VC.
Minute Respiratory Volume –
You are now done with the spirometer. Determine your subject’s respiratory rate by counting how many times your subject breathes in one minute.
Multiply that number (their respiratory rate) by your subject’s TV.
Inspiratory Capacity -
Calculate IC by subtracting ERV from VC (IC = VC - ERV).
Inspiratory Reserve Volume –
Calculate IRV by subtracting TV from IC (IRV = IC – TV).
What do you think accounts for the differences in respiratory volumes and capacities between men and women?
Why do you think vital capacity might differ with height?
How might the volume measurements change if your data were collected right after vigorous exercise?
Can you think of other factors that might affect lung capacity?
Based on your answers to the above questions, how does your lung capacity compare to the average values listed? Why do you think this may be?
In general, what is the difference between volume measurements and capacities?
Bio 221 - Lab 11
Identify all assigned organs and structures on all lab specimens in which they appear.