Respiratory Airflow and Volume

Respiratory Airflow and Volume In this laboratory, you will be introduced to spirometry as a technique for
recording respiratory variables and you will analyze a recording to derive
respiratory parameters. You will examine lung volumes and capacities, as
well as the basic tests of pulmonary function and simulate an airway
restriction. Written by staff of ADInstruments.
[pic] Background Gas exchange between air and blood occurs in the alveolar air sacs. The
efficiency of gas exchange is dependent on ventilation; cyclical breathing
movements alternately inflate and deflate the alveolar air sacs (see Figure
1). Inspiration provides the alveoli with some fresh atmospheric air and
expiration removes some of the stale air, which has reduced oxygen and
increased carbon dioxide concentrations.
[pic] Figure 1. A schematic diagram of the human respiratory system. Spirometry is becoming more and more important, as respiratory diseases are
increasing world wide. Spirometry is the method of choice for a fast and
reliable screening of patients suspected of having Chronic Obstructive
Pulmonary Disease (COPD). COPD is the 12th leading cause of death
worldwide and the 5th leading cause in Western countries. Studies suggest
COPD could climb to be the 3rd leading killer by 2020. Most COPD cases are
completely avoidable; 85-90% of cases are caused by tobacco smoking. Many important aspects of lung function can be determined by measuring
airflow and the corresponding changes in lung volume. In the past, this was
commonly done by breathing into a bell spirometer, in which the level of a
floating bell tank gave a measure of changes in lung volume. Flow, F, was
then calculated from the slope (rate of change) of the volume, V: [pic] Equation 1 More conveniently, airflow can be measured directly with a pneumotachometer
(from Greek roots meaning "breath speed measuring device"). The PowerLab
pneumotachometer arrangement is shown in Figure 2. [pic]
Figure 2. The PowerLab pneumotachometer. Several types of flow measuring devices are available and each type has
advantages and disadvantages. The flow head you will use today is a
"Lilly" type that measures the difference in pressure either side of a mesh
membrane with known resistance. This resistance gives rise to a small
pressure difference proportional to flow rate. Two small plastic tubes
transmit this pressure difference to the Spirometer Pod, where a transducer
converts the pressure signal into a changing voltage that is recorded by
the PowerLab and displayed in LabTutor. The volume, V, is then calculated
as the integral of flow: [pic] Equation 2 This integration represents a summation over time; the volume traces that
you will see in LabTutor during the experiment are obtained by adding
successive sampled values of the flow signal and scaling the sum
appropriately. The integral is initialized to zero every time a recording
is started. A complication in the volume measurement is caused by the difference in air
temperature between the Spirometer Pod (at ambient temperature) and the air
exhaled from the lungs (at body temperature). The volume of gas expands
with warming, therefore the air volume expired from the lungs will be
slightly greater than that inspired. Thus a volume trace, as calculated by
integration of flow, drifts in the expiratory direction. To reduce the
drift, the flow has to be integrated separately during inspiration and
expiration, with the inspiratory volume being corrected by a factor related
to the BTPS factor (body temperature, atmospheric pressure, saturated with
water vapor). The LabTutor software makes this correction. Spirometry allows many components of pulmonary function (see Figure 3
below) to be visualized, measured and calculated. Respiration consists of
repeated cycles of inspiration followed by expiration. During the
respiratory cycle, a specific volume of air is drawn into and then expired
from the lungs; this volume is the Tidal Volume (VT). In normal
ventilation, the breathing frequency (f) is approximately 15 respiratory
cycles per minute. This value varies with the level of activity. The
product of f and VT is the Expired Minute Volume (VE), the amount of air
exhaled in one minute of breathing. This parameter also changes according
to the level of activity. Note that the volume of air remaining in the
lungs after a full expiration, residual volume (RV), cannot be measured by
spirometry as a volunteer is unable to exhale any further. [pic] Figure 3. Lung volumes and capacities. Terms that you should be familiar with before coming to class. |Term |Abbreviation / Symbol |Units |
|Respiratory Rate |RR |breaths / min |
| | |(BPM) |
|Expired Minute Volume |[pic] |L/min |
|Lung Volumes |
|Tidal Volume |VT |L |
|Inspiratory Reserve Volume |IRV |L |
|Expiratory Reserve Volume |ERV |L |
|Residual Volume |RV (predicted) |L |
|Lung Capacities |
|Inspiratory Capacity |IC = VT + IRV |L |
|Expiratory Capacity |EC = VT + ERV |L |
|Vital Capacity |VC = IRV + ERV + VT |L |
|Functional Residual Capacity|FRC = ERV + RV |L |
|Total Lung Capacity |TLC = VC + RV |L |
|Pulmonary function tests |
|Peak Inspiratory Flow |PIF |L/min |
|Peak Expiratory Flow |PEF |L/min |
|Forced Vital Capacity |FVC |L |
|Forced Expired Volume in one|FEV1 |L |
|second | | |
|% FVC expired in one second |FEV1/FVC x 100 | |
What you will do in the laboratory There are five exercises that you will complete during this Lab. 1. Becoming familiar with the equipment. In this exercise, you will learn
the principles of spirometry, and how integration of the flow signal
gives a volume. 2. Lung volumes and capacities. Here you will examine the respiratory cycle
and measure changes in flow and volume. 3. Pulmonary function tests. Here you will measure parameters of forced
expiration that are used in evaluating pulmonary function. 4. Simulating an airway restriction. In this exercise, you will simulate an
airway restriction. 5. Variability amongst group members. In this exercise, you will compare
the parameters of forced expiration measured in different students. Required Equipment A computer system
Chart for Windows, version 5.4.2 or later
Spirometry extension 2.0 for Chart 5
PowerLab 4/25T or other Chart 5 compatible PowerLab.
Spirometer Pod or Spirometer amp
Respiratory flow head (1000 L/min) with connection tubes
Clean bore tubing
Disposable filters
Disposable vinyl mouthpieces
Nose clip
Tape measure or wall chart for measuring height
Vital capacity prediction tables Procedures
Set up and calibration of equipment
A. Connecting the equipment Connect the Spirometer Pod to the Pod Port for Input 1 on the PowerLab. Since the Spirometer Pod is sensitive to temperature and tends to drift
during warm-up, we recommend that the PowerLab and Spirometer Pod be turned
on for at least 5-10 minutes before use. To prevent temperature drift,
place the Spirometer Pod on a shelf or beside the PowerLab, away from the
PowerLab power supply to avoid heating. Connect the two plastic tubes from the respiratory flow head to the short
pipes on the back of the Spirometer Pod, as shown in Figure 2 Attach clean bore tubing, a filter and mouthpiece to the flow head. [pic]
Figure 2. Setting up the spirometry experiment: connecting the flow head
and attachments to the Spirometer Pod. The cable from the back of the
Spirometer Pod to the Pod Port for Input 1 on the front of the PowerLab is
not shown in this figure. B. Hygiene [pic] NOTE: A clean mouthpiece and air filter should be supplied for each
volunteer. The vinyl mouthpiece can be cleaned between uses by soaking it
in boiling water or a suitable disinfectant. If you are suffering from a
respiratory infection, we suggest that you do not volunteer for this
experiment. C. Starting the software 1. Locate Chart on your computer and start the software. 2. In the Experiments Gallery dialog box, select "Respiratory" from the
left-hand list. Select "Respiratory Settings" from the right-hand list,
and click the Open button to apply those settings. If the Experiments
Gallery dialog box does not appear in front of the Chart View, choose the
Experiments Gallery... command from the File menu. 3. After a short time, the Chart View on the computer screen should be set
up for the experiment. Channels 1 and 2 are visible, with Channel 2
turned off; Channel 1 is named "Flow" and Channel 2 "Volume".
D. Calibrating the Spirometer Pod 6. The flow head must be left undisturbed on the bench during the zeroing
process. 7. Choose Spirometer... from the Flow Channel Function pop-up menu. The
Spirometer Pod dialog box appears, as shown in Figure 3. Click the Zero
button. 8. When zeroing has finished, have the volunteer breathe out gently through
the flow head, and note the recorded signal in the data display area
(Figures 3). If the signal shows a down