Lab 9: Respiratory Physiology – College of Charleston

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Lab 8                                                                  Respiratory Physiology


                                         Laboratory 8

                                    Respiratory Physiology

The primary function of the respiratory system is to exchange oxygen and carbon dioxide
between air and blood. This function sustains metabolism (via increasing blood oxygen and
releasing blood carbon dioxide) and regulates blood pH. To completely understand how the
respiratory system works you must understand:

        1) how air moves in and out of the lungs = Lung Ventilation.
        2) how blood moves to and from the alveoli = Pulmonary Circulation.
        3) how oxygen and carbon dioxide are transported across the capillary-alveoli interface =
             Pulmonary Gas Exchange.
        4) the neural control of breathing.


                                       Lung Ventilation

The lung moves air in and out via BULK FLOW, which is governed by the following simple
equation:
                   Air Flow = Pressure Gradient  Pulmonary Resistance.

        Where: Pressure Gradient = Atmospheric Pressure  Alveolar Pressure

The Pressure Gradient is equal to the difference in pressure between atmospheric air (outside
the lungs) and alveolar air (inside the lungs). The PRESSURE GRADIENT is the primary
mechanism by which the lungs generate airflow and this is achieved by altering the
pressure of the alveolar air! Alveolar air pressure can be altered very simply by changing the
volume of the pleural (lung) cavity. And changing the volume of the pleural cavity is simply
achieved by moving the diaphragm muscle and the accessory breathing muscles (intercostals,
abdominal muscles, scalenes) on the ribcage! The following diagram shows how alveolar air
pressure is altered by changing pleural volume via movements of the diaphragm and ribcage:




When you INHALE, the diaphragm contracts by moving DOWN, which INCREASES the pleural
cavity volume. Increasing this volume DECREASES the ALVEOLAR PRESSURE to less than
atmospheric pressure. This creates a LARGE POSITIVE PRESSURE GRADIENT, which
causes air to move into the lungs via bulk flow.


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Lab 8                                                                   Respiratory Physiology


When you EXHALE the exact opposite happens. The diaphragm relaxes moving UP, which
DECREASES the pleural cavity volume. Decreasing pleural volume INCREASES ALVEOLAR
PRESSURE to greater than atmospheric pressure. This creates a LARGE NEGATIVE
PRESSURE GRADIENT which forces air OUT of the lungs.

In both cases, air moves DOWN ITS PRESSURE GRADIENT from HIGH TO LOW
PRESSURE.

While changes in pressure gradients are the primary mechanism responsible for normal lung
ventilation, INCREASE in Pulmonary Resistance is the primary mechanism responsible for
reduced airflow associated with a variety of disease states. (Think back to the equation; an
increase in Resistance will make the denominator bigger thus decreasing airflow in or out of the
lungs).

The Pulmonary Resistance is inversely proportional to the size of the anatomic structures
through which air flows (nose, mouth, trachea, bronchi, bronchioles, and alveoli). Thus
DECREASING the diameter of these structures INCREASES pulmonary resistance and thus
DECREASES airflow.

COPD (chronic obstructive pulmonary disease) and asthma are two diseases that increase
pulmonary resistance. In COPD, the airways experience an increase in resistance due to either:
1) chronic long term narrowing (e.g. via excess mucus in bronchitis) or 2) destruction of the
bronchioles and alveoli (emphysema). In asthma and allergies, spastic smooth muscle
contraction of the muscle surrounding the airway leads to a very fast and dramatic increase in
resistance. In both diseases, airway resistance is INCREASED by a decrease in airway
diameter.

The amount of air moving into or out of the lungs during any one breathing cycle is called the
tidal volume (TV). The tidal volume is smaller than the maximum amount of air that can be
moved through the lungs, the vital capacity (VC). The difference between the tidal volume and
the vital capacity are the reserve volumes (IRV and ERV) that can be "tapped" to change the
tidal volume and increase the depth of breathing. The amount of air moving into and out of the
lungs can also be altered by changing the breathing rate. The depth and the rate of breathing are
controlled by the respiratory control center, which is located in the medulla of the brain. The
respiratory control center insures that the exchange of oxygen and carbon dioxide at the lungs
takes place at a rate that matches the body's requirements. This is a dynamic process, since the
body's requirements change over time.




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Lab 8                                                                      Respiratory Physiology



Directly measuring blood flow, gas exchange, and neural control is EXTREMELY INVASIVE and
thus impossible for this laboratory.


OBJECTIVES
This week you will:
1) use PhysioEx simulations to examine normal lung physiology and the effects of obstructive and
restrictive diseases, and

2) use the iWorx spirometer to actually measure air movement into and out of the lungs at rest,
during forced expiration, after Exercise, and under simulated Restrictive and Obstructive Lung
Diseases.


Program 1: physioEX Exercise 7: Respiratory System Mechanics
Reading the introduction in the lab manual for each of the activities will help you to better follow
and understand this week's lab.

Complete Activities 1-9 (pp.87-97). Answer the questions listed at the end of each activity.



Program 2: LabScribe2 Respiration Experiments
The SAME SUBJECT (one person per group) should make ALL RECORDINGS using the
Spirometer!

This lab involves MANY, MANY, MANY calculations and variables. Record your data
carefully and make your calculations carefully so that you can sort out the variable and
understand what they mean and why they are important!




Activity 1: Breathing While Resting

Aim: To measure breathing parameters in a healthy, resting subject.

1.1. Procedure:

    1.  Sit quietly and become accustomed to breathing through the spirometer flowhead.
    2.  Breathe normally before any recordings are made.
    3.  Hold the flowhead so that its outlets are pointed up.
    4.  Remove the flowhead from his or her mouth and hold it at the mouth level in a position
        that prevents a breath from moving through the flowhead.
    5. The LabScribe software will zero the Volume channel during the first five seconds
        of recording. No air should be moving through the flow head during this time.
    6. Click on the Record button. After waiting five seconds for the Volume channel to zero,
        have the subject place the flowhead in his or her mouth and begin breathing.
    7. Record five normal breaths followed by a inhaling as deeply as possible, followed by
       exhaling as quickly and completely as possible. Every sixty seconds into the
       recording, the baseline of the Volume channel automatically resets itself to zero, but you
       should be able to complete the five normal breaths and deep inhalation/complete
       exhalation within that time. See figure below for example of what your data should look




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Lab 8                                                                  Respiratory Physiology


        like. Do not forget to AUTOSCALE your data!! The bottom (blue) display is the data you
        will analyze.




   8. Click Stop to halt recording.


1.2. Data Analysis-Normal Breathing at Rest

   1. Scroll through the recording and find the section of data recorded when the subject was
      breathing while resting.
   2. Use the Display Time icons to adjust the Display Time of the Main window to show at
      least four complete breathing cycles on the Main window.

   3. Click on the Analysis window icon in the toolbar.
   4. Look at the Function Table that is above the uppermost channel displayed in the Analysis
      window. The mathematical functions, V2-V1, Max_dv/dt, Min_dv/dt, and T2-T1 should
      appear in this table.

   Tidal Volume (TV): the volume of air inhaled or exhaled during a normal breathing cycle. To
   measure the tidal volume of the subject during breathing at rest, place one cursor in the
   trough prior to inhalation, and the second cursor on the peak of the cycle (see Figure 1). The
   value for the V2-V1 function on the Volume channel is the Tidal Volume.


                                              Figure 1.




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Lab 8                                                                   Respiratory Physiology


   Breath Period (BP): the duration of each breathing cycle. To measure the breath period of
   the subject during breathing at rest, place one cursor on a peak of a breath cycle, and the
   second cursor on the peak of an adjacent cycle (see Figure 2). The value for T2-T1 on the
   Volume channel is the Breath Period.

                                              Figure 2




   Calculate the normal breathing rate of the subject at rest using the following equation:
       Breath Rate (breaths/minute) = {60 seconds/minute } / { mean breath period
       (sec/breath)}

   5. Multiply the mean tidal volume by the breathing rate to calculate the volume of air
      passing in and out of the resting subject's lungs each minute (Minute Volume).
   6. Record the all values below:.

        REST

               Tidal Volume:

               Breath Period:

               Breath Rate:

               Minute Volume:

1.3. Data Analysis-Forced Expiration at Rest

   1. Use the slider or the arrows on the scroll bar, at the bottom of the Analysis window, to
      position data recorded when the subject exhaled with maximum force in the window.
   2. Use the Display Time icons to adjust the Display Time of the Analysis window to show
      the forced expiration curve and the two normal breaths that occurred before the force
      expiration curve on the same window.

   Record the following variables:

   Inspiratory Reserve Volume (IRV): Place one cursor on the peak of the normal breath prior
   to the maximum inhalation and the second cursor on the peak of the forced breath cycle
   (refer to Figure 3). The value for the V2-V1 function on the Volume channel is the inspiratory
   reserve volume.

   Forced Inspiratory Flow Rate: Keep the cursors in the same positions used for measuring
   IRV. The value for the Max dv/dt function on the Volume channel is the forced inspiratory
   flow rate.



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