Exercise Physiology Lab

THE ASSESSMENT OF VENTILATORY FUNCTION

Click here for  data table and questions

Purpose

The purpose of this laboratory exercise is to familiarize students with the assessment of, and terminology associated with the human ventilatory system. Many of the tests to be employed have been developed for diagnostic purpose.  In exercise physiology these tests are used to classify or describe participants in experiments.

Introduction

The lung is designed for gas exchange.  Its prime function is to allow oxygen to move from the air into the venous blood and carbon dioxide to move out. Although the lung performs other functions, its primary responsibility is to exchange gas. Oxygen and carbon dioxide (CO2) move between air and blood by simple diffusion that is from an area of high to low partial pressure. Ficks Law of diffusion states that the amount of gas that moves across a sheet of tissue is proportional to the area of the sheet but inversely proportional to its thickness. The blood-gas barrier is exceedingly thin and has an area of between 50 and100 square meters.

 
The airways consist of a series of branching tubes which become narrower, shorter, and more numerous as they penetrate deeper into the lung. The trachea divides into right and left main bronchi, which in turn divide into lobar, then segmental bronchi. The process continues down to the terminal bronchioles, which are the smallest airways outside the alveoli. All these bronchi make u p the conducting airways. Their function is to lead inspired air to the gas exchanging regions of the lungs. Since conducting airways contain no alveoli, they do not participate in gas exchange. The terminal bronchioles divide into respiratory bronchioles, which have few alveoli. Finally, we come the alveolar ducts that are completely lined with alveoli. This alleviated area of the lung where gas exchange occurs is called the respiratory zone.

 
During inspiration, the volume of the thoracic cavity increases and air is drawn into the lung. The increase in volume is brought about partly by contraction of the diaphragm and partly by the actions of the intercostals muscles. These muscular actions increase the size of the thoracic cavity and air flows in due to the reduced pressure inside the chest (inhalation; governed by Boyles law which states that the pressure of a gas is inversely proportional to its volume). Inspired air flows down to the terminal bronchioles by bulk flow. Beyond that point, the combined cross-sectional area of the airways is so enormous because of the large number of branches, that the forward velocity of the gas becomes very small. Diffusion of gas within the airways then takes over as the dominant mechanism of ventilation in the respiratory zone. The rate of diffusion within the airways is so rapid, and the distances covered are so short, that differences in concentration within the alveoli are virtually abolished within a second.

An increase in thoracic volume results in a decrease in intrapulmonary pressure causing air to be pushed out of the lungs (exhalation). The lung is elastic and returns passively to its pre-aspiratory volume during resting breathing. It is remarkably easy to distend. For example, a normal breath of about 500 ml requires distending pressure of 3 cm water. By contrast, a balloon may need a pressure of up to 30 cm water for the same change in volume.

As discussed in your text, oxygen is carried in the blood in two forms:

   1. Dissolved in plasma, and

   2. In combination with hemoglobin. 

Carbon dioxide is carried in three forms:

   1. Dissolved in plasma and

   2. As bicarbonate (HCO3-), and

   3. In combination with hemoglobin.

 The transportation of CO2 has a profound effect on the acid-base status of blood and the body as a whole. The lung excretes over 10,000 meq of carbonic acid (H2CO3) per day compared to less than 100 meq of mixed acids by the kidneys. Therefore, by altering alveolar ventilation (i.e.. gas exchange) and thus the elimination of CO2, the body has great control over its acid-base balance.

 
Objective

The purpose of this lab is twofold:

   1. Measure and describe the different ventilatory volumes and capacities

   2. Explain how ventilation is adjusted to help maintain acid-base balance

 An important practical application of respiratory physiology is the testing of pulmonary function. These tests are useful in a variety of settings. The most important is the hospital pulmonary function laboratory where these tests help in the diagnosis and management of patients with pulmonary or cardiac diseases. In addition they may be valuable in deciding whether or not a patient is fit enough for surgery. The volume obtained after the subject inspires maximally and then exhales as hard and fast as possible is called the Forced Expiratory Volume (FEV). The volume exhaled in the first second is called the FEV1 the total volume exhaled is the forced vital capacity (FVC). Normally, the FEV1 is about 80% of the FVC.

In disease states, two general patterns appear. In restive pulmonary diseases such as pulmonary fibrosis, both FEV and FVC are reduced, but characteristically, the FEV/FVC are normal or increased. In obstructive diseases such as bronchial asthma, the FEV1.0 is reduced much more than the FVC, giving low FED/FVC ratio. Frequently mixed restrictive and obstructive patterns are seen.  

Definitions

Procedures:

Divide lab into four groups, but record data for all groups.  Test all members of your group on each phase of this experiment.  It is very important that the specific directions be followed exactly as outlined.  Do not rush through this experiment.  Take your time and be certain that your results are accurate and meaningful. Enter ALL data into the computer if requested. 

Experiments

1.  Weigh all subjects.

2.  Measurement of Fractional Lung Volumes (except residual volume).

a. Use the 9-liter Collins Respirometer filled with room air, with the canister containing the CO2 absorbent (soda lime) in place.

b. Have the subject sit quietly with the mouthpiece positioned comfortably in his or her mouth and the nose clip applied firmly on his or her nose.

c. Once breathing becomes regular, with the subject fully relaxed, turn on the respirometer kymograph to slow speed (32 mm/min) and record the breathing pattern for approximately 45 seconds (tidal volume).

d. At the end of this 45 second period turn the speed selector switch to the intermediate speed (480 mm/min) and have the subject take in as deep an inspiration as possible followed by his fullest maximal expiration (vital capacity). After the breathing pattern has returned to normal, repeat this maximal inspiration and expiration once again.

e.  Be certain to record the temperature of the spirometer during each test.

f.  From the obtained recording it should be possible to measure the tidal volume, vital capacity, aspiratory and expiratory reserve volumes, inspiratory capacity and respiration rate (breaths/min).

3.Estimation of MVV. In addition to the above norms, several authors have attempted to derive prediction formulas for vital capacity and maximum voluntary ventilation. Use the equations below to estimate your MVV. They're as follows:

Ref.#3 V.C. (males) = (34.36 - 0.154 age) x ht. (cm)

Ref.#1 V.C. (males) = (27.63 - 0.112 age) x ht. (cm)

Ref.#1 V.C. (females) = (21.78 - 0.101 age) x ht. (cm)

Ref.#9 MVV (liters/min) males = (97 - 0.50 age) x BSA* (m2)

Ref.#9 MVV (liters/min) females = (83 - 0.50 age) x BSA (m2)

*BSA = body surface area in square meters

4.  Measurement of Peak Expiratory Flow Rate (FVC and FEV)

a. Follow directions discussed in class to use the computer system to measure PEFR, FVC, and FEV. 

5.  Studies on the Respiratory Center (Paper Bag Experiment).  Acid-Base Balance.  Please read pages 118-122 in text book.  See Directions at station.

Results

1.  Place the results of each experiment into a table below.

2.  Place the MVV data that you calculated into the table below.

3.  Turn in a copy of your Ventilating chart with all lung volumes calculated and labeled.

Results

1.Place the results of each experiment into a table below.

2.Place the MVV data that you calculated into the table below.

3.Turn in a copy of your Ventilating chart with all lung volumes calculated and labeled.

DATA TABLE (Lung Volumes):

Questions to turn in at the end of class.

1.What is the relationship between lung volumes and a) body size and b) gender?

2.What factors seemingly influence the respiratory center? Why did you have to breath ?(Paper Bag Experiment)

3. Why is it dangerous to hyperventilate and then try and swim underwater?

4.  Which is greater, MVV or VE at VO2max? (look in text book for Ve at VO2max).  Does lung volume (and Ve) limit VO2mzx?  Does your data support your answer?

Discussion(Questions to think about but not turn in!)

1.  What is all of the evidence that in most cases, Lung function does not Limit VO2max.  Look in lecture notes as well as text book. 

2.  Of what significance could large lung volume and MVV be for physical endurance?  What is the correlation between lung volumes and exercise?

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