PULMONARY FUNCTION AND RESPIRATORY REGULATION

Lung Volumes and Hyperventilation

Sherwood reading: Chapter13, see especially, p. 466-480

Objectives:

1) Define the variou lung volumes and capacities under different conditions and understand how to measure them.

2) To observe the effect of altering breathing patterns on breath hold duration.

 

Introduction

In physiology thus far, you have been introduced to the concept of cellular or internal respiration, which refers to the cellular metabolic processes that break down nutrient molecules, using O2 and producing CO2. The respiratory system of the body (lungs, airways and muscles) is not directly involved in this process, rather it is involved in the exchange of O2 and CO2 between the blood (brought to the alveoli in the lungs) and the inspired air (filling the alveoli in the lungs). Respiration is composed of four steps: 1) ventilation (or breathing), 2) gas exchange in the lungs, 3) circulation of blood between the lungs and tissues and, 4) gas exchange at between the blood and tissues. Spirometry is a method for measuring lung volumes during ventilation. It is used to assess lung function and is particularly helpful for diagnosing obstructive lung diseases. During this laboratory, we will be using spirometry to understand how lung volumes change during exercise. During resting respiration, only a small portion (about one tenth) of the lung capacity is used. This allows plenty of reserve capacity for those occasions (such as strenuous exercise) when the body requires much greater flow of oxygen to generate energy. Furthermore, the lungs are never completely empty. Even when a lung is removed, and collapses, sufficient air is trapped inside to permit it to float in water.

Breathing

During inspiration, air is forced into the lungs due to expansion of the thoracic cavity. Expansion of the thoracic cavity is caused by the contraction (flattening out) of the diaphragm at the bottom of the rib cage and the contraction of the external intercostal (between rib) muscles, causing the ribs to move upwards and outwards. The expansion of the thoracic cavity increases thoracic volume and decreases thoracic pressure so that the net flow of air is down its pressure gradient and into the lungs. During exercise, the body's need for oxygen increases dramatically and ventilation rate is increased. The depth of breathing also increases during exercise during exercise due to the anatomical dead space of the respiratory system. The anatomical dead space is the air in the nose, mouth, larynx, tracheas, bronchi and bronchioles. This air reaches the alveoli first upon inspiration. This air also has a higher concentration of CO2 because of its prolonged exposure to the tissues. Therefore, increasing the depth of a breath increases the proportion of "fresh air" that gets to the alveoli, increasing gas exchange.

Spirometry

A wet Spirometer measures lung volumes based on the simple mechanical principle that air, exhaled from the lungs, will cause displacement of a closed chamber that is partially submerged in water. The spirometer consists of two chambers: (1) a larger chamber which is filled with water and has a breathing hose attached to it, and (2) a smaller chamber which is inverted inside the first and "suspended" in water. A counterweight and indicator are attached to the inverted chamber. Air blown into the inverted chamber causes it to rise and move an indicator along a scale. The scale is calibrated in liters to give lung volume measurements (Figure 1). The various lung volumes are defined below and illustrated in Figure 2.

Figure 1: Wet spirometer

Figure 2: Principle of using a wet spirometer to measure lung volumes

Figure 3. Lung Volumes and Capacities.

Clinical significance of spirometry

Measurement of lung volumes and forced expiratory flow rates are useful in the clinical setting. Two types of lung disorders can be identified by spirometry measurements:

1. Obstructive lung disorders such as bronchitis and asthma. In these conditions, there is an obstructive process in the airways (the bronchi) of the lung and this is detected by a decreased ability to empty the lungs quickly during a forced expiration. This is measured as the FEV1/VC ratio.

2. Restrictive lung disorders are characterized by a decrease in lung compliance, in diseases such as emphesyma, which results in reduced alveolar volume. Abnormal VC measurements are not necessarily accompanied by alteration in the FEV1/VC ratio.

Lung diseases are not of one specific type, but rather result from a combination of the above two disorders or in combination with a variety of factors that lead to compromised respiratory functions. These factors can include neuromuscular disorders which compromise the inspriatory and expiratory muscles, dysfunction of the respiratory control center in the brain stem, or some other defect relating to gas exchange across the lung airways or in the blood.

 

Table 1: Definitions of lung volumes

Lung volume

Definition

Tidal volume (TV)

The volume of air moved during normal quiet breathing (about 0.5 L).

Inspiratory reserve volume (IRV)

The volume of air that can be forcefully inspired following a normal quiet inspiration. (about 2.5 - 3.5 L).

Expiratory reserve volume (ERV)

The volume of air that can be forcefully expired after a normal or resting expiration (about 1.0 L).

Residual volume (RV)

The volume of air remaining in the lungs after a forceful expiration (about 1.0 L).

Vital capacity (VC)

The greatest extreme in air volume moved between inspiration and expiration (about 4.5 L).

Inspiratory capacity (IC)

The amount of air that the lungs will hold after a normal expiration (i.e. inspiratory reserve + tidal volume).

Functional residual capacity (FRC)

The amount of air remaining in the lungs after a normal quiet expiration (i.e. expiratory reserve volume + residual volume).

Table 2: Typical Volume and flow rate patterns (mL)

Volume (ml)

Normal

Obstructive disease

Restrictive disease

Total lung capacity (TLC)

6000-7500

8000

5000

Vital Capacity (VC)

6000

4000

4000

FEV1

4800

1800

3500

FEV1/VC (%)

80

50

88

Fig. 4. Typical recording of various lung volumes from a recording spirometer.

 

Materials and Methods

Measuring lung volumes using a wet spirometer.

For each member of the lab group:

At rest:

1. Measure resting heart rate and respiration rate for each subject.

2. Attach a disposable mouthpiece to the valve. Clamp the subject's nostrils closed and have the subject breathe normally to adjust to the apparatus. DO NOT INHALE from the spirometer - ONLY EXHALE into the spirometer.

Protocol:

Obtain the following lung volumes for each subject by carefully following each set of instructions: Each group member should measure resting heart rate and respiration rate and the resting lung volumes below. Then each group should choose one set of data to be entered on the computer to be used as class data.

Resting Lung Volumes:

Tidal Volume:

1) Breathe normally a few times. Inspire normally and blow a normal exhalation into the tube. Record this volume as Tidal Volume.

Inspiratory reserve volume:

1) Inhale as deeply as possible, then blow into the mouthpiece until you've emptied what you've forcefully inspired, but do not forcefully exhale (return to a normal level of exhalation). This is your inspiratory capacity (IC) To calculate inspiratory reserve volume, subtract tidal volume value from inspiratory capacity value (IRV=IC-TV).

2) Breathe normally a few times.

Expiratory reserve volume:

1) After a normal exhalation, exhale as forcefully and fully as possible into the mouthpiece. Record this volume as expiratory reserve volume.

2) Breathe normally a few times.

Vital Capacity:

1) Breathe in as deeply as possible, and then exhale into the mouthpiece as fully as possible. Record this volume as Vital Capacity.

2) Breathe normally a few times.

Post Exercise Lung Volumes:

This is for one subject from the lab group. This data, along with their rest volumes, will be entered on page 1 of the spreadsheet on the instructor's computer for class data.

1. Exercise vigorously, by running in place for 5 minutes, doing knee squats, running halls or stairs.

2. Repeat all the measurements after exercising, starting with respiration rate and heart rate.

Breath Hold Duration following Hyperventilation:

This is for one subject from the lab group - should not be the same subject that completed the post- exercise lung volumes above. This data will be enetered on page 2 of the spreadsheet on the instructor's computer for class data.

1) Pre- Hyperventilation - Measure duration of breath hold while resting and seated comfortably. (If you feel lightheaded or dizzy during this part of the lab, STOP immediately and record the data you have up to that point.)

2) While SEATED - inhale and exhale deeply according to a set pace for 30 seconds. At 30 seconds, inhale deeply and hold breath. Measure breath hold duration. Rest for 5 minutes.

3) While SEATED - inhale and exhale deeply according to a set pace for 60 seconds. At 60 seconds, inhale deeply and hold breath. Measure breath hold duration. Rest for 5 minutes.

Breath Hold Duration following Exercise:

1) After 5 minutes of vigorous exercise, measure breath hold duration, while SEATED. Inhale deeply and begin breath hold.

 Peak Flow Measurement:

1) Use one hand to hold your paper mouth piece over the opening of the Peak Flow Meter and use the other hand to cover the back side opening of the Peak Flow Meter.

2) Inhale as deeply as possilbe, then blow into the mouthpiece as fast and as forcefully as you can.

3) Insert the rubber tubing into the paper mouth piece. Repeat steps 1 and 2 above.

4) Record the flow rate (L/min)

LINK TO RESPIRATION REPORT

 

 References:

1. Wagner and Olfert. "Lab3: Spirometry and Simple Lung Mechanics." SOMC 206/206L Winter quarter 2002. January 9 & 11, 2002.