 |
HUMAN RESPIRATORY PHYSIOLOGY
PURPOSE:
The purpose of this laboratory exercise is to become acquainted with some mechanical aspects of respiration and factors which influence breathing activity.
THEORY/INTRODUCTION:
"Ventilation" to the physiologist usually means the motion of the thorax (i.e. chest region) and the flow of air in and out of the lungs. To the biochemist, "ventilation" is the process within the cells that utilizes oxygen and produces carbon dioxide ("internal" or "tissue respiration"). On an average, an adult inhales and exhales between two million and five million liters of air each year. About 20% of this air is oxygen. During exercise, the oxygen consumption can increase as much as 30 times.
In normal breathing, the thorax is expanded through the muscle action of the diaphragm and rib cage (thus, also expanding the lungs) and allows air to flow into ducts (bronchi) that divide into finer tubes (bronchioles) that ultimately end in the sacs called "alveoli". The breathing rate in an infant is about 30-50 times (breaths)/min; children about 18-30 times/min; and adults about 8-18 times/min. In order for inhalation (inspiration) to occur, the gas pressure in the alveoli (Palv) must be less than the atmospheric pressure (Patm). As the pressure drops below atmospheric, the outside air flows in through the nose, mouth, and tracheobronchial air paths until the pressure is equalized. In the case of exhalation (expiration), gas pressure in the alveoli must be greater than the atmospheric pressure in order to have air leave the lungs.
|
The lungs are filled during inspiration by the difference in atmospheric pressure when the ribs and diaphragm decrease the inside pressure (intrathoracic) around the lungs by moving downward. This muscular movement is controlled by nerve impulses originating in the inspiratory centers of the brain (medulla oblongata). For expiration, a reverse sequence occurs as the diaphragm and rib cage relax, thereby increasing intrathoracic pressures above atmospheric, forcing the air back out and the alveoli.
At the end of a complete (forced) expiration, the lungs of a healthy adult contain more than a liter of gas. This quantity is known as the "residual volume". When the lungs are expanded to the maximum (full lung stretch), they contain about six liters of air; this is called the "total lung capacity" (the sum of the maximum intake known as the "vital capacity" and the "residual volume").
Under normal quiet breathing, a single inspiration by an average human lung takes in about a half-liter of air. This is called the "tidal volume" (TV).
 |
Schematic illustrating the components of the Vital Capacity (VC) of the Lungs. A definition of each component is contained within the text. Note the approximate value of each volume at the left-hand side of the schematic. How do your values compare with those above? You will be asked to perform many of these measurements. Do all the students have the same measurements? Are the students dissimilar in weight, height, age, sex, athletic ability?
An adult at rest breathes from 10-14 times/min so that his/her ventilation, the volume of air entering and leaving the lungs, is from 5-7 liters/min ("minute ventilation"). The maximum capacity for breathing is about 30 times the resting rate, a flow of from 150-200 liters/min. Even during vigorous exercise, ventilation averages only between 80-200 liters/min. During exercise, both the body’s oxygen consumption and its carbon dioxide production increase as does the rate of ventilation.
From this we can assume that ventilation is somehow regulated by sensing receptors in the body which are sensitive to changing concentrations of oxygen and/or carbon dioxide.
TIDAL VOLUME (TV):
The "tidal volume" (TV) is the amount of air entering or leaving the lungs during a single breath under resting conditions. To measure "tidal volume", the subject should be seated comfortably and be breathing a normal resting rhythm. The Spirometer Hose with Mouthpiece fitted should be in the subject’s hand. After inhaling a normal breath, the subject inserts the Mouthpiece into the mouth and exhales normally into the Spirometer. A second person should read the volume scale and record the value. Several trails should be performed to achieve reliable data.
Compare the data collected from all subjects. Does the amount of air inhaled in a single breath appear to be related to physical stature (height, weight) or physical fitness, age, sex or other physical characteristics?
It may help to plug your nose and try to relax. It is always easiest to read the values directly off of the spirometer.
EXPIRATORY RESERVE VOLUME (ERV):
The "expiratory reserve volume" is the additional volume of air which can be expired beyond the normal expiration. To measure the "expiratory reserve volume", the subject exhales normally then inserts the Mouthpieces and exhales maximally. An observer should read the Spirometer and record the value.
INSPIRATORY RESERVE VOLUME (IRV):
The "inspiratory reserve volume" is the volume of air which can be inspired beyond the normal resting inspiration. IRV is determined by subtracting the "tidal volume" from the "inspiratory capacity" (IC) which can be measured with Spirometer. To measure "inspiratory capacity", the subject inspires maximally, then expires the air into the Spirometer until the lungs deflate to the normal resting position. Avoid expiring beyond the point where the lungs are relaxed completely. The "inspiratory reserve volume" is calculated as IRV = IC - TV where the "tidal volume" (TV) is that value measured in the section entitled TIDAL VOLUME (TV).
VITAL CAPACITY (VC):
The "vital capacity" is the maximum volume of air which can be expired in a single breath following a maximal inspiration. To measure "vital capacity", the subject inspires as deeply as possible then breathes the air into the Spirometer exhaling as completely as possible. An observer reads the Spirometer scale and records the volume in liters. Several measurements of "vital capacity" should be done to ensure reliable data. "Vital capacity" is the sum of "tidal volume" (TV), "expiratory reserve volume" (ERV), and "inspiratory reserve volume" (IRV). the vital capacity" found by direct spirometric measurement can be compared with the value computed from VC = TV + ERV + IRV where TV, ERV, and IRV are measured values from the previous sections.
THE FORCED EXPIRATORY VOLUME (FEV):
In contrast to previous sections which discuss measuring various "static" lung volumes, this section deals with a "dynamic" measurement of air flow from the lungs. Now you will have to use the strip chart recorder.
The "forced expiratory volume" (FEV) is the volume of air expired over a given time period during a person’s forced exhalation of a vital capacity-sized breath. The time period of the expiration is given as the subscript to FEV. For example, FEV 1.0 is the volume of air expired after 1 sec. The FEV 1.0 is a measure of air flow from the lungs. A person of normal health can exhale about 75 percent to 85 percent of the "vital capacity" in one sec. In cases where there is an obstructed airway, the FEV 1.0 is lessened, and FVC is lower than normal.
The Spirometer is designed to couple to the Displacement Transducer which affords a means for recording the flow rate of air from the lungs.
The Spirometer and recording apparatus set-up for recording are setup as below. In operation, air breathed into the Spirometer causes the heart lever of the Displacement Transducer to rotate. The Transducer converts the rotary motion into a proportional electrical signal which, in turn, is amplified and deflects the pen of the Strip Chart Recorder. Vertical deflection of the pen represents a change in volume. Constant horizontal movement of the paper marks off time. Hence, the slope of the Strip Chart Recorder tracing is volume/unit of time of flow rate.
It is important to note that the Replacement Mouthpiece should be disposed of after each use by each student in order to maintain sanitary conditions and prevent the transmission of contagious diseases. Also, following each laboratory, the respiration tubes should be washed with a bactericidal agent and air dried.
The first step in setting up the Spirometer for recording is to attach the heart lever (.080" diameter fiberglass rod) to the Type 424 Displacement Transducer. Attach both stop posts to the Transducer body. Slide the heart lever holder over the Transducer shaft with the set of screws facing upward. Secure the holder to the shaft by tightening the shaft set screw down on the flat of the shaft. Slide the heart lever between the stop posts into the lever hole. Tighten the lever set screw to secure it to the holder.
Clamp the Displacement Transducer to a lab stand beside the Spirometer. Adjust the height of the Transducer so that the right end of the heart lever can be thrust through the hole in the end of the coupling lever arm of the Spirometer. Make adjustments until the distance from the lever set screw to the end of the Spirometer coupling lever is four inches, and the heart lever just touches the upper stop post of the Transducer. It is helpful to pencil mark the heart lever at a distance of four inches away from the lever set screw.
 |
When set-up is complete and the scale factor judged satisfactory, the FEV 1.0 can be measured. The subject should be seated comfortably and breathing normally. At a convenient point in time, the subject takes a maximal inspiration, inserts the Spirometer Mouthpiece into the mouth, and then exhales as rapidly and completely as possible. To conserve chart paper, the recorder "chart drive" can be switched on just prior to the advent of the subject exhalation and switched off when exhalation is complete (chart speed should be set to 25 mm/sec). Note that the time after the VC point in the recording is of no significance. At least three trial recordings should be done to assure reliable data.
A normal recording will look like:
|
NORMAL RESPIRATION RATE:
Normal human respiration is a smooth rhythmic process of inhalation and exhalation of gases. To record normal respiration patterns, set up for the equipment as shown below. Record normal breathing activity for 10 sec.
 |
Note that there is a slight pause after expiration (C-D). The inspiration phase (A-B) is also shorter than the expiration phase (B-C).
 |
---------------------------------------------(A-B) INSPIRATION (B-D) EXPIRATION
Schematic illustrating inspiratory and expiratory excursions. Note that there is a slight pause (C-D) after expiration (B-C).
To observe the effects of a stimulus on respiration, place an ice cube on various parts of the body (back of neck, back, earlobe, palm of hand, etc.) recording each location. Interpret your results. (What does hypothermia do?) Determine the respiration rate during resting conditions. Is there a short pause after the expiratory phase? Is there a pause during inspiration?
With the Strip Chart Recorder on, interrupt the respiratory rhythm by swallowing a glass of water. During the act of swallowing, the epiglottis closes over the opening of the trachea (i.e. glottis), thus interrupting the respiratory rhythm.
RESPIRATORY RATE:
The resting adult breathes from 10-14 time/min with the result that his ventilation, the volume of air entering and leaving the lungs, is from 5-7 liters/min. The maximum human capacity for breathing is about 30 times the resting ventilation rate. Many factors, however, such as size, weight, stature, and physical fitness can influence the respiratory rate.
To measure the respiratory rate, set up the equipment as shown above. Record the respiration rate for a period of 10 sec during:
Observe the rates for each position. Note any differences. Next, record the breathing rates of both a male and female who are approximately the same size (i.e. height, weight) during resting conditions. Record for a period of 10-20 sec. Note any differences. Record the rates of two students with a notable difference in size. Now, record the rate of two students with varying degree of physical fitness. Note any differences in their rates.
EFFECTS OF EXERCISE ON THE RESPIRATION RATE:
We know that during exercise both the body’s oxygen consumption and carbon dioxide production increase, and so does the rate of respiration and hart rate.
For about 10-20 sec, monitor the respiration rate during a resting condition. While still hooked up to the equipment, run in place for two min. Once again, record respiration rate. Chart the differences in respiration rate as you go from a resting condition to vigorous exercise.
DETERMINE BREATH-HOLDING TIME:
In this experiment, we will determine how long a subject can hold his or her breath after a forced expiration ("expiratory reserve volume", ERV), after a normal expiration ("functional residual capacity" and "tidal volume"), and after maximal inspiration ("vital opacity"). It is particularly important in doing this experiment that the subject hold his or her breath absolutely as long as possible.
Set the Strip Chart Recorder speed at 5mm/sec. Each large square on the chart paper represents one sec. Therefore, the time between markers (solid lines on the top of the chart paper) is 15 sec.
Tabulate on a chart the breath-holding time of as many students as possible.
Wait a minimum of five min between breath-holding sequences.
Return to Physiology Syllabus
House's Home | Biology Department | Elon University
Copyright © 2001 [sdh]. All rights reserved.
