Lab #13: Respiration and respiratory capacities

Introduction The link between the circulatory system and the atmosphere is the respiratory system. A capacity is a measure

of lung function that consists of two or more volumes. Total lung capacity (VT) is composed of four volumes:Tidal volume (Vt)- the volume of air that is inhaled and exhaled during a single, unforced breathInspiration reserve volume (Vi)- the volume of air that can be inhaled beyond inhaling that occurs during tidal

breathingExpiratory reserve volume (Ve)- the volume of air that can be exhaled beyond exhaling that occurs during tidal

breathingResidual volume (Vr)- the volume of air that remains in the lungs even after forceful expiration (volume that can

never be forced out)

Therefore, VT = Vt + Vi + Ve + Vr.

Vital capacity (Vv), the maximum amount of air that can be moved by forceful inhalation and exhalation is the sum of tidal volume, inspiration reserve volume and expiratory reserve volume (Vv = Vi + Ve + Vt). An individual's body size, sex and physical condition affect vital capacity. For example, males of a given body size have an approximately 25% greater vital capacity than females of equal size (2.5 l/m2 of body surface area vs. 2.0 l/m2).

Vital capacity was widely used as an index of the functional capacity of lungs, though there are many more sophisticated clinical techniques available now. In restrictive disorders, such as pneumonia, emphysema, lung or thoracic cavity tumor and enlargement of a blood vessel in the thoracic cavity, the vital capacity is reduced due to decreased lung or thoracic cavity volume. The rate at which air is exchanged is unaffected since the air pathway is clear. In obstructive disorders, such as asthma, the vital capacity is normal, since no lung tissue is damaged. The rate of air exchange is slowed due to constriction in the air pathway. The rate of expiration (FEV1.0) is typically used to diagnose these two broadly different classes of disorders. An expiration rate reduced by approximately 75% suggests the presence of an obstructive pulmonary disorder.

The number of breaths taken per unit time is the respiratory rate. The volume of air entering or leaving the lungs in one minute is the respiratory minute volume.

Gaseous exchange between the alveolar air and the blood takes place at the pulmonary capillaries. These thin-walled vessels are distensible and easily collapsed. The pressure difference between the inside of the capillary (blood pressure) and the outside of the capillary (alveolar pressure) determines the diameter of the pulmonary capillaries. If the pressure in the alveoli is greater than the blood pressure, the pulmonary capillaries collapse and blood will not go through them. Therefore, less gas is exchanged. This stimulates increased respiration depth and/or rate (by mechanisms to be described below).

The respiratory rate is controlled by several factors. Gas partial pressures (O2 (PO2) and CO2 (PCO2)) are monitored centrally and peripherally. Under normal circumstances the body is much more responsive to changes in PCO2 than PO2. The strongest respiratory response to changes in PCO2 originates in the brain (the central response). Circulatory CO2 readily passes out of the circulatory system and across the blood-brain barrier into the cerebrospinal fluid surrounding the brain. There, CO2 reacts with water by the following reaction CO2 + H2O H2CO3 H+ + HCO3

- resulting in a decrease in pH. Brain chemoreceptors (in the medulla) respond strongly and rapidly to changes in pH brought about by this process. Peripheral chemoreceptors, responsible for the peripheral response, are located in the aortic and carotid bodies. They monitor PO2 and PCO2 directly. They feed centrally via the glossopharyngeal (n. IX) and vagus (n. X) cranial nerves.

Breath holding and hyperventilation affects respiratory rate. When you hold your breath, PO2 falls and PCO2 rises. If breath holding is preceded by hyperventilation, PO2 rises and the duration of breath holding increases.

The changes in lung volume that occur during breathing can be measured using a spirometer. This instrument takes many forms, including:

a) Breathing into a mouthpiece forces a set of bellows or a flexible bag attached to a recording device to rise and fall. The more air forced into the bellows or bag, the more a pen is displaced. Thus, this form of the instrument measures the volume of air forced in to and out of it.

b) Breathing into a mouthpiece spins an impeller (like a little propeller) that spins a set of gears that turns a calibrated dial. The greater the volume of air pushed in to the mouthpiece, the more the impeller and gears turn and the more the dial turns. Thus, this form of the instrument also measures the volume of air forced through it.

In both, an estimate of volume of air exchanged (in liters) combined with the time during which breathing was sampled (in seconds or minutes) can be used to calculate a crude average rate of airflow (liters/sec, liters/min).

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c) The third form has at its heart a "differential pressure transducer" used to measure small pressure differences between two points. The presence of more pressure on one side of a sealed membrane, or vacuum on the other, forces it to bulge in one direction. This membrane is connected to a strain gauge. Changing the shape of a strain gauge results in a change in voltage that is read by a recorder such as a PowerLab system.

When the spirometer is assembled, a subject blows into a "flow head" composed of a plastic tube through which air is forced. Halfway down this tube is a mesh screen. As air is forced down the plastic tube a slight positive pressure is produced on the front surface of the screen and a slight negative pressure on the back surface of the screen. Two tubes pass the positive and negative pressure to the two sides of the sealed membrane differential pressure transducer.

PRESSURE + - TRANSDUCER:

+ -AIRFLOW + -

Flexible membrane

The greater the airflow passing through the screen, the greater the pressure difference between the front and back and the greater between the difference in pressures carried by the two tubes. This form of the instrument allows for the direct measurement of airflow velocity (liters/min). Volume (litres) is estimated by multiplying the flow rate (liters/min) by the flow duration (min).

In this laboratory you will measure pulmonary function and carry out experiments on the regulation of breathing. We will calculate all respiratory volumes and capacities except the residual volume (V r), which in a normal adult is approximately 1.2 liters.

Materials and Methods:

Part I- Setting up spirometer1. Connect the PowerLab, turn on the computer and start the Chart software.2. Firmly clamp the flowhead in place. Note the tubing should be at the top. (This prevents accumulated moisture

from entering the tubing and disrupting the functioning of the spirometer pod.)3. To the flowhead, add the blue-colored adaptor, clean-bore tubing, disposable filter and disposable mouthpiece.

4. Firmly push the other ends of the two air flow tubes into the two outlets on the spirometer pod unit.5. Connect the cable of the spirometer unit into CHANNEL 1.

Part II- Configuring the software1. The Chart software automatically detects that a spirometer pod is connected to the PowerLab and loads

specialized software for respiratory analysis.

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Flowhead (note that the flowhead is rotated so that the tubing exits at the top)

Adaptor

Clean-bore tubingDisposable

filter

Disposable mouthpiece

2. Open the CHANNEL 1 pulldown menu called <Spirometer Pod>. Note that as you inhale and exhale into the mouthpiece the window indicates a change in voltage from the pod. a. Set the <Low Pass> filter to 10 Hz.b. Set the <Range> to 1V.c. Check the <invert> radio box so that when you inhale the trace deflection moves upwards; and the

deflection moves downward during exhaling.d. Click <OK>e. If the baseline is not at 0.0V, click the <Zero> button.

3. Open the CHANNEL 1 pulldown menu called <Spirometry Flow>.a. If the “MLT1000L” flowhead is not selected, select it now.b. Select <OK>.

4. Get your instructor’s attention and he will assist in calibrating your unit.5. Attach a set of nose clips to a volunteer. Instruct the volunteer that ALL air passing into and out of the lungs

must pass through the mouth and the spirometer. Otherwise, the data will be wrong.6. Start recording. Note the label on the CHANNEL 1 output and take careful note of the KIND of data you are

recording from this channel.7. Start recording. Note the label on the CHANNEL 2 output and note the KIND of data it provides.8. PLEASE NOTE: it is essential that the CHANNEL 1 be “zeroed” prior to any experiment. That is, the voltage

from CHANNEL 1 should be at 0.0V (or very close) before recording data. To “zero” the pod, select from the pulldown menu <Spirometer Pod> and select the radio box <Zero>. The baseline in the data window should settled to 0.0V (giving a value in CHANNEL 1 of about 0.0 L/min).

Part III- Breathing in a resting and lying volunteer1. Instruct the volunteer to breathe normally. (Practice for a while until it is comfortable.)2. Set the chart speed on a slow rate (e.g. 100/s) and while the subject is standing, record normal breathing for a

few cycles; until they have gotten into a normal rhythm- annotate as "tidal".3. Ask the volunteer to inhale; taking in as much air into the lungs as possible- annotate as "inhale".4. Resume tidal breathing.5. Ask the volunteer in exhale; completely emptying the lungs- annotate as "exhale".6. Repeat steps 2.- 5. a sufficient number of times with new volunteers to collect data for two males and two

females.7. Ask the volunteer to inhale completely to fill the lungs, then exhale as strongly as quickly as possible to fully

empty the lungs.8. Estimate surface area for each subject using the table at the end of this exercise.9. Access each subject's approximate physical fitness.10. Repeat steps 2.- 5. with two of the same volunteers used previously (steps 2.- 5.). This time, do this with the

volunteer laying down fully.11. A volunteer should exercise sufficiently to elevate breathing rate.12. The volunteer should sit and repeat steps 2.- 5.

Part IV- Control of breathing rate and/or depth1. A volunteer should breath normally until used to the nose clip and spirometer.2. The volunteer should:

i) Breath normally for at least 15 sec.ii) Then inhale and exhale rapidly (hyperventilate) for as long as possible. (Avoid significant dizziness, nausea

and/or loss of consciousness!)3. Record (and annotate) all steps, including recovery back to approximately the initial rate and depth of

respiration.4. The volunteer should:

i) Take and inhale ten (10) deep breaths.ii) Then expire and hold their breath for as long as possible.

5. Record and annotate each step, including recovery.

6. The volunteer should:i) Breath normally for 15 sec.ii) Breath into a sack (plastic or paper) for 2 minutes. (The sack is wrapped securely around the spirometer

tube so that all air comes from and returns to the sack.)7. Record and annotate each step, including recovery.

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Results-

Part III- a) Calculate each of the following for the resting volunteer and summarize in a Table:

i) Tidal volume (Vt).ii) Mean respiratory rate (breaths/minute) (f).iii) Peak inspiratory flow (PIF)- maximum rate of air exchange (in L/min) during inspiration by noting the peak

value seen in CHANNEL 1.iv) Peak expiratory flow (PEF)- maximum rate of air exchange during exhalation calculated in the same

manner.v) Inspiratory reserve volume (Vi), expiratory reserve volume(Ve) and vital capacity (Vv).vi) Respiratory minute volume (VE; multiply mean tidal volume * respiration rate).vii) Forced expired volume in 1 second (FEV1.0)

b) Calculate each set of values for the two males and two females of known surface area and approximate physical condition.

c) Recalculate, and compare the values for the two volunteers laying down and compare with their values when standing.

d) Repeat steps a)- b) for volunteers immediately after exercise.

Part IV-a) Describe the course of recovery from i) hyperventilation, ii) breath holding and iii) breathing into a sack.b) Calculate tidal volume and respiration rate for the 15 sec. period at the start of recovery.

Discussion (some suggestions)-a) For standing volunteers:

i) Did tidal volume change after exertion?ii) Did exertion influence the time taken for each breathing cycle?iii) Did airflow rates (inhalation/exhaling) change in response to exertion?iv) Did the respiratory minute volume change with exertion? If so, did this happen due to an increase in

respiratory rate, depth of breathing (tidal volume) or a combination of both?v) Did exertion influence the vital capacity of individuals?vi) Is there a consistent relationship between physical condition and vital capacity? Sex?

b) For laying volunteers (compared with their data when seated):i) What effect does lying down have on the total volume of air moved (respiratory minute volume)?ii) What effect does lying down have on various lung volumes and capacities?iii) Without adding to your report, consider the following sequence of questions:

a. In a seated individual, would the blood pressure in capillaries in the base of the lung be the same as in those at the top of the lung?

b. Which portion of the lung would have the lower blood pressure?c. If you assume that the lower the blood pressure the more likely those pulmonary capillaries are to be

collapsed, where are there more collapsed capillaries, the base or the top?d. If some capillaries are collapsed, what would be the effect of this on the surface area available for gas

exchange and, for a given respiration rate and depth, the amount of gas exchanged?e. In a lying individual, there is less of a difference in blood pressure across the lung and it would be

uniformly high. What effect should this have on the number of capillaries collapsed?f. What effect should this have on gas exchange?g. Assuming equal oxygen demand, what effect should this have on respiratory rate and/or depth?h. Interpret your data for sitting versus lying volunteers.

c) Interpret the data generated in Part IV in light of presumed PO2 and PCO2 and the recognition that the latter is the most important influence on respiration.

Appendix: Table to estimate total body surface area (in m2)

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