CPR 44-45 - Lung Function, Respiratory Gases, and Spirometry

Question 1

What drives Oxygen from the outside environment into the blood?

Answer 1

Gas moves from the outside environment through the conducting portion of the respiratory system and into the alveoli via bulk flow which is caused by pressure in the alveoli being lower than atmospheric pressure. Once air is in the alveoli, gas moves across the alveolar-capillary membrane by simple diffusion.

Question 2

What is and what causes chronic bronchitis? What symptoms characterize this disease?

Answer 2

Chronic bronchitis is an inflammation of the bronchi as a result of an increase in mucous gland secretions and an increase in the viscosity of that mucus. This is commonly caused by cigarette smoking which may increase the number of goblet cells in the bronchi and cause mucous glands hypertrophy. A cough with sputum expectoration for at least 3 months a year during a period of 2 consecutive years is used to characterize chronic bronchitis.

Question 3

What is CF? How does it inherit and how does it affect the respiratory system?

Answer 3

Cystic Fibrosis is an autosomal recessive mutation of the CFTR gene which impairs the CFTR protein’s ability to transport chloride ions. This decreases/eliminates the ability of airway epithelial cells to secrete chloride into the lumen. This causes a build up of thick viscous mucus causing airway obstruction and creating a medium for bacterial growth.

Question 4

How thick is the blood-gas barrier? What forms this barrier?

Answer 4

The blood-gas barrier is 0.5μm thick and is formed by the alveolar-capillary membrane which consists of:

1. A thin layer of surface liquid
2. Type 1 pneumocytes, plus basement membrane
3. Thin layer of interstitial fluid
4. Capillary endothelial cells, plus basement membrane

Question 5

What is Fick’s law?

Answer 5

V = D(A/t)(ΔP)

V - rate of gas diffusion

D - diffusion coefficient

A - surface area available for gas exchange

t - thickness of diffusion barrier

ΔP - pressure difference across barrier

Question 6

What pneumocyte type is most numerous in the alveolus and takes up the most surface area?

Answer 6

There is an equal number of Type 1 and Type 2 pneumocytes in an alveolus but Type 1 pneumocytes occupy the most surface area

Question 7

What are the primary functions of lung surfactant and what is the main component of lung surfactant?

Answer 7

The main component of lung surfactant is the phospholipid dipalmitoylphosphatidylcholine (DPPC). It primarily serves to reduce surface tenstion across the alveoli which will increase lung compliance and stabilize alveolar size. It also helps to keep the lungs dry.

Question 8

What is the thickness of the pleural space?

Answer 8

5-30μm

Question 9

What are the gas laws we should know?

Answer 9

Boyle’s P₁V₁ = P₂V₂

Charles’ V₁/T₁ = V₂/T₂

Combined P₁V₁/T₁ = P₂V₂/T₂

Question 10

List the relevant respiratory system pressures. Inclue their definitions and abbreviations

Answer 10

• Atmospheric Pressure (P_atm)
• Airway Pressure (P_aw)
• Alveolar Pressure (P_a)
• Intrapleural Pressure (P_ip) - pressure in pleural space
• Chest Recoil Pressure (P_cwr)
• Transairway Pressure (P_ta) = P_aw - P_ip
• Transmural/Transpulmonary Pressure (P_tm/tp) = P_a - P_ip

Question 11

What is a pneumothorax? What are the types of pneumothorax? What causes a pneumothorax?

Answer 11

A pneumothorax is characterized by the presence of air or gas in the pleural cavity. A simple pneumothorax is a non-expanding collection of air while a tenstion pneumothorax is a progressive build-up of air that creates a enough pressure that it causes a shift of the mediastinum and can compromise hemodynamic stability. Typically caused by trauma or can be spontaneous

Question 12

What is tidal volume?

Answer 12

TV is the volume of air inhaled or exhaled with each normal breath

Question 13

What is inspiratory reserve volume?

Answer 13

IRV is the volume of air that can be inhaled after a normal tidal inspiration

Question 14

What is expiratory reserve volume?

Answer 14

ERV is the volume of air that can be exhaled after the end of a tidal exhalation.

Question 15

What is residual volume?

Answer 15

RV is the air remaining in the lungs after a maximal expiration (this volume of air cannot be exhaled and therefore cannot be measured using spirometry)

Question 16

What is functional residual capacity?

Answer 16

FRC is the total volume of air remaining in the lungs at the end of a tidal exhalation

Question 17

What is total lung capacity?

Answer 17

The volume of air in the lungs after maximal inspiration

Question 18

What is vital capacity?

Answer 18

VC is the maximal volume of air that can be exhaled after a maximal inspiration.

Question 19

What is forced vital capacity?

Answer 19

The maximal volume of air that can be forcefully exhaled after maximal inhalation.

Question 20

What is FEV1?

Answer 20

Forced expiratory volume in one second - the volume of air exhaled in the first second of a FVC test

Question 21

Answer 21

Question 22

Differentiate an obstructive from a restrictive lung disease.

Answer 22

An obstructuve disease makes breathing difficult because it occludes the airway in some way

A restrictive disease makes breathing difficult because it makes the act of expanding or contracting the lungs difficult

Question 23

What are normal values for FVC, FVE₁, and FEV₁/FVC?₁

Answer 23

FVC = ~5.5L

FEV₁ = ~4.5L

FEV₁/FVC = 0.8

Question 24

What is FEF_25-75? How is it calculated?

Answer 24

The flow (or speed) of air coming out the lungs between 25% to 75% of VC during an FVC test.

It is the slope of the volume vs time spirometry line acquired during an FVC test. Only the segment of the line between 25%-75% of VC is used.

Question 25

How can spirometry be used to detect airway obstructions?

Answer 25

The FEV1/FVC ratio should be about 80%. A decrease in this value is indicative of an airway obstruction.

While the FEV1/FVC ratio is more commonly used, the FEF_25-75 is much more sensitive to airway obstructions and a low FEF_25-75 will indicate an airway obstruction before the FEV1/FVC ratio will decrease.

Question 26

T/F - the FVC decreases in patients with obstructive lung diseases?

Answer 26

False

Question 27

How can spirometry be used to detect restrictive lung diseases?

Answer 27

FEV1 and FVC will both be decreased but the FEV1/FVC ratio will still be normal or may be increased

Question 28

What is peak expiratory flow?

Answer 28

PEF is the maximal flow rate of exhaled air acheived druing an FVC test

Question 29

What is forced inspiratory flow?

Answer 29

The flow (or speed) of air inhalation

Question 30

Draw a generalized spirometry flow-volume loop and label PEF, FEF₂₅, FEF₅₀, FEF₇₅, VC, and where the 1s mark would be on a health patient.

Answer 30

Question 31

How would a spirometry flow-volume loop appear for a patient with obstructive lung disease?

Answer 31

Question 32

How would a spirometry flow-volume loop appear for a patient with restrictive lung disease?

Answer 32

Question 33

What portion of an expiratory flow-volume loop is said to be effort-independent? Why?

Answer 33

The expiratroy flow-volume graph is effort dependent until PEF is achieved. Regardless of effort, the flow after PEF is limited due to compressed airways.

Question 34

What types of lung diseases (restrictive or obstructive) are emphysema, chronic bronchitis, and pulmonary fibrosis?

Answer 34

Obstructive - chronic bronchitis, emphysema

Restrictive - pulmonary fibrosis

Question 35

Which lung volumes/capacities cannot be measured with only spirometry? What other methods must be employed?

Answer 35

RV, FRC, and TLC

Helium dilation and Body Plethysmography can be used to find FRC which can then be used in combination with the other spirometry values to find RV and TLC

Question 36

Describe how the helium dilation technique is used to find FRC?

Answer 36

A known concentration of helium (C1) is placed in a known volume of gas (V1). At end of a normal tidal expiration, a person is then asked to continually breathe this mixture until the helium concentration (C2) equilibrates. (C1)(V1) = (C2)(V2). V2 will be V1 plus the FRC of the patient.

Question 37

Describe the major problem with the helium dilation technique and how it can be overcome?

Answer 37

If there is an airway obstruction, helium will not get past it which will give you a false FRC. Body plethsmography can be done instead

Question 38

Describe how body plethysmography can be used to calculate FRC.

Answer 38

A patient is placed inside an airtight box that has the ability to measure changes in volume (which will be caused by chest expansion and contraction). The patient breathes only through a tube that leads outside of the box (so they’re not breathing air inside the box). This tube has a barometer in it to measure lung pressure. At the end of a tidal expiration the pressure in the lungs is measured (P1). A shutter then blocks the tube and the patient tries to inhale against it. The pressure in the lungs is measured again at max possible chest expansion (P2). The volume in the lungs at this point (V2) is calculated by adding V1 (still unknown, this is FRC) to the change in volume calculatd by the box. P1V1 = P2V2 is then used to solve for V1 which is FRC.