Lecture 18 - Mechanics of Breathing

Question 1

Name and define the 3 steps of respiration

Answer 1

Pulmonary ventilation (insp/exh of air between atm and lungs)
Pulmonary/external respiration (exchange of gases - alveoli <-> blood)
Tissue/internal respiration (exchange of gases - blood in systemic capillaries <-> tissues)

Question 2

State Boyle’s Law

Answer 2

When temperature is constant, the pressure of a gas varies inversely with volume

Question 3

What is a good benchmark for atmospheric pressure in most places?

Answer 3

760 mmHg

Question 4

What is intrapleural pressure and how is it formed?

Answer 4

The pressure within the pleural cavity - it exists due to the elastic recoil of the lungs

Question 5

How does intrapleural pressure compare to atmospheric and intrapulmonary?

Answer 5

It is always lower than both

Question 6

Define pulmonary compliance

Answer 6

The ease with which the lungs can be expanded

Question 7

Which 3 factors affect compliance?

Answer 7

Elasticity of lung connective tissue
Mobility of the Chest/Thoracic Wall
Surface tension

Question 8

What is the equation for compliance?

Answer 8

Compliance = (Delta) Volume / (Delta) Pressure

Question 9

State Laplace’s Law

Answer 9

P (pressure) = 2T (tension) / r (radius of alveoli)

Question 10

What 3 things does surfactant achieve?

Answer 10

Reduces surface tension, increases compliance and equalises pressure differences between small and large alveoli

Question 11

What issue related to surface tension can premature babies experience?

Answer 11

Neonatal Respiratory Distress Syndrome (not enough surfactant produced yet, reduced compliance, difficult to inflate lungs)

Question 12

What two factors affect airway resistance?

Answer 12

Lung volume (bronchi dilate as lungs expand)
Bronchial smooth muscle (PSNS -> bronchoconstriction, SNS + Adrenaline -> bronchodilation)

Question 13

Name 2 simple methods of assessing lung function

Answer 13

Breath Sounds
Peak flow meter (measures the max speed at which you can breath out)

Question 14

What is the name of the piece of equipment used for measuring inspiratory and expiratory volumes?

Answer 14

Spirometer

Question 15

Define Tidal Volume (+ Normal M+F Values)

Answer 15

The volume of air inhaled or exhaled in one quiet breath (500ml both)

Question 16

Define Expiratory Reserve Volume (+NMFV)

Answer 16

The volume of air that CAN be exhaled AFTER a normal tidal volume exhalation (1000ml, 700ml)

Question 17

Define Inspiratory Reserve Volume (+NMFV)

Answer 17

The volume of air that CAN be inhaled AFTER a normal tidal volume inhalation (3300ml, 1900ml)

Question 18

Define Residual Volume (+NMFV)

Answer 18

The volume of air remaining in the lungs AFTER maximum expiration (1200ml, 1100ml)

Question 19

Define Vital Capacity (+NMFV +Calc)

Answer 19

The maximum volume of air that can be expired after a maximum inspiratory effort, VC = TV + IRV + ERV (4800ml, 4200ml)

Question 20

Define Inspiratory Capacity (+Calc)

Answer 20

Maximum volume of air that can be inspired after a normal expiration, IC = TV + IRV

Question 21

Define Functional Residual Capacity (+Calc)

Answer 21

The volume of air remaining in the lungs after a normal expiration, FRC = RV + ERV

Question 22

Define Total Lung Capacity (+NMFV +Calc)

Answer 22

The maximum volume of air contained in the lungs after a maximum inspiratory effort, TLC = TV + IRV + ERV + RV (6000ml, 4200ml)

Question 23

Formula for Pulmonary Ventilation Rate (Respiratory Minute Volume)?

Answer 23

PVR = Respiratory Rate (no. of breaths per min) x Tidal Volume (vol. of air moved per breath)

Question 24

Define Alveolar Ventilation (as opposed to Pulmonary Ventilation) and name the reason for the difference

Answer 24

The volume of air Reaching The Alveoli (per minute) -> Anatomical Dead Space