Lecture 38 - Measuring Breathing: Spirometry

Question 1

Describe the respiratory volumes measured using spirometry

Answer 1

o Tidal volume
 Volume of air moved in and out of the lungs at rest
 Around 500 mL/breath
o Expiratory reserve volume
 Volume of air expired (exhaled) maximally out of the lung after a normal breath
 Around 700-1200 mL
o Inspiratory reserve volume
 Volume of air inspired (inhaled) maximally into the lung after a normal breath
 Around 1900-3100mL

Question 2

Total lung capacity

Answer 2

Inspiratory reserve volume + tidal volume + expiratory reserve volume + residual volume

Question 3

Vital capacity

Answer 3

Inspiratory reserve volume + tidal volume + expiratory reserve volume

Question 4

Inspiratory capacity

Answer 4

Inspiratory reserve volume + tidal volume

Question 5

Functional residual capacity

Answer 5

Expiratory reserve volume + residual volume

Question 6

Describe factors that can affect spirometry measurements (i.e. ventilation)

Answer 6

o Airway narrowing – obstructive lung disease, slower flow rate
o Reduce elasticity – restrictive lung disease, reduced volume and capacity

Question 7

Minute ventilation

Answer 7

o Total volume of air moved in and out of lungs in one minute
o Ve = Fr x Vt

Question 8

Alveolar ventilation

Answer 8

o The total volume of air moved in and out of the alveolar in one minute. Important for gas exchange
o Va = Vt – Vd
o Va = (Vt-Vd) x Fr

Question 9

What is anatomical dead space (Vd)?

Answer 9

Portion of the respiratory system where air does not participate with gas exchange

Question 10

Effect of anatomic dead space

Answer 10

o Conditioning incoming air by warming and humidifying it to filter out some impurities before it continues to respiratory zone where gas exchange takes place.

Question 11

Describe the basic reflex pathways for the control of breathing

Answer 11

o Chemoreceptor reflexes
o Stretch reflexes
o Stimulus – sensors – brainstem (control centre) – effectors

Question 12

What are the central control centres?

Answer 12

o VRG = ventral respiratory group
o PRG = pontine respiratory group
o DRG = dorsal respiratory group

Question 13

Identify and describe the locations of the different chemoreceptors

Answer 13

o Peripheral chemoreceptors
 Nucleus of the solitary tract (NTS)
 Carotid bodies
 Aortic bodies
o Central chemoreceptors
 Located on ventral surface of the brainstem
 Other central chemoreceptor neurons throughout the brain

Question 14

Describe the stimuli primarily responsible for activating the different chemoreceptors

Answer 14

o Central chemoreceptor activation
 Increase end tidal (expired) Pco2 – increased ventilation
 Thus high Pco2 or low pH
o Peripheral chemoreceptors
 Low PaO2, high Pco2, low pH
o Control centres for breathing
 Inspiration
* Diaphragm = phrenic nerve
* External intercostals = thoracic intercostal nerves
 Expiration
* Internal intercostals = thoracic intercostal nerves
* Abdominal muscles = abdominal nerves

Question 15

PRG

Answer 15

Integrating centre of respiratory phases, integrates some peripheral afferents

Question 16

DRG

Answer 16

Integrating centre of peripheral afferents

Question 17

response of chemoreceptor activation

Answer 17

o keep Pao2 high, Paco2 low
o ventilation is modified to maintain homeostasis and metabolism

Question 17

VRG

Answer 17

Source of respiratory rhythm, output of respiratory muscles