Week 7 - Respiration during exercise (Part 1)

Question 1

Whats the primary function of the respiratory system

Answer 1

Maintain arterial blood-gas homeostasis

Question 2

How is the maintenance of arterial blood-gas homeostasis done

Answer 2

1. Pulmonary ventilation
2. Alveolar gas exchange
3. Gas transport
4. Systematic gas exchange

Question 3

Structural and Functional organisation

Answer 3

The epiglottis separate the upper and lower respiratory tracts.
The lungs are encolsed within membranes called pleura - intrapleural pressure < atmospheric pressure, which prevents the alveoli from collapsing

Question 4

Airways

Answer 4

There are 23 main airways
The main bronchi is Z1 - conducting zone extends to terminal bronchioles (Z16)
Gas exchange occurs in the respiratory zone (Z17-23)

Question 5

Alveolar (pulmonary) gas exchange

Answer 5

Pulmonary gas exchange takes place across the pulonary capillary
Oxygen and co2 move between blood and air by simple diffusion (high to low partial pressure)

Question 6

What are the 2 types of alveolar cell
(ON SHEET)

Answer 6

Type 1 - cover 95% of the internal surface of the alveoli and are critical for gaseous exchange
Type 2 - release surfactant which is a molecule that lowers the surface tension

Question 7

Fick’s law of diffusion

Answer 7

Volume of gas passing through a sheet is dependent on:
- surface area
- thickness
- diffusion coefficient
- pressure gradient

Question 8

Blood gas barrier interface

Answer 8

The diffusion path from alveolar gas to the erythrocyte includes 5 layers:
1. Surfactant
2. Alveolar epithelium
3. Interstitium
4. Capilary endothelium
5. Plasma
The blood/gas barrier is very thin and has vast surface area 950-1000m2(make it ideal for gas exchange/diffusion)

Question 9

Mechanics of breathing

Answer 9

Mechanics of brathing are concerned with the movement air into and out of the lungs by changes in pressure, flow and volume.
During inspiration the volume of the thoracic cavity increases as the respiratory muscles contract.

Question 10

Whats the bucket handle motion
(ON SHEET)

Answer 10

The bucket handle motion of the ribs increases the transverse diameter of the thorax during inspiration

Question 11

What is the pump handle motion of the ribs
(ON SHEET)

Answer 11

The pump handle motion of the ribs increases the anteroposterior diameter of the thorax during inspiration

Question 12

Muscles of respiration
(ON SHEET)

Answer 12

At rest diaphragm contraction is responsible for the majority of pulmonary ventilation - expiration is passive
During exercise the diaphragm is assisted by external intercostal muscles, scalenes, sternocleidomastoid and others to increase pulmonary ventialtion 10-20 fold above resting levels

Question 13

Ohm’s Law

Answer 13

Current = voltage/resistance
this can be applied to breathing as airflow is dependent on a pressure gradient and airway resistance

Question 14

Poiseuille’s Law

Answer 14

Resistance is dependent on length and radius. Radius is raised to the fourth power thus the major determinent of airway resistance

Question 15

What is dead space

Answer 15

The volume of air not participating in gaseous exchange

Question 16

Obstructive airway disease
(ON SHEET)

Answer 16

Spirometry can be used to diagnose pulmonary disease such as COPD (chronic obstructive pulmonary disease)
Forced vital capacity (FCV) is the maximum volume air that can be forcefully expired after a maximal inspiration, COPD is characterised as an increased airway resistance and a reduced FEV/FCV

Question 17

Exercise hyperpnoea
(ON SHEET)

Answer 17

PaCO2 regulation due to proportional changes in alveolar ventialtion and metabolic rate

Question 18

Incremental exercsie

Answer 18

Ventilation increases linearly with exercise intensity until a certain point ventilatory threshold (lactate/anaerobic threshold) tVent. Once Tvent is reached ventilation increase exponentially resulting in hyperventilation

Question 19

Exercise induced arterial hypoxaemia (EIAH)
(ON SHEET)

Answer 19

EIAH is defined as a reduction in Paco2 of >10mmg from rest. Occurs in higly trained males and the majority of females regardless of fitness or exercise intensity.
Theorised to occur because ventilatory demand exceeds capacity.
Causes are believed to be due to:
Diffusion limitation
V/Q mismatch
Relative hyperventilation

Question 20

Control of ventilation

Answer 20

Neural control of breatthing is very complex
There are 3 main groups of neurons:
1. Ventral respiratory group (inspiratory and expiratory)
2. Dorsal respiratory group (inspiratory)
3. Pontine respiratory group (modulatory)

Question 21

Control of ventilation 3 compartmental model

Answer 21

Central controller (pons, medulla, other brain parts) output information to the effectors (respiratory muscles) then transferred to the sensors (chemoreceptors, lung and other receptors) then input this back to the central controller to control ventilation

Question 22

Peripheral chemoreceptors

Answer 22

Located at the aortic arch and carotid of the body.
They detect changes in Po2 of blood perfusing systemic and cerebral circulation
Relay sensory information to the medulla via vagus and glossopharangeal nerves
Decreased Pa02 = increased Expired volume.
Other factors can also stimulate peripheral chemoreceptors such as temperature, adrenaline and CO2

Question 23

Central chemoreceptors (pco2 sensors)

Answer 23

Located primarily in the ventral surface of the medulla known as the retrotrapezoid (RTN).
The RTN is sensitive to change is Paco2/h+

Question 24

Chemoreceptor feedback

Answer 24

1. Detect error signals (disturbances to blood-gas homeostasis)
2. Central and peripheral chemoreceptors increase afferent input to the brainstem in response to Paco2 increase or decrease paO2 or pH.
3. Premotor neurons in the dorsal respiratory group are activated
4. Inspiratory muscle contract Increasing expiratory volume
5. Changes in expiratory volume elicit changes in paO2, paCO2 and pH thus restoring blood-glucose balance

Question 25

What is hypoxaemia

Answer 25

When oxygen levels in the blood are lower than normal

Question 26

Ventilatory responses to o2 and co2
(ON SHEET)

Answer 26

The ventilatory response to o2 is curvilinear whereas the response to co2 is linear.
Small changes in paco2 elicit much greater changes in expiratory volume than small changes in pao2

Question 27

Ventilatory control during moderate-intensity exercise

Answer 27

With no change in mean paco2 during moderate exercsie rhe primary exercise stimulus
must be feedforward in origin
- Both central and peripheral neurogenic stimuli play a major role in the exercise hyperpnoea
- Peripheral chemoreceptors ‘fine-tune’ breathing

Question 28

Ventilatory control during heavy and severe exercise

Answer 28

During exercise above Tvent, metabolites accumulate, including H+ and K+, which can
stimulate breathing—remember that PaCO2 falls and therefore actually inhibits breathing
Additional sources of ventilatory stimulus come from increased body temperature and
augmented muscle afferent input

Question 29

Effects of endurance training

Answer 29

Expiratory volume is 20-30% lower during submaximal exercise in trained vs untrained athletes
Chronic training adaptations that improve aerobic capacity:
- decreased metabolite accumulation
- decreased afferent feedback
- decreased ventilatory drive

Question 30

Do the lungs adapt to exercise training

Answer 30

With few exceptions the lungs adn airways do not adapt to physcial activity. Airways and lungs do not get bigger, diffusing capacities are unchanged
Respiratory muscles may become stronger and more fatigue resistant
Some adaptations may be maladaptive

Question 31

Does the pulmonary system limit maximal exercise performance
(ON SHEET)

Answer 31

5 examples of how the pulmonary system may impact performance:
1. Exercise induced arterial hypoxaemia (EIAH)
2. Exercise induced laryngeal obstruction (EILO)
3. Expiratory flow limitation
4. Respiratory muscel fatigue
5. Intrathoracic pressure effects on cardaic output