Breathlessness and control of breathing

Question 1

How do you calculate minute ventilation

Answer 1

minute ventilation = tidal volume x frequency

Question 2

What proportion of breathing is inspiration

Answer 2

40%

Question 3

How does tidal volume differ between chronic bronchitis sufferers , emphysema sufferers and normal people

Answer 3

Similar inspiration rates
Chronic bronchitis much lower tidal volume
emphysema lower tidal volume

Question 4

Where is the involuntary / metabolic centre found

Answer 4

medulla/ bulbo-pontine

Question 5

Where is the voluntary / behavioural centre found

Answer 5

Motor area of the cerebral cortex

Question 6

Give some features of the metabolic/involuntary centre

Answer 6

Will always override the behavioural

Responds to metabolic demands for and production of carbon dioxide + determines set point

Question 7

What is the metabolic centre influenced by

Answer 7

Limbic system
Frontal cortex
Sensory inputs

Question 8

What determines impulse frequency to the respiratory spinal motor neurones

Answer 8

Metabolic controller

Changes based on the H+ concentration in the blood

Question 9

Describe the response when carbon dioxide increases in concentration

Answer 9

1. Increase in H+ is detected by the carotid bodies
2. Impulses sent to the metabolic controller
3. Increase frequency to the respiratory spinal motor neurones (+ upper airway muscles)
4. impulse to respiratory muscles
5. Minute ventilation increases
6. Stretch and irritant receptors and muscle spindles and tendon organs in the lung feedback to the metabolic controller

Question 10

How is the diaphragm driven to contract

Answer 10

Metabolic controller via the phrenic nerve

Question 11

Where does the behavioural controller feed into to control breathing

Answer 11

Respiratory spinal motor neurones

2 situations: breath holding, sneeze and cough

Question 12

Where do emotions feed into to control breathing

Answer 12

1. Frontal cortex
2. Limbic system
3. reticular formation
4. Metabolic receptor

Question 13

Where is the peripheral chemoreceptor found

Answer 13

The junction between internal and external carotid arteries in the neck

Question 14

Describe the peripheral chemoreceptor

Answer 14

Responsible for 40% of change to the controllers
Well perfused carotid body acts as a rapid response system
Sends signals to the medulla via cranial nerve IX, glossopharyngeal

Question 15

What is the function of the Pre-Botzinger complex

Answer 15

(near 4th ventricle)
Gasping centre
Coordination of this with other controllers allows gasping to be orderly and responsive

Question 16

Where is the central part of the metabolic controller found and what does it respond to

Answer 16

In the medulla

Responds to H+ of extracellular fluid

Question 17

Which nerves respond to irritants

Answer 17

V - trigeminal (nose + face)
IX - glossopharyngeal (larynx + pharynx)
X - vagus (bronchi + bronchioles)

Question 18

Why do fast and slow responses to H+ concentration exist

Answer 18

CO2 is very diffusible, and H+ changes mirror PCO2 changes, very rapidly for the hyperperfused carotid body, but more slowly in the ECF bathing the medulla.
lung - fast
kidney - slow

Question 19

What is the magnitude of response for changes in pCO2 and what happens when pO2 is lower

Answer 19

small changes in pCO2 causes a large change in minute ventilation and response
Increase in sensitivity when pO2 is lower

Question 20

Describe acute respiratory acidosis

Answer 20

Decrease in PaO2 and PaCO2 while H+ increases
Metabolic centre increases minute ventilation to restore blood gas and H+
Due to metabolic centre poisoning e.g. drugs, anaesthetics

Question 21

Describe chronic respiratory acidosis

Answer 21

Ventilatory compensation may be inadequate for PaCO2 homeostasis
Resolved by renal excretion of weak acids (lactate and keto) and retention of chloride

Question 22

What are the causes of chronic respiratory acidosis

Answer 22

Vascular/ neoplastic disease of the metabolic centre
Congenital central hypoventilation syndrome
Obesity hypoventilation syndrome
Chronic mountain sickness

Question 23

What is peripheral respiratory acidosis caused by

Answer 23

Acute: muscle relaxant drugs, myasthenia gravi

Chronic: neuromuscular with respiratory muscle weakness

COPD

Question 24

What are the causes of respiratory alkalosis

Answer 24

Chronic hypoxaemia
Excess H+ (metabolic)
Pulmonary vascular disease
Chronic anxiety (psychogenic)
High altitude

Question 25

Describe dyspnoea

Answer 25

Breathlessness with the connotation of discomfort or difficulty
At rest - difficulty with inspiration or expiration
On exercise - excessive breathing for the task

Question 26

Describe tightness

Answer 26

Difficulty in inspiring due to airway narrowing
Feeling that the chest is not expanding properly
Increased work and effort
Breathing at a high/normal minute ventilation but at a high lung volume, or against inspiratory or expiratory resistance

Question 27

Describe air hunger

Answer 27

Sensation of a powerful urge to breathe
Experimentally produced by driving breathing with added CO2, while restricting tidal volume by breathing from a bag of fixed volume
Mismatch between VE demanded and the VE achieved

Question 28

How can breathlessness be measured

Answer 28

Borg CR-10 scale
+ visual analogue
Breath holding time - behavioural vs metabolic controller

Question 29

Describe the hearing-breuer reflex

Answer 29

Stretch receptors in the airways and intercostal muscles send afferent signals to the medulla via the vagus nerve

These signals dampen down the respiratory centre activity

Decreased firing of the phrenic nerve, decreased respiratory rate

Question 30

What, other than CO2, can cause an increase in H+ conc

Answer 30

Lactate in infection

Ketones in diabetic ketoacidosis