control of breathing

Question 1

functions of respiratory muscles linked to control

Answer 1

maintenance of arterial PO2, PCO2, pH; defence of airways and lung; during exercise; communcation (under voluntary control)

Question 2

determinants of a tidal breath

Answer 2

minute ventilation = volume difference (tidal volume) x frequency (60/duration of breath (TTot))

Question 3

calculating TTot

Answer 3

inspiratory volume + expiratory volume

Question 4

minute ventilation calculation

Answer 4

VT/TI (mean inspiratory flow - neural drive) x TI/TTot (timing)

Question 5

features of tidal breath in disease (chronic bronchitis and emphysema)

Answer 5

more difficulty breathing out than in, airflow limitation so breathe faster and more shallowly

Question 6

involuntary (metabolic) and voluntrary (behavioural) breathing controllers in brain: location and function

Answer 6

automatic bubopontine controller (brainstem) - adjusts ventilation rate in response to pH in blood; behaviour suprapontine control (widely distributed but mainly in motor cortex) - controls breath holding, singing, talking etc. and can be overridden by involuntary; reflex in limbic system and CNS

Question 7

metabolic centre: mechanism of automatic bubopontine controller (medulla brainstem); where is distension and chemical information sent from and to in response to change to confirm (in)adequacy of response

Answer 7

H+ receptor in carotid bodies detects H+ in EC fluid → glossopharyngeal nerve firing to medulla → impulse frequency affects phrenic nerve, contracting diaphragm → repeat to switch on inspiration, then expiration, to clear CO2 (example of metabolic acidosis cleared by respiratory compensation); upper airway muscles also dilate and narrow to ensure smooth inspiration and expiration; distension info sent back from lung and respiratory muscles to brain; chemical info sent back from carotid bodies to brain

Question 8

other influencers over breathing

Answer 8

emotions, pain, sleep

Question 9

3 chemoreceptors: location and detection

Answer 9

central (slow): ventrolateral surface of medulla to detect ECF pH; aortic: detect oxygen and CO2; carotid body (fast): at junction of external and internal carotid arteries in neck for pH, CO2 and oxygen

Question 10

features group pacemaker activity for pace of breathing

Answer 10

complex, subtle and specialised; about 10 groups of neurones in medulla

Question 11

early inspiratory

Answer 11

initiates inspiratory flow via respiratory muscles

Question 12

inspiratory augmenting

Answer 12

dilate pharnyx, larynx, airways

Question 13

late inspiratory

Answer 13

brake start of expiration

Question 14

expiratory decrementing

Answer 14

brake passive expiration by adducting larynx and pharynx

Question 15

expiratory augmenting

Answer 15

activate expiratory muscles

Question 16

late expiratory

Answer 16

signal end of expiration and onset of inspiration

Question 17

reflex control: V, IX and X

Answer 17

V: afferents from nose and face (irritants); IX: from pharynx and larynx (irritant); X: from bronchi and bronchioles (irritant and stretch)

Question 18

what is the Hering-Breuer reflex (mechanism and purpose)

Answer 18

pulmonary stretch receptors (mechanoreceptors) in bronchi and pleura detect stretch → signal to medulla pons via Vagus nerve → terminates inspiration (phrenic to diaphragm) to prevent overinflation (pneumotaxic centre of pons inhibits apneustic centre, stopping inspiration); weak in humans; continuous as then lower minute ventilation so hypoxaemia develops, so must increase minute ventilation again

Question 19

what are CO2 responses potentiated by

Answer 19

acidosis and hypoxia; apneic threshold sensitive to acid-base status in sleep

Question 20

O2 sensitivity at high PCO2

Answer 20

at high PCO2, more sensitive to smaller changes in PO2; SaO2 defended, as decreased PO2 will increase sensitivity of carotid bodies to PCO2 to increase breathing and correct hypoxia

Question 21

when do PaO2 and PaCO2 fall together

Answer 21

at high altitude, as body becomes more sensitive to PaCO2

Question 22

compensatory mechanisms for too much acid or alkali

Answer 22

lung (fast) and kidney (slow)

Question 23

causes of acidosis and alkalosis

Answer 23

metabolic and respiratory

Question 24

determining [H+]

Answer 24

constant x PaCO2/HCO3-; strong ion difference: [Na+ + H+] - Cl-; pH = -log[H+]

Question 25

respiratory acidosis: cause and outcome

Answer 25

lung failing to excrete CO2 produced by metabolic processes, so high PaCO2

Question 26

acute respiratory acidosis: cause, outcome and response

Answer 26

hypoventilation causes low PaO2 and high PaCO2 and H+; stimulates metabolic centre to increase minute ventilation and restore blood gas and H+ levels

Question 27

chronic respiratory acidosis: outcome and response

Answer 27

ventilatory compensation inadequate for PaCO2 homeostasis, but renal excretion of weak acids and renal retention of Cl- return H+ to normal, even though PaCO2 remains high and PaO2 low

Question 28

central causes of acute respiratory acidosis

Answer 28

metabolic centre poisoning

Question 29

central causes of chronic respiratory acidosis

Answer 29

vascular, neoplastic disease of metabolic centre, congenital central hypoventilation syndrome, obesity hypoventilation syndrome, chronic mountain sickness

Question 30

peripheral causes of acute respiratory acidosis

Answer 30

muscle relaxant drugs, myasthenia gravis

Question 31

peripheral causes of chronic respiratory acidosis

Answer 31

neuromuscular with respiratory muscle weakness

Question 32

respiratory alkalosis: feature and outcome

Answer 32

ventilation in excess of metabolic needs, lowering PaCO2 and raising blood pH

Question 33

causes of respiratory alkalosis

Answer 33

chronic hypoxaemia, excess HCO3- (metabolic causes), pulmonary vascular disease, chronic anxiety

Question 34

normal pH range

Answer 34

7.35-7.45, to allow enzyme and protein function

Question 35

dissociation of H2CO3 and locations

Answer 35

(lungs) CO2 + H20 H2CO3 H+ + HCO3- (kidney)

Question 36

arterial blood gas measurements

Answer 36

pH, pO2, pCO2, base excees

Question 37

what is base excess

Answer 37

+ve or -ve difference depending on how much base is present (if +ve, noo much alkali, so body decreases pH to restore base excess to normal level)

Question 38

ROME

Answer 38

respiratory opposite, metabolic equal

Question 39

diagram of ROME

Answer 39

diagram (HCO3- mops up H+)

Question 40

what do opiods effect

Answer 40

repress respiratory centre, causing pin-point pupils

Question 41

what does hyperventilation cause

Answer 41

respiratory alkalosis as loss of CO2 so increase in pH

Question 42

what does diarrhoea cause

Answer 42

metabolic acidosis as loss of HCO3-, decreasing pH

Question 43

what does vomiting cause

Answer 43

metabolic alkalosis as loss of HCl from stomach, increasing pH

Question 44

if issue is respiratory, what compensates

Answer 44

metabolic (and vice versa; lungs respond quicker)

Question 45

define hypoxia

Answer 45

PaO2 <10

Question 46

define hypoxia with respiratory failure

Answer 46

PaO2 <8

Question 47

2 types of respiratory failure

Answer 47

type 1: low O2, normal CO2 (PaCO2<6), caused by V/Q mismatch e.g. pulmonary embolism; type 2: low O2, high CO2 (PaCO2>6), caused by chronic COPD e.g. alveolar hypoventilation