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Respiratory Physiology > Control of Ventilation > Flashcards

Control of Ventilation Flashcards

1
Q

What kind of feedback does breathing involve?

A

Rapid positive feedback group

Cyclical - 500ml breathed in and 500ml breathed out

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2
Q

Describe the process of inspiration in terms of nerve activation

A

Triggered by neural activity of medullary respiratory centres (but with voluntary override)
Cyclical activation of phrenic and intercostal nerves causes diaphragm and external intercostal muscles to contract

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3
Q

Describe the process of expiration in terms of nerve inhibition

A

Motor signals to external intercostals and diaphragm cease

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4
Q

What other muscles need to be activated for ventilatory control?

A

Tongue and pharynx muscles to prevent airway collapse

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5
Q

What percentage of inspiration is carried out by the diaphragm vs the intercostal muscles?

A

70% vs 30%

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6
Q

Where are the respiratory centres located?

A

Pons and medulla of brainstem

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7
Q

Is breathing conscious or subconscious?

A

Normally subconscious but can be subject to voluntary control eg singing, talking, holding breath etc

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8
Q

Does the breathing have pacemaker activity?

A

No, breathing is entirely dependent on brain signalling.

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9
Q

Cutting above what region in the spinal cord would cause breathing to cease?

A

C3-5 (phrenic nerve)

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10
Q

Where are central chemoreceptors and what is their function?

A

Located in medulla

Responsible for primary ventilatory drive

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11
Q

Describe the process by which central chemoreceptors stimulate primary ventilator drive.

A

Respond to change in hydrogen ion concentration of CSF and thus directly reflect PaCO2 since H+ ions only cross the blood brain barrier if they have dissociated from H2CO3 (from when CO2 combines with water)
Cause reflex stimulation of ventilation following hypercapnia

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12
Q

Do central chemoreceptors respond to changes in plasma hydrogen ion concentration?

A

No, central chemoreceptors only respond to changes to hydrogen ions in the CSF because only hydrogen ions from dissolved CO2 are able to cross the BBB.

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13
Q

How is ventilation reflexly inhibited by central chemoreceptors?

A

Reduced PaCO2 and thus reduced CSF hydrogen ion concentration leads to the reflex inhibition of ventilation. This explains why you are unable to hyperventilate for a long time.

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14
Q

Where are peripheral chemoreceptors located?

A

Carotid and aortic bodies

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15
Q

What changes are peripheral chemoreceptors sensitive to?

A

Changes to PaO2 and plasma (NOT CSF AND THEREFORE NOT ONLY CARBON DIOXIDE) hydrogen ion concentration.

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16
Q

When do peripheral chemoreceptors cause reflex stimulation of ventilation

A

At significant drop in PaO2 (haemoglobin dissociation at 60mmHg)

17
Q

What three events does in increase in plasma H+ concentration usually accompany

A

Increase in PaCO2
Lactic acid build up
Disease

18
Q

What is the function of respiratory centres?

A

Set automatic rhythm of breathing by co-ordinating the firing of smooth and repetitive bursts of action potentials in the DRG to travel to inspiratory muscles.
Adjust this rhythm in response to stimuli.

19
Q

What is the input to the PRG (pneumotaxic centre)?

A

Higher brain centres (voluntary override)

20
Q

What is the function of the PRG?

A

As the pneumotaxic centres, the PRG provides tonic input into medullary centres for a smooth breathing response.
Controls the DRG

21
Q

What is the main input to the DRG?

A

The PRG

22
Q

Aside from the PRG, what are the other inputs to the DRG?

A 
Mechanosensory input from the thorax (eg stretch reflex)
Medullary chemoreceptors (PaCO2/CSF hydrogen ion concentration)
Chemosensory input (PaO2 and plasma hydrogen ion concentration)
23
Q

What is the function of the dorsal respiratory group (DRG)?

A

Fires APs to activate inspiratory muscles

24
Q

What is the main input to the VRG?

A

The PRG

25
Q

What is the function of the ventral respiratory group (VRG)?

A

Fires APs to activate expiratory muscles and muscles of the tongue and the pharynx

26
Q

What system has emotional input to respiratory centres?

A

Limbic system

27
Q

How does acid-base balance affect ventilation?

A

Changes in pH alter the peripheral chemoreceptor pathway and vary depending on the amount of dissolved CO2 that has dissociated according to the equation
CO2 + H2O H2CO2 HCO3 + H+

28
Q

Describe the effect of acidosis on plasma pH, ventilation and the following equation:
CO2 + H2O H2CO2 HCO3 + H+

A

Plasma pH falls leading to increased ventilation and shifting the equation to the left to get rid of the CO2

29
Q

Describe the effect of alkalosis on plasma pH, ventilation and the following equation:
CO2 + H2O H2CO2 HCO3 + H+

A

Plasma pH is increased and hydrogen ion concentration is reduced. This inhibits ventilation and drives the equation to the right to increase CO2

30
Q

Explain hypoxic drive

A

Chronic lung disease leads to prolonged elevated CO2 levels leading to the desensitisation of central chemoreceptors. Patients depend on peripheral chemoreceptors meaning care must be taken if they are given oxygen because it is not detected that ventilation needs to increase in hypercapnia

31
Q

What involuntary stimuli cannot be overridden by voluntary control from descending neural pathways?

A

Arterial PCO2 or H+ content
Why you can’t hold your breath for too long without fainting or why you can’t hyperventilate for too long (because you’re no longer blowing off CO2)

32
Q

What happens to respiration during swallowing?

A

Respiration is inhibited during swallowing to prevent aspiration. It is then followed by an expiration to remove particle outwards from a closed glottis.

33
Q

Would it be more unpleasant to be in a chamber with high PCO2 and normal PO2 or a chamber with a low PO2 and no PCO2? Why?

A

It would be more unpleasant to be in a chamber with high PCO2 and normal PO2 or a chamber with a low PO2 and no PCO2 because the partial pressure gradient would be impaired. CO2 could not be removed from the pulmonary artery. This would also have an effect on the gradient pulling CO2 out of cells and would cause CO2 to be pulled out of cells.

34
Q

What is the effect of barbiturates and opioids on the respiratory system?

A

Depress respiratory centres. Can result in respiratory failure and death after overdose.

35
Q

What is the effect of gaseous anaesthetic agents on the respiratory system?

A

Increased respiratory rate but reduced tidal volume.

36
Q

What is the effect of nitrous oxide (gas and air) on the respiratory system?

A

Sedative/light anaesthetic.

Blunts peripheral chemoreceptors so should not be given to those on hypoxic drive.

Respiratory Physiology (6 decks)

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