Physiology of the respiratory system

Question 1

What are the 2 major functions of nasal breathing?

Answer 1

• To heat and moisten the air
• To remove particulate matter

Question 2

What is lung compliance?

Answer 2

Is a measure of the relationshup between retractive force and lung volume.

Question 3

What is the functional residual capacity?

Answer 3

• The volume of air remaining in the lung after a quiet expiration.

Question 4

What are the accessory muscles of ventilation?

Answer 4

Sternomastid and scalene muscles

Question 5

What can contribute to resporatory failure in patients with severe chronic airflow limitation and in those with primary neurologial and muscle disorders?

Answer 5

Inspiratory muscle fatigue (n.b. respiratory muscles are less prone to fatigue than skeletal muscles)

Question 6

Provide the normal values for respiratory physiology

Answer 6

• Pulmonary blood flow = 5L/min
• 11 mmol/min of O2 to tissues
• Ventilation = 6 L/min
• CO2 removal from body = 9mmol/min
• Arterial O2 pressure = 11-13 kPa
• Arterial `CO2 pressure = 4.8-6.0 kPa

Question 7

What innervates the respiratory musculature and where do the nerves orignate?

Answer 7

Rhythmical discharges arise from neurones in the reticular substane of the brainstem, known as the respiratory centre. Signals travel to the respiratory musculature via the phrenic and intercostal nerves.

Question 8

What is the main driver for ventilation and when can this be compromised?

Answer 8

• A rise in PaC02 which increases [H+] (Arterial pH) (Hypercapnic drive. Oxygen levels in arterial blood are usually above the level that triggers respiratory drive)
• Sensitivity to hypercapnic drive may be lost in COPD patients where hypoxaemia is the chief stimulus to respiratory drive.

Question 9

Roughly what is the difference in time required to remove particles from the nasal mucosa and the alveoli?

Answer 9

• Nasla mucosa = 15 minutes
• Alveoli = 60-120 days

Question 10

What cells does nasal secretion contain? (3)

Answer 10

• Immunoglobulin A (IgA) antibodies
• Lysozyme
• Interferons

Question 11

Is mucocillary protection less effective against bacteria or virus and why?

Answer 11

• Less effective against viruses
• Viruses bind to receptors on epithelial cells

Question 12

What does the majority of rhinoviruses bind to and on what cells (2) are this found?

Answer 12

• Intercellular adhesion molecule 1 (ICAM-1)
• Neuotrophils / eosinophils

Question 13

What is the natural tendenacy of the lungs?

Answer 13

• The lungs have an inherent elastic property that causes them to tend to collapse away from the thoracic wall, creating negative pressure within the pleural space.

Question 14

Describe the mechanisms of inspiration and expiration. (Intraplueral pressure, alveolar pressure….)

Answer 14

….

Question 15

In what patients can inspiratory muscle fatigue contribute to respiratory failure? (2)

Answer 15

• Severe chronic airflow limitation (COPD??)
• Primary neurological and muscle disorders

Question 16

What three sources is the sensation of breathless derived from?

Answer 16

• Changes in lung volume - sensed by receptors in thoracis wall muscles signalling changes in their length.
• Tension developed by contracting muscles - sensed by Golgi tendon organs
• Central perception of the sense of effort

Question 17

List the neurogenic factors controlling ventilation.

Answer 17

• Pulmonary receptors - sensitive to stretch and bronchial irritation - stimulated in asthma / pulmonary embolism / pneumonia
• Juxtacapillary (J) receptors - stumulated by asthma / pulmonary congestion (heart failure)
• Muscle and joint receptors - stimulated by exercise

Question 18

List the chemical factors controlling ventilation.

Answer 18

• Respiratory centre - stimulated by an increase in PaC02 and [H+]
• Carotid and aortic bodies - stimulated by Pa02 < 8kPa

Question 19

What other than neurogenic and chemical factors can alter ventillation?

Answer 19

Voluntary control - anxiety / hysteria

Question 20

Why do you need to be careful when treating COPD patients with respiratory failure?

Answer 20

• Normal pure oxygen is given to patients with respiratory failure. However, in patients with COPD giving oxygen may reduces respiratory drive and lead to a further rise in PaCO2.

Question 21

What happens to ventilation in patients with metabolic acidosis (i.e. diabetic ketoacidosis)?

Answer 21

• The increase in [H+] will cause ventilation to increase to reduce PaCO2 - this causes deep sighing (Kussmaul) respiration.

Question 22

What can caused the respiratory centre to be depressed? (2)

Answer 22

• Severe hypoxaemia (why??)
• Sedatives (e.g. opiates)

Question 23

Where is airflow greatest?

Answer 23

• In the trachea - it slows progressively towards the periphery - since the velocity of airflow depends on the corss-sectional area)

Question 24

How is the narrowing of the small airways in patients with COPD partially compensated?

Answer 24

• Breathing closer to total lung capacity (TLC)
• (At full inspiration (TLC) the airways are 30-40% larger in calibre than at full expiration (residual volume)).

Question 25

How is bronchomotor tone maintained?

Answer 25

* By vagal efferent nerves that can be reduced by atropine or Beta-adrenoreceptor agonists. * Adrenoreceptors on the surface of broncial muscles respond to circulating catecholamines; there is no direct sympathetic innervation.

Question 26

Airway tone shows a circadian rhythm. When is this tone greatest and lowest?

Answer 26

* Greatest = 04:00 * Lowest = mid-afternoon

Question 27

What can transiently increase airway tone and what is the mechanism? When can this response be increased?

Answer 27

* Inhaled stimuli acting on epithelial nerve endings trigger reflec bronchoconstriction via the vagus. * Stimuli - cigarette smoke / solvents / inert dust / cold air * Following respiratory tract infections

Question 28

Why are asthmatic symptoms usually worse in the mornings?

Answer 28

* Because of the circadian rhythm that airway tone shows - greatest tone at 04:00

Question 29

What is alveolar pressure?

Answer 29

* Alveolar pressure = pleural pressure + elastic recoil pressure of the lung

Question 30

During quiet breathing does the pleural pressure stay negative throughout? When may this change?

Answer 30

* Yes * With vigourous expiratory efforts, e.g. cough

Question 31

What stops the lungs from collapsing when there is no airflow?

Answer 31

* The positive recoil pressure is exactly balanced by an equivalent negative pleural pressure.

Question 32

What happens to to air pressure as air flows from the alveoli towards the mouth? Why does this happen?

Answer 32

* It drops * There is low flow resistance

Question 33

Explain dynamic collapse of the airways in health individuals.

Answer 33

* In forced expiration, the driving pressure raises both the alveolar pressure and the intrapleural pressure. * Betwen the alveolus and the mouth, there is apoint where the airway pressure equals the intrapleural pressure, and the airways collapse. * The collapse is temporary, as the transient occlusion of the airway results in an increase in pressure upstream, and this raises the intra-airway pressure so that the airways open and flow is restored.

Question 34

* Why can dynamic collapse be a problem in patients with COPD? * What is a useful clinical index of this phenomenon? * How do COPD patients compensate for this problem? * Why is dynamic collapse only a problem during expiration?

Answer 34

* The pathological loss of recoil pressure causes the collapse point to be further upstream and causes expiratory flow limitation. * Forced expiratory volume in 1 second (FEV1) * Purse their lips - to increase airway pressure * During inspiration, the intrapleural pressure is always less than the intraluminal pressure within the intrathoracic airways.