Intro to respiratory system (physiology) Flashcards
What is the difference between external and internal respiration?
External respiration - between air and blood
Internal respiration - between blood and cells
What is pulmonary ventilation?
The movement of air into and out of lungs
What does ventilation rely on?
A pressure gradient along the airways
What is the equation for flow pressure and resistance? (like Ohm’s Law)
Flow = pressure gradient/resistance
What is a low flow rate caused by?
Low pressure gradient/high resistance
What must be the relationship between the atmospheric pressure and the alveolar pressure for inspiration to occur?
Atmospheric pressure (at mouth/nose) must be greater than alveolar pressure
What is Boyles law?
The pressure of a fixed number of molecules is related to the volume of the container.
ie pressure and volume are inversely related - decreasing the volume increases the pressure and vv.
What mechanically couples the lungs to the chest wall?
The pleural fluid
What prevents the lungs from collapsing inwards?
The outward recoil of the chest wall
What pressure is the intrapleural space held at resting end expiration?
Negative pressure (-5cm H20)
Which thoracic structure wants to recoil outwards and which inwards?
Lungs want to spring inwards
Chest wall wants to spring outwards
2 opposite elastic forces
These forces are exactly equal just before inspiration
What happens during inspiration?
Contract respiratory muscles to increase volume of thoracic cavity
Decreases the intrapleural pressure - becomes more negative
Lung expands even further (pressure lower inside than outside) –> air moves in
At rest, is expiration active or passive?
Passive
Are pressures given absolute in respiratory physiology?
No - relative to atmospheric pressure
Is inspiration active or passive?
Always active - inspiratory muscles contract (diaphragm esp important)
Name the obligate inspiratory muscles
Diaphragm
External intercostal muscles
Scalenes
Parasternal intercostal muscles
Name the accessory inspiratory muscles
Sternocleidomastoids
Name the expiratory muscles
Internal intercostals Rectus abdominis External oblique Internal oblique Transversus abdominis
What is Ppl?
Intrapleural pressure
What is PA?
Alveolar pressure
What is Pb?
Barometric pressure
How do you calculate transmural pressures?
Pressure differential of the inside compartment minus the outside
What is PL and how do you calculate it?
Transpulmonary pressure/distending pressure that inflates the lung
PL = PA - Ppl
What is PL at rest?
+5 (0–5)
Positive pressure holding the lung open (‘distending pressure’)
What happens to PL during inspiration?
It increases
When may the intrapleural pressure become positive?
During forced expiration
What is a pneumothorax?
After a chest wall puncture - air is sucked into the pleural space
Collapse of the lung due to elastic recoil inwards
Chest wall springs outwards
What is a respiratory cycle?
A single cycle of inhalation and expiration
What is the term for the volume of air moved in 1 respiratory cycle?
Tidal volume
What is a normal value for a tidal volume?
500ml
What is FRC?
Functional residual capacity
Volume of air that you start breathing in from
What is the vital capacity?
The difference between the maximum amount of inspired air and the volume after a maximum expiration
What is TLC?
Total lung capacity (total volume of long)
What is the expiratory reserve volume?
Difference between the vital capacity and the inspiratory capacity
(volume left over after a normal breath out)
What is the inspiratory reserve volume?
Volume that you have left to breath into after a normal breath in to take you up to the vital capacity
What is the inspiratory capacity?
Difference between functional residual capacity and total lung capacity
What is the residual volume?
The volume of air left in the lungs after forced expiration that cannot be breathed out
Which lung volumes cannot be measured directly by spirometry?
Total lung capacity
Residual volume
Functional residual capacity
What is dead space? (Vd)
Airway volume with no gas exchange
What is anatomic dead space?
All of airway except alveoli and respiratory bronchioles, e.g. trachea
What is physiologic dead space?
Anatomic plus areas where gas exchange is dysfunctional
Which kind of dead space increases in respiratory disease e.g. emphysema?
Alveolar dead space (therefore physiologic dead space)
What is the equation for physiologic dead space?
Physiologic dead space = anatomical dead space + alveolar dead space
What is the relationship between alveolar and anatomical dead space in a healthy individual?
They should be approximately equal
What is a typical total ventilation rate?
7500ml/min
What is a typical anatomical dead space?
150ml
What is a typical alveolar gas volume?
3000ml
What is a typical pulmonary capillary blood volume?
70ml
What is a typical ventilation frequency (resps)?
15/min
What is a typical pulmonary blood flow rate?
5000ml/min
What is the equation for alveolar ventilation?
Minute ventilation - dead space ventilation
What is a typical value for alveolar ventilation?
5250ml/min
What is important about the values for alveolar ventilation and pulmonary blood flow rate?
It is well matched (both around 5000 ml/min)
What are the two main sources of resistance to breathing?
- Elastic resistance of the lung (due to elastic tissues and air-liquid interface in alveoli)
- Airway resistance to airflow (due to friction from air flowing within tube)
What is dyspnoea?
Breathlessness
What is lung compliance?
Stretchiness of the lung
What is the equation for lung compliance?
Change in long volume/change in transmural pressure gradient (V/P)
What is the equation for airway resistance?
Airway resistance = alveolar pressure-mouth pressure/flow at mouth
What are the two types of flow?
Laminar or turbulent
What is turbulent flow?
Disruption of laminar flow due to hitting a branch point etc - more oscillations of airflow (wheeze)
Increases resistance
What causes a wheeze?
Oscillations of airflow (turbulent flow) down a narrow airway
What could a silent wheeze from an asthmatic suggest?
Very severe obstruction - insufficient airflow to generate wheeze
What determines airway resistance?
Poiseuille’s law (R is proportional to 1/r^4)
Radius has largest effect on resistance
What are the main sites of airway resistance?
Wherever the tubes get narrower
Nose, pharynx, larynx
Medium bronchi
Which part of the airway contributes most to airway resistance?
Medium bronchi at generation 3-5
What are the two main factors causing variations in airway resistance (RAW)?
Factors within the airways, e.g. bronchial SM tone
Pressure across airway wall (if collapsing the airway down)
What effect does CO2 have on bronchial muscle tone?
Relaxes
What effect do NANC nerves have on bronchial muscle tone?
Relax
What effect does B2 receptor stimulation have on bronchial muscle tone?
Relaxes
What does salbutamol do?
B2 agonist
Relaxes bronchial SM in ashtmatics
What effect does histamine and prostaglandins have on the bronchial SM?
Contract SM
What affect does activation of airway irritant receptors have?
Contraction via brainstem pathway
inhibited by pulmonary stretch receptors
What occurs during dynamic compression of the airways?
Positive pressure in alveoli during forced expiration
(due to expiratory muscles contracting plus inward recoil of lungs) +38 within alveoli
At some point this alveolar pressure decreases below the intrapleural pressure so there is a positive pressure pushing the lung in –> airway collapse
Where is dynamic compression of the airways most likely to occur?
Bronchi at generation 3/4
those without collagen/cartilage
What does dynamic compression of the airways limit?
Forced expiration - it is effort independent at low lung volume (can’t decrease the volume anymore)
What causes dynamic compression of the airways?
High intrapleural pressures
What is the problem with dynamic compression of airways in lungs with RAW?
It causes marked limitation in airflow and slow expiration
- low peak flow, wheeze and air trapping
