Introduction to the respiratory system and lung mechanics Flashcards
Definition of internal respiration
Exchange of cases between blood, interstitial fluid and cells
Definition of external respiration
Exchange of gases (O2, CO2) between blood and the external environment
Definition of pulmonary ventilation
Physical movement of air into and out of the lungs.
Movement of air needs pressure gradient to be generated along the airways
Definition of functional residual capacity
Volume of lung at end of a normal expiration
Definition of transmural pressure
Pressure differences between the inside compartment minus the outside compartment
Definition of respiratory cycle
Single cycle of inhalation and exhalation
Definition of tidal volume
Amount of air moved in 1 cycle (500ml)
Definition of dead space
Airway volume with no gas exchange
Definition of dyspnoea
Breathlessness
Definition of elastic resistance
Resistance to stretch of lung tissues and air liquid interface lining alveoli
Definition of airway resistance
Resistance due to friction between layers of flowing air and between the air and airway walls
Definition of compliance
∆V/∆P, the measure of elastic resistance (stiffness)
What is the difference between external and internal respiration
Internal
Exchange of gases between blood, interstitium and cells
External
Exchange of gases between blood and lungs
Describe step 1 of inspiration
-muscle contraction (obligate and accessory)
Inspiratory muscles contract => expands cage
Obligate
- ext intercostals
- diaphragm
- scalenes
Accessory
-sternocleidomastoid
Describe step 2 of inspiration
-how does cage expansion affect the pleural cavity
Cage expands => pulls on the pleural cavity => pleural cavity pressure gets more -ve => lungs expand
PC starts -ve due to natural cage recoil out and lung recoil in
Describe step 3 of inspiration
-how does the change in Ppl affect the Pl
Pl gets more +ve => holds lungs open => Pa becomes more -ve
Pl = -Pa – Ppl
Pl starts +ve due to both recoils in equilibrium => lungs held open
Describe step 4 of inspiration
-how does the change in Pa affect the movement of gas
More +ve Pl => more -ve Pa
As Pa is more negative than Pb => bulk air flow into lung
Describe step 1 of expiration
-muscle contraction (obligate and accessory)
Expiratory muscles contract => shrinks cage
Obligate
- Int intercostals
- Passive process
Accessory
- RA, EO, IO, TA
- Chest wall, limb girdle muscles
Describe step 2 of expiration
- pleural cavity
- what can happen in forced expiration
PC becomes more +ve => lungs recoil
PC can become +ve if expiration is forced
Describe step 3 of expiration
- how does the change in Ppl affect the Pl
- what happens in end expiration
Pl pressure becomes more -ve => lungs recoil => Pa increases
At the end of expiration, Pl is +ve to keep the lungs open
Describe step 4 of expiration
-how does the change in Pa affect bulk air flow
Pa is more +ve than Pb => bulk air flow out of lungs
What happens in a pneumothorax
Chest wall punctured => Ppl = Pb
Lung recoils in, cage recoils out
What is the respiratory cycle?
What is the typical tidal volume
Single cycle of inhalation and exhalation
Tidal volume, amount of air moved in 1 cycle = 500ml
What is the tidal volume at rest for a typical person
500ml
What is the vital capacity for a typical person
5500ml
What is the inspiratory reserve volume for a typical person
3300ml
What is the expiratory reserve volume for a typical person
1700ml
What is the inspiratory capacity for a typical person
3800ml
What is the total lung capacity in a typical person
7300ml
What is the functional residual capacity in a typical person
3500ml
What is the residual volume for a typical person
1800ml
What is dead space (Vd)
Airway volume with no gas exchange
What is anatomical dead space
What volume of the lung makes up anatomical Vd
All except alveoli and respiratory bronchioles
150ml
What is physiological dead space
How much physiological dead space is normally present in a healthy individual
How much physiological dead space is present in others?
Anatomical plus areas with dysfunctional gas exchange
Normally in healthy people, PVd=AVd
In others PVd=AVd + AlvVd
What volume does the alveoli take up in the lung is a typical person
3000ml
What volume of blood is present in the pulmonary capillary beds
70ml
What is the rate of total ventilation in a typical person
How would you calculate this value
7500ml/min
7500 = 15 x 500
What is the typical frequency of ventilation
15/mins
What is the rate alveolar ventilation
How would you calculate this value
5250ml/min
5250 = 7500 - (15 x 150)
What is the rate of pulmonary blood flow
What is the rate of alveolar ventilation
PBF = 5000ml/min AV = 5250ml/min
What are the sources of resistance in breathing and what equations are they determined by
If R increases, what can happen?
Why is high resistant flow dangerous in asthma
Elastic resistance of lung
- Inverse of compliance = ∆V/∆Pl
- If compliance low => R is high
Airway resistance
- R = Pa-Pb/F
- Determined by F = r4 , R = 1/r4, R = 8VL/πr4
- Increased flow, sharp bends (decreased r) => turbulent flow => increased R and noise
Can lead to dysnpoea
If airway r too small => can’t generate noise => ominous silent wheeze
Where are the main sites of airway resistance in the lungs
Nose, larynx, pharynx
3rd gen bronchi
More distal bronchi have high R, but net R is low due to parallel flow
What factors can affect the airway in airway resistance
SM tone
- Bronchodilation
- Bronchoconstriction
Inflammation
SM tone Bronchodilation -CO2 -NANC (VIP NO) -B2 agonists
Bronchoconstriction
- Histamine, prostaglandins
- NANC (SP, neurokinins)
- Ach M3 due to irritants
Inflammation
-gland hypertrophy => mucus prod
What factors can affect the pressure across the airway wall in airway resistance
Normally, Pl = -ve to keep lungs open
However in forceful expiration, Pl can become +ve => dynamic compression of gen 3-4 bronchi
What are the effects off effort on expiratory flow
Dynamic compression occurs in forceful expiration
-Effort independent
Occurs in everyone, more likely in those with higher airway resistance
