mechanisms of ventilation Flashcards
What is external respiration?
- exchange of oxygen and carbon dioxide between the body and external environment
What is internal respiration?
- Uptake and utilisation of oxygen by cells and release of carbon dioxide
What are pneumocytes?
- surface epithelial cells of alveoli
- type I: part of barrier, for gas exchange, flat and thin
- type II: secrete surfactant to reduce surface tension + prevent alveolar collapse, large and cuboidal
How is ventilation driven?
- by mechanical forces
- air is moved into and out of lungs by pressure gradients
- gas pressure is the force that gas exerts on the wall of its container
What is Boyle’s Law?
- For a fixed mass of enclosed gas at constant temperature, PV remains constant
- P1V1 = P2V2
PV = k, decreasing volume increases pressure (more collisions)
What is the relationship between pulmonary and pleural pressure? and why?
- pleural pressure < pulmonary pressure
- lungs are pulling inwards
- thoracic wall pulls outwards
756<760, pleural sac seperates lung from thoracic wall
What changes the pressure equilibrium in the lungs?
- Inspiration and Expiration
- Air is drawn into or pushed out of lungs passively
- pressure in lungs decreases during inspiration and increases during expiration
What are the 8 events of inspiration?
- Inspiratory muscles contract
- Thoracic cage diameters increase
- Intrapleural pressure (PPL) becomes more negative
- Transmural pressure (PTM) increases and further distends alveoli
- Intra-alveolar pressure falls < atmospheric pressure
- Air flows down pressure gradient from atmosphere to alveoli
- Tidal volume (VT) of about 500 mls is added to resting volume or FRC
- At end of inspiration – no airflow and intra-alveolar pressure = atmospheric pressure.
What is transmural pressure?
Intra-alveolar pressure - Intrapleural pressure
What are the primary inspiratory muscles?
- Diaphragm: moves down during inspiration, causes 75% of it
- External intercostals: lifts ribs upwards and outwards
What are the accessory inspiratory muscles?
- Scalenes: raise first 2 ribs
- Sternomastoid: raise the sternum
used during exercise and respiratory disease
What diseases require the use of accessory muscles?
- Chronic bronchitis
- Asthma
- Emphysema
- COPD
- Bronchiolitis (RSV in kids)
What are the airway inspiratory muscles?
- Laryngeal
- Pharyngeal
- Genioglossus
- dilation of airway → reduced flow resistance → stabilisation of airway (pharynx) → preventing collapse
What is obstructive sleep apnea?
- decreased upper airway muscle activity during sleep
- pharynx can collapse due to negative pressure during inspiration
person has to wake up to open airways so muscles can activate
What are the 2 types of expiration?
Passive
- occurs at rest
- inspiratory muscles relax
Active
- contraction of abdominal muscles and internal intercostals
When is active expiration required?
- coughing, sneezing, exercise, resp. diseases, screaming, singing, vomiting
How do the expiratory muscles work?
- Diaphgram and external intercostals relax
- Abdominal muscles contract (pushes diaphragm up)
- Internal intercostals contract (flattens ribs and sternum)
What is Tidal volume (TV)?
seen on spirogram
- Air taken in during a breath normally
- 500ml
What is IRV and ERV?
- Inspiratory and expiratory reserve volume
- breathing in and out as much as possible
- IRV: 3000ml
- ERV: 1000ml
both are additional air that you can breath in and out from normal
What is VC?
- Vital capacity: total volume of air expelled after a full inhalation
important as it is used to check a persons lung capacity
What is RV and FRC?*
- Residual volume: air left in lungs after breathing out to max
- Functional residual capacity: volume of air left in lungs after normal breath (RV +ERV)
Why can a spirometer not measure RV, FRC and TLC?*
- All these values contain the RV, the air that cannot be expelled from the lungs during spirometry
What is FEV1 and FVC?*
- FEV1: Forced expiratory volume in one second
- FVC: Forced vital capacity; max inhalation followed by max exhalation
- FEV1/FVC ratio, 80% for healthy people
FEV1 determined in pulmonary function test
What is PEFR?*
- Peak expiratory flow meter
- used to measure airway resitance
- useful in asthma
max speed of expiration
What are obstructive lung diseases?
- reduction in air flow, difficulty exhaling
- Asthma, COPD
- FEV1 + FEV1/FVC reduced
- RV higher
FEV1 can be normal or slightly decreased
What are restrictive lung diseases?
- reduction in lung volume, difficulty inhaling
- lung fibrosis, scoliosis
- reduced FEV1, but normal or increased FEV1/FVC
- RV normal
What is the function of a spirometer?
- measures volume of air individual inhales or exhales as a function of time
can be set up with PC too
What is the helium dilution technique?
- used to measure RV, FRC, TLC
- helium/oxygen mixture in spirometer
- FRC = (C1 x V1)/C2 - V1
doesnt work with obstructive pulmonary disease
What is body plethymosgraphy?
- measures change in volume of an organ
- FRC can be calculated using Boyle’s Law
- patient sits in body box and breathes through mouthpiece (closed at FRC)
used for RV, FRC, TLC
How does lung volume vary?
- body size
- age
- sex
- muscular training
- posture
- race
- respiratory diseases
What is dead space? and what are the 3 types?
- Volume occupied by gas in the lungs which does not participate in gas exchange
- Anatomical
- Physiological
- Alveolar
What is anatomical dead space and how is it measured?
- dead space in mouth, nose pharynx, trachea etc.
- TV is 500ml, so 150ml occupied in dead space
- Fowler’s method
350ml goes to alveoli. Tidal Vol = alveolar vol + dead space vol
What is alveolar dead space?
- Air in alveoli that are surrounded by pulmonary capillaries without blood flow
What is physiological dead space and how is it measured?
- TOTAL DEAD SPACE
- Physiological dead space = anatomical dead space + alveolar dead space
- Bohr’s method
How is Fowler’s method done?
- Nitrogen washout
- exhaled N2 is measured
3 phases:
1. no N2 (DEAD SPACE vol)
2. rapid rise in N2 - mixture of dead space and alveolar gas
3. plateau of N2
How is Bohr’s method done?
- calculated by measuring partial pressures of CO2 in alveoli and expired air
What is pulmonary/minute ventilation?
- Total volume of air breathed per minute
- VT x f = VT x RR
- VT = tidal volume (L)
- f = RR, respiratory rate (breaths/min)
tidal volume x resp rate, to find alveolar, just do VT - VD = VA
