Respiratory Flashcards
How does compliance vary with lung volume?
Lower at high and low lung volumes.
If you draw out pressure volume curve - it is a sigmoidal shape. the gradient is compliance hence since it is not a linear curve it shows it varies with lung volume
what factors decrease and increase lung compliance?
decreased - fibrosis, oedema
increased - elderly, emphysema
what are the units for compliance of a lung. what is roughly the normal value for compliance of the lung?
0.1 L/ cm H20
How is dynamic compliance related to the frequency of ventilation
inversely related.
how is physiological and anatomical deadspace related?
physiological DS = anatomical DS + alveolar DS
how does dead space change with changes in tidal volume?
Changes in lung volume affect conducting airway diameter and pulmonary vascular resistance, altering regional pulmonary blood flow and V/Q ratios throughout the lung.
how can physiological dead space be calculated?
Bohr equation -
VD/VT = (PaCO2 - PECO2)/PaCO2 (PACO2 is assumed to equal PaCO2)
how does the resistance change in bronchioles as lung volumes increase?
increase in lung volume, diameter of bronchioles increases, resistance decreases.
can terminal bronchioles collapse in expiration?
yes with forced expiration or in disease states
what is the closing volume?
Closing volume is the volume above residual volume at which measurable small airways closure occurs.
do terminal bronchioles have abundant smooth muscle?
yes
how do PO2 and PCO2 affect minute volume ?
PO2 increases resp expontentially when below 7Kpa
PCO2 - proportional increase in MV with increase in PCO2. however above 10kpa this is diminished = carbon dioxide narcosis
what is closing capacity equal to?
closing volume + residual capacity
how does closing capacity change with lying down?
increaases
how does closing capacity change with age?
increases with age
how does intrapleural and alveolar pressure change with inspiration ?
intrapleural pressure - decreases -5 to -8
intralveolar pressure - decreases
what is equation for total compliance of lung?
1/CTOTAL = 1/CLUNG + 1/CCHEST WALL
Compliance of the lungs is approximately 200 ml.cm H2O-1 and that of the chest wall is also 200 ml.cm H2O-1. Total compliance, 1/CTOTAL = 1/CLUNG + 1/CCHEST WALL (c.f. resistance of two electrical resistors in parallel) = 100 ml.cm H2O-1.
how does dynamic compliance compare to static compliance?
Dynamic compliance is always less than static compliance.
Dynamic - when breathing , includes lung / chest wall elastic compliance and resistance to breathing.
Static - when no air flow , only affected by lung and chest wall.
how does lung compliance change with age?
increases
how is CO2 carried in blood?
As HCO3 - bicarbonate (main way ) (NOT Carbonate)
as carbamino compounds - with Hb mainly but also plasma protiens
dissolved in blood
what type of shunt will reduce PaO2 of blood?
right to left
(be careful with direction in MCQ)
how does PaO2 alter with exercise or hyperventilation?
exercise - relatively constant
hyperventilation - drop in CO2 hence increase in PaO2 as per alveolar gas equation
is deadspace negligble in healthy adults?
no there is still some anatomical and alveolar dead space
how is deadspace calculated?
alveolar = bohr equation
anatomical = fowlers method- one breath N2
