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
what can increase bronchi diameter?
inspiration
sympathetic NS - hence exercise
reduced by coughing
how does glucagon affect the heart
increases contractility
GPCR –> increase cAMP
how does increasing extracellular calcium affect myocardial contractility ?
increases heart contractility
how does acidosis affect myocardial contractility?
inhibits it
how does pH and CO2 affect pulmonary vasculature?
A low blood pH and/or high CO2 cause pulmonary vasoconstriction, a direct effect of CO2 itself.
how does vagus nerve/ parasympathetic effect anatomical deadspace?
bronchoconstriction –> less anatomical dead space
how can pCO2 and pH be presented graphically
a plot of log PCO2 on x axis
against pH on y
straight line in the physiological range - negative gradient i.e high ph = low co2
what is the equation for surface tension?
Surface tension may be defined as energy per unit area or force per unit length.
P = 2T/r, so T = Pr/2,
expressed in S.I. units = N.m-1
is surface tension bigger in small or larger alveoli?
T=Pr/2 - the larger the radius, the bigger the tension
what is the intrapleural pressure during normal breathing?
Intrapleural pressure is approximately -5 cm H2O at end-expiration. During inspiration, intrapleural pressure falls further to approximately -8 cm H2O
how is intrapleural pressure measurements estimated?
oesophageal pressures
how does the intrapleural pressure between base and apex of the lung compare?
Thus the pressure at the base is higher (less subatmospheric) than that at the apex.
how does intrapleural pressure change in valsalva?
increases above atmospheric
what does the helium dilution test measure and is this an over estimate or underestimate?
FRC
underestimate - excludes unventilated areas of the lung behind closed airways.
what is a normal value for FRC in an adult male?
2.5-3 L
how does CO2 alter CBF?
vasodilation hence increase in blood flow in a linear fashion.
which area of the brain does CO2 affect arousal?
reticular activating system
what is normal CO2 for arterial and mixed venous blood?
mixed venous - 6.1
arterial 5.3 kpa
what is the CO2 and O2 content of arterial blood?
The arterial oxygen content of blood is approximately 200 ml.L-1. Arterial carbon dioxide content is approximately 480 ml.L-1.
