Pulmonary Mechanics: Dynamics of Breathing Flashcards
which direction is flow during inspiration and how does this reflect alveolar pressure?
it is negative and has the same shape of the curve as the alveolar pressure
during eupnea how much time is spent during inspiration and expiration?
inspiration 1/3 of time and expiration 2/3
what is the tidal volume of the lungs? what is the functional residual capacity?
- 5 L
2. 5L
what pressure drives the airflow and what pressure sets the lung volume?
alveolar pressure-airflow
pleural pressure-volume
what is the value of Palv at the beginning and end of inspiration and expiration? what is the flow?
both are 0
how much does the alveolar pressure change to get to max inspiration? what percentage of total pressure is that?
1 cm H2O
0.1% change from atmospheric
what is the lung pressure?
the transmural pressure across the lung
P alv-P pl
what does contraction of the diaphragm do to the pleural pressure and the lung pressure?
it makes the pleural pressure more negative and increases the transmural lung pressure
why is the pleural pressure curved and not a straight line during breathing?
because there is a need for extra pressure to overcome frictional tissue and airway resistance
when is frictional tissue and airway resistance a consideration?
only when air is flowing
what can happen to the intrapleural pressure during exercise expiration that does not happen during eupnea?
it can become positive
what is the mechanical equilibrium position of the respiratory apparatus compared to the vital capacity?
it occurs at 36% of the vital capacity
at functional residual capacity, how do chest pressure and lung pressure compare?
chest pressure is equal to the negative of lung pressure
what does the compliance of the lung depend on?
the degree of inflation
what is the difference between total compliance and lung compliance?
total compliance includes the pressure volume curve for the lung plus the chest wall (two compliances in series)
what is total compliance near the resting position of the lung?
it is about 0.1 L/cm H2O
how do the pressures recorded during the measurement of compliance compare to the pressures during breathing?
they are not the same- it becomes positive during the test
what is the dynamic lung compliance?
the compliance obtained from measurements of change in volume and intrapleural pressure at end inspiration and expiration during breathing
what happens to the dynamic lung compliance if there is abnormally increased resistance? what disease may cause this?
the C dyn will be less than static compliance
less flow for a given pressure change
small airway disease
does the dynamic compliance change with altered breathing rates?
no
in small airway disease, when is the tidal volume decreased? why?
at an increased respiratory rate because of increased airway resistance
when is the flow of air laminar and when is it turbulent in the bronchial tree?
it is laminar in the trachea but turbulent at each bifurcation
what does turbulent flow in the lungs produce?
the sound of quiet respiration and surface roughness in the conductive zone
what type of flows are seen in at bifurcations and the glottis?
eddy flow at bifurcations and orifice flow at the glottis
describe orifice flow
there is turbulence after the stenosis of the flow reopens
what is the equation for reynold’s number? when does flow become turbulent?
Re= (density x velocity x diameter of tube)/ viscosity of air
becomes turbulent at Re>3000
what is reynold’s number in the trachea? what creates the noise of flow in this part of the airway?
1800
geometrical irregularities account for the sound
how does bronchitis change the sound of breathing?
it increases surface roughness due to the altered geometry
what percentage of resistance to breathing is due to tissue resistance and which is due to airway resistance?
20% due to tissue and 80% due to airway
where is airway resistance highest? where is it lowest?
highest in the nose or mouth
lowest in the bronchioles
when can the bronchioles become a site of airway resistance?
in bronchitis
what is tissue resistance and airway resistance? what causes them?
resistance from the motion of tissues (chest wall)
resistance from the motion of the air
both caused by viscous flow of either tissue or air
when is tissue resistance increased?
in fibrotic disease
how does replacing nitrogen gas with helium affect breathing?
helium has a slightly higher viscosity than nitrogen and a much lower density so it decreases turbulence and therefore work required for breathing
what is the relationship of airway resistance as you move through the bronchial tree?
resistance increases for the first three bifurcations because the cross sectional area decreases. it then decreases as cross sectional area increases
how does airway resistance compare to lung volume?
as lung volume increases, airway resistance falls
why do inhaled particles settle out in small airways?
because the velocity of air moving through these areas is low
why does it take considerable small airway disease before the measurement of total airway resistance would detect a problem?
because it affects the bronchioles where there is a large cross sectional area and therefore low resistance
what receptors does epinephrine bind to in the smooth muscle of the airway?
high affinity beta 2 receptors
what intracellular cascade causes epinephrine to decrease airway resistance?
increase of cAMP and stimulation of PKA
PKA phosphorylates MLCK and decreases its sensitivity for calmodulin
what is the effect of decreasing the sensitivity of MLCK for calmodulin and how does it effect breathing?
it inhibits the activation of myosin to form cross bridges and contract the smooth muscle, relaxing it and opening the airway
what is the typical value for airway resistance and what is its normal range?
typical value: 1.2 cm H20 sec/L
normal range: 0.5-1.5
what factors reflexively cause constriction of the airway?
smoke particles, noxious gases and extreme cold
how does the parasympathetic nervous system cause airway constriction?
the vagus nerve interacts with muscarinic receptors
what effects does histamine have on the bronchi and blood vessels? what receptor mediates these effects?
it is a bronchoconstrictor but a vasodilator
H1 receptor
how does airway resistance change in asthma?
inflammatory swelling of bronchial mucosa increases the airway resistance
what does the positive end expiratory pressure do in patients on respirators?
decreases the airway resistance
does breathing through the nose or mouth have greater resistance?
the nose
how are isovolume pressure flow curves constructed?
by measuring flow rate, lung volume and alveolar pressure during a series of forced expirations of increasing vigor
what do isovolume pressure flow curves demonstrate?
the dependence of flow on pressure at constant lung volume
what is the trend of IVPF curves?
at low lung volumes, increasing driving pressure leads to a maximal flow rate and it increases with decreasing lung volumes
when the flow is maximal what does V equal? how does it change with changing pressure?
change in pressure/resistance
it does not change with changing pressure so R and delta P must change in direct proportion
what causes the increase in resistance with increasing alveolar pressure?
dynamic compression of the airways
when is there deviation from Ohm’s law during expiration?
when there is greater expiratory efforts, especially when there are low lung volumes
where on the IVPF curve is there a plateau and where is there not?
there is not a plateau for inspiration but there is for expiration
what is the equal pressure point?
the point between the alveolus and the mouth where the pressure inside the airway increases the intrapleural pressure
what is the pressure downstream of the EPP (towards the mouth)? what occurs in this area?
downstream, airway pressure is less than intrapleural pressure. this is where dynamic compression occurs (partially collapsed airway)
when is dynamic compression more pronounced and why?
low lung volumes because the lung is more compliant at low volumes
what is the result of increased compliance on dynamic compression? what occurs when this person tries to forcibly exhale?
more of the airway will close during expiration, creating difficulty in exhaling
if there is forced exhalation, the EPP will be closer to the alveoli and more of the airways will be compressed
how can the alveolar pressure be maintained and compression prevented during expiration with low compliance lungs?
pursed lips breathing
