Dynamics Resistance to Flow Flashcards
what is flow equal to?
change in pressure divided by resistance….think about it more pressure pushing helps but more resistance makes it harder to go down
in laminar flow, what provides resistance?
the walls of the tube
in laminar flow, what is the change in pressure proportional to?
the velocity of flow
in turbulent flow, what is the change in pressure proportional to?
the velocity of flow squared
what parts of the respiratory tract have turbulent flow?
the trachea and mainstem bronchi
what parts of the respiratory tract have transitional flow?
most of the bronchial tree
what parts of the respiratory tract have laminar flow? why is this?
the small airways…bc the cross sectional area is so high
what is the relationship between resistance and radius of the tube?
resistance is inversely proportional to radius to the 4th power…halving the radius raises the resistance to the 16th
does cross sectional area increase or decrease as you move down the respiratory tract?
INCREASE
does resistance increase or decrease with expiration? what about inspiration?
resistance increases during expiration and decreases during inspiraition
increase due to smaller radius in small airways
decrease due to increasing radius in small airways
on a flow volume loop, when a forced exhalation occurs…explain what the curve looks like and why it is this shape?
the curve is initially sharply increasing then it peaks and has a smaller decreasing slope because the airways are getting more resistance and recoil is running the show not muscles
describe how the alveolus pressure changes as you begin forced expiration and transition from end inspiration
the pressure raises from 0 to about 30 and is driving the air out
what happens when the intrapleural pressure overcomes the pressure in the airways during expiration?
the airways collapse
what causes the decrease in pressure during expiration? what can this cause?
resistance of the airways as they are becoming smaller is increasing…this can lead to airway collapse if pressure becomes smaller than intrapleural pressure
what are the two phases of forced expiration?
effort dependent and effort independent
in effort dependent forced expiration, where does the pressure of intrapleural cavity overcome the pressure in the airways?
this is in bronchus/trachea so you do not get collapse in effort dependent forced expiration
in effort independent forced expiration, where does the intrapleural cavity pressure overcome the pressure in the airway? what happens?
this is in the smaller airways like bronchioles and can lead to airway collapse…the resistance of the small vessels is dropping the pressure faster and leads to their collapse
what is the driving force of expelling air in effort independent phase?
elastic force of the lung
why are alveoli tethered to small airways?
they help keep them open during expiration and avoid collapsing
do obstructive lung breathers breath at higher or lower than normal volumes?
higher volumes to help overcome the resistance of the tightened airways
do restrictive lung breathers breath at higher or lower than normal volumes?
breath at lower volumes because of less recoil
do obstructive or restrictive flow/volume curves have a scooped out appearance during expiration? why?
obstructive…because airways are collapsing so much quicker due to the increased resistance
what is the FEV?
forced expiratory volume in 1 second
what is the FVC?
forced vital capacity
what is FEV/FVC?
this is the percentage of the forced vital capacity that one can expel in forced expiration
what is the normal value for FEV/FVC?
80%..some say 70% (4/5L)
is the FEV/FVC higher or lower in obstructive lung disease?
lower…because of the quick collapse of airways
40%
is the FEV/FVC higher or lower in restrictive lung disease?
higher…close to 90%
but this is less volume relatively
what is the FEF25-75 value representative of in forced expiration?
middle 50% of the FEV
more refelctive of the smaller airways
why are the small airways called the silent zone when it comes to obstructive pulmonary disease?
because they barely contribute to the overall resistance of the flow…the flow experiences most of its resistance in the upper airways
in forced expiration, how high can you raise intrapleural pressure?
close to 100 cmH2O
do restrictive and obstructive lungs have higher or lower maximum flow rates than
lower
