Respiration Lecture 05: Resistance Flashcards
2 types of resistance
elastic and airways resistance
Resistance
The opposition to airflow. THE RATIO OF PRESSURE TO FLOW.
R=(P1-P2)/flow rate
elastic resistance
resistance due to moving lung tissue and related to the compliance and tendency of lung to collapse when lung volume is increased above FRC
Airways resistance
due to the properties of the tubes which oppose the movement of air through them
resistance primarily affects
rate of air flow
compliance primarily affects
volume
How do radius and length of tube affect resistance?
Radius - 1:16 increase or decrease!
Length - 1:1 increase or decrease
5 things airway resistance is dependent on:
1) rate of airflow
2) driving pressure
3) diameter of tube
4) length of tube
5) viscosity or density of the gas
Poiseuille’s Law
describes airflow. Airflow = [pie(P1-P2)r^4]/[8nl] where n=density and l=length of tube
How does total cross sectional area and resistance change as you move from large to small airways in the lung?
A increases, R decreases
Path of trachea to alveolar sacs
Trachea–> primary bronchi–>lobar bronchioles (?)–>terminal bronchioles–>respiratory bronchioles–>alveolar ducts–>alveolar sacs
when does cartilage disappear from bronchioles?
past the hilus, between lobus bronchus and terminal bronchioles
How does resistance change as a fx of volume?
increasing volume decreases resistance (inverse relationship) due to increased surface area
alveolar sacs
terminal endpoints of branching respiratory system
alveolar ducts
where alveoli bud off bronchioles
turbulence effect on R
increases resistance
Turbulent vs. laminar flow
turbulent flow - molecules hit side of airways and produces sound and airway resistance and decreased flow. Occurs at branch points.
laminar flow - nice smooth flow of molecules in airway
Why is actual inspiratory Ppl more negative and expiratory Ppl more positive than expected in a direct pressure to compliance relationship?
Due to resistance in tubes, muscle has to generate enough force to stretch AND make air go through tubes (as you breathe in you have to generate enough force to produce change in volume that overcomes compliance AND generates neg. PA) THEREFORE, PLEURAL PRESSURE IS RELATED TO BOTH COMPLIANCE AND RESISTANCE
resistive pressure
difference b/w the elastic recoil pressure and the total pleural pressure
alveolar pressure is ____when there is no airflow
zero
Resistance of airway=
change in PA/change in air flow
how does increased smooth muscle contraction (i.e asthma) affect R?
increases R
If airway resistance increases, how must alveolar pressure change if flow rate remains constant?
PA must become more negative to maintain the same flow rate with increased resistance
3 main things effort independent flow limitation is due to
resistance, compliance, and expiratory driving pressure
effort independent flow limitation
linear area on air flow rate vs. % vital capacity where flow rate decreases linearly with volume and increased effort will not increase flow rate. Occurs after about 75% vital capacity during expiration
PA is _____ at rest and becomes ______ during inspiration.
zero at rest, neg. during insp.
Transpulmonary pressure PTP. How does it change during inspiration?
difference between PA and Ppl. Becomes more positive as you get closer to mouth (less of a difference between PA and Ppl as you move up airway)
How are airways kept open for airflow during inspiration?
transpulmonary pressure surrounding airways becomes progressively more positive closer to mouth, and pressure inside airway becomes progressively less negative closer to mouth, resulting in a distending pressure to keep airways open. ???
What conditions are required for airway to stay open?
Intra-airway pressure must be greater (more positive) than the Ppl
equal pressure point
PTP = 0. Where airway pressure equals plueral pressure. Airway has collapsing force beyond this point because PTP becomes negative
How does increased expiratory effort affect Ppl and equal pressure point?
makes Ppl more positive, moving equal pressure point down airway and causing airway collapse
Decreasing airway diameter –> airway resistance?
increases airway R
Where does equal pressure point normally occur?
In cartilaginous airways (cartilage prevents collapse)
Increased compliance –> lung elastic recoil
decreases
decreased lung elastic recoil –> difference between Ppl and PA?
decreased difference
emphysema –> compliance and elastic recoil
increased C, decreased recoil. Leads to trouble expiring and increased collapsing force on small airways. Gas trap
emphysema –> equal pressure point?
moves closer to alveolus
asthma –> equal pressure point?
moves towards alveolus b/c of increased resistance and large pressure drop in small airways
lung recoil/collapsing force is a fx of
compliance
lung recoil produces what kind of force?
inward collapsing force
Active P + Recoil P =
Net expiratory P
2 ways to generate active force to produce a P gradient:
1) elastic recoil
2) applying expiratory mm. to system and increasing P as a fx of active + passive force
