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