Compliance and Elastance Flashcards
What is compliance?
ΔV/ΔP
what is elastance?
ΔP/ΔV
What is the definition of compliance?
Ability of lungs to expand in response to an increase in pressure
What does hysteresis refer to?
Unrecoverable/delayed recovery of energy in a system
What factors contribute to hysteresis?
Surface tension
Part of respiratory cycle occuring
What is greater at all times in deflation: volume or pressure?
Volume
Why is compliance measured on the inspiration wing of the pressure-volume loop?
Inspiration wing is complicated by the decrease in compliance at maximal expanding pressures
Deflation wing of the compliance curve is not as subject to experimenter technique and is more reproducible
Better understood - representing essential elastic recoil
Why does compliance decrease as volume increases?
Pressure increases also
Define elastance
Property of a body to return to its original size after being distorted by a force
What does elasticity depend on?
Elastin fibre content
SURFACE TENSION
What are the functions of alveolar fluid?
Physical barrier protecting monolayer of cells exposed to air
Solvent for surfactant, cytokines, antimicrobials etc
Medium in which macrophages can move as one
How does fluid secretion in lungs work?
Active transport of Cl- accompanied by water flow from interstitium to air space
How does fluid absorption in lungs work?
Active transport of Na+ accompanied by water flowing down osmotic gradient
What is the role of surface tension in the respiratory system?
Acts to collapse small airways and alveoli, and increases the pressure
What does surfactant do?
Reduce surface tension in alveoli
Makes it easier to inflate lungs
What type of cells secrete surfactant?
Type II alveolar cells
What is surfactant made up of?
90% phospholipids 10% proteins
What is the formula for the work of breathing?
ΔPΔV/Δt
What does the energy used to breathe overcome?
65% - elastic resistance
35% - airway resistance
What is the work of breathing increased by?
Increased airway resistance
Decreased lung compliance
Decreased thoracic compliance
What are the implications for the increased work of breathing?
Increased force and duration of muscle contraction
Increased O2 consumption
Respiratory muscle fatigue
