Lung Volumes Flashcards
Vt
TLC
RV
Volume inhaled or exhaled each breath
Volume in lung after max inspiration
Volume remained in lung after max exp
VC
FRC
Max volume that can be exhaled after max inspiration
Volume remaing in lung after normal expiration
IRV
ERV
IC
Max volume inhaled starting at end of normla inspiration
Max volume exhaled starting at end of normal expiration
Max volume that can be inhaled starting at end of a normal expiration
What influences lung volume (non-postural)
Age, height and gender…as age and heigh increase, vital capacity decreases
What cannot be measured by spirometry?
RV, TLC, and FRC
Postural influences on LVs
Difference generated by weight of abdominal contents and more exaggerrated in obese patients
Sitting or standing has lower IRV with higher ERV…TLC and VC are the same…this makes IC lower in sitting and standing and FRC higher
Equation TLC
TLC = FRC + IC = VC + RV
Lung dz effects
Restrictive - lower everything…change in elastic property of the lung…TLC and FRC lowered with VC
Obstructive - increase in airway resistance…higher TLC and FRC…but VC compromised
FRC determination helium
Helium dilution method
Helium not taken up by pulmonary blood circulation
Inital amount of helium in system - C1 * V1
After = C2 * (V1+FRC)
FRC=(V1(C1-C2))/C2
Body plethysmograph method
Uses Boyle’s law
P*V=constant
Patient instructed to exhale against a closed shutter at the mouthpiece…pressure in lung will increase and pressure in box will decrease
Difference of measurement methods
SHould not be different in healthy
If individual has a portion of the lung obstructed, then they are not exposed to helium…technically still part of FRC but cannot be detected by helium…body pleythysmoraphg method CAN detect this
FRC by body plethysmograph also called
Thoracic gas volume
Why is body plethysmograph method often higher than helium?
Alveoli distal to obstruction cannot be reached by helium gas…bc of compressibility of tthe air, it can still be changed so included with body plethysmograph
Difference between two can suggest obstruction in the intra-pulmonary airways
