L13 - respiratory physiology - volumes and pressures Flashcards
define tidal volume (Vt)
total vol of air breathed in and out in one breath at rest
define inspiratory reserve volume (IRV)
the max amount the lung vol can be increased by above Vt (forceful inhale)
define expiratory reserve volume (ERV)
further vol that can be exhaled forcefully after Vt
what is residual volume (RV)
volume left in lungs after max expiratory effort (cant be measured)
what is inspiratory capacity
vol of air that can be inhaled in one forceful inhale (Vt + IRV)
what is expiratory capacity
vol of air that can be exhaled in one forceful exhale (Vt + ERV)
what is vital capacity
max volume of air breathed in and out in one forceful breath (ERV + Vt + IRV)
what lung capacities can a spirometer measure
any not involving RV
what is total lung capacity
RV + ERV + Vt + IRV
define alveolar ventilation
vol of fresh air entering alveoli every min
Va
define alveolar minute ventilation
total ventilation per minute (Ve)
what is the equation for alveolar minute ventilation
Ve = R x Vt
R= breathing rate - breaths per min Vt = tidal vol
why are Va and Ve different
because gas exchange doesn’t occur in conducting zone so isn’t fresh air
what is anatomical dead space?
air in the pharynx to terminal bronchioles (conducting zone)
what is the value for anatomical dead space
~150ml (fixed)
what is the equation for Va
Va = Ve - Vd
Vd = breathing rate x 150 (dead space vol)
what is Vd
dead space ventilation (breaths per min x dead space vol)
explain physiological dead space
in healthy lungs physiological ds = anatomical ds
if some alveoli have poor blood supply there will be no gas exchange there (alveolar dead space)
equation for physiological Dead space
physiological ds = 150 + alveolar dead space
what is the equation that shows how lung ventilation occurs
flow = change in pressure (Palv - Patm)
___________
resistance
what is boyles law
if vol increases = pressure decreases
if vol decreases = pressure increaes
what is intrapleural pressure (Pip)
pressure between the pleural membranes
what is balanced at FRC?
inward recoil of lungs and outward recoil of chest wall
what happens to the pleural membranes at FRC?
inward recoil of lungs and outward recoil of chest wall pull the membranes apart slightly creating a small pressure for Pip
what is Palv at FRC?
0
function of Ptp
the force that makes alveoli expand in response to chest wall expansion
describe sequence of events (and pressure changes ) during inspiration
- chest wall expands
- Pip falls (more -ve)
- causes Ptp to increase causing alveoli to expand
- Palv decreases due to increased volume
- Palv
describe sequence of events (and pressure changes ) during expiration
- chest wall recoils inward
- Pip increases (less -ve)
- causes Ptp to decrease
- expanded lungs recoil compressing alveoli
- Palv > Patm so air forced out
what causes Pip to increase
expiration
what happens to Ptp when Pip
increases
decreases
Ptp does the opposite
decreases
increases
what causes alveoli to expand
increase in Ptp
what causes Pip to decrease
inspiration
