ventilation dynamics Flashcards
respiratory rate
calculation is Vm/Vt
or 60/TCT
number of breaths in one min
Vt (tidal volume)
formula
Vt=Vm/RR or Vt=V x Ti
can be expressed in L or mL
volumes of gas inhaled and exhaled during a normal breath
Vm ( minute ventilation)
total amount of gas inhaled and exhaled in one minute
Vm= RR x Vt
can be expressed in L or mL over a min !
V ( flow) dynamic
during inspiration diaphragm pushes down, external intercostal contracts, thoracic cavity expands. exhalation diaphragm goes up and thoracic cavity reduces, external intercostal relax.
v flow
V= Vt / Ti
expressed in mL/sec or L/min
speed of gas traveling through the airways.
Function of VT and Ti
TCT (total cycle time)
beginning of inspiration and end of exhalation
TCT= Ti +Te
TCT= 60sec /RR
expressed in sec or min
Ti ( inspiratory time)
length of inspiration (beginning of inspiration to end of inspiration)
Ti= TCT-Te
Ti= Vt/V
express in secs
Te (expiratory time)
length of expiration period (from beginning of expiration to end of exp.)
Te= TCT-Ti
expressed in sec
I:E ration
comparison of Ti and Te
(Ti/Ti) : (Te/Ti)
Ti is always one the only variable is Te
Driving pressure
pressure gradience (difference) that exist btw two areas.
Intrapulmonary pressure ( Palv)
alveolar pressure
pressure within the lungs
760mmHg (0mmHg) at rest
Transaiway pressure (pta)
pressure gradient that exists btw the mouth/ pahrynx and alveoli
Pta= Ptm- Palv
intrapleural pressure (Ppl)
usually neg ( makes lung want to shrink or collapse)
pressure within the pleura space
756 mmHg at rest (-4mmHg)
transpulmonary pressure
distending pressure (pressure distance btw alveolar and pleural space) Ptp= Palv-Ppl)
pressures during inspiration
Diaphragm contracts, moves downward, Thorax expands
Intrapleural (Ppl) and intra-alveolar (Palv) P Down: Alveolar Vol up
At this pt, intra-alveolar P is less than barometric P, gas moves into the lungs
Continues until equilibrium between barometric and P alv = end inspiration
Diaphragm stops downward movement
pressure during exhalation
Diaphragm and thorax relaxes
Thoracic Volume in Ppl and Palv
Palv becomes > than barometric P (PB)
Note: diaphragm continues to move upwards
Gas flows out of the lungs and Alveolar volume
This continues until Palv and PB reach equilibrium = end expiration
Ppl remains at resting level
Ppl regardless of the breathing cycle is always less than PB
PIP peak inspiratory pressure
pressure right at the beginning of air flow. (oral cavity)
Plateau pressure
pressure that’s in the lungs at the end of inspiration where there is zero flow. independent of resistance
plateau is always less than PIP due to RAW
raw
RAW is the resistance through the airway ( 6cmH2O)
usually takes 2 cmH20 of water from PIP
