Mechanics of ventilation 2 Flashcards
tidal volume - TV
amount of air inhaled or exhaled during normal quiet breathing w/o effort
inspiratory reserve volume - IRV
The maximum amount of air that can be inhaled after a quiet inhale
expiratory reserve volume - ERV
the amount of air that can be exhaled with maximum effort after normal inhalation
residual volume - RV
the amount of air remaining in the lungs after maximum exhalation
inspiratory capacity
maximum amount of air that can be inhaled - IRV
after quiet inhalation - TV
TV + IRV
Functional residual capacity
the amount of air remaining in the lungs - RV after quiet exhalation - ERV
Total lung capacity
RV + ERV + TV + IRV
Vital capacity
amount of air that can be exhaled w/ max effort - ERV after maximum inhalation - TV + IRV
cane be forced FVC or slow
FEV1 - Forced Expiratory Volume
amount of air that is exhaled during 1st second of forced exhalation after full inhalation
normal FEV1/FVC ratio
70-80%
low FEV1/FVC ratio indicates
increased lung resistance
how is inspiratory restrictive disease evident in spirometers
reduced lung compliance - limited lung expansion during inhalation
significant decrease in IRV and TV only
example of restrictive inspiratory disease
fibrosis -
how is expiratory restrictive disease evident in spirometers
weakness of accessory muscles in deep exhalation
decreased lung volumes - ERV,
and TLC
Signs of obstruction in spirometer
increased lung resistance, making it harder and slower to breath out - causes increased residual lung volume
normal vital capacity
reduced FVC
helium dilution technique
spirometer - V1 contains a measured conc of helium - C1
patient starts breathing in normal outside air in normal tidal volume
when the patient is at the functional residual capacity patient begins to inhale helium/air mixture until the air mixture has reached equilibrium with the tank and the patients lungs - FRC = V2 - V1
V2 = FRC + V1
volume of lungs - V2
Helium conc in lungs = C2
Initial amount of helium calculation
conc of helium = C1
Volume of spirometer = V1
C1 X V1
Final amount of helium calculation
C2 (V2 + FRC)
FRC calculation using the helium dilution method
C1 x V1 = C2 x V2
V2 = V1 + FRC
C1 x V1 = C2 x (V1 + FRC)
FRC = (C1 x V1)/C2 – V1
Process of body plethysmography
Patients sits in a “body box” (airtight chamber) and breathes through a mouthpiece
At FRC, the mouthpiece is closed
Patient tries to breathe in
consequences of body plethysmography
- Chest and lungs expand, pressure in lungs drop as volume increases
- Expanding chest compresses the air inside the chamber, air volume in chamber decreases, pressure in chamber increases
key principle in body plethysmography
Boyles law
P1V1 = P2V2
how can Boyle’s law to find ∆V
Change in lung volume: trying to find FRC and therefore ∆V
FRC = FRC + ∆V
Change of air volume in box:
V1 = V1 - ∆V
Change of pressure in box:
P1 = P1 + ∆P
P1 x V1 = (P1 + ∆P) x (V1 - ∆V) [Boyle’s Law]
- P1 x V1 = P1 V1 + ∆P V1 - ∆V P1 - ∆P ∆V
- ∆V = ∆P V1/ (P1+ ∆P)
how can Boyles law be used to find FRC in body plethysmography
P1 x FRC = (P1 - ∆P) x (FRC + ∆V) [Boyle’s Law]
FRC = ∆V(P1- ∆P)/ ∆P
lung volumes vary with
body size age sex muscular training posture race respiratory diseases
dead space
the volume occupied by gas in the lungs which does not participate in gas exchange.
3 types of dead space
anatomical dead space
physiological dead space
alveolar dead space
calculating dead space volume
tidal volume - alveolar volume
alveolar dead space
Air in alveoli that are surrounded by pulmonary capillaries without blood flow
when can alveolar dead space increase
pulmonary embolism
physiological dead space calculation
Anatomical Dead Space + Alveolar Dead Space
fowlers method nitrogen washout
messures conc of nitrogen exhaled
inspiration - N2 decline rapidly
exhalation - inclines rapidly but not to the same - mixture of dead space and alveolar gas magnitude and plateau
phase 1 of fowlers method
low N2 - end of inspiration
all of the dead space air - air in alveoli w/ no blood vessel to diffuse air into
only oxygen that has been exhaled
phase 2 of fowlers method
mix of dead space air and alveolar space air
Bohrs method
VT x PeCO2 = VA x PaCO2
tidal volume x expire partial pressure of CO2 = Alveolar space x partial pressure of CO2 in arterial blood of alveoli
how can we use Bohrs method to find dead space
VT x PeCO2 = VA x PaCO2 VT = VA + VD -> VA = VT - VD Replace VA with VT - VD VT x PeCO2 = (VT - VD) x PaCO2 VD = VT x [(PaCO2 - PeCO2)/PaCO2]
Pul. Ventilation
VT x f = VT x RR
VT = Tidal volume [L]
f = RR = respiratory frequency, respiratory rate [min-1
