Equations Flashcards by Savannah Smith

Flow (F or Q)

deltaP / R
P= pressure difference between atm and alv
R= resistance

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minute ventilation (Vmv)

Vi x f
Vi= tidal volume
f= respiratory rate

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alveolar ventilation (Valv)

(VT - VD) x respiratory rate
VT= tidal volume
VD= dead space
slow, deep breaths increase alveolar ventilation

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Pressure (P)

F/A
F= force
A= area

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ideal gas law

PV= nRT
P= pressure
V= volume
n= moles
R= gas constant
T= temperature
gas phase: BTPS
liquid (blood): STPD

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Boyle’s Law

P1V1 = P2V2

at constant T and constant number of molecules

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Trans-respiratory system pressure (Prs)

Palv - Patm
determines air movement in/ out of lungs
Palv= alveolar pressure
Patm= atmospheric pressure

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transpulmonary or transmural pressure (Ptp)

Palv - Pip
Palv= alveolar pressure
Pip= intrapleural pressure
determines inflation of lung
positive: lung inflated

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Compliance (C)

deltaV/ deltaP
V= lung volume
P= Palv

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Laplace’s Law

P= 2T/r
T= tension; r= radius, P=pressure

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Resistance (R)

(8nl)/ (πr^4)
n= viscosity
l= length
r= radius
medium bronchioles: highest resistance (small ones are in parallel

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Partial pressure of oxygen (Po2)

Patm x FIO2

Fo2= oxygen percentage= 0.21

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Partial pressure of oxygen inspired (PIO2)

(Patm- partial pressure of water vapor) x FIO2
partial pressure of water vapor= 47 mmHg
Fo2= 0.21

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Concentration of gas (Cx)

alpha(Px)
alpha= solubility of gas in solution
Px= partial pressure
(this is for dissolved gas only; NOT bound gas)
CO2 greater solubility than O2

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Fick’s Law of Diffusion

rate of DIFFUSION
gas flow (vol/time) = (A x D x (deltaP)) / z
A= area
z= thickness
D= diffusion constant
P= partial pressure of gas

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Alveolar PCO2 (PACO2)

k (VCO2/Valv)
k= constant (863)
Valv= alveolar ventilation
VCO2= rate of CO2 production
at sea level: 100 mmHg is normal
determined by CO2 production: no CO2 in inspired gas
if CO2 production is constant, then PACO2 determined by alveolar ventilation

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Alveolar PO2 (PAO2)

PIO2- (PaCO2/R)
PIO2= inspired O2
PaCO2= arterial PCO2
R= CO2 production/ O2 consumption

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A-a gradient

PAO2- PaO2
PAO2= alveolar
PaO2= arterial
increased: indicates lung disease
normal: excludes structural lung disease
normal: (age + 4) / 4

Physiologic dead space (VD)

VT x (PaCO2 - PEco2) / Paco2
VT= tidal volume
PaCO2= arterial PCO2
PECO2= PCO2 of mixed expired air
estimate: using weight in pounds

O2 content of blood

(O2 binding capacity x % saturation) + dissolved O2 in plasma
NOT affected by hemoglobin

What does a right shift of the hemoglobin saturation curve indicate?
What factors affect it?

decreased affinity for O2: want in tissues

increased PCO2
decreased pH
increased T
increase 2.3-DPG

What does a left shift of the hemoglobin saturation curve indicate?
What factors affect it?

increased affinity for O2: want in pulmonary circulation

decreased PCO2
increased pH
decreased T (hypothermia)
Fetal Hb
decreased 2,3-DPG

2, 3 diphosphoglycerate

binds strongly to deoxygenated Hb, lowering its affinity for O2
increased in hypoxia

Factors that affect O2 content of blood

CO poisoning
anemia
hypoxemia
cyanide poisoning

What causes respiratory acidosis?

hypoventilation | ex: inhibition of respiratory center, paralysis of respiratory muscles, obstruction, poor gas exchange

What causes respiratory alkalosis?

hyperventilation | ex: stimulation of respiratory center, hypoxemia, mechanical ventilation

dorsal respiratory group (DRG)

provides rhythmic drive to ventral medullary group | causes inspiration

ventral respiratory group (VRG)

causes expiration in exercise (normally passive)

water vapor pressure (P(H20))

47 mmHg

fraction concentration of O2 (FIO2)

0.21

fraction concentration of N2 (FIN2)

0.78

tissue O2 consumption

250 ml/min

CaO2 (O2 content)

``` (K x Hb x SaO2) + O2 dissolved in plasma Hb= hemoglobin SaO2: O2 saturation of Hb K= 1.39 O2 dissolved in plasma= negligible and ignored= 0.003 x PaO2 normal= 20 ml/dl ```

respiratory quotient (R)

``` VCO2/VO2 VCO2= CO2 produced VO2= oxygen consumed normal: 0.8 depends on what we eat normal: 0.8 on 100% O2= 1 carbs= 1 fat= 0.7 protein: 0.8 ```

Delivery of O2 to tissues (DO2)

CO x CaO2 x 10 CO = cardiac output CaO2= O2 content 10= because CaO2 is ml/dl and DO2 is in ml/min Can: convert CO to mL (multiply by 1000), convert CaO2 to just ml (multiply by 0.001/0.1)

cardiac output (CO)

HR x SV HR= heart rate SV= stroke volume normal= 5L

diffusion coefficient (D)

(constant x alpha) / (square root MW) alpha= solubility CO2 diffuses 20x faster than O2 because it is more soluble

pulmonary vascular resistance (PVR)

(Ppa- PLa)/ CO Ppa= pulmonary artery pressure PLa= left atrial pressure (pulmonary wedge pressure) CO= cardiac output

pulmonary HTN

greater than 25 mmHg at rest

When do pulmonary vessels constrict?

low O2: depol of pulmonary vascular sm. muscle cells open voltage gated Ca channels, lead to Ca entry and cell contraction opposite of systemic

VA/Q

ventilation / perfusion

anatomic dead space (VDanat)

air that remains in the conducting airways at end inspiration increases with increasing lung volume

alveolar dead space (VDalv)

alveoli ventilated but not perfused decreases with exercise increase is ALWAYS pathologic