Equations Flashcards
Flow (F or Q)
deltaP / R
P= pressure difference between atm and alv
R= resistance
minute ventilation (Vmv)
Vi x f
Vi= tidal volume
f= respiratory rate
alveolar ventilation (Valv)
(VT - VD) x respiratory rate
VT= tidal volume
VD= dead space
slow, deep breaths increase alveolar ventilation
Pressure (P)
F/A
F= force
A= area
ideal gas law
PV= nRT P= pressure V= volume n= moles R= gas constant T= temperature gas phase: BTPS liquid (blood): STPD
Boyle’s Law
P1V1 = P2V2
at constant T and constant number of molecules
Trans-respiratory system pressure (Prs)
Palv - Patm
determines air movement in/ out of lungs
Palv= alveolar pressure
Patm= atmospheric pressure
transpulmonary or transmural pressure (Ptp)
Palv - Pip Palv= alveolar pressure Pip= intrapleural pressure determines inflation of lung positive: lung inflated
Compliance (C)
deltaV/ deltaP
V= lung volume
P= Palv
Laplace’s Law
P= 2T/r T= tension; r= radius, P=pressure
Resistance (R)
(8nl)/ (πr^4) n= viscosity l= length r= radius medium bronchioles: highest resistance (small ones are in parallel
Partial pressure of oxygen (Po2)
Patm x FIO2
Fo2= oxygen percentage= 0.21
Partial pressure of oxygen inspired (PIO2)
(Patm- partial pressure of water vapor) x FIO2
partial pressure of water vapor= 47 mmHg
Fo2= 0.21
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
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
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
Alveolar PO2 (PAO2)
PIO2- (PaCO2/R)
PIO2= inspired O2
PaCO2= arterial PCO2
R= CO2 production/ O2 consumption
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
