Pulmonary equations Flashcards
What is Laplace’s law?
Pressure = 2 X Surface tension/radius
What is the equation for lung compliance?
Change in lung volume/change in transpulmonary pressure
What is the equation for chest wall compliance?
Change in chest volume/change in transthoracic pressure
What is the equation for total compliance?
1/total compliance = 1/CW+1/CL
What is normal CW and CL?
200 ml/cm H2O
What is normal total compliance?
100 ml/cm H2O
What is the equation for oxygen content?
CaCO2 = (1.34 X Hb X SaO2) + (0.003X PaO2)
What is a normal oxygen content?
16-22
What is the equation for ventilation?
PaCO2 = VCO2/VE-VD
What is the equation for VE?
Tidal volume X RR
What is VE?
total minute ventilation
What is VD?
Dead space ventilation
What is the equation for alveolar ventilation?
VA = (VT-VD) X RR
What is the the equation for physiologic dead space?
VD = anatomic dead space + alveolar dead space
What is the normal dead space to tidal volume fraction?
0.3 = VD/VT
What is the equation for mixed venous saturation (SvO2)?
VO2/CO X Hb X 13
What is normal SvO2?
65-75%
What is normal PvO2?
35-45 mmHg
What is normal P50?
27 mmHg
What is P50?
the partial pressure of oxygen at which hemoglobin is 50% saturated
What is the normal V/Q ratio?
1
What does it mean if V/Q = infinity?
There is a perfusion problem - lots of dead space
What does it mean if V/Q is below 1
There is a ventilation problem (Interstitial lung disease)
What is an absolute shunt?
When there is perfusion, but no ventilation. V/Q = 0
What is the equation for a shunt fraction?
QS/QT = CcO2-CaO2/CcO2 - CVO2
What is a normal QS/QT?
0.1
What is the equation for partial pressure of oxygen in the alveoli?
PAO2 = (PB - PH2O) X FiO2 - (PaCO2/0.8)
What is the equation for the A/a gradient?
PAO2-PaO2
What is a normal A/a gradient?
10-20 mmHg
What is the equation for normal PaO2 associated with age?
102-age/3
What is the equation for normal PaO2 using FiO2?
5 X FiO2