Respratory Physiology II Flashcards
How is alveolar ventilation calculated?
PaCO2 = CO2 / Alveolar ventilation
= K X Vco2/Qa
K = .863 ml/min
Differentiate Hypo/hyperventilation
Hypo -> If ratio is high, PA CO2 rises
Hyper -> If ratio is low, PaCO2 is low
What is normal alveolar ventilation?
4.3 L/min
What is the alveolar gas equation?
PaO2 = (Patm - 47) X FIO2 - PACO2[FIO2 + (1-FIO2)/R]
How is PAO2 calculated at seal level on room air?
PAO2 = 150 - (1.2 X PACO2)
How is transmural pressure and compliance different for alveoli at different parts of lung?
Lower down:
- Higher pressure
- Less transmural pressure
- Higher compliance
What is the time constant?
A measure of the rate of change of filling and emptying of the lungs
What is the total amount of O2 carried in the blood?
20 ml O2/dL
How much O2 does a human need delivered per minute?
300 ml O2/dl/min
What four main factors determine diffusion of O2 across the membranes?
- Area
- Thickness
- dP
- Diffusion coefficient
How is Lung Diffusion capacity calculated?
DL = ml O2/min f/ Alv to blood / PAO2 - PaO2
How does reduced ventilation affect changes in blood content and pressure for O2 vs CO2?
O2 concentration changes very little with decreased ventilation and decreased pressure
CO2 concentration changes much more with changes in CO2 Pressure and decreased ventilation
What is Hypoxemia?
Low PaO2
What are factors which cause Hypoxia and/or hypoxemia?
Low FIO2 —> Fire
Low pATM
Low QA —> Airway resistance
Low V/Q
Low DL
R-L Shunt —> Bypasses alveoli
Hematological Hypoxia —> Anemia/ CO poisoning
Ischemic Hypoxia —> Low Systemic blood flow to area
Histotoxic Hypoxia —> Cyanide poisoning
How does V/Q differ from base to top of lung?
Top: Lower Perfusion than ventilation; High V/Q
Bottom: Higher perfusion and higher ventilation, but Vis lower than Q; Low V/Q
What occurs from a change in CO2?
Increase: Hypercapnea —> Respiratory Acidosis
Decrease: Hypocapnia —> Respiratory Alkalosis
How does a pulmonary embolism affect V/Q?
Blocked vessel —> Less perfusion and Hypoxemia —> Lower V/Q
How does hyperventilation affect V/Q?
Increased Ventilation —> Hyperoxemia + Hypocapnia —> Increased V/Q
What is Hypoxia vasoconstriction?
When alveoli have low perfusion, Veins will constrict and shunt blood to other alveoli
What makes up the physiological shunt?
Anatomical shunt + Intrapulmonary shunts
Intrapulomonary shunts —> Zero gas exchange; Low V/Q, etc
How is acceptable A-a gradient calculated?
Age/4 + 4
What do the peripheral chemoreceptors sense?
- O2
- CO2
- pH
What do central chemoreceptors sense in the blood?
- CO2
- pH
What is the pre-botzinger complex?
Possible pacemaker region in VRG.
