cvpr physiology 2 Flashcards
What is the primary defect in perfusion limited O2 (normal health) CO2 N2O gas equilibrates early along the length of the capillary
Diffusion can be ↑ only if blood flow ↑
What is the primary defect in diffusion-limited O2
Gas does not equilibrate by the time blood reaches the end of the capillary
A consequence of pulmonary hypertension is cor pulmonale and subsequent right ventricular failure
Diffusion Vgas = A x D x (P1-P2)/T where A = area Dk= diffusion coefficient of gas P1-P2 = pressure difference
Manipulations of the diffusion equation in emphysema
A↓ in emphysema
Manipulations of the diffusion equation in pulmonary fibrosis
↑T in pulmonary fibrosis
What is DLCO
Diffusing capacity of the lungs for carbon monoxide (DLCO) is a medical test that determines how much oxygen travels from the alveoli of the lungs to the blood stream.
DLCO a good measure of lung disease severity
The extent to which CO, a surrogate for O2 passes from air sacs of lung into blood Pg 650
Equation for Pulmonary vascular resistance
PVR = (P pulm artery - PL atrium) / Cardiac output
What is hypoxemia
(↓PaO2)
Alveolar gas equation
PaO2 = PIO2 - PaCO2/R PAO2 = alveolar PO2 (mmHg)
PIO2 = PO2 in inspired air (mmHg) PaCO2 arterial PCO2 (mmHg)
R = respiratory quotient = CO2 produced/O2 consumed A-a gradient = PAO2 - PaO2
Normal range = 10-15 mmHg
↑ A-a gradient may occur in hypoxemia
Causes of ↑ A-a gradient
Shunting, V/Q mismatch, Fibrosis (impairs diffusion)
What is hypoxia?
(↓O2 delivery to tissue)
Causes of hypoxia
4 listed
- ↓ cardiac output
- Hypoxemia
- Anemia
- CO poisoning
What causes hypoxemia?
Normal A-a gradient
High altitude
Hypoventilation (eg opioid use)
↑ A-a gradient
V/Q mismatch
Diffusion limitation
Right-to-left shunt
What is Ischemia?
(Loss of blood flow)
Causes of ischemia
2 listed
Impeded arterial flow or ↓ venous drainage
Ventilation/perfusion mismatch
Ideally ventilation is matched to perfusion (ie V/Q = 1) for adequate gas exchange
Lung zones and V/Q properties
V/Q at apex of lung = 3 (wasted ventilation)
V/Q at base of lung = 0.6 (wasted perfusion)
Both ventilation and perfusion are greater at the base of the lung than at the apex of the lung
Effects of exercise on V/Q matching
With exercise (↑ Cardiac output) there is vasodilation of apical capillaries → V/Q ratio approaches 1
Organisms in the lung
Some organisms that thrive in high O2 (eg TB) flourish in the apex
V/Q = 0 = 0
“oirway” obstruction (shunt), In shunt, 100%, O2 does not improve PaO2 (eg foreign body aspiration)
V/Q = ∞
Blood flow obstruction (physiologic dead space) Assuming <100% dead space, 100% O2 improves PaO2 (eg pulmonary embolus)
Methods of CO2 transport 3 listed
HCO3- (70%)
Carbaminohemoglobin or HbCO2 (21-25%)
CO2 bound to Hb at N-terminus of globin (not heme)
CO2 favors deoxygenated form (O2 unloaded)
Dissolved CO2 (5-9%)
In lungs oxygenation of Hb promotes dissociation of H+ from Hb
This shifts equilibrium toward CO2 formation Therefore CO2 is released from RBCs (Haldane effect)
Describe the Bohr effect
In peripheral tissue ↑H+ from tissue metabolism shifts curve to the right unloading O2 (Bohr effect)
The majority of CO2 is transported as?
HCO3- in the plasma
