Respiratory - Systemic/Pulmonary Circulation Flashcards
Systemic circulation pathway
LV -> aorta -> body
Pulmonary circulation pathway
RV -> main pulmonary artery -> lungs
The lungs receive the entire right ventricular cardiac output
What are the 2 pathways of circulation in the pulmonary pathway?
Pulmonary Circulation
Bronchial Circulation
Define:
Pulmonary Circulation
What is its job? What feeds it?
Job: Perfuse alveoli for gas exchange
Arises from R
Receives 100% RV output
Define
Bronchial Circulation
What is its function? What feeds it?
Job: Meet the needs of the lung similar to coronaries for the heart - nourishes conducting airways and parenchyma up to terminal bronchioles
Arises from the aorta
Part of the systemic circulation
Receives 2% of LV output
Everywhere that needs O2 but no gas exchange
How does the bronchial circulation function?
Blood from bronchial circulation (deoxygenated) mixes with O2 - enriched blood in the pulmonary vein; contributes to the small A-a O2 difference
Characteristics of Pulmonary Circulation
Flow/Pressure/Resistance/Compliance
High Flow
Low Pressure
Low resistance
High compliance
Pulmonary Flow =. Systemic Flow
Why is the pulmonary circulation low pressure?
Only need to pump to top of the lungs
RV is weak
Not as much redirection of blood
Why is resistance lower in the pulmonary circulation?
Pulmonary arteries shorted, in dilated state (lg diameter)
Pulmonary arterioles are thin walled, have less smooth mucle and lower resting tone
More distensible (7X more compliant)
Enormous number of capillaries, in unique arrangement to create sheets of blood flowing past alveoli
High compliance = less work, relied on weak pump RV
What are the 3 factors that alter pulmonary vascular resistance?
Changes in blood flow (perfusion)
Changes in lung volume
Changes in local O2 concentration
How does changing blood flow affect pulmonary vascular resistance?
Increase pulmonary artery pressure -> decrease pulmonary vascular resistance (PVR) due to recruitment and distention
Open more artiers to stop increasing resistance
Exercise
How does changing lung volumes affect Pulmonary Vascular Resistance?
Pulmonary resistance follows a U shape curve with resistance lowest at FRC
How do changes in local O2 concentration affect PVR?
Hypoxia (low O2) causes constriction
opposite of systemic smooth muscle
What is the major difference between the pulmonary and systemic circulation?
Pulmonary vsculature is not significantly regulated by ANS
What is the relationship between CO, Pulmonary Blood Flow, and Resistance?
Increase CO (exercise) -> Increase PBF -> increase resistance
Capillary recruitment
All available vessels not open at rest (esp. at apex) b/c low perfusion pressure
Helps decrease Resistance
Capillary distention
Increase diameter with minimal pressure
Help decrease R
What are the two types of pulmonary vessels?
Extra-alveolar (arteries, veins)
Alveolar (arterioles, caps, venules)
What influences extra-alveolar vessels?
Not influences directly by PA due to location
Subject to Pip
Far from alveoli
What influences alveolar vessels?
Capillaries within interalveolar septa
Subject to PA
close to alveoli - increase alveoli size, increasse R
Inspiration
At high lung volumes…
Pip/Extra-alveolar/Resistance
Pip more negative -> increase transmural pressure -> distended extraalveolar vessels -> Decreases resistance
Increase alveolar diameter, crushing alveolar vessels (increase R)
Experience resistance
Expiration
At low lung volumes
Pip, alveolar diameter, extraalveolar vessels
Pip more positive - compresses extra alveolar vessels (Increase R) -> Alvelar diameter decreases (Decrease R)
Where is PVR lowest? When does it increase?
PVR is lowest at FRC and increases at lower and high lung volumes
resistance additive because vessels are in series
Define
Hypoxia
Low O2 in alveoli
Define:
Hypoxemia
Low O2 in blood -> triggers vasoconstriction
No dilation (Hypoxic vasoconstriction)
Why would we want to deliver blood to a region of lung that has low O2?
We want to match ventilation and perfusion
O2 influences..
Vascular Diameter
CO2 influences
Airway diameter
In an upright person, blood flow is highest…and lowest..
Highest near the base and lowest near the apex
gravitational effect contributes to uneve distribution of BF
When leaving the pulmonary artery, blood must…
travel up to the apex
Every 1 cm above heart, hydrostatic pressure in the arterials dropos
gravity effects blood flow in the veins too
Regional distribution of blood flow in the lungs is due to:
Effects of gravity on hydrostatic pressure
Influence of alveolar pressure on alveolar vessels
Lungs divided into 3 zones based on pressure affects on capillaries
Pressures affecting pulmonary blood flow
Zone 1
What is it? Characteristics , occurance, etc.
Apex
occurs when PA> Pa
Pulmonary capillaries collapse; no flow
created when alveolar pressure is increased (positive pressure ventilation) or arterial pressure is decreased (hemorrhage)
Increases alveolar dead space: ventilated, not perfused
Pressures affecting pulmonary blood flow
Zone 2
What is it? What happens here?
Middle 1/3 of lung
Primary area of distension, recruitment of vessels during exercise
Flow increases enough to pass alveoli
Pa > PA -> drives flow
PA > PV, PA partially collapses downstream capillarieis
Pressures affecting pulmonary blood flow
Zone 3
What is it? What occurs here?
Pa > Pv > PA
Optimal gas exchange; V/Q = 0.8-1.0
Normal Pressure
Define
Bulk Flow
What is it? What causes it? When does it occur?
How gas moves in airways from trachea to alveoli
Due to mass movement - like water out of faucet
Occurs when there are differences in total pressure
Define
Diffusion
What is it? Why?
How gas moves in us from air -> liquid; liquid -> air
gases moving due to their individual pressure gradients
What 2 factors determine gas diffusion?
Diffusion properties of membrane (Fick’s Law)
Pulmonary Capillary Blood Flow
Fick’s law- Vgas = [AxDx(P1-P2)]/T
Fick’s Law of Diffusion
Diffusion of a gas across a sheet of tissue is dependent on:
Partial Presure Gradients (ΔP)
Surface area of membrane (A)
Thickness of membrane (T)
Diffusion constant (D) - solubility of gas/MW
Fick’s Law of Diffusion
According to Fick’s Law, kwhat is the major determinant of rate of diffusion of a gas?
Partial Pressure gradients (ΔP)
Fick’s Law of Diffusion
Rate of diffusion increases, as partial pressure…
increases
Fick’s Law of Diffusion
Rate of Diffusion increases, as surface area…
Increases
Fick’s Law of Diffusion
Rate of Diffusion increases, as thickness…
Decreases
Increase thickness, decrease rate
Fick’s Law of Diffusion
Rate of diffusion increases, as the diffusion constant…
Increases
Fick’s Law of Diffusion
What might cause thickness of the membrane to increase?
Edema
Pneumonia
Fibrosis
O2 is found in the blood in what two forms?
Physically dissolved
Bound to Hemoglobin (Hb)
Transport of O2 in Blood
Physically Dissolved
O2 is poorly soluble in body fluids
Amount dissolved is directly proportional to PO2
Makes up about .3 mL of total O2 content in arterial blood
Transport of O2 in Blood
Bound to Hemoglobin (Hb)
O2 bound to Hb does not contribute to PO2 in blood
Enhances carrying capacity of blood
Most O2 is bound to Hb (98.5%, 19.7 mL/20)
Binding is reversible
What does Blood PO2 measure?
The portion of O2 dissolved in the blood
It is not a measure of total O2 content in blood
Transport of O2 in Blood
Oxyhemoglobin
Hb with bound oxygen
can have up to 4 O2 on 1 Hb -> saturated
bright red
Transport of O2 in Blood
What is the importance of Saturated Hb?
It is relatively unstable and easily releases O2 in regions where the PO2 is low
Transport of O2 in Blood
Deoxyhemoglobin
Non-O2 bound Hb
Deep maroon
The amount of HbO2 is a function of
PO2 in blood
When blood PO2 is high, what happens to Hb?
Form HbO2 (increased % saturation)
When blood PO2 is low, what happens to Hb?
O2 is released from Hb
Decreased % saturation
The PO2 is the primary factor determining…
the % Hb saturation
Define
SO2
% saturation of Hb with O2
(O2 actually bound to Hb/Potentially bound to Hb) x 100
What effect does O2 binding have on Hb?
Binding of O2 to each heme group increases affinity of the Hb to bind additional O2
What is it?
The Oxyhemoglobin Dissociation Curve
How plasma PO2 affects O2 loading and unloading from Hb
What does P50 mean?
Hb is 50% saturated
Advantages of S shaped curved:
Plateau
Enables O2 to saturate Hb in lungs (high PO2)
At a PO2 of 60, Hb is 90% percent
Increases above 60, hve minor effect on Hb sat
If PO2 drops from 100 -> 60, Hb sat still 90%
Large range of PO2 Hb can still be loaded
Advantages of S shaped curved:
Steep
Gives up large amounts of O2 in tissues
Small change in PO2 that leads to large drop in HbO2
Hb results in a large net transfer of O2 by…
Keeping PO2 low
Blood PO2 depends only on….
Concentration of dissolved O2
Hb acts as a…
storage depot for O2
How does Hb interact with O2?
Why is it important?
Hb acts as a storage depot for O2, removing it from solution as soon as it enters blood from alveoli
allows more O2 to enter blood
Once bound to Hb, O2 molecules no longer exert any pressure
Oxyhemoglobin Dissociation Curve
A shift in either direction has the greatest effect on which phase?
Steep
Oxyhemoglobin Dissociation Curve
Right Shift
What effect does it have to HbO2 binding? What does it do?
Decrease in Hb’s affinity for O2
Increase in P50 (when 50% of Hb is saturated with O2
Aids in release/unloading of O2
What factors besides PO2 can shift the oxyhemoglobin dissociation curve?
CO2
Acidity
2,3 diphosphoglycerate
Exercise
Temperature
CADET face right -> factors shift curve right
Why is CO so dangerous to us?
CO and O2 compete for Hb binding sites
CO out competes CO2 and shifts the curve to the far left -> inhibiting the unloading/delivery of O2 to tissues
What 3 ways is CO2 transported in the blood?
As bicarbonate ions (main transporter)
Physically dissolved
Chemically bound to Hb
Total CO2 content in arterial blood is 59 mL CO2/100 mL blood
What tells us how much O2 is in the blood?
CaO2
To answer “how much” need to know how much O2 bound to Hb
CaO2 - total O2 content in blood; given by SaO2 and Hb content
What does PaO2 tell you?
O2 molecules dissolved in plasma
adequacy of gas exchange within the lungs when it is subtracted from calculated PAO2
What does SaO2 tell you?
Heme sites occupied by O2 (saturated)
The % of all the available heme binding sites saturatrd with O2
Mainly determined by PaO2
What does CaO2 tell you?
Directly reflects the totaly number of O2 in arterial blood (bound and unbound)
incorporates Hb content
Calculate by oxygen content equation
PaO2 is determined by…
PAO2 and the state of alveolar capillary membrane (not by amount of Hb available to soak up)
PaO2 determines…
the O2 saturation of Hb
What determines the total amount of O2 in blood or CaO2?
The SaO2, the concentration of Hb, and PaO2
On one visit, a patient has a PaO2 of 85 mmHg, an SaO2 of 98% and a Hb of 14 gm/dlm. One year later, her Hb is 7 gm/dl. Assuming no lung disease, what will her new PaO2, SaO2, and CaO2?
PaO2 unchanged, SaO2 unchanged, CaO2 reduced (half)
Which patient is more hypoexemic?
A: PaO2 85 mmHg., 85% SaO2, 95% Hb 7 gm%
B: PaO2 55 mmHg, SaO2 SaO2, Hb 16 gm %
Total O2
A: PaO2 85 mmHg., 85% SaO2, 95% Hb 7 gm%
APEX Summary
Decreased Blood flow
Decreased ventilation
Increased V/Q ratio
PaO2
PaCo2
Base Summary
Increased blood flow (over perfused)
Increased ventilation
Decreased V/Q ratio
Decreases PaO2 (blood not fully oxygenated)
Increases PaCO2
The functional importance of V/Q ratios is…
Matching regional ventilation to blood flow
Alveolar (A) - arterial (a) difference in PO2
Measure of gas exchange efficiency across alveolar-capillary membrane
PAO2 - Calculated, PaO2 - measured
Normal P(A-a)O2: < 20 mmHg. What causes this?
Normal V/Q mismatch
Return of bronchial and coronary blood (deoxygenated) through the thesbian veins to the left side of her heart
_ helps determine cause of hypoxia
A-a O2 gradient
What are the 5 causes of Hypoxemia?
Hypoventilation
Low inspired O2
Right-to-left-shunt
V/Q mismatch
Diffusion impairment
Hypoventilation
Not ventilating well
When would you have low inspired O2, resulting in low PO2.
High altitude
How does the right-to-left shunt work?
Send deoxygenated blood into oxygenated
Hypoxemia: Effects on PaO2, increasing A-aO2 difference, FiO2 = 1.0
Hypoventilation
PaO2 = decreased
Inc to A-aO2 difference = no (unchanged)
FiO2 = Increased
FiO2 = fraction of O2 in inspired air
Hypoxemia: Effects on PaO2, increasing A-aO2 difference, FiO2 = 1.0
Low PIO2
PaO2 = decreased
Inc to A-aO2 difference = no (diffusion unchanged)
FiO2 = Increased
FiO2 = fraction of O2 in inspired air
Hypoxemia: Effects on PaO2, increasing A-aO2 difference, FiO2 = 1.0
Right-to-Left Shunt
PaO2 = Decreased
Inc to A-aO2 difference = yes (Increase, O2 volume in arterial is diluted)
FiO2 = No (mostly; PO2 doesn’t improve)
FiO2 = fraction of O2 in inspired air
Hypoxemia: Effects on PaO2, increasing A-aO2 difference, FiO2 = 1.0
V/Q mismatch
PaO2 = Decreased
Inc to A-aO2 difference = yes (increased, not good match)
FiO2 = Increased
FiO2 = fraction of O2 in inspired air
Hypoxemia: Effects on PaO2, increasing A-aO2 difference, FiO2 = 1.0
Diffusion Limitation
PaO2 = Decreased
Inc to A-aO2 difference = Yes (Increased, thickened)
FiO2 = Increased
FiO2 = fraction of O2 in inspired air
In which of the following states would the oxygen content of alveoli (O2=100) resemble the trachea (O2 = 150, CO2=0)?
A. Emphysema
B. Pulmonary Fibrosis
C. Pulmonary Embolism
D. Foreign body obstruction distal to trachea
E. Exercise
Pulmonary Embolism
Clot blocks blood flow to lungs - no gas exchange
Which of the following causes of arterial hypoxemia is NOT associated with an increase in the alveolar-arterial (A-a)O2 gradient?
A. V/Q mismatch
B/ Right-to-left shunts
C. Hypoventilation
D. Diffusion Limitation
Hypoventilation
