Pulmonary & Bronchial Circulation - Quiz 3 Flashcards
(94 cards)
1
Q
Factors that vary blood flow throughout lung
A
Vascular Pressures
Gravity
Distensible Pulmonary Vessels
2
Q
The right ventricle ejection fraction into the lungs is equal to what?
A
Left Ventricular Cardiac Output
3
Q
Why is pulmonary pressure lower than systemic pressure?
A
Pulmomary flow is 10 x LESS resistant than systemic circulation
4
Q
Describe the wall of the Pulmonary Artery
A
Thin & Compliant - 1/3 thickness of Aorta
5
Q
What are the Pulmonary Vessels Divided Into
A
Alveolar and Extra-Alveolar
6
Q
Alveolor Vessels
A
- Related to Acini
- Capillary network gas exchange
- Directly affected by alveolar pressure
- High Positive pressure during lung expansion collapses vessels
- Capillaries can be compressed so that they contain no blood
7
Q
Extra-Alveolar Vessels
A
- the arteries and veins that move blood to/from respiratory units
- Large vessels: thick walls and connective tissue
- Not effected by lung pressures
- No compression during positive pressure
- Lung tissues pull these vessels open during lung volume expansion
- Bronchial Vessels: oxygenated blood from systemic circulation, 1-2% CO, empty into left atrium
8
Q
Alveolar vessels provide what kind of resistance to flow?
A
Longitudinal
2 Ways: Dimensions and Distensibility
(Dimensions NOT controlled by autonomic or hormonal)
9
Q
??????What are the mechanisms to decrease pulmonary vascular resistance as vascular pressures are raised
A
Recruitment (opening of closed vessels)
and
Distension (Increase in Caliber of Vessels)
10
Q
Pulmonary Capillaries
A
- Covers 70-80% of alveolar surface area
- Total Capillary surface area almost equals alveolar surface area
- RBC travels 600-800 micrometers thru network
- Blood volume = RV stroke volume
11
Q
Functional Capillary Volume
A
- Capillary volume increased by opening closed segments (recruitment)
- 1mL/kg normal volume (70mL)
- 200 mL at max volume
12
Q
How long does RBC remain in capillary network?
A
One Cardiac Cycle - 0.75 sec
13
Q
How much time does RBC need for gas exchange in the capillary network?
A
Less than 0.25 Seconds
14
Q
Pulmonary Circulation Volume
A
- TBV from pulmonary artery to LA: 500 mL
- Lung is 40%-50% blood by weight; > than any other organ
- Reservoir for LA, can alter volume from 50% to 200%
- Prevents blood return to RV from affecting LV diastolic fillimg pressures over 2-3 cardiac cylces
15
Q
How does increased CO effect Pulmonary Vascular Pressures?
A
Increases Pulmonary Pressure, but Decreases Pulmonary Resistance
16
Q
When does Recruitment Occur
A
During stress and increased tissue oxygen demand
17
Q
What is the chief mechanism for Decrease in Pulmonary Vascular Resistance
A
Recruitment
18
Q
What is Capillary Distension
A
Rise in internal vessel pressure - open capillary beds
19
Q
Elevated pressures in the _________ distends capilary beds.
A
Left Atrium
(Mitral Regurgitation, LV Failure)
20
Q
Capillary Distension
A
Leads to Lung Congestion and Heart Failure
Occurs at High Pulmonary Vascular Pressures
21
Q
What Happens to Capillary Volume During Exercise
A
- CO Increase
- Increase Pulmonary Arterial Pressure
- More Recruitment
- Volume doubles to give time for gas exchange during increased blood flow
22
Q
Pulmonary Blood Flow on Inspiration
A
- Greater Subatmospheric Pleural Pressure
- Increased pressure gradient for blood flow into thorax
- RV gets greater volume in diastole
- Increase venous blood return into thorax
- LV ejects less blood due to increased pressure gradient b/t LV and systemic pressures
23
Q
Pulmonary Blood Flow on Expiration
A
- Lower Pleural Pressure Gradient
- More positive thoracic pressure DECREASES venous blood return
- Decreased pressure gradient prevents venous blood return to RV
- Less RV ejection pressure
- Reduce gradient b/t LV and Systemic arteries allows increased stroke volumes
24
Q
How does PVR change with Lung volume close to FRC
A
Minimal Change
25
How does Higher and Lower lung volumes effect Pulmonary Vascular Resistance
Increased PVR
26
What happens to Extra-Alveolar vessels during Inspiration?
Dilation
* Diameter increased by radial traction and flow resistance
* Vessels receive more blood volume as higher alveolar pressure compresses vessels
27
What happens to alveolar vessels during inspiration?
Compression
* Capillary resistance increase during elevated alveolar pressures
* Pulmonary capillaries - major vascular resistance
28
How does mechanical positive pressure ventilation effect Alveolar pressure
Increases alveolar pressure
29
How does mechanical Ventilation effect Zone 2 Lung Volume
Increases amount of Zone 2 Lung Volumes relative to pulmonary venous pressure
30
How does the rise in Alveolar Pressure effect Zone 2
Increases resistance to blood flow in Zone 2
31
Positive-Pressure Ventilation can _______ CO or ________ V/Q imbalance.
Decrease CO and Increase V/Q Imbalance
32
What lung structures does the oxygenated blood from the aorta nourish?
* Conducting airways to Terminal Bronchials
* Parenchyma - pleura, interlobal septal tissues, pulmonary arteries and veins
33
How much Bronchial Blood Circulation returns to where via which vein?
50% returns to Right Atrium via Azygos Vein
34
How does the other 50% of bronchial blood exit lungs?
Exits through small anastomoses with pulmonary veins contributing to normal venous admixture - right-to-left shunt
35
What _system_ is critical to keep alveoli free of fluid moving from capillaries?
Lymphatic System
36
What forces tend to move fluid out of capillaries and how fast?
Hydrostatic starling forces at 20mL/hr
37
Interstitium
Lymphatics drain fluid from interstitium
Kept at a slight negative pressure
38
Fick Principle
* Method to measure CO, blood flow through lungs per minute
* O2 Consumption/min = Oxygen uptake by blood in lungs/min
* VO2 at rest: 300 mL/min
* Measures arterial and mixed venous blood and determines O2 consumption
* CO = O2 consumption (VO2) / Arteriovenous [O2] difference
39
Indicator Dilution Principle
* Inject Dye into venous circulation
* Diluted concentration measured on arterial side
* Thermodilution technique also used to measure CO
40
How does Gravity effect Systemic BP
* Degree of pressure change from heart level
* Pressure gradient of 0.74 mmHg / cm
* Postural dependent relationship with gravity
* Supine: Arterial pressure feet \> head
41
How does Gravity effect Pulmonary Circulation
* Greater changes in flow occur because pulmonary pressures are much lower
* Distribution of blood flow in lung affected by gravity
* Changes in pulmonary arterial pressure effect distribution of blow flow over height of lung
42
How does exercise effect blood flow to Lungs?
Converts entire lung to Zone 3 Flow
Increases blood flow 4-7x
43
What is Hydrostatic Pressure
The Pressure Effect gravity has on a Column of Fluid
* Alters potential energy of the fluid column
44
What are considered the Zero Reference Points?
The Right Atrium
and
Middle of Lung
45
How does Supine or Prone position effect Hydrostatic Pressure
Hydrostatic Pressures are minimized
46
How is Lung Perfusion effected by Gravity?
* Bottom/base of lung gets more of RV ejection fraction than the top of lung
* Hydrostatic pressure cause distension and recruitment of pulmonary capillaries in base of lung
47
What does Blood flow to Lungs depend on?
Pressures in Pulmonary vessels relative to Alveolar Pressure
* Pressures depend on:
* Hydrostatic Pressure
* Gravity
* Transmural Compressive Pressure
* Lung Volume
48
Lung Perfusion Zone 1
Does NOT receive blood flow
* PA \> Pa: Alveolar pressure \> Regional pulmonary blood pressure
* Pulmonary capillaries are collapsed by higher PA
49
Lung Perfusion Zone 2
Arterial-Alveolar Pressure Gradient drives Blood Flow
* Pa \> PA \> Pv
* Intermittent blood flow
* Water Fall effect - downstream venous pressure changes do not alter flow
50
Lung Perfusion Zone 3
Lung Base d/t Gravity
* Pa \> Pv \> PA
* Hydrostatic pressure cause distension and recruitment of pulm. capillaries -\> decreases resistance to blood flow
51
Lung Perfusion Zone 4
Abnormal Condition of Reduced Blood Flow
* Pa \> Pi \> Pv \> PA
* High Pulmonary Venous Pressure (LV Failure, Mitral Stenosis)
* Pulmonary edema - vascular cuffing
* Increased Vascular Resistance & reduced local blood flow
52
What are Lung Pressures dependent on?
Hydrostatic Pressure
Gravity
Transmural Compressive Pressure
Lung Volume
53
What creates the Lung Zones
Differences of Pulmonary arterial, venous, and alveolar pressures
54
What Factors Expand Zone 1
* Decreased Pulmonary Artery Pressure - shock, hypovolemia
* Increased Alveolar Pressure - PEEP
* Occlusions - PE
55
Factors that Reduce Zone 1
* Increased Pulmonary Artery Pressure - IVF, Blood Infusion
* Reduced Hydrostatic Effect - change in position, standing to supine
56
Pressure Flow Curves
Pulmonary-Hemodynamic Curve
* Assesses driving pressurs across pulmonary vasculature as CO varies
* Increased PA pressures w/ increased CO (exercise)
* PVR is change in pressure over CO
* PVR = Slope of line from point of orgin to point on curve
* Hypoxia raises resistance over entire curve
57
Pulmonary Vascular Resistance
Active Regulation of Blood Flow
* Active regulation occurs by altering vascular smooth muscle tone in arterioles
* Pulmonary capillary smooth muscle alters PVR
* Vasomotor tone of pulmonary vessels affected by many things
58
Vascular Innervation
* Motor innervation from sympathetic branch of Autonomic Nervous System
* Increase in sympathetic outflow = vasoconstriction - stiffening
* Sensory Innervation Adventitia - vascular stretching and chemicals
59
What is the most active regulation pulmonary vessels mediated by?
Local Metabolic Influences
60
Pulmonary Vasoconstrictors
* _Reduced PAO2_
* _Increased PCO2_
* _Histamine_
* Thromboxane A2
* Alpha-Catecholamines
* Norepi
* Angiotensin
* Serotonin
61
Pulmonary Vasodilators
Increased PAO2
Nitric Oxide
Beta Catecholamines
Dopamine
Prostacyclin
62
Thromboxane A2
Potent Local Vasoconstrictor
* Product of cell membrane arachidonic acid metabolism
* Constrictor of Pulmonary Arterial & Venous smooth muscle
* Produced during acute lung tissue damage by macrophage, leukocytes, and endothelial cells
* Effect localized to injured region d/t half-time of thromboxane inactivation is only seconds
63
Prostacyclin
Prostaglandin I2 - Potent Vasodilator
* Inhibits platelet activation
* Produced by endothelial cells
* Product of arachidonic acid metabolsim
64
Nitric Oxide
Epithelial Vasodilator
* **_Potent endothelium-derived endogenous vasodilator_**
* Strictly localized effect
* Formed from L-arginine lead to **_smooth muscle relaxation through synthesis of cyclic GMP_**
* **__**Activates guanylyl cyclase and increases cGmp
* Basis for how **Nitroglycerin and Sodium Nitroprusside wrok**
* Very Toxic
* Methemoglobinemia - HGB doesnt let go of oxygen to tissues
65
What is the critical factor governing pulmonary circulation?
Partial Pressure of Oxygen (PAO2) in Alveoli
66
PO2 in alveoli is _________ important than oxygen tension in mixed venous blood
MORE
67
What does Oxygen Diffusion into Pulmonary Arteriole Walls Cause?
Cause Smooth muscle dilation
* As alveolar oxygen tension decreases - surrounding aterioles constrict
* Low alveolar PO2 - increase in local vascular resistance
* Blood flow shifted to area of lung with higher PO2
* These small changes in local resistance do not effect overal PVR
* (If \< 20% of lung volume involved)
68
How does global reduction in alveolar oxygen tension effect PVR?
Increases total PVR by constriction of arterioles and small arteries
69
What does Alveolar Hypoxia Cause
Hypoxic Pulmonary Vasoconstrction (HPV)
* _Localized_ response of pulmonary arterioles
* Enahnced by hypercapnia and acidosis
* Contraction of smooth muscles in region of hypoxia
* Important mechanism of balancing V/Q ratio
* _Shift of flow to better ventilated areas_
* Happens because less Nitric Oxide in hypoxic area.
70
Pulmonary HTN
* High PVR
* Generalized alveolar hypoxia increases total pulmonary resistance
* Hypoventilation
* Low Inspired PO2, Increased PCO2
* Pain
* Histamine Release
* High Altitudes
71
What causes increased work for the Right Ventricle?
Pulmonary HTN
* RV Hypertrophy
* Tricuspid Regurg
* Right Heart Failure - Cor Pulmonale
72
Pulmonary HTN is considered a _________ pumonary vascular condition
SERIOUS
* Narrowing of small musclar pulm. arteries
* Increase in pulm. arterial pressure
* RV pressures rise to compensate until failure
* Lung Transplant ONLY effective treatment
73
Distribution of Ventilation
* Normal lung is more ventilated at base
* Difference between regional & local ventilation due to differences in airway resistance, compliance, and hydrostatic effects
74
Regional Nonuniform Ventilation
* Gravity causes hydrostatic interpleural pressure gradient
* Alveoli more expanded at top of lung than base
* Alveolar volume parallels lung compliance curve
* Regional lung volume changes vary b/c transpulmonary pressures influenced by interpleural pressure gradient
* Differences in transpulmonary pressure affect lung compliance
75
What causes Local Nonuniform Ventilation
Variable Airway Resistance and Localized Difference in Compliance
* Healthy lungs have equal constants in all acini
* Acini ventilation not as effected by hydrostatic pressure changes
76
Lower Lung Ventilation vs Apex of Lung
More ventilation to base than to top
* FRC is less at base
* Base compliance \> Top compliance
77
Local Ventilation Distribution
* Ventilation not even throughout lung
* Time constant establishes rate of acinar volume change
* Longer time constant = Slower Ventilation of Lung Unit
* Increased Resistance and/or Decreased Compliance = Longer Alveolar Filling Time
* Decreased compliance (stiff lung) reduces lung volume changes
78
V/Q Matching
Maintains PaO2 of 85-100 mmHg
* Distribution of VQ ratios not normally uniform
79
Alveolar-Arterial (A-a) PO2 Differences
Express Unequal Match of V/Q
* Normal PO2 differences are 10-15 mmHg
* Larger PO2 gradients indicate intrinsic pulm. disease - \> shunting
* Hypoxemia with normal PO2 gradient -\> hypoventilation
* V/Q mismatch is most common cause of inefficient gas exchange
* Wasted ventilation & venous admix cause abnormal PO2 differences.
80
Right to Left Heart Shunt
Pulmonary Venous Admixture
* Shunt = Perfused but not Ventilated
* Reduces systemic arterial oxygen tension and concentration
* Reduce efficiency of gas exchange
* Small shunts are normal b/c some venous blood bypasses lung to left heart
| (Allowing nonoxygenated right side heart blood to the left)
81
True Anatomical Shunts
Bronchopulmonary Venous Anastomoses
Intracardiac Thesbian Veins
Mediastinal Veins
Pleural Veins
82
What is Venous admixture of blood equivalent to?
Wasted Ventilation
83
Left-to-Right Heart Shunt
Pulmonary Venous Recirculation
* Part of CO returns to right heart without flowing through body
* Does not affect systemic arterial oxygen tension
* Increased Right Heart oxygen tension
* Location of increased oxygen concentration indicates site of L-to-R shunt
* Amount of change PO2 allows estimate of shunt
84
What kind of Regualtion of blood flow through capillaries occur in response to changes in Cardiac Output
Passive Regulation
* Increases blood flow - recruitment & distension
* Prevent rise in Pulmonary pressure with increase in blood flow
85
How much do alveolar walls contribute to total resistance?
40%
86
How much do alveolar arterioles contribute to resistance?
50%
87
How much do arterioles contritubute to systemic circulation resistance?
75%
88
Right Atrial Pressure
2-5 mmHg
89
Left Atrial Pressure
6 - 12 mmHg
90
Right Ventricle Pressure
25/0 mmHg
91
Left Ventricule Pressure
120/0 mmHg
92
Pulmonary Capillary Pressure
10.5 mmHg
93
Pulmonary Artery Pressure
25/8 mmHg
Mean: 15
94
Pressure of the aorta
120/80
Mean: 90
