Ch 4 Blood Flow Part 2 Flashcards
What happens to pulmonary vascular resistance as pulmonary arterial or venous pressure increases?
Pulmonary vascular resistance falls
This is due to recruitment of previously closed capillaries and distension of capillary segments.
What are the two main mechanisms that cause a decrease in pulmonary vascular resistance with increased pressure?
- Recruitment of capillaries
- Distension of capillaries
What is recruitment in the context of pulmonary vascular resistance?
Opening of previously closed capillaries
What does distension refer to in pulmonary circulation?
Increase in caliber of capillary segments
How does lung volume affect pulmonary vascular resistance?
Resistance is low at large lung volumes and high at low lung volumes
What is the critical opening pressure in the pulmonary circulation?
The pressure that must be raised above downstream pressure for flow to occur
What substances increase pulmonary vascular resistance by causing contraction of smooth muscle?
- Serotonin
- Histamine
- Norepinephrine
- Endothelin
What substances relax smooth muscle in the pulmonary circulation?
- Acetylcholine
- Phosphodiesterase inhibitors
- Calcium channel blockers
- Prostacyclin (PGI2)
What principle can be used to measure pulmonary blood flow?
Fick principle
What does the Fick principle relate to in pulmonary blood flow measurement?
Oxygen consumption per minute (V·O2) and the difference in O2 concentration in blood entering and leaving the lungs
What effect does posture have on the distribution of blood flow in the lungs?
Blood flow distribution becomes more uniform when lying supine
What is zone 1 in the lung concerning blood flow?
A region where pulmonary arterial pressure falls below alveolar pressure, leading to no flow
In zone 2, how is blood flow determined?
By the difference between arterial and alveolar pressures
In zone 3, what determines blood flow?
The difference between arterial and venous pressures
What is hypoxic pulmonary vasoconstriction?
Contraction of smooth muscle in small arterioles in response to reduced Po2 in alveolar gas
What primarily determines the response in hypoxic pulmonary vasoconstriction?
The Po2 of the alveolar gas
How does blood flow distribution in the lung change during mild exercise?
Both upper and lower zone blood flows increase, reducing regional differences
What is the effect of gravity on blood flow distribution in the lungs?
Causes large differences in blood flow from bottom to top of the lung
What is the Starling resistor effect in the lung?
Blood flow behavior determined by the pressure difference between arterial and alveolar pressures
What happens to blood flow in the lung at low lung volumes?
Resistance of extra-alveolar vessels increases, reducing regional blood flow
What are the effects of lung collapse on pulmonary circulation?
Increases resistance due to smooth muscle tone, requiring higher pulmonary artery pressure for flow
What happens to capillary resistance when alveolar pressure rises relative to capillary pressure?
Capillaries tend to be squashed, increasing their resistance
What can cause an increase in pulmonary vascular resistance at high lung volumes?
Stretching of capillary walls reduces their caliber
What is the effect of reducing alveolar Po2 on pulmonary blood flow?
Marked vasoconstriction may occur below approximately 70 mm Hg
At very low Po2, local blood flow may be almost abolished.
What is the major trigger for smooth muscle contraction in hypoxic pulmonary vasoconstriction?
Increase in cytoplasmic calcium ion concentration
This occurs due to inhibition of voltage-gated potassium channels and membrane depolarization.
What role does nitric oxide (NO) play in pulmonary vascular tone regulation?
Promotes vasodilation by increasing cyclic GMP synthesis
NO is formed from L-arginine via endothelial NO synthase (eNOS).
What happens when the eNOS gene is disrupted?
Pulmonary hypertension occurs in animal models
This suggests the critical role of NO in regulating pulmonary vascular resistance.
What are potent vasoconstrictors released by pulmonary vascular endothelial cells?
- Endothelin-1 (ET-1)
- Thromboxane A2 (TXA2)
These substances play roles in both normal physiology and disease.
What is the primary function of hypoxic vasoconstriction?
Directs blood flow away from hypoxic regions of the lung
This helps reduce deleterious effects on gas exchange.
What is Starling’s equation used to describe?
Fluid exchange across the capillary endothelium
It accounts for hydrostatic and colloid osmotic pressures.
What is interstitial edema in the lung?
Engorgement of peribronchial and perivascular spaces
It is an early stage of pulmonary edema.
What causes alveolar edema?
Fluid crossing the alveolar epithelium into alveolar spaces
This interferes with pulmonary gas exchange.
What is a key function of the pulmonary circulation besides gas exchange?
Acts as a reservoir for blood
The lung can increase blood volume with small rises in pulmonary pressures.
What is the fate of angiotensin I in the pulmonary circulation?
Converted to angiotensin II by angiotensin-converting enzyme (ACE)
Angiotensin II is a potent vasoconstrictor.
Which vasoactive substance is largely inactivated in the lung?
Bradykinin
Up to 80% of bradykinin is inactivated by ACE.
What metabolic function does the lung perform with serotonin?
Major site of inactivation through uptake and storage
Some serotonin may be transferred to platelets or stored in other ways.
What are the two major synthetic pathways for arachidonic acid metabolism?
- Lipoxygenase pathway
- Cyclooxygenase pathway
These pathways produce leukotrienes and prostaglandins, respectively.
What is a significant synthetic function of the lung?
Synthesis of pulmonary surfactant
Dipalmitoyl phosphatidylcholine is a key component.
What happens to blood flow distribution in the upright lung?
Higher flow at the base than at the apex due to gravity
Capillary pressure can be less than alveolar pressure at the top, causing collapse.
True or False: Hypoxic pulmonary vasoconstriction increases blood flow to well-ventilated areas.
True
It reduces blood flow to poorly ventilated regions.
What is the relationship between pulmonary vascular resistance and cardiac output?
Pulmonary vascular resistance decreases as cardiac output increases
This occurs due to recruitment and distension of capillaries.
Fill in the blank: The capillary hydrostatic pressure is approximately halfway between _______ and _______.
[arterial pressure], [venous pressure]
This varies significantly depending on lung position.
What mechanism reduces blood flow to poorly ventilated regions of the lung?
Pulmonary vasoconstriction
This mechanism is released at birth, causing a large increase in blood flow to the lung.
What governs fluid movement across the capillary endothelium?
Starling equilibrium
If the circulation to the left lower lobe was occluded, what happened to the pulmonary artery pressure?
Only rose a small amount above normal
What would be expected to happen to the blood flow to the apex of the right lung?
Increased blood flow
What happens to dead-space ventilation and alveolar ventilation in this scenario?
Dead-space ventilation increases; alveolar ventilation decreases
What is the ratio of total systemic vascular resistance to pulmonary vascular resistance approximately?
20:1
True or False: Tension in the surrounding alveolar walls tends to widen the extra-alveolar vessels.
False
Which vessels contain smooth muscle and elastic tissue?
Extra-alveolar vessels
What primarily determines blood flow in zone 2 of the lung?
Arterial pressure minus alveolar pressure
What is the pulmonary vascular resistance if mean pulmonary arterial and venous pressures are 55 and 5 mm Hg respectively, with a cardiac output of 3 liters·min−1?
17 mm Hg·liters−1·min
What causes the fall in pulmonary vascular resistance during exercise?
Distension of pulmonary capillaries
What is the cardiac output in liters·min−1 using the Fick principle if O2 concentrations are 16 and 20 ml·100 ml−1, and O2 consumption is 300 ml·min−1?
2.5 liters·min−1
What reduces pulmonary vascular resistance?
Acutely increasing pulmonary venous pressure
What is hypoxic pulmonary vasoconstriction?
Partly diverts blood flow from well-ventilated regions of diseased lungs
What is the net pressure moving fluid into the capillaries if capillary and interstitial pressures are 3 and 0 mm Hg, and colloid osmotic pressures are 25 and 5 mm Hg?
23 mm Hg
What are some metabolic functions of the lung?
Producing bradykinin, secreting serotonin, removing leukotrienes, generating erythropoietin
What likely accounts for the increased systolic pulmonary artery pressure in the patient with pneumonia?
Decreased alveolar PO2
What factor most likely accounts for the development of pulmonary edema in the patient with myocardial infarction?
Increased pulmonary capillary hydrostatic pressure
