Blood Flow In Lungs Flashcards by Emily Mosher

Pulmonary circulation

. Main pulmonary a. Receives mixed venous blood pumped by RV
. Artery branches successively, following in close proximity w/ branching of airways to level of terminal bronchioles
. Pulmonary capillaries cover alveoli
. Oxygenated blood collected from capillary bed by small pulmonary vv.
. Veins coalesce to form the 4 large veins that drain into LA

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Bronchial circulation

. Bronchial aa. Branch from descending aorta and return to the lungs
. Aa. Contain fully oxygenated blood that supply oxygen and nutrients to intrapulmonary structures (tracheobronchial tree, pulmonary nn., and smooth muscle and CT)
. Blood from bronchial circulation returns to the RA via azygos and intercostal vv.

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How bronchial and pulmonary arteries anastomose

. Bronchial capillary bed can anastomose w/ pulmonary capillary bed
. Blood becomes reoxygenated in pulmonary capillaries and then leaves lungs via pulmonary vein
. Bronchial capillary bed can also drain into pulmonary v. Where deoxygenated blood would return to LA (right to left shunt)
. Blood returning from lungs to the LA is not 100% oxygenated

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Pressures w/in pulmonary circulation

. Bps are low compared w/ systemic circulation
. Pulmonary a. Pressure: 25/8 mmHg w/ mean of 15 mmhg
. Mean pressure of LA is 5-8 mmHg
. Pulmonary arteriovenous pressure gradient is 10 mmHg
. Mean pulmonary capillary hydrostatic pressure is 10 mmHg

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Pulmonary blood vessel characteristics

. Due to lower pressure, the vessel branches are much thinner and contain less smooth muscle and elastin than aorta
. Pulmonary arterioles do not have same capacity for vasoconstriction as systemic arterioles

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Blood volume of lungs

. Normally 450 ml (9% total BV)

. Lung can act as reservoir as lung blood volume can vary

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Blood volume during valsalva maneuver

. Dec. to 200 ml

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Blood volume in lungs in CHF

. Double normal volume to 900 ml

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Pulmonary vascular resistance

. Vascular resistance = (input pressure-output pressure)/blood flow

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Passive changes in pulmonary vascular resistance

. Circulation maintains low resistance even when CO inc.
. When pulmonary arterial or venous pressure inc. pulmonary vascular resistance dec.
. Recruitment of new pulmonary beds that open up and distension of already opened pulmonary vessels
. Distension inc. caliber of individual capillary segments (dominant mechanism for fall in pulmonary vascular resistance as pulmonary arterial pressure inc.

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Pulmonary vascular resistance during exercise

CO inc. about linearly as work rate inc.
. Inc. in pulmonary arterial blood flow is accompanied by only slight inc. in pulmonary arterial pressure
. Due to great compliance of pulmonary vasculature which distends and recruiters pulmonary vascular beds as CO inc.
. The diffusing capacity of the lung may inc. up to 3x during exercise
. Difference between alveolar and arterial PO2 dec. slightly which may reflect more even distribution of flow-perfusion

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Effect of lung volume on pulmonary extra-alveolar vascular resistance

. Extra-alveolar blood vessels (aa. And vv. Going through lung parenchyma) has dec. resistance at high lung volumes
. Extra-alveolar vessels partially collapse and have high resistance at small lung volumes
. Diameter of blood vessels w/in lung is inc. during inspiration
. Radial forces stretch open vessels at higher lung volumes at the expand

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Effect of lung volume on alveolar capillaries

. As lung volume inc. during normal inspiration, the alveoli inc. in volume
. As they expand the capillaries btw alveoli are compressed
. At high lung volumes the pulmonary capillary resistance inc. and at low volumes it dec.

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Starling’s law in pulmonary system

. Net fluid out = Kf [(Pc-Pi)-(pic-pii)]
. Fluid transfer across pulmonary capillaries depends on hydrostatic and osmotic forces
. Values unknown for pulmonary circulation though
. Net force favors mall continuous leak from capilaries into interstitial space
. Fluid passes through interstitial spaces into lymph which goes to hilar lymph nodes by smooth mm. Contraction in lymph vessels

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Pulmonary edema

. Inc. i hydrostatic pressure or inc. inc capillary permeability causes this
. Inc. LA pressure (mitral stenosis) can produce edema by inc. capillary hydrostatic pressure
. Inc. pressure makes capillary more per able by widening endothelial pores
. Damage to pulmonary capillary membrane form infections or toxins (Cl or S2 gas) can also cause edema

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Types of pulmonary edema

. Interstitial

. Alveolar

Interstitial pulmonary edema

. Precedes alveola redema
. Enforcement of peripronchial and perivascular spaces
. Lymph system tries to dec. amount of lucid accumulating

Alveolar edema

. Occurs when maximal lymph drainage of interstitial is exceeded
. Interstitial pressure inc. is too high and fluid enters alveolus
. More serious bc it interferes w/ pulmonary gas exchange
. Can occur in acute left-sided heart failure
. Death can ensure in less than 30 minutes from acute alveolar edema

Clinical problems causing inc. capillary permeability (Kf)

. Adult respiratory distress syndrome
. O2 toxicity
. Inhaled or circulating toxins

Clinical problems that cause inc. LA pressure

. Inc. capillary hydrostatic pressure (Pc)

Clinical problems that dec. interstitial hydrostatic pressure (Pi)

Top rapid evacuation of pneumothorax

Clinical problems that cause dec. colloid osmotic pressure (pic)

. Protein starvation

. Renal problems resulting in urinary protein loss

Clinical problems causing insufficient pulmonary lymph drainage

. Tumors

. Interstitial fibrosis

Clinical problems that can cause pulmonary edema w/ unknown etiology

. High altitude pulmonary edema
. Pulmonary edema after head injury
. Drug overdose

Pulmonary circulation during left-sided heart failure

. Blood builds up in LA . LA pressure may rise from normal 5-8 mmHg to 40-50 mmHg . Initial rise in blood has almost no effect on pulmonary pressure due to recruitment and distension . Once LA pressure rises above 10 mmHg there will be similar inc. in both pulmonary capillary and pulmonary arterial pressure . Inc. workload of the right heart . When pressure rises over 30 mmHg pulmonary edema starts to develop

How to look at pulmonary blood flow using xenon

. Dissolved in saline and then injected into pierpheral v. . When xenon reaches pulmonary capillaries it is evolved into alveoli due to its low solubility . Evolved xenon is counted by radiation detectors over chest . Measured amount of xenon radiation is directly proportional to pulmonary blood flow

Hydrostatic pressure difference in lungs from gravity

. Pulmonary arterial and venous pressures are both lower at the lung apex and both higher at the base

Starling resistors when dealing with gravity

. Pulmonary capillaries are surrounded by alveoli and receive little support from lung parenchyma . If alveolar pressure is greater than arterial pressure the capillary is squeezed shut and there is no flow

Zone 1 of pulmonary blood flow

. alveolar pressure is greater then arterial pressure which is greater than venous pressure . Capillary is quizzed shit and there is no blood flow . Zone is ventilated but not perfused, considered alveolar dead space

Zone 2 of pulmonary blood flow

. Arterial pressure is greater than alveolar pressure whic is greater than venous pressure . Blood flow is determined by pressure difference btw alveoli and arteries . As the difference inc. towards bottom of zone 2 the pulmonary blood flow inc.

Zone 3 of pulmonary blood flow

. Both arterial and venous pressure are higher than alveolar pressure . Flowis dependet on arterial-venous pressure difference . Capillaries are permanently open . The pulmonary vessel diameter inc. towards bottom of zone 3 so flow inc. and resistance dec.

T/F alveolar pressure stays constant and arterial and venous pressure inc. as you move down the lung

T/F ANS has a lot of control over pulmonary blood vessels

F, there do not have major function i normal control of blood flow

Hypoxic pulmonary vasoconstriction

. Distribution of pulmonary blood flow dec. when PO2 of small airways or alveoli is dec. . Smooth muscle in hypoxic region contract and blood is directed away from hypoxic region . Hypercapnia, acidosis, and hypertrophy of vascular smooth mm. Accentuate this . Benefit: diverts mixed venous blood away from poorly ventilated areas w/ low PO2 by locally inc. vascular resistance . Mixed venous blood is sent to better ventilated areas so it can be oxygenated . Different from systemic vasoconstriction that dilates w/ dec. O2 and constricts w/ inc. O2

Hypoxic pulmonary vasoconstriction in global hypoxia

. Occurs at high altitudes . Pulmonary arterioles constrict throughout entire pulmonary circulation . Inc. vascular resistance leading to pulmonary edema and pulmonary artery hypertension . Supplemental O2 helps this

Hypoxic pulmonary vasoconstriction in COPD

. Chronic alveolar hypoxia can lead to vasoconstriction, pulmonary artery hypertension, and RV hypertrophy . Supplemental O2 helps this

Mechanism for hypoxic pulmonary vasoconstriction

. Local effect intrinsic to lungs . May involve mitochondrial O2 sensor that inhibits K channels . Leads to depolarization of vascular smooth mm. Causing VG Ca channels to open . Inc in intracellular Ca conc. Causes pulmonary a. Smooth mm. To contract