Blood Flow In Lungs Flashcards
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
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.
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
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
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
Blood volume of lungs
. Normally 450 ml (9% total BV)
. Lung can act as reservoir as lung blood volume can vary
Blood volume during valsalva maneuver
. Dec. to 200 ml
Blood volume in lungs in CHF
. Double normal volume to 900 ml
Pulmonary vascular resistance
. Vascular resistance = (input pressure-output pressure)/blood flow
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.
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
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
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.
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
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
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
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
