Pulmonary Circ and Gas Exchange

Question 1

What are the characteristics of zone 1?

Answer 1

region of lung which pulmonary flow is zero because pulmonary arterial pressure is less than the alveolar pressure; ventilated but not perfused, contributes to alveolar dead space and wasted ventilation

Question 2

What are the characteristics of zone 2?

Answer 2

region of the lung between 1 and 3, flow present because pulm. arterial pressure is greater than alveolar pressure but flow is not influenced by venous pressure because there is not blood in pulmonary veins due to gravity

Question 3

What are the characteristics of zone 3?

Answer 3

region of lung which flow is determined by the difference between arterial and venous pressures in systemic vessels; most occupies dependent portion (below the lung), majority of pulmonary blood flow occurs in this region, increases from top to bottom of region bcuz gravity pulls blood toward lower part of lung

Question 4

What are the characteristics of zone 4?

Answer 4

region of lung below zone 3 with impeded flow of blood due to edema, present only in abnormally high pulmonary venous pressure, edema around blood vessels, termed vascular cuffing which causes pulmonary vessels to collapse (tamponade)

Question 5

What is Pascal’s law?

Answer 5

P=pgh; effect of gravity on blood pressure in pulmonary circulation

Question 6

What factors affect the zones of the lung?

Answer 6

posture (supine position- zone one typically does not exist), hemorrhage or shock (tends to increase zone 1), positive pressure ventilation (increases region of zone 1)

Question 7

What are the methods of passive regulation?

Answer 7

recruitment: increasing pulmonary arterial pressure initiates flow through previously unperfused pulmonary capillaries in upper parts of the lung; distension: increasing blood volume in pulmonary arteries distends pulmonary capillaries thus increasing flow (zone 3), inflation during inspiration pulls blood into chest and distends pulmonary capillaries.

Question 8

What are the methods of active regulation?

Answer 8

no neurogenic regulation, pulm. arterioles respond to several metabolic factors, hypoxic pulmonary vasoconstriction- decreased PO2 in alveoli constricts pulm. arterioles locally, increased PO2 in alveoli dilates arteries locally, PO2 in venous blood does not affect this response, primary mech. for local control; vascular endothelial factors- ET-1, PGI2, NO

Question 9

What is the effect of endothelin 1?

Answer 9

potent pulmonary vasoconstrictor

Question 10

What are the effects of PGI2 and NO?

Answer 10

potent pulmonary vasodilators

Question 11

What is starlings law for the pulmonary capillaries?

Answer 11

Jv= Kf [(PHcap- PHis) - (Ppicap-Ppiis)] or net fliud movement = permeability x (net hydrostatic pressure - net oncotic pressure)

Question 12

What is interstitial pulmonary edema? What happens with the lung zones?

Answer 12

engorgement of pulmonary interstitial spaces with fluid due to one or more of the following: due to large Jv or lymphatic obstruction/inflammation; promotes formation of zone 4

Question 13

What can cause a large JV?

Answer 13

increased pulmonary capillary hydrostatic pressure (heart failure, pulm. hypertension, large movement of fluid throughout lungs) and increased permeability of capillary membrane due to release of inflammatory mediators (pneumonia- around alveoli) and decreased plasma oncotic pressure due to depletion of plasma proteins (liver or renal disease)

Question 14

What factors promoting pulmonary edema?

Answer 14

interstitial pulmonary edema and alveolar edema

Question 15

What is alveolar edema?

Answer 15

more severe stage of pulmonary edema in which interstitial fluid accumulates to the extent that it overcomes the stabilizing force and fills the alveoli

Question 16

What are the different kinds of anatomical shunts?

Answer 16

atrial septal defects, eisenmengers syndrome: combination of VSD with pulmonary hypertension, natural shunts: bronchial circulation, thesbian veins-(<1% cardiac output)

Question 17

What conditions promote pulmonary shunting?

Answer 17

airway obstruction: bronchospasm (asthma or bronchitis) and mucus plus or foreign object; greatly suppressed ventilation (hypoventilation, respiratory arrest); alveolar/interstitial edema or fibrosis (decreased diffusion capacity); atelectasis (alveolar collapse)

Question 18

what is the compensatory response to limit pulmonary shunts?

Answer 18

increase minute ventilation, local pulmonary capillaries vasoconstrict in response to low PAO2 (hypoxic pulmonary vasoconstriction) to limit perfusion

Question 19

what are the different types of pulmonary hypertension? causes?

Answer 19

vasoconstrictive: hypoxic pulmonary vasoconstriction, acidemia (pH< 7.2); obstructive: pulmonary embolism or tumor; passive: elevated left atrial pressure (heart failure) or mitral stenosis; other: vascular disease, interacardiac shunts, and pulmonary arteriovenous fistulas; and chronic pulmonary hypertension leads to right heart failure or cor pulmonale

Question 20

What is a pulmonary embolism?

Answer 20

obstruction of pulmonary circulation due to intravascular clot or air bubble; results in V/Q mismatch (increased dead space), hypoxemia ensures stimulation of peripheral chemoreflex and a rapid increase in minute ventilation to compensate for wasted ventilation created by embolus; rapid onset of breathlessness in patient unexplained hyperventilation