Pulmonary Circulation

Question 1

lung as a filter

Answer 1

clears small emboli (has protesases) and particles associated with recreational drugs

Question 2

lung as a metabolic clearance organ

Answer 2

1. Angiotensin I- Converted to angiotensin II in one pass
2. Angiotensin II- Untouched
3. Bradykinin- 80% removed in one pass
4. 5-Hydroxytryptamine (serotonin)- 90% removed in one pass
5. Epinephrine- Not affected
6. Norepinephrine- Up to 30% removed

Question 3

pulmonary arterial pressure

Answer 3

pulsitile, 25/8 (systolic over diastolic, units of mm Hg).

mean pressure = 15mmHg

does not increase with exercise bc resistance decreases with cardiac output

Question 4

Mean pulmonary venous pressure

Answer 4

2 mm Hg and is virtually the same as left atrial pressure.

Question 5

pulmonary capillary pressure

Answer 5

highly pulsitile (unlike systemic)

contribute significantly to the total pulmonary (circulatory) resistance

Question 6

arteries and arterioles

Answer 6

carry little pressure, they do not have considerable smooth muscle tissue around the walls

Question 7

pulmonary resistance

Answer 7

If the mean arterial pressure is about 15 mm Hg, the mean venous pressure is about 2 mm Hg, and the cardiac output is about 5 L/min, the resistance is therefore (15-2)/5 or around 2 to 3 mm Hg per (L/min). This is about 10 fold less than the systemic circulation

decreases with increasing cardiac output

Question 8

decrease in pulmonary resistance

Answer 8

passive phenomenon. It is due to

1) distension of vessels that are already well-perfused
2) recruitment (opening up) of vessels not perfused

Question 9

Hypoxic vasoconstriction

Answer 9

unique to the pulmonary arterial bed

acute- caused by blockage in small airways -> blood flow is “re-routed” to regions of the lung which have better ventilation

generalized- vasoconstriction throughout the entire lung -> resistance of the entire pulmonary vasculature is increased -> pulmonary arterial pressure rises -> “pulmonary hypertension”

Question 10

pulmonary hypertension

Answer 10

change in right ventricular structure and function, and that is named Cor Pulmonale

Question 11

Cor Pulmonale

Answer 11

a dilation, or hypertrophy, of the right ventricle due to this increase in the resistance of the pulmonary vasculature

Question 12

Regional differences in ventilation and perfusion

Answer 12

In an upright individual, there is less ventilation and less perfusion in the top, or apex, of the lung, than there is at the base of the lung

Question 13

West Zones

Answer 13

“three zone model” of lung perfusion

Zone1: PA>Pa>Pv
Zone2: Pa>PA>Pv
Zone3: Pa>Pv>PA

Question 14

Zone1

Answer 14

lung apex
no perfusion due to gravity
PA>Pa>Pv -> capillary collapses

Question 15

Zone2

Answer 15

middle lung
some perfusion
Pa>PA>Pv -> capillary open on arterial side, constriction on venous side

Question 16

Zone3

Answer 16

lung base

Pa>Pv>PA -> no vessel constriction

Question 17

RQ

Answer 17

respiratory quotient is the ratio of CO2 produced to oxygen consumed
RQ= V(.)CO2/V(.)O2
Or, = (Cv(CO2)-Ca(CO2))/(Cv(O2)-Ca(O2))
normally ~ .8

Question 18

Glucose metabolism:

Answer 18

C6H12O6 + 6 O2 = 6 CO2 + 6 H2O

RQ= 6/6 = 1

Question 19

Fat metabolism

Answer 19

RQ <1 ~.7

Question 20

alveolar air equation

Answer 20

If RQ =1.0 or FI(O2)=100%O2:
PA(O2) = PI(O2) - Pa(CO2)

If RQ =.8 and or FI(O2)=21%O2:
PA(O2) = PI(O2) - 1.2*Pa(CO2)
Because RQ<1 lowers the PA(O2) because more oxygen is consumed than CO2 produced so the alveoli restores atmospheric pressure by drawing in air that is 2partsO2 and 8parts N

Question 21

alveolar ventilation equation

Answer 21

V(.)A = V(.)(CO2)/Pa(CO2) x 863

units of L/min

Question 22

shunt

Answer 22

a pathway by which blood flows from the venous circulation to the arterial circulation without participating in gas exchange

different from poorly ventilated regions

• > substantial A-a O2 diff
  dx: breathe 100% O2, if there is a A-a diff then there is a shunt

Question 23

ventilation-perfusion mismatching

Answer 23

can be corrected by breathing high oxygen mixtures

Blood traversing poorly ventilated regions can be oxygenated if the inspired oxygen partial pressure is raised to sufficiently high levels

people with mild to moderate Q/V mismatching have a near normal PaCO2 and below normal PaO2. This is because a well ventilated region of the lung can compensate for a poorly ventilated region of the lung with respect to CO2 gas exchange BUT cannot compensate with respect to O2 gas exchange due to the oxyhemoglobin dissociation curve.

Question 24

ventilation perfusion ration

Answer 24

V(.)A/Q(.)
=0 = shunt, lung is not ventilated but well perfused
-> The gases in this alveolar region will come into equilibrium with the mixed venous blood

= infinity = physiological dead space -> alveolar gases will come into equilibrium with the inspired gases

Question 25

ventilation-perfusion line

Answer 25

describes different ventilation-perfusion ratios on the gamut from shunts to dead space

the lung regulates ventilation to keep PA(CO2) in a narrow range

Question 26

c’

Answer 26

end-capillary blood

Question 27

poorly ventilated

Answer 27

low V/Q

-> PA(O2) lower and PA(CO2) higher

Question 28

well ventilated

Answer 28

high V/Q

-> PA(O2) highe and PA(CO2) lower

Question 29

central chemoreceptor

Answer 29

regulates spontaneous respiration

ventral lateral surface of medulla

monitors the partial pressure of CO2 but responds to H+

can only respond to changes in PaCO2 because dissolved carbon dioxide (but not bicarbonate nor hydrogen ion) can diffuse rapidly across the blood-brain barrier into the cerebrospinal fluid (CSF)

in CSF:
CO2 + H2O HCO3- + H+

Question 30

carotid bodies

Answer 30

located at the bifurcation of the common carotid arteries

send signals through the glossopharyngeal nerve

only structure responsible for the ventilatory response to hypoxia

principal sensor responsible for the ventilatory response to non-carbonic acids (metabolic acidosis)

Question 31

aortic bodies

Answer 31

in man, no ventilatory role for the aortic bodies can be assigned

Question 32

set point

Answer 32

partial pressure of carbon dioxide which we try to maintain in the arterial circulation
35-40mm Hg CO2

as PACO2 increases, rate of ventilation V(.)E increases

Question 33

hypercapnia

Answer 33

increased PI(CO2)

Question 34

hyperoxia

Answer 34

elevated partial pressures of oxygen in the inspired air)

no ventilatory response

Question 35

hypoxia

Answer 35

decreased partial pressures of oxygen in the inspired air)

ventilatory response is hyperbolic in relationship to decreased PAO2 and linear with hemoglobin saturation

Question 36

Response to metabolic acidosis

Answer 36

ex: lactate (anaerobic exercise) and various acids (diabetic ketoacidosis)

increase in ventilation is due to stimuli coming from the carotid bodies

Question 37

Acute vs. chronic hypoxia/acidosis

Answer 37

acute: a minor increase in ventilatory rate but the PaCO2 drops and the brain reduces ventilatory rate
chronic: pH of the cerebrospinal fluid is adjusted. The alkaline CSF pH value, brought about by the hypoxia, changes to a more normal pH -> higher ventilatory rate is then observed chronically