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ACEM Primary Written > Respiratory: Physiology - Pulmonary blood flow and metabolism > Flashcards

Respiratory: Physiology - Pulmonary blood flow and metabolism Flashcards

1
Q

RA pressure

A

2mmHg

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2
Q

RV systolic and diastolic pressures

A

25/0 mmHg

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3
Q

Pulmonary artery pressure: systolic, diastolic and mean

A

25/8 mmHg
Mean 15mmHg

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4
Q

Pressure at arterial and venous ends of alveolar capillary beds

A

Arterial: 12mmHg
Venous: 8mmHg

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5
Q

LA pressure

A

5mmHg

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6
Q

LV systolic and diastolic pressures

A

120/0 mmHg

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7
Q

Systemic arterial pressure: systolic, diastolic, and mean

A

120/80 mmHg
Mean 100mmHg

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8
Q

Pressure at arterial and venous ends of systemic capillary beds

A

Arterial: 30mmHg
Venous: 10mmHg

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9
Q

What is the difference in structure between pulmonary and systemic arterial branches?

A

Pulmonary arterial branches have very little smooth muscle (low-pressure system)

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10
Q

Describe the difference in pressure around alveolar, extra-alveolar, and large hilar vessels in the lung

A

Alveolar: transmural pressure is equal to difference between pressure within capillary and alveolar pressure (which normally equals atmospheric pressure)
Extra-alveolar: vessels pulled open by radial traction during inspiration and so pressure around them is lower than alveolar vessels
Large hilar vessels: subject to intra-pleural pressures

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11
Q

Formula for vascular resistance

A

Vascular resistance = pressure difference / blood flow

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12
Q

What fraction of systemic resistance is pulmonary vascular resistance?

A

~1/10th

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13
Q

What two mechanisms reduce pulmonary vascular resistance in response to increased pulmonary arterial or venous pressure?

A

Recruitment and distension

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14
Q

What is the effect of lung volume on pulmonary vascular resistance?

A

Reduced with large volumes due to traction of extra-alveolar vessels up to an extent: after this resistance is increased due to stretching of vessels

Reduced with small volumes due to alveolar collapse

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15
Q

List 6 factors which induce smooth muscle contraction in the lung

A

5HT
Histamine
NA
Endothelin
TXA2
Alveolar hypoxia

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16
Q

List 5 factors which induce smooth muscle relaxation in the lung

A

ACh
CCBs
NO
PDE
PGI2 (prostacyclin)

17
Q

Describe the Fick principle and give the equation

A

O2 consumption/min measured at mouth is equal to O2 taken up by blood in lungs/min

Q = VO2/(CaO2-CvO2)
Where Q = lung blood flow/min, VO2 = O2 consumption/min (from flow sensor), CaO2 = arterial O2 concentration (from radial artery puncture), CvO2 = mixed venous O2 concentration (from pulmonary artery catheter)

18
Q

Explain two methods of measuring pulmonary blood flow

A
  1. Using Fick principle (measuring O2 consumption by lung and arterial-venous O2 difference)
  2. Dilution techniques (indicator injected into venous circulation and arterial concentration measured)
19
Q

How can regional distribution of pulmonary blood flow be measured?

A

By injection of xenon-saline solution: xenon evolves into alveolar gas due to its low solubility in blood, then distribution of radioactivity can be measured by counters over the chest during breath-holding

20
Q

Describe the difference in distribution of pulmonary blood flow in upright vs supine position

A

Upright: decreasing blood flow from base to apex
Supine: increased apical blood flow while basal maintained, meaning more uniform distribution overall (although dependent posterior regions have increased blood flow compared with anterior)

21
Q

Describe the changes in distribution of pulmonary blood flow seen with exercise

A

Increased blood flow overall, less regional differences

22
Q

Describe the difference between zones 1, 2 and 3 of the lung

A

Zone 1: PA > Pa > Pv (therefore flow is obstructed; does not occur under normal conditions)
Zone 2: Pa > PA > Pv (flow determined by alveolar-arterial difference; recruitment occurs here)
Zone 3: Pa > Pv > PA (flow determined by arterial-venous difference; distension occurs here)

23
Q

What kinds of conditions may result in zone 1 description of pulmonary blood flow?

A

Decreased Pa (e.g. in shock)
Increased PA (e.g. PPV)

24
Q

What does zone 4 refer to as a description of pulmonary blood flow?

A

Decreased regional blood flow in under-inflated lung due to narrowing/collapse of extra-alveolar vessels (no traction to pull them open)

25
Q

What is the trigger for pulmonary hypoxic vasoconstriction? What is the impact of the CNS on this response?

A

Reduced PAO2 (NOT PaO2)
Effect is not dependent on CNS

26
Q

Is pulmonary hypoxic vasoconstriction a linear response?

A

No: little change with PO2 >100mmHg, marked response with PO2 <70mmHg

27
Q

Vasodilatory factor important in regulating pulmonary vascular tone

A

NO

28
Q

Two vasoconstricting factors important in regulating pulmonary vascular tone

A

ET-1
TXA2

29
Q

Three clinical settings which would induce pulmonary vasoconstriction

A
  1. Acidosis
  2. Hypothermia
  3. Increased sympathetic stimulation
  4. Iron deficiency
30
Q

What changes occur at high altitudes with relation to the effect of pulmonary hypoxic vasoconstriction?

A

Globally reduced PO2 causes increased pulmonary artery pressure

31
Q

What is the role of pulmonary hypoxic vasoconstriction in the transition from placental to air breathing at birth?

A

First breath increases PO2 causing reversal of hypoxic vasoconstriction -> increased pulmonary blood flow

32
Q

Starling’s equation

A

Net fluid out = K[(Pc - Pi) - σ(πc - πi)]

Where K = filtration coefficient, Pc - Pi = capillary and interstitial hydrostatic pressure difference, σ = reflection coefficient (effectiveness of capillary wall in preventing protein passage), πc - πi = capillary and interstitial colloid pressure difference (in lung πc = 25-28, πi = 20)

33
Q

What is the normal lymph flow from pulmonary vessels?

A

~20ml/hr

34
Q

Describe the flow of lymph in the lung

A

Lymph tracks to perivascular and peribronchial space, then drains via lymphatics to hilar lymph nodes

35
Q

Describe the pattern of fluid accumulation in early vs late pulmonary oedema

A

Early: fluid collects as interstitial oedema (engorgement of perivascular/peribronchial spaces)
Later stage: fluid in alveoli when interstitial lymph drainage rate is exceeded

36
Q

How is fluid in alveolar spaces removed on a cellular level?

A

Pumped out via Na+/K+ ATPase

37
Q

What vasoactive peptide is synthesised in the lung?

A

Angiotensin II is formed from angiotensin I via action of ACE in the lung

38
Q

List 5 metabolically active molecules removed from the circulation in the lung

A

Bradykinin
5HT
NA
PGE2 and PGFa2
Leukotrienes

ACEM Primary Written (160 decks)

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