Pulmonary Circulation

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Pulmonary Circulation Pulmonary Edema and Pleural
Fluid
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The pulmonary circulation
O2
CO2
Pulmonary capillaries
Pulmonary artery
Pulmonary vein
LA
RV
tissue
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Lobes
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Intrapulmonary airways (1)
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Intrapulmonary airways (2)
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Pulmonary circulation
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Gas exchanges
Systemic circulation
Pulmonary circulation
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Pulmonary circulation is the part of the
circulatory system that takes the blood from the
heart to the lungs, where it is oxygenated, and
returns it to the heart. The main parts of the
pulmonary circulation system include the heart,
pulmonary arteries, capillaries of the lungs, and
pulmonary veins.
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The pulmonary artery quickly divides into two
branches. Each branch of the pulmonary artery
carries blood to a lung. In the lungs the
pulmonary arteries branch into capillaries that
surround the alveoli.
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Anatomy
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Bronchioles and Alveoli
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Physiologic Anatomy of the Pulmonary Circulation

• Pulmonary vessels Pulmonary arteries have larger
  diameters than their counterpart systemic
  arteries
• Vessels are thin and distensible
• These features give the pulmonary arterial tree a
  large compliance and accommodate the stroke
  volume output of the right ventricle
• Lymphatics Lymph vessels are also present in all
  the supportive tissues of the lung
• They mainly open into the right thoracic lymph
  duct

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Physiologic Anatomy of the Pulmonary Circulation

• Bronchial vessels Blood also flows to the lungs
  through small bronchial arteries that originate
  from the systemic circulation (1-2 of the
  cardiac output)
• This bronchial arterial blood is oxygenated in
  contrast to the partially deoxygenated blood in
  the pulmonary arteries
• It supplies to the supporting tissues of the lung
• Then it empties into the pulmonary vein and into
  left atrium
• Left ventricular output is about 1-2 more than
  the right ventricular output

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Pulmonary and Bronchial Circulation
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Pulmonary and Bronchial Circulation
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Pressures in the Pulmonary System

• Pressure pulse curve in the right ventricle
• Systolic pressure is about 25 mmHg
• Diastolic pressure averages about 0 to 1 mmHg
• Pressures in the pulmonary artery During
  systole, pulmonary artery pressure is equal to
  the pressure in the right ventricle
• Diastolic pulmonary pressure is about 8 mmHg
• Mean pulmonary pressure is 15 mmHg
• Pulmonary capillary pressure Mean pulmonary
  capillary pressure is 7 mmHg

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Pressures in the Pulmonary System
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Left atrial and pulmonary venous pressures

• The mean pressure in the left atrium and the
  major pulmonary veins averages about 2 mmHg in
  the recumbent human

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Blood Volume of the Lungs

• Blood volume in the lungs is about 450 ml (9 of
  the total blood amount)
• 70 ml of this is in the pulmonary capillaries
• Lungs as a blood reservoir expelling blood from
  the lung to the systemic circulation
• Shift of blood between the pulmonary and systemic
  circulatory systems as a result of cardiac
  pathology
• Mitral stenosis, mitral regurgitation and damming
  of blood in the pulmonary circulation

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Blood Flow Through the Lungs and Its Distribution

• Blood flow thorugh the lungs is essentially equal
  to the cardiac output
• Effect of diminished alveolar O2 on local
  alveolar blood flow automatic control of
  pulmonary blood flow
• When O2 concentration in the alveoli decreases
  below normal, adjacent blood vessels constrict
• This is opposite to the effect observed in the
  systemic vessels
• Blood is routed to ventilated areas in response
  to the alveolar oxygen pressure

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Effect of Hydrostatic Pressure Gradients in the
Lungs on Regional Pulmonary Blood Flow

• In the standing position at rest, there is little
  flow in the top of the lung but about 5 times as
  much flow in the bottom
• Zones 1, 2 and 3 Pulmonary Blood Flow
• Any time the lung alveolar air pressure becomes
  greater than the capillary blood pressure, the
  capillaries close and there is no blood flow
• Zone 1 No blood flow during all portions of
  cardiac cycle
• Zone 2 Intermittent blood flow during systole
• Zone 3 Continuous blood flow because alveolar
  capillary pressure is higher than the alveolar
  air pressure

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Effect of Hydrostatic Pressure Gradients in the
Lungs on Regional Pulmonary Blood Flow
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Effect of Hydrostatic Pressure Gradients in the
Lungs on Regional Pulmonary Blood Flow

• Blood flow in a normal person is entirely zone 3
• Zone 1 blood flow occurs only under abnormal
  conditions
• Effect of exercise on blood flow through the
  different parts of the lungs

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Effect of Increased Cardiac Output on Pulmonary
Blood Flow and Pulmonary Arterial Pressure During
Heavy Exercise

• Increased blood flow during exercise is
  accommodated in the lungs in three ways
• 1) Increasing the number of open capillaries
• 2) Distending all the capillaries and increasing
  the flow rate
• 3) Increasing the pulmonary arterial pressure
• This ability of compliance prevents a significant
  rise in pulmonary capillary pressure

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Effect of Increased Cardiac Output on Pulmonary
Blood Flow and Pulmonary Arterial Pressure During
Heavy Exercise
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Function of the Pulmonary Circulation

• The left atrial pressure in a healthy person
  almost never rises above 6 mmHg during most
  strenous exercise
• When the left side of the heart fails, blood
  begins to dam up in the left atrium
• Left atrial pressure increases (up to 40 - 50
  mmHg)
• This increases pulmonary capillary pressure and
  pulmonary edema develops

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Pulmonary Capillary Dynamics

• The capillary blood flows in the alveolar walls
  as a sheet flow rather than in individual
  capillaries
• Pulmonary capillary pressure is about 7 mm Hg
• Blood passes through the pulmonary capillaries in
  about 0.8 second

Lung capillaries
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Capillary Exchange of Fluid in the Lungs and
Pulmonary Interstitial Fluid Dynamics

• 1) Pulmonary capillary pressure 7 mmHg
• 2) Interstitial fluid pressure is more negative
  - 8 mmHg
• 3) Pulmonary capillaries are leaky to protein
  molecules Interstitial fluid colloid osmotic
  pressure is about 14 mmHg
• 4) Plasma colloid osmotic pressure is 28 mmHg
• Mean filtration pressure is 1 mmHg (outward)
• Negative pulmonary interstitial pressure and the
  mechanics for keeping the alveoli dry

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Keeping the alveoli dryactive transport
removes alveolar liquid
NaCl
alveolar space
NaCl transporter
active liquid transport
Na-K pump
Na
K
Cl
interstitium
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Capillary Exchange of Fluid in the Lungs and
Pulmonary Interstitial Fluid Dynamics
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Pulmonary Edema

• Most common causes
• 1) Left-sided heart failure or mitral valve
  disease with consequent great increases in
  pulmonary venous pressure
• 2) Damage to the pulmonary blood capillary
  membranes caused by infections (pneuminia) or by
  breathing noxious substances (chlorine gas,
  sulfur dioxide)
• Pulmonary edema safety factor

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Pulmonary edema
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Pulmonary Edema

• Safety factor in chronic conditions in patients
  with chronic mitral stenosis, PCP of 40 to 45
  mmHg have been measured without development of
  lethal pulmonary edema
• Rapidity of death in acute pulmonary edema

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Fluid in the pleural cavity

• The total amount of fluid in each pleural cavity
  is normally slight, only a few ml
• Whenever the quantity becomes more, the excess
  fluid is pumped away by the lymphatic vessels
• Negative pressure in the pleural fluid
• Pleural effusion Collection of large amounts of
  fluid in the pleural space (edema of the pleural
  cavity)

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Fluid in the pleural cavity
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Pulmonary embolism (1)
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Pulmonary embolism (2)