Pulmonary circulation

DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
PULMONARY
CIRCULATION

OBJECTIVES.
 FUNCTIONAL ANATOMY
 CHARACTERISTIC FEATURES
 FUNCTIONS
 REGULATION OF PULMONARY BLOOD FLOW.

FUNCTIONAL ANATOMY
Lungs have 3 circulation.
 Pulmonary
circulation
 Bronchial circulation
 Lymphatic
circulation.
Thursday, December 5, 2019

PULMONARY CIRCULATION
 Pulmonary trunk
 Right & left pulm
artery
 Right & left lungs
 Capillaries lining of
alveoli
 Get oxygenated &
return back via pul
veins to left atrium.

BRONCHIAL CIRCULATION
 Descending thoracic aorta
give right & left bronchial
arteries
 Supply oxygenated blood to
lungs (connective tissue,
septa & bronchi) & after joins
pulm veins without (Bypass)
oxygenation.
 So forms Physiological
shunt.

OTHER EXAMPLE OF
PHYSIOLOGICAL SHUNT
 Drainage of Coronary vessel in to left side of
heart.
 Effects of shunts –
 Reduce oxygenation of arterial blood slightly.
 Increase left ventricular output by 1-2% than right.

LYMPHATIC CIRCULATION.
 Present in walls of
terminal bronchioles
& supportive tissues
of lung.
 Removes particulate
matter, plasma
proteins – thus
prevents pulmonary
oedema

LYMPHATIC CIRCULATION.
Drainage pathway
 Deep lymphatic
 Pulmonary nodes
 Bronchopulmonary
nodes
 Tracheobronchial
nodes
 Bronchomediastinal
trunk.

PULMONARY CIRCULATION
CHARACTERISTIC FEATURES.
 Pulmonary circulation is low pressure, low
resistance & high capacitance system.
 Thickness of Right ventricle and pulmonary
artery 1/3rd of left ventricle & aorta
 Pulmonary capillaries are larger in diameter
than systemic capillaries.
 Each alveolus is enclosed in basket of
capillaries.

PRESSURES IN PULMONARY
SYSTEM.
 Right ventricular pressure.
 Pulmonary artery pressure.
 Left atrial pressure.
 Pulmonary capillary pressure.

RIGHT VENTRICULAR
PRESSURE.
 During each cardiac cycle,
 During Systole – reaches peak 25 mm
Hg.(120 mm Hg in Left ventricle)
 During Diastole – 0-1 mm Hg (5 mm Hg in
left ventricle)

PULMONARY ARTERY
PRESSURE.
 Systolic pressure 25 mm Hg (120 mm Hg in
Aorta)
 Diastolic pressure 8 mm Hg (8 mm Hg in
Aorta)
 Mean arterial pressure 15 mm Hg (100 mm
Hg in Aorta)
 Pulse pressure 17 mm Hg (40 mm Hg in
Aorta)

LEFT ATRIAL PRESSURE.
 Major pulmonary veins pressure avg 5 mm
Hg
 So Pressure gradient in pulmonary system
Mean pulmonary artery pressure – mean
pulmonary vein pressure
15-5 = 10 mm Hg.

PULMONARY CAPILLARY
PRESSURE.
 10 mm Hg.
 Colloidal osmotic pressure is 25 mm Hg
 So net suction force of 15 mm Hg draw fluid
from pulmonary interstitial fluid into
pulmonary capillary
 So keeps Alveoli dry

SIGNIFICANCE OF LOW PULMONARY
CAPILLARY PRESSURE
 So if pulmonary capillary pressure rises above
25 mm Hg
 Fluid escapes into interstitial spaces
 Lead to pulmonary oedema
 Conditions raising this pressue
 Exercise at high altitude
 Left heart failure
 Mitral stenosis
 Pulmonary fibrosis.

PULMONARY WEDGE
PRESSURE
 Estimate left atrial
pressure.
 Measured by passing a
catheter through right
ventricle, pulmonary artery
up to smallest branch of
pulmonary artery.
 Used to study left atrial
pressure in patients of CCF

PULMONARY BLOOD VOLUME
 Pulmonary vessels contains – 600 ml; its
capacitance vary from 200-900 ml
 Pulmonary blood volume decreases during
standing & during haemorrhage to
compensate , so acts as Reservoir.

PULMONARY BLOOD FLOW
 Pulmonary blood flow
nearly equal to cardiac
output.
 Blood flow through lung
depend on –
 Relationship between
pressures of Pulmonary
artery, pulmonary vein &
alveolar artery.

EFFECT OF GRAVITY ON REGIONAL
PULMONARY BLOOD FLOW.
 In supine position
mean arterial pressure
is same all over lung
so all regions equally
perfused.
 In erect position
gravity affects due to
hydrostatic pressure
effect.

EFFECT OF GRAVITY ON REGIONAL
PULMONARY BLOOD FLOW.
 Zero reference plane is
at level of right atrium.
 So pulmonary arterial
pressure
 In middle of lung –is 15
mm Hg
 At apex – 4 mm Hg
 At the base 26 mm Hg.

PERFUSION ZONES OF LUNG
 Depending on
relationship between
alveolar pressure
(PA), Pulmonary
arterial pressure (Pa)
& Pulmonary venous
pressure (Pv) 3 zones
 Zone 1
 Zone 2
 Zone 3

 Zone 1- area of zero
flow. (Pa<Pv)
 Does not exist in normal
lung.
 In hypovolaemic shock,
pulmonary embolism.
 Zone 2 – Intermittent
blood flow.(Pa>PA>Pv)
 Occurs during systole.

 Blood flow is
determined by arterial-
alveolar pressure
gradient not arterio-
venous gradient. so
called Waterfall effect.

 Zone 3
 Continuous high blood
flow. (Pa>Pv>PA)
 Generally occurs near
bottom of the lung.

EFFECT OF GRAVITY ON
ALVEOLAR VENTILATION
 In Supine Position – alveolar ventilation evenly
distributed
 In Upright Position –
 Alveolar pressure is zero throughout lung
 Intrapleural pressure – at apex -10 mmHg & at base -2
mm Hg.
 So transpulmonary pressure -10 & -2 at apex & base
respectively.
 So linear reduction in regional alveolar ventilation from
base to apex.

CLINICAL SIGNIFICANCE
 So arterial
oxygenation in
unilateral lung
diseases is improved
by keeping good lung
in Dependent
Position.
 Opposite is done in
INFANT.

ALVEOLAR VENTILATION :
PERFUSION RATIO
 Ratio of alveolar
ventilation per minute
to quantity of blood
flow to alveoli per
min.
 VA/Q = 4.2/5 = 0.84-
0.9

EFFECT OF GRAVITY
 Linear Reduction of blood flow and
alveolar ventilation from base to
apex.
 But gravity affects perfusion more
than ventilation.
 So as we go up from middle VA/Q
goes on increasing , about 3 at apex.
 At the base it is over perfused than
over ventilated so at the base is 0.6

CAUSES OF ALTERATION.
 Causes of altered
alveolar ventilation
 Bronchial asthma
 Emphysema
 Pulmonary fibrosis
 Pneumothorax
 Congestive heart failure
 Causes of altered
pulmonary perfusion.
 Anatomical shunts
 Pulmonary embolism
 Decrease in pulmonary
vascular bed in
emphysema
 Increase pulmonary
resistance in pulmonary
fibrosis, Pneumothorax,
CHF

EFFECTS OF ALTERATION IN
VA/Q RATIO.
 Normal VA/Q ratio –both normal alveolar
pO2 = 104 mmHg, pCO2 =40 mmHg.
 Increased VA/Q ratio. – alveolar dead space
air, VA/Q = infinity, pO2 = 149 mmHg, pCO2
= 0 mmHg.
 Decreased VA/Q ratio, pO2 = 40 mmHg,
pCO2 = 45 mmHg.

EFFECT OF EXERCISE ON REGIONAL
PULMONARY BLOOD FLOW
 During exercise blood flow
increases in all regions of
blood.
 Near base increased by 2-3
time
 Near apex increased by 8
times.
 It occurs due to
 Recruitment of capillaries.
 Distension of capillaries.

PULMONARY CAPILLARY
DYNAMICS
 Pulmonary transit time – mean transit time
in pulmonary circulation from pulmonary
valves to left atrium – 4 sec.
 Capillary transit time for RBC is 0.8 sec at
rest and 0.3 sec during exercise.

MEAN FILTRATION PRESSURE AT
PULMONARY CAPILLARY = 1 mm Hg.
 Starling’s forces at capillary membrane
are
 Outward forces (29 mm Hg)
 Interstitial oncotic pressure – 14 mmHg
 Interstitial hydrostatic pressure - -8 mm Hg
 Capillary Hydrostatic pressure 7 mm Hg
 Inward forces (28 mm Hg)
 Plasma oncotic pressure 28 mm Hg.

PULMONARY OEDEMA
 Occur due to increase capillary filtration
from pulmonary capillary.
 Conditions –
 Increase capillary hydrostatic pressure from 7 mm
Hg to 28 mm Hg (safety factor of 21 mm Hg)
 Capillary permeability increase – due to infection,
irritant gases.
 Acute left heart failure – increase in capillary
pressure to 50 mm Hg.

FUNCTIONS
 Respiratory gas exchange
 Other functions
 Reservoir for left ventricle
 Filter for removal of emboli & other particles from
blood.
 Removal of fluid from alveoli.
 Role in absorption of drugs.
 Synthesis of Angiotensin converting enzyme.

REGULATION OF PULMONARY
BLOOD FLOW.
 Neural control.
 Efferent sympathetic vasoconstrictor
nerves
 Innervates pulmonary blood vessels.
 Participate in vasomotor reflexes.
 Baroreceptor stimulation – causes reflex
dilatation of pulmonary vessels
 Chemoreceptor stimulation – causes pulmonary
vasoconstriction.

Afferent control through vagus
is mediated through receptors.
 Pulmonary
baroreceptors
 pulmonary volume
receptors
 J receptors.

CHEMICAL CONTROL
 Local Hypoxia – causes
change in blood flow by
vasoconstriction.
 Hypercapnia &
acidosis – causes
vasoconstriction.(Vasod
ilatation in systemic
circulation)

CHEMICAL CONTROL
 Chronic Hypoxia
 Occurs in high altitude dwellers associated with
pulmonary hypertension followed by right
ventricular hypertrophy, right heart heart failure &
pulmonary oedema.

Pulmonary circulation

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