Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings.

PowerPoint® Lecture Slide Presentation by Robert J. Sullivan, Marist College

RESPIRATIONRESPIRATION

Chapter 38 PULMONARY CIRCULATIONPULMONARY EDEMA PLEURAL FLUID

DR FARZANA MAJEED

Functional anatomy

• It is 9% of total COP

• The lungs have three circulations i.e pulmonary ,bronchial and lymphatics

Pulmonary circulation

• Pulmonary trunk arises from the right ventricle

• Divides into right and left pulmonary arteries conveying deoxygenated blood to right and left lung respectively

• Blood reaches the capillaries surrounding alveoli and exchange of gasses take place

• Oxygenated blood reaches heart through four pulmonary veins.

Bronchial circulation

• Small arterial branches arising from systemic circulation

• Receive oxygenated blood • Amounts to about 1-2% of total COP• Supply blood to connective tissue,

septa, large and small bronchi of lungs• Empties to left atrium via pulmonary

veins…. Physiological shunt

Lymphatic circulation

• Lymph vessels are present in supporting tissue

• Open in right thorasic duct • Remove particulate matter entering

alveoli• Prevent leakage of plasma proteins

therefore prevent development of edema

Characteristic features of pulmonary circulation

• Pulmonary arteries are thin walled and distensible

• This makes the pulmonary circulation low resistance, low pressure and high capacitance system

• Pulmonary capillaries surround the alveoli as a result alveoli seem to be enclosed in basket of capillaries.

Pressures in pulmonary circulation

• Left Ventricle 120/ 0 mmHg• Aorta 120/ 80 mmHg• Right Ventricle 25 / 0 mmHg • Pulmonary artery 25 / 8 mmHg

Blood volumes of lungs

• 450 ml or 9% of COP• Out of this 70 ml is in pulmonary

capillaries.• 190 ml in pulmonary arteries and

same in pulmonary veins

• Volume of blood flow to the lungs vary with various physiological and pathological conditions.

• It can vary from a small rise to 1-1/2 to 2 times the normal

• Person blowing trumpet……250 ml blood from pulmonary to systemic circulation

• Hemorrhage…… shift of blood from pulmonary to systemic circulation

Distribution of pulmonary blood flow

• Regulated by the factors that regulate COP

• Normally pulmonary vessels act as passive and distensible tubes which enlarge with increase in pressure and narrows on decreasing pressure.

• For adequate aeration of blood it should reach those alveoli which are fully oxygenated

Regulation of pulmonary blood flow

1…..Cardiac output2…..Vascular resistance3…. Nervous factors4….Chemical factors5… Gravity and hydrostatic pressure

Cardiac output

• Pulmonary blood flow is directly proportional to COP

• Any factor that affect COP effects pulmonary blood flow

Venous returnForce of myocardial contractionHeart ratePeripheral resistance

Vascular resistance

• Pulmonary blood flow is inversely proportional to pulmonary vascular resistance (PVR)

• PVR is low as compared to systemic circulation

• It changes with phases of respiration i.e During inspiration pulmonary vessels are dilated as there is decrease in intra thoracic pressure

• This causes a decrease in PVR resulting in increased pulmonary blood flow

• During expiration….increased PVR….decreases pulmonary blood flow(PBF)

• During exercise PVR decreases …increasing PBF..hypoxia and hypercapnea

Nervous factors

sympathetic stimulation

Release of vasoconstrictor substances from capillary epithelial cells

Adjacent blood vessels constrict

5 fold increase in vascular resistance

parasympathetic stimulation

Release of vasodilator substances from capillary epithelial cells

Adjacent blood vessels dilate decrease in vascular resistance

Chemical factors• Excess of CO2 or lack of O2 causes

vasoconstriction• Exact cause of vasoconstriction is

not known• This is of significance in those

conditions which lead to hypoxia of some alveoli, blood is redirected to those alveoli which are better aereated.

Hydrostatic pressure gradient in lungs

IN STANDING POSITION• Pulmonary arterial pressure (PAP) in

the uppermost portions of the lungs = 15 mmHg < than PAP in lower parts of lungs

• PAP in the lowermost portions of the lungs = 8 mmHg > than PAP at the level of heart

The distance between upper and lower portions of lungs is 30 cm….20 cm above heart and 10 cm below.

1cm of H2O= 0.77 mmHg

30 cm of H2Ox 0.77 mmHg=23mmHg

At apex 20 cm of H2Ox 0.77 mmHg=15 mmHg

At base 10 cm of H2Ox 0.77 mmHg= 8mmHg

Z0nes of blood flow

• Alveolar capillaries distend with increase in pressure inside them but simultaneously being compressed by alveolar pressure on their outer surfaces.

• Therefore increase in alveolar pressure causes closure of capillaries…no blood flow

ZONES OF LUNGS

Zone i

• No blood flow during any phase of cardiac cycle

• Alveolar pressure always remain higher than local alveolar capillary pressure

Zone ii

• Intermittent blood flow because• During systole PAP increases than

pulmonary alveolar pressure and decreases during systole

Zone iii

• Continuous blood flow because• During entire cardiac cycle (systole

and diastole) PAP remains increased than pulmonary alveolar pressure

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PULMONARY BLOOD FLOW DISTRIBUTION

(THREE ZONES OF BLOOD FLOW) NORMAL LUNG IN UPRIGHT

POSITIONZone II (Apex)Zone III (Base) Zone I ( No )

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ZONE II• Pulmonary arterial pressure (PAP) at

level of heart=25/8 mmHg• PAP at apex of the lung is 15mmHg

less than PAP at the level of heart 25-15=10mmHg

• This pressure is greater than the alveolar pressure i.e =0mmHg

• Therefore during systole blood flows through the pulmonary capillaries

• During diastole PAP at level of heart is 8mmHg which is not sufficient to push blood to a level of 15mmHg pressure to cause pulmonary capillary blood flow

• Hence blood flow at apices is intermittent.

ZONE III During systole and diastole PAP

remains higher than the zero alveolar pressure so there is continuous blood flow

IN LYING (SUPINE) POSITION No part except few cm are above the

level of heart so there is only zone III which includes lung apices as well

Blood flow in zone i• It always occurs in abnormal conditions

i.e pulmonary alveolar pressure increases too much or PAP decreases too much

• In upright position when a person breaths against positive pressure alveolar pressure is 10 mmHg higher than normal…zone I no zone II

• In severe blood loss PAP decreases much …….zone I

Pulmonary capillary dynamics

CAPILLARY EXCHANGE OF FLUIDS

FORCES TENDING TO MOVE FLUIDS OUTWARDS FROM CAPILLARIES TO INTERSTITIUM

• Capillary pressure 7mmHg• Interstitial fluid colloid osmotic pressure 14mmHg• Negative interstitial fluid pressure 8mmHg TOTAL OUTWARD FORCE 29mmHg

FORCES TENDING TO MOVE FLUIDS inWARDS FROM INTERSTITIUM

TO CAPILLARIES

Capillary pressure 7mmHg Plasma colloid osmotic pressure

28 mmHg TOTAL INWARD FORCE 28mmHgThus the normal outward forces areslightly greater than the inward forces

Mean filtration pressure at capillary membrane

• Total outward force + 29mmHg• Total inward force - 28mmHg• Mean filtration pressure +1mmHg • This filtration pressure causes

continual and slow flow of fluid from pulmonary capillaries into interstitium..small amount evaporates in the alveoli rest drained by lymphatics.

PULMONARY OEDEMA

• Pulmonary edema is a condition characterized by fluid accumulation in the lungs caused by back pressure in the lung veins. This results from malfunctioning of the heart.

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Causes:

• Pulmonary edema is a complication of a myocardial infarction (heart attack), mitral or aortic valve disease, cardiomyopathy, or other disorders characterized by cardiac dysfunction.

Pathophysiology:

• Fluid backs up into the veins of the lungs. Increased pressure in these veins forces fluid out of the vein and into the air spaces (alveoli). This interferes with the exchange of oxygen and carbon dioxide in the alveoli.

Symptoms:

• Extreme shortness of breath, severe difficult breathing

• Feeling of "air hunger" or "drowning" • "Grunting" sounds with breathing • Inability to lie down • Rales• Wheezing • Anxiety

Symptoms:

• Restlessness • Cough • Excessive sweating• Pale skin• Nasal flaring• Coughing up blood• Breathing, absent temporarily

Signs:

• Auscultation may show crackles in the lungs or abnormal heart sounds.

• A chest x-ray may show fluid in the lung space.

• An echocardiogram may be performed in addition to (or instead of) a chest x-ray.

Tests:

Blood oxygen levels (low) A chest X-ray may reveal the following: Fluid in or around the lung space Enlarged heart

Tests:

Echocardiogram may reveal the following:

Weak heart muscle Leaking or narrow heart valves Fluid surrounding the heart

Treatment:

• Oxygen is given, by a mask or through endotracheal tube using mechanical ventilation.

• Medications include diuretics such as furosemide to remove fluid, vasodilators to help the heart pump better, drugs to treat anxiety, and other medications to treat the underlying cardiac disorder.

PULMONARY OEDEMA – SAFETY FACTOR

• Increased lymph flow: Increased fluid filtration causes increased lymph flow which tends to remove the fluid.

• Decrease in interstitial oncotic pressure : When filtration increases, the albumin loss in the filtrate increases. This combined with the increased lymph flow washes the albumin out of the interstitium and interstitial oncotic pressure decreases.

• High interstitial compliance: A large volume of fluid can accumulate in the gel of the interstitium without much pressure rise.

PLEURAL EFFUSIONDefinition:

Accumulation of fluid in pleural space

Causes: Lymphatic blockage Cardiac failure Greatly reduced plasma colloid osmotic pressure

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