Chapter: 38Pulmonary Circulation,

Pulmonary Edema, Pleural Fluid

By Dr. Mudassar Ali Roomi (MBBS, M.Phil.)

Assist. Prof. Physiology

Physiological anatomy of pulmonary circulatory systemThe pulmonary vessels

the pulmonary arterial tree has a large compliance

Bronchial blood vessels1 to 2 % of the total

cardiac output.the left ventricular

output is about 1 to 2 % greater than the right ventricular output.

Lymphatic from the lungs enter into right thoracic lymph duct

Blood volume of the lungs

500 milliliters

9 % of the total blood volume of the entire circulatory system.

Approximately 70 ml in the pulmonary capillaries

Lungs as a Blood Reservoir (100-250 ml)

Automatic Control of Pulmonary Blood Flow DistributionHypoxia vasoconstrictionWhen concentration of oxygen in the air of the alveoli decreases

below 70 % of normal ,the adjacent blood vessels constrict. This is opposite to effect observed in systemic vessels

Undiscovered vasoconstrictor substance to be released from the lung tissue

Important function: to distribute blood flow to most oxygenated alveoli.

Pressure Pulse Curve in the Right Ventricle.Systolic: 25 mm HgDiastolic: about 0

to 1 mm Hg

Pressures in the Pulmonary Artery.Systolic: 25 mm HgDiastolic: 8 mm Hg.Pulse pressure: 17

mm Hg.

Pulmonary Capillary Pressure: 7 mmHg

Left Atrial and Pulmonary Venous Pressures: The mean pressure in the

left atrium and the major pulmonary veins averages about 2 mm Hg

estimated with moderate accuracy by measuring the pulmonary wedge pressure (5 mm Hg). It is 2 to 3 mm Hg greater than the left atrial pressure

Comparison of pressures in systemic and pulmonary circulations.

Length of Time Blood Stays in the Pulmonary Capillaries (0.3-0.8 sec).

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

During heavy exercise, blood flow through the lungs increases fourfold to sevenfold.

This extra flow is accommodated in the lungs in three ways:

(1) by increasing the number of open capillaries,

(2) by distending all the capillaries(3) by increasing the pulmonary arterial

pressure.

Shift of Blood Between the Pulmonary and Systemic Circulatory Systems as a Result of Cardiac Pathology (left heart failure).

affects the pulmonary system greatly but usually has only mild systemic circulatory effects.

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

Hydrostatic pressure is affected by gravity

Pulmonary arterial pressure at the apex of lung of a standing person is about 15 mm Hg less than the pulmonary arterial pressure at the level of the heart

The pressure in the base of the lungs is about 8 mm Hg greater than the pulmonary arterial pressure at the level of the heart.

Zone 1 blood flowNo blood flow during all

portions of the cardiac cycle

Zone 1 Blood Flow Occurs Only Under Abnormal Conditions.

occurs when either the pulmonary systolic arterial pressure is too low or the alveolar pressure is too high to allow flow

1. Too high alveolar pressure e.g. Breathing against a positive air pressure

2. After severe blood loss.

Zones of Pulmonary Blood Flow

Zones of PulmonaryBlood FlowZone 2 (intermittent fblood low) in

the apices. In normal lungs, this zone is about

10 centimeters above the midlevel of the heart and extends from there to the top of the lungs

Blood flows during systole but not during diastole.

Zone 3 (continuous blood flow throughout the cardiac cycle) in all the lower areas. from about 10 centimeters above

the level of the heart all the way to the bottom of the lungs,

In lying posture, all lung has got zone 3 .

Effect of exercise on pulmonary blood flow

Capillary Exchange of Fluid in the Lungs, and Pulmonary Interstitial Fluid Dynamics

STARLING FORCES: Capillary Exchange of Fluid in the Lungs, and

Pulmonary Interstitial Fluid Dynamics

Negative Pulmonary Interstitial Pressure and the Mechanism for Keeping the Alveoli “Dry.”

Pulmonary Edema

CAUSESLeft-sided heart failure mitral valve diseaseDamage to the pulmonary

blood capillary membranes1. Infections (pneumonia) 2. Breathing noxious

substances such as chlorine gas or sulfur dioxide gas

Pulmonary Edema Safety Factor

pulmonary capillary pressure must rise from the normal level of 7 mm Hg to more than 28 mm Hg

Safety factor against pulmonary edema of 21 mm Hg.

Safety Factor in Chronic Conditions (>2 weeks) e.g. Chronic mitral stenosis

No lethal edema in chronic lung conditions. This is because Lymph vessels expand greatly and increase the drainage of fluid (upto 10 fold).

Pulmonary capillary pressures may rise upto 40 to 45 mm Hg even without development of pulmonary edema.

Rapidity of Death in Acute Pulmonary Edema

A medical emergencyCause: Acute left-sided heart failurePulmonary capillary pressure may rise more than 50

mmHgDeath frequently ensues in less than 30 minutes in severe

cases

Pleural Cavitythe pleural space—the space

between the parietal and visceral pleurae

It is a potential space only It contains only a few

ml fluid.

a thin layer of mucoid fluid lies between the parietal and visceral pleurae for easy slippage of moving lungs.

The pleural membrane

serous membrane through which small amounts of interstitial fluid transude continually into the pleural space.

Pumping of fluid from the space by the lymphatics provides negative pressure in pleural cavity (–7 mm Hg).

Pleural EffusionDefinition: Pleural effusion

means the collection of large amounts of free fluid in the pleural space.

The effusion is analogous to edema fluid in the tissues and can be called “edema of the pleural cavity.”

Causes:1. Blockage of lymphatic2. Cardiac failure3. Greatly reduced plasma

colloid osmotic pressure4. Infection or any other

cause of inflammation