Pulmonary artery

Bronchial artery

Lymphatic circulation

Two left and one right

From descending aorta

Contributes to a physiological shunt

Thin walled , distensible , large compliance

Low pressure , low resistance , high

capacitance system

Pul capillaries are larger and have more

anastamosis

Helps in gas exchange

Serves as a filter

Metabolic functuions

Serves as a blood reservoir

PVR falls with increased pulmonary

arterial pressure

› Occurs because of two reasons

› Recruitment

› Increased capillary distension

Importance :- prevents pulmonary edema

reduces velocity

Vessels contain 600 ml of blood at rest

Increases and decreases according to

posture and pathological conditions

Pressure Pulmonary system Systemic vasculature

Ventricular pressure RV- 25 (systolic) LV- 120 systolic

Pulmonary artery 25 sys

8 diastolic

120 sys

80 dias

MAP 15 mm/hg 100

Pulse pressure 17 40

atrial pressure LA – 5 RA - 0

Pressure gradient Pp= MAP- MVP= 15-5

=5

100

Mean value is 10 mmHg

Is less than colloid osmotic pressure

25mmHg

So a net suction force of 15mmHg is

keeping the alveoli dry

However if hydrostatic pressure raises

more than 25mmHg then pulmonary

edema ensures

Is measured to give the LAP

Direct measurement of LAP is difficult

So indirect measurement is done

LAP corresponds to PCWP

Measures by swans gans catheter

Catheter is wedged in the tip of the small

branch of pulmonary artery

Stops flow of blood in that

Same as the CO or LV output

Effect of gravity :-

› in supine position MAP is same allover the

lungs so uniform perfusion

› Gravity changes the hydrostatic pressure

› Zero reference plane is at the level of RA

› Which is approximately at the middle of the

lung or hilum

In a 30cm height lung

In the middle pressure is 15mmHg

In the apex its 11 mmHg less ie 4mmHg

In the base its 26mmHg

Depends upon three pressure

› PA - alveolar pressure

› Pa – pulmonary arterial pressure

› Pv – pulmonary venous pressure

Divided into three zones in erect

posture – 1, 2, 3

Area of zero perfusion

Does not exist in normal lungs

Occurs when Pul arterial pressure

becomes less than alveolar pressure

Pulmonary capillaries become collapsed

Flow becomes zero

Ex- pulmonary embolism , shock ,

obstructive lung diseases ,

Region of intermittent blood flow

This occurs during systole when the pul

arterial pressure raises more than PA

In normal lungs this zone occurs from

apex to hilum of the lungs

Systolic pa pressure is 25 and diastolic is 8

In a 30cm height lung

In the middle pressure is 15mmHg

In the apex its 11 mmHg less ie 4mmHg

In the base its 26mmHg

This zone has continues high blood flow

Here pa is greater than PA during the

entire cardiac cycle

this region occurs in from the middle

zone of lungs to bottom

Blood flow increases 4- 7 times

Near base its 2-3 times

In apex its 8 times

So whole lungs becomes zone 3

Possible because of two reasons › Recruitment

› Distensibility

Ability of lungs to accommodate large blood serve two purpose

Reduces rt heart work and prevents pulmonary edema

Pulmonary transit time 4sec

Net filtration pressure › Net outward forces :-

Interstitial oncotic pressure = 14mmHg

Intersttial hydrostatic pressure = -8

Capillary hydroststic pressure = 7

Total = 29mmHg

› Net inward pressure:-

Plasma oncotic pressure = 28mmHg

NFP = 29-28= 1

Neural regulation is not very effective

Chemical control is major regulatory

mechanism