The pulmonary circulation has several key characteristics: 1) It has low pressure and resistance but high compliance, allowing the lungs to accommodate large blood volumes. 2) Pulmonary blood flow increases with elevated pulmonary arterial pressure due to recruitment of new vessels and increased vessel distension. 3) Hydrostatic pressures in the lungs vary based on posture, creating three zones of blood flow.

2.  Pulmonary artery
 Bronchial artery
 Lymphatic circulation

5.  Two left and one right
 From descending aorta
 Contributes to a physiological shunt

6.  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

7.  PVR falls with increased pulmonary
arterial pressure
› Occurs because of two reasons
› Recruitment
› Increased capillary distension
 Importance :- prevents pulmonary edema
reduces velocity

8.  Vessels contain 600 ml of blood at rest
 Increases and decreases according to
posture and pathological conditions

9. 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

10.  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

11.  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

14.  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

15.  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

16.  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

17.  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 ,

18.  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

19.  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

20.  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

21.  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

22.  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

23.  Neural regulation is not very effective
 Chemical control is major regulatory
mechanism