Date post: | 16-Jul-2015 |
Category: |
Documents |
Upload: | yogesh-ramasamy |
View: | 159 times |
Download: | 1 times |
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