1. The document discusses the pulmonary circulation, which carries deoxygenated blood from the heart to the lungs to be oxygenated, and then back to the heart. 2. It describes characteristics of the pulmonary blood vessels, such as their thin walls, elasticity, and low pressure system. Pulmonary arterial pressure is typically 25/10 mm Hg. 3. Pulmonary blood flow is measured using Fick's principle, which involves measuring oxygen consumption and the arterial and venous oxygen content difference to calculate cardiac output.

1. Exchange of Gases II (V/P Ratio)
Dr Sushil Kharel

2. • Pulmonary circulation is the flow of blood
from the right ventricle through the pulmonary
artery to the lungs, where carbon dioxide is
exchanged for oxygen, and back through the
pulmonary vein to the left atrium.
• Also known as lesser circulation.

4. CHARACTERISTIC FEATURES OF
PULMONARY BLOOD VESSELS
1. Pulmonary artery has a thin wall. Its
thickness is only about one third of
thickness of the systemic aortic wall.
2. Pulmonary blood vessels are highly
elastic and more distensible

5. 3. Pulmonary capillaries are larger than
systemic capillaries.
4. Vascular resistance in pulmonary circulation is
very less; it is only one tenth of systemic
circulation
5. Pulmonary vascular system is a low pressure
system. Pulmonary arterial pressure and
pulmonary capillary pressure are very low

6. „PULMONARY BLOOD PRESSURE
• Pulmonary Arterial Pressure
Systolic pressure : 25 mm Hg
Diastolic pressure : 10 mm Hg
Mean arterial pressure : 15 mm Hg.

7. Pulmonary blood flow
• The lungs receive whole amount of blood
pumped out from the right ventricle.
• The output of blood per minute is same in
both ventricles, it is around 5 Liters.
• Thus, lung accommodates the amount of
blood which is equal to that
accommodated by all the other organs of
the body.

8. MEASUREMENT OF PULMONARY
BLOOD FLOW
• Adolph Fick described Fick principle in
1870.
• According to this principle, the amount of a
substance taken up by an organ or given out in
a unit of time is the product of amount of
blood flowing through the organ and the
arteriovenous difference of the substance
across the organ.

9. • By modifying Fick principle, cardiac
output is measured in two ways:
i. By using oxygen consumption
ii. By using carbon dioxide given out.

10. • Fick principle is used to measure the cardiac
output by determining the amount of oxygen
consumed in the body in a given period of time
and dividing this value by the arteriovenous
difference across the lungs.

11. • Cardiac output = O2 consumed (in mL/minute)
Arteriovenous O2 difference
Calculation
O2 consumed (by lungs) = 250 mL/minute
O2 content in arterial blood = 19 mL/100 mL of
blood
O2 content in venous blood = 14 mL/100 mL of
blood

12. CO= (250/ 5) X100 mL/min
=5000 mL/min
= 5 L/min

14. Pulmonary Ventilation
• Pulmonary ventilation is a process by
which fresh air enters the lungs and
equal volume of air leaves the lungs.
• Air move in and out per minute so
also called RMV( Respiratory
Minute Volume)

15. Pulmonary Ventilation
• Normal value of Pulmonary ventilation is
6000 ml
• TV X RR= 500 X 12/min
= 6000ml/min

16. Alveolar ventilation
• Amount of air utilized for gaseous
exchange every minute
• Normal value= 4200ml
• (TV-Dead Space) X Respiratory Rate
= (500-150) X 12
=4200 ml

17. •Pulmonary blood flow 5l/min
•The alveolar capillary membrane
has surface area of 50 to 100 m²
PULMONARY PERFUSION

18. •Due to gravitational influence the
lower – dependent areas receive more
blood
•Upper zone – nondependent areas are
less perfused

21. •Ventilation[VA] less increased
towards lower zone than
Perfusion[Q]
•Perfusion more increased
towards lower zone than
Ventilation
•Ventilation Perfusion ratio
VA/Q: Less towards lower zone
VA/Q
VA
Q
Ventilation Perfusion ratio VA/Q

22. The overall V/Q = 0.8
Ranges between 0.3 and 3.0
Upper zone –nondependent area has higher ≥ 1
Lowe zone – dependent area has lower ≤ 1
VP ratio indicates overall respiratory functional
status of lung
V/Q = 0 means ,no ventilation-called SHUNT
V/Q = ∞ means ,no perfusion – called DEAD
SPACE
VENTILATION PERFUSION RATIO VA/Q

24. Shunted Blood Flow
• Perfusion exceeds ventilation
–Obstructive lung disease (due to an overall
reduction in ventilation)
–Restrictive lung disease (due to reduced
lung volumes)
–Hypoventilation
–Inability of alveoli to remain inflated
(surfactant deficiencies)

25. Ventilation/Perfusion ratio is the ratio of
A. Pulmonary ventilation to pulmonary
blood flow
B. Minute ventilation to pulmonary
capillary pressure
C. Alveolar ventilation to pulmonary
blood flow
D. Alveolar ventilation to pulmonary
capillary pressure

26. Ventilation Perfusion ratio is
maximum in
A.Zone 1 ( Apex)
B.Zone 2 ( middle )
C.Zone 3 ( Base)
D.Equal in all zones

27. Important KU question
• Describe the method of measurement
of Cardiac Output by Fick’s
principle.
• Peculiarities of Pulmonary
circulation
• Exchanges of gases
• Ventilation perfusion ratio