RespirationRespiration

Blood supply to lungsBlood supply to lungs

• Pulmonary arteries

• Pulmonary capillaries

• Pulmonary veins

• Bronchial vessels

Pulmonary Pulmonary CirculationCirculation

• Pulmonary arteries highly distensible with compliance of 7ml/mmHg = compliance of total systemic arterial tree

• Pulm. Arteries so accommodate whole stroke volume

• 1 – 2 % venous drainage through bronchial blood vessels into oxygenated blood, so volume of blood coming to left atrium ↑ by 1 – 2 %

• Also PO2 ↓ by 1 – 2 % (shunted blood)

• Pulmonary blood flow of low pressure – 25/8 mmHg

• Compliance of pulmonary vasculature is due to

• Shorter length of pulmonary arteries and arterioles

• Increase diameter

• Thin vascular walls

• Left atrial pressure = 2mmHg

• Rises in cases of CCF

• Pulmonary capillary wedge pressure

• BLOOD VOLUME OF LUNGS

• 450 ml, 70 ml in pulmonary capillaries

• Lungs act as reservoirs of blood

• e.g. in cases of shock- shift of blood from pulmonary to systemic circulation

• Automatic control of pulmonary blood flow distribution

• Secretion of unknown vasoconstrictor agent by hypoxic alveoli

• So the supply of blood flow to the areas that are better aerated

• Effect of CO2 - ↑ CO2 → Vasoconstriction

↓ CO2 → Vasodilatation

• Effect of O2 - ↓ O2 → Vasoconstriction

↑ O2 → Vasodilatation

• During exercise – Opening of pulm. Capillaries by three folds– Distension of already open capillaries by two

folds– ↑ pulmonary arterial pressure

• No pressure on Rt. Heart

• Normal Lt. Atrium pressure – 1 – 5 mmHg

• Any rise in this pressure compensated in pulm. Capillaries by compliance & distention of pulm. capillaries

• In case of Lt. heart failure – – Retrograde pressure in pulm. Vessels– If ↑ in pressure more than 7mmHg → Also ↑in

pulmonary arterial pressure– So concomitant increased load on Rt. Heart– If ↑ in Lt arterial pressure more than 30mmHg

→ pulmonary edema

• Zones of blood flow in lungs

• Height difference of uppermost and lowermost point of lungs= 30cm

• 23mmHg pressure difference

• Level of heart= tricuspid valve

• In standing person

• Pap in upper part of lung=15mmHg lesser

• Pap in lower part =8mmHg greater

• Pressure differences affecting blood flow

• Little flow on top and 5 times more flow at bases of lungs

• Capillary exchange of fluid in the lungs and pulmonary interstitial fluid dynamics

• Pulmonary edema• Causes• Lt sided ht failure• Damage to pulmonary

capillary membrane• TYPES• Acute• Chronic

• SAFETY FACTOR• Acute: pulmonary

capillary pressure of 21mmHg

• Chronic: expansion of lymph vessels

• Increase in draining capacity by 10 folds