pulmonary circulation

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by Dr. Chethan H. A.

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Pulmonary circulation:

Pulmonary circulation Dr. Chethan H. A.

Functional anatomy of pulmonary circulation:

Functional anatomy of pulmonary circulation Pulmonary circulation – From right heart, supplies deoxygenated blood, gets oxygenated , drains to left atrium Bronchial circulation From descending thoracic aorta, supplies oxygenated blood, supplies lung parenchyma , gets deoxygenated and drains into left atrium

Physiological shunt:

Physiological shunt Bronchial circulation Coronary vessels Effects Reduce the oxygen saturation Increases left ventricular output

Pulmonary lymphatics:

Pulmonary lymphatics Richly supplied Drains particulate matter, leaked proteins and exuded fluids Flow - pulmonary node – bronchopulmonary nodes – tracheobronchial nodes – bronchomediastinal trunk

Pulmonary circulation – special features:

Pulmonary circulation – special features Thin walled Distensible Highly compliant Low pressure, low resistance high compliance Thickness of rt. Ventricle and pul . Artery is one third the systemic counterpart Arterioles have less smooth muscle, capillaries highly anastomosed

Pressures in the Pulmonary system:

Pressures in the Pulmonary system Rt. Ventricular pressure 25/0 mmHg Pul . Artey – 25/8 mmHg Left atrium – 5mmHg Gradient 10mmHg Pulmonary capillary pressure - measured indirectly 10 mmHg Safety factor of 15mmHg

Pulmonary oedema:

Pulmonary oedema If pul . Cap. Pressure raises above 25mmHg Exercise, high altitude, left heart failure, mitral stenosis and pulmonary fibrosis Even small layer of fluid affects diffusion

Pulmonary wedge pressure:

Pulmonary wedge pressure Direct determination is difficult Indirectly via rt. Heart. Used in conditions of congestive heart failure

Pulmonary blood volume:

Pulmonary blood volume Contain 600ml to 1000 ml Acts as reservoir of blood Increased in mitral stenosis, mitral regurgitation and left heart failure 3 main consequences of Rheumatic heart disease ?

Pulmonary blood flow regional distribution:

Pulmonary blood flow regional distribution Pul . Blood flow is nearly equal to lt. heart flow Pressure difference should be greater than alveolar pressure Effect of gravity 15mmHg at middle of lung 4mmHg at apex 26mmHg at base

Perfusion zones of lungs:

Perfusion zones of lungs Zone I : a<A Zone II a>A>v Zone III a>v>A zoneI – zero flow.. Hypovolaemic shock, pul . Embolism Obstructive lung disorders

Perfusion zones of lungs:

Perfusion zones of lungs Zone II – intermittent blood flow in systole Waterfall effect From apex to hilum 14mm to -3mmHg

Effect of exercise on regional pulmonary blood flow:

Effect of exercise on regional pulmonary blood flow Entire lung becomes zone III Highest increase at the apex Mediated by Recruitment of capillaries Distension of existing capillaries Pulmonary transit time Total 4 seconds, across alveoli reduces from 1 to 0.3 sec

Interstitial fluid in lungs:

Interstitial fluid in lungs Low capillary pressure 7mmHg More negative interstitial pressure -8mmHg High capillary permeability 14mmHg

Starling ‘s forces :

Starling ‘s forces Outward forces Oncotic 14 Interstitial pressure -8 Capillary hydrostatic 7 Total 29 Inward pressure Plasma oncotic pressure 28 Net outward of 1 mmHg

Pulmonary oedema:

Pulmonary oedema Safety factor of 21mmHg Causes of oedema Increased capillary permeability Acute left heart failure Chronic cases lymphatic drainage compensates

Pulmonary circulation - functions:

Pulmonary circulation - functions Respiratory gas exchange Reservoir for left ventricle Filters fibrin, clots, debris, emboli, cells etc. Keeping alveoli dry Absorption of drugs Synthesises ACE

Regulation of pulmonary blood flow:

Regulation of pulmonary blood flow Neural control Chemical control

Neural control:

Neural control Efferent sympathetic vasoconstrictors Baroreceptor reflex – vasodilatation Chemoreceptor reflex – vasoconstriction The result Is more on capacitance than on resistance

Neural control:

Neural control Vagal Pulmonary baroreceptors: - hypotension and bradycardia Pulmonary volume receptors – Bainbridge reflex – tachycardia and diuresis J receptors – (AS Paintal ) exercise – justapulmonary fluid and emboli – tachypnoea , dyspnoea , decreases muscle tone. Neural mechanisms not very effective.

Chemical control:

Chemical control Local hypoxia – vasoconstriction to prevent wasted ventilation Mechanism – decreased formation of NO Hypercapnia and acidosis:- Vasoconstricion opposite to that of systemic circulation Chronic hypoxiq – pulmonary hypertension right ventricular hyprtrophy and failure

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