Regional Circulation Prof. K. Sivapalan

2013 Regional Circulation 2 Regional blood flow. Every organ has specific functions to perform. The blood flow to each organ will vary depending on the functional state of the organ, metabolic requirements and general conditions. Blood flow to each organ can be measured by –Fic principle using substances released into or removed from blood. –Plathysmography. –Flow meters.

2013 Regional Circulation 3 Pulmonary circulation. Pressure: 25 / 10 mm Hg. Thickness of the wall of Pulmonary artery is only 30 % compared to aorta and arterioles also contain less muscles ml of blood in pulmonary vessels when erect. When erect, base of the lungs are at the level of the heart. When lying, most of the lungs are below heart level. When lying 400 ml more accumulates.

2013 Regional Circulation 4 Pulmonary circulation ctd. Bronchial vein opens into the pulmonary vein resulting in 2 % deoxygenated blood mixing with oxygenated blood. Capillaries form baskets around alveoli and their diameter is 8μ. Abundant lymphatics. No tissue fluid formation in alveoli: –Pressure less than oncotic pressure. –Surfactant. Function – gas exchange, filtration of clots, etc. Ventilation perfusion ratio: –Alveolar ventilation / cardiac output = 4.2 / 5.5 = 0.8 –Varies within regions of lung due to gravity.

2013 Regional Circulation 5 Regulation of Pulmonary circulation. All cardiac output goes through lungs. Inspiration increases venous return to right atrium and reduces to left atrium. Expiration reverses the inequality resulting in differences in stroke volume Local metabolites: –Hypoxia, hypercapnoea and acid → arteriolar constriction [different from other areas]. Arteriolar constriction by, –Sympathetics, catecholamines, angeotension II, thromboxans,PGF2 Arteriolar dilatation by, –Acetylcholine, PGI2, histamine.

2013 Regional Circulation 6 Splancnic circulation. Blood flow through liver [1500 ml per min.]. From portal vein [1L] and hepatic artery to hepatic vein through sinosoids. Sympathetic: vasoconstriction Reduces during heavy exercise and hemorrhage. Dogs: spleen reservoir for red cells. Parasympathetic: vasodialatation. Vasoactive intestinal peptide from intestine dialates. Blood flow doubles after meals. Congestive cardiac failure: enlarged liver, necrosis around central vein. Cirrhosis of the liver [fibrosis]: acytis due to portal hypertension.

2013 Regional Circulation 7 Cerebral circulation. Two internal carotid and two vertebral arteries supply blood to brain. Arteries anastomose at the circle of Willis but mixing blood is minimal under normal conditions. Precapillary anastomosis between arteries are minimal and not effective and so arteries in brain are known as end arteries. If they are occluded, the area supplied by them will result in ischemia and infraction. Deep veins empty into Venus sinuses in dura and internal carotid vein. Blood from eye and nose also drain into internal carotid vein.

2013 Regional Circulation 8 Exchange of substances in cerebral vessels. Blood brain barrier: tight junctions in endothelium & pia mater [choroid epithelium] or end feet of astrocytes applied to endothelium. No fenestrations in capillaries. Only water, CO 2 and O 2 cross BBB. Cerebrospinal fluid formed in choroid plexus. Astrocytes feed neurons.

2013 Regional Circulation 9 Cerebral blood flow. Cranium contains brain [1400 g.], blood [75 ml], CSF [75 ml, 550 ml/d]. Flow: 750 ml/min. [54 ml/100 g.] Kept constant by, –Cranium. –Auto regulation [negligible VMC effect]. –Cushing reflex- ↑ ICP → ↓ blood flow → ischemia → + VMC, +CIC, ↑BP Regional flow within the brain is affected by metabolites. Serious reduction of systemic blood pressure reduces blood flow. No blood for 1 minute – faint, 5 minutes: serious damage to cortical areas. Further ischemia – death.

2013 Regional Circulation 10 Coronary circulation. Coronary arteries arise from sinuses behind two cusps of aortic valves. Veins →coronary sinus →right atrium. Interior parts of ventricles drain directly into chambers, into left heart as well. Arteries anastomose to a certain extent. It can be improved by exercise.

2013 Regional Circulation 11 Coronary flow. At rest: 250 ml/min. (84 ml/100g/min.) oxygen extraction 70 – 80 %. Left ventricle is responsible for ejection resulting in higher tissue pressure than the aortic pressure in systole. Flow in left coronary artery is highest during diastole.

2013 Regional Circulation 12 Regulation of coronary flow. Mechanical factors. –Left ventricle- during systole intra muscular tension compresses arteries and therefore blood flows only during diastole. Metabolites: –Hypoxia, hypercapnoea, acidity, potassium ions, lactic acid, adenine nucleotides, adenosine- vaso dilators. Neural: –α constriction. [ in muscle, ↑force, metabolites → dilatation] –β dilatation

2013 Regional Circulation 13 Abnormalities of coronary flow. Atherosclerosis is deposition of fatty material below intima, calcification, damage to intima, etc. This narrows the lumen and prevents dilatation and promotes thrombosis which can block completely. When this occur in coronary arteries, angina pectoris and myocardial infarction can occur. Risk factors: over eating, diabetes, smoking, lack of exercise, stress. Alcohol – dilator but promotes atherosclerosis. ? benefit to heart. Aspirin 150 mg daily, glyceryl trinitrin and other drugs better care.

2013 Regional Circulation 14 Cutaneous circulation. Function of skin: heat loss and protection. Flow 1 to 150 ml/min/100g. Cutaneous vaso dilatation in hot and constriction in cold under thermoregulatory center. Extreme cold, arterio-venus anastomosis shunt blood in fingers, toes, palm and ear lobes. Prolong exposure to cold – exhaustion of smooth muscles, vaso dilatation and bleeding [frost bite] Subdermal venous plexus- reservoir of blood.

2013 Regional Circulation 15 Control of flow. Vasomotor tone – constriction. Circulating catacholamines- constriction. Thermoregulatory influence over rides baro receptor influences. [blanket and shock] Local metabolites – dilatation. Reactive hyperaemia- after occlution. Dilatation caused by alcohol.

2013 Regional Circulation 16 Response to injury. Mild stroke- – white reaction. –[Mechanical stimulation to pre capillary sphincters.] Deeper stroke- triple response: –Red reaction [ cap. Dilatation.] –Wheal [cap. Permeability] –Flare. [art. Dilatation] Axon reflex.

2013 Regional Circulation 17 Capillary circulation. Contain 5 % of the blood. Active blood [exchange]. Transition time – 1 -2 sec. –Pre capillary sphincters- controlled by local metabolites. Fluid exchange. Pulse pressure from 5 → 0. [pulsatile → non pulsatile]

2013 Regional Circulation 18 Special capillaries. Liver – sinusoids. Brain – BBB. Kidney – glomerular tuft and vasa recta.

2013 Regional Circulation 19 Uterus. 8 x 5 x 3 cm, 70 grams. Pregnancy – well developed uterus and fetus. Uterine artery develops and blood flow increases more than 20 times.

2013 Regional Circulation 20 Placental circulation. The placenta has to provide oxygen and nutrients to and remove wastes from the fetus. Umbilical vein and artery form villi covered with chorion. Inter villus space is filled with maternal blood. Arterioles open into and venules drain the blood from this space. [no capillaries] This increases cardiac output but reduces peripheral resistance. Pulse pressure increases.

2013 Regional Circulation 21 Fetal respiration. Gas exchange through placenta. Fetal Hb % = 18 g/100 ml. Fetal hemoglobin attaches to oxygen at lower partial pressure than adult Hb.

2013 Regional Circulation 22 Fetal circulation. Umbilical vein: 80 % saturated. Venous blood from lower body: 26 % saturated. IVC: 67 % saturated. Left atrium gets IVC blood through foramen ovale. Upper body gets this blood through aorta. SVC [60 % saturated] drains into right ventricle through the atrium and goes to lower body and placenta through ductus arteriosus [lung high resistance] Pressure in pulmonary artery is higher than in aorta. 55% of cardiac out put goes to placenta.

2013 Regional Circulation 23 Change at birth. Placental circulation cut. Foramen ovale is closed [left atrial pressure rises, umbilical vein closed] Ductus arteriosus is closed as lungs expand and draw blood in.