BLOOD PRESSURE - PHYSIOLOGY ROBYN DANE AND KATY DAVIDSON

How do you calculate MAP? MAP = CO x SVR MAP = (2DBP + SBP)/3 How do you calculate pulse pressure? Difference between diastolic and systolic pressures PP = SBP - DBP

What factors affect cardiac output? (2) Changes in Heart rate Stroke volume What factors affect SVR? (2) Changes in Compliance (of the aorta or arterioles) Arteriolar resistance

What is compliance? The rigidity of vessles What may affect compliance? Age makes vessels more rigid Poiseuilles equation How is resistance related to the size of the vessel? Resistance is inversely related to the radius cubed.

Describe the neuronal controls of blood pressure Baroreceptor reflex Stretch receptors located in the carotid sinus (CN IX) and the aortic arch (CN X) Vasomotor and cardiac control centres in the medulla Parasympathetic and sympathetic effectors to the heart and blood vessels Fall in blood pressure ↑ sympathetic ↓parasympathetic Rise in blood pressure ↓ sympathetic ↑parasympathetic

Chemoreceptor reflex Increase in blood acidity caused by increase in CO2 and lactic acid levels. Detected by chemoreceptors (in carotid arteries and aortic bodies) Nerve impulse sent to cardiac centre in medulla oblongata Via CN X and CN IX Nerve stimulation to SAN decreases vagal and increases sympathetic impulses to increase heart rate. Results in an increased cardiac output.

Local control of BP Blood pressure is also controlled locally Firstly via stretch receptors to maintain flow - Increase in transmural pressure should increase radius, causes muscle contraction, which reduces radius and maintains flow Also by release of vasoactive agents locally – NO causes dilation and endothelin 1 causes constriction Metabolites that result in vasodilation include; H+ K+ adenosine CO 2 hypoxia (systemic circulation only) This is to increase flow in areas of increased metabolism to reduce the concentration of the metabolites in the area.

Hormonal control of blood pressure Mainly involves which hormones? Adrenalin and angiotensin II What affect does angiotensin II have on blood pressure ? angiotensinogen angiotensin I angiotensin II renin angiotensin converting enzyme from kidney acts on vascular smooth muscle causing contraction

Starlings compensation Works initially to maintain stroke volume in early heart failure, however, an optimal fiber length exists. Excessively high filling pressures that over-stretch the myocardial fibers, reduces the pumping capacity of the ventricles. Therefore eventually reducing stroke volume later on in the disease. The stretch of cardiac myocytes is directly related to the force at which they contract

Performers will often use running as part of their training programme. Both heart rate and stroke volume increase when running. Use 'Starling's law of the heart' to explain how stroke volume increases when running (4)

St arling’s Law states that the greater venous return, the greater stroke volume is. As venous return increases the walls of the ventricles are stretched further. Results in a more powerful contraction. Increases the amount of blood pumped around the body during exercise.

Briefly explain the terms cardiac output and stroke volume and the relationship between them Explain how it is possible for a trained performer and an untrained performer to have the same cardiac output for a given workload

Cardiac output is the volume of blood leaving left ventricle per minute. Stroke volume is the volume of blood leaving left ventricle per beat. Stroke volume x heart rate = cardiac output Trained atheltes will have larger stroke volume. Can therefore achieve same cardiac output with lower heart rate. Untrained athlete compensates for smaller stroke volume by increasing heart rate.

Calculate the MAP and PP for someone with a systolic BP of 120 and a diastolic BP of 90 MAP = 100 PP = 30 Calculate the cardiac output for a patient with a HR of 100 and a stroke volume 70ml? 7000ml/minute or 7L/min MAP = (2DBP + SBP)/3 PP = SBP - DBP CO = SV x HR

How do the following effect blood pressure Endothelin 1 Angiotensin II NO H+ vasoconstricts (increases BP) locally vasodilates