Blood Pressure Regulation

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Cardiac Output =	heart rate x stroke volume
Typical resting values: CO HR SV	CO = 5 – 6 l/min HR = 60 – 80 bpm SV = 80 – 100 ml
Summary of Factors Controlling Cardiac Output - Venous Return - End-diastolic Volume - Sympathetic - Parasympathetic -SV -HV -Co	- Venous return increases end-diastolic volume - End-diastolic volume increases stoke volume - Sympathetic increases stoke volume and heart rate - Stroke volume and heart rate increase cardiac output - Parasympathetic decrease heart rate
Heart Rate	Determined by rate of depolarisation in autorythmic cells
Stoke volume	Determined by force of contraction in ventricular myocardium Influenced by: - Contractility - End-diastolic volume - Resp pump - Skeletal muscle pump
Blood Pressure = Cardiac Output x Vascular resistance	Arterial blood pressure (BP), is the pressure exerted by circulating blood upon the walls of blood vessels – DO NOT CONFUSE THIS WITH VENOUS PRESSURE When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure. Typical values are 120 mmHg systolic, and 80 mmHg diastolic. Mean blood pressure decreases as the blood moves away from the heart through arteries and capillaries. Mean blood pressure drops over the whole circulation, although most of the fall occurs along the small arteries and arterioles.
Mean arterial blood pressure is determined by: and what each sub section is determined by	- Blood volume, -> Fluid intake and loss - Effectiveness of the heart as a pump (CO) -> HR, SV - Resistance of the system to blood flow -> Diameter of the arterioles - Relative distribution of blood between arterial and venous blood vessels -> Diameter of the veins
Reflex (Neural) control of increase blood pressure 1-5 steps	1. Stimulus: Increases blood pressure. (arterial blood pressure rises above normal range) 2. Baroreceptors in carotid sinuses and aortic arch are stimulated 3. Increase impulses from baroreceptors stimulate cardioinhibitory centre (and inhibit cardioacceleratory centre) and inhibit vasomotor centre 4a. Decrease sympathetic imposes to heart, causing decrease HR, Contractility and CO 4b. Decrease rate of vasomotor impulse allows vasodilation causing decreased R 5. Decrease CO and Decrease R return blood pressure to homeostatic range
Reflex (Neural) control of decrease blood pressure 1-5 steps	1. Stimulus: Decrease blood pressure. (arterial blood pressure falls below normal range) 2. Baroreceptors in carotid sinuses and aortic arch are inhibitied 3. decrease impulses from baroreceptors activate cardioinhibitory centre (and stimulate cardioacceleratory centre) and stimulate vasomotor centre 4a. Increase sympathetic imposes to heart, causing Increase HR, Contractility and CO 4b. Vasomotor fibers stimulate vasoconstriction causing increase R 5. Increase CO and Increase R return blood pressure to homeostatic range
electrical system	Electrical system: SA node, AV node, Bundle of His, Purkinje fibres Automaticity: generate spontaneous depolarisation (SA & AV nodes) SA node is pacemaker (rate 70/min.) Depolarisation of atria reflected in P-R interval of the ECG Depolarisation of ventricles is reflected in the QRS complex on the ECG
Preload	Volume of blood in ventricles at end of diastole
Preload increased in	Hypovolemia Regurgitation of cardiac valves Heart Failure
After load	Resistance left ventricle must overcome to circulate blood what the left ventricle has to push against, the back pressure exerted by arterial blood
After load increased	Hypertension Vasoconstriction Increased afterload = increased cardiac workload
Frank-Starling law	Exercise increases sympathetic activity which increases cardiac output and venous return (skeletal muscle pushes blood through venous system) EDV (End-diastolic volume) or pre-load: degree of stretch in the cardiac muscle (rubber band) ↑Venous return → ↑EDV → ↑SV → ↑Cardiac output
Parasympathetic	Slows rate Decreases contractility Slows conduction through the AV node
Sympathetic	Speeds up rate Increases contractility Speeds up conduction through av node
Central venous pressure (CVP) (also known as: right atrial pressure; RAP	) describes the pressure of blood in the thoracic vena cava, near the right atrium of the heart. CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood into the arterial system. 5-10mmHg normal.
What is mean arterial pressure (MAP)?	MAP is the average blood pressure in an individual. It is the average arterial pressure during a single cardiac cycle An indicator of tissue perfusion Adequate tissue perfusion keeps organs safe from tissue death MAP of 60mmHg – 70mmHg is adequate

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Blood Pressure Regulation

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	Erstellt von Jonathan Cash vor mehr als 8 Jahre