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Week 12 Arterial Blood pressure & Heart sounds • Systole: ventricle contraction • Diastole: ventricle relaxation • Systole and diastole = one cardio cycle BLOOD PRESSURE • Blood pressure is defined as the pressure of the blood exerts against the blood vessel walls (arteries). • The highest blood pressure that results from contraction of the ventricles of the heart is the systolic pressure – the force of blood in your arteries as the heart contracts and pushes it out • The lowest blood pressure that results from relaxation of the ventricles is the diastolic pressure – the force of your blood between heartbeats • A measurement of 130 / 85 reflects a systolic pressure of 130 and diastolic pressure of 85. MEASURING BLOOD PRESSURE • To measure blood pressure, place the blood pressure cuff, sphygmomanometer, and stethoscope as shown in the diagram. • measured as the brachial artery compressed by a blood pressure cuff • A stethoscope is used to hear sounds that result from the compression and release of pressure on the blood vessel. Pronounced (sfig’-mo-ma-nom-e-ter) Blood pressure reading • Place the cuff so that it just fits the arm, and is neither too tight nor too loose. • Inflate the cuff so that the sphygmomanometer reads at least 160. You should not hear any sounds at this point. • Slowly deflate the cuff, and note the reading when you begin to hear thumping/sharp tapping sounds through the stethoscope. This reading is the systolic pressure (the first sound of Korotkoff). • Continue deflating the cuff until the thumping sound stops/muffles, and note the reading. This is the diastolic pressure (the second sound of Korotkoff). • Finish deflating the cuff, and remove it from the arm. • Wait ten minutes before attempting to take a second blood pressure reading on the same person. Sounds of Korotkoff • Sound is created by turbulent flow of blood through the compressed vessel • Sound disappear when the vessel is no longer compressed by the pressure cuff and normal (non-turbulent) laminar flow resumes Factors that affect BP • • • • • Genetics Age Body weight State of physical activity Level of salt, caffeine, or drugs Closed circulatory system - Arterial system is connected to the venous system by means of capillaries - Allows for gas exchange to occur - Pulmonary circulation: - (Lungs) Pick up O2 and drop off CO2 - Systemic circulation: - (Tissues) Pick up CO2 and drop off O2 Relationship between flow, pressure & resistance • F = P/R – F = flow – P = pressure – R= resistance Average rate of blood flow (pressure) • Mean Arterial Pressure = pulse pressure + diastolic pressure 3 *Pulse Pressure= systolic pressure – diastolic pressure OR (systolic pressure + 2x diastolic pressure) 3 MAP 120mmHg 75mmHg Heart sounds Pathway of blood flow • (from tissues) dO2 blood enters R. atrium via superior & inferior vena cava tricuspid valve R. ventricle pulmonary semilunar valve pulmonary (trunk) arteries lungs drop off dO2 blood & pick up O2 blood • (from lungs) O2 blood enters L. atrium via pulmonary veins bicuspid valve L. ventricle aortic semilunar valve aorta rest of the body Auscultation areas using a stethoscope. SL valves: -Aortic valve -Pulmonary valve AV valves -Tricuspid valve -Bicuspid valve Four major heart sounds • Heart Sounds: “lub” and “dup” • First Sound (S1): occurs during ventricular systole. Under low pressure, closure of the atrioventricular (AV) valves and opening of the semilunar (SL) valves “lup” • Second Sound (S2): occurs during ventricular diastole. Under high pressure, closure of the SL valves and opening of the AV valves “dup” • Third Sound (S3): turbulence associated with rapid filling of the ventricles shortly after opening of the AV valves • Forth Sound (S4): turbulence associated with the passage of blood from the atria into the ventricles during atrial systole Ventricles • Diastole: the period of ventricular filling (relaxation), the AV valve open; SL valves are closed to prevent arterial blood from re-entering the heart • Systole: when the ventricles contract & compress the blood in their chambers, closes the AV valves (prevents backflow into atria); SL valves are forced open as the ventricles discharge the blood into the large arteries Phases of the Cardiac Cycle Fig. 12-18 on p 374 End-Diastolic Volume Isovolumetric contraction Isovolumetric relaxation End-Systolic Volume Stroke Volume Fig. 12-19 1. (a) Atrial contraction begins (S4) 2. Atria eject blood into ventricles 3. (b) Atrial systole ends; AV valves close (S1) 4. (c) ventricular contraction 5. (d) Ventricular ejection occurs 6. Semilunar valves close (S2) 7. (e) relaxation occurs 8. (f) AV valves open; passive ventricular filling occurs (S3)