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Cardiac Output monitoring: Pressure , Volume , Flow

Cardiac Output monitoring: Pressure , Volume , Flow. Cardiovascular System. Components include: Heart – pump Blood vessels – closed delivery system Arteries Veins Capillaries Blood – cells & plasma Ensures blood pumped continuously round the system

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Cardiac Output monitoring: Pressure , Volume , Flow

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  1. Cardiac Output monitoring:Pressure, Volume, Flow

  2. Cardiovascular System • Components include: • Heart – pump • Blood vessels – closed delivery system • Arteries • Veins • Capillaries • Blood – cells & plasma • Ensures blood pumped continuously round the system • Supplying cells with O2, nutrients, hormones • Removing CO2, nitrogenous waste • Temperature regulation • Transporting hormones

  3. Normal Values • Blood pressure 90-140/60-90 mmHg • Stroke volume 60-130 mls/beat • Cardiac output 4-8 L/min • Preload (CVP) 2-6 mmHg • Contractility • Afterload (SVR) 770-1500 dynes/sec/cm-5

  4. Pressure,Volume & Flow • Combination of all 3 ensure perfusion to all areas • Blood pressure • Cardiac output or index -flow • Stroke volume • Preload • Afterload • Contractility • Systemic vascular resistance • Frank Starling Law

  5. Blood Pressure • Force of blood against the wall of an artery • 3 components • Driving force (cardiac output or LV ejection) • Afterload (resistance to flow distally) • Fluid resistance (blood viscosity) • BP = Cardiac output x Peripheral resistance (Pressure = Flow x Resistance)

  6. Blood Pressure • Comprised of 2 figures: • Systolic (contraction) 120 mmHg - maximum stretch of vessel wall • Diastolic (relaxation) 80 mmHg • Pulse Pressure • SBP - DBP • Mean Arterial Pressure (MAP)

  7. Mean Arterial Pressure MAP = (SBP) + 2 x (DBP) 3 • Normal 70-100 mmHg • May have a target for patients on vasoactive drugs or haemofiltration

  8. Cardiac Output • Important measurement in assessment of cardiovascular function • Essential in calculating • Stroke volume • Systemic vascular resistance • Blood oxygen transport • CO = SV x HR • CO = MAP - CVP/ SVR Flow = Pressure/Resistance

  9. Cardiac Output • CO = SV x HR • Using normal parameters for HR & SV • CO = 70beats per minute x 70mls = 4900 mls/min • Or approx 5L/min • BUT does not account for body size • Cardiac index • More specific • CO/m2 relates to body surface area • Normal value 2.5 - 4 L/min/m2

  10. Stroke Volume • Volume of blood ejected by a ventricle with each heart beat (ml/beat) • SV = CO/HR • Normal 60 - 130 ml/beat • SV = EDV - ESV • 60% EDV ejected with each beat leaving reserve of 40% within ventricle • Influenced by • Preload • Afterload • Contractility

  11. Preload • Affected by the volume of blood in the ventricles at the end of diastole (LVEDV) • Degree of stretch of the cardiac muscle fibres immediately before contraction • The greater the preload (stretch) before contraction, the greater the force of contraction • Frank Starling Law • stretch = volume • Dependent on physiological limits

  12. Frank Starling Curve

  13. Contractility • Pumping ability of the heart • Independent of muscle stretch and LVEDV • Enhanced contractility results in more complete ejection of blood • Lower ESV, SV • Positive inotrope drugs

  14. Afterload • Pressure that must be overcome for ventricles to eject blood from the heart • Load on muscle as contraction starts • Back pressure exerted on aortic and pulmonary valves • Influenced by lumen size and fluid viscosity • SVR • SVR (Woods Units) = (MAP-RAP)/CO • SVR (index units) =(MAP-RAP)/CI • SVR (dynes/sec/cm-5) = (MAP-RAP)/CO x 80

  15. Systemic Vascular Resistance • Resistance heart has to pump against • Derived value • Component of afterload • Vasoconstriction causes an in SVR • Reduction in circulating volume causes an in SVR, maintaining BP

  16. Preload & Afterload •  filling pressure =  preload • Preload refers to EDV • Afterload relates to the aortic pressure during ejection, or aortic valve opening

  17. Regulation of BP • Dependent on vasomotor tone • Specialised cells • Baroreceptors • Chemoreceptors • Neural mechanisms • ANS • Cardiac centre • Neurohormonal control • Catecholamines • RAAS • Atrial natriuretic peptide (ANP)

  18. Perfusion • Essential supply of O2 to tissues • O2 carried by Hb • Need adequate flow to prevent organ dysfunction, multiple organ failure and death • Detection vital • Oxygen delivery • Dependent on pulmonary gas exchange, Hb level, binding of O2 to Hb, cardiac output

  19. Oxygen Demand & Metabolic Rate • Determinant of cardiac output • metabolic rate causes oxygen demand and therefore  CO • Seen in critically ill and trauma patients by 50%in CI • Metabolic rate rises with • Sepsis • Strong emotions • Major trauma • Surgery •  Body Temperature •  Body Size/Mass

  20. Any Questions?

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