Cardiac output and oxygen consumption

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Integrated Cardiac Output and Respiratory FunctionM1 – Cardiovascular/Respiratory Sequence Louis D’Alecy, Ph.D. Fall 2008


ExerciseVentilationCirculationMuscle Utilization


ExerciseWith exercise, VO2 increases one initially increases both ventilation and cardiac output Ventilation and perfusion remain matched DO2 remains much greater than VO2˙˙


Strenuous ExerciseSkeletal MuscleM&H 10.4Mohrman and Heller. Cardiovascular Physiology. McGraw-Hill, 2006. 6th ed.




ExerciseAt higher levels of exercise, DO2 can not keep up with increasing VO2 VO2 is maintained by increasing oxygen extraction VO2 = CO x (CaO2 – CvO2) CvO2 falls and eventually MvO2 falls Eventually, oxygen delivery is inadequate for the level of work, and the muscle shifts to anaerobic metabolism Anaerobic threshold˙˙˙


Oxygen delivery and oxygen saturation of mixed venous bloodNormal mixed venous oxygen saturation (MvO2) = 75% If oxygen delivery falls, and tissue metabolism continues, then MvO2 will fall In principle, we should know that oxygen delivery is sufficient if we know that MvO2 is normal There are a few caveats…


CaveatsSuppose blood moves from the arterial circulation to the venous circulation without unloading oxygen Large shunts, congenital and man-made Micro shunts Toxins poisoning mitochondria If oxygen isn’t removed from arterial blood, the MvO2 may be normal, despite inadequate oxygen delivery


REVIEW OF Worked Problems as time permits.


Prior questions What is the total O2 content of 100 ml of plasma (PO2 100 mmHg)? Ans. 0.31 ml


Henry’s Law for O22CdO2content of dissolved O2 mL/dLaO2solubility coefficient for O2 in blood==The content of dissolved oxygen is equal to the product of the oxygen solubility coefficient and oxygen partial pressure.Linear straight line Relationship like y = mx. dL = 100 mL


Prior questions What is the O2 content of 100 ml of blood (Hb 15 gm/dL; PO2 100 mmHg)? Ans. 20 ml


Typical Arterial Blood Oxygen ContentOP2= 100 mm HgSO2= 97%[ Hb ] = 15 gm/dLCdO2aO2PO2= 0.0031 x 100 = 0.31 mL / dLDissolved O2Bound O2CbO= SO2[ Hb ] Hb2= 0.97 x 15 x 1.36 = 19.79 mL / dLTotal Oxygen ContentCdO2+CbO2= 0.31 + 19.79 = 20.1 mL / dL=s1.34 mL O2 /gm Hb = O2 capacity =Hbs


Integrated Question 1CaO2 = 19 ml/dL CvO2 = 14.5 ml/dL Cardiac output by thermal dilution = 8 liters/min What is the VO2?VO2 = CO x (CaO2 – CvO2)VO2 = 80 dL/min x (19 – 14.5 ml/dL) = 360 ml/min˙˙˙


Integrated Question 2 VO2 = 250 ml/min CaO2 = 20.5 ml/dL CvO2 = 16 ml/dL What is the cardiac output?CO = VO2/(CaO2 – CvO2) CO = 250 ml/min / (20.5 – 16 ml/dL) = 250/4.5 = 55 dL/min = 5.5 L/min˙˙


Integrated Question 3Determine oxygen delivery PaO2 = 96 mmHg O2 saturation = 97% Hb = 12 gm/dL Cardiac output = 6 liters/minDO2 = CO x CaO2CaO2 = (1.34 x 12 gm/dL x .97) + (96 x .003) = 15.6 + .29 = 15.9 ml/dL DO2 = 60 dL/min x 15.9 ml/dL = 954 ml/min


Integrated Question 4Which of the following maneuvers will increase oxygen delivery to the greatest degree (all else being equal)? supplemental oxygen to increase PO2 from 90 to 120 mmHg – little effect supplemental oxygen to increase O2 saturation from 88% to 98% - <12% increase transfusion to increase hemoglobin from 9 gm/dL to 12 gm/dL – 33% increase increase cardiac output from 5 liters/min to 8 liters/min – 60% increase


Integrated Question 5A healthy individual is a given a drug that increases cardiac output from 5 to 7 liters/min. One would anticipate which of the following as a consequence of this change? A. Oxygen consumption increases arterial oxygen saturation increases arterial oxygen saturation decreases mixed venous oxygen saturation increases mixed venous oxygen saturation decreases


right shift tissues  H+ (Bohr shift) CO2 temperature 2,3 BPGH+  CO2 temperature 2,3 BPGleft shift (lungs)SummaryAt any PO2 less O2 bound.At any PO2 more O2 bound.Hemoglobin affinity for oxygen is not staticSource Undetermined


Slide 6: Mohrman and Heller. Cardiovascular Physiology. McGraw-Hill, 2006. 6th ed. Slide 7: McGraw-Hill Slide 21: Source Undetermined Additional Source Information for more information see:

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Last Updated: 8th March 2018

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