24. parameters of the cardiac cycle: volume fractions, factors influencing cardiac output

Question 1

Volume Fractions:

Answer 1

• Cardiac output (CO):the volume of blood pumped into the circulation by the heart in one minute.(heart rate times stroke volume )
• End diastolic volume (EDV): The ventricles are maximally filled at a time just before the heart contracts.
• End systolic volume (ESV): When the ventricles are maximally emptied, there isstill some blood remaining in them.
• Stroke Volume (SV)= EDV-ESV
• Cardiac Output = (EDV – ESV) x Frequency, CO = SV x Frequency

Question 2

Measuring Cardiac Output

Answer 2

1. According to Fick’s principle (based on Law of Conservation of Mass)
   a. CO: the amount of O2 taken up by the lung per minute is equal the amount taken up by the tissues, so CO = total O2 consumption (l/min) / a-v O2 difference (l/l)
2. According to Stewart’s principle
   a. Injecting Evans-blue i.v., sample collection & analysis, plot curve, just before recirculation do extrapolation, Area under the extrapolated curve= CO