3 Cardiac Output and Cardiac Index Free Online FlashCards

What does cardiac output measure?

Cardiac output is the volume of blood pumped by a ventricle each minute, usually expressed in $\mathrm{L/min}$.

How is cardiac output calculated from heart rate and stroke volume?

Calculate cardiac output as $\mathrm{CO} = \mathrm{HR} \times \mathrm{SV}$. Convert from $\mathrm{mL/min}$ to $\mathrm{L/min}$ by dividing by $1{,}000$.

How is stroke volume calculated from ventricular volumes?

Stroke volume is $\mathrm{SV} = \mathrm{EDV} - \mathrm{ESV}$: end-systolic volume is subtracted from end-diastolic volume.

What is cardiac index, and how is it calculated?

Cardiac index is cardiac output adjusted for body size: $\mathrm{CI} = \frac{\mathrm{CO}}{\mathrm{BSA}}$. It is reported in $\frac{\mathrm{L}}{\mathrm{min}\cdot\mathrm{m}^2}$.

What is a commonly cited adult resting cardiac index range?

A commonly cited adult resting reference range is approximately $2.5$–$4.0\ \frac{\mathrm{L}}{\mathrm{min}\cdot\mathrm{m}^2}$. It is a guide, not a stand-alone diagnostic cutoff.

What does the Fick method use to calculate cardiac output?

The Fick method calculates $\mathrm{CO} = \frac{\mathrm{VO}_2}{\text{arterial O}_2\text{ content} - \text{mixed-venous O}_2\text{ content}}$.

Why does the Fick method require oxygen content rather than saturation alone?

Oxygen content matters because oxygen saturation alone is not the same as oxygen content.

How is the temperature change produced in thermodilution?

A pulmonary artery catheter injects a known amount of cooler fluid into the right atrium; a downstream temperature sensor records the blood-temperature change.

How does thermodilution relate the temperature–time curve to flow?

The monitor estimates flow from the temperature–time curve. Faster flow produces a shorter, smaller temperature change; slower flow produces a larger, more prolonged change.

How does Doppler echocardiography estimate forward stroke volume?

Doppler estimates forward stroke volume as $\mathrm{SV} = \text{LVOT cross-sectional area} \times \text{LVOT VTI}$, then calculates $\mathrm{CO} = \mathrm{SV} \times \mathrm{HR}$.

Why can LVOT diameter error affect Doppler stroke volume?

Because LVOT area is calculated from its diameter, an error in diameter measurement can affect the calculated stroke volume.

What is preload, and how can it affect stroke volume?

Preload is ventricular filling and stretch at the end of diastole. Within limits, greater filling can increase stroke volume through the Frank–Starling mechanism.