5 Hemodynamic Measurements and Interpretation Free Online FlashCards

How is cardiac output calculated?

Cardiac output is blood pumped per minute: $\mathrm{CO}=\mathrm{HR}\times\mathrm{SV}$. Typical adult resting $\mathrm{CO}$ is about $4\text{–}8\,\mathrm{L\,min^{-1}}$.

What does cardiac index adjust for?

Cardiac index adjusts cardiac output for body size: $\mathrm{CI}=\frac{\mathrm{CO}}{\text{body surface area}}$. It helps compare people of different sizes.

How is mean arterial pressure estimated from blood pressure?

At ordinary heart rates, estimate mean arterial pressure as $\mathrm{MAP}\approx\mathrm{DBP}+\frac{1}{3}(\mathrm{SBP}-\mathrm{DBP})$, where $\mathrm{DBP}$ and $\mathrm{SBP}$ are diastolic and systolic pressures.

How are MAP, flow, and systemic vascular resistance related?

A useful approximation is $\mathrm{MAP}-\mathrm{RAP}\approx\mathrm{CO}\times\mathrm{SVR}$, with unit conversions for clinical calculations. High vascular resistance can preserve a reasonable MAP despite low cardiac output.

What is preload?

Preload is myocardial stretch at the end of diastole. Filling volume is conceptually closer to preload than filling pressure; right atrial pressure and wedge pressure are imperfect surrogates.

When can increased preload raise stroke volume?

More preload can increase stroke volume when the ventricle is on the ascending Frank–Starling relationship. It may have little effect or cause harm when the heart is volume-replete or failing.

What is afterload, and what do SVR and PVR approximate?

Afterload is the load opposing ventricular ejection. Systemic vascular resistance approximates left-ventricular arterial load, while pulmonary vascular resistance approximates right-ventricular vascular load; neither fully measures myocardial afterload.

Does elevated CVP prove excess circulating blood volume?

No. CVP is a right-sided pressure, not a direct measure of circulating blood volume. PEEP and intrathoracic pressure, among other factors, can raise it.

What does PAWP estimate, and what does it not directly measure?

PAWP estimates left atrial pressure under appropriate conditions. It is not a direct measure of left-ventricular filling volume and may not equal left-ventricular end-diastolic pressure.

How is systemic vascular resistance calculated?

Calculate systemic vascular resistance as $\mathrm{SVR}=80\times\frac{\mathrm{MAP}-\mathrm{RAP}}{\mathrm{CO}}$. It is a derived value, so errors in pressure or cardiac output affect it.

How is pulmonary vascular resistance calculated?

Calculate pulmonary vascular resistance as $\mathrm{PVR}=80\times\frac{\text{mean pulmonary artery pressure}-\mathrm{PAWP}}{\mathrm{CO}}$. Its accuracy depends on reliable input measurements.

What does mixed venous oxygen saturation indicate?

SvO₂ reflects the balance between oxygen delivery and consumption. A low or falling value is concerning but nonspecific, and ScvO₂ is not interchangeable with SvO₂.