Cardiac Output and Hemodynamics Calculator

Cardiac output (CO) is the volume of blood pumped by the heart per minute. It is the product of heart rate and stroke volume:

CO (L/min) = HR (beats/min) x SV (mL/beat) / 1000

A resting adult has a CO of roughly 4-6 L/min. During maximal exercise, trained athletes can reach 30-40 L/min.

Cardiac index (CI) normalizes CO to body surface area, allowing comparison across patients of different sizes:

CI = CO / BSA (L/min/m^2)

Normal CI is 2.5-4.0 L/min/m^2. Values below 2.2 suggest cardiogenic shock. This calculator uses the DuBois formula for BSA:

BSA = 0.007184 x height^0.725 x weight^0.425 (m^2)

Systemic vascular resistance (SVR) measures the resistance the left ventricle must overcome to eject blood. It requires mean arterial pressure (MAP) and central venous pressure (CVP):

SVR = (MAP - CVP) / CO x 80 (dynes s/cm^5)

Normal SVR is 800-1200 dynes s/cm^5. The factor of 80 converts from mmHg/(L/min) to CGS units. Elevated SVR means the heart is working harder to push blood through constricted vessels.

Mean arterial pressure can be estimated as: MAP = diastolic + (systolic - diastolic)/3, though direct measurement is preferred in clinical settings.

Pulse pressure = systolic - diastolic. Narrow pulse pressure (less than 25 mmHg) can indicate low stroke volume. Wide pulse pressure may indicate aortic regurgitation or high stroke volume states.

There is no systolic or diastolic box on this calculator, only MAP, so use the formula above to work MAP out from a cuff reading before you type it in.

Stroke volume index (SVI) is stroke volume divided by body surface area, normally 33 to 47 mL/m^2. It answers the question cardiac index cannot: whether a low cardiac output comes from a weak beat or simply from a slow one. A small adult with a 55 mL stroke volume looks alarming next to the textbook 70, and usually is not.

The Fick principle runs the whole thing backwards into oxygen. Oxygen consumption equals cardiac output multiplied by how much oxygen the tissues strip out of each litre of blood:

VO2 = CO x (arterial O2 content - venous O2 content)

At rest that arteriovenous difference is about 5 mL of oxygen per 100 mL of blood, so a 5 L/min cardiac output supports roughly 250 mL of oxygen per minute, which is exactly the textbook resting figure for a 70 kg adult. Under maximal effort the difference widens to around 15 mL/100 mL as working muscle extracts far more from each pass. That is why an untrained heart and a trained one can differ threefold in VO2 max on a cardiac output difference of far less: extraction does part of the work. The calculator reports both ends of that range.