predicted heart volume =
= K * M * L * B * D
relative heart volume =
= (predicted heart volume) / (body surface area in sq meters)
where:
• relative heart volume is in mL per square meter of BSA
• K is a constant for the anode to film distance and M is the magnification factor; for a frontal film with target-to-film distance of 2 meters and a lateral film with target-to-film distance of 1.5 meters, K * M = 0.42
• D = greatest antero-posterior measurement ("depth) of the heart in the lateral film, in centimeters
• L = diagonal distance in AP film from junction of the cardiac apex (left ventricle with the left hemidiaphragm) to the junction of the right atrium and superior vena cava, in centimeters
• B = diagonal distance in AP film from junction of right ventricle with the right hemidiaphragm (cardiophrenic angle) to the junction of the left atrium and pulmonary arteries (base of the main pulmonary artery), in centimeters
Interpretation:
• upper limit of normal in relative heart volume for adult males: 500-550 mL/m^2
• upper limit of normal in relative heart volume for adult females: 450-500 mL/m^2
• upper limit of normal in relative heart volume from birth to 3 months: 284-311 mL/m^2
• upper limit of normal in relative heart volume from 3 months to 2 years: 334-371 mL/m^2
• a change >= 90 mL/m^2 between 2 successive examination of the heart in the same patient indicates a significant change in the relative heart volume
