= Femoral vein
The \b[<femoral vein>] is a deep <vein> carrying <blood> from the lower limb towards the <external iliac vein>. It continues proximally beneath the <inguinal ligament> as the <external iliac vein>, which later meets the <internal iliac vein>. The <femoral vein> therefore names a connected drainage route, rather than a fixed amount of <blood flow>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§20.5, Veins Draining the Lower Limbs and Table 20.16]{ref}
A flow measurement must distinguish the velocity sampled by an instrument from the average velocity over the vessel's <cross-sectional area>. For an original circular-lumen model with radius $R$ and an illustrative axial velocity profile $v(r)=v_{\max}(1-r^2/R^2)$,
$$
Q=\int_0^R v(r)\,2\pi r\,dr=\frac{\pi R^2v_{\max}}2,\qquad \bar v=\frac{v_{\max}}2.
$$
At stipulated $R=4$ mm and $v_{\max}=20$ cm/s, the <blood flow> is approximately $5.03\,\mathrm{cm^3/s}=302\,\mathrm{mL/min}$. Multiplying the central speed by the whole <area> would give twice that value. These are chosen model values, not normal human measurements or a claim that every venous velocity profile is parabolic.
In <Doppler ultrasound>, the measured frequency shift depends on the velocity component along the acoustic beam. Imaging the <femoral vein> and measuring that component address different parts of the inference: geometry identifies the vessel and its lumen, while the velocity measurement needs a direction and spatial-sampling model. The professional ultrasound description identifies sound-wave imaging and <Doppler ultrasound> as tools for evaluating venous <blood flow>.<Venous Ultrasound by RadiologyInfo.org>[How does the procedure work?, conventional imaging and Doppler information]{ref}
A useful measurement comparison holds the anatomical segment fixed and records lumen <area> and the velocity distribution over the same interval. Changes in area or the profile can alter the relation between a central reading and total <blood flow>. The resulting quantity belongs to that region's return; it is not automatically whole-body <cardiac output>.
Back to article page
