Cardiovascular Invasive Technology: Hemodynamics, Waveforms, and Measurement
Cardiovascular invasive technology centers on acquiring and interpreting pressure data and translating it into physiology. You must understand the fluid-filled catheter system: transducer leveling at the phlebostatic axis, zeroing to atmosphere, and the fact that a compliant air bubble or long tubing dampens the waveform (underdamped systems overshoot and ring; overdamped systems flatten and lose the dicrotic notch). Know normal chamber pressures, the cardiac cycle timing of the a, c, and v waves, and how to distinguish an elevated v wave (regurgitation) from a prominent a wave (reduced compliance or obstruction).
Catheterization calculations appear constantly: Fick cardiac output (VO2 divided by the arteriovenous oxygen content difference), thermodilution curves, and derived indices such as cardiac index, stroke volume, systemic and pulmonary vascular resistance, and valve areas by the Gorlin equation. Traps include mixing units (Wood units vs dynes·s·cm⁻⁵), forgetting to index to body surface area, and confusing mean with systolic pressures when computing gradients. Also expect questions on oxygen saturation step-ups that localize shunts and on recognizing catheter-induced artifacts.
Rule of thumb: resistance (Wood units) = mean gradient ÷ flow (L/min); multiply by 80 for dynes. Worked example: mean aortic-to-LV gradient 40 mmHg with 4 L/min flow gives 10 Wood units, or 800 dynes·s·cm⁻⁵. If the question supplies a gradient and a cardiac output, the answer is almost always a resistance or valve-area calculation - watch the units carefully.