When I started The Dependent Variable, one of my worries was that I might eventually run out of things I wanted to write about. I now have the opposite problem. Already outlined is an article exploring terms such as stressed volume, unstressed volume, compliance, capacitance, venous tone and mean systemic filling pressure. They are closely related. They are often used almost interchangeably. But they are not the same thing. Also mapped out is a six-part series on the way we often over-complicate haemodynamics by measuring or calculating ever more numbers: ScvO₂. The CO₂ gap. P(v−a)CO₂ / C(a−v)O₂. Pulse pressure, diastolic shock index, PPV and SVV. Dynamic arterial elastance: Eadyn = PPV/SVV. Ees/Ea and ventriculo-arterial coupling. For each of them, I want to start from zero (no prior knowledge assumed) work through what the number actually represents, where it comes from, what physiology sits underneath it, and whether it genuinely helps us make better clinical decisions. The aim is to take you from novice to expert without making the subject unnecessarily complicated. Lots more to come from thedependentvariable.com Stay tuned.