1/ In our last thread, we explored how vessels can collapse when MAP falls below a threshold — the Critical Closing Pressure (CCP) — creating a vascular choke point. But there’s a common misunderstanding we need to clear up 🧵👇 #MedX #Physiology #Haemodynamics
2/ The concept of the vascular waterfall helps explain this: When CCP rises above venous pressure, blood flow can cease completely — even if a pressure gradient still exists. Why “waterfall”? Because flow is no longer influenced by the pressure downstream.
3/ Think of a real waterfall: 💧 The height of the pool at the bottom (CVP) doesn’t control whether water flows over the edge. 🌊 Flow is governed by the pressure at the lip of the cliff — that’s your CCP. If pressure at the top drops below the lip, flow stops — regardless of
4/ A classic paper from 2012 by Maas et al. demonstrated this effect in ICU patients. Using inspiratory hold manoeuvres, they transiently reduced flow to near zero — and found: 🩸 CCP > Pmsf ➡️ Flow couldn’t occur despite a pressure gradient. That’s a vascular waterfall.
5/ But here’s the critical point: 🧠 The vascular waterfall only exists when collapse occurs. It is not a structure, and it’s not always “on.” It’s a physiological state that appears when the internal pressure falls below a dynamic threshold.
6/ Once the vessels are open and flow resumes, the “disconnection” disappears. The arterial and venous sides are rejoined, and flow is governed again by the entire circuit. No collapse = no waterfall.
7/ Maas et al. proposed that systemic vascular resistance (SVR) might be better understood by splitting it into: – Arterial resistance (Ra) – Venous resistance (Rv) This idea stems from their observation that CCP and Pmsf appear disconnected during low-flow states.
8/ They also speculated that this framework might help explain flow limitation in humans — and hinted that the vascular waterfall could persist in normal physiology. But this risks implying that vessel collapse is a continuous feature — which is misleading.
9/ You can’t generalise from a no-flow manoeuvre to a fully perfusing system. If flow has resumed and vessels are open, then CCP no longer limits flow — and SVR remains a valid lumped parameter. No choke point = no disconnection.
10/ So yes — CCP is real. The waterfall is real. But they’re state-dependent, not constant features of the circulation.
11/ Some authors have even proposed therapies to “manipulate” the vascular waterfall — to shift it, widen it, or restore it. But this makes no sense unless collapse has occurred. You can’t treat a phenomenon that isn’t present.
12/ 🧠 Bottom line: ✅ Maas et al. demonstrated a vascular waterfall — but only during flow cessation ❌ That doesn’t mean it exists during normal circulation ❌ And it doesn’t mean SVR must always be split into Ra and Rv Context matters.
13/ Start here ⬇️
@icmteaching Great threads, Tx! Still, one Q though- The pressure in the arterial tree gradually goes down as blood flows distally to smaller arterioles, so eventually the pressure in the vessel will be low enough to hit the choking point of CCP (~30-40mmHg) right? so MAP-CCP is always valid?
@icmteaching Thanks for the great thread! As one of the many who get confused by the literature as you alluded to, would like to know if you have any recommended articles / books for further reading on the concept of CCP.
@JCHCheung No not really I’m afraid. Hence my threads to try make it easier for people to understand.
@icmteaching 👌👌
@icmteaching Interesting descriptions. I am trying to apply these concepts to the cardiovascular system. Its application seems particularly relevant to CTO, CTO PCI, and FlowReducer. Thank you again