Ahmed T Abdellah

What is VExUS actually measuring? A new multicentre study provides a useful answer. D’Alto and colleagues studied 187 patients referred for pulmonary hypertension assessment across 7 centres. VExUS was performed within one hour of right-heart catheterisation, allowing direct comparison with invasively measured right atrial pressure (RAP). The relationship was striking: VExUS 0: mean RAP 3.9 mmHg VExUS 1: 8.4 mmHg VExUS 2: 13.5 mmHg VExUS 3: 15.8 mmHg For identifying RAP >12 mmHg, VExUS had an AUC of 0.97. The association held across patients with precapillary pulmonary hypertension, postcapillary pulmonary hypertension and those without pulmonary hypertension. What does this tell us? VExUS is often discussed as a tool for assessing “volume status” or “venous congestion”. But these data reinforce a more precise interpretation: VExUS is primarily a marker of the venous pressure environment, especially right atrial pressure and its transmission into the systemic veins. High RAP is not the same thing as excess intravascular volume. RAP may be elevated because of: • RV dysfunction or RV–pulmonary arterial uncoupling • severe tricuspid regurgitation • pericardial constraint • raised intrathoracic pressure • pulmonary hypertension • excess circulating volume • or a combination of these So an abnormal VExUS score tells us that systemic venous pressures are high. It does not, by itself, tell us why they are high and it does not automatically mean the patient needs diuresis or fluid removal. The key takeaway: VExUS appears to be an excellent non-invasive marker of elevated RAP. Use it to identify an adverse venous pressure state. Then work out the mechanism @ThinkingCC @NephroP journal.chestnet.org/article…

Blood Doesn't Flow Because of Pressure On misreading equations as mechanisms We are taught that blood flows because of a pressure gradient. It is one of those statements that is true enough to be useful and simple enough to be dangerous. It gives us a clean mental model: the heart generates pressure, pressure is higher in the arteries than the veins, and blood flows down the gradient. The equation seems to confirm it: Q = ΔP / R Flow equals pressure difference divided by resistance. Pressure difference sits on the right-hand side. Flow is the output. The story almost writes itself. But the equation does not say what we often make it say. It describes a relationship between variables in a solved system state. It tells us that, for a given flow through a given resistance, there must be a corresponding pressure difference. It does not tell us that the pressure difference is the independent cause of the flow. That causal interpretation has to come from somewhere else. It has to come from the physics. And the physics is more interesting than the shorthand... Read on for free on my Substack. substack.com/@icmteaching/no…

A lot of haemodynamic confusion comes from one basic error: treating descriptions of the system as if they were causes. Pressure gradients, preload, RAP, afterload, Starling... all are useful, but often misread. This review tries to put them back together into a coherent framework. doi.org/10.1111/anae.70238

🧵 Thread: Why cardiovascular physiology feels confusing (even to experts) Part 1 of my 'The physics of circulation' series Cardiovascular physiology isn’t confusing because it’s complex. It’s confusing because we routinely mix up description with causation. And our language subtly reinforces the error.