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The study by Thornton et al1 demonstrates the pitfalls in recommending blowing into a syringe of a certain size to assure a given pressure for the Valsalva manoeuvre (VM) for the non-invasive treatment of supraventricular tachycardia. To expand on their findings, I would like to draw attention to the basic physics of a syringe and its consequences with regard to determining pressures for the VM.
In discussing the pressure needed to move the plunger of the syringe, one must distinguish between the pressure required to actuate a stationary plunger, that is the pressure needed to overcome the static friction between the plunger and the barrel (the so-called ‘break loose force’) and the pressure required to counterbalance the kinetic friction between the barrel and the plunger once it …
Competing interests None declared.
Provenance and peer review Not commissioned; internally peer reviewed.