Starting a New Thread As...
Highlights
- Starting a new thread as the original got too messy to keep track of. A few points:
- Yes, inspiratory Pmus (Pmus,i) is positive. I implied as such in the calculation. This was an unintended distraction due to the erroneous depiction of Pmus in the Xlung simulator. https://t.co/Y7AL9hwCff (View Tweet)
- A non-mathematical way to think about this is that both Pvent and Pmus work together to drive ventilation. They're both additive. If Pmus was negative, it would cancel the Pvent effect.
Hope that's more intuitive, @GkuhnRRT.
2. Not only do Ppl and Pmus have opposite vectors,
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their amplitudes are also different. This is because the part of Pmus spent on expanding the chest wall is not captured by ΔPpl. The amplitude of Pmus is always higher than that of ΔPpl.
The relationship between Pmus and ΔPpl is evident from the following equation (image)
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- Back to the original discussion with @ArielG_RRT : the crux of it is the definition of Paw vs Pvent. I know Rob likes to define Pvent as the pressure driving ventilation exclusive of PEEP. I differ with him on this.
(BTW, even with this definition, your eqn doesn't stick👇)
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- I'm proposing that 'Paw' and 'Pvent' are synonymous.
This is irrespective of whether you write the equation where ΔV equals volume change from FRC (adding PEEPtot on the RHS) or from EELV.
Here are a few standard sources where Paw and Pvent are considered synonymous: (View Tweet)
- (a) Dean Hess, in his review, defines Pvent as "the proximal airway pressure applied by the ventilator", which is nothing but Paw/Pao: image
(b) In this classic ATS "50 years" respiratory mechanics review, it is explicitly stated that Pvent and Paw are identical (image)
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- If nothing else, this discussion demonstrates how lack of standardization in vocabulary is one of the major challenges faced in the study of respiratory mechanics.
Related articles on this issue👇
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