Thank you Ivan, good afternoon, how is everybody? Still falling in, pretty good? Having a good day? All right, so we are gonna go ahead and get started here. I'm gonna kind of place us into, I hope, place us into a spot where we can take, excuse me, where we can take some of the physiology of breath delivery, some of the basics of it, and then apply it to patient ventilator interaction. If we kind of make a laundry list of ideas and pictures in our heads, we kind of lose grasp of some of those interactions. So I'm gonna start out with the physiology of the breath delivery and its modes of mechanical ventilation. Some of my disclosures, really not totally relevant to this particular talk, but I will disclose relationships with Medtronic Vire and Ingmar Medical, and all of these slides are mine. I'm gonna go through the parts of the respiratory cycle, I'm gonna pick them apart, we're gonna talk about how it turns on, how the breath is then delivered to the patient, from the machine to the patient, and that physiology, which is what we'll use to help us kind of figure out the interaction and the complexity and the abnormalities of the interaction, and then how the breath actually turns off. And so that's what we'll attempt to do here in the next 20 minutes or so, so keep me honest here, guys. All right, all right, so physiology of breath delivery. So here's a typical respiratory cycle, what you're looking at is the graphics display of a ventilator, which specifically on the top is a pressure timescaler, and down on the bottom is a flow timescaler. So nothing fancy here in terms of monitoring. Every ventilator will be able to display this to you. So regardless of where you practice or what machine you walk up to, this is what you're gonna be able to see. So we're kind of starting at this really foundational level. And what we're gonna do is pluck one individual breath out of that entire respiratory cycle, and we're gonna pick it apart here, all right? So the first part of any breath here is the trigger, all right, and that is how the breath turns on or how inspiration is initiated. There are a couple different ways. One way is by time in the event that the patient does not have a respiratory drive. The ventilator has a time-based mechanism according to the set respiratory rate in which it turns on. If the patient wants to turn the breath on, they drop the pressure or drop the flow in the circuit, all right, so that's how the breath turns on. The next part of the breath, once it turns on by whatever mechanism, is the breath delivery portion. I think in the textbook, a respiratory therapy or mechanical ventilation textbook, this would be called the limit. It's kind of clunky. It's an okay way to think about it, but it's kind of clunky in some of its descriptors, that type of thing. But really what's happening here is how does the machine get the gas, flow, volume, and pressure delivery from the machine sitting three feet away from the patient? How does it go to the patient? How does that happen? So we're gonna kind of pick this apart in a little bit more detail because I really, really want to set us up nicely for this interaction in subsequent talks. So the first idea with this whole breath delivery is this question. Well, what makes a gas, in our case here with the mechanical ventilator, or a liquid, what makes a gas or liquid flow from one end of this tube to the other end of this tube? And so that idea is a pressure difference or a pressure gradient. And so what I have labeled at one end of the tube is P1, the other end of the tube is P2, and the difference, that pressure gradient is how flow moves across that tube. The higher the pressure gradient, the higher the flow, and then the lower the pressure gradient, the lower the flow, all right? So how does gas move through the tube? It moves across a pressure gradient, right? And we'll represent it mathematically here by that change in pressure equals the flow, all right? The next question that we have to ponder in terms of breath delivery is, well, what would make it difficult for that gas to flow across that tube? And that answer is resistance, essentially, right? And so if we continue to build this mathematical model of how does gas move from the machine over to the patient, we have a change in pressure equals flow times resistance, or F and R from now on, okay? So we have this anatomical model. I'm gonna take it from the tube, essentially, and P1 and P2, and make it more anatomically soothing for us, and we're gonna relabel this, all right? So P1, we'll relabel airway pressure, and P2, we will relabel alveolar pressure, all right? And so this is how it sets up anatomically for us, all right? And we're gonna apply that to our equation. So instead of P1 minus P2 equals the flow across that tube, we're gonna say the difference between airway pressure and alveolar pressure is equal to that flow and resistance, and make it a little bit more real for us, all right? So that's our equation as we have it built so far, all right? I'm going to not do anything fuzzy or smoke and mirrors, but I'm gonna mathematically move this alveolar pressure over to the other side of the equation for us. And what we end up with is that airway pressure equals F times R plus the alveolar pressure, okay? So I'm gonna continue to build this here and pose this concept in this question. Well, what is it that makes up that alveolar pressure? Like what are its components, its physiologic components? And so if we think about this, it is the volume and compliance in the PEEP, all right? And so if we kind of ponder this, the PEEP is directly related to how much pressure is in the alveolus. So if the PEEP goes up, the alveolar pressure goes up, and vice versa also holds true, all right? So that's on the top of that equation essentially if we're thinking about what builds alveolar pressure. The next thing is volume, all right? So as you put more volume into the alveolus, the alveolar pressure is gonna start to increase, and the vice versa also holds true. So we're gonna end up with alveolar pressure equals PEEP plus the volume. And then the third component that I lend it to you was the compliance, right? And compliance is inversely related to the amount of alveolar pressure. So as compliance goes down, the alveolar pressure goes up, and all of that is inherent and kind of makes sense, and we can kind of feel that, right? But mathematically, this is how we're gonna set it up, and these are the nuts and bolts of the logistics of it, is that your alveolar pressure equals PEEP plus volume over compliance essentially, right? And we're gonna pull this back out to our whole big idea, in that airway pressure equals F times R plus this whole other alveolar pressure component, which we just built. So I'm gonna put it all together here, and you end up with this big, long equation. And don't worry, I hate math too, especially if there's division involved. Don't do math at all possible costs, right? Don't do any math. You need to feel this equation, because this is how your breath is being delivered, the foundational principles of how it moves from the ventilator over to the patient. And that is the airway pressure equals flow times resistance plus the volume over compliance plus PEEP. And that is a derivative of that first concept, which is called Ohm's law, that first concept of how does flow happen across a tube? And it is the pressure gradient. And what you come up with is something called the equation of motion. And this is essentially kind of the holy grail of mechanical ventilation and breath delivery. This is how it happens. This is how it works, right? And the interaction is keyed off of this, and becomes really, really important, is why I build it in this way for us here, right? So this is the equation of motion. The other thing that really, really kind of is striking is that your equation of motion, although a mathematical equation here, is given to you in a waveform display. This is the waveform version of the equation of motion, that pressure time scaler, right? And so if I kind of look at this, there's again another pressure time scaler, and we say what makes pressure happen on the ventilator, and how is it displaying it to us, right? We can kind of pick this apart, and there are components of that airway pressure built on this equation of motion, PEEP being down here at the bottom, that first part of inspiration being resistance and flow, and then followed by the filling of the alveolus with volume and compliance. So that graphical representation of the equation of motion is there in your face, and we just don't kind of contemplate it or translate it in such a way, but that's what it is, and that's how it's built, all right? And so we first turn the breath on by triggering, time, drop in pressure, drop in flow. We then delivered the breath according to that equation of motion that we built out, pressure equals flow times resistance plus volume over compliance plus PEEP, and now that we have the breath delivered to the patient, we have to turn inspiration off somehow, and that is called the cycle, and so how the breath ends is really based on a mode, how we'll kind of think about a mode is based on that mode and that control variable, all right? And so in VC, it is the volume that turns inspiration off or ends inspiration. With a set PC, with a set inspiratory pressure level, what I think a lot of people kind of label as pressure control or PCAC, that is time in an adaptive pressure mode, that is also time, and in pressure support, that is flow, all right, and so that is how the breath kind of picks apart in terms of how it turns on, how it gets to the patient, and then how it turns off, all right, in a nutshell, essentially, right, in that 10 minutes that we just spent talking about it. The fourth part of any one breath is exhalation, completely passive on behalf of the ventilator, the patient is allowed to exhale, all right, and so those are, you know, essentially what are called the phase variables or the parts of a breath, all right, in terms of all of its intricacies. We as clinicians control each part of that breath, you know, whether we relinquish the control or we actually set it with our knobs and our buttons, and so understanding and becoming really familiar with how you impact each segment of those is really imperative if you want to be fluent in mechanical ventilation and the interaction with the patients. So let's take that idea and that concept of this physiology of breath delivery and really start to clinically apply it and then set the table for the rest of the guys coming up. So in VCAC, during passive inspiration, this is kind of what we look like. So that screenshot is taken off of a test lung, there's no interaction on behalf of the patient, all right, and so in this, grant me this here, once inspiration is started, resistance and compliance are fixed if you have the right set level of P, all right, I know that's a big if and there's no change in compliance and we can argue about this, but just grant me that here for application of this. So the resistance and compliance, once the breath starts, doesn't change, it's fixed. In VCAC, you as the clinician, me as the respiratory therapist, we set the P, although during exhalation, but over there, it's set, it doesn't change, but during inspiration, the flow and the volume do not change, they are set by us, the operators of that machine, all right, and so what you end up having, you know, coming down in this analysis is that the airway pressure is variable and we always take away, well, if I set volume, then pressure is variable, but that's the why, this is the why of its occurrence, right, so the airway pressure is variable. If you have an active patient or they're vigorously inspiring, we also apply the same model, the same equation of motion and we're gonna represent this patient as PMOS in this equation here, all right, and so if a patient is actively or vigorously inspiring and we are controlling the entire right-hand side of that equation, it's fixed, it doesn't change at all and we contemplate what's going on with what's dependent or variable, the airway pressure there, you can then start to feel the interaction and why things are particularly happening, right, and so in this active and vigorous inspiration on behalf of the patient, the PMOS is going up, right, the amount of muscle pressure is going upwards and if we are fixing or controlling the entire right-hand side of the equation and there's a little pesky equal sign in between the left and the right side of that equation, that means the left has to remain equal to the right and if the PMOS is increasing like what we see here, what has to occur in order for the left to remain equal to the right is that the airway pressure has to go down by the same exact amount that the PMOS is going upwards and that there is reflected to you on an abnormal waveform, that's why the waveform looks like that and that drop or that dip in the airway pressure as the work shifts from the ventilator onto the patient as indicated by the PMOS is described to you based on that equation of motion and the clinical application of it, all right, and that's why the picture looks like that. We typically memorize that looks like this and this is how I kind of fix this, but this is the why, this is the theory and the physiology underneath of it. If we kind of switch gears a little bit over to the other side of the control variable and contemplate pressure during passive inspiration, again, resistance and compliance under the same idea are fixed once inspiration starts. We set now the airway pressure on the left, the PEEP is still set by us and that means that the flow and volume are dependent variables, right? We do not control those, right? And so in the same idea, in the same logic, if we put an active or vigorous patient accordingly into this equation and plop them down with an increase in PMOS, you can see how this equation reacts differently now. The airway pressure is set by us, so therefore will not change and if PMOS goes up on this left side of the equation, what has to happen in order for the left to remain equal to the right is that those things that are dependent on that right side of the equation also have to change by the same exact amount. So the flow then goes up and you see that as a patient sucks in really hard in a pressure limited type of mode, they can pull out as much flow, but this is again is the why as we start to apply these things going forward. So the flow goes up and what ends up happening is that the volume goes up, possibly and absolutely potentially injurious in this case, right? And so the flow goes up and really that is demonstrated to you on your ventilator graphics, the why. That same vigorous inspiration that created that dip or the cup or the depression in the pressure timescaler because you've changed the control variable is now showing up on the flow timescaler instead of being a decent or decelerating or an exponential decay on the flow in passivity, now it is rounded in its appearance because the patient is pulling flow out and that is variable and the flow remains high throughout the entirety of inspiration and it's displayed to you in pictures. You just have to be able to understand what is creating those pictures in order to really get to the nitty gritty of this patient and ventilator interaction and what's occurring. All right, did I make it in time? All right, very good. That's my first time ever probably.

physiology

breath delivery

patient ventilator interaction

respiratory cycle

pressure gradient