Pressure-volume loops in cardiac surgery Citation for published version (APA): Dekker, A. L. A. J. (2003). Pressure-volume loops in cardiac surgery. Datawyse / Universitaire Pers Maastricht. https://doi.org/10.26481/dis.20030912ad Document status and date: Published: 01/01/2003 DOI: 10.26481/dis.20030912ad Document Version: Publisher's PDF, also known as Version of record Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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F.H. van der Veen Beoordelingscommissie Prof.dr.ir. T. Arts (voorzirter) Prof.dr. J. Baan, Universiteit Leiden Prof.dr. M.J.H.M. Jacobs Prof.dr. B. Meyns, Katholieke Universiteit Leuven Dr. G.V.A. van Ommen Financial support by the Netherlands Heart Foundation and Stichting I lartsvriondon Rescar for the publication of this thesis is gratefully acknowledged. Additional support was granted by Medtronic, CD Leycom, Datascope, TD Medical, AB Medical and Sulzer Cardiovascular. Contents Chapter 1 Introduction /oops in iH?/i>M/<?r disease Chapter 2 Aortic stenosis 45 Chapter 3 Aortic regurgitation 63 ps m ojff-pMmp coronary tfrft'ry hyrwss Chapter 4 Cardiac tilting 75 Chapter 5 Right ventricular support 89 /oops in mtr/ftiMtoi/ s Chapter 6 Intra Aortic Balloon Pump in acute mitral regurgitation 101 Chapter 7 Propeller pump versus Intra Aortic Balloon Pump 117 Chapter 8 Future pressure-volume loops in cardiac surgery 131 Summary 137 Samenvatting 141 Nawoord 145 Publicaties 147 Biograf ie 151 Introduction 17 Chapter 1 Introduction 1.1 Relationships between pressure and volume 9 1.2 Interpretation of pressure-volume loops 14 1.3 Measurement of pressure-volume loops 28 1.4 Pressure-volume loops in cardiac surgery 32 1.5 Aim and outline of the thesis 34 1.6 References 37 Introduction 19 1.1 Relationships between pressure and volume Relationships between pressure and volume are part of thermodynamics. They were first employed at the start of the nineteenth century as a result of the industrial revolution, when the interest in steam engines sparked the start of a new theoretical framework now known as thermodynamics. Until then, heat was assumed to be a substance named caloric, but this theory could not explain the principles governing steam engines which were not well understood at that time. The French engineer Carnot took on this challenge and constructed a theoretical model of an ideal heat engine which he applied to study real heat engines (Figure 1-1). Camot's work ultimately led to the formulation of the Second Law of Thermodynamics which is among the most basic and powerful in physics (or as F.instein put it: "// is f/it* o/i/y /»/lysira/ //n'ory o/'Miiiivrsfl/ cwifenf, tc/rir/i / rim a>m>rnm/ /.../ in'// m*ivr Ktn t no** MirniKT UIIU UIWU> Figure 1-1: Left: Nicolas Sadi Lazare Carnot (1796-1832). French engineer and founder of thermodynamics. Middle: Carnot's pivotal publication "Reflexions sur la puissance motrice du feu...". Right: A Carnot cycle for an ideal gas consisting of reversible phases. The second law of thermodynamics can be applied to numerous subjects and therefore surfaces in many different forms. The one most useful for this introduction is: /\ /wsswre-i'o/wme /oop o/rj Marm/a/Zy t^n't'«/ ITI^/HC tonsjste on/y o/ ra>ers»W<? /i/ws«. This ideal pressure-volume loop is called a Carnot cycle (Figure 1-1). The Carnot cycle of a heat engine of an ideal gas can be found in every physics textbook; it consists of reversible adiabatic (at constant entropy) and isothermal phases. Carnot and university thermodynamics deal with heat engines made of an ideal gas. However, this thesis focuses on pressure-volume loops of another thermodynamic subject: the heart. The largest difference with a heat engine is that the heart is a biochemical engine and does not rely on a difference in temperature to perform mechanical work. So, rather than using differences 101 Chapter 1 in temperature as the driving force, a change in biochemical potential should by analyzed. • ., -\ « <*v n »•- • Although such a "biochemical" thermodynamic analysis is more complicated than the "thermal" case for an ideal gas, the Carnot principle still holds in the human heart-: The maximally efficient pressure-volume loop of the heart consists of only reversible phases. In that case the available biochemical energy is maximally converted into mechanical work. The real pressure-volume loop of the heart, discussed shortly, is not an ideal Carnot cycle. The main deviation is that a certain blood pressure needs to be maintained, so valves and thus isovolumic phases are present in a cardiac pressure-volume loop. However, Carnot's theorem does enable us to define the maximum achievable efficiency with a certain amount of biochemical energy available. It can be shown- that Carnot's principles lead to the pressure-volume area concept of Suga\ which will be introduced in detail later. First the pressure-volume loop of the heart is discussed. Introduction 111 1.1.1 Pressure-volume loop of the heart During a heart beat, the pressure and volume inside the heart change with time as shown in Figure 1-2. Each beat can be divided into four phases: (isovolumic) contraction, ejection, (isovolumic) relaxation and the filling phase that consists of rapid filling, diastasis and the atrial kick. Note that pressure and volume are out-of-phase; when pressure is high, volume is low and vice versa. A consequence of this phase difference, is that the plot of pressure versus volume results in a loop: the pressure-volume U>op. 100-, 08 1.0 12 14 1.6 1.8 2.0 2.2 Figure 1-2: Changes in left ventricular pressure and volume over time. The pressure-volume loop constructed from the data of Figure 1-2 is shown in Figure 1-3. Each heartbeat is represented by one pressure-volume loop. The aforementioned four phases are visible. Starting at the bottom right corner and working counterclockwise, these are: contraction, ejection, relaxation and the filling phase. The four corners of the loop are determined by valve opening and closure. For the left ventricle these are counterclockwise mitral valve closure, aortic valve opening, aortic valve closure and mitral valve opening. A pressure-volume loop is constructed from the simultaneous measurement of volume and pressure over time, but the variable time is not seen in the loop. Part of the time aspect can be brought back by showing the individual samples as is done on the right in Figure 1-3 (time between points is 12ms). It can be seen that contraction and relaxation are very fast phases, while the filling phase consists of a rapid phase followed by a waiting period, the diastasis. After diastasis, the atrial contribution to filling takes place (atrial kick). 121 Chapter 1 40 «0 «0 V<*Mtr|ml| Vulumr |ml| Figure 1-3: A normal left ventricular pressure-volume loop. Left: The four phases and corners of the loops. The width of the loop is the stroke volume. Right: Individual samples of pressure and volume, time between samples is 12ms. The diastasis and the atria] kick can clearly be seen. The loop of Figure 1-3 is taken from a healthy pig and it has the normal almost rectangular shape. This shape is determined by the valves; in patients with valvular disease the rectangular appearance is lost. In this thesis, two valvular diseases will be discussed: aortic stenosis (Chapter 2) and aortic regurgitation (Chapter 3). In aortic stenosis, the aortic valve has become too narrow, usually due to calcific deposits on the leaflets.