1. CS 2015 Pressures, Flows and Volumes during the Cardiac Cycle. Christian Stricker Associate Professor for Systems Physiology ANUMS/JCSMR - ANU Christian.Stricker@anu.edu.au http://stricker.jcsmr.anu.edu.au/Cardiac_cycle.pptxChristian.Stricker@anu.edu.auhttp://stricker.jcsmr.anu.edu.au/Cardiac_cycle.pptx THE AUSTRALIAN NATIONAL UNIVERSITY

2. CS 2015

3. Aims At the end of this lecture students should be able to outline the events are used to time the CC; describe what delimits systole and diastole; i.e. heart sounds (S 1 and S 2 ); draw the important features of pressure, volume and flow changes during cardiac cycle in ventricles, atria and aorta; outline when and how atria and ventricles are filled; explain how stroke volume is determined by both, systolic and diastolic pressures; and recognise the relative timing between left and right atria and ventricles.

4. CS 2015 Contents Linking elements within the CC ECG for objective timing Cardiac sounds (phonocardiography) Heart as two serially connected pumps Left ventricle, aorta and left atrium Blood pressure change and stroke volume Right ventricle and central venous pressure Relative timing between two ventricles

5. CS 2015 Events within Cardiac Cycle Electrical events (“Pump control”) –Ionic current flow and action potentials: ECG EC-coupling Mechanical events (“Pump action”) –Muscle contraction: Auscultation Pressure generation –Movement of valves (directionality of flow) »Sounds, clicks and murmurs –Flow of blood out of ventricle –Volume changes –Pressure and volume waves (pulse; see later)

6. CS 2015 Clinical Relevance Why are these concepts important? Interpretation of clinical signs/findings to get insight into cardiac function: –Auscultation and phonocardiography –ECG –Pulse pressure curves –Echocardiography (ultrasound) –Cardiac catheter –…–… Used daily many times… Complexity

7. CS 2015 Electrical Events From action potentials to ECG. ECG provides precise way to determine timing/phase –P wave: Atrial depolarisation. –QRS complex: Ventricular depolarisation - start of systole. –T wave: Ventricular repolarisation - end of systole. Modified from Berne et al., 2004

8. CS 2015 Mechanical Properties of Heart Two serially connected pumps with a high (left) followed by a low (right) pressure vascular bed. Directionality enforced by a pair of valves at in- and out- flow of each chamber. Failing of one part dramatically imposes load on preceding element(s).

9. CS 2015 Systole - Diastole Clinical term. Systole = period between S 1 → S 2 = contraction and ejection period. Diastole = period between S 2 → S 1 = relaxation and filling period. Duration of systole is quite constant, however, diastole varies with heart rate. To identify systole and diastole, no fancy tool required… just ears and stethoscope: you hear it…

10. CS 2015 Heart Sounds S 1 : Closure of the mitral/tricuspid valves. S 2 : Closure (”slamming shut”) of the aortic/pulmonary valves. Typically split during respiration; during inspiration, venous return to RA↑ but LA↓ (pooling in pulmonary bed; see later). S 3 : Faint rumble; opening of mitral/tricuspid valve with flow murmur into ventricles (typically heard in young people). S 4 : Faint rumble; flow murmur caused by atrial contraction.

11. CS 2015 Left Ventricle Contraction after electrical pacing Pressure range: 0 - 120 torr Systole duration: ~ 0.3 s @ 75 bpm Diastole duration: variable (~0.5 s) Peak diastolic volume: 120 mL End-systolic volume: 40 mL Stroke volume (SV): 80 mL

12. CS 2015 Role of Valves The role of valves is to –separate pressures when closed; i.e. P before ≤ P after ; –and direct flow when open; i.e. P before > P after. Valve abnormalities cause murmurs. –Valvular stenosis: narrowing of open valve diameter; requires increased ventricular pressure to maintain flow through narrowed valve. –Valvular regurgitation: failure of valve to seal properly: no pressure separation → flow in both directions; may involve large volumes.

13. CS 2015 Aortic Trunk SV (homeostatic requirement): 80 mL If P LV > P AO : Aortic valve opens. –AV does not close at P peak → due to highest flow and elasticity of AO. Notches indicate valve movements. Pressure difference (ΔP):40 torr Duration of blood ejection: ~200 ms Ejected volume = SV = 80 mL ΔP determines SV: longer ejection → SV↑.

14. CS 2015 Left Atrium SV (homeostatic requirement): 80 mL If P LA < P LV : Mitral valve closes. Atrium fills towards end of systole. If P LA > P LV : Mitral opening (early diastole). Under resting conditions, atrial contraction represents only a “last little push” to fill ventricle (15%).

15. CS 2015 Valvular Plane Displacement Systole: Movement of valvular plane towards cardiac apex (~16 mm) causes mechanical “suction” on central veins: –Increased atrial filling during late systole. –Mechanism: “horror vacui” imposed by pericardial space. Diastole: Movement back (early filling phase) rises atrial pressure slightly, aiding ventricular filling. Modified from Schmidt & Thews, 1977

16. CS 2015 7 phases of the cycle Systole –Contraction phase (isovolumetric) –Ejection phase Fast Slow Diastole –Relaxation phase (isovolumetric) “elastic recoil” –Filling phase Passive ventricular filling –Rapid ventricular filling –Slow ventricular filling Atrial contraction Synopsis

17. CS 2015 SV (homeostatic requirement): 80 mL Largely analogous to phases in left ventricle, except for slightly changed valve timings. Pressure difference (ΔP): 20 torr Ohm’s law: I = ΔP / R; to maintain flow, R pulm. must be no more than half R syst.. Right Ventricle

18. CS 2015 Timing of Right and Left Ventricle Cycle starts right atrium (pacing in SAN) and ends in right ventricle (delayed contraction). S 1 and S 2 are “composed” of contributions from both respective valves in both ventricles. Boron/Boulpaep 2003

19. CS 2015 Right Atrium & Central Veins SV (homeostatic requirement): 80 mL Can be seen on jugular vein. Measured via a pulse transducer. Pulse wave in central veins results from volume and pressure changes in RA. Timing and amplitudes depend on location (delay and attenuation).

20. CS 2015 Systole and Diastole Timing Pulse rate can be altered over a 3 - 4 fold range. At heart rates (HR) >100 bpm, t diastole < t systole : Filling ↓. –Systole at 150 bpm is shorter than that at 50 bpm. At high HR, atrial contractions become important. Modified from Koller, 1979

21. CS 2015 Take-Home Message Systole: S 1 → S 2 Diastole: S 2 → S 1 The 7 phases of the cardiac cycle are: isovolumetric contraction, fast and slow ejection, isovolumetric rela- xation, fast and slow ventricular filling, atrial contraction. Whilst diastole is variable, systole is ± constant. SV is dependent on difference between systolic and diastolic pressure: difference ↑ → SV ↑. Most of atrial filling occurs during systole. “Insignificance” of atrial contraction at rest. “Pump failure” causes load on preceding element(s).

22. CS 2015 MCQ Joe Ackermanis, a 26 year-old male, was diagnosed with an aortic valve stenosis (narrowing of valve opening). Compared to a normal heart, which of the following descriptions best describes the pressures in the heart of this person? Peak atrial pressure Peak ventricular pressure Peak aortic pressure a) ↑↑↑ b) ↓↓↓ c) ↓↓↑ d) ↓↑↑ e) ↑↑↓

23. CS 2015 That’s it folks…

24. CS 2015 MCQ Joe Ackermanis, a 26 year-old male, was diagnosed with an aortic valve stenosis (narrowing of valve opening). Compared to a normal heart, which of the following descriptions best describes the pressures in the heart of this person? Peak atrial pressure Peak ventricular pressure Peak aortic pressure a) ↑↑↑ b) ↓↓↓ c) ↓↓↑ d) ↓↑↑ e) ↑↑↓