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heart as a pump
Today- Heart as a Pump ! Cardiac cycle ! ! Cardiac Output ! ! ! ! Pressure/volume relationships Stroke volume/heart rate Length/tension relationships Limitation to Cardiac Output Effects of training on Cardiac Output Cardiac Cycle All events associated with the flow of blood through the heart during one single complete heart beat Approx 0.83sec if heart rate is 72 bpm 2 Main Periods of the Cardiac Cycle ! Systole ! Ventricles contract AV valves close ! SL valves open ! Blood flow into arteries ! ! Diastole ! Ventricles relax SL valves shut ! AV valves open ! Blood flows into ventricles ! Phases of the Cardiac Cycle ! Ventricular filling ! ! ! ! ! Pressure atria > Pressure ventricles AV valves open, SL valves still closed Passive Phase-Blood flows from atria to ventricles Active phase- Atria contract Isovolumetric ventricular contraction ! ! ! Ventricle contracting Ventricle pressure> atrial pressure AV snap shut, SL valves already closed Phases of the Cardiac Cycle ! Ventricular ejection ! ! ! ! Pressure ventricles > pressure arteries Semilunar valves open, AV valves closed Blood flows into arteries Isovolumetric ventricular relaxation ! ! ! Ventricle relaxes Aortic pressure > ventricular pressure AV and semilunar valves closed Cardiac Cycle Wiggers diagram ECG Aortic pressure Left ventricular pressure Left atrial pressure Left ventricular volume Heart sounds Sherwood, Figure 9-21, pg. 302 Electrical events ! ! ! P-wave precedes atrial contraction QRS complex precedes ventricular contraction T-wave precedes ventricular relaxation Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Ventricular pressure during cardiac cycle Large variation in ventricular pressure to allow for: " opening of valves " pressure in atria and arteries Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Atrial Pressure Changes A wave C wave V wave aa c v Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Normal value for 80mmHg < aortic BP > 120mmHg Pulse pressure = systolic - diastolic = approx 40mmHg Mean Arterial pressure = 1/3 systolic + 2/3 diastolic = approx 93mmHg Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Aortic pressure during cardiac cycle 1 5 4 2 3 EDV = end diastolic volume ESV = end systolic volume Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Ventricular Volume & Stroke Volume SV = volume of blood ejected by the ventricle each beat SV = EDV - ESV Heart Sounds Sounds occur during turbulent blood blow when valves close Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings First sound = soft lubb 2nd sound = louder dubb AV valves close Semilunar valves close Cardiac Output Volume of blood pumped by each ventricle each min ! CO= HR X SV ! ! Average CO = 5 liters/min at rest Extrinsic & Intrinsic regulation of CO ! ! Extrinsic- neural (ANS) and hormonal (epinephrine) Intrinsic - local Parasympathetic SA node Sympathetic " rate of depol., " HR " excitability, ! AV nodal delay ! rate of depol., ! HR ! excitability, " AV nodal delay Conduction pathways No effect ! excitability, ! conduction Atrial muscle " contractility, ! contractility, weaken contraction strengthen contraction Ventricular muscle No effect AV node ! contractibility, strengthen contraction Heart Rate controlled by ANS Threshold potential = Inherent SA node pacemaker activity = SA node pacemaker activity on parasympathetic stimulation = SA node pacemaker activity on sympathetic stimulation Limitations of CO imposed by: ! A/V node conduction ! ! ! Decremental conduction Fewer gap junctions Ventricular refractory period ! ! Safety mechanism 0.25 to 0.3s Sherwood, Fig. 9-20, p. 322 Threshold potential Control of Stroke Volume Venous return and sympathetic activity ! Intrinsic Control ! ! ! End-diastolic volume (Frank Starling law) Afterload Extrinsic Control ! Sympathetic stimulation ! Ventricular contractility Sherwood, 5th edition, fig 9.22, pg. 323 Frank Starling Mechanism Sherwood, 5th edition, Fig. 9-24, p. 324 Sympathetic stimulation on contractility Limitations to CO imposed by: # $ Ventricular preload %$ Ventricular filling time &$ Ventricular & pericardial compliance '$ Ventricular afterload ($ Ventricular contractile duration Sherwood 4th edition, fig 9.22, pg 304 Ventricular Preload/ Filling Time Compliance Rigidity Ventricular Afterload Ventricular Contraction Duration If contraction too short SV may be decreased Dependent on venous return Copyright © 2005 Pearson Education, Inc., Publishing as Benjamin Cummings Effects of training on Cardiac Output SV ! ! ! HR At rest Sinoatrial Node Activation Eccentric vs. Concentric Hypertrophy Ventricular Compliance = CO During exercise SA nodal firing ! First adaptation ! Within few weeks – decrease resting HR ! ! ! ! Due to increases in SV Increases in BP Baroreceptor resetting HR changes quickly during detraining Hypertrophy ! ! After a few months of training Physiological adaptation to increased workload ! Concentric- anaerobic exercise ! Eccentric- aerobic exercise Ventricular Compliance Eccentric hypertrophy Concentric hypertrophy Physiological vs. Pathological Hypertrophy Dimension Runners Swimmer Wrestler Normal LV mass, g 302 308 330 211 Septum, mm 10.9 10.7 13 10.3 LV wall, mm 11.3 10.6 13.7 10.3 LVvolume ml 160 181 110 101 LV internal 54 dimension at end diastole 57 48 46 http://w3.ouhsc.edu/phar5442/Lectures/Cardiovascularexerciseeffects.html Normal Vs. Elite 30 yr old male, 76kg Resting SV (ml) “Normal” Elite* 85 170 Resting HR (bpm) 70 35 Resting CO (L/min) 6 6 Max SV (ml) 100 200 Max HR (bpm) 190 186 Max CO (L/min) 20 37 *Peter Snell (1500m Olympic Gold Medal, 1964) Adapted from Prof Chris Bell Lecture 2002 Summary ! Wiggers diagram ! ! Pressure/volume relationships Frank Starling -law of the heart ! Length/tension relationships ! Limitations of Cardiac Output ! Adaptations to training
