Cardiovascular Physiology & Pharmacology (2) PDF

Cardiovascular Physiology & Pharmacology (2) Dr Stella Koutsikou MSOP1003 Office: Anson 307 Email: [email protected]  What did we learn in the previous lecture? v Intrinsic electrical conduction system R...

Cardiovascular Physiology & Pharmacology (2) Dr Stella Koutsikou MSOP1003 Office: Anson 307 Email: [email protected]  What did we learn in the previous lecture? v Intrinsic electrical conduction system R L SA Node = Autorhythmic, Pacemaker of the heart (Intrinsic rate: 100 -110 bpm) Sympathetic Nervous Heart rate (HR): System control Increases HR Ø Number of times the heart beats in 1 minute (bpm) Ø Gets set by the SA node AV Ø Regulated by the autonomic Node nervous system Parasympathetic Nervous System control Average Resting HR: Inhibition 70 bpm Excitation  Learning Objectives 1. Describe the heart’s mechanical events during systole and diastole 2. Understand cardiac output and the factors that affect it 3. Align intrinsic excitability with contraction of the myocardium 4. Define blood pressure (BP) and factors that affect it 5. Understand the normal control of BP 6. Pharmacology relating to heart contractility and blood pressure control  The Cardiac Cycle The orderly process of cardiac cell depolarisation that triggers atrial and ventricular contractions and relaxations Ø Diastole = relaxation of cardiac muscle Ø Systole = contraction of cardiac muscle Ø Depolarization of cardiac myocytes leads to contraction of cardiac muscle Ø The cardiac cycle repeats with every heartbeat  The Cardiac Cycle The cardiac cycle is divided into two major phases, both named for events related to ventricular relaxation and contraction Alignment of ECG activity to ventricular systole and diastole Ø Systole: period of ventricular contraction & blood ejection (0.3 sec) Ø Diastole: ventricular relaxation & blood filling (0.5 sec) For a typical HR = 72bpm the cardiac cycle lasts ~ 0.8 sec  Blood Pressure Consider how the pressure levels change in the chambers of the heart as the blood volume changes P Ø Blood flows from higher to lower pressure P P Ø Contraction (systole) increases the pressure Ø Relaxation (diastole) reduces the pressure P Ø Valves open/close according to pressure gradients Diastole Ø Semilunar valves open during systole, when ventricular pressures are P higher than aortic and pulmonary arterial pressures Ø AV valves open during diastole, when ventricular pressures are lower P PP than pressure in the atria Systole  Blood Pressure Measuring arterial blood pressure = pressure that the blood exerts on the wall of the arteries (mmHg) Ø Systolic pressure (the higher number) = pressure the blood exerts on the arterial wall when the ventricles of the heart contract to pump the blood out of the heart Ø Diastolic pressure (the lower number) = pressure the blood exerts on the arterial wall when the ventricles of the heart are relaxed  Mechanical Events during Cardiac Cycle & Diastole P t l iza it on ria lar tion P A po c de ntra P coPhase 1 P Diastole  Mechanical Events during Cardiac Cycle , n ( S1 s n atio lve c tio Diastole i z a lar Vv n tra o n f A & o p de ctio se o und tric ) c Systole l ria tra lo o e At con C ub s lum & L ovo 1 2Is Beginning of Systole Lub  Mechanical Events during Cardiac Cycle , o n ( S1 d zati lves tion loo Diastole i va c b P P P o lar V n tra n of p n A & o l de ctio e of nd) ric c ctio Systole ria tra os u et Eje At con Cl b so um pid Lu ol a P & 1 Isov2 3 R PP Systole Lub  Mechanical Events during Cardiac Cycle , d S1 o ( n lood f blo it on s lve i t bo o Diastole iza va a c of ion P P P la r AV t n o r n ct e po ion of d) & ic co ecti Eje Systole d t e n r j d ri al tracClos sou met id E uce At c o n p ub volu Ra Red P L PP & 1 Iso2 3 4 Systole Lub  Mechanical Events during Cardiac Cycle , od S1 d blo lves n& s ( n o o f atio lve c tio f bl n o r va Diastole P iz a ra o io na lar AVv o nt tion ject ilu & tion p o of ) & c c E m d) xa de tionose und tric Eje ced f Se un rela Systole l P ria c l so e id u e o so ic At ntra C ub olum Rap Red los ub etr P co 1 L Iso2v 3 4 5 C S2, D olum ( ov P Is Diastole Lub Dub  Mechanical Events during Cardiac Cycle r u n a d) & il n n Diastole m sou atio les P o s Se f u lab e o , D c re ven 2 i x tri c Systole Cl s (S etr f the P P ) e 5 lv lum g o va ovo illin P 1 2 3 4 5 Is 6 6) F Diastole Lub Dub  Cardiac Output CO = HR x SV Ø CO = Cardiac Output (litres / minute) Ø Cardiac Output (CO): the volume of blood each ventricle pumps expressed in litres/min Ø HR = Heart Rate (beats / minute) Ø Heart Rate (HR): number of heart beats per minute (bpm) Ø SV = Stroke Volume (litres / heartbeat) Ø Stroke Volume (SV) : volume of blood ejected from each ventricle during systole (litres/beat) P P P Question: P PP Calculate the cardiac output when 72bpm eject 70ml of blood with each heartbeat Systole Factors affecting Cardiac Output & Blood Pressure CO = HR x SV v Factors that affect HR v Factors that affect SV SV = EDV - ESV Effects of beta Blockers on Cardiac Output e.g. Bisoprolol CO = HR x SV  Factors affecting Cardiac Output CO = HR x SV v Factors that affect SV SV = EDV - ESV SV is affected by preload: Ø Preload = the degree to which the myocardium is stretched before contraction Ø determined by venous return / EDV (end diastolic volume) Ø The bigger the EDV the higher the preload Ø The higher the preload, the bigger the myocardial stretch, the more forceful the contraction  Factors affecting Cardiac Output CO = HR x SV v Factors that affect SV SV = EDV - ESV SV is affected by afterload: Ø Afterload = the peripheral resistance that the contracting ventricular muscle needs to work against when ejecting blood Ø Back pressure exerted by arteries Ø The higher the back pressure, the higher the afterload which leads to larger ESV (end-systolic volume) Ø The larger the ESV the lower the SV ANS affecting Cardiac Output & Blood Pressure vBaroreflex PVR BP = CO x PVR Blood Pressure (BP) = Cardiac Output (CO) x Peripheral Vascular Resistance (PVR) ANS affecting PVR & Blood Pressure vBaroreflex PVR BP = CO x PVR Blood Pressure (BP) = Cardiac Output (CO) x Peripheral Vascular Resistance (PVR)  Additional reading Ø Rang & Dale’s Pharmacology Ø Any human physiology textbook of your choice Ø Human Biology by Mader & Windelspecht