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Cardiovascular Physiology A

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Objectives

• To learn the basic anatomy and physiology of the heart– Muscle/ pump

• To understand the mechanism for the delivery of oxygen and nutrients to the organs and tissues of the body

• To become familiar with mechanisms to control blood pressure

• To understand the process of atheroma formation (Next Class)

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Outline

• Needs for energy distribution• Anatomy of the heart• The heart as a pump• Circulation• Introduction to EKGs• Blood pressure• Atheroma formation (next lecture)

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The Need for Circulation• All living cells require metabolic substrates (e.g. oxygen,

glucose, amino acids) and a mechanism to remove the byproducts of metabolism (e.g. carbon dioxide, lactic acid- stuff we need to remove)

• In human beings most cells are not in contact with the external environment

• The ultimate purpose of the cardiovascular system is to facilitate exchange of gases, fluid, electrolytes, large molecules and heat between cells and the outside environment

The heart and vasculature ensure that adequate blood flow is delivered to organs so that this exchange can take place.

Klabunde, RE Cardiovascular Physiology Concepts Lippincott, Williams and Wilkins, 2005

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Exchanges

• External:– Lungs (oxygen, carbon dioxide)– Gastrointestinal tract- guts (glucose, amino acids, fatty acids,

etc. and elimination.)– Kidneys (water, electrolytes, and elimination)– Skin (water, electrolytes, heat)

• Internal:– Arteries – Arterioles - Capillaries (close to cells for nutrient

exchange) – Venules - Veins

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Test material***

Capillary – no muscle – where exchanges take place

- System is very important

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Circulation

• Veins

• Heart

• Aorta

• Delivered in parallel to organs

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Heart Anatomy

Heart Muscles• Right Atrium • Right Ventricle• Left Atrium• Left Ventricle

• Heart Valves:– Between the atria and ventricles

• Right: Tricuspid Left: Mitral– Between ventricles and outflow

• Right: Pulmonic Left: Aortic

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Cardiac Cycle

• Rhythmic contraction of the heart relies on the organized propagation of electrical impulses along its conduction pathway.

• The electrical impulse spreads along each cardiac cell and rapidly between neighbouring cells

• Electrical action potential leads to physical contraction of the cardiac muscle cells

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Heart Sounds

• First Heart Sound:– Closing of mitral and tricuspid valves and contraction of the

Ventricles

• Second Heart sound:– Closure of the Aortic and Pulmonary valves

• Systole: (Contraction)– The time between the 2 heart sounds

• Diastole: (Relaxation)– The time between the second heart sound and the first

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Electrocardiogram

• Measures the electrical currents generated by the depolarization and repolarization of the cardiac cells

• Diagnosis:– Rhythms– Blockages– An indication of heart diseases

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Not in exam***

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Refer to Page 24 in your handout (Chapter 13)

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Summary 1

• Heart is a very efficient pump• Pump needs a distribution system

Arteries Veins… because system is closed

• Why distribution? Needs a means of carrying blood Cells need O2 & nutrients for metabolisms to work Closed system… Returns deoxygenated blood &

metabolites

• Needs an electrical system To initiate/transmit impulses, create action potentials

(AP) to accomplish specific cell function (i.e., pumping action)

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Summary 2If you understand the basic elements … then you can appreciate what might go

wrong•Problem with Pump – when aging pump doesn’t work well – high salt intake

Congenital – perforation of the septal wall and/or malformation of heart vessels

Disease – enlargement, thickening•Failure of the valves – disease such as syphilis –Leakage – pressure build up behind fluid in lungs/extremities

atrial enlargement

•Blockages Clogged arteries – insufficient fuel – cell death

Heart cannot contract

•Ruptures Aneurysm – weakening aorta

•Changes over time In flexibility/elasticity of distribution system

•Electrical Interruptions Conduction blocks – may need pacemaker

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Summary 3… then primary care assessment• History – The story

Pain on exertion or at rest Shortness of breath, etc.

• Look – diagnosis Edema – swelling – blood flow doesn’t get pumped back

• Listen The heart sounds Blood pressure – resistance in the distribution system

• Feel The pulses

• ECG Assess the electrical conductivity & efficiency of heart cycle

THESE ARE THE BASIC TOOLS FOR THE GPs

Obviously more sophisticated methods are needed/available for further investigation

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Blood Pressure

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Objectives

• Review of structure & function• Learn the role of various blood vessels in oxygen and

nutrient supply and removal• Blood Pressure and its determinants• Understand how different factors might influence blood

pressure levels • Become familiar with mechanisms of controlling blood

pressure• Learn how blood pressure is measured• Hypertension or High blood pressure• Impact of hypertension

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Outline

• Structure of blood vessels• Blood circulation• Capillary exchange• Physiologic methods to control blood pressure • Blood pressure measurement• Causes of altered blood pressure• Guidelines for measuring BP• Public health consequences of high BP• Management of High Blood Pressure – Lifestyle• Management of High Blood Pressure – Drug therapy• Benefits of treating/controlling High Blood Pressure

Normal Arterial Wall

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Blood Vessel Structure

• Intima: Inner Layer – Endothelium and sub endothelial layer-loose connective tissue-

• Media: Smooth Muscle

• Adventitia: Fibrous Tissue/Connective tissue

Blood Vessel Structure **

Blood Flow During Rest

Capillary Exchange

• Most capillary exchange is by

• diffusion (between cells)

• or transcytosis (through cells)

• Gases (O2) (CO2) diffuse freely

• Capillary filtration and Absorption is by bulk flow: Hydrostatic

pressure (pushes)

Osmotic pressure (mainly proteins- pulls fluid)

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Venous Blood Flow

• Blood vessels are similar (in reverse) to the arterial system Small very thin-walled venules

to larger veins

• Blood begins at very low pressure Moved by skeletal muscles,

respiratory pump Valves prevent backflow

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*Handling the Overflow

• Outflow is greater than inflow• Return is helped by the Lymphatic

System Lie next to the capillaries Even thinner walls than capillaries Fluid enters (one-way) Empty into venous system or continue into larger

lymph ducts Fluid is moved by

smooth muscle contractions, endothelial contractions, skeletal muscle contractions

Valves prevent backflow

Lymphatic System

• Returns fluid and proteins to circulatory system

• Picks up fat absorbed by small intestine

• Filter to capture and destroy pathogens

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Edema: Swelling

• “Accumulation of fluid in the interstitial space”

• Edema varies with capillary exchange: A. Inadequate lymphatic drainage

Obstruction (parasite, cancer, fibrous growth)

B. Filtration is much greater than absorption Venous back-up (heart failure) Low plasma protein concentration (starvation) Increased interstitial plasma protein

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Blood Pressure

• Systolic pressure: Ventricles contracting

• Diastolic pressure: Ventricles relaxing(but there is still pressure in the arteries)

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Determinants of Blood Pressure

• Cardiac Output (CO)• Peripheral Resistance (TPR)• MAP = CO X TPR

CO = Stroke Volume X Heart Rate

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BP Regulation – Role of CV & Renal Systems

MAP = CO X TPR

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Factors influencing MAP

Volume CO=SVXHR 1/R = 1/R1 + 1/R2+…

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Factors Affecting Blood Pressure

Blood volume Raise intake of fluids Blood loss These are “regulated” by vasoconstriction of the

vessels, sympathetic nervous system (make the blood pump faster) and the renal system

Arterial-venous blood distribution Heart pump effectiveness Resistance in the blood vessels

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Blood Pressure Controls

• Local: Myogenic autoregulation of blood

flow Meets the needs of the respective

tissue/organ Paracrine concentrations stimulate

smooth muscle contractions Adjusts metabolic product

concentrations

• Central: Sympathetic nervous system (fight

or flight) stimulates hormone release causing vasoconstriction and kidney excretion

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Homeostatic Regulation:Baroreceptors

Carotid arteries (on the way to the brain)

Aortic arch (on the way to the heart)

Sensitive to distension of the vessel

Send message to medulla

Adjust sympathetic and parasympathetic activity

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BP Regulation – Orthostatic

Hypotensionheart isn’t adjusting but the pressure is high so you get

dizzy

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Blood Pressure Regulation

Systems involved:

• Heart• Blood vessels• Kidneys• Hormones (modulate the functions of

the above)

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Blood Pressure Measuring Devices

• Sphygmomanometer• Aneroid manometers• Random Zero Sphygmomanometers• Digital devices• Ambulatory BP Monitors

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Blood pressure Measurement

• Use Sphygmomanometer

1. Stop the blood flow

2. Release pressure gradually

The first sound we hear will be the highest pressure = systolic

3. When there is no sound the ventricles are relaxed. There is still pressure in the arteries = diastolic

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Blood Pressure Cuff

Effect of Hypertension• On the heart itself: Heart attack, Myocardial

infarction

• On the brains: Stroke

• On the kidneys: kidney failure/chronic kidney disease

• Eyes: retinopathy: retinal microvascular signs

• Periphery: Peripheral vascular disease

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Errors in the Measurement of BP

• Patient Errors• Observer Errors• Equipment Errors

1994

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Hypertension or High BP• Hypertension refers to a blood pressure measurement of greater

than 140/90 mm Hg (or on medication) consistently, at rest

• Pre Hypertension Blood pressure is between 120/80 mmHg and 139/89 mmHg.

• You will see in manuals 90%: Unknown cause = Essential Hypertension. This is incorrect. Most can be attributed to some factor, usually overweight, high sodium intake, alcohol, physical inactivity, etc.

• Pathogenic process: Vessels: Damages endothelial wall, promoting the formation of

atherosclerotic plaques Heart: Increases strain on the heart, leading to hypertrophy

(pump is working harder), then back-up causing pulmonary edema, and then congestive heart failure

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Hypertension• target in terms of definition

• Levels for defining hypertension have shifted down, from 165/95 mmHg to DBP >=90 mmHg to currently 140/90 mm Hg or on treatment

• Canadian recommendations include for diagnosis at different visits specific BP levels + presence of target organ damage or BP >=140/90 at visit 5

• Epidemiologic diagnosis usually based on one or the mean of a few measures (2-6) >=140/90

• Creates some difficulty for comparison of studies

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Prevalence of High Blood Pressure in CanadaCHHS- 1986-1992

22%

4.1 million hypertensive adults

Total: 22%; Women 18%Men 26%

BP > 140/90 mm Hg or treated; survey n = 23,129

Joffres et al. AJH, 1997

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21%13%

43%22%

Hypertensive patients who are treated

but BP uncontrolled

Hypertensive patientswho are treated

and BP controlled

Hypertensive patients who are unaware

Patients who are awarebut remain untreatedand BP uncontrolled

9%

Diabetic patientswho are treated and

BP controlled

HBP Was a Challenge In Canada

Joffres et al., Am J Hypertens 2001; 14: 1099-1105

Prevalence: 22% 18-74 yrs or about 4 million Canadians

Percentage with hypertension† who are aware,

treated by medication,controlled,‡ CHMS 2007-2009

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Prevalence: 19% (4.6 million) of Canadian adults aged 20 to 79 years

Wilkins K, Campbell NR, Joffres MR, McAlister FA, Nichol M, Quach S, HL, Tremblay MS. Blood pressure in Canadian adults. Health Rep. 2010Mar;21(1):37-46

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Global Prevalence of HBP

• Nearly 1 in 5 persons live with HBP• i.e. Almost 1.5 billion people have

hypertension in the world• HBP = Silent killer - Symptoms are not

overt & hence more people are UNAWARE

• In Canada about 19% of the adult population is hypertensive (approx. 4.6 million) (2009)

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Attributable Mortality by Selected Factors

Ezzati et al. Lancet 2002

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% Attributable DALY by Selected Factors

Ezzati et al. Lancet 2002

DALY: Disability Adjusted Life Years

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Risk Factors for High Blood Pressure

• Family history• Overweight• Physical inactivity• Alcohol• Diet (high sodium and low potassium, magnesium, calcium.• (smoking- lose appetite – blood pressure goes down)• Age- But no or little increase with age in Brazil, Papua New

Guinea, South Korea, Tokelau Islands etc. Raises question of the influence of lifestyle on age related increase in BP.

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Building Awareness of HBP• National and International Hypertension

Societies. See http://www.hypertension.ca/images/stories/dls/2011gl/FullCHEPRecommendations_EN_2011.pdf

• World Hypertension League• World Hypertension Day

2005 – Awareness of hypertension 2006 – Treat to Goal 2007 – Healthy Diet…Healthy Blood Pressure 2008 – Measure your blood pressure … at Home 2009 – Salt and Hypertension 2010 – Healthy Weights-Healthy Blood pressure 2011 – Know Your Numbers and Target Your

Blood Pressure

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Hypertension Treatment

• LIFESTYLE MANAGEMENT Reduce salt intake, weight, chronic alcohol intake High fruit/vegetable diet, Stop smoking Increase exercise

• DRUGS: Diuretics first drug of choice Beta-blocking drugs to bind beta receptors Calcium channel blockers – helps smooth muscle not to constrict so easily ACE inhibitors and angiotensin receptor blockers (ARBs) - decrease

angiotensin activity Renin-Angiotensin-Aldosterone Systems (RAAS) Combination therapy for high risk patients

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Guidelines – Management of HBP

• Canadian High Blood Pressure Education Program (CHEP) http://www.hypertension.ca/images/stories/dls/2011gl/FullCHEPRecommendations_EN_2011.pdf

• USA -Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC)

• WHO/International Society of Hypertension (WHO-ISH)

• European Society of Hypertension (ESH)• National Societies (Culturally sensitive)

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The “Seventh Report of the Joint National Committee on Prevention, Detection,

Evaluation, and Treatment of High Blood Pressure” (JNC VII)

• Provides a guideline for hypertension prevention and management. The following are the report’s key messages:

• In persons older than 50 years, systolic blood pressure greater than 140 mmHg is a much more important cardiovascular disease (CVD) risk factor than diastolic blood pressure.

• The risk of CVD beginning at 115/75 mmHg doubles with each increment of 20/10 mmHg; individuals who are normotensive at age 55 have a 90 percent lifetime risk for developing hypertension.

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JNC VII (Cont’d)

• Individuals with a systolic blood pressure of 120–139 mmHg or a diastolic blood pressure of 80–89 mmHg should be considered as prehypertensive and require health-promoting lifestyle modifications to prevent CVD. (High normal BP)

• Thiazide-type diuretics should be used in drug treatment for most patients with uncomplicated hypertension, either alone or combined with drugs from other classes. Certain high-risk conditions are compelling indications for the initial use of other antihypertensive drug classes (angiotensin converting enzyme inhibitors, angiotensin receptor blockers, beta-blockers, calcium channel blockers).

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JNC VII (Cont’d)

• Most patients with hypertension will require two or more antihypertensive medications to achieve goal blood pressure (<140/90 mmHg, or <130/80 mmHg for patients with diabetes or chronic kidney disease).

• If blood pressure is >20/10 mmHg above goal blood pressure, consideration should be given to initiating therapy with two agents, one of which usually should be a thiazide-type diuretic.

• The most effective therapy prescribed by the most careful clinician will control hypertension only if patients are motivated. Motivation improves when patients have positive experiences with, and trust in, the clinician.

• Empathy builds trust and is a potent motivator.

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How to measure BP at home

• Do not talk• Keep back supported• Place cuff mid-arm at

heart level• Be seated• Ensure arm is supported• Keep legs uncrossed• Keep feet flat on the floor

CHEP 2008

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Leading diagnoses resulting in visits to physician offices

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Source: IMS HEALTH Canada 2002. http://www.imshealthcanada.com/

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Benefits of Lowering Blood Pressure

• In clinical trials, antihypertensive therapy has been associated with reductions in

• (1) stroke incidence, averaging 35–40 percent;

• (2) myocardial infarction (MI), averaging 20–25 percent; and

• (3) Heart Failure, averaging >50 percent.

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• It is estimated that in patients with stage 1 hypertension (SBP 140–159 mmHg and/or DBP 90–99 mmHg) and additional cardiovascular risk factors, achieving a sustained 12 mmHg reduction in SBP over 10 years will prevent 1 death for every 11 patients treated.

• In the added presence of CVD or target organ damage, only nine patients would require such BP reduction to prevent one death

Ref: adapted from SHEP, SYST-EUR, STONE studies.

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CAD Death Rate per 10,000 Person-years

100+ 90-99 80-89 75-79 70-74 <70<120

120-139

140-159

160+

Diastolic BP (mmHg)

Systolic BP (mmHg)

20.610.3 11.8 8.8 8.5 9.2

11.812.612.813.9

24.6 25.3 25.2 24.9

16.923.8

31.025.8

34.743.8

38.1

80.6

37.4

48.3

Neaton et al. Arch Intern Med 1992; 152:56-64.

Effect of SBP and DBP onAge-Adjusted CAD Mortality:

MRFIT

CAD Death rate per 10,000 person years