Cardiovascular physiology.Cardiovascular physiology.Dr James KerDr James Ker

2 scenario`s in cardiology:2 scenario`s in cardiology:• Systemic diseases affecting the Systemic diseases affecting the

cardiovascular system.cardiovascular system.

• Primary cardiovascular diseases.Primary cardiovascular diseases.

How can these diseases affect How can these diseases affect the cadiovascular system ?the cadiovascular system ?Components Components of the cardiovascular of the cardiovascular

system:system:

•Myocardium: Myocardium: myocarditis, cardiac myocarditis, cardiac failure etcfailure etc

•Valves: Valves: Stenosis, incompetence etcStenosis, incompetence etc•Electrical system: Electrical system: Dysrhythmias.Dysrhythmias.•Vessels: Vessels: Arteries, veins, lymphatic Arteries, veins, lymphatic

vessels.vessels.

Physiological disturbances:Physiological disturbances:• Disturbances in the following may Disturbances in the following may

occur:occur:• Blood pressureBlood pressure• Cardiac rhythmCardiac rhythm• Valvular functionValvular function• Cardiac systole and diastoleCardiac systole and diastole• Blood flowBlood flow

Blood pressure:Blood pressure:• BP = Cardiac output (CO) x BP = Cardiac output (CO) x

peripheral vascular resistance (PVR)peripheral vascular resistance (PVR)

• 3 components of blood pressure:3 components of blood pressure:• Systolic componentSystolic component• Diastolic componentDiastolic component• Mean arterial pressureMean arterial pressure

• BP = 120/80 mmHgBP = 120/80 mmHg• Mean arterial pressure = (S + 2D)/3 Mean arterial pressure = (S + 2D)/3

or or • D + 1/3 PPD + 1/3 PP

• Pulse pressure=S – D (120-80=40 Pulse pressure=S – D (120-80=40 mmHg)mmHg)

Cardiac output:Cardiac output:• CO = Stroke volume x heart rateCO = Stroke volume x heart rate• Thus:Thus:

2 ways to increase CO: SV vs CO2 ways to increase CO: SV vs CODetermines systolic BPDetermines systolic BPSystolic vs diastolic HTSystolic vs diastolic HTNormal CO: 5L/minNormal CO: 5L/minCardiac index=CO corrected for body surface areaCardiac index=CO corrected for body surface area

Causes of increased CO:Causes of increased CO:• FeverFever• AnaemiaAnaemia• HyperthyroidismHyperthyroidism• PregnancyPregnancy• ExerciseExercise• Etc..Etc..

Presents as:Presents as:• Systolic HT with:Systolic HT with:• ↑ ↑ pulse pressurepulse pressure

• Stroke volume: Volume of blood Stroke volume: Volume of blood pumped by ventricle during systole pumped by ventricle during systole (70 ml at rest)(70 ml at rest)

Physiological control of CO:Physiological control of CO:• Preload: Venous fillingPreload: Venous filling

• Afterload: BP against which LV must Afterload: BP against which LV must expel stroke volumeexpel stroke volume

• Inotropy: Strength of myocardial Inotropy: Strength of myocardial contraction. Starling`s law, contraction. Starling`s law, catecholaminescatecholamines

Physiological control of heart Physiological control of heart rate:rate:• Intrinsic: SA nodeIntrinsic: SA node• Extrinsic:Extrinsic:Hormonal: thyroid, catecholaminesHormonal: thyroid, catecholaminesNeurological: Autonomic nervous Neurological: Autonomic nervous

systemsystemFever, electrolytesFever, electrolytes

Peripheral vascular Peripheral vascular resistance:resistance:• Determined by diameter of Determined by diameter of

peripheral arteries.peripheral arteries.

• Determines diastolic blood pressureDetermines diastolic blood pressure

Control of PVR:Control of PVR:• Hormonal: AT II, endothelins, NO, Hormonal: AT II, endothelins, NO,

bradykinin, catecholamine etcbradykinin, catecholamine etc

• Neurological: Autonomic nervous Neurological: Autonomic nervous systemsystem

• Myogenic/Local.Myogenic/Local.

The ECG:The ECG:• Einthoven`s trangleEinthoven`s trangle

• Einthoven`s lawEinthoven`s law

Einthoven`s triangle:Einthoven`s triangle:I

II

III

+-

--

+ +

Einthoven`s law:Einthoven`s law:• Lead II = Lead I + Lead IIILead II = Lead I + Lead III

• Standard limb leads: I, II, IIIStandard limb leads: I, II, III• Lead I: connects 2 armsLead I: connects 2 arms• Lead II: connects right arm with left legLead II: connects right arm with left leg• Lead III: connects left arm with left legLead III: connects left arm with left leg

aV leads:aV leads:• Limb leads are Limb leads are bipolarbipolar• Unipolar Unipolar limb leads=aV leads: aVR, limb leads=aV leads: aVR,

aVL and aVFaVL and aVF

Precordial (V) leads:Precordial (V) leads:• V1: Just to the right of the sternum in V1: Just to the right of the sternum in

the 4`th intercostal space.the 4`th intercostal space.

• V2: Just to the left of the sternum in V2: Just to the left of the sternum in the 4`th intercostal space.the 4`th intercostal space.

• V3: Halfway between V2 and V4V3: Halfway between V2 and V4

• V4: Left midclavicular line in the 5`th V4: Left midclavicular line in the 5`th intercostal spaceintercostal space

• V5, 6: 5`th intercostal space in V5, 6: 5`th intercostal space in anterior and midaxillary line anterior and midaxillary line respectivelyrespectively

Physiological use of the Physiological use of the ECG:ECG:• Rhythm: Sinus vs otherRhythm: Sinus vs other• Chamber thickening: Atrial and Chamber thickening: Atrial and

ventricular hypertrophyventricular hypertrophy• Damage: Endocardial, myocardial, Damage: Endocardial, myocardial,

pericardialpericardial• Info on systemic conditions: Info on systemic conditions:

Hypothermia, electrolyte disturbances, Hypothermia, electrolyte disturbances, pH disturbancespH disturbances

Rate, complexes, intervals:Rate, complexes, intervals:• P-wave: Atrial depolarizationP-wave: Atrial depolarization• QRS-complex: Ventricular QRS-complex: Ventricular

depolarizationdepolarization• T-wave: Ventricular repolariationT-wave: Ventricular repolariation