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 CO

Determines systolic BPDetermines systolic BP

Systolic vs diastolic HTSystolic vs diastolic HT

Normal CO: 5L/minNormal CO: 5L/min

Cardiac index=CO corrected for body surface Cardiac index=CO corrected for body surface areaarea

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, catecholamines

Neurological: Autonomic nervous Neurological: Autonomic nervous systemsystem

Fever, 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 Hypothermia, electrolyte disturbances, pH disturbancesdisturbances, pH 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