Transcript Cardiovascular physiology.

Cardiovascular physiology.
Dr James Ker
2 scenario`s in cardiology:
• Systemic diseases affecting the
cardiovascular system.
• Primary cardiovascular diseases.
How can these diseases affect the
cadiovascular system ?
Components of the cardiovascular system:
• Myocardium: myocarditis, cardiac failure
etc
• Valves: Stenosis, incompetence etc
• Electrical system: Dysrhythmias.
• Vessels: Arteries, veins, lymphatic
vessels.
Physiological disturbances:
• Disturbances in the following may occur:
• Blood pressure
• Cardiac rhythm
• Valvular function
• Cardiac systole and diastole
• Blood flow
Blood pressure:
• BP = Cardiac output (CO) x peripheral
vascular resistance (PVR)
• 3 components of blood pressure:
• Systolic component
• Diastolic component
• Mean arterial pressure
• BP = 120/80 mmHg
• Mean arterial pressure = (S + 2D)/3 or
• D + 1/3 PP
• Pulse pressure=S – D (120-80=40 mmHg)
Cardiac output:
• CO = Stroke volume x heart rate
• Thus:
2 ways to increase CO: SV vs CO
Determines systolic BP
Systolic vs diastolic HT
Normal CO: 5L/min
Cardiac index=CO corrected for body surface area
Causes of increased CO:
• Fever
• Anaemia
• Hyperthyroidism
• Pregnancy
• Exercise
• Etc..
Presents as:
• Systolic HT with:
• ↑ pulse pressure
• Stroke volume: Volume of blood pumped
by ventricle during systole (70 ml at rest)
Physiological control of CO:
• Preload: Venous filling
• Afterload: BP against which LV must expel
stroke volume
• Inotropy: Strength of myocardial
contraction. Starling`s law,
catecholamines
Physiological control of heart rate:
• Intrinsic: SA node
• Extrinsic:
Hormonal: thyroid, catecholamines
Neurological: Autonomic nervous system
Fever, electrolytes
Peripheral vascular resistance:
• Determined by diameter of peripheral
arteries.
• Determines diastolic blood pressure
Control of PVR:
• Hormonal: AT II, endothelins, NO,
bradykinin, catecholamine etc
• Neurological: Autonomic nervous system
• Myogenic/Local.
The ECG:
• Einthoven`s trangle
• Einthoven`s law
Einthoven`s triangle:
I
+
-
-
III
II
+ +
Einthoven`s law:
• Lead II = Lead I + Lead III
• Standard limb leads: I, II, III
• Lead I: connects 2 arms
• Lead II: connects right arm with left leg
• Lead III: connects left arm with left leg
aV leads:
• Limb leads are bipolar
• Unipolar limb leads=aV leads: aVR, aVL
and aVF
Precordial (V) leads:
• V1: Just to the right of the sternum in the
4`th intercostal space.
• V2: Just to the left of the sternum in the
4`th intercostal space.
• V3: Halfway between V2 and V4
• V4: Left midclavicular line in the 5`th
intercostal space
• V5, 6: 5`th intercostal space in anterior
and midaxillary line respectively
Physiological use of the ECG:
• Rhythm: Sinus vs other
• Chamber thickening: Atrial and ventricular
hypertrophy
• Damage: Endocardial, myocardial,
pericardial
• Info on systemic conditions: Hypothermia,
electrolyte disturbances, pH disturbances
Rate, complexes, intervals:
• P-wave: Atrial depolarization
• QRS-complex: Ventricular depolarization
• T-wave: Ventricular repolariation