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Lecture about electrophysiology, from the University of Cambridge.
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The Autonomic nervous system and the circulation
• The main efferent limb of all cardiovascular reflexes.
• Can change resistances and volumes of vessels• Can change rate and force of contraction of
heart• Can alter renal excretion of salt and water
Circulation
• Bulk transport
• Diffusion, limited by distance, gradient and √molecular mass
• Circulation ensures exchange vessels in all tissues provided with nutrients
• All cells linked via the capillary exchange vessels
The Roles of the Circulation
• Respiration • Nutrition• Excretion• Homeostasis (regulation of the constancy of the
milieu interieur of Claude Bernard)• Thermoregulation • Defence• Reproduction• Communication (e.g. endocrine regulation)
Trunk and legs
Brain
Splanchnic circulation
Kidneys
Placenta
Head and arms
Liver
Lungs
Foramen Ovale
Ductus venosus
Ductus arteriosus
Physiological Overview
• Bulk flow system with variable demand• Components are pump, fluid and vessels,
potentially each of these can change properties to meet the bodies needs
• Flow created by energy differences• Heart creates flow by creating energy
differences, vessel properties modify the flow and this is reflected in the pressure gradients.
Llandis’ diagramLV Large arteries
Arterioles
Capillaries
Veins and venules
RV
Pulmonary artery
Pulmonary arterioles
Pulmonary capillaries
Pulmonary veins
Regional blood flow and cardiac output
Rest Exercise Blood flow Oxygen
consumption Blood flow Oxygen consumption
ml/min % of total
ml/min % of total
ml/min % of total
ml/min % of total
Brain 750 15 50 20 800 4 50 2 Cardiac muscle
150 3 25 10 1000 5 230 9
Skeletal muscle
750 15 50 20 14700 74 2080 83
Kidneys 1250 25 20 7 1200 6 20 0.8 Skin 150 3 8 3 1000 5 10 0.4 Splanchnic bed
1250 25 40 15 800 4 40 2
Other 700 14 57 23 500 2.2 70 3 Cardiac output
5000 250 20000 2500
The cardiac cycle
• Simple observation of the heart shows an orderly sequence of contraction
• Ventricles empty (ventricular systole)
• Ventricles fill rapidly
• Atria contract (atrial systole)
• Ventricles pump again
The cardiac cycle
• Heart is a good pump because– Orderly sequence of contraction– Low impedance to filling– One way flow (valves)– Variable output– Autonomous
The cardiac cycle
• Ventricles relax – ventricular diastole– Isovolumetric
relaxation– Rapid ventricular filling– Atrial contraction
Auscultation
• First and second sounds• First (mitral and tricuspid)
– Normal – Split
• Second (aortic and pulmonic)– Normal– Split
• Split both
Auscultation
• 3rd and 4th heart sounds
• 3rd (often normal in young, pathological in older ones – rushing in)
• 4th (ventricular malfunction in older people – a stiff wall)
Auscultation
• Murmurs– Characterised by timing, duration and
localisation
• AS
• MS
• MI
• ASD
• Patent Ductus
Heart rate and cardiac phases
Heart rate 75bts/min 200bts/min Duration of cardiac cycle 0.8s 0.30s Duration of ventricular systole 0.3s 0.16s Duration of ventricular diastole 0.5s 0.14s
Key Features of the Preparation *.
The flow of blood into the heart (pre-load)
and the resistance against which the heart has to pump (after-load)
can be varied independently
Key Features of the Preparation*
Ventricular volume, and therefore SV, and CO, and arterial and venous pressures can be measured.
Key Features of the Preparation *
The heart is isolated from the central nervous system so that there is no reflex control, heart rate therefore does not change significantly
The chest is open so that intrathoracic pressure is constant at atmospheric pressure and does not vary with respiration
Starling, Paterson and Piper - pre-load experiments.
• Varied the preload by changing venous return.
Increasing volume of heart
S
•After a number of beats the heart was expelling all the blood returning to it but from a greater diastolic volume.•The output of the heart was now increased and this increased the cardiac work rate (power)•At this point the balance between venous return and cardiac output was restored
•On returning the venous input to previous level the heart went back to initial state
Starling, Paterson and Piper - after-load experiments.
• Varied the afterload by changing the pressure against which the heart had to pump
Increasing volume of heart
S
•After a number of beats the heart was expelling all the blood returning to it but from a greater diastolic volume.
•The cardiac output was restored but the work rate (power) was increased because the heart was pumping against a greater pressure.•Repeated in up and down directions