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 heart

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

The cardiac cycle

• Ventricles relax – ventricular diastole– Rapid ventricular filling

The cardiac cycle

• Ventricles relax – ventricular diastole– Isovolumetric

relaxation– Rapid ventricular filling– Atrial contraction

The cardiac cycle

• Ventricles contract – ventricular systole– Isovolumetric contraction

The cardiac cycle

• Ventricles contract – ventricular systole– Ventricular ejection

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

ECG

ECG

Parasternal Long Axis

Volumes during the cardiac cycle

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

Pressures during the cardiac cycle

E.H.Starling

The heart-lung preparation.

Effectively an isolated heart preparation.

Heart lung apparatus

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

Heart lung apparatus

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

Observations 1

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

Observations 2

Starling Stated His Law in the Linacre Lecture of 1915:

• "The law of the heart is thus the same as the law of muscular tissue generally, that the energy of contraction, however measured, is a function of the length of the muscle fibre."