PBL 2 Flashcards
define systole
this is contraction of the heart muscle, the ventricles and atria both undergo systole and contract
define diastole
relaxation of the heart muscle both the ventricles and atria relax
define stroke volume
this is the volume of blood pumped from the left ventricle per beat
define pulse pressure
pulse pressure is the difference between systolic and diastlolic blood pressure, it is measured in mmHG
- it represents the force the heart generates with each conditions
define mean arterial pressure
the mean arterial pressure is an average blood pressure in the arteries an individual during a single cardiac cycle
define total peripheral resistance
this is the mean arterial pressure – mean venous pressure divided by the cardiac output – this is the resistance of the arteries to flow, resistance increases as they constrict and resistance decreases as they dilate
define cardiac output
the volume of blood pumped out the heart from the ventricles to the body per minute
- measured using an echocardiogram or a doppler ultrasound
how does systole change during exercise
Systolic
Systole = contraction of the heart
Systolic blood pressure = maximum pressure in the arteries
Limits
>140 mm Hg systolic marginal hypertension.
>160 mm Hg definite intervention threshold.
Exercise
- decreased end systolic residual volume as the stroke volume is maintained due to the contraction of the atria which help transfer blood into the ventricles during diastole
- there is a progressive increase in systolic blood pressure it rises to between 160 – 220mmHg during exercise
how does diastole changes during exercise
- Shortens allows increase in heart rate – once you get above 200 beats per minute no time to fill the ventricles and heart during diastole less tiem for the blood to go into the heart
- Diastolic blood pressure remains the same
how does cardiac output change during exercise
- Increases nearly 4 times to cope with increased demand for oxygen
- Increases by either increasing heart rate up to 2.5 times resting or increasing stroke volume up to 1.5 times
- Most of the increased volume goes to exercising muscles that need the extra oxygen supply
- Measured by heart beat x stroke volume
How does pulse pressure change in exercise
Pulse pressure increases with exercise due to increased stroke volume
- this is because the systolic pressure increases whereas the diastolic pressure remains about the same this causes an increase in stroke volume and cardiac output
- pulse pressure is systolic – diastolic pressure
how does mean arterial pressure change in exercise
- during exercise the cardiac output increases more than the total resistance decreases so the mean arterial pressure increases by a small amount
- mean arterial pressure is calculated as diastolic plus 1/3 of pulse pressure
- diastolic pressure does not increase but pulse pressure does therefore it has a slight increase in pressure during exercise but not as much as pulse pressure
describe the structure of the sympathetic nervous system
- prevertebral and paravertebral ganglia
- chain extends from T1 to L2
- prevertebral is T1-T4
- paravertebral is T5-L2
- prevertebral has three cervical ganglia these are the superior middle and inferior cervical ganglia
- paravertebral have 3 ganglia – these are the coelic, superior and inferior mesenteric ganglia
- 25 pairs of ganglia that are joined by nerve trunks
- Sympathetic – supply vascoconstrictor nerves
what happens to the sympathetic system during exercise
- When exercise begins local chemical vasodilators are released from the exercising muscles
- Increase muscle blood flow to supply the extra oxygen needed by the muscles
- Vasodilation reduces total peripheral resistance this could cause a total drop in blood flow but sympathetic outflow causes a global vasoconstriction which increases vascular resistance in nonactive muscles resulting in the total peripheral resistance being maintained
- Sympathetic activity also increases heart rate which increases cardiac output
- Cardiac output supplies more blood and oxygen to the exercising muscles
- Noreadnrealine – globally constricts blood vessels enabling there to be an adequate supply of blood to the vasodilated active muscle and redistributes the cardiac output to the exercising muscle – released from the medulla of the adrenal glands
- Adrenaline – releases glucose into the blood from the liver and muscle cells for extra energy this increases cardiac output and respiration and dilates airways which increases oxygen intake – released from the medulla of the adrenal glands
name the alpha receptors and what they do
Alpha 1 is the main receptor on vascular smooth muscle
Acts to increase contraction.
Alpha 2 receptors are found on presynaptic sympathetic nerve terminals
Act to reduce noradrenaline release by negative feedback
name the beta receptors and what they do
Beta 1 receptors found mainly in heart (and kidneys)
Act to increase force & rate of contraction of myocardium
Beta 2 found mainly in bronchial smooth muscle (but also in smooth muscle of gastrointestinal tract, liver, uterus)
Act to relax the muscle
Beta 3 receptors increase lipolysis and gluconeogenesis in adipose tissue, thus providing energy-rich substrates for the actively metabolizing muscles.
what is the normal pulse pressure
30-50 mmHg
- it is raised during exercise and can reach 100mmHg
what is a low pulse pressure
- a low pulse pressure less than 25% of systolic pressure
- decrease in stroke volume usually - for example in aortic stenosis, heart failure blood loss, shock, and cardiac tamponade
what is a high pulse pressure
- greater than 100mmHg is high
- increase in stroke volume or reduction of arterial compliance- for example aortic regurgitation, volume overload and ageing
what are the calculations for mean arterial pressure
MAP (estimation) = DP + 1/3(PP)
MAP (calculation) = (CO x TPR) + CVP
Normal: 65-110 mmHg
how do you measure stroke volume
EDV-ESV
- measured using an echocardiogram
what is the stroke volume of a typical man
Typically 70ml/min at rest in a 70kg man
what is the definition of preload
end-diastolic ventricular volume
what is the definition of afterload
the systemic resistance the ventricles must
overcome to eject blood into vasculature aka total
peripheral resistance
