Tut3: Blood Pressure Flashcards
Only completed up to drugs beta blockers etc
What is blood pressure?
A measure of pressure of blood against the walls of the arteries
A ration of maximum (systolic) over minimum (diastolic) pressure
Normal blood pressure 120/80
List the functions of the circulatory system
- Obtains O2 from lungs, nutrients from GIT, hormones from endocrine glands and delivers to the tissues that need them
- moves metabolic waste products CO2, lactic acid, urea from tissues
- transports antibodies and leukocytes to areas of inflammation
What is mean arterial pressure?
Systolic - diastolic gives the pulse pressure,
the heart is in systole 2/3 of the time ?????
MAP= diastolic + 1/3 pulse pressure
MABP = COxTPR
What are the four ways of blood pressure measurement?
Invasive- penetrating arterial wall e.g. In ICU
Non-invasive - routine examinations and monitoring
Auscultatory method- using stethoscope and sphygmomanometer
Oscillometric method - using sphygmomanometer cuff with an electronic pressure sensor (transducer), electronics and automatic inflation and deflation of the cuff
What is hypotension?
A fall in the blood pressure
May cause insufficient blood flow to brain > dizziness & fainting
What is postural hypotension?
Standing from a supine position - may cause falls in elderly as their baroreceptors are not as sensitive as ours
What is Hypertension ?
Consistent elevation in blood pressure
> or equal to 140/90mmhg
What can chronic hypertension cause?
Changes in Vasculature and in the heart
What are the risks associated with chronic hypertension?
Atherosclerosis, aneurysm, stroke, myocardial infarction, heart failure, kidney failure
How do you classify hypertension?
Normal S160 or D>100
What is the goal blood pressure for patients with diabetes or chronic kidney disease?
<130/80
What are the mechanisms which regulate mean arterial pressure?
Autonomic nervous system
Vasoactive substances
Venous return
How does the ANS regulate MAP
PNA- innervates heart. Influences HR and CO
SNS- innervates heart, arterioles and veins. Influences CO and TPR
What do baroreceptors do?
Monitor Bp in the systemic circulatory system
Where are baroreceptors found.
In the arch of aorta
In the carotid sinuses
What are baroreceptors?
Stretch receptors which monitor blood pressure at every heart beat
Describe baroreceptors reflex
An increase in blood pressure increases the stretch of aorta and carotid Arteries
This stimulates baroreceptors
Baroreceptors increase their firing of impulses per second in afferent nerves to the vasomotor cortex
This causes a change in autonomic nervous system activity to the CV system
SNA is decreased: veins and arterioles will dilate, heart rate decreases, contractility decrease, > decreased VR, decreased CO, decreased TPR > decreased BP to normal
PNA is increased: decreases HR, decreases CO, > decreased BP to normal
What are the two types of vasoactive substances?
Vasoconstrictors and vasodilators
Where are some vasoconstrictors?
Adrenaline and noradrenaline AngiotensinII Vasopressin (ADH) Endothelin Thromboxane A2
What are some vasodilators?
Prostacycline
Nitric oxide
Atrial natriuretic peptide
What does angiotensin II do?
Causes secretion of aldosterone > enhances Na+ reabsorption, expands plasma volume, increases MAP
It is a vasoconstrictor which increases TPR and MAP
It vasoconstricts in efferent renal arterioles to help maintain perfusion pressure through kidney
Effects beneficial bp or blood volume decrease
What does venous return do.,
It helps to regulate CO by way of changes in VR
What is VR influenced by?
Blood volume
SNA stimulation of veins
Skeletal muscle activity
Respiratory activity
What are antihypertensives?
Drugs which reduce blood pressure. They can affect CO, or PR
What factors affect the cardiac output?
Cardiac: Heart rate, Inotropic state, Neural, Hormonal
Renal fluid volume control:
Renin-Angiogensin, Pressure Natriuresis, Aldosterone, Atrial Natriuetic factor
What factors affect Peripheral Resistance?
SNA:
Vasoconstrictor (α), Vasodilator (β)
Humoural:
vasodilator, prostaglandins, kinins, vasoconstrictor, angiotensin, catecholamines
What drugs act on the Cardiac Output?
Beta blokers
Ca2+ channel blockers (non dihydropyridines) - decreases force of contraction of myocardium
Diuretics
What are antihypertensives?
Drugs which reduce blood pressure. They can affect CO, or PR
What factors affect the cardiac output?
Cardiac: Heart rate, Inotropic state, Neural, Hormonal
Renal fluid volume control:
Renin-Angiogensin, Pressure Natriuresis, Aldosterone, Atrial Natriuetic factor
What factors affect Peripheral Resistance?
SNA:
Vasoconstrictor (α), Vasodilator (β)
Humoural:
vasodilator, prostaglandins, kinins, vasoconstrictor, angiotensin, catecholamines
What drugs act on the Cardiac Output?
Beta blokers
Ca2+ channel blockers
Diuretics
What drugs act on the peripheral resistance?
beta blockers Ca2+ channel blockers (all) ACEI/AT receptor blockers Alpha2 blockers Alpha2 agonists vasodilators
How do beta blockers work?
beta blokers = beta-adrenergic receptor antagonists
- Reduce cardiac contrcaility and CO
- Inhibit release of renin from the kidney which decreases production of angiotensin II leading to vasodilation and decreased TPR
What are some examples of calcium channel blockers and what do they do?
Verapamil decreases HR and myocardial contractility which decreases CO, causes some vasodilation
Nifedipine is a potent vasodilator and decreases TPR. It has weaker myocardial effects
Diltiazem has an intermediate moderate effect on heart and smooth muscle
What do ACE inhibitors do?
Cause vasodilation (Increase TPR) and inhibit aldosterone response to net sodium loss
What do Angiogensin Receptor Blockers do?
Promote vasodilation
Increase TPR
Increase sodium and water excretion
Which decreases Plasma volume and decreases CO
What do alpha blockers do?
Alpha blockers = alpha adrenergi receptor antagonits
reduce vascular resistance therefore reducing BP
What is hydralazine and what does it do?
Hydralazine = vasodilator
Causes direct relaxation of vascular smooth muscle
Causes reflex tachycardia (IncreasedCO)
Sodium retention (Increased plasma volume)
Administer with beta blocker to counteract unwanted compensatory mechanisms of the heart
What does methyldopa do?
Centrally acting sympatholytic
Exerts its effects at vasomotor centre in brainstem and inhibits sympathetic discharge
Decreases SNA stimulation of the heart, especially vascular smooth muscle results in some decreased CO and marked decrease in TPR
What is hypovolaemia?
abnormal reduction in fluid
can be due to haemorrhage or dehydration
reduction in circulating blood volume
What is Euvolaemia/normovolaemia
maldistribution of fluid. Vasoconstriction of certain areas
What is hypervolaemia?
fluid overload
What three situations can cause fluid imbalance?
hypovolaemia, euvolaemia, hypervolaemia
what is ardiovascular shock?
inadequate blood flow throughout the body
results from reduced blood volume (hypovolumic shock)
profound vasodilation (low resistance shock)
acute failure of the heart to pump (Cardiogenic shock)
What is haemorrhage?
Excessive blood loss.
20% can be lost -no problem
Mean arterial pressure is maintained by baroreceptor reflex
- Volume is restored within 24 hours
Arteriolar constriction reduces capillary pressure and fluid moves from tissues -> plasma
Urine production is suppressed,
ADH and angiotensin II stimulate thirst - > 30-50% requires transfusion within the golden hour otherwise will lead to irreversible shock - multi organ failure
What are the first mechanisms to respond following acute change in pressure?
Baro receptors and Chemoreceptors followed by CNS isotonic response
Stress relaxation also respond immediately but their actions are slightly slower
When do capillaries and fluid shift responses kick in?
Within 2 minutes and 8 minutes respectively
When does Aldosterone kick in?
by 2 hours
When does renal blood volume pressure control kick in?
by 4 hours
List the responses in order of increasing maximum feedback gain at optimal pressure
Capillary Fluid shift Stress relaxation Aldosterone Chemoreceptors Baro receptros CNS Isotonic response Renal blood volume pressure control
What effect does gravity have on the determination of blood pressure?
Gravity affects the Hydrostatic pressure
When standing, BP at ankle ~90mmHg higher than that of heart due to weight of column of blood between the two points
Pressure at the head is ~30mmHg less than at the level of heart
For this reason, BP is always measured at the level of the heart
what is the primary goal of the circulatory system
increase blood flow to the working muscles
How does the circulatory system compensate for exercise?
By sympathetic stimulation
By increasing MAP and decreasing local vascular resistantce
CO can increase by 4-5fold due to 3-fold increase in HR and 1.5fold increase in SV
What is postural hypotension?
A decrease in standing blood pressure.
>10mmHg decrease when associated with dizziness/fainting
In which patients is postural hypotension more likely to occur?
Patients with Systolic HT (elevated BP) Diabetes Taking diuretics/venodilators Taking psychotropic trugs like PKD
What can be done to reduce postural hypotension?
Caution to avoid volume depletion and excessively rapid dose titration of antihypertensive drugs
Advise to take time and care when rising from lying/sitting position
How is the circulatory system affected in regards to the electrical activity of the heart?
- alteration in rate or rhythm of heart will affect how effectively the heart can pump
- e.g. in atrial fibrillation there is a lack of meaningful atrial contraction which decreases ventricular filling pressures which in turn decreases CO by about 10-20%
- MABP = CO x TPR
- Decreased CO will decrease MAP
