Sedation Physiology - Cardiovascular Flashcards
list the 4 main valves in the heart and their location
- tricuspid – between the right atrium and ventricle
- pulmonary – between the right ventricle and the pulmonary circulation
- mitral (bicuspid) – between the left atrium and left ventricle
- aortic – between the right ventricle and the systemic circulation
what is the function of the coronary arteries?
supplies arterial blood to the myocardium
where do the coronary veins drain into?
The right atrium
What percentage blood volume is involved in pulmonary circulation?
20% blood volume
What percentage blood volume is involved in systemic circulation?
80%
Describe what occurs during pulmonary circulation
Deoxygenated blood leaves the right ventricle of the heart, enters the lungs and becomes oxygenated and comes back to the left atrium.
Describe what occurs during pulmonary circulation
Describe what occurs during systemic circulation
Oxygenated blood leaves the left ventricle of the heart, supplies the whole body and and returns to the right atrium.
What are the cardiac muscle contractions controlled by?
controlled by electrical signals fired from nodes
List the 3 main nodes that control muscle contractions within the heart.
• Sino-atrial node = natural pacemaker which defines the cardiac rhythm
• Atrio-ventricular node
• Purkinje system
- Bundle of his
- Left bundle branch
- Right bundle branch
What innervation does the heart receive?
Autonomic innervation via the;
parasympathetic NS - from vagus nerve
Sympathetic NS
Describe the effect that the parasympathetic NS has on the heart and how this is achieved.
Acts on SA node and AV node - Via muscarinic cholinergic receptors
= Negative chronotropic and dromotropic effect
= slowing down the pacemaker (SA node) and increasing the delay (hence reducing conduction velocity)
Where does the parasympathetic NS act on?
– Acts on SA node and AV node Via muscarinic cholinergic receptors
Where does the sympathetic NS act on? (3) and with what receptors?
SA Node, AV Node and myocytes
- Act mostly Via B1 adrenoreceptors (also B2 present
Describe the effect that the sympathetic NS has on the heart. (2)
Positive chronotropic, dromotropic and Positive inotropic effect = increasing heart rate, conduction velocity as well as contractility.
– The effect on the myocytes will increase the rate of relaxation.
List the 5 stages in the cardiac cycle.
atrial systole
ventricular contraction
ejection
ventricular relaxation
ventricular filling
What occurs during the ventricular contraction stage of the cardiac cycle? (3)
Isovolumetric contraction = contraction but there is no volume change in the ventricular chamber
- closure of the respective valve that filled the ventricle from the respective atrium.
- There is an increase in ventricular pressure which forces the atrio ventricular valves, tricuspid and mitral, to close and avoid reflux of the blood.
Describe what occurs in the ejection phase.
allows the opening of the pulmonary and aortic valves and ejects the blood towards the pulmonary and system circulation
Describe what occurs in the ventricular relaxation stage of the cardiac cycle. (2)
Isovolumetric relaxation = allow the respective atrio ventricular valve to open by relaxing the ventricle and reducing pressure without changing the volume.
Systemic blood returns to the right atrium and pulmonary blood returns to the left atrium.
Describe what occurs in the passive filling stage of the cardiac cycle.(1)
Once the valve opens, the difference in pressure causes the blood to start to flow from the atrium into the ventricle
Describe what occurs in the atrial systole/active filling stage of the cardia cycle (1)
requires the contraction of the respective atria for the active filling by an atrial systole.
On an ECG, what does the P wave indicate?
atrial depolarisation
On an ECG what dies the QRS wave indicate?
ventricular depolarisation
on an ECG what does the t wav indicate?
ventricular repolarisation
What is coronary blood flow decreased by? (2)
– Increased heart rate (Coronary arteries are compressed during systole)
– Low aortic diastolic BP = less force to sustain the coronary BF
What is cardiac output?
How much blood heart pumps into the circulatory system (over time).
How do we calculate mean arterial blood pressure?
Cardiac output x total peripheral resistance
How do we calculate cardiac output?
stroke volume (the volume of blood ejected from the ventricle on every beat) x heart rate
List the stroke volume variables. (3)
Preload
ventricular contractility
after load (TPR)
What is preload?
The tension/stretching in the heart wall as a result of filling
Define afterload.
Force that the heart must generate to pump blood against the arterial BP and peripheral resistance
Describe the blood pressure of blood when it leaves the heart, reaches the capillaries and when it returns to the heart in systemic circulation.
leaves the heart with 120/80 mmHg
35 – 15mmHg at the capillaries.
returns from the veins with values of 0-5 mmHg.
Describe the blood pressure of blood when it leaves the heart, reaches the capillaries and when it returns to the heart in pulmonary circulation.
Arterial blood leaves with 25/12mmHg
reaches the lungs with 8mmHg
drops to 0-4 mmHg when returning to the heart.
Describe the blood pressure of blood when it leaves the heart, reaches the capillaries and when it returns to the heart in pulmonary circulation.
Arterial blood leaves with 25/12mmHg
reaches the lungs with 8mmHg
drops to 0-4 mmHg when returning to the heart.
How do we measure BP?
use a sphygmomanometer to provide pressure against the brachial artery. At the same time we use a stethoscope to hear the sound flowing arterial blood is generating
What arteries can we use to monitor the pulse? (4)
The external carotid artery,
The facial artery,
The superficial temporal artery and
The radial artery
What can affect the radius of the arteries? (3) provide examples
local factors = oxygen, carbon dioxide, pH, temperature and vasoactive agents regulating the diameter of our arteriolas
sympathetic nerves acting via alpha and beta adrenoreceptors
hormones such as adrenaline, antidiuretic hormone and angiotensin II.
What is TPR (total peripheral resistance)
The combined resistance of all the systemic blood vessels.
What value is the hydrostatic pressure of gravity when we are standing? how does the body account for this?
around 80 mmHg (depending how tall you are)
As veins are more compliant than arteries, they convert that hydrostatic pressure in to distention creating a venous pooling = reducing the venous return.
What causes hypovolaemia?
loss of blood
What are the effects of hypovolaemia? (3)
= reduce the stroke volume
= reduced cardiac output
= reduced mean arterial pressure.
Describe how the body repsonds to hypovolaemia. (1)
The body response is to increase heart rate and increase the total peripheral resistance by vasoconstriction = improves stroke volume and cardiac output as well as the mean arterial pressure.
What occurs in the compensatory reflex? (5)
Reduction in arterial blood pressure will trigger the reduction of baroreceptor firing
The brainstem cardiovascular centres will act on the autonomic nervous system = reducing parasympathetic activity and increasing sympathetic activity.
The sympathetic NS will stimulate heart ventricular contraction as well as venous and arteriolar constriction.
Increase in ventricular contraction and venous constriction will increase stroke volume, increase arteriolar constriction and will increase the total peripheral resistance.
The reduction of parasympathetic and the increase in sympathetic activities will act on the sino atrial node to increase heart rate - With an increase in heart rate and stroke volume there will be an increase in cardiac output.
What are the advantages of cannulating the dorsum of the hand?
easy access
-no nearby arteries
-no nearby nerves
-no joints
What are the disadvantages of cannulating the dorsum of the hand?
small veins
- susceptible to cold/anxiety
- veins can move
- more painful
What are the advantages of cannulating the antecubital fossa? (5)
- Larger veins
- predictable location
- Better tethered to underlying connective tissue = less mobile
- Less painful
- Less susceptible to venoconstriction
What are the disadvantages of cannulating the antecubital fossa? (4)
- Difficult access (have to have the correct position of the arm)
- potential risk of nerve damage
- potential risk of intra arterial injection
- Have to immobilise the joint
