Cardiovascular system: Lecture 9 -Cardiovascular responses to stress Flashcards
How do we calciulate cardiac output?
cardiac output = heart rate x stroke volume
How do we calculate mean systemic arterial pressure? (blood pressure)
mean systemic arterial pressure = cardiac output x total peripheral resistance
What is total peripheral resistance?
the amount of resistance to blood flow present in the vascular system of the body
Intrinsic cardiac regulation: Draw the Frank-starling curve
What is preload?
What you put into the heart - best measured by end diastolic volume (amount of blood in the ventricles before the ventricles contract)
How do we measure end diastolic volume?
An echo cardiogram
What is the relationship between pre load and stroke volume?
- increase in preload increases stroke volume
- high levels of preload eventually lead to decrease in stroke volume
Give 8 ways we can increase preload
Increasing preload is achieved by increasing stroke volume by:
- increase circulating volume (e.g giving fluids)
- increase central venous pressure
- increase respiratory pump
- decrease venous compliance (stiffer veins = reduced resistance = increased SV)
- increase atrial filling or contraction
- increase ventricular compliance (greater force of contraction = greater SV)
- decrease heart rate (prolongs diastole)
- increase aortic and pulmonary pressure
What is central venous pressure?
blood pressure in the vena cava
CVP reflects the amount of blood returning to the heart and the ability of the heart to pump the blood back into the arterial system.
What is the Bowditch effect?
- increase in heart rate increases force of contraction and vise versa
- High heart rate eventually leads to decreased force of contraction
Is the bowditch effect related to Frank-Sterling?
No they’re independent as length of muscle not affected in the Bowditch effect
What happens to your contractility if you suffer from heart disease?
It decreases
Whats the relationship between peak contractibility and left ventricular ejection fraction? (%)
What is venous return?
Flow of blood back to the heart
What is the Bainbridge reflex?
- increased venous return
- baroreceptors in the atria detect increased stretch
- heart rate increased via sympathetic stimulation to SAN
- involved in sinus arrhythmia
What is sinus arrhythmia?
Irregular heartbeat thats either too fast or too slow
What are the two body parts involved in the sympathetic nervous system but not the parasympathetic nervous system?
Kidneys and adrenals
What are the 4 direct cardiac sympathetic actions to increase heart rate?
- Positive chronotropy - affects the SA node
- Positive dromotropy - affects the AV node so speeds up conduction
- Positive Inotrophy - increases contraction of ventricles and atria
- Positive Lusitrophy - relaxation of ventricles and atria
What is the relationship between inotropy/preload and chronotropy and cardiac performance?
dobutamine - drugs mimic the sympathetic system so can increase hwart rate
Explain how the Renin Angiotension Aldosterone System works (RAAS)
- liver produces angiotensinogen
- Renin (produced in kidney) coverts angiotensinogen into angiotensin I
- ACE (angiotensin converting enzyme) converts Angiotensin I into Angiotensin II
- Angiotensin II acts on the adrenal galdn
- Adrenal gland secretes Aldosterone which causes water retention
- Blood pressure increases!
Where are baroreceptors located in th heart?
Carotid sinuses, aortic arch
How would decreased arterial pressure effect sympathetic and parasympathetic tone?
- decreased arterial pressure
- decreased baroreceptor firing of impulses
- increases sympathetic response
- decreases parasympathetic response
How would increased arterial pressure effect sympathetic and parasympathetic tone?
- increased firing
- decreases sympathetic tone
- increases parasympathetic tone
Why would a patient who has been bleeding and lost a lot of blood have a decreased preload?
loosing blood means theres reduced central venous pressure (less blood going into heart) so preload decreases
Give two overall summaries of initial response mechanisms to blood loss
slide 53 and 54
What are the signs of haemorragic shock?
- low BP e.g 90/50
- large pulse/ high HR e.g 130
- confused- reduced BP meaning less 02 getting to the brain
- poor urine output: reduced renal perfusion
- tachypnoeic (abnormally rapid breathing)
What is the initial intervention for blood loss and why?
Giving IV/ blood transfusion
This will increase central venous pressure and therefore preload and therefore stroke volume
