Neural interventions in heart failure Flashcards
What is the normal neural control of the heart?
heart is autorhythmic- therefore without any neural input the heart will continue to beat
intrinsic HR= 100bpm due to SAN
at rest, parasympathetic input decreases HR to 60-70bpm- slows the SAN activity
maximum HR= 220-age-
- as you age your max HR decreases as it cannot maintain as high a HR
Which is the initial effect of heart failure?
it causes decreased cardiac output
What happens in heart failure to attempt to improve cardiac output?
neurohumoral activation
- sympathetic system increases to increase vasoconstriction and HR
- renin-angiotensin system is activated to induce sodium and fluid retention
BUT both these effects actually adds further stress to the heart and increases damage therefore potentiating heart failure - progressive disorder
What can cause heart failure?
myocardial infarction is the main cause of HF
- blockage of one of the coronary arteries causes part of the heart to die and once you’ve damaged cardiac muscle cells you cant replace them- they are replaced by fibrous scar tissue that is not contractile therefore reducing cardiac output
What does it mean by a compensated heart and a decompensated heart ?
compensated heart= a heart that has undergone the neurohumoural changes causing hypertrophy- muscle cells enlarged as they are being told to work harder
decompensated heart= the extra work load induced by neurohumoural changes has caused heart cells to die and be replaced by fibrous tissue making it less contractile- its a floppy heart - thin walls and poor at contracting
What is class 1 heart failure?
without limitations of physical activity. Ordinary physical activity does not cause undue fatigue, palpitations to dyspnea - mild
What is class 2 heart failure?
slight limitation of physical activity. They are comfortable at rest. ordinary physical activity causes fatigue, palpitations or dyspnea - difficulty breathing
What is class 3 heart failure?
marked limitations of physical activity. They are comfortable at rest. Less than ordinary activity causes fatigue, dyspnea or palpitations
What is class 4 heart failure?
inability to carry out any physical activity without discomfort. Symptoms are present at rest or minimal exertion
What are the current treatments?
Beta-blockers= propanolol- helps to mitigate the effects of the sympathetic nervous system - reduce HR
ACE inhibitors= reduce angiotensin 2 production, reduce it increase in BP both peripherally and centrally
What is an indicator of autonomic function ?
heart rate variability
reliant on the fact the heart is not a metadrome
measure cardiovascular autonomic function
What happens to HR when you are breathing?
when you breathe in your HR increases slightly whereas as you breathe out your HR decreases slightly
What 2 things can be looked at by measuring the difference between R-R intervals?
TIME-DOMAIN= looking at statistical analyses
FREQUENCY DOMAIN= spectral methods to look at oscillation
it provides a measure of the contraction of the ventricles
What are the important peaks in a power spectrum?
HF peak= beat to beat changes in HR controlled by parasympathetic nerve- fast chnages in HR
LF peak= controlled by both parasympathetic and sympathetic nervous system - slower changes in HR
look at the ratio between these peaks to get a balance of autonomic balance - low = higher parasympathetic activity
high- low parasympathetic activity
What is microneurography?
recording muscle sympathetic nerve activity
- insert electrode into tibular nerve and record the actions potentials upon vasoconstrictor axons
very direct measure
When sympathetic activity is stimulated what is shown in microneurography?
increased HR and BP
if you’ve recorded from 1 axon then all the action potentials recorded should overlap perfectly to give you one trace
What should be indicated about baroreflex sensitivity when systolic BP is plotted against R-R interval?
as BP increases you should get a decrease in HR and therefore an increase in R-R interval producing a pstitive linear line
BUT if the graph is a horizontal line it indicates that as BP increases the R-R isn’t increasing and so the HR isn’t slowing so there is very little vagal input
With normal baroreflex sensitivity what should be shown about R-R interval ?
normal baroreceptor sensitvity should correlate with increase of 3ms in R-R for every 1mmHg increase in BP
With impaired baroreflex activity what is shown about the R-R interval?
low levels of parasympathetic activity indicated by a change in R-R interval of
What is characterised of HF?
sympathetic activation and parasympathetic withdrawal
What happens to % change in HR when propanolol is given to normal and HF people?
HR is decreased in both groups, slightly more in HF but not much
- sympathetic activity is reduced in both groups by relatively similar amounts
What happens to the % change HR when propranolol and atropine are given to normal and HF people?
normal group have a substanially higher HR but HF group doesn’t increase nearly as much
- this indicates that their parasympathetic activity was low to begin with, therefore blocking with atropine hasn’t made much of a difference
What happens to baroreflex sensitivity when propranolol is given ?
in normal group they become slightly less sensitive and the HF group become slightly more sensitive but it doesn’t appear to make a huge difference
What happens to baroreflex sensitivity when atropine and propranolol are both given ?
