Heart Rate Variability

Question 1

Outline the somatic and adrenal pathways

Answer 1

ACh released to nicotinic receptor in skeletal muscle

Adrenal cortex releases adrenaline into the blood which goes to receptors

Question 2

What is the effect of the PNS and SNS on the heart and where do they have their effect?

Answer 2

PNS reduces heart rate on the atria SA/AVN

SNS increases heart rate and contractility on SA/AVN and muscle fibres of atria and ventricles

Question 3

How does SNS have its effect on the heart?

Answer 3

Increased SNS - increased Nor/adrenaline - activate beta receptors - increase calcium and sodium influx

• depolarise quicker increasing HR
• more Ca2+ for myocardium contraction increasing contractility

Faster depolarisation and less repolarisation

Question 4

How does the adrenal gland affect the heart (mechanism)?

Answer 4

More noradrenaline released activating beta cells causing calcium influx and CICR causing faster, stronger contractions

Question 5

What is the PNS effect on the heart?

Answer 5

ACh causes K+ efflux and less Ca2+ influx causing hyperpolarisation and therefore slower depolarisation and slower

Question 6

Where are B1 and B2 receptors found? What is the effect of activating them?

Answer 6

Myocardium increase HR and contractility

Bronchioles relax and dilate

Question 7

What is the difference in left and right sympathetic fibres? (Never heard this shit before)

Answer 7

Left contractility more

Right heart rate more

Question 8

What causes variation of the heart rate?

Answer 8

Respiration, BP, temperature, O2 delivery/waste removal, hormones

Question 9

What is the effect of inspiration on the heart?

Answer 9

Inhibit PNS causing a tachycardia

Question 10

When is heart rate variability higher?

Answer 10

Slow heart rate under PNS control

Question 11

Why is the PNS a more variable heart rate?

Answer 11

Removal of neurotransmitter - AChE, diffusion and transport is faster than SNS - reuptake and diffusion

Question 12

What is the effect of BP, O2 and temp on HR and variability?

Answer 12

Decreased BP stimulate angiotensin increase SNS increase BP and HR, lower HRV. Reverse for baroceptors
Decrease temperature increase SNS to vasoconstrict but lower HRV
Hypoxia, hypercapnia, bainbridge all increase HR and decrease HRV

Question 13

How can heart rate variability be measured?

Answer 13

SDNN - SD of all RRP intervals

NN50 - number of adjacent RR intervals that differ by more than 50ms

Question 14

Very low, low and high frequency: how long and what effects them

Answer 14

Very low - 25s-6min - RAAS, Catecholamines, SNS
Low - 7-25s - BP, chemo, PNS and snsn
High 2.5-7s - ventilation and PNS

Question 15

What is the effect of exercise and sleep on HR and HRV?

Answer 15

Exercise increase HR and decrease HRV

Sleep decrease HRV and increase HRV - when wake up the opposite

Question 16

What is the effect of CHD on HRV?

Answer 16

Decrease variability - more SNS - arrhythmias - MI

Question 17

What is the effect of aerobic fitness on HRV and HR? Why?

Answer 17

Increase V and lower HR
Less SNS, less b receptors, less sensitive b receptos, less adrenaline
Increased PNS prolongs AVN conduction
More plasma and more SV

Question 18

Outline the SNS and PNS pathway

Answer 18

Short preganglionic release ACh to nicotinic receptor. Long post ganglionic release NA to adrenergic receptor alpha/beta
Long pre release ACh to nicotinic. Short post release ACh to muscarinic