CVS Regulation in Action

CVS REGULATION

IN ACTION

Cardiovascular Module – Phase I

Dr. Udara SenarathneDepartment of Biochemistry

Faculty of Medical SciencesUniversity of Sri Jayewardenepura

REVISED BY

Dr. Chandana Hewage(Chairperson of the Cardiovascular Module)

Department of Physiology Faculty of Medical SciencesUniversity of Sri Jayewardenepura

IN THE MORNING… When his mother starts shouting, Siri immediately jumps out of the bed which makes him feel dizzy.

BUT WHY?

a) Reduced sympathetic output

b) Reduced venous return c) Vagal stimulation

CORRECT ANSWER!

Immediate standing from supine position

Decrease venous return to the LA due to venous pooling in the lower limbs

Reduction in EDV causes a fall in stroke volume

CO = HR x SV Thus CO reduces

BP = CO x TPR Thus systolic BP falls

Cerebral perfusion is reduced due to low BP

Feels dizzy

A FACT THAT SIRI ALWAYS KNEW…

That’s why I always turn off the alarm and sleep a little more…

It’s a medical fact. Not because I’m lazy…

AFTER GETTING UP FROM THE BED…

Within a second the dizziness would settle.

BUT WHY?

a) Increased venous returnb) Increased adrenaline

actionc) Decreased baroreceptor

discharge

‘After been

kicked out of

the bed by

his mom’

CORRECT ANSWER!

Fall in the Systolic BP

Baroreceptor discharge rate decrease

Inhibition on vasomotor centre is decreased

Unopposed tonic sympathetic discharge of vasoconstrictor system

Decreased vagal stimulation of heart

BP = CO x TPRThus systolic BP increases

Feels better

He’s been

receiving ‘nice’

comments since then

AFTER COMING TO THE FACULTY…

Anatomy dissection is his least favourite period.WHY IS THAT? Why else? Siri fainted during the very 1st session!

Only after doing the CVS module did he realise the reason…

a) Sympathetic vasodilation in skeletal muscle

b) Vagal stimulationc) Both above

CORRECT ANSWER!

Emotional disturbance

Sympathetic vasodilation in skeletal

muscle causing reduced TPR and venous return

Vagal stimulation causing bradycardia

CO and TPR are reduced.

BP = CO x TPRThus systolic BP

decreases

Faints due to reduced blood flow to brain

+

BOTH MECHANISMS CONTRIBUTE TO VASOVAGAL SYNCOPE

TRY TO WORK OUT LOGICALLY!

“Just a minute! Yesterday she said that X equals 2”

Always ASSESS

yourselfso that you know what

you don’t know!

Click icon to add picture

Practice answering!

Else you might

end up doing this!

Click icon to add picture

Click icon to add picture Practice answering!

Else you might

end up doing this!

Good luck!