CR08 - Integrative Functions of CV System I

What does systemic cardiovascular regulation directly influence in the eye?

• Retinal perfusion

• Optic nerve head blood flow

• Visual symptoms during exams

What do optometrists frequently detect before systemic diagnosis?

End-organ vascular disease

What are some clinical examples of CV disorders in optometry?

• Hypertensive retinopathy

• Orthostatic hypotension with transient visual loss

What is ocular perfusion pressure (OPP)?

The balance between how much pressure is pushing blood into the eye (MAP) and how much pressure inside the eye is resisting that flow (IOP)

What is the equation for OPP?

OPP = MAP - IOP

What does OPP determine?

The blood flow to the retina and optic nerve head.

What increases OPP?

Increased MAP or decreased IOP.

What is reduced OPP associated with?

Glaucoma risk and progression (high IOP)

What is nocturnal hypotension?

An excessive drop in blood pressure during sleep.

What is normal nocturnal dip?

A physiological BP reduction at night.

What does excessive nocturnal BP drop result in?

Decreased optic nerve head perfusion.

What is nocturnal hypotension associated with?

Normal-tension glaucoma (NTG).

What increases risk of nocturnal hypotension and normal-tension glaucoma?

Risk increases with night-time antihypertensive dosing.

What factors are transiently altered by exercise?

• Retinal perfusion

• Chroroidal circulation

• Visual symptoms (blur, photopsia, tunnel vision in extreme exertion)

What are the initial impacts of exercise on the CV system?

Increased HR, SV, CO, arterial pressure, and pulse pressure. Decreased TPR due to vasodilation of skeletal muscle beds).

What is the response of central command during exercise?

Increased sympathetic, decreased parasympathetic → Increased HR, contractility, CO → constriction of arterioles (reduce blood to unnecessary regions) → constriction of veins (increased VR) → increased blood flow to skeletal muscles

What are the local responses during exercise?

Increased vasodilator metabolites → dilation of skeletal muscle arterioles → decreased TPR → increased blood flow to skeletal muscles

What happens when you stand for too long?

Blood volume shifts to the lower extremities, causing peripheral edema.

What is the body’s response to blood pooling in the lower extremities?

Decreased central venous volume, increased venous and arterial pressure in the extremities

What does decreased central venous volume lead to?

Decreased central venous pressure and cardiac filling → decreased SV, CO, MAP, PP → decreased baroreceptor firing

How do medullary cardiovascular centers respond to decreased barorecepter firing?

Decreased parasympathetic activity, increased sympathetic activity → increased HR, contractility, venoconstriction, and vasoconstriction (immediately), and increased fluid retention in the kidney (long-term)

What is the skeletal muscle pump?

The skeletal muscles in the legs help push blood up the veins to avoid pooling of blood.

What is the initiating event when a person stands up?

Pooling of blood in the extremities

Why does blood pool in the lower extremities upon standing?

High compliance of veins and delayed constriction of lower extremity vasculature

What symptoms may result from venous pooling when standing?

Lightheadedness and sometimes fainting

What happens to capillary hydrostatic pressure (Pc) with venous pooling?

Pc increases

What does increased Pc cause?

Increased fluid filtration into the interstitium

What happens to intravascular volume as fluid moves into the interstitium?

It decreases

What occurs if lymphatics cannot return filtered fluid to circulation?

Edema

What happens to venous return (preload) with venous pooling?

It decreases

What happens to stroke volume (SV) and cardiac output (CO) with decreased preload?

SV decreases and CO decreases

What can severe decreases in arterial pressure (Pa or MAP) cause?

Syncope (fainting)

What reflex compensates for decreased arterial pressure during standing?

Baroreceptor reflex

Which baroreceptors detect the decrease in Pa?

Carotid sinus baroreceptors

How do baroreceptors signal decreased Pa?

By decreasing firing rate

Where do signals from baroreceptors go?

Vasomotor center in the medulla

What happens to sympathetic outflow during the baroreceptor response?

It increases to the heart and blood vessels

What happens to parasympathetic outflow during the baroreceptor response?

It decreases to the heart

What cardiovascular changes result from increased sympathetic activity?

Increased heart rate, contractility, total peripheral resistance, and venous return → arterial pressure increases toward normal

When does orthostatic hypotension occur?

On standing up from a supine position

How is orthostatic hypotension defined by BP change?

SBP decrease >20mmHg and/or DBP decrease >10mmHg

What is orthostatic hypotension related to?

Inadequate reflex vasoconstriction

What are the causes of orthostatic hypertension?

• Idiopathic (unknown cause)

• Neurogenic (ANS issues)

• Non-neurogenic (hypervolemia, etc)

• Medications (diuretics, opioids, etc)

What lifestyle change can help manage orthostatic hypotension?

Increased fluid consumption, physical exercise before rising, elastic support stockings, pharmacological treatments

What is the optometrist’s role in managing orthostatic hypotension?

• Recognize symptoms during case history

• Modify exam positioning (lift chair slowly)

• Refer for medical evaluation when recurrent

What visual systems occur with systemic hypotension?

• Transient visual dimming or blurring

• “Gray-out” or brief blackout of vision

• Delayed visual recovery after postural change

  • Orthostatic

Why are elderly patients more at risk for orthostatic hypotension?

They have reduced autonomic responses

What medication classes increase OH risk?

Antihypertensives, sedatives, antidepressants

What cardiovascular conditions increase OH risk?

Hypertension and heart failure

How does diabetes increase OH risk?

Autonomic dysfunction and impaired baroreceptor reflex

How do dehydration or fasting increase OH risk?

Lower blood volume

What are clinical cues to indicate OH in an optometry practice?

• Patient has dizziness when sitting up

• Transient vision loss after dilation

• Delayed visual recovery

How can an optometrist prevent an episode of OH?

• Raise exam chair slowly

• Allow patient to sit before standing

• Ask about dizziness before ambulation

How do you manage an OH episode as an optometrist?

• Recline patient and elevate legs (Trendelenburg position)

• Check BP, HR, responsiveness

• Provide fluids

• Make sure patient is stable before standing or leaving

• Emergency referral if symptoms persist