BIOS 162-a Review: Cardiovascular II

September 26, 2011

Important Regulated Variable: Mean Arterial Pressure (MAP)

• MAP = Diastolic Pressure + 1/3 (Systolic Pressure – Diastolic Pressure)

Systolic pressure

Diastolic pressure

Feedback mechanism for mean arterial pressure

Stimulus:decrease in MAP

Sensor:Stretch receptors in

arteries

Feedback mechanism for mean arterial pressure

Stimulus:decrease in MAP

Sensor:Stretch receptors in

arteries

Afferent pathway:Afferent neurons

Integrating center:Brainstem

Set point: 100 mmHg

How much can the set point vary?

Feedback mechanism for mean arterial pressure

Stimulus:decrease in MAP

Sensor:Stretch receptors in

arteries

Afferent pathway:Afferent neurons

Integrating center:Brainstem

Set point: 100 mmHg Efferent pathways

Neurons Endocrine

Effectors

How to change MAP?

• MAP = Cardiac Output x Total Peripheral Resistance

Heart Rate Stroke Volume

Arteriolar Resistance

Feedback mechanism for mean arterial pressure

Stimulus:decrease in MAP

Sensor:Stretch receptors in

arteries

Afferent pathway:Afferent neurons

Integrating center:Brainstem

Set point: 100 mmHg Efferent pathways

Neurons Endocrine

Effectors

Heart Arteries

Increased Stroke Volume

Increased Heart Rate

IncreasedResistance

-

More Detailed: Control of Heart Rate

• Neural– Sympathetic/parasympathetic activity at SA and

AV node

• Endocrine– Epinepherine from the adrenal gland

More Detailed: Control of Stroke Volume

• Neural– Sympathetic activity increases contractility

More Detailed: Control of Arteriolar Resistance

• Note: resistance is directly proportional to diameter of blood vessel!

• Neural– Increase in sympathetic activity

(epinepherine/norepinepherine)• Endocrine– Local (vasodilation): metabolites, decreased oxygen,

NO, prostaglandins, EDHF– Systemic (vasoconstriction): vasopressin, angiotensin

II

Hypertension

• Increased blood volume– Blood glucose and change in osmotic pressure– Renal dysfunction

• Increased total peripheral resistance– Atherosclerosis

Quiz!

Why might women have lower hematocrit than men?

• Low hematocrit = anemia• Blood loss can lead to low hematocrit when

blood cell production can’t keep up: menstrual cycle

• Nutritional deficiencies?

What is the problem with “blood doping”?

• Increases risk of abnormal blood clotting• Enlargement of spleen• Can damage bone marrow, may lead to

leukemia

Explain why my ankle would swell after a sprain? How does the swelling

go down after it heals?• Swell: normally, proteins can’t get through blood

vessels. This provides osmotic pressure to keep fluid in blood vessels. When damage occurs (ankle sprain), immune cells release cytokines that increase permeability of blood vessels (to allow in macrophages). But, proteins can move in too, changing osmotic gradient.

• Decrease swelling: ice (causes vasoconstriction), lymphatic vessels (return interstitial fluid to circulatory system)

Swelling of the feet may be an indication of what?

• Right heart failure leads to build up of fluid in the systemic organs, especially the feet

Why might a soldier standing at attention eventually faint?

• Skeletal muscle pump, which requires contraction of skeletal muscles, moves blood back to heart. Without contraction (as in during standing at attention), blood cannot get back to heart and therefore to brain.

Someone with AV block would have a heart rate that is the same

as/higher/lower than someone without AV block

• Lower:

Partial AV block

Complete AV block

Indicate which is atrial/ventricular defibrillation, and the concerns

associated with each?Atrial: less concerning, because only ~15% of cardiac output comes from atrial contraction. However, concern for blood clotting

Ventricular: more concerning, most cardiac output provided here. Describe how a heart would look during ventricular defibrillation?

Describe the abnormal heart sounds, and what causes each?

• Normal heart sounds: lub=AV valve closing, dub=semilunar valves closing

• S3: tensing of chordae tendineae (indicates excessive volume in ventricles in adults, normal in children)

• S4: Atrium contracting against a stiffening ventricle

• Murmur: insufficient valve closing