Cardiac Output, Blood Flow, and Blood Pressure Regulation

Cardiac Output (CO)

The volume of blood ejected by the ventricles per minute, typically around 5 liters at rest, calculated as the product of heart rate (HR) and stroke volume (SV).

Heart Rate (HR)

The number of heartbeats per minute, influenced by factors like metabolic demands, sympathetic nervous system activity, and parasympathetic nervous system activity.

Stroke Volume (SV)

The volume of blood pumped by a ventricle per beat, determined by venous return and sympathetic activity, calculated as the difference between end-diastolic volume (EDV) and end-systolic volume (ESV).

Frank-Starling Law of the Heart

States that the heart pumps most of the blood it receives during diastole in systole, showing that the more the ventricles are stretched, the harder they contract.

Cardiac Reserve

The maximum percentage by which cardiac output can increase above the resting level, calculated as the difference between maximum and resting cardiac output.

Factors Affecting Stroke Volume

Includes inotropy (contractility), preload (tension in the left ventricle before contraction), and afterload (resistance the heart has to push against).

Blood Flow and Perfusion

Perfusion is the amount of blood flowing through an organ or vessel per unit time, regulated locally, short-term, and long-term to meet metabolic needs.

Mean Arterial Pressure (MAP)

The average pressure driving blood forward into tissues throughout the cardiac cycle, calculated as diastolic pressure plus one-third of the pulse pressure.

Vasoactive Chemicals

Vasoconstrictors and vasodilators that regulate blood pressure and vascular tone, including epinephrine, norepinephrine, angiotensin II, and nitric oxide.

Control Centers for Cardiovascular Function

The autonomic nervous system control centers in the medulla oblongata, including the vasomotor center and reflexes like the baroreceptor, chemoreceptor, and medullary ischemic reflexes.

CO=HVxSV

cardiac output (CO) equation

SV=EDV-ESV

Stroke volume equation

end diastolic/systolic volume

what does EDV/ESV mean?

cardiac reserve = COmax-COrest

cardiac reserve equation → The maximum percentage that the cardiac output can increase above the resting level.

Inotropy

• _________= contractility

  • The ability of the heart muscle to generate force during myocardial ventricular contraction

Positive

• ____ inotropic agents:↑contractility

  • Include: Hypercalcemia, Catecholamines, and sympathetic stimulation 

Negative

• ______ inotropic agents:↓contractility

  • Include:Hypocalcemia, Hyperkalemia, Parasympathetic stimulation 

SV∝ EDV

Frank-Starling law of heart

• ventricles eject as much blood as they receive

  • the more they are stretched, the harder they contract 

Anrep Effect

• Sudden increase in afterload results in an increase in myocardial contractility to compensate → due to increased myocardial stretch

• Due to increases Ca2+ entering the cytoplasm through the Na+/Ca2+ exchanger in the T-tubules

  • A very important consequence of these events is that the cardiac output of the left ventricle must equal the output of the right ventricle so that the blood flow through both the pulmonary and systemic circulations are equal. 

MAP(BP)= COxTPR

Mean Arterial Pressure (MAP)

• diastolic pressure + 1/3 pulse pressure 

BNP

• Released by the ventricles in response to volume expansion and pressure overload

• Also, NT-proB-type Natriuretic Peptide 

• Helps the body compensate in congestive heart failure 

• Blood test is diagnostic for heart failure 

• Effects of Natriuretic Peptides

  • Downregulate the effects of the Sympathetic NS and the RAAS

  • Sodium and water excretion via the kidneys

  • decreasing peripheral vascular resistance by causing smooth muscle relaxation

  • May inhibit cardiac growth and hypertrophy 

vasoconstrictors

1. Epinephrine

2. Norepinephrine

3. Angiotensin I and angiotensin II***

4. Serotonin

5. Vasopressin (ADH) 

Vasodilators

1. Histamine

2. Bradykinin

3. Prostacyclin (PGI2)

4. NO 

medulla oblongata

the _____ is the control center for cardio vascular function and BP Regulation

baroreceptors

_______ reflex: Stretch-sensitive receptors

• Monitor blood pressure 

• Important in short-term regulation of BP

  • Postural changes 

• adapt to chronic high or low BP → NOT useful for long-term BP regulation

Chemoreceptor

• _______ reflex

  • Located in:

    • Carotid artery

    • Aortic artery

  • Sensitive to:

    • ↓O2 or ↑CO2

    • ↑H+ 

  • Main function: ↑respiration

    • Also ↑BP via activation of vasomotor center

Medullary ischemic

• ________ reflex 

  • Automatic response to a drop in perfusion of the brain

    • Medulla oblongata monitors its own blood supply

      • ↑Sympathetic stimulation to the heart and blood vessels →

        • ↑ HR and force of contraction

        • Widespread vasoconstriction

        • ↑BP and restores normal perfusion to the brain