Hemodynamic parameters

Hemodynamic parameters

measurements of blood flow, heart function, and blood pressure used to evaluate the cardiovascular system in clinical and critical care settings

What are the common hemodynamic parameters?

cardiac output, heart rate, stroke volume

Cardiac output

volume of blood pumped by each ventricle per min

What is the standard cardiac output?

5 L/min

How does exercise affect CO?

increases

Heart rate

number of heart beats per minute

What is the standard HR range?

60-100 bpm

How is HR affected by exercise?

increases

Stroke volume

volume of blood pumped out of each ventricle of the heart during each beat

What is the standard SV in individuals?

70mL

How does exercise impact SV?

increases SV

How do CO, HR, and SV mathematically relate to one another?

CO = HR x SV

What heart structures does the PSNS innervate?

SAN and AVN

How does PSNS affect HR?

decreases HR (decreases chronotropy and dromotropy)

Chronotropy

anything that alters HR by altering the electrical impulses and firing rate of the SAN

Dromotropy

 anything that affects the conduction velocity of the AV node, and subsequently the rate of electrical impulses in the heart

What is intrinsic HR and why?

100-110 bpm which is caused by the SAN

Why is HR usually less than intrinsic HR?

PSNS innervation (vagal tone)

Why does HR increase during exercise?

rapid withdrawal of the PSNS initially and then subsequent HR increase is due to SNS innervation

Describe the mechanism of PSNS heart innervation

1. PSNS postganglionic neuron releases ACh which binds to M2 muscarinic ACh receptor

2. Adenylyl cyclase inhibited so cAMP levels reduced

3. Funny channel (HCN channel) probability of opening greatly decreased so funny channel current decreases and Na+ influx reduced and subsequent Ca2+ influx reduced

4. Increase in K+ efflux through the cardiac muscarinic potassium channel causing some hyperpolarization

5. Phase 4 slope then decreases (takes cells longer to reach threshold i.e., HR slows)

What heart structures does the SNS innervate?

SAN, AVN, and contractile cells

How does SNS activity affect HR?

increases HR (increases chronotropy and dromotropy)

Describe the mechanism of SNS innervation in cardiomyocytes

1. SNS postganglionic neuron releases norepinephrine which binds to B1-adrenergic receptor on cardiomyocyte

2. Adenylyl cyclase activated and creates cAMP from ATP

3. cAMP binding to funny channel allow Na+ influx and further depolarization so Ca2+ enters via L-type VG channels

4. Phase 4 slope increases (reach threshold quicker) increase in HR

What other metabolic structure can enact SNS innervation?

adrenal medulla can release epinephrine

Describe the relationship between CO and HR

as HR increases, CO increases, but as HR becomes super fast, CO decreases

Why does a very fast HR decrease CO?

decrease lusitropy (i.e., myocardial relaxation rate) which in turn decreases venous return to the heart

How does SNS innervation affect contractile cells?

increases intracellular Ca2+ influx

Inotropy

contractility

How does SNS innervation affect SV extrinsically?

increases SV

How does SNS innervation intrinsically affect SV?

Frank-Starling Law → increase in venous return (i.e., preload) to the heart increases SV (i.e., the more blood that fills the heart during diastole, the more forcefully the heart contracts during systole, resulting in a greater SV)

Describe the mathematical relationship between EDV, ESV, and SV

SV = EDV - ESV

Ejection fraction

measure of percentage of blood pumped out of the left ventricle with each heartbeat

It tells us how well the heart is pumping blood

Why is ejection fraction a better tool than SV in determining the heart’s pumping efficiency?

everyone has different sized hearts and therefore different SV

Describe the mathematical relationship between EF, EDV, and SV

EF = SV/EDV

What is the normal EF for an individual?

55-75%

How does preload affect SV?

increases EDV and SV

How does afterload affect SV?

increases ESV and decreases SV

How does inotropy affect SV?

decreases ESV and increases SV