cardiovascular physiology

CARDIAC OUTPUT - amount of blood pumped into the

aorta by the heart each minute. - overall blood flow in the total circulation of an adult person at rest 5000 ml/min

TOTAL PERIPHERAL RESISTANCE ∆P from the systemic arteries to the systemic veins ~

100mmHg. resistance of the entire systemic circulation, TPR ~ 100/100,or 1 PRU Ex. Pulmo circulation – mean PAP 16mmHg, mean LA P 2mmHg ∆P = 14mmHg ∆P / CO (100ml/sec) Total PVR = 0.14 PRU

CONDUCTANCE a measure of the blood flow

through a vessel for a given pressure difference.

ml/sec/mmHg

blood pressure = force exerted by the blood against any unit area of the vessel wall

measured in mmHg (millimeters mercury)

1 mmHg pressure = 1.36 cm water pressure specific gravity of mercury is 13.6 times that of water

1 cm is 10 x > 1 mm.

1.The rate of blood flow to each tissue of the body is almost always precisely controlled in relation to the tissue need.

2.The cardiacoutput is controlled mainly by the sum of all the local tissue flows.

3.In general the arterial pressure is controlled independently of either local blood flow control or cardiac output control.

Nervous signals ↑inotropy

constriction of venous reservoir

constriction of small arterioles

Long-term renal mechanisms hormone release

Systolic P 120

Diastolic P 80

35 O mmHg 10

33cm/sec

0.3mm/sec

Systolic P 25mmHg

Diastolic P 8mmHg

7mmHg

•Adding more blood vessels to a circuit reduces the total vascular resistance. •Many parallel blood vessels,however,make it easier for blood to flow through the circuit because each parallel vessel provides another pathway,or conductance,for blood flow. •Total conductance (Ctotal) for blood flow is the sum of the conductance of each parallel pathway

fourth power law makes it possible for the arterioles,responding with only small changes in diameter to nervous signals or local tissue chemical signals, either to turn off almost completely the blood flow to the tissue or at the other extreme to cause a vast increase in flow.

(impedement to blood flow)

(pressure difference bet 2 ends of the vessel)

Laminar flow velocity of flow in the center of the vessel is far greater than that toward the outer edges.

= “parabolic profile for velocity of blood flow.” Turbulent flow blood flows crosswise in the vessel as well as

along the vessel, usually forming whorls in the blood called eddy currents.

Reynolds’ number and is the measure of the tendency for turbulence to occur.

Conditions appropriate for turbulence to occur:

(1) high velocity of blood flow (2) pulsatile nature of the flow (3) sudden change in vessel diameter (4) large vessel diameter

Reynold’s number ∝ velocity, diameter, density

1/ ∝ viscosity

Acute control local vasodilation or vasoconstriction

Long-term control increase or decrease in physical sizes and numbers of blood vessels

Decrease in oxygen

Release of Vasodilators (adenosine, CO2, adenosine phosphate compounds, histamine, K ions and H ions)

Metabolic vs Myogenic Theory

↑ ↑ arterial P

↑ ↑ blood flow

↑ ↑ O2/nutrients

Vasoconstriction

↓ blood flow to N despite ↑ P

sudden stretch of small blood vessels

vessel smooth

muscle contraction

Vasoconstriction

↓ blood flow to N

Prolonged increase in metabolism

Change in Oxygen tension

Formation of vascular growth factors

ANGIOGENIC FACTORS Vascular endothelial growth factor (VEGF),

fibroblast growth factor, angiogenin

ANGIOGENESIS Change in the amount of vascularity of the tissues

VASOCONSTRICTORS Vasopressin / ADH pituitary Norepinephrine nerve endings Epinephrine Endothelin damaged blood vessels Angiotensin II kidney Calcium ions Slight increase in H ions Carbon dioxide in vessels

VASODILATORS

blood & tissue fluids

Bradykinin

Damaged tissue (mast cells) Blood (basophils)

Histamine

Potassium ions

Magnesium ions

Hydrogen ions

Anions (acetate/citrate)

Carbon dioxide in brain

blood pressure = force exerted by the blood against any unit area of the vessel wall

measured in mmHg (millimeters mercury)

1 mmHg pressure = 1.36 cm water pressure specific gravity of mercury is 13.6 times that of water

1 cm is 10 x > 1 mm.

CARDIAC OUTPUT = Heart Rate X Stroke Volume CO = HR (75/min) x SV (70ml/beat) = 5.25L/min

Stroke volume = End diastolic volume – End systolic volume

SV= EDV (120ml) – ESV (50ml) = 70ml/beat

Factors affecting SV – preload, afterload and contractility