OBJECTIVES Overview Relationship between pressure and flow Understand the differences between series and parallel circuits Cardiac output and its distribution Cardiac function Control of blood pressure Review of lab
Berne and Levy 2005
Properties of Pressure Hydrostatic pressure Pressure=0 cm water Hydraulic pressure Created by pushing fluid through a tube H=100 cm Pump Pressure=100 cm water Height of water column is~pressure
Units of Pressure Atmospheric pressure is considered to be zero The common units is based upon the height of a column of mercury Since mercury is 13.6 times denser than water a 100 mmhg is equivalent to 136 cm of water In more common units 136 cm of water is equal to 54 inches or 4 6 of water
120 80 systolic Pressure (mmhg) mean diastolic
What is a normal arterial pressure Diastolic<80 mmhg Systolic<140 mmhg High blood pressure places a large strain on the arterial blood vessels High blood pressure increases the work of the heart
Blood moves down a tube if the inflowing pressure is greater than the outflowing pressure P=100 mmhg flow P=10 mmhg
If resistance increases pressure has to increase if flow is kept constant If you narrow a tube and try to keep flow constant you will have to exert a larger pressure to pump the same amount of fluid through the tube If the pressures at the beginning and the end of the tube are the same there will be no flow no matter how great the pressure
Is there flow in this tube? Answer: FLOW=0 P=100 mmhg P=100 mmhg Which flow is greater? Answer: A=B P=200 mmhg Flow A P=100 mmhg P=100 mmhg Flow B P=0 mmhg
P=FLOW X RESISTANCE RESISTANCE= P/FLOW
P=FLOW X RESISTANCE RESISTANCE= P/FLOW
Series Circuit P=100 mmhg P=0 mmhg R 1 R 2 R 3 R 4
Series Circuit 120 100 Pressure (mmhg) 80 60 40 20 0 R 1 R 2 R 3 R 4 R t =R 1 +R 2 +R 3 +R 4
Parallel Circuit R 1 P=100 mmhg R 2 P=0 mmhg R 3 R 4
Pressure R=100 Q=1 R=25 Q=4 R=5 Q=20
Comparison of series and parallel circuits In a series circuit the largest resistor is the major determinant of total resistance In a parallel circuit the lowest resistor is the major determinant of total resistance
Berne and Levy 2005
Resistances Large arteries=1 Arterioles=14 Capillaries=4 Veins=1 Total resistance= R i =20
Control of tissue blood flow Intrinsic Extrinsic
BLOOD FLOW Rate of metabolism
Extrinsic Control Autonomic Nervous system Circulating hormones
Autonomic Nervous System pregang lionic cholinergic Sympathetic thoracico-lumbar Paravertebral postganglionic adrenergic Exception: sweat glands Parasympathetic cranial & sacral postganglionic cholinergic preganglionic cholinergic at organ
Autonomic Nervous System Nerves Neurotransmitter Distribution Effect SNS Cervical Thoracic Pregang: ACH Postgang: NE Heart, Arteries & Most veins β 1 ( HR) α 1 β 2 PNS Vagus and lumbar Pregang: ACH Post gang ACH Heart Vessels of Genitalia & colon HR
Epinephrine Source: Adrenal medulla Increase heart rate and contractility (β 1 ) low concentrations vasodilation (β 2 ) high concentrations vasoconstriction (α 1 ) decrease venous compliance (α 1 )
Norepinephrine Source: Adrenal medulla Increase heart rate and contractility (β 1 ) Limited effect on β 2 At all concentrations vasoconstriction (α 1 ) decrease venous compliance (α 1 )
Control of tissue flow Intrinsic Control Extrinsic control Long term control (vascular remodeling)
OBJECTIVES Overview Relationship between pressure and flow Understand the differences between series and parallel circuits Cardiac output and its distribution Cardiac function Control of blood pressure Review of lab
Determinants of Cardiac Output Heart rate Stroke volume Ventricular end-diastolic volume Contractility Afterload (aortic pressure)
Berne and Levy 2005
Determinants of stroke volume Volume in heart at end of diastole Time to fill Filling pressure Property of ventricle Stiffness Ability to relax after contraction Ability to eject (systole) Contractility After load (arterial pressure)
We have two major systems to sense and control arterial pressure
Control of pressure Short term Arterial barroreceptors Long term Renin angiotensin system ( Kidney and volume regulation)
Arterial Baroreceptors
The heart is under net basal parasympathetic tone 120 110 Heart rate (bpm) 100 90 80 70 Atropine Propranolol Atropine 60 50 40 Propranolol
Activation of Barroreceptor reflex In response to an increase in arterial pressure Withdrawal of sympathetic tone Activation of parasympathetic tone Results: Decrease heart rate and contractility Arterial vasodilation Decrease in venous compliance
The lab Chronically catheterized conscious rat Epinephrine (β 1, β 2 + α agonist) Norepinephrine (β 1 + α agonist) Phentolamine (α-receptor antagonist) Propranolol (β-receptor antagonist)