Properties of Pressure

Transcription

1 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

2 Berne and Levy 2005

3 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

4 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

5 systolic Pressure (mmhg) mean diastolic

6 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

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8 Blood moves down a tube if the inflowing pressure is greater than the outflowing pressure P=100 mmhg flow P=10 mmhg

9 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

10 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

11 P=FLOW X RESISTANCE RESISTANCE= P/FLOW

12 P=FLOW X RESISTANCE RESISTANCE= P/FLOW

13 Series Circuit P=100 mmhg P=0 mmhg R 1 R 2 R 3 R 4

14 Series Circuit Pressure (mmhg) R 1 R 2 R 3 R 4 R t =R 1 +R 2 +R 3 +R 4

15 Parallel Circuit R 1 P=100 mmhg R 2 P=0 mmhg R 3 R 4

16 Pressure R=100 Q=1 R=25 Q=4 R=5 Q=20

17 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

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20 Berne and Levy 2005

21 Resistances Large arteries=1 Arterioles=14 Capillaries=4 Veins=1 Total resistance= R i =20

22 Control of tissue blood flow Intrinsic Extrinsic

23 BLOOD FLOW Rate of metabolism

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25 Extrinsic Control Autonomic Nervous system Circulating hormones

26 Autonomic Nervous System pregang lionic cholinergic Sympathetic thoracico-lumbar Paravertebral postganglionic adrenergic Exception: sweat glands Parasympathetic cranial & sacral postganglionic cholinergic preganglionic cholinergic at organ

27 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

28 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 )

29 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 )

30 Control of tissue flow Intrinsic Control Extrinsic control Long term control (vascular remodeling)

31 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

32 Determinants of Cardiac Output Heart rate Stroke volume Ventricular end-diastolic volume Contractility Afterload (aortic pressure)

33 Berne and Levy 2005

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35 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)

36 We have two major systems to sense and control arterial pressure

37 Control of pressure Short term Arterial barroreceptors Long term Renin angiotensin system ( Kidney and volume regulation)

38 Arterial Baroreceptors

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40 The heart is under net basal parasympathetic tone Heart rate (bpm) Atropine Propranolol Atropine Propranolol

41 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

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43 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)