Special Lecture 10/28/2012clinsoft.org/drmayrovitz/PHYSIOLOGY_2012/Special_Lectures_2012/HT… · Pulse Wave Velocity (m/s) BP-Normal ... TPR=150%. C. TPR SV ... 160 60 80 100 120

Special Lecture – 10/28/2012

HYPERTENSION

Dr. HN Mayrovitz

Special Lecture –

10/28/2012

• Arterial Blood Pressure (ABP) -

Definitions

• ABP –

Review Indirect Oscillographic Method

• Resistance (R), Compliance (C) and

Volume as Determinants of ABP

• Hypertension –

Secondary and Primary

• Central ABP and Role of Reflection

• Differential Effects of R and C Changes

on Systolic and Diastolic Pressures©Dr. HN Mayrovitz 2011Dr. HN Mayrovitz

Systolic

Diastolic

Pulse Pressure SV

Mean and Pulse Pressure

MAP

MAP = Pd + 1/3PP

Ps

PdPP

Arterial Blood Pressure (ABP)

P

Dr. HN Mayrovitz © 2012

Non‐invasive Measurement• Sphygmomanometer• Oscillographic

Pressure oscillations in cuff

Cuff pressure

MAP = 80 + 30/3 = 90 mmHg

“start”

of oscillations

NearSystolic

cuff

ABP via Oscillographic Method

AmAS /Am = 0.55

AD /Am = 0.85

systolic

mean

diastolic

Cuff PressureSensor Pressure (m

mHg) Cuff P

ressure (m

mHg)

•Resistance•Volume •Compliance

Some ABP Determinants

MAP = CO x TPR

Resistance as a ABP Determinant

Capacitance Exchange Resistance Distribution

Aorta

LargeArtery

Arteriole

SmallArtery

Capillaries

Pre-CapillarySphincter/TerminalArteriole

Venule

Vein

VenaCava

CARDIOPUMP

PCardiacPump

VV

1. Mechanical+ Volume + Pressure

2. F‐S+ Volume+ CVP+ Filling+ SV+ CO+ MAP

Blood Volume as an ABP Determinant

CARDIOPUMP

PCardiacPump

VV

ComplianceRelatedV/C


CARDIOPUMP

PCardiacPump

VV

Compliance as an ABP Determinant

P = V / C

SVLow

C

Higher C

Mainly Systolic and Pulse Pressure Effects

+ dV/dt+ SV- C

P = SV / C

+Systolic


Specifically Known Hypertension Causes (Secondary Hypertension)

~ 5 -

10 % of Hypertension Patients

Remainder Essential HTN

Hypertension = High Blood PressureSo ……….. What’s High?

OR >= 100>= 160Stage 2 Hypertension

OR 90-99140-159Stage 1 Hypertension

OR 80-89120-139Prehypertension

AND <80< 120Normal

DBP (mmHg)SBP (mmHg)BP CLASSIFICATION

OR >= 100>= 160Stage 2 Hypertension

OR 90-99140-159Stage 1 Hypertension

OR 80-89120-139Prehypertension

AND <80< 120Normal

DBP (mmHg)SBP (mmHg)BP CLASSIFICATION

Hypertension

If DBP is normal but SBP is high then calledIsolated Systolic Hypertension Decreased Arterial Compliance


“Central Aortic Pressure”

14

Most heart-related effects ofelevated BP are due to increased

‘central’

aortic pressure

But BP is measured here!

So, what are we missing?

Artery ‘stiffening’

Decreased Compliance

Increased wave speed

Earlier return of reflected pressure

Age-Related Issues


•Why do shapes & values differ?•What adequately representscentral aortic pressure?

Values and ShapesDiffer by site

Transmission and Reflection of Pulses

Transmission and Reflection of PulsesCompliance

Resistance

1. Pulse “wave-speed” (S0 ) is inverse to Compliance (C)

Stiffer arteries ~ higher speed

3. Pulses at any point in the artery are the algebraic

sum of forward and reflected pulses2. Reflections

mainly at arterial branch points

S0s0 ~

1C

Composite is what is measured!


4

5

6

7

8

9

10

11

12

13

14

20 25 30 35 40 45 50 55 60 65 70 75 80

Median Age (years)

Puls

e W

ave

Velo

city

(m/s

) BP-NormalBP-HTN 1BP-HTN 2/3

Pulse Wave Velocity (PWV)

Adapted and Modified from European Heart Journal (2010) 31, 2338–2350

PWV• Increases with age• At any age increases with BP

Earlier Reflection Arrival

70

110

mmHg

SystolicPeaking

Increased VentricularSystolic Loading

Reduced DiastolicPressure


70

110

mmHg

SystolicPeaking(strokerisk)

Increased ventricularsystolic afterload

(LVH risk)

Reduced diastolicPressure

(Ischemic risk)

Earlier Reflection

NormalReflection

(Pb )

NormalComposite

(Pm

)

Summary of Major Aspects


So –

Standard BP by sphygmomanometry, though important and clinically useful

only tells PART of the story

Aortic Central Pressuremay be a more accurate

risk assessment

Reasons have to do with pressure wave interactions that are most directly influenced by:

A. Pulse wave speed (Artery compliance) B. Reflection amplitudes (Vasoconstriction state)

Both tend to increase with ageing and HTNDr. HN Mayrovitz © 2012

Effects of R and C changes on Systolic and Diastolic Pressure

SIMULATION RESULTS

Systolic

Diastolic

Pulse Pressure SV

Arterial Blood Pressure (ABP)

P

TPRCSV

TPR

C


Pre

ssu

re (

mm

Hg

) C=100% of Normal

Aortic Blood Flow

Pressure HR = 60

Systolic

DiastolicPulsePressure

TPRCSV

Pressure Resulting from a Single Simulated Initial Beat

SimulatedCompliance

Effects

Pre

ssu

re (

mm

Hg

) C=100%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=90%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=80%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=75%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=70%

TPRCSV


Systolic and pulse pressures increase with decreasing compliance but most

times small effect on diastolic pressure

Effect of Compliance Changes

0

20

40

60

80

100

120

140

160

180

60 70 80 90 100 110

Psys

Pdia

PP

mm

Hg

% of normal artery compliance

Systolic

Diastolic

PP

SimulatedResistance (TPR)

Effects

Pre

ssu

re (

mm

Hg

) C=100%TPR=100%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=100%TPR=120%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=100%TPR=150%

TPRCSV


Pre

ssu

re (

mm

Hg

) C=100%TPR=200%

TPRCSV


Systolic and diastolic pressures increase with increasing TPR but PP tends to decrease.

Diastolic Increases more than systolic.

Effect of TPR Changes

0

20

40

60

80

100

120

140

160

60 80 100 120 140 160 180 200 220

Psys

Pdia

PP

% of normal TPR

mm

Hg

Systolic

Diastolic

PP

MAP

CO x TPR

SV x HR Rartle

BV C

MAP ~ CO x TPR + f(BV/C)

SBP & PP

SBP & DBPDBP > SBP

PP LESS

Isolated Systolic

HTN

Essential HTN

Summary (Kind‐of)


QUESTIONS?

Documents

Special Lecture 10/28/2012clinsoft.org/drmayrovitz/PHYSIOLOGY_2012/Special_Lectures_2012/HT… · Pulse Wave Velocity (m/s) BP-Normal ... TPR=150%. C. TPR SV ... 160 60 80 100 120