Diverse Techniques to Detect Arterial Stiffness

Transcription

1 Diverse Techniques to Detect Arterial Stiffness 백상홍가톨릭대학교강남성모병원순환기내과 혈관연구회창립심포지움 2005, 3, 3

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3 Small Arteries Arterial Remodelling Thickness Internal diameter Wall / Lumen Large Arteries Cross sectional area: (or ) Thickness Internal diameter (or ) Cross sectional area Wall / Lumen MEDIA: SMC Elastic fiber Collagen m Collagen and Lipid Core

4 Determinants of Blood Pressure Systolic Pressure Ejection time + Wave reflection ++ Arterial compliance +++ Diastolic Pressure Arterial compliance + Peripheral resistances +++ * MAP: Steady component: MAP Pdiast + 1/3 (Psyst - Pdiast) * PP: Pulsatile component: Pulse Pressure Systolic and diastolic determinants. At given peripheral resistances: arterial compliance wave reflection Compliance Pulsatility

5 Pulsatile Hemodynamics PWV= X / T Normal Hypertension

6 Pulsatile Hemodynamics PWV= X / T PWV, characteristic impedence forward wave TH< TN Premature returned RW Augumented central Psyst Load on heart and central vessels Pulse pressure: near 0 (P1 P2) Normal Hypertension

7 Decomposition of the Pressure Wave in an Incident and a Reflected Wave MEASURED WAVE FORWARD WAVE BACKWARD WAVE systole diastole systole diastole Young Suject Old Subject Pulse velocity = 8 m/s Pulse velocity = 12 m/s

8 Reduced Arterial Compliance Impaired Ventricular-Vascular Interaction Blood Vessel Damage Intima (Endothelial dysfunction) Atherogenesis Plaque rupture Vasoconstriction Dilator reserve Thrombogenesis Ischemia Cardiovasacular Events LV hypertrophy CHF Media (Impaired pulsatile function) Systolic BP Pulse pressure Diastolic BP Impedence load

9 Clinical Conditions Hypertension DM Dyslipidemia Atherosclerosis CAD CVA Heart failure Peripheral artery disease Renal failure Smoking

10 Multiple Indices of Arterial Stiffness No one has proved superior All have problems in measurement and interpretation Influenced by one or more of the followings: Use of inappropriate arterial model (eg. Windkessel) Assume values of cardiac output that are not, or poorly validated Relate proximal diameter change to pressure change at a distant site Influenced by heart rate or cardiac contractility Fundamental problems: Arterial media : a mix of collagen and elastin with consequent nonlinear relationship between pressure and diameter Measured stiffness varies with smooth muscle tone

11 Compliance Definitions of Some Parameters Commonly Measured in the Assessment of Arterial Stiffness Parameter Definition Formula The absolute change in vessel diameter (or area) for a given change in pressure D/ P, A/ P Compliance, capacitative (C 1 ) Compliance, oscillatory (C 2 ) Distensibility Elastic modulus Pulse wave velocity Stiffness index (ß) Young s modulus (Incremental Elastic Modulus) Relationship between decline in pressure and decline in volume in the arterial tree during the exponential component of diastolic pressure decay (said to reflect Large Artery Compliance) Relationship between oscillating pressure change and oscillating volume change around the exponential pressure decay during diastole (said to reflect Small Artery Compliance) The relative change in vessel diameter (or area) for a given change in pressure The pressure change required for (theoretical) 100% stretch from resting diameter (inverse of distensibility) The speed with which the pulse wave travels along a length of artery The ratio of the natural logarithm of SBP/DBP to the relative change in diameter Elastic modulus per unit area (accounts for wall thickness) V/ P V/ P D/( PxD), A/( PxA) ( PxD)/ D Distance/ t ln(p s /P d )/[(D s -D d )/D d )] ( PxD)/( Dxh)

12 Methods Used to Estimate Arterial Compliance No gold standard for estimating arterial compliance in human subjects DIRECT Ultrasound/catheter tip manometer tip system Angiography MRI TTE/TEE Transcutaneous ET/IVUS Venous occulusion plethysmography INDIRECT Stroke volume/pulse pressure ratio Pulse wave velocity (PWV) Fourier analysis of pressure and flow waveforms Pulse contour analysis

13 Carotid Pressure Waveform Contours Wave reflection method Windkessel model method Pulse pressure Pi 20 mmhg PWV method 1 sec Foot of the curve (PWV method), Wave reflections (using the determination of Pi, the early inflection point of the BP curve) Diastolic decay (Windkessel model)

14 Comparison of Major Methods Used in the Noninvasive Assessment of Arterial Stiffness With Regard to Their Potential For Wider Clinical Use PWV Arterial MRI SPCA Carotid DPCA Ultrasound AIx Ease of use Quality of validation Affordability Freedom from operator bias Evidence of prognostic value Endothelial function testing Systolic Pulse Contour Analysis (SPCA), Diastolic Pulse Contour Analysis (DPCA)

15 The Pulse Wave

16 Pulse Wave Velocity LV ejection generates a pulse wave which will propagate throughout the arterial wall at a finite speed. Blood = incompressible fluid } Artery = elastic conduit Propagation occurs along the arterial wall Systole LV * Propagation velocity = an index of arterial distensibility and stiffness

17 Pulse Wave Velocity Time interval Distance Pulse Wave Velocity (PWV) = Distance / time interval

18 The Speed of the Wave Increases as Arterial Stiffness Increases E p 2.(c u) 2 E; Young s modulus c is pulse wave velocity u is blood velocity (u<<c) is density of blood c E p 2 Increase stiffness by 2 increase wave speed of 1.4

19 The Speed of the Wave Increases as Arterial Stiffness Increases E p 2.(c u) 2 E; Young s modulus c is pulse wave velocity u is blood velocity (u<<c) is density of blood c E p 2 Increase stiffness by 2 increase wave speed of 1.4 Increase stiffness by 4 increase wave speed of 2

20 Regional Assessment of Arterial Properties Central Conduit Stiffness = Characteristic Impedence = Carotid- Femoral PWV Peripheral (muscular) Conduit Stiffness = Carotid- Brachial PWV = Carotid- Radial PWV

21 Methods for the Measurement of PWV Tonometry : Pressure Wave Detection Good sensitivity and time resolution. Very sensitive to arterial movement. Superficial arteries only. Doppler Ultrasound : Flow Wave Detection Widely used. Ability to detect deeper vessels. Photoplethysmography (PPG) : Diameter Wave Detection High sensitivity and time resolution. Very easy to use. Superficial arteries only.

22 Factors Influencing PWV Age Blood pressure Gender Heart rate Salt intake Genetic factors Others: respiration, blood flow Ethnic factors

23 Tonometry Method for Detection for Arterial Distensibility

24 Oscillometric Method for Detection of Arterial Distensibility

25 PWV (Complior * ) 3 large arteries (Carotid-radial, Carotid-femoral)

26 SphygmorCor Pulse Wave Analysis System Aortic Sp/Dp Aortic Pulse Pressure Augmentation Pressure Aortic Pressure/Time Waveform Ejection Duration Left Ventricular Load Coronary Artery Perfusion Pressure Subendocardial Viability Index Transit Time of Reflected Wave

27 Non-invasive portable tonometer for determining arterial pressure wave and pulse wave velocity: the PulsePen device Journal of Hypertension: 2004:22;2285

28 Photoplethysmogram Waveform: Optical Detection of the Diameter Wave LED (emitter) Photo-transistor (detector) Infra red emitter Upstream probe Detector Downstream probe SKIN FLOW ARTERY MUSCLE/BONE Physiological Measurement 2002:23: 581

29 Carotid Augmentation Index (AI) AI=-21 AI=0 AI= % 90% 80% (+)AI (0)AI (-)AI 70% 60% 50% 40% AI (Augmentation Index) =S2-S1/Pulse pressure 30% 20% 10% 0% <20(n=14) 30(n=36) 40(n=61) 50(n=48) >60(n=39) AGE SHBaek

30 Augmentation Index(%)=P/PPx100% SphygmocorTM pulse wave analysis system

31 Diameter (mm) Wall Track System Wall track system Prototype system RF M-mode RF ROI B-mode cineloop Inner wall tracking Outer wall tracking WTS Outer wall tracking Inner wall tracking Time (s) IMT

32 etracking Technology. The stiffness index ß: =In(Ps-Pd)/(Ds-Dd/Dd) Ps and Pd are systolic and diastolic blood pressure in the brachial artery measured by an automated sphygmomanometer Ds and Dd are the maximal and minimal diameters of the right common carotid artery measured by ultrasonic high resolution wall tracking (Aloka SSD-5500; 7.5 MHz linear array probe). Adjustable gates were positioned at the junctions of the intima and media, and diameter was calculated and displayed in real time as the difference between the displacement waveforms of the anterior and posterior walls. Measurements were taken as a mean of five beats; ß was log transformed for analyses, because its distribution was skew.

33 Ratio of Stroke Volume to Pulse Pressure (SV/PP) an indirect measure of total arterial compliance, simple, and based on the principle that in a steady-state condition, the arterial tree can be modeled as an elastic chamber with a constant compliance (2-element Windkessel model). LV end-diastolic and end-systolic volumes were calculated with the Z-derived method by Two-dimensionally targeted M-mode echocardiograms SV was calculated in ml/beat as LVEDV-LVESV and normalized for body surface area (stroke index). SV/PP Estimation Blood pressure (BP) was measured at the first and fifth Korotkoff phases with the use of an arm-cuff sphygmomanometer at the end of the initial echocardiograms. Brachial Pulse Pressure was calculated as the difference between systolic and diastolic BP and used as a raw inverse estimate of total arterial compliance together with SV/PP and the ratios of stroke index to pulse pressure (SVi/PP).

34 Modulus of Elasticity (Einc) Common Carotid Artery (CCA) systolic and diastolic diameters (Ds and Dd), IMT, and wall motion: measured by a high-resolution B-mode (7.5-MHz transducer) echotracking system (Wall track system) allowing the assessment of arterial wall displacement during the cardiac circle. Measurements were done on the right CCA, 2 cm beneath the bifurcation. Common Carotid Artery Intima-Media Thickness (CCA IMT) CCA-lumen cross-sectional area (LCSA)= (CCA diameter) 2 /4 IMCSA= (CCA diameter/2+imt) 2 - (CCA diameter/2) 2 wall/lumen ratio =(2 IMT/CCA diameter) CCA compliance= [ Dd(Ds-Dd)/2]/ P(m 2 kpa ); CCA distensibility=2[(ds-dd)/dd]/ P(kPa ) CCA pulse pressure ( P) was assessed by determination of CCA pressure waveform recorded noninvasively with a pencil-type probe incorporating a high-fidelity Millar strain-gauge transducer Distensibility provides information about "elasticity" of the artery as a hollow structure, Einc provides information on the properties of the wall material, independent of the geometry. Einc = [3(1+LCSA/IMCSA)]/CCA distensibility

35 Pulse Contour Analysis CVProfilor * Blood Pressure Waveform Systolic Blood Pressure Diastolic Blood Pressure Mean Arterial Blood Pressure Pulse Pressure Pulse Rate Estimated Cardiac Ejection Time Estimated Stroke Volume Estimated Stroke Volume Index Estimated Cardiac Output Estimated Cardiac Index Large Artery Elasticity Index (Capacitive Arterial Compliance) Small Artery Elasticity Index (Oscillatory/Reflective Arterial Compliance) Systemic Vascular Resistance Total Vascular Impedance Young normotensive Middle-aged HBP, DM

36 Digital Volume Pulse Photoplethysmographic finger probe Young normotensive Middle-aged HBP, DM

37 Peripheral Arterial Tone (PAT) Signal

38 A Man is Only As Old As His Arteries (William Osler; in The Principles & Practice of Medicine, NY, 1906)

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40 A man is only as old as his arteries (William Osler; in The Principles & Practice of Medicine, NY, 1906)

41 Amplification (%) Amplification of the Pressure Waves Age 68 years Age 54 years Age 24 years Femoral artery Thoracic aorta Ascending aorta Abdominal aorta Renal artery Iliac artery Age (Years) Youngest subject 60% amplification Oldest subject small amplification Age related amplification of the BP wave between aorta and iliac artery

42 Arterial Changes with Aging Calcium, collagen, and collagen cross-linking Intima-medial thickness Vessel diameter Elastin Systolic and pulse pressures Vascular stiffness indices, pulse wave velocity Altered central arterial pressure wave contour Net effect: LV pulsatile load (afterload)

43 Endothelial Function Marked decline in endothelium-mediated vasodilation from age 40 to 70 No change in vasodilator response to nitroglycerin Age-related effects on endothelial function exacerbated by hypertension, dyslipidemia, coronary disease, and heart failure, but attenuated by regular aerobic exercise

44 Arterial Stiffness Index (ASI)

45 Doppler Waveforms