Pulse analysis: stroke volume, vascular stiffening and cardiovascular disease Tom Archer, MD, MBA UCSD Anesthesia
Pulse analysis is an ancient practice, now making a comeback. http://www.itmonline.org/image/pulse2.jpg
Traditional pulse “analysis”: subjective and hard to quantify • “Waterhammer pulse”-- AI • “Slow upstroke”-- AS • “Pulsus paradoxus”– cardiac tamponade • Is this silly and obsolete stuff?
Pulse analysis was serious business in the 19th century • Sphygmographs in common use. • Insurance companies relied on their results.
Etienne-Jules Marey (1830-1904) invented the sphygmograph to record the arterial pulse on smoked paper. It was used by Engelmann, Mackenzie and Wenckebach. Sphygmograph 1876 http://www.mamweb.org/modules.php?name=Content&pa=showpage&pid=32000
Life insurance examination manual from 1891 discussed pulse analysis by sphygmography.
Tom Archer, 58 y.o., good general health. Takes Crestor for high cholesterol. Radial and predicted ascending aortic pressure waveform when subject is cold.
Scipione Riva-Rocci introduced the mercury sphygmo-manometer in 1896. Measured systolic BP only.
Harvey Cushing used it. Korotkoff introduced auscultation for diastolic pressure in 1905. history.library.ucsf.edu/.../chapter2_03.html
In the 20th century, Riva-Rocci and Korotkoff’s sphygmomanometer eclipsed pulse analysis • Two simple numbers: systolic / diastolic. • Easy to use. • Pulse analysis fell into disuse. • 20th century saw tremendous gains from simple sphygmomanometry: dangers of high BP.
High diastolic blood pressure is associated with increased risk of coronary disease. Increased diastolic BP is associated with CAD– multiple large studies. K Hirata (Circ J 2006; 70: 1231–1239)
High systolic pressure and pulse pressure are also associated with coronary disease. For any given systolic pressure, cardiac risk increases with decreasing diastolic BP! Both increased brachial SBP and increased brachial pulse pressure are associated with increased coronary disease. K Hirata (Circ J 2006; 70: 1231–1239)
But simple sphygmomanometry ignores valuable information within the pulse trace. • Extra information can be extracted from the pulse using transducers and computers. • Pulse analysis is becoming reproducible and objective. • Pulse analysis is JUST SOFTWARE analyzing the BP signal.
Pulse analysis gives two types of information • “Central blood pressure” • Ascending aortic blood pressure from radial waveform. • Specifically, we get “Augmentation Index” (AIx)– a measure of extra heart work. • Stroke volume (CO, SVR)
Central blood pressure (CBP) • Systolic pressure in the ascending aorta is NOT the same as brachial or radial systolic BP. • Diastolic and mean pressures are very similar at radial / brachial and central sites.
LV “sees” the SBP in the ascending aorta. With normal aortic valve, LV wall tension depends on pressure in ascending aorta (and diameter of LV chamber). health.yahoo.com/topic/heart/overview/article...
Heart “sees” central aortic systolic pressure, not brachial artery pressure. • Obviously, it’s hard to measure ascending aorta pressure directly. • Ascending aortic (“central”) BP can be extrapolated from the radial pulse.
What creates central BP? • Stroke volume • Aortic stiffness (compliance / Windkessel) • Systemic vascular resistance (“runoff”) • Reflected pressure wave
What creates central BP? #2 Stiffness of aorta (“windkessel”) AIR BLOOD heart Central BP #1 SV veins arteries #4 Wave reflection– timing and amount #3 Systemic vascular resistance (resistance arterioles) Muscular arteries
Augmentation index– extra cardiac work due to wave reflection AIx = Augmentation Pressure / Pulse Pressure Kozo Hirata, MD; Masanobu Kawakami, MD; Michael F O’Rourke, MD, DSc*Circ J 2006; 70: 1231–1239
Augmentation index is a deadly backdraft of pressure which exhausts the heart over time.
Run animation • Wave reflection animation can be found at: • http://atcormedical.com/wave_reflection.html
Augmentation Index (AIx) • AIx = unnecessary heart work. • High AIx leads to LVH and cardiomyopathy. • Lower AIx is better. • Treatments that lower AIx help the patient.
Hypertensive patients treated to identical brachial BP endpoints with amlodipine and atenolol show lower central BPs and AIx with amlodipine CAFE / ASCOT study, M. O’Rourke (Circulation. 2006;113:1213-1225.)
A given brachial BP measurement does not say what central BP the heart is actually generating. Antihypertensive drugs may exert their beneficial effects via effects on central blood pressure. These effects may not be appreciated by just measuring brachial BP
Central BPs– ASCOT / CAFE study • Lower central BPs are associated with better CV outcomes. • Amlodipine achieved lower central BPs and had better CV outcomes than atenolol, despite achieving the same brachial artery BPs. CAFE / ASCOT study, M. O’Rourke (Circulation. 2006;113:1213-1225.)
When is AIx high-- chronically? • Normal aging • Obesity • Atherosclerosis • Diabetes • Pre-eclampsia • Inflammatory arthritis • Renal failure
As healthy individuals age, reflected wave arrives at ascending aorta earlier and increases augmentation index and central pulse pressure. WW Nichols Curr Opin Cardiol 2002, 17:543–551
77 y.o. man. Never smoked. Aix = 29%.
42 y.o. obese female, smoker. Aix = 36%
77 yo male, ESRD, AV fistula, CAD, HBP Takes atenolol, lisinopril, terazosin, finasteride. Aix = 39%
When is Aix high– acutely? • Arterial compression in legs (squatting) • Cold body temperature. • Nicotine ingestion
Tom Archer, 58 y.o., while squatting. Aix = 21%
Exposure of healthy young adults to cold air for 30 min increases augmentation index. David G. Edwards,1 Amie L. Gauthier,2 Melissa A. Hayman,2 Jesse T. Lang,2 and Robert W. Kenefick2J Appl Physiol 100: 1210–1214, 2006.
Perioperative hypothermia increases cardiac event rate. Is this due to increased AIx with hypothermia?
What makes AIx go down-- chronically? • Exercise • Weight loss • Red wine • Statins • Control of blood pressure (ACEI and CCB) • NTG
64 yo obese male. HBP on lisinopril. Moderate ETOH consumption. Aix = 14%.
What makes Aix go down-- acutely? • Exercise • Red wine • Lowering blood pressure • NTG
NTG reduces wave reflection and AIx by dilating muscular arteries. Is this its primary mechanism of action? S. C. MILLASSEAU, R. P. KELLY, J. M. RITTER and P. J. CHOWIENCZYK Clinical Science (2002) 103, 371–377
What determines augmentation index? • Timing of wave reflection– pulse wave velocity. Faster wave return is bad. • Amount of wave reflection– muscular artery tone. • NTG reduces muscular artery tone and wave reflection • Does NTG work by decreasing AIx? Yes, at least in part.