Pulse wave analysis

‘ Since the information which the pulse affords is of so great importance, and so often consulted, surely it must be to our advantage to appreciate fully all it tells us, and to draw from it every detail that it is capable of imparting’ F.A. Mahomed 1872 1 It is now possible to generate the ascending aortic pressure wave from the arterial pressure pulse, recorded noninvasively by applanation tonometry in the radial or carotid artery. This represents a blend of nineteenth century sphygmography with cuff sphygmomanometry, and is made possible by introduction of high fidelity tonometers, by characterization of arterial hydraulic properties in the upper limb and neck, and through application of mathematical engineering techniques in modern computer systems. This review will consider historical development, theoretic background, present status and future potential, as well as comparing this technique with radial and carotid tonometry alone, and with analysis of flow pulse and volume pulse waveforms as determined by Doppler or photoplethysmographic techniques. The arterial pulse is the most fundamental sign in clinical medicine, and has since antiquity been identified with the physician and the art of medicine. Palpation of the pulse forms the crest of the Royal College of Physicians of London, which was established to improve the scientific basis and practice of medicine and in an era when William Harvey, as anatomist to that college, wrote his classic text ‘de Motu Cordis…’2. William Bright 3 based his diagnosis of high blood pressure on ‘hardness’ of the pulse, and on the pressure required to extinguish the pulse. A scientific basis only arose after Marey 4, and then Mahomed 1 developed graphic methods to record the arterial pulse. By the beginning of the twentieth century, sphygmography was well established in medical journals and in medical textbooks and had been used to describe heart block and effects of antianginal medication as well as hypertension and other conditions 5–9. In life insurance examinations sphygmocardiography was widely used for detecting persons with ‘arterial senility’ and increased risk of premature death 10. Unfortunately sphygmography lapsed with introduction of the cuff sphygmomanometer, which provided numbers for the extremes of the pulse, and a veneer of scientific accuracy. Frederick Akbar Mohamed established the foundation of pulse wave analysis in a short medical lifetime from 1872 to 1884. He described the normal radial pressure waveform and showed the difference between this and the carotid wave 1. He showed the effect of high blood pressure on the radial waveform, and used the waveform to describe the natural history of essential hypertension, and the difference between this and chronic nephritis 7, 8. He also described the effects of arterial degeneration with ageing on the arterial pulse 7. These features were identified and utilized in the life insurance studies of the late nineteenth century 10. Mahomed's sphygmogram, and the popular Dudgeon sphygmogram which followed, and which was used by Sir James MacKenzie 9 were mechanical devices, awkward to use and prone to artifact. Modern tonometer systems are piezo-electric and are far more accurate, reliable, and easy to use. While originally introduced clinically to measure intraocular pressure, they have been adapted for vascular use by Drzwiecki 11, Millar and others 5, 6. While Mahomed was the first to recognize the difference between pressure waves in central and peripheral arteries, McDonald 12 was responsible for explaining this phenomenon on the basis of wave reflection, and for introducing transfer functions to characterize properties of vascular beds in the frequency domain, and (with his colleague J.R. Womersley) for establishing the validity of assuming linearity in the arterial tree 13. The work of McDonald, Womersley, Taylor and others, originally from Harvey's own hospital (St Bartholomew's, London) has led on to the techniques described here for pulse wave analysis. The technique of noninvasive aortic pulse wave analysis, as described here, depends on accurate recording of the radial pressure wave, its calibration against brachial pressure, then generation of the ascending aortic pressure waveform through use of a generalized transfer function in a computerized process. Ascending aortic waveforms are ensemble averaged into a single calibrated wave whose different features can be identified automatically with clinically important measures of pressure and time intervals measured and printed out in an interpretive report (Figure 1). Steps in the process are described below. The Sphygmocardiograph: computerized report on analysis of radial artery and synthesized aortic pressure waves. A series of radial artery pressure waves, recorded over an 8 s period (upper continuous tracing) are used to synthesize a series of ascending aortic pressure waves (lower continuous trace) using a convolutional algorithm and a generalized transfer function which characterizes hydraulic properties of the upper limb vasculature. The radial waves are ensemble-averaged into a single wave (centre left), and the aortic waves into a single synthesized aortic wave (centre right), with the radial wave calibrated to brachial systolic and diastolic pressure, and integrated mean pressure taken to be identical at radial and aortic sites. Features of the waves (foot, shoulder, peak, incisura) are identified automatically using differentials, and flagged. The detailed report gives information relevant to ventricular/vascular interaction from both pressure and time values, as calculated from the synthesized aortic waveform. Accurate applanation tonometry requires that the artery be applanated (flattened) underneath the sensor. This requires pressure from the operator with the vessel supported behind by the radius bone at the wrist or vertebral column and ligaments in the neck 14, 15, 16. Complete confidence is gained when the device is applied to the eyeball to measure ocular pressure, or to an exposed artery, and where applanation can be confirmed visually. Reasonable confidence is gained if the pressure waves are completely consistent, beat to beat, if amplitude is the greatest that can be achieved, and if the pulse wave measured has the same character as one would expect in the artery i.e. sharp upstroke, straight rise to the first systolic peak, a definite sharp incisura, and near-exponential pressure decay in late diastole (Figure 1). Requirements for accurate quantitive tonometry cannot be achieved in practice because of the soft tissue which intervenes between the skin and anterior wall of the artery, but they can be approximated. Though others have been more fortunate, we have never been confident about relying on the instrument's internal calibration even for of wave and to systolic and diastolic pressure in the radial artery from cuff in the brachial artery. carotid we on through use of transfer functions from the radial artery to ascending and then from the ascending to carotid artery or through assuming that the mean and diastolic pressure are the same in the carotid artery as in the brachial and radial artery and systolic pressure high or systolic and pulse be recorded in the carotid artery when the internal calibration is high systolic carotid pressure be a of so that the vessel is the it is most often when the carotid are of the aortic from the radial or carotid pressure wave a generalized transfer function to describe arterial properties between the ascending and peripheral recording of a generalized transfer function that properties of the arterial between the are the same in all persons and all this is the since vascular on and vascular properties with arterial pressure, with and with it were it would be to the transfer function to from using a generalized transfer function are and to in features of the ascending aortic pressure wave be to the that upper is different between different that upper limb pulse wave with 5, or with of arterial pressure [5, or with the of used in clinical practice [5, in upper limb properties to have a effect on the frequency of where of the pressure wave are with far effect at the whose are The transfer functions that we have established in a of at are to that we had originally determined from aortic to brachial artery and in determined by a of others at and from noninvasive studies These are also to calculated for our of the upper limb of our own methods have been described by in and the studies that the radial and brachial artery pressure are different to in the ascending with and as the the calculated for diastolic and pulse pressure the for the and at for recorded radial for of this technique for noninvasively recorded waveforms to be of systolic and diastolic for the wave with a cuff on the of this for one the of the cuff and for pressure then use of this technique is a in central pressure from of applanation tonometry is but it of theoretic of normal waveforms and use. It is possible to record and even waveforms when the tonometer is applied and we have been of waveforms in from with use. (Figure information on of pulse pressure and diastolic pressure and recorded waveforms as a have it to from ascending aortic pressure waves from the carotid waveform to against that from the radial waveform when the is or studies and for tonometry and These with our own in using techniques are to own studies of and as well as comparing from both radial and from the would be to with use of they and to in In the arterial pulse has the same in central and peripheral arteries, and is to that in amplitude is of but it wave in and the of the wave is in late [5, to late the peripheral pulse with the central pulse, the of the wave into and the diastolic wave in These pressure wave for the in peripheral pulse pressure and systolic pressure between and late which is so in studies The pressure pulse waveform in and to the is on the basis of of wave from peripheral to central In this is to short the and pulse wave In the the is and its high pulse wave for of wave normal have and heart [5, of and heart have so that waves are in diastole The generalized transfer function used by and others to generate ascending aortic pressure waves have been established in fully and are to whose wave and in the upper limb as well as in the and most wave first out by Mahomed ageing has effects on the arterial pulse at different The most studies on normal have been by and in the late systolic pressure in both radial and carotid arteries, with of the diastolic pressure are at both but at the late systolic pressure wave is in the radial artery in the have been in the ascending from taken at but late systolic is in the carotid and far in the radial artery. in and amplitude of pressure waves recorded in the radial artery and carotid in normal between the first and of are ensemble averaged into from different with of the is the to late systolic pressure after the systolic shoulder, and can be in or in as pulse pressure by the pressure to the first systolic shoulder, or as by pulse the aortic wave in is measured as or as as of pulse In late amplitude of the ascending aortic systolic pressure wave the with This to life with of in In radial pressure wave is to with a pressure wave of amplitude to the from in late in life is to of wave from the and at the of arterial the where high of is by arterial which pulse wave aortic is as in pulse wave which has also been by our in normal and in normal have of [5, wave more between and [5, This is a normal ageing and is responsible for the in pulse pressure and in systolic pressure which is with The phenomenon is by hypertension and by arterial and is by as well as by arterial as below. to the effects of ageing on the arterial pulse and to be with systolic of the pulse in different This is one expect if had a effect on function the of and to both of wave and of pulse wave have the effect of of the carotid and aortic pulse, but the has been is that persons with of aortic ageing more with and so are more to and in While of function in is between and pulse wave The of upper limb function with in different is with definite in pulse wave or other of arterial in the upper limb [5, of even a can wave from the and so the of the arterial pressure wave, the of late systolic [5, this be to It that of of or of effect be in the the and the of This to in of the arterial pressure wave, the of waves with the wave by with of heart in period to of and and with in heart of This has been by and and for in aortic in heart in heart also of the pulse wave between and peripheral arteries, on of the of at to the of of the transfer function for this in generation of the ascending aortic from the peripheral pressure wave at different heart The effects of heart are most with pulse pressure be more as great in the radial artery as in the ascending and when radial systolic pressure be pressure waves that in the arterial pulse It that in a of be achieved, with heart and and with the greatest a phenomenon have a if were and systolic pressure were and diastolic pressure and for artery, is on in in persons in in between and is to be a risk for wave with increased aortic systolic pressure and with increased and be the While have effects on arterial in pulse between and and after the can be on the basis of in has the most and effect on the arterial pulse. This is from the with in aortic pulse wave and of wave reflection, that the wave in diastole into with of pressure in late This has been as a phenomenon since it is in all with The aortic is by and of the is by from to in the and is with aortic this process in and of the and arteries, where the of This ageing into a process which must be as a and is It in in pulse pressure and systolic pressure, which is described as systolic systolic pressure by wave for a to systolic pressure in central [5, hypertension be a of aortic hypertension can also aortic and by the same pressure wave as with ageing but at an The here is and and is to increased and pulse wave in the more in the arterial pulse, with increased amplitude of the systolic pressure wave in the radial artery, was by Mahomed [7, as the of arterial pressure, and was so used by in clinical studies over the cuff was It that the upper limb generalized transfer function for generation of central from peripheral pressure in the of hypertension, since of the brachial artery and its and transfer function with of arterial pressure [5, are studies in arterial in with artery or with other of and our every we have been to the of on the basis of the arterial pressure wave, and we are that others have been to this in have been to definite difference in aortic pulse wave in with generalized and can this as a for can others have this own for aortic pulse wave were identical in with and high of [5, must the and must to wave are that it has so effect on measured of arterial or on the of the arterial pulse, which is so to in with has been described as arterial of aortic or of pulse wave have been to in the diagnosis of to in of its studies have but definite of aortic in with and with in aortic this in it can only be that the effects of ageing and of hypertension to over the effects on aortic and on pulse wave of as and In clinical one persons with aortic for or for of arterial from one are in In our persons are often and in but with an history of vascular of the we have have had vascular the of of persons is to be and These well the of persons with premature by Mahomed his pulse will and the of medical for life insurance [10. In to with and pulse wave analysis is as a in heart In diastolic is on of often in with have utilized this to a diagnosis of diastolic in with and to in the of this from systolic (Figure and heart effects of wave on from on brachial and aortic pressure waves and on ascending aortic flow trace) with of systolic pressure in life from left), then with of and heart and from and heart of with from chronic in is the normal pressure is of and in 1). in with increased pressure most of diastole of systolic pressure is and is and pressure is are the systolic of the aortic pressure waves taken from and on an for and (with of systolic as by In systolic is on of wave a effect on flow on pressure This phenomenon for the of a pulse in systolic heart with with central pressure or and with of wave in diastole 5, have used this phenomenon to systolic and diastolic and to the of systolic [5, as well as to systolic from diastolic as the of is through use of through in wave reflection, and and to is to the of wave analysis the effects of which are or fully from cuff of arterial in amplitude of the systolic wave in the radial artery, even with of the in ascending aortic and systolic pressure (Figure a in radial artery after (Figure the antianginal effect of this is at in to in [5, (Figure this to effects of and other to effects from the synthesized aortic pressure pulse, for and to other of vascular and because it is often possible to the systolic on the radial pressure wave after is to measure in of the in the of on of the ascending aortic and brachial pressure waves recorded in the ascending and brachial artery of an at conditions and represents amplitude of the wave by represents the of the artery the effects of as in the late systolic of the radial artery pressure pulse. from the first in of the of as an antianginal of of peripheral systolic pressure in central aortic and systolic pressure after as has been confirmed and a more effect of on the heart measured by The are on the basis of in wave from the The that brachial transfer function is by and that the ascending aortic pressure wave can be determined from the radial that has a effect on wave in the upper limb in the the synthesized aortic pulse to the effects of in hypertension, and with is to wave reflection, and to aortic and aortic and systolic pressure, and to of ventricular/vascular In systolic to of the aortic pulse waveform is as described through wave reflection, and of can be on the and aortic pulse [5, The of is to of and has been as a measure of this have used aortic flow waveforms to describe the effects of wave on the ascending aortic flow and to describe the effects of in wave with wave analysis is in effects of since this in has effects on or on peripheral effects in wave are on the basis of [5, interaction between and is of great clinical importance, and the by the have been made of pulse wave analysis, and on the basis of of blood pressure in when of were used own studies of based on pulse wave analysis, and that the effect of and this for to 8 wave analysis, with to late systolic a for this and of required after at by the and effects of can be from the arterial pressure pulse. to wave as well as and in in central and in aortic and systolic pressure This is the effects of in and diastolic are to in diastolic with with [5, aortic systolic pressure through and this is they and diastolic even in persons This effect can to by if This effect well of and of with we pulse wave analysis in clinical The cuff information only on the between which pressure through the in the upper limb this is and information on and (with generation of the ascending aortic pulse wave analysis more accurate systolic and pressure, and with the to other of ventricular/vascular of a using a tonometer an this in hypertension in diagnosis and can the diagnosis of hypertension by the of late systolic in the aortic pressure wave, and the diagnosis when brachial systolic pressure is but this is present can a diagnosis of systolic hypertension of other and that would be on a well [5, In with systolic hypertension we would be more about a with one In with in the of systolic a of when and to is by of the arterial pulse. In we can peripheral from in mean pressure, wave from in pressure heart and effect of a from in diastolic period as well as in heart (Figure in a with hypertension and with in aortic systolic pressure of is to of and of mean pressure in we can systolic from diastolic from wave and of of systolic can be from and and from the by In with of of short at or with that be to or [5, a for and for of medical to can be from pulse wave for pulse wave analysis are to be in the are by of high in of premature arterial but have been completely to this from risk have in the pulse waves of with or that in of but recognize that are but have been to have Mahomed and his in persons with for heart arterial and have that persons often have that persons have premature arterial degeneration that has been by other The has a between carotid and and are the of carotid and aortic in the The of pulse wave with in but with review with is at It is that first made a and first clinical described the of late systolic of the radial pulse in an normal his pulse will Mahomed was in the process of a clinical record in with the at the time of his premature death at This is the of modern studies and of the College of is that had it pulse waveform analysis would have been and as now be about the arterial pulse as a as is about blood pressure a which was introduced more after Mahomed's use of pulse wave analysis by life insurance lapsed when work in established the of the technique [10. While is here to the most of pulse waveform analysis of the ascending aortic pressure to be made on the of other pulse The radial pressure pulse all the information from which the ascending aortic pulse is that is determined from the aortic pulse can be from the of and diastole are measured from the radial pulse, and its with ageing and with can be in the same as the it is more to in late on the radial pulse. and systolic pressure cannot be systolic pressure, the from which is calculated [5, of the radial pulse be for and on of brachial systolic and diastolic pressure and of have developed a for analysis of the diastolic of the peripheral pressure waveform This consider pulse pressure the period of and has and theoretic The diastolic of the pulse is the most when recorded systolic pressure beginning of is in the radial artery in the The requires noninvasive of from arterial pressure and a of the arterial and to the to wave from the pressure A has been developed and is use the carotid pulse waveform to against the radial when this use the carotid pulse as a of the ascending its is to the aortic the it cannot be calibrated with the same of confidence as the and is the and persons the are to be with are also about never in the this is at a theoretic Doppler flow are recorded from the carotid and peripheral to with on arterial is from increased flow The Doppler technique is for ascending aortic flow and for the of late systolic in flow that the of and systolic heart flow also be in the diagnosis of or [5, The is widely used for volume in and is to the waveform. have that this the carotid pressure pulse, and a to the aortic pulse. have to the of the and use this as an of vascular ageing and This developed in more in the The of this technique is from is in is to this at present by our so that others will of confidence is in journals is difference between aortic and brachial pressure This be the conditions in persons as after but it to the to persons with with heart or with The technique described here to a of to between central and peripheral systolic the most a difference of mean has to the that were when the most report is of a mean using the of with confidence intervals of of this are to our own and of In the we have that a be applied to aortic systolic pressure from from over in well with of but we are with the which has confidence which pulse waveform, in of to measured aortic systolic pressure, and with (Figure from in different the between aortic systolic pressure and brachial artery systolic pressure, determined by cuff between aortic systolic pressure and measured radial artery systolic pressure for different conditions in at to of between aortic systolic pressure and measured aortic systolic pressure for in is of is The greatest in accurate noninvasive of aortic pressure to the pressure wave or convolutional process but to calibration from the here that the radial waveform, calibrated from recorded arterial pressure, can be used to generate an accurate ascending aortic pressure waveform a of the same cannot be for calibration against the studies have between and cuff blood pressure to ascending aortic pressure noninvasively will be at the of cuff it be that studies have been based on the cuff on so that the the the this were we that the ascending aortic pressure waveform that we generate and of the of the cuff sphygmomanometer, and so improve on the information that it has provided over the a is of and This review is based on Mahomed's it must be to our advantage to appreciate fully all the pulse tells us, and to draw from the pulse all that it is capable of it is William Harvey's to and his on the of on the one or of on the in of a is a of a for pulse wave analysis.