Cardiovascular Research 2001 51(2):205-216; doi:10.1016/S0008-6363(01)00307-8
© 2001 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Those who faced turbulence and launched the era of flow dynamic concepts for cardiac investigation
Colette Veyrat*
Department of Cardiology, University Hospital Bicêtre, 78, rue du Général Leclerc, 94275 Le Kremlin-Bicêtre, Cedex, France
* Tel.: +33-1-4521-3769; fax: +33-1-4521-3293 colette.veyrat{at}bct.ap-hop-paris.fr
Received 31 January 2001; accepted 3 April 2001
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Abstract
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This paper puts emphasis on pioneers who developed cardiac flow
dynamics concepts during the second half of the 20th century
at a period where pressure measurements were the rule. Thinking
flow instead of pressure dynamics corresponded to in-depth conceptual
changes: whereas blood pressure generally has a single positive
sign and a similar pattern at all points of a cardiac chamber
or a vessel, flow fluctuates around the zero line and its pattern
changes within a given cardiac chamber or vessel level. These
specific changes and fluctuations were the exciting tools needed
to renew our pathophysiological insights, just in time with
the take off of Doppler ultrasound making noninvasive investigation
of fluid dynamics easily available. Each decade was marked by
a specific historical contribution to evolving concepts. Instead
of a merely phenomenological approach to flow dynamics, pioneers
assigned a value of paradigms to basic flow patterns. They generated
a system of heuristical hypotheses which turned out to underlay
a modernistic understanding of flow dynamics in normal and diseased
hearts. So far, flow investigation had definitely gained acceptance
completing pressure data at the middle of the 1980s, widely
opening a breakthrough for future pathophysiological insights.
KEYWORDS Blood flow; Ultrasound
Once, Thalès of Miletus arrived with a companion in front
of a pyramid. "How could we know how high it is?" Rather than
looking at the written answer handed to him by his companion,
Thalès said "There is a better way to know. When the
shadow of a man will have reached his height, then we will have
only to measure that of the pyramid to know its true height".
Thalès, by associating the pyramid, a man, their respective
shadows and the sun, provided a method which clearly passes
the interest of the specific answer. This parabole might apply
to the breakthrough provided by the investigation of flow dynamics
in cardiology in the last half of the 20th century. Most of
these new insights were carried out by the growing Doppler ultrasound
techniques: rather than the mere numerical values of new parameters,
they provided an approach to a new conceptualisation of the
cardiovascular system and improved our pathophysiologic understanding.
The aim of this paper is to acknowledge, at the turning point of the millennium, the contribution of some pioneers, some of them forgotten, to changes into our cardiovascular concepts. These changes overrode the ‘pre-Doppler’ era and the growing edge of the Doppler era.
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1 Conceptual mutation from the era of pressure measurements to that of flow dynamics; relationships between flow and pressure data
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The relatively modern era of cardiology roughly took off in
the 3rd to 5th decades of the 20th century. It became obvious
that medicine needed objective data. Efforts were, at first,
focused on pressure measurements and catheterisation, with or
without contrast angiography. Patients generally suffered from
valvular heart diseases. Making decision relied on catheterisation.
Progresses in cardiac surgery, however, evidenced diagnostic
limitations in many clinical situations and possible pitfalls
due to pressure measurements alone while the increased rate
of insertion of prosthetic valves reduced the feasability of
catheterisation. Problems arose in cases of prosthetic dysfunction
and errors were frequent. Although the concept had been introduced
by Kolin as early as 1936
[1], flow remained ignored because
it required expensive and highly traumatic electromagnetic probes,
surgically implanted around vessels.
A fundamental step was made by McDonald around the 1960s: he had computed blood flow in arteries from pressure data using Womersley calculations reported in the 1950s [2,3]. McDonald had shown that flow was not related to the absolute value of pressure but to the pressure gradient between two points. Briefly stated, pressure traces have the same sign during a phase and their patterns do not vary within a cavity. This is very different from what occurs with flow dynamics: two close points of a vessel wall are successively reached by a pulse pressure wave initiated by the source of pressure. Pressure becomes higher at the first point than at the farthest one, generating a pressure gradient between the points recorded as a positive vector of flow velocity since the fundamental law of fluid dynamics indicates that flow runs from higher to lower pressure areas. The reverse situation occurs when the farthest point is reached by the pulse pressure wave. The pressure gradient becomes negative and a negative vector of flow velocity is recorded, accounting for the possibility of a backflow in arteries. This explains the similarity between flow velocity and pressure derivative traces. Pressure and flow recordings are related both through the pressure derivative versus time (dP/dt) and through the local pressure gradient versus space (dz/dt), z being the distance between the close points aligned on the vessel wall. It is the pulsatile character of the pressure wave that entails the oscillatory pattern of flow velocity.
A considerable amount of research into flow studies developed around the 1960s. Methods, mainly experimental, often relied on catheterisation and became less traumatic than surgical insertion of a sutured flow probe. Spencer and Denison made the first clinical applications of the pressure gradient technique through pulmonary and aortic pressure catheterisations in 1956 and could derive flow velocity ejectional traces of great vessels from their data [4]. Later on, Noble et al. and Schultz et al. studied flow velocity distribution in large vessels using hot thin film anemometers and thin film techniques, respectively in 1967 [5] and in 1969 [6]. Another trend of equipment consisted of an electromagnetic velocity catheter-tip by Mills in 1967 [7]. From 1956 to 1970, a series of studies, mainly on experiments or during surgery, were dedicated to vena cava flow investigation [8–11]. Flow profiles were studied by Taylor and Wade by means of an optical Janus needle with wide-angled lens [12]; when the direction of flow was not constant, it was possible to derive flow at any time within the cardiac cycle, by locating the needle in two positions at right angles. Flow paths could also be cinefilmed and correlated with timing of cusp motions. So far, models only involved a left ventricular cavity and a mitral valve [13]. Physicians needed information on the assessment of prosthetic hydraulic performances; thus, prostheses were studied through experiments involving electromagnetic probes inserted on both sides of the heart and by means of two dimensional visualisation of flow vortices [14]. Specific measurement of annular flow-rates, however, still required surgical insertion of an electromagnetic probe around the annulus on animals [15–18]. J.P. Shillingford was a conceptual pioneer. He organised a symposium entitled ‘The growing edge of the theory and measurement of blood flow’ at the Royal Society of Medicine in London, UK, on April 21 1969 (Fig. 1). Only a handful of about thirty scientists acquainted with the cutting edge of these cardiovascular advances attended the symposium! The fact that a noninvasive clinical method of flow velocity measurement, namely the Doppler directional velocimeter, was admitted for lecturing among presenters of invasive and mainly experimental procedures, was also ‘avant-garde’.
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Fig. 1 Content of the program of the symposium held at the Royal Society of Medicine, section of measurement in medicine on April 21, 1969, entitled ‘The growing edge of the theory and measurement of blood flow’, under the chairmanship of J.P. Shillingford. In 1969, the newness and promises of this topic were overlooked by most of the scientific community.
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2 Launching the Doppler era; from ‘heart beat’ analysis to ‘flow’ concept
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Early Doppler ultrasound developments, delayed more than one
century after the publication of Christian Doppler's so-called
‘principle’ in 1843
[19], were boosted by ultrasonic
sophisticated developments during World War II. A tight cooperation
between physicians, engineers and physicists succeeded to bridge
the gap between invasive and noninvasive techniques in flow
measurement and to yield the bases of the Doppler technique
in less than 15 years.
In spite of the maturation of minds toward flow concepts, the first Doppler studies achieved with the early ultrasonic Doppler device [20], later known as an ‘ultrasonic Doppler cardiograph’, were not aimed on flow recordings, but solely dedicated to heart beat and valve motion velocity recordings. Thus, the first Doppler apparatus was designed to record their typically rough signal, under the direction of Nimura. 1956 was the birth of the Doppler technique with the report of Yoshida, Nimura and Satomura, on the examination of the heart with the ultrasonic Doppler method in Osaka, Japan.They used a 3-Mhz continuous wave Doppler transducer with a frequency spectrogram output signal (Fig. 2). Nimura initiated and directed cardiac applications. A series of princeps reports was dedicated to heart beat and valve motion velocity recordings [21–25]. Thus, the Japanese group, particularly Nimura, were true pioneers in equipment and in tissue Doppler [26–29]. High-pitched signals were also heard but they were discarded at this early phase of the Doppler era, because of their uncertain origin. Kaneko, however, a Japanese neurologist, thought they could possibly be attributed to flow signals and asked Satomura to enhance these signals heard in the area of the extracranial carotid artery. Equipment was designed for this goal. Flow signal acquisition was facilitated by some alterations in gain and filtering. Frequencies under 120 Hz were cut-off to eliminate noise related to walls [30]. The report was promisingly entitled ‘Study of the flow patterns in peripheral arteries by ultrasonics’ [31]. Indeed, the so-called ‘flow patterns’ appeared more as the inscription of sound vibrations than as traces. Practical applications to carotid arteries on patients could start under the guidance of Kaneko and co-workers [32,33].
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Fig. 2 First applications of Doppler ultrasound to heart wall and valve motions. Recording of the low frequency Doppler signals related to heart wall motion velocity (top, 1961) and mitral valve opening and closing motion velocities (bottom, 1968); (from Yoshida et al. Am Heart J 1961;61:61–75 and Nimura et al., Am Heart J 1968;75:49–65, with permission of Mosby and Co.).
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Some time elapsed between the birth of the Doppler equipment
and its validation. The rationale for the development of Doppler
flowmetry was reported in 1962 by Kato et al. showing a positive
correlation between the magnitude of Doppler frequencies and
the number of corpuscles on experiments
[34]. Finally, Reneman
et al. validated Doppler versus electromagnetic flowmeters
[35].
Although the gap between Doppler ultrasound and flowmetry was
bridged, many users continued to only record the human or fetal
heart beats and sounds with Doppler ultrasounds
[36,37].
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3 Onset of the ‘Doppler flow velocimetry’ era, an explosive ‘avatar’ of early ultrasonic approaches
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Meanwhile, the various invasive procedures used to record flow
velocity had alerted physicians to flow concept in the US. Convenient
analog demodulated flow traces had been developed. In 1961,
Franklin and co-workers seized the crucial interest of the ultrasonic
continuous wave equipment for investigation of peripheral arteries
[38,39]. They are pioneers for the first Doppler equipment available
for peripheral flowmetry, i.e. the nondirectional Doppler device.
They were followed by George and Pourcelot and co-workers in
France in 1965
[40]. Light investigated the aortic arch for
purposes of monitoring aortic velocities as a surrogate for
cardiac output in emergency cases in 1969
[41]. The technique
was also applied to aortic lesions
[42,43]. Benchimol also was
a pioneer. He and co-workers investigated arterial, venous and
coronary vessels by means of an ultrasonic non-directional Doppler
catheter-tip
[44–46]. At the turning of the 1970s, however,
these scientists had not succeeded in demonstrating the interest
of flow velocity recordings because the latter were not directional.
All deflexions were seen as positive, a fact which prevented
them from having physiological meaning. Accordingly, management
of patients continued to be classically ruled by pressure measurements.
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4 Advantages drawn from traces with an effective ‘zero’ line to initiate the era of physiological significance of arterial and venous ‘Doppler flow velocimetry’
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In the mid-1960s, the introduction of directional Doppler recordings
launched this era. Directionality enabled recognition of spectral
velocity signs toward and away from the transducer with respect
to a zero line. Studies emerged nearly simultaneously in three
locations. In 1966, Kato and Izumi in Japan
[47] and in November
1967, McLeod in the US
[48], reported a directional continuous
wave Doppler velocimeter prototype in engineering meetings.
In France, Kalmanson et al. presented a new device designed
by Toutain, on January 19 1968 at the French Society of Cardiology
[49]. The equipment involved a phase detector. Kalmanson anticipated
that the new flow data would underlie major pathophysiological
messages and that, to gain acceptance, data needed a simple
readout displayed as a single channel output for both velocity
signs, successively displayed on each side of the zero line
on a stripchart. The output waveform was transformed into a
demodulated curve by an analogue converter. At the end of 1968,
Kalmanson's pioneer works had been issued, reporting all arterial
and venous directional Doppler flow velocity patterns in controls
and patients and singling out the fundamental features of flow
velocity recordings
[50–53]: namely, the pattern was oscillatory;
there could be backflow in arteries; specific patterns were
assigned according to each site of recording with minor possible
variations. For several years, the fact that there could be
backflow in arteries appeared particularly iconoclastic to many
scientists familiar with pressure measurements but it finally
got acceptance. As for venous return, Doppler data were consistent
with those obtained by electromagnetic probes on experiments
[54]. Accurate timing of changes in flow direction had been
demonstrated in pipes, validating the use of a single channel
for Doppler recordings
[55] (
Fig. 3). For a while, separate
channels, one for positive, the other one for reverse flow,
also recorded as a positive vector, could be shown (
Fig. 4)
[56,57]. Finally, recording on one single channel prevailed.
Flow recordings were similar to those obtained nowadays. It
is noteworthy that probe frequency allowed only peripheral traces
to be transcutaneously recorded.
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Fig. 3 Experimental study of the linearity of the Doppler output (left) and of the directionality of the equipment (right) (explanations in text). Reprinted from Kalmanson, Ann Méd Intern 1969;120:685–700, ©Masson with permission of the editor.
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Fig. 4 Directional continuous wave Doppler ultrasound in peripheral arteries using two separate channels. Forward (upper channel) and reverse (middle channel) output components of the flow pattern in a brachial artery of a patient with aortic insufficiency are shown on two separate channels. Combined outputs are shown on the left lower raw (from Strandness et al., Am Heart J 1969;78:65–74, with permission of Mosby and Co.).
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5 New systemisation of intracardiac flow dynamics drawn from changes in patterns: from a three-wave pattern (venous inlet) to a single wave pattern (arterial outlet)
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In 1969, flow patterns had hardly, if at all, been studied in
detail within the heart. Information existed about patterns
in vena cava
[8–11,54] and about aortic flow
[4,5,44].
Non-directional Doppler catheterisation would soon be applied
to right atrium
[45] and to coronary arteries
[46]. What could
be guessed for intracardiac flow patterns was anticipated from
pressure traces: when the veins enter the right atrium, pressure
trace fluctuates throughout the cardiac cycle and shows an abrupt
descent when the tricuspid valve opens with flow taking place
into the ventricle at the onset of diastole. Although smoothing
of aortic pressure and decrease of the mean pressure level had
occurred during the passage through the systemic microcirculation,
pulsation was still high enough at the venous end of the capillary
bed to generate flow towards and within the heart and there
was still basically a steady driving force. In addition to the
effects of the muscular pump and of respiration, pressure changes
related to cardiac contraction were expected to add further
oscillations
[58].
During 1968, a new directional Doppler probe was devised and inserted at a catheter-tip to investigate heart cavities. A series of lens enabled to focus 2 or 3 mm ahead of the tip. Results obtained in dogs and in man in the heart cavities by venous route and in large vessels by retrograde catheterisation with this prototype were first published in 1969 [55].
Recording from the vena cava through the heart to the pulmonary artery on the right side evidenced a continuum of progressive changes in flow velocity patterns within the heart: in order to obtain a single systolic wave in the arterial system from a venous return trace involving three waves, two positive, S systolic and D diastolic, one negative A diastolic waves, flow within the heart must undergo progressive changes, each one being specific of a given site of recording and of a given timing of the cardiac cycle (Fig. 5).
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Fig. 5 Schematic drawing of the continuum of changes in flow patterns from the venous inlet to the outlet arterial chamber. After having assigned a physiological significance to these three archetypes, pioneers started the systemization and modelling of their pathophysiological patterns (after Kalmanson et al. [55,60] explanations in text).
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6 From phenomenology to heuristics
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Beyond a mere description, pioneers assigned a physiological
significance to flow velocity patterns. Through heuristical
hypotheses, their specific features, including the tricuspid
annular flow pattern recorded for the first time in man, were
systematised. Not a single detail lacked: the small negative
deflexion during the isometric contraction (ic) no flow velocity
during systole, a small deflexion during the isovolumic relaxation
ending with the atrio-ventricular opening which started ventricular
filling. Both filling waves were described, the early filling
which was labelled D like diastole, later renamed E by similarity
to early-diastolic valve echocardiographic labelling and the
late filling wave A. This was achieved for the left side by
a new orientable catheter-tip which enabled the recording of
the mitral annular trace through transseptal catheterisation
in 1970
[59–61]. The trace was similar to that recorded
at the tricuspid annulus in 1969. Electromagnetic flow probes
validated these patterns at the annuli on experiments
[15–18].
Physiological significance of flow velocity patterns gave rise
to new system dynamics concepts from 1969 to 1972. For instance,
the finding of two possible outcomes for the atrial A wave depending
on the site of recording, suggested the hypothesis that, beyond
a certain atrial plane, which could be labelled the ‘watershed
plane’, the atrial contraction drives blood ahead toward
the annulus, and above this plane, it pushes it back toward
venous return. This suggested that the venous return extended
to this plane in a wider concept of a lump return system. Conversely,
the diastolic double-wave pattern transformed abruptly into
a high systolic–low diastolic pattern at the junction
between inflow and outflow tracts. Furthermore, preferential
flow paths were singled out within the ventricles. Importantly,
capability of any organic or functional alteration of atrial
relaxation, downward displacement of the annular closed floor,
ventricular relaxation or filling and atrial contraction to
induce anomalies on-site and in venous return patterns, was
demonstrated
[62–64].
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7 Modern ‘diagnostic’ era of Doppler with one-dimensional echo imaging and range-gated Doppler
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Unless a catheter-tip was used, the frequency of the probe confined
continuous wave Doppler applications to superficial vessels.
Some physicists found an elegant solution to sampling within
the heart by designing a range-gated pulsed Doppler, namely
Wells in the UK
[65], Peronneau et al. in France in 1969
[66],
and in 1970, Baker in the US
[67] and Ohtsuki and Okujima in
Japan
[68]; there were two piezo-electric crystals, one emitter
and one receiver. The range-gating system made it possible to
pick-up any sample of blood, generally tear-drop shaped known
as the ‘Doppler gate’ along the axis of the beam.
Optimal spatial resolution allowed unequivocal recognition of
the sampling site and noninvasive access to velocity profiles
and velocity distribution across a vessel diameter, previously
available only from invasive equipment. Besides the investigation
of the left posterior wall
[69] and of small vessels
[70], evaluation
of graft patency after coronary by-pass was proposed by Gould
et al. in 1972
[71]. A separate one-dimensional echocardiogram
imaging checked the location of the graft and was followed by
a Doppler flow velocity recording at its approximate depth.
A true breakthrough occurred when simultaneous imaging and Doppler recordings were developed and proposed by Johnson and Baker in 1975 [72]. The range-gated pulsed Doppler was combined with one-dimensional echocardiographic imaging. The authors recorded the disturbances generated by heart lesions using a time-interval histogram and a zero-crossing detector. This application was a kind of intracardiac stethoscope, yielding the ‘diagnostic era’. Thus, it was possible to relate the spectral disturbances to specific valvular or heart cavities, as shown by Stevenson et al. for ventricular septal defects [73]. A demodulated analog trace was also added to reproduce the flow velocity traces previously recorded by catheterisation. This method was applied to valvular and congenital lesions from 1975 to 1980 [74–78] (Fig. 6 bottom left). Regrettably, the occurrence of ‘aliasing’, due to the inability of pulsed Doppler to record velocities exceeding the physic ‘Nyquist’ limit, prevented calibration of velocities. Conversely, ‘aliasing’ was a reliable marker of increased velocities usually related to lesions. Although far from perfect, pulsed Doppler turned out to be a reliable diagnostic tool on the basis of a recognition pattern. It compared favourably with diagnostic capabilities of one-dimensional echocardiography. In addition, pulsed Doppler step-by-step sampling in the left atrium in case of mitral stenosis yielded unexpected information on the progressive flow acceleration proximal to a narrowed orifice, consistent with the flow net theory in fluid dynamics, ten years ahead from its demonstration by colour Doppler. Anomalies of flow velocity traces led to devise indices for grading severity of the lesions (Fig. 6, bottom left). Extension of disturbances in the cardiac chambers was also proposed for grading [79]. The success rate was limited by frequent changes in the direction of the valvular jet out of the scanning line [80].
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Fig. 6 Three steps of the Doppler ultrasound capabilities in the assessment of valvular lesions. (top left, 1973) Peripheral era: directional Doppler continuous wave preoperative recording of the subclavian artery displayed with a demodulated analog trace and a single channel for positive (above) and negative (under the zero line) velocity signs in a case of aortic insufficiency. Postoperative prosthetic dysfunction by thrombosis with fibrinolytic therapy: from left to right, preoperative recording showing diastolic backflow related to aortic regurgitation (arrows 2.22.73), postsurgery recording with normal pattern of the subclavian artery (small backflow wave, 3.31.73), obstruction by thrombosis with aortic regurgitation entailing reappearance of a major backflow wave in diastole (arrows 11.12.73), regression of the backflow wave after thrombolytic therapy but no restitutio ad integrum of the subclavian flow velocity pattern (12.19.73). The patient required later surgery. (Bottom left, 1977) Intracardiac era, range-gated pulsed Doppler combined with one-dimensional imaging. Effect of tricuspidectomy for tricuspid regurgitation due to infective endocarditis on a patient; The Doppler gate (G on right) is located at the site of the tricuspid annulus in the right ventricle. The signal consists of both a demodulated analog trace (on left) and a spectral trace (SP on right). The regurgitation is shown by the negative systolic wave under the zero line. From left to right, there is a progressive increase in the depth of the negative wave with time (vertical arrows), consistent with an increasing grade of tricuspid regurgitation requiring later prosthetic insertion in this patient. (N/P: negative systolic to positive diastolic velocity ratio). (Right 1979) Pulsed Doppler assessment of the regurgitant aortic valvular area relying on the detection of a disturbed diastolic signal (oblique arrows) under two-dimensional echocardiographic guidance at the aortic orifice in the short axis view in a patient with aortic regurgitation.
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8 ‘Grading’ and ‘pathophysiological’ eras through two-dimensional flow mapping
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After the diagnostic preliminary phasis, surgeons boosted Doppler
users to grade valvular lesions. This was made possible by a
new breakthrough: combination of pulsed Doppler with two-dimensional
echocardiography. The first pioneer paper was published in 1977
by Matsuo et al.
[81] followed by Griffith et al. in the US
[82]. Even more exciting than the improved grading it provided,
this era yielded new pathophysiological insights. The new technology
enabled to follow the trajectory of the jet in a two-dimensional
plane, such as for mitral valve prolapse
[83,84]. Indices for
a semiquantitative grading gained acceptance and were first
reported by Miyatake and Kalmanson's groups between 1980 and
1984
[85,86]. Three-dimensional indices were devised for valvular
regurgitations by combination of two orthogonal planes
[87,88].
A new quantitative procedure was also proposed by measuring
the jet area, later called the vena contracta at the site of
the valvular regurgitant or stenosed lesions in the short axis
view from 1983
[89] (
Fig. 6, right). Noninvasive quantification
of flow-rate became possible and several two-dimensional innovative
methods were proposed and validated
[90,91]. Two other progresses
took also place in the early 1980s: colour Doppler was first
designed by Brandestini, who studied congenital defects with
Stevenson
[92], and by Bommer and Miller
[93] and Namekawa et
al.
[94]; the time interval histogram was replaced by the more
reliable fast Fourier transform signal processing.
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9 ‘Quantitative’ era with continuous wave Doppler
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Except for planimetry of regurgitant and stenosed flow areas
[95,96], other grading indices were semiquantitative and a lot
of parameters of crucial usefulness were lacking with pulsed
Doppler, such as the measurement of pressure gradients and that
of functional valve areas, because of the Nyquist limit. This
was a fundamental reason to return to continuous wave Doppler,
the more so as progresses in transducers had made available
lower frequency probes allowing sampling deep in the heart.
Spatial resolution was still lacking but with a minimal physiological
knowledge and training, it was easy to distinguish a regurgitant
from a stenosed jet by their timing. A pioneer in this field
was Jarle Holen, Norway. He applied the Bernoulli equation to
the calculation of the pressure drop in mitral stenoses and
prostheses as early as 1976
[97]. He validated the calculations
derived from ultrasound versus simultaneous invasive pressure
measurements. He understood that pressure drop depending on
cardiac output, valve area calculation was the needed parameter
and reported this calculation combining the ultrasound technique
with an invasive measurement of flow-rate
[98]. True quantitative
Doppler methods could start. From 1978 to 1985, Bjorn Angelsen
and Liv Hatle proposed to simplify the Bernoulli equation as
4
V2 and popularized this Doppler procedure
[99–101]. The
formula is routinely used in all laboratories and its efficiency
has been validated in most clinical situations. Finally, Skaerpe
et al. proposed to calculate valve areas using the continuity
equation from 1985
[102]. Valvular heart diseases are less frequent
but the formula found a series of applications providing a true
noninvasive hemodynamic evaluation in nonvalvular cardiology,
diastology and emergency situations.
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10 Present status and future trends
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The year 1984 marks the entrance to present time because colour
flow Doppler evidenced the adequacy of flow concepts with pathophysiology.
Consequently, explosive trends of research could occur. These
were generated by new transoesophageal and intravascular approaches,
new tools like contrast agents, technological improvements such
as multidimensional and harmonic imagings and re-emergent tissue
Doppler processing. Importantly, Doppler modalities are complementary:
For instance, we may cross-check the assessment of a valvular
lesion at three levels, downstream the lesion with measurement
of pressure drop, at the vena contracta by planimetry of the
jet area, and in the upstream chamber, by calculating the proximal
isovelocity surface area derived from cardiac output calculations.
Future directions will depend on a pluridisciplinary cooperation. Studies should not dissociate intra-cardiac and -vascular flow dynamics from their surrounding tissues. Much remains to do for higher accuracy, resolution, insensitiveness to noise of signal processing, better 3D outline of jets relying on new fuzzy reasoning algorithms, relaxation technology, clinically relevant investigation of new diagnostic targets such as, for instance, the whole spectrum of coronary artery disease. Finally, flow investigation might be optimised by other physical sources.
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11 Conclusions
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This historical review recalled the impact of audacious pioneers
who cleared the way in an unbroken field of cardiology during
the last half of the past century. At the turning of the new
millennium, princeps descriptions of flow events and innovative
paradigms from which deviated patterns could be declined according
to pathology, trace the way toward a promising continuum, whatever
the available technology might be.
Time for primary review 35 days.
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Acknowledgements
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I wish to thank Professors Matsuo, Nimura, Wells and Peronneau
for the historical information which they kindly provided.
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1 Conceptual mutation from...