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Chapter 9
Transcranial Doppler (TCD/TCCS)
andCerebral Blood Flow Velocities:
Parameters ofNormality
JorgeH.Mejía Mantilla, PabloF.Amaya, andLeidyGaviriaVillarreal
Key Points
1. The interpretation of the values obtained by TCD/TCCS examination is depen-
dent on the clinical context and the systemic circulatory status, with reference to
the normal values expected for a patient.
2. The identication of the insonated vessel depends on the window, the direction
of the probe points, the depth of insonation and the direction of ow in the vessel; therefore, after appropriate training an examiner can accurately identify the
vessels.
3. Studies discovered that cerebral blood ow velocity is not the same in women as
in men. It found that females usually have higher velocity than contemporary
males without differences in pulsatility or resistance indexes.
4. Cerebral blood ow is auto-regulated, and its distribution throughout the brain
depends partially on the metabolic activity of the tissue. Therefore, in actively
working brains, we can expect to nd higher CBF, hence higher cerebral blood
ow velocities (CBFV) in the side with higher metabolic activity.
5. Cerebral blood ow velocities (CBFVs) are higher in younger persons. The
decline in velocities is found in most series after the fth decade, and thereafter
there is a steady decrease in mean velocity in most series.
J. H. Mejía Mantilla (*)
Head Neurointensive Care Unit, Department of Critical Care and Anesthesiology, Hospital
Universitario Fundación Valle del Lili, Cali, Colombia
e-mail: Jorge.mejia@fvl.org.co
P. F. Amaya
Hospital Universitario Fundación Valle del Lili, Cali, Colombia
e-mail: pablo.ricardo@fvl.org.co
L. G. Villarreal
Clinical Research Unit, Hospital Universitario Valle del Lili, Cali, Colombia
e-mail: leidy.gaviria@fvl.org.co
C. N. Rodríguez et al. (eds.), Neurosonology in Critical Care,
https://doi.org/10.1007/978-3-030-81419-9_9
163© Springer Nature Switzerland AG 2022
164
J. H. Mejía Mantilla et al.
6. Reference values for a local population should be constructed by insonating
healthy subjects at rest in a calm and comfortable setting. The operator should be
an expert in the TCD technique, and it is preferable to limit the number of operators in order to avoid potential bias of inter-observer variability.
9.1 Introduction
Transcranial Doppler (TCD) is a low-cost bedside, noninvasive method to evaluate
a patient’s cerebral haemodynamics in real time [1]. TCD variations have a good
correlation with invasive methods for the measurement of cerebral blood ow
(CBF), as intravenous Xenon
changes in CBF.
TCD allows the measurement of blood ow velocity in intracranial arteries and
the indexes derived: pulsatility, resistance and hemispheric index. It allows to evaluate the anterior and posterior circulation throughout the cranial windows: transorbital and transtemporal for supra-tentorial circulation, and suboccipital for
infra-tentorial circulation. Cervical Doppler allows to evaluate internal carotid
artery in its extracranial portion, to estimate the hemispheric Lindegaard ratio,
which is useful to discriminate between situations of hyper-ux and vasospasm [3].
The reproducibility of TCD has been studied by Maeda et al. both for interobserver and intra-observer variabilities; they found a good agreement for repeated
measurements provided arterial pressure and PaCO2 are kept constant in the subject
[4]. They found a Coefcient of Variation (CV) of 7.5% and a correlation coefcient
(r) of 0.95 for Middle Cerebral Artery (MCA) mean blood ow velocity, and a CV
of 13.5% and r of 0.83 for Basilar Artery (BA) mean blood ow velocity for intraobserver reproducibility. The values for inter-observer variability show a slightly
wider variability: CV of 10.5% and r of 0.9 for MCA and CV of 17.5% and r of 0.78
for BA assessment. Even though these values are statistically signicant, the clinical impact of such differences is considered acceptable for a bedside measurement
method of CBF velocity, especially for MCA.According to their analysis, the main
source of variation of results is the position of the probe in the sonographic window
of the patient, since small variation in the insonation angle can lead to important
discrepancy in reported blood ow velocity [5]. They note that the insonation window is smaller for MCA than the window for BA exam; this might explain the wider
variation in the assessment of posterior circulation.
The interpretation of the values obtained by TCD/TCCS examination is dependent on the clinical context and the systemic circulatory status, with reference to the
normal values expected for a patient; those normal values have been published by
several authors since the beginning of the technique. We will discuss in this chapter
the published reference values for different populations, the normal values we found
in our city, and the recommendations for local reference value ndings.
133
[2], indicating that TCD accurately evaluates
9 Transcranial Doppler (TCD/TCCS) and Cerebral Blood Flow Velocities: Parameters…
165
9.2 TCD/TCCS andCBFV: Normal Values inEarly Studies
The identication of the insonated vessel depends on the window, the direction the
probe points, the depth of insonation and the direction of ow in the vessel; therefore, after appropriate training an examiner can accurately identify the vessels [6].
It is important to know the reference values for depth of insonation, direction of
ow and normal velocity for a correct interpretation of the examination, so early
authors undertook the task of building reference values’ tables that are commented
in this text.
Since the beginning of the technique in 1980s, the use of TCD ultrasonographers
committed to the task with 1 to 2MHz dedicated probes has produced similar results
in various countries. It was later evident that the reference values varied according
to age and sex of the subjects (Arnolds 1986). The rst works reported the shift of
ultrasound in its original units: Kilohertz, but this was not useful to the clinician [7].
Soon afterward, the corresponding velocity of ow was reported in cm/s, a much
more useful information at the bedside. One of the rst reports of normal values for
peak (systolic), end-diastolic and mean velocities is by Hennerici et al. from
Düsseldorf [8] (Table9.1), one of the rst reporting an age drift. Other investigators
reported the reference values for daily variation [4, 9], spontaneous or induced vari-
ations of EtCO
cycle [12]; we will not address those topics here.
[9, 10], right and left side velocities [11] and wakefulness–sleep
2
Table 9.1 Normal values as reported by Hennerici in normal subjects from Germany
Arteries
(depth in
mm)
MCA
(50mm)
ACA
(70mm)
PCA
(60mm)
VA/BA
(75mm)
MCA middle cerebral artery, ACA anterior cerebral artery, PCA posterior cerebral artery, VA verte-
bral artery, BA basilar artery
Systolic peak velocity
(cm/sec)
94.5±13.6
91.0±16.9
78.1±15.0
76.4±16.9
86.4±20.1
73.3±20.3
53.2±11.3
60.1±20.6
51.0±11.9
56.3±7.8
59.5±17.0
50.9±18.7
Averaged mean velocity
(cm/sec)
58.4±8.4
57.7±11.5
44.7±11.1
47.3±13.6
53.1±10.5
45.3±13.5
34.2±7.8
36.6±9.8
29.9±9.3
34.9±7.8
36.4±11.7
30.5±12.4
Diastolic peak
velocity (cm/sec)
45.6±6.6
44.3±9.5
31.9±9.1
36.0±9.0
41.1±7.4
34.2±8.8
25.9±6.5
28.7±7.5
22.0±6.9
27.0±5.3
29.2±8.4
21.2±9.2
Age
(years)
<40
40–60
>60
<40
40–60
>60
<40
40–60
>60
<40
40–60
>60
166
J. H. Mejía Mantilla et al.
9.3 TCD Hemodynamic Parameters: Variations by Sex
The earliest studies did not agree in their results about this point; Macchi etal. in a
sample of 120 volunteers from 19 to 89 years old found no difference between
males and females [13] in artery calibre, systolic and mean blood ow velocity,
despite differences in cranial size and body weight.
By contrast, other studies discovered that cerebral blood ow velocity is not the
same in women than in men; Vriens in 120 subjects aged 20 to 70years found that
females usually have higher velocity than contemporary males [10] without differences in pulsatility or resistance indexes [14]. Other groups report the same nding
[13, 15–17]; this difference disappears with hyperventilation, resulting in a decrease
of CBF velocity to similar values in both sexes. We summarized those reports in
Tables 9.2, 9.3, and 9.4.
Table 9.2 Mean ow velocity (MFV) in TCD by sex. Data extracted from the original publications
MFV Velocity (cm/seg)
Study Country Year N Sex
P.Grolimund Switzerland 1986 535 Female 59.9±31 51.1±33 40.2±22 39.2±19
Macchi C Italy 1994 120 Female 61.9±23 49.9±23 42.8±26
Tegeler CH USA 2013 364 Female 61.6±23 51.9±19 30.6±12 37.2±20 36.2±19 43.7±21
Dixon Yang USA 2015 369 Female 32.8±1 30.6±1 27.9±1 19.8±1 22.0±1
MCA middle cerebral artery, ACA anterior cerebral artery, PCA posterior cerebral artery, ICA
Internal Carotid Artery, VA vertebral artery, BA basilar artery
MCA ACA PCA ICA VA BA
Male 55.7±28 48±7 35.2±19 34.3±25
Male 63.0±23 50.0±26 44.0±22
Male 56.4±24 47.1±20 27.5±10 35.4±16 29.3±16 35.8±18
Male 33.9±1 30.9±1 28.7±1 20.3±1 23.3±1
Table 9.3 Resistance index (RI) in TCD by sex. Data extracted from the original publications
Resistance Index (RI)
Study Country Year n Sex
Dixon
USA 2015 369
Yang
MCA ACA PCA VA BA
Female 0.78±0.01 0.80±0.01 0.78±0.01 0.70±0.01 0.72±0.01
Male 0.74±0.01 0.76±0.01 0.76±0.01 0.69±0.01 0.72±0.01
MCA middle cerebral artery, ACA anterior cerebral artery, PCA posterior cerebral artery, VA verte-
bral artery, BA basilar artery
Table 9.4 Pulsatility in TCD by sex. Data extracted from the original publications
Pulsatility Index
Study Country Year n Sex
Tegeler CH USA 2013 364 Female 0,80±0.26 0,80±0.3 0,76±0.24 0,87±0.34 0,79±0.26 0,79±0.26
Dixon Yang USA 2015 369 Female 1.64 1.75 1.65 1.33 1.41
MCA ACA PCA ICA VA BA
Male 0,84±0.26 0,85±0.3 0,79±0.34 0,87±0.4 0,81±0.36 0,84±0.54
Male 1.51 1.59 1.55 1.33 1.45
MCA middle cerebral artery, ACA anterior cerebral artery, PCA posterior cerebral artery, ICA inter-
nal carotid artery
VA vertebral artery, BA basilar artery
,
9 Transcranial Doppler (TCD/TCCS) and Cerebral Blood Flow Velocities: Parameters…
It has been suggested that the gender difference was due to the lower haematocrit
in women; furthermore, the hormonal status, especially oestrogen levels, appeared
to contribute to the reactivity and in the vascular tone in the cerebral microcirculation of women [7, 18].
167
9.4 TCD Hemodynamic Parameters: Variations by Age
The seminal work by Aaslid in 50 subjects aged 20 to 65years reported similar
velocities in CBF [1]; several other studies have addressed this issue, with highly
concordant results in every population reviewed: CBF velocity is higher in younger
persons [7, 8, 10, 14, 19]. The Brazilian group found that the variations in velocity
are more consistent in MCA, probably because the characteristics of this artery have
little variability with age and are easier to insonate than the other intracranial vessels
[20]. The decline in velocity is found in most series after the fth decade [21], and
thereafter there is a steady decrease in mean velocity in most series. The results of
the available studies are summarized in Table9.5.
9.5 TCD Hemodynamic Parameters: Variations by Laterally
Cerebral blood ow is auto-regulated, and its distribution throughout the brain
depends partially on the metabolic activity of the tissue [22]; therefore, in actively
working brains, we can expect to nd higher CBF, hence, higher CBF velocity in the
side with higher metabolic activity. Most studies for the determination of reference
values are performed in resting subjects. Nevertheless, asymmetry between left and
right sides has been described by Schmidt [11] as well as Farhoudi [23] in a recent
study in Iranian population and by us in subgroups of subjects. This inconstant nding is probably due to mental activity during the insonation and not a permanent
anatomical or physiological characteristic of cerebral circulation.
9.6 TCD Hemodynamic Parameters: Geographic
andEthnic Trends
We did not nd any pattern in the distribution of reference values, as reported in
several studies in Table9.5 for velocity and Tables 9.6 and 9.7 for resistance and
pulsatility indexes, respectively.
We searched for differences in cerebral haemodynamics related to living in altitude, but most studies have been performed in cities below 1000m above sea level;
one report from Iran was made at 1400m above sea level. They report higher velocities in one of its tables, but the values are not consistent with another table in the
168
J. H. Mejía Mantilla et al.
Table 9.5 Mean ow velocity in TCD by age
MFV velocity cm/s
Author Country Date n Age
Rune Aaslid Switzerland 1982 50 20–65 62±24 51±24 44±22
P.Grolimund Switzerland 1986 535 22–86 57.3±30 49.2±30 37.2±19
M.Hennerici Germany 1987 50 <40 58.4±17 47.3±27 34.4±16
E.B.Ringelstein USA 1990 106 10–29 70±32 61±30 55±18 45±20 46±22
RGA Ackerstaff The
Netherlands
P.J.Martin UK 1993 115 20–39 74±3 60±3 53±2 44±3 50±3
J.Krejza Poland 1998 182 20–40 81±40 56±14 52±34
M.F Barbosa Brazil 2006 88 16–68 62±20 48±20 37±16 32±16 43±9
S.Demirkaya Turkey 2008 63 21–30 57.4±23 43.6±18 33.1±11
M.Farhoundi Iran 2010 80 25–55 62±20 52±20 43±14 36±18 48±16
Tegeler CH USA 2013 364 <30 66.6±29 53.6±20 30.9±11 36.1±22 42.1±26
Dixon Yang USA 2015 369 70–74 33.8±1 32.2±2 29.8±2 20.7±1 24.6±2
1990 125 14–70 60.9±28
MCA ACA PCA VA BA
40–60 57.7±23 53.1±19 36.6±19
>60 44.7±22 45.3±27 29.9±27
30–49 57±23 48±15 42±18 35±17 38±18
50–59 51±20 46±19 39±20 37±20 32±14
60–70 41±14 38±14 36±16 35±14 32±14
40–59 47±3 61±4 49±2 40±2 44±5
>60 58±3 51±3 42±3 33±3 35±4
41–60 73±38 53±16 51±26
>60 59±22 44±22 40±18
31–40 57.9±22 41.2±19 37.7±24
41–50 65.9±29 43.0±19 35.9±19
51–60 51.3±26 39.3±19 32.2±17
>60 46.9±11 37.7±13 31.6±17
30–39 64.6±17 54.4±17 31.8±10 35.1±16 41.0±19
40–49 60.0±23 51.0±18 30.0±15 35.6±18 40.7±19
50–59 56.6±19 48.5±18 28.8±10 32.9±17 38.0±19
60–69 51.2±20 43.8±18 26.4±11 30.6±16 35.5±17
70–80 49.6±21 42.4±23 25.3±11 30.8±23 35.6±21
75–79 33.9±2 29.4±2 28.3±1 19.4±1 22.7±1
80–84 32.9±3 30.1±2 26.9±2 20.9±2 22.8±2
>85 32.2±4 31.0±3 27.6±1 19.0±2 21.0±2
Data extracted from the original publication. Early works reported the shift of frequency instead of
velocity, we performed the conversion to velocity according to Doppler equation. Data shown is
limited to mean velocity, see original report for systolic or diastolic velocities
MCA middle cerebral artery, ACA anterior cerebral artery, PCA posterior cerebral artery, ICA
Internal Carotid Artery, VA vertebral artery, BA basilar artery
9 Transcranial Doppler (TCD/TCCS) and Cerebral Blood Flow Velocities: Parameters…
169
Resistance Index
MCA ACA PCA VA BA
Author Country Date n Age
Table 9.6 Resistance index in TCD by age
40–59 0.54±0.01 0.53±0.01 0.53±0.02 0.53±0.01 0.53±0.02
RGA Ackerstaff The Netherlands 1990 125 14–70 0.53±0.12
P.J.Martin UK 1993 115 20–39 0.55±0.01 0.53±0.02 0.54±0.02 0.54±0.02 0.51±0.05
>60 0.62±0.02 0.59±0.02 0.60±0.02 0.59±0.02 0.60±0.04
41–60 0.55±0.02 0.56±0.02 0.53±0.02
J.Krejza Poland 1998 182 20–40 0.54±0.02 0.53±0.02 0.52±0.03
>60 0.60±0.03 0.62±0.03 0.60±0.04
M.F Barbosa Brazil 2006 88 16–68 0.51±0.05 0.52±0.07 0.53±0.08 0.51±0.08 0.74±0.02
Dixon Yang USA 2015 369 70–74 0.75±0.02 0.77±0.02 0.76±0.02 0.69±0.02 0.72±0.02
75–79 0.76±0.02 0.79±0.02 0.76±0.02 0.70±0.02 0.71±0.02
80–84 0.76±0.02 0.78±0.02 0.77±0.02 0.71±0.02 0.73±0.02
>85 0.78±0.02 0.80±0.02 0.78±0.02 0.69±0.02 0.72±0.02
170
J. H. Mejía Mantilla et al.
Pulsatility Index
MCA ACA PCS VA BA
Study Country Year N Age
Table 9.7 Pulsatility index in TCD by age
40–59 0.81±0.02 0.76±0.03 0.78±0.03 0.78±0.04 0.77±0.04
P.J.Martin UK 1993 115 20–39 0.84±0.02 0.82±0.04 0.84±0.04 0.82±0.03 0.81±0.05
RGA Ackerstaff The Netherlands 1990 125 14–70 0.8±0.34
41–60 0.82±0.06 0.85±0.08 0.79±0.06
>60 0.97±0.04 0.92±0.05 0.97±0.06 0.94±0.05 0.95±0.09
J.Krejza Poland 1998 182 20–40 0.83±0.07 0.80±0.07 0.76±0.06
>60 0.96±0.09 1.02±0.09 0.94±0.08
M.Farhoundi Iran 2010 80 25–55 0.76±0.24 0.83±0.34 0.76±0.32 0.73±0.26 0.82±0.40
M.F Barbosa Brazil 2006 88 16–68 0.75±0.13 0.78±0.17 0.76±0.18 0.73±0.20 0.74±0.19
40–49 0.76±0.20 0.77±0.22 0.74±0.22 0.76±0.30 0.77±0.26
30–39 0.80±0.30 0.78±0.24 0.71±0.20 0.77±0.25 0.76±0.28
Tegeler CH USA 2013 364 <30 0.85±0.26 0.85±0.28 0.77±0.22 0.79±0.26 0.82±0.30
70–80 0.95±0.34 1.06±0.66 0.99±0.52 1.01±0.48 1.03±0.42
60–69 0.85±0.20 0.86±0.20 0.83±0.26 0.84±0.22 0.85±0.18
50–59 0.80±0.20 0.79±0.20 0.77±0.22 0.78±0.24 0.79±0.22
Dixon Yang USA 2015 369 70–74 1.55±0.08 1.61±0.10 1.60±0.08 1.29±0.06 1.42
75–79 1.56±0.06 1.71±0.08 1.58±0.08 1.32±0.06 1.40
80–84 1.61±0.08 1.71±0.08 1.63±0.08 1.37±0.06 1.46
>85 1.66±0.08 1.73±0.10 1.64±0.06 1.33±0.08 1.42
9 Transcranial Doppler (TCD/TCCS) and Cerebral Blood Flow Velocities: Parameters…
171
same paper [23]. We found a report from Sao Paulo [20], a multiethnic metropolis
in Brazil, located at 760m above sea level, and our own results are from 1000m
above sea level; we found no differences in transcranial Doppler results.
9.7 TCD Normal Values: Latin American Population Sample
We performed an evaluation of normal subjects in order to build our local reference
values for Cali, Colombia, a multiethnic city at 995 meters above sea level [24]. Our
published results on 51 healthy volunteers showed variation of velocities in intracranial arteries pending on age, sex, laterality and body mass index, but the magnitude
of these variations and the strength of the associations are limited by the power of
the study. We found slightly higher CBF velocity in subjects with body mass index
under 25 than the CBF velocity in subjects over 30, but the comparison did not
reach statistical signicance. Therefore, we complemented our sample to improve
the statistical power of our analysis, and the results are summarized in Table9.8.
9.8 TCD Hemodynamic Parameters: Altitude
Analysis of the hemodynamic parameters (CBFVs and hemodynamic indexes/
ratios) of cerebral basal arteries makes it possible to assess the changes that occur in
each clinical situation and arrive at a specic diagnosis. Keep in mind, these hemodynamic parameters are inuenced by anatomical and physiological variables as
well as by the altitude.
Table 9.8 Normal values for the entire sample in Cali, Colombia
Artery Pulsatility Index MFV Velocity (cm/s) Depth (mm)
Left side
MCA 0.81 (0.63–1.14) 61.5 (35–93) 52 (48–59)
ICA 0.89 (0.62–1.26) 53 (33–75) 64 (59–71)
ACA 0.93 (0.65–1.78) 46 (27–64) 69 (62–78)
PCA 0.9 (0.61–1.28) 44 (27–64) 63 (57–72)
Right side
MCA 0.83 (0.58–1.12) 62 (33–87) 53 (48–58)
ICA 0.86 (0.64–1.14) 53.5 (36–77) 64 (59–71)
ACA 0.93 (0.64–1.52) 45 (28–63) 70 (62–79)
PCA 0.865 (0.63–1.49) 41.5 (26–63) 64 (58–70)
Sub-occipital
Basilar 0.78 (0.75–0.82) 45.0 (41.7–48.4) 87.5 (85.5–89.5
Vertebral 0.76 (0.72–0.80) 36.1 (33.0–39.2) 66.4 (64.7–68.1)
MCA middle cerebral artery, ICA Internal Carotid Artery, ACA anterior cerebral artery, PCA poste-
rior cerebral artery
172
Table 9.9 Comparison of hemodynamic parameter values obtained with the results of other
studies [27]
Study Parameter MCA(A1) ACA(A1) eICA
Ecuador (2850m)
S.Matamoros etal.
(2019)
n=45
Colombia (995m)
Franco etal. (2015)
n=51
Sao Paulo (760m)
Fregonesi B. etal.
(2006)
n=88
Bern (Switzerland)
(540m)
Aaslid etal. (1982)
n=50
Girona (Spain)
(76m)
Segura etal. (1999)
n=118
ACA anterior cerebral artery, MCA middle cerebral artery, eICA extracranial internal carotid artery,
PCA posterior cerebral artery, PI pulsatility index, V4 intracranial vertebral artery, MFV mean ow
velocity
MFV
(cm/s)
PI 0.8 0.8 0.8 0.8 0.8 0.7
MFV
(cm/s)
PI 0.74 1.01 0.8 0.77 0.78 0.76
MFV
(cm/s)
PI 0.51 0.52 – 0.53 0.51 0.51
MFV
(cm/s)
PI – – – – – –
MFV
(cm/s)
PI 0.98 1.01 – 1.01 1.03 1.01
49.3 39.9 34.6 34.6 36.7 26.0
59.8 47.4 31.5 37.4 45.1 35.8
62 48 – 37 43 32
62 51 37 44 – –
54 43 – 34 37 29.1
J. H. Mejía Mantilla et al.
PCA
(P1) Basilar Vertebral(V4)
In populations living at altitude, increased haemoglobin concentration is observed
as a result of physiologically elevated red blood cell production, with a concomitant
increase in blood viscosity [25]. This rheological change of the blood, together with
arterial lumen area and vessel length, is the main determiners of CBF resistance,
meaning that CBFV is inversely correlated with haematocrit level [26].
Table 9.9 compares the results of several studies conducted in normal subjects in
populations at different altitudes.
Matamoros etal. (2019) [27] recruited 47 healthy Ecuadorian volunteers (altitude 2850m); two patients were excluded because they did not have a viable cranial
window for TCD study. Thus, we recorded mean ow velocity (MFV), peak systolic
velocity, end-diastolic velocity and pulsatility indices (PI) in 45 patients (62.2%
women; mean age, 35.9years); recorded patient’s age, sex and haematocrit; and
analysed cerebrovascular hemodynamic parameters by sex and age groups.
Analysing the relationship between MFVs and sex, Table 9.10 showed results
very similar gures to those obtained in other series. We recorded higher MFV values for women, a difference that appears to be dependent on the lower haematocrit
levels found. Age is the most important factor modifying CBFVs in TCD.In the
study, Table 9.11 showed analysed CBFVs in two age groups (over and under
40years) and found a difference of 16.4% for the MCAs and 14.9% for the ACAs