Fyziologický ústav, Lékařská fakulta Masarykovy univerzity1
Physiological
demonstration
Continual blood pressure
measurement
Baroreflex sensitivity
(spring semester 2024)
Blood pressure
blood pressure is in the entire cardiovascular
system
̶ Arterial pressure – the driving force for
blood flow through blood vessels
(mainly through brain – cerebral perfusion pressure
CPP = MAP-ICP)
– basic vital function variable
other pressures and their significance
̶ Atrial and ventricular pressures – cardiac function variables
̶ Pulmonary pressure (<20 mmHg) – increased pressure is a
sign of pulmonary hypertension
(primary – of endothelial origin, secondary – a consequence of lung diseases or left heart failure)
̶ Central venous pressure (0-8 mmHg)
monitoring of right heart function and intravascular filling (venous return, hydration)
̶ Capilary pressure (15 – 30 mmHg) –
assessment of tissue blood supply, risk of edema
Blood pressure
measurement in the heart
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rizace
̶ Right access – catether with pressure
sensor through
v. subclavia/jugularis/femoralis
̶ Vena cava → right atrium → right ventricle → a. pulmonaris →
Pulmonary Capillary Wedge Pressure (equal to pressure in left
atrium)
̶ Left access – catether through
a. radialis/brachialis/femoralis
̶ Aorta → left ventricle
Swan-Ganz catether
Arterial blood pressure
is a continual variable
𝑴𝑨𝑷 = 𝑪𝑶 ∙ 𝑹 = 𝑺𝑽 ∙ 𝑯𝑹 ∙ 𝑹Constant component
Pulsation component 𝑷𝑷 =
𝑺𝑽
𝑪
Variables determining arterial pressure:
• CO – cardiac output
• SV – stroke volume
• HR – heart rate
• R – resistance
• C – compliance
PP
MAP
SBP
DBP
̶ Methods of continual blood pressure measurement
̶ Invasive – arterial catether
̶ Non-invasive – photoplethysmography (Peňáz´s method)
Invazivní metoda měření arteriálního tlaku
̶ In patients with critical threat to vital functions (ICU)
̶ critical hypotension, vasopressor administration
̶ Brain perfusion monitoring (CPP = MAP-ICP)
̶ Advantages
̶ accurate
̶ Collection of arterial blood for analysis of ABR, iont balance, etc.
(needle-less acces)
̶ disadvantages
̶ infection
̶ bleeding
Principle of non-invasive continual
blood pressure measurement
̶ Photoplethysmographic/Peňáz/volume-clamp method
Arterial lumen
(finger volume)
Pressure
in the cuff
Control
systemConstant finger volume
Pressure in the finger cuff
Before application of
control system
Control system:
Correction of the pressure in the
finger cuff according to the arterial
lumen changes.
Aim: maintaining of constant arterial
lumen through pressure changes in
the cuff.
Tlak v manžetě pak kopíruje
arteriální tlak
application of control system
Neinvazivní kontinuální měření krevního tlaku
̶ advantages
̶ non-invasive (safer, painless),continuous recording (evaluation of short-term variability, detection
of beat-to-beat values, research, monitoring)
̶ disadvantages
̶ Long-term pressure of the finger with the cuff affects the results, it is not accurate for part of the
population, calibration with the arm cuff is necessary
150/90
127/92SBP
DBP
Extrasystoles
supraventricular ventricular
Orthostatic hypotension diagnosis
̶ Tilt-table test
If there is such a significant drop in blood pressure when patient is tilting that syncope occurs, the test is positive
Valsalva manuever
̶ Phase I: exhalation against a closed glottis. Transiently,
the intrathoracic pressure rises and so does the pressure
on the arteries in the chest. There will be a transient
increase in pressure.
̶ Phase II. Exhalation continues against the closed glottis.
High intrathoracic pressure compresses the vena cava.
Venous return decreases and thus cardiac filling, cardiac
output, and blood pressure decreases. The baroreflex
responds to this by accelerating the heart rate.
̶ Phase III. Release of intrathoracic pressure and free
breathing. Blood pressure drops temporarily because the
pressure in the chest on the thoracic arteries decreases.
̶ Phase IV. A drop in intrathoracic pressure will restore
venous return. Increased cardiac filling and systolic
volumes will increase blood pressure and pulse amplitude.
The baroreflex responds to an increase in blood pressure
and reduces the heart rate. This phase is used to assess
baroreflex sensitivity.
̶ Note The Valsalva maneuver with its bradycardic part is
used as the first method to stop supraventricular
tachycardia.
Baroreflex
̶ Fast regulation of arterial blood pressure by changes of heart rate and
peripheral vascular resistance
Baroreflex sensitivity (BRS)
̶ Evaluation of cardiac baroreflex function through SBP and heart rate
(cardiac cycle) changes
̶ BRS: change of cardiac cycle caused by SBP change by 1 mmHg
[ms/mmHg]
RR interval
BRS:
slope of
line
RR
SBP
R
ECG
SBP
BP
DBP
Standard (oxford) method of BRS evaluation
̶ Application of phenylephrine (vasoconstrictor) – increase of SBP
̶ RR prolongation is measured
normal
BRS
RR
SBP
RR
SBP
decreased
BRS
Decreased BRS
̶ Physiologically
̶ psychic stress – increased sympathetic activity
̶ Physical exercise – increased sympathetic activity
̶ In old age
̶ Pathologically
̶ hypertension – decreased baroreceptor sensitivity
(atherosclerosis, increased arterial stiffness)
̶ diabetes – neuropathy of autonomic nervous
system
̶ Chronic depression (neurogenic)
̶ Heart insufficiency/failure – heart do not response
̶ Transplanted heart - denervation
̶ Myocardial infarction – heart do not response
Cardiovascular signal variability
̶ Cardiovascular signals
̶ Easy to measure
EGG: RR intervals, heart rate - HR (1/RR)
Blood pressure: systolic (SBP), diastolic (DBP), mean (MAP), pulse pressure (PP)
̶ Difficult to measure directly (bioimpedance method), can be
evaluated indirectly from blood pressure wave (Windkessel model)
Stroke volume (SV), cardiac output (CO), total peripheral resistance (TPR)
̶ Very difficult to measure directly (invasive measurement)
Blood flow and pressure in various places of vessels
Signal: time series
̶ Beat to beat (for example 5 minutes)
• RR interval: 805, 820, 815, 817, 822, 816,….. ms
• Hear rate: 70, 73, 68, 65, 67, 71,….. bpm
• Systolic blood pressure: 115, 117, 120, 116, 121, 119,….. mmHg
SBP
[mmHg]
RR
[ms]
700
800
900
110
120
130
20 40 60 80 100 120 s
RR interval
R
ECG
SBP
Blood
pressure DBP
Metody frekvenční domény - spektrální analýza
Spectrum
Signal in frequency domain
Time series
Signal in time domain
Signal is decomposed in individual frequenciesamplituda
čas (s)
504030200 10 0.50.40.30.20 0.1
amplituda
frekvence (Hz)
Metody frekvenční domény - spektrální analýza
Spectrum
Signal in frequency domain
Time series
Signal in time domain
Signal is decomposed in individual frequenciesamplituda
čas (s)
504030200 10 0.50.40.30.20 0.1
amplituda
frekvence (Hz)
Metody frekvenční domény - spektrální analýza
Spektrum
Signál ve frekvenční doméně
Časová řada
Signál v časové doméně
Rozložení signálu na jednotlivé frekvence
amplituda
čas (s)
504030200 10 0.50.40.30.20 0.1
amplituda
frekvence (Hz)
How the spectrum is formed?
amplitude
time (s) frequency (Hz)
T=50 s
T=10 s
T=3 s
a=0.5
a=0.3
a=0.2
period T amplitude a frequency f = 1/T
f = 1/3 = 0.33 Hz
f = 1/10 = 0.1 Hz
f = 1/50 = 0.02 Hz
0.5
0.2
0.3
+
+
=
+
+
=
0.5
0.2 0.3
0.330.02 0.1
f = 0,02 Hzf = 0,1 Hzf = 0,33 Hz
Spectrum
Frequency domainTime domain
Blood pressure signal (270 s)
time (s)
Bloodpressure
(mmHg)
Krevnítlak(mmHg)
Sitting, paced breathing
Standing, paced breathing
Meyer waves (10 s rhythm)
respiration
sequentions of SBP, DBP and RR intervals
time (s)
BP
(mmHg)
Sitting, paced breathing
Standing, paced breathing
RR(ms)
BP
(mmHg)RR(ms)
Spectra of SBP and IBI
SBP
Sitting, paced
breathing
Standing, paced breathing
0,1 Hz
Sympathetic activity
Respiratory frequency
vagal activity
IBI
↓symp. act., ↑vagal act.
↑ symp. act., ↓vagal act.
frequency (Hz)
SBPIBI
Coherence a BRS
coherence: synchronization
between signals (correlation
on particular frequency)
frequency (Hz)
Sitting, paced breathing
Standing, paced breathing
coherence
BRS
(ms/mmHg)
coherence
BRS
(ms/mmHg)
0,1 Hz
baroreflex
Respiratory
frequency
Physiological significance – frequency bands
High frequency (HF)
Intrathoracal pressure changes
influencing blood pressure
Very low frequency
(VLF)
Low frequency
(LF)
Slow hormonal changes, RAS, changes of
vascular tonus
Respiratory sinus arrhythmia
baroreflex
band:
baroreflex
Systolicblood
pressure
0.50.40.30 0.1 0.2
0
0,04
0,08
0,12
0
0,0
0,2
SpectrumSBP(n.u.) Variability source:
respiration
Variability
source:
High frequency (HF)
Intrathoracic pressure changes
influencing blood pressure
Very low frequency
(VLF)
Low frequency
(LF)
Respiratory sinus arrhythmia
baroreflex
band:
baroreflex
Systolicblood
pressure
Heartrate
0.50.40.30 0.1 0.2
0
0,04
0,08
0,12
0
0,0
0,2
SpectrumSBP(n.u.)SpectrumHR(n.u.)
parasympathetic activity
Sympathetic activity
Time lag < 1 s
Time lag > 6 s
Slow oscillations
Fast oscillations
High frequency (HF)Very low frequency
(VLF)
Low frequency
(LF)
band:
Systolicblood
pressure
Heartrate
0.40.30 0.1 0.2
0
0,04
0,08
0,12
0
0,0
0,2
SpectrumSBP(n.u.)SpectrumHR(n.u.)
parasympathetic activity
Sympathetic activity Time lag < 1 s
Time lag > 6 s
Slow oscillations
fast oscillations
baroreflex
Mechanical
transfer
CNS (n. vagus)
Thoracic
pressure
changes
Changes of TPR
(sympathetic
nerves)
???
Variability – for exam
̶ The variability of cardiovascular rhythms provides information about
the regulation of the cardiovascular system
̶ Evaluated parameters (time series):
̶ beat-to-beat heart rate (or RR intervals) - easy to measure (ECG)
̶ systolic pressure sequence (slightly more difficult measurement, Peňáz method)
̶ The main methods of evaluating the variability of a single signal
̶ Variations to standard deviations (sometimes used in the clinic and some devices have them
implemented)
̶ Spectral analysis
̶ The main methods of evaluating the relationship between two signals
̶ Baroreflex sensitivity (definition: change in RR induced by a 1 mmHg change in SBP)
Variability – for exam
̶ Heart rate variability – autonomic nervous system activity analysis
̶ high – good regulation of heart
̶ low – increased cardiovascular risk
̶ Baroreflex sensitivity (BRS)
̶ sufitient (> 4 mmHg) – baroreflex aktivity probably OK
̶ low (< 3 mmHg) – increased cardiovascular risk
in hypertension, heart failure, diabetes, in stress
̶ Predictors of sudden cardiac death: near-zero HRV and BRS values
̶ Spectra HR and SBP
̶ Frequency bands (VLF, LF a HF)
HF (0.15-0,5Hz): parasympathetic activity, respiration
(in HR – respiratory sinus arhytmia)
LF (around 0,1 Hz): sympathetic/parasym. activity, baroreflex
VLF (< 0,03): low changes in vascular system (hormones, TPR, RAS,…)
Non-invasie blood pressure measurement
Auscultatory SBP
(141) Auscultatory DBP
(78)
Pressure in the
arm cuff
Oscilations in the
arm cuff
Oscilometric SBP
(145)
Oscilometric MAP
(106)
Oscilometric DBP
(80)
200
0
Non-invasie blood pressure measurement
- advantages/disadvantages, measurement errors
Good luck in exam
if you focus too much on the
problem,
you may miss the solution