Non-invasive methods of blood pressure measurement



Arterial blood pressure curve
SBP
Systolic blood pressure
area above MAP
area under MAP
DBP
Diastolic blood pressure
MAP
Mean arterial pressure
inter-beat interval
Mean arterial pressure (MAP) : mean value of blood pressure in the inter-beat interval (IBI)
•area under MAP = area above MAP
•approximation: MAP » DBP + 1/3 PP (PP = SBP – DBP)
•
PP
pulse pressure
Blood pressure (BP):  pressure on the vascular wall (a continual variable)
Definition:
SBP  - maximum of BP in the inter-beat interval
DBP – minimum of BP in the inter-beat interval
Attention: Values of SBP and DBP varies in different parts of cardiovascular system!

MAP is a function of cardiac output and total peripheral resistance
•SBP is given mainly by CO
•DBP is given mainly by TPR
Mean arterial pressure (MAP)
Total peripheral resistance
(TPR)
Heart rate
(HR)
Stroke volume
(SV)
 =
*
*
Cardiac output
(CO)

Methods of the arterial blood pressure measurement
24-hour blood pressure monitoring
Palpatory
(sphygmomanometer)
Auscultatory
(sphygmomanometer,
stethoscope)
Oscillometric
Photoplethysmographic
(volume-clamp method, Peňáz)

Laminar / turbulent flow, Korotkoff sounds
Reynolds number Re: predicts the transition from laminar to turbulent flow
v: velocity of blood flow
S: area of vascular lumen (p.r2)
r: density of blood
h: viscosity of blood
     (lower in anemias)
S1 < S2 , v1≈ v2  → Re1 < Re2 → turbulent flow
laminar flow Re < 2000
turbulent flow Re > 3000
r1
r2
cuff
a. brachialis
laminar flow
turbulent flow
Re1
Re2
v1
v2
right behind the narrowing of the artery:

Korotkoff sounds
(auscultatory method)
Continually measured BP
Pressure in the cuff
Pressure oscillations in the cuff
(Oscillometric method)
SBP
DBP
SBP
MAP
DBP
Blood flow in the artery
Principles of blood pressure measurement

•Patient is sitting and resting for a few minutes before the measurement.
•Only validated measuring equipment must be used.
•At least two measurements have to be performer, in the course of 1–2 minutes.
•Use cuff of standard size (12–13 cm width and 35 cm length); smaller and bigger cuffs must however
be available for patients with smaller or bigger arms, respectively.
•Cuff must always be at the level of heart of examined person.
•Pressure in the cuff must be decreased slowly: 2mmHg/s.
During BP measurement, following rules must be observed:

24-hour blood pressure monitoring
BP decrease during night: 10 - 15%
8
9
11
10
12
13
14
16
15
17
18
19
21
20
22
23
24
2
1
3
4
5
7
6
120
140
100
80
60
[mmHg]
SBP
DBP
Heart rate
waking
sleeping
Blood pressure
hours

Photoplethysmography
Control system
Constant finger volume
pressure
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.
cuff
SBP
DBP

Variability of circulatory parameters
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
0.33
0.02
0.1
f = 0,02 Hz
f = 0,1 Hz
f = 0,33 Hz
Spectrum
Frequency domain
Time domain

Baroreflex
•Inotropic
•Chronotropic
•Dromotropic
•Batmotropic
Aferent pathway
Parasympathetic pathway
Sympathetic pathway
BP=HR x SV x R
R
HR
BP=HR x SV x R

Valsalva maneuver