I. Blood pressure
& plethysmography
Blood-vessel system
➢ Arteries – aorta, soften
pulse waves, highest
pressure
➢ Arterioles – resistance
vessels, regulation of
blood flow in body parts
(→plethysmography)
➢ Capillaries - exchange
➢ Veins – holds up to 75% of
blood, almost zero
pressure, valves
➢ Arteries – aorta, soften
pulse wave, highest
pressure
➢ Arterioles – resistance
vessels, regulation of
blood flow in body parts
(→plethysmography)
➢ Capillaries - exchange
➢ Veins – holds up to 75% of
blood, almost zero
pressure, valves
Blood pressure
= is the pressure exerted by circulating blood
upon the walls of blood vessels
➢ Systole of left ventricle → 70 – 100 ml of blood goes
to aorta, aorta have to stretch and expand
➢ Pulse wave of stretching goes through the
cardiovascular system
➢ Tension of arteries sends blood further
➢ Systolic/diastolic (125-140)/(80-90) mmHg, Torr
➢ systolic – high pressure wave due to contraction
of the heart
➢ diastolic – low pressure wave due to tension of
the aorta and arteries return to their normal
diameter
➢ Dicrotic notch – aortic valve closure
Systolic pressure
Diastolic pressure
http://www.med.muni.cz/patfyz/practic/prezentace/tk_MM.pdf
Blood pressure
➢ BP = cardiac output x peripheral resistance
➢ Blood pressure can be modulated:
➢Elasticity of arteries and resistance of blood vessels
(radius of the vessels)
➢Smoothness of blood vessel walls (fatty deposits etc.),
blood volume, viscosity of blood
➢ age, sex, diesases, drugs, body position,…
Blood pressure regulation
• Accute regulation – baroreceptor reflex
Drop of pressure: ↓ artery wall tension, ↓ activity
of baroreceptors,↑ activity of sympaticus, ↑
heart frequency and contractility, peripheral
vazoconstriction (e.g. in position change), blood
pressure increase
• Long-term (chronic) regulation
– Volume of urine produced by kidneys – increased pressure: ↑ filtration pressure in
kidneys, ↑ urine volume, ↓ blood volume, decreased BP
– ADH, aldosteron, renin-angiotenzin – increased back resorption of water in kidneys
↑ BP
• Local control of BP
– Autoregulation – force onto vessel wall induces vasocontriction, vasodilatators
promote dilatation, methabolic factors like CO2, local hormones; e.g. inflammation
→ histamin and bradykinin → vasodilatation; Serotonin, Vasopresin → constriction
BP increases with age
Meassurement of BP:
➢ Diastolic pressure – condition and elasticity of
vessels
➢ Systolic pressure – condition of heart
➢ Invasive methods:
S. Hales - 1733 – lenght of blood spray
➢ Non invasive methods:
auscultatory - listening of blood in vessels
➢ Sphygmomanometers (sphygmos = pulse) –
mercury manometers, digital manometers,
aneroid m. etc.
How to use a manometer:
➢ A cuff is fitted smoothly and snugly, then inflated manually
by repeatedly squeezing a rubber bulb until the artery is
completely occluded.
➢ Listening with the stethoscope to the brachial artery at the
elbow, the examiner slowly releases the pressure in the cuff.
➢ When blood just starts to flow in the artery, the turbulent
flow creates a "whooshing" or pounding (first Korotkoff
sound). The pressure at which this sound is first heard is the
systolic blood pressure. The cuff pressure is further released
until no sound can be heard (fifth Korotkoff sound), at the
diastolic arterial pressure.
Pressure in
cuff
Pressure in a.
brachialis
Artery – open
- closed
Sounds
Pressure: systolic diastolic
Pressure
(Torr)
Principle of manometer:
Laminary vs. turbulent flow
Korotkoff sounds
= blood turbulences
Experiment n.1
Determination of blood pressure and
comparisson between several types of
medical blood pressure gauges
➢ mercury manometer vs. digital manometer
Plethysmography
➢ Determination of optical parameters
of translucent tissue, depends of blood
volume in capillaries under the skin,
modulated by arterioles → reflexive
changes in arterial radius (two layers of
smooth muscle in arterioles wall)
➢ Meassurement on middle finger or
index finger, detecting amount of light
passing through a finger (contraction of
arterioles → smaller radius → lower
amount of light)
➢ Pulse wave in arterioles: dicrotic notch
LED diode
Photodetector
Vasomotoric reactions
Various chemicals or physical stimuli causes reflexive
reactions:
➢ Vasoconstriction
Contraction of smooth muscle cells
Sympaticus; adrenalin, vasopresine,…
➢ Narrow vessel- lower wave in graph
➢ Vasodilatation
relaxation of smooth muscle cells
Parasympaticus; acetylcholin, metabolites, NO, …
➢ Dilated vessel – higher wave in graph
Experiment n.2
1. Pulse wave
2. Change of body position (sitting - standing)
3. Reactive hyperemia (brachial artery strangulation)
4. Valsalva experiment - increase in intrathoracic
pressure
5. Effect of temperature (cold - heat)
Finger heated
Artery strangulation and reperfusion
Valsalva experiment