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
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
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 has to 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 as they return to their
normal diameter
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 has 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 as they 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 by:
➢Heart activity
➢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,
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
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 baloon 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 systolic
echoes (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, at the diastolic arterial pressure.
Principle of manometer:
Laminary vs. turbulent flow
Korotkoff sounds = blood
turbulenceshttps://www.youtube.com/watch?v=KnYfreaRQe4
https://www.youtube.com/watch?v=9SNiwK8SydU
Experiment n.1
Determination of blood pressure and comparisson between
several types of medical blood pressure gauges
➢ mercury manometer vs. digital manometer
Table of Results
INITIALS Blood pressure
Stethoscope
Blood pressure
Digital
/ /
Means / /
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
Vasomotorics controls perfusion
➢ In rest, different organs need
to be perfused compared to
exercise
Vasomotoric reactions
Various chemicals or physical stimuli causes reflexive reactions:
➢ Vasoconstriction
Constriction of smooth muscle cells
Sympatic nerves; adrenalin in gut, vasopresine,…
Parasympatic nerves in muscles
➢ Narrow vessel- lower wave in graph
➢ Vasodilatation
relaxation of smooth muscle cells
Parasympatic nerves; acetylcholin in gut, metabolites, NO, …
Sympatic nerves in muscles
➢ Dilated vessel – higher wave in graph
Vasomotoric reactions
Local blood flow control
Autoregulation - more blood pressure in the vessel
wall causes active constriction - this is a reflex of
blood spilling over due to gravity. They maintain
the same blood flow whether the limb is up or
down.
Release of dilators, metabolic factors, accumulated
metabolites dilate blood vessels (CO2)
Local hormones; e.g. inflammation → release of
histamine and bradykinin → vasodilation
Temperature - higher temperature has a
vasodilating effect
Experiment n.2
1. Pulse wave
2. Change of body position (sitting - standing)
3. Reactive hyperaemia (reaction to brachial artery strangulation)
4. Valsalva experiment - increase in intrathoracic pressure and peripheral
hyperperfusion
5. Effect of temperature (cold - heat)
Finger heated
Artery strangulation (ischemia) and
reperfusion – accumulated metabolites
Valsalva experiment – forceful attempt of exhalation against a closed airway