(XI.) Digital model of aortic function
(XVI.) Blood flow in veins
Physiology I – practicals
Dep. of Physiology, Fac. of Medicine, MU 2015 © Michal Pásek

Definitions of key words and symbols
R
Pv
arterial system
venous system
HEART
SV, HR
Pa
Va
Ca
Stroke volume  (SV) – volume of blood ejected from the left ventricle to the aorta during one
contraction
Heart rate (HR) – number of heart contractions per1 minute
Compliance of aorta (Ca) – ability of aorta to change its volume according to changes of blood
pressure
Peripheral vascular resistance (R) – resistance of small arteries (mainly arterioles and
capillaries)
Q
Mean blood flow through circulatory system
Aortic volume
Blood pressure in arterial system
Blood pressure in venous system

Arterial blood pressure in case of changing circulatory parameters and cardiac output
R
Pa
Pv
Q
venous system
Va
HEART
SV, HR
Ca
Pa,m - Pv,m = Q · R
Pa,m = SV · HR · R + Pv,m
Pa,m @ SV · HR · R
Q =
R
Ca=
DVa
Pa- Pv
DVa @ SV
DPa @
SV
Ca
DP
Pa,m
DPa
arterial system

Stačí znát pouze rovnice v červeném pozadí a studenti si mohou sami (bez modelu) dovodit změny P[a
]při změnách SV, TF, R nebo C!
Rovnice pro P[a,stř] v červeném pozadí ukazuje, že při zvýšení SV, TF nebo R dochází ke zvýšení
středního arteriálního tlaku a naopak.
Rovnice pro P[a ] v červeném pozadí ukazuje, že zvýšením SV nebo snížením C[a] dochází k nárůstu
pulsového tlaku a naopak.
Změny R tedy ovlivní P[a,stř, ]avšak P[a] zůstane nezměněn.

Model of aortic function
R
Pa
Pv
Fi
Ca
venous system
Va
HEART
SV, HR
Fo
Fi [ml/s]
t [s]
D t
   DVa
 Ca
(Pa – Pv)
     R
Fo =
DVa = (Fi - Fo)×Dt
DPa  =
t = t+Dt
Calculation of Pa
Pa = Pa +DPa
arterial system
Blood flow through aortic valve

Postupně (pro daný časový krok t) se počítá F[i], F[o], V[a],[ ]P[a],[ ]P[a  ]a t. Tento postup
se stále opakuje, až do dosažení času t.

SV – increase: hyperhydration – rapid administration of i.v. infusion, intake of large amount of
water in short time; decrease: dehydration, loss of blood (haemorrhage)
HR – increase: activation of sympathetic nervous system – stress, physical activity; decrease:
increase of vague tonus, adaptation of heart in sportsmen (athletic heart)
R – increase: predominance of vasoconstriction – e.g. in cold environment; decrease: predominance
of vasodilation – sauna, distributive shock (anaphylaxis, adrenal crisis)
C – higher values: in children, young people; lower values: in elderly people, atherosclerosis,
elastic fibers degeneration – isolated systolic hypertension (systolic blood pressure is higher
than normal, diastolic blood pressure is predominantly at normal level)
Modeled situations

Color Atlas Of Physiology 5th Ed (A Despopoulos Et Al, Thieme 2003)_Page_218
1.Pressure gradient between venous system and right atrium („a force acting from behind“ – vis a
tergo)
2. Suction effect of systole          („a force acting from in front“ – vis a fronte)
3. Skeletal muscle contractions – muscle pump
4. Suction effect of inspirium – increased intraabdominal pressure and decreased intrathoracic
pressure
5. Venous valves
1
2
4
3
5
Mechanisms of venous return

Picture sources
• Slide 7 – Atlas Of Physiology, Silbernagl & Despopoulos, Georg Thieme Verlag 2003
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