(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.

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•
•
•
•
•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

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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
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•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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