(XI.) Digital model of aortic function
(XVI.) Blood flow in veins
Physiology – practicals
Dep. of Physiology, Fac. of Medicine, MU 2018 © Michal Pásek
Definitions of key words and symbols
R
Pv arterial systemvenous 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 per 1 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=
Va
Pa- Pv
Va  SV
PPa  SV
Ca
PPa
Pa,m
Pa
arterial system
Mean and pulse arterial pressure (Pa,m, PPa)
Model of aortic function
R
Pa
Pv
Fi
Ca
venous system
Va
HEART
SV, HR
Fo
Fi [ml/s]
t [s] t
Va
Ca
(Pa – Pv)
R
Fo =
Va = (Fi - Fo)t
Pa =
t = t+t
Calculation of Pa
Pa = Pa +Pa
arterial system
Blood flow through aortic valve
• Physiological conditions: SV=70 ml, HR=75/min, R=1 mmHg·s/l, C=1.2 ml/mmHg
• Changes of SV– increase: hyperhydration – rapid administration of i.v. infusion, intake
of large amount of water in short time; decrease: dehydration, loss of blood
(haemorrhage)
• Changes of HR – increase: activation of sympathetic nervous system – stress, physical
activity; decrease: increase of vagal tone, adaptation of heart in sportsmen (athletic
heart)
• Changes of R – increase: predominance of vasoconstriction – e.g. in cold
environment; decrease: predominance of vasodilation – sauna, distributive shock
(anaphylaxis, adrenal crisis)
• Changes of C – higher values: predominance of elastic fibers – in children and young
people; lower values: elastic fibers degeneration – in elderly people, atherosclerosis
(leads to isolated systolic hypertension – systolic blood pressure is higher than normal,
diastolic blood pressure is predominantly at normal level)
Modeled situations
• Reaction to physical activity: increase of SV to 100 ml, increase of HR to 150/min,
decrease of R to 0.6 mmHg·s/l
• Simulation of hypertension: increase of SV and HR by 20% – essential hypertension;
increase of R by 40% at physiological resting values of SV and HR – fully developed
hypertension
• Simulation of cardiac arrest: after stabilization of values of blood pressure, decrease
of SV to 0 ml at different values of HR, C and R
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
Atlas Of Physiology, Silbernagl & Despopoulos, Georg Thieme Verlag 2003