Circulatory Reactions
Assoc. Prof. MUDr. Markéta Bébarová, Ph.D.
Department of Physiology, Faculty of Medicine, Masaryk University
This presentation includes only the most
important terms and facts. Its content by
itself is not a sufficient source of
information required to pass the
Physiology exam.
Circulatory Reactions
• Regulation of circulation – a complex system
of feed backs which are continually in a
dynamic balance.
• Individual parameters (BP, blood flow through
organs, etc.) regulated by neural and humoral
mechanisms, both systemic and local – their
quantitative ratio changes dynamically.
• Physiological stimuli (a change of the body
position, exertion, etc.) induce rather standard
reaction in a healthy person (integration of many
particular reflex changes).
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
→ ↑ BP in all vessels below the heart level
→ ↓ BP in all vessels above the heart level
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
veins – a sudden closure of valves due to ↑ BP
(prevention of backward flow; persists only shortly, valves
open immediately again to keep a continual blood flow) + ↑
venous pressure due to continuous blood inflow
from arteries → total filling of veins considerably ↑,
blood flow sustained → dilation of veins
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
→ ↑ BP in all vessels below the heart level
↓ BP + direct action of gravity – inhibition of
baroreceptors → ↓ activity of vagus nerve and ↑
activity of sympathetic system → ↑ HR + ↑ SV + ↑ PR
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
veins – ↓ volume (in chest veins by 20%) → ↓ central
venous pressure → ↓ venous return → ↓ stroke
volume (from 70 to  45 ml) → ↓ BP
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
→ ↑ BP in all vessels below the heart level
→ ↓ BP in all vessels above the heart level
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
a) acute reaction – passes within 1 min
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
Tilt-up test
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
b) subsequently:
↑ capillary filtration → ↓ plasma volume (within
40 min; by 10 %)
↑ level of ADH + ↑ activity of RAS + reflex
vasoconstriction in kidneys → ↓ excretion of salt
and water in kidneys
a) acute reaction – passes within 1 min
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
The above described complex reaction provides
maintenance of BP and, thus, sufficient perfusion of
brain. Despite, the brain blood flow ↓ even by 20%.
The brain blood flow is ↓ due to a reflex vasoconstriction
induced by ↓ pCO2 (↑ ventilation during the orthostatic
reaction) and sympathetic vasoconstrictive activity.
• orthostatic hypotension
• a change of the body position from lying to standing / from
standing to lying
• orthostatic reaction – due to gravity:
Circulatory Reactions
• Valsalva Maneuver
• forced expiration over closed or narrowed glottis
(cough, defecation, lifting of heavy objects, etc.)
Circulatory Reactions
• Valsalva Maneuver
• start of maneuver→ ↑ intrathoracic pressure:
→ ↑ BP (the intrathoracic pressure
contributes to the aortal pressure)
→ compression of chest vessels → ↓
venous return → ↓ stroke volume (FrankStarling)
→ ↓ pulse and mean BP →
inhibition of baroreceptors → reflex
tachycardia and vasoconstriction → mean
BP at the level before maneuver
• forced expiration over closed or narrowed glottis
(cough, defecation, lifting of heavy objects, etc.)
Circulatory Reactions
• Valsalva Maneuver
• end of maneuver → ↓ intrathoracic pressure:
→ ↓ BP
→ compression of chest vessels released
→ ↑ venous return → ↑ stroke volume
(Frank-Starling) → ↑ pulse and mean BP
→ stimulation of baroreceptors → fast
reflex bradycardia and gradual
vasodilation ( ↓ peripheral resistance) →
normalizing of BP
• forced expiration over closed or narrowed glottis
(cough, defecation, lifting of heavy objects, etc.)
Circulatory Reactions
• Valsalva Maneuver
• forced expiration over closed or narrowed glottis
(cough, defecation, lifting of heavy objects, etc.)
Circulatory Reactions
• Diving Reflex
• well developed in diving animals (duck, whale, …)
• diving – excitation of receptors of n. trigeminus
(namely around eyes and nose) by cold water:
→ apnoe
→ bradycardia
→ peripheral vasoconstriction
 conservation of limited O2 reserves for function
of brain and heart → prolongation of diving period
(whale 2 hours, seal 70 min; they have also higher O2 reserves
in haemoglobin and myoglobin, higher tolerance to hypoxia)
Circulatory Reactions
• Reaction on loss of blood
• bleeding → hypovolemia →  venous return →  SV
→  CO →  BP (even shock)
• The resulting state is dependent on the amount of lost
blood and on the velocity of loss of blood!
Circulatory Reactions
• Reaction on loss of blood – sudden
• loss of 10 % of the blood volume ( in a blood donor):
• → slightly and transiently  BP
• loss of 20-30 % of the blood volume :
• →  mean BP to about 60-80 mmHg
• loss of 30-40 % of the blood volume :
• →  mean BP to about 50-67.5 mmHg → shock with brain
and heart ischemia and with anuria, may shift into an
irreversible state
• bleeding → hypovolemia →  venous return →  SV
→  CO →  BP (even shock)
Circulatory Reactions
• Reaction on loss of blood – sudden
time (hod)
mean BP
(mmHg)
97.5
48.5
0 642
according to prof. N. Honzíková
(Comments to the physiological
lectures, 1992; in Czech)
• bleeding → hypovolemia →  venous return →  SV
→  CO →  BP (even shock)
Circulatory Reactions
• Reaction on loss of blood – sudden
• Instantaneous reaction (seconds till minutes)
• Reaction within 5 - 60 min
• Reaction within hours till days
• bleeding → hypovolemia →  venous return →  SV
→  CO →  BP (even shock)
Circulatory Reactions
• Reaction on loss of blood – sudden
•  stimulation of baroreceptors →  activity of
parasympathicus and  activity of sympathicus →  HR +
 CO +  PR →  BP
• limited tissue perfusion due to  PR → metabolic acidosis
• Instantaneous reaction on ↓ BP (seconds till minutes)
• limited renal perfusion due to  PR (v. eff.  v. aff.) →  FF
but, anyway,  urine formation → retention of Na+ in body
(prospectively also of waste nitrogen products – uremia – a risk of
renal tubule damage)
• RAS activation (angiotensine II, aldosteron) +  secretion
of ADH, thirst → vasoconstriction + retention of salt and
water in body →  PR +  volume of body fluids →  BP
Circulatory Reactions
• Reaction on loss of blood – sudden
•  capillary hydrostatic pressure → oncotic pressure >
hydrostatic pressure → reabsorption of fluids from the
interstitial tissue into cappilaries →  volume of intravasal
fluid even by 500 ml in adults („internal transfusion“) → 
BP +  haematocrit +  concentration of plasmatic proteins
• Reaction on  BP within 5 - 60 min
• The so far described reactions provide the sufficient blood
flow through brain and myocardium.
Circulatory Reactions
• Reaction on loss of blood – sudden
• restoration of content of salt and water in the
organism (↓ GFR due to sympathetic constriction of v.
aff., RAS, ADH, thirst)
• restoration of plasmatic proteins including albumin
(liver)
• stimulation of erythropoiesis in the bone marrow
(erythropoietin)
• Reaction on  BP within hours till days (even weeks)
Circulatory Reactions
• Reaction on loss of blood – sudden
• bleeding → hypovolemia →  venous return →  SV
→  CO →  BP (even shock)
time (hod)
mean BP
(mmHg)
97.5
48.5
0 642
according to prof. N. Honzíková
(Comments to the physiological
lectures, 1992; in Czech)
Circulatory Reactions
• Reaction on loss of blood – sudden
• irreversible state (shock) may be caused by:
• primary heart failure:  BP → insufficient perfusion of
myocardium →  contractility →  CO →  BP
(positive feed back, circulus vitiosus)
• serious tissue hypoxia: accumulation of metabolites
→ metabolic acidosis +  permeability of capillaries
→ vasodilation → loss of fluid into the interstitial
tissue →  BP (positive feed back)