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 feedbacks, dynamic balance.
• Individual parameters regulated by neural
and humoral mechanisms, both systemic and
local – their quantitative ratio changes
dynamically.
• Physiological stimuli in a healthy person rather
standard reaction.
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
• a change of the body position from lying to standing / from
standing to lying
• due to gravity:
 ↑ BP in all vessels below the heart level
 ↓ BP in all vessels above the heart level
sudden closure of venous valves due to ↑ BP + ↑ venous
pressure due to continuous blood inflow from arteries 
total filling of veins considerably ↑, blood flow sustained 
dilation of veins
↓ venous return  ↓ stroke volume  ↓ BP (also due to the
direct effect of gravity)  inhibition of baroreceptors (baroreflex)
orthostatic hypotension
Circulatory Reactions
• Orthostatic / Clinostatic Reaction
b) subsequently:
↑ capillary filtration  ↓ plasma volume
↑ 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:
(tilt-up test)
Circulatory Reactions
• Valsalva Maneuver
• forced expiration over closed or narrowed glottis
(cough, defecation, lifting of heavy objects, etc.)
Ganong´s Review of Medical Physiology, 23rd edition.
Circulatory Reactions
• Valsalva Maneuver
• start of maneuver ↑ intrathoracic pressure:
 ↑ BP
 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
Circulatory Reactions
• Valsalva Maneuver
• end of maneuver  ↓ intrathoracic pressure:
 opposite changes
Circulatory Reactions
• Respiratory Sinus Arrhytmia
• rhythmic changes of heart rate related to breathing
• several mechanisms discussed, namely:
- mechanoreceptors in lungs
- Bainbridge reflex
- baroreflex
Circulatory Reactions
• Respiratory Sinus Arrhytmia
• rhythmic changes of heart rate related to breathing
• inspiration  ↑ HR, expiration  ↓ HR
• inspiration
 ↓ intrathoracic pressure:
 ↑ lung volume (stretch rec.)  ↑ HR
↑ venous return
Bainbridge reflex
(distension of atria)
 ↑ HR
↑ stroke volume  ↑ BP 
stimulation of baroreceptors
 ↓ HR
(during expiration)
Circulatory Reactions
• Diving Reflex
• diving – excitation of receptors of n. trigeminus by
cold water:
 apnoe
 bradycardia
 peripheral vasoconstriction
 conservation of limited O2 reserves for function
of brain and heart  prolongation of diving period
Circulatory Reactions
• Reaction on loss of blood
• 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
• 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, may shift
into an irreversible state
• 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
• 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
• 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!)
• RAS activation (angiotensine II, aldosteron) +  secretion
of ADH, thirst
Circulatory Reactions
• Reaction on loss of blood – sudden
•  capillary hydrostatic pressure  oncotic pressure >
hydrostatic pressure  reabsorption of fluids from the
interstitial tissue into capillaries   volume of intravasal
fluid („internal transfusion“); consequences!
• 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
• restoration of plasmatic proteins including albumin
• stimulation of erythropoiesis in the bone marrow
• Reaction on  BP within hours till days (even weeks)
Circulatory Reactions
• Reaction on loss of blood – sudden
• irreversible state (shock) may be caused by:
• primary heart failure
• serious tissue hypoxia
• in both cases - circulus vitiosus!