Circulatory Reactions
Assoc. Prof. MUDr. Markéta Bébarová, Ph.D.
Department of Physiology, Faculty of Medicine, Masaryk University
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
-» i 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
i venous return -> J, stroke volume -> I BP (also due to the
direct effect of gravity) -> inhibition of baroreceptors
orthostatic hypotension
Circulatory Reactions
Orthostatic / Clinostatic Reaction
a change of the body position from lying to standing / from standing to lying
orthostatic reaction - due to gravity:
a) acute reaction - passes within 1 min
(tilt-up test)
b) subsequently:
t capillary filtration    j, plasma volume
t level of ADH + f activity of RAS + reflex vasoconstriction in kidneys -»I excretion of salt and water in kidneys
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 maneuvers t intrathoracic pressure:
-> t BP
-> compression of chest vessels -> J, venous return -» j stroke volume (Frank-Starling) -> I 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
z
Circulatory Reactions
Diving Reflex
diving - excitation of receptors of n. trigeminus by cold water:
-» apnoe
-> bradycardia
-> peripheral vasoconstriction
~ conservation of limited 02 reserves for function of brain and heart -» prolongation of diving period
Circulatory Reactions
• Reaction on loss of blood
• bleeding -» hypovolemia -» I venous return -» I SV -> I CO -> I BP (even shock)
mean BP (mmHg) !
97.5
48.5
according to prof. N. Honzíkova (Comments to the physiological lectures, 1992; in Czech)
\
\
\
0
4
6  time (hod)
Circulatory Reactions
Reaction on loss of blood - sudden
The resulting state is dependent on the amount of lost blood and on the velocity of loss of blood!
loss of 10 % of the blood volume (~ in a blood donor): ->• slightly and transiently I BP
loss of 20-30 % of the blood volume : ->• I mean BP to about 60-80 mmHg
loss of 30-40 % of the blood volume :
->• i mean BP to about 50-67.5 mmHg -»• shock, may shift into an irreversible state
Circulatory Reactions
Reaction on loss of blood - sudden
bleeding
^co'
-> hypovolemia -> i venous return -> i
-> I BP (even shock)
Instantaneous reaction (seconds till minutes) Reaction within 5-60 min Reaction within hours till days
irculatory Reactions
• Reaction on loss of blood - sudden
• Instantaneous reaction on j BP (seconds tin minutes)
• i stimulation of baroreceptors
• limited tissue perfusion due to t PR -» metabolic acidosis
• limited renal perfusion due to t PR (v. eff. >v. aff.)^t FF but, anyway, -i- urine formation -» retention of Na+ in body
(prospectively also of waste nitrogen products - uremia!)
• RAS activation (angiotensine II, aldosteron) + t secretion of ADH, thirst
Circulatory Reactions
Reaction on loss of blood - sudden
Reaction on I BP within 5-60 min
I capillary hydrostatic pressure -> oncotic pressure > hydrostatic pressure -» reabsorption of fluids from the interstitial tissue into capillaries -» t volume of intravasal fluid („internal transfusion"); consequences!
The so far described reactions provide the sufficient blood flow through brain and myocardium.
Circulatory Reactions
• Reaction on loss of blood - sudden
• Reaction on I BP within hours till days (even weeks)
• restoration of content of salt and water in the organism
• restoration of plasmatic proteins including albumin
• stimulation of erythropoiesis in the bone marrow
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\