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‫االسراء اية ‪58‬‬
‫‪Dr abdelaziz Hussein, Mnasoura‬‬
‫‪Faculty of Medicine‬‬
By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Member of American Society of Physiology
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
•The veins conduct the blood from the tissues to the heart.
•They contain the main bulk of blood volume (about 60%)
→ capacitance vessels.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Innervation of veins:
1. Vasoconstrictor symp fibers → to veins of skin and
splanchnic area
2. Vasodilator supply (not sure) → result from inhibition of
symp. vasoconstrictor tone or passively by the force of blood.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Function of veins:
1) Drainage of blood from all parts of the body to the
heart.
2) They act as blood reservoirs→ contain about 3 liters
of blood.
3) Venous pump → aids in propelling the blood forward
(towards the heart) and helps to regulate the COP.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
•Definition: it is the pressure inside veins
1. Value at different levels
a) Hydrostatic indifferent point (HIP):
b) Central venous pressure (CVP):
c) Peripheral venous pressure (PVP):
2. Measurement
3. Factors affecting
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
a) Hydrostatic indifferent level or point (HIP):
◊Def,
•It lies 5-7 cm below the diaphragm, at which the venous
pressure (VP) is kept constant, independent of the body
posture.
•-VP below this point ↑es and above this point ↓es.
◊Value:
•10-11 mmHg
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
b) Peripheral venous pressure
(PVP):
◊Def
• It is VP in peripheral veins.
◊Value;
• It depends upon the site of
vein and the gravity.
-Above right atrium→ VP is
subatmospehric but
intrathoracic veins are not
collapsed due to the -ve
intrathoracic pressure.
Dr abdelaziz Hussein, Mnasoura
and vice versa.
Faculty of Medicine
b) Peripheral venous pressure Neck veins→ VP = 0 and veins are
collapsed by atmospheric pressure.
-Inside the skull→ VP = -10 mmHg in
the sagittal sinus i.e. is
subatmospehric, but the dural
sinuses are not collapsed because
they have rigid walls.
.
- At Rt atrium on standing → VP = 0
because the heart pumps all blood
into arteries.
- At feet: VP is 90 mmHg, due to the
distance from the feet to the heart, as
VP is ↑ed by 0.77 mmHg for each cm
Dr abdelaziz Hussein, Mnasoura
of Medicine
below the Rt atrium andFaculty
vice
versa.
c) Central venous pressure
(CVP)
◊Def,
It is VP in big veins at right
atrium (intrathoracic portions of
vena cavae).
◊Values:
It averages 4-6 mmHg in
recumbancy and 2 mmHg on
standing.
It is 2 mmHg during inspiration
and 6 mmHg during expiration.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Measurement of the CVP:
• a) Direct method:
• By a cardiac catheter introduced into the thoracic
large veins→ connected to a saline manometer.
• Patient must be recumbent, and under anaesthesia.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Measurement of the CVP:
b) Indirect method:
• Patient lies in a semisitting position with the head
raised 45° and the degree of filling of the external
jugular vein is noted.
• Normally these veins are only distended at their lower
1/3 indicated by the sternal angle.
• The level of vein distension is ↓ed when the CVP is
↓ed e.g. haemorrhage.
• The level of vein distension is ↑ed when the CVP is
↑ed e.g. CHF
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Measurement of the PVP:
• a) Direct method:
• By a needle connected to a saline or a citrate
manometer, which is introduced in the
anticubital vein, while the arm is in the level
of the heart to avoid the effect of gravity on
VP.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
◊ Measurement of the PVP:
b) Indirect method (hand to heart method):
• The hand is lowered, so the veins on the dorsum
distend, then the hand is slowly raised until the veins
just collapse, this normally occurs at the level of the
sternal angle (level of the Rt atrium).
• They collapse completely at 9 cm above this level.
• If PVP is high as in CHF, the collapse occurs at higher
level.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
a) CVP is ↑ed in
b) CVP is ↓ed in
+ve intrathoracic pressure e.g.
-ve intrathoracic pressure
straining.
during breathing.
Congestive heart failure (CHF). Standing (CVP decreases to 2
mmHg).
Hypervolemia (blood
Hypovolaemia (haemorrhage).
transfusion).
Sympathomimetic due to
Sympatholytic due to
abdelaziz
Hussein, venodilatation
Mnasoura
venoconstriction and ↑Drthe
VR.
and ↓ the VR.
Faculty of Medicine
1) Gravity:
- In recumbent position → gravity has no effect
on circulation.
- On standing,
•PVP is ↑ed in lower limbs to 90 mmHg in feet
veins
•CVP is ↓ed from 4-6 mmHg to 2 mmHg→↓ VR
and the cardiac filling.
•Also the COP and ABP are ↓ed (postural
hypotension) in prolonged standing.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
1) Gravity:
• This effect is compensated by;
a) Venoconstriction → corrects the fall of VP above the
heart and helps VR to prevent stagnation of blood in
veins of the lower limbs.
b) Skeletal ms tone → helps the VR (peripheral hearts)
and ↓es PVP.
c) Capillary tone → helps the VR and ↓es PVP
d) Respiratory movement → ↑es pressure gradient and
helps the VR by ↑ing the +ve intraabdominal pressure
and the -ve intrathoracic pressure→ ↓ PVP.
e) Arterial pulsation → helps the VR.
f) Presence of valves in veins of the lower limbs →
prevents overdistension
ofHussein,
bigMnasoura
veins and regurgitation of
Dr abdelaziz
Faculty of Medicine
blood in veins.
1) Gravity:
If the PVP ↑ due to gravity is not corrected, it leads to:
a) Filtration of fluid from the blood to the tissues →
edema in lower limbs.
b) Distended veins accommodate a large portion of
blood volume →↓ the VR, COP and ABP (postural
hypotension).
c) Varicose veins occur when the valves are damaged
and unable to divide blood column into segments.
It is common in the veins of legs and scrotum.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
2) Rate of blood inflow into veins:
-VD of arterioles without capillary dilatation
→↑inflow into veins →↑es CVP and PVP.
-If the capillaries are dilated→↓ the blood inflow
to veins→ ↓ CVP and PVP.
3) Rate of blood outflow from veins:
If the outflow is less than the inflow, the VR is ↓ed and
consequently the CVP and PVP are ↑ed e.g.:
Rt side heart failure or local venous obstruction.
↑ed +ve intrathoracic pressure (straining).
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
4) Venomotor tone:
• Tonic contraction in veins, maintains normal VP.
• Venous tone is ↑ed reflexly in haemorrhage to
maintain VP.
• ↑ venous tone by symp. stimulation or
noradrenaline→↑ CVP and PVP
• ↓ venous tone by α- adrenergic blockers→↓ CVP and
PVP.
5) Blood volume:
- CVP and PVP are ↑ed in hypervolemia (blood
transfusion).
- CVP and PVP are ↓ed in hypovolaemia (haemorrhage).
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
6) Muscular exercise:
- Contracting skeletal ms press on veins, ↑ing the VP.
- Arteriolar VD of active ms, ↑ing the VP.
7) Respiratory movement:
- Inspiration:
The diaphragm descends, the VP in abdominal veins is
↑ed and the VP in intrathoracic veins is ↓ed →↑ venous
return → ↓VP to the normal level.
- Expiration:
The opposite effect occurs.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
7) Respiratory movement:
- Forced inspiration with closed glottis (Muller's
experiment)
The -ve intrathoracic pressure is ↑ed to -30 mmHg →
marked ↑ in the VR and ↓VP.
- Forced expiration with closed glottis (Valsalva's
experiment).
The VP in intrathoracic veins is ↑ed (+40 to +50 mmHg)
→stops the VR in the extrathoracic veins with bulging of
the neck veins and VP is much ↑ed.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
8) Acceleration force:
• Constant speed has no effect on the circulation.
• Anteroposterior acceleration has no effect on the
circulation.
• Acceleration in the direction of longitudinal axis
of the body → blacking out or reddening out.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
8) Acceleration force:
a) Blacking out:
-When the head is upward, the blood is drained to the
lower limbs→ no blood goes to the head and temporary
blindness (blackout) occurs i.e. blood is drained from the
retinal vessels of the eyes and loss of consciousness
(fainting) occurs due to cerebral ischemia.
-It occurs in:
• Jet plane pilots (during ascent).
• Astronauts.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
8) Acceleration force:
b) Reddening out:
- When the head is downward, the blood is
shifted from the lower limbs to the head →
marked congestion of the eyes occurs and the
fields of vision become suddenly bright red with
temporary loss of vision (reddening out).
-It occurs in Pilots during descent.
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
• Veins show no pulsations→ no pulse
pressure (no pulse waves).
• However veins show pulsations in marked
arteriolar VD with conduction of pulse
pressure into the corresponding veins.
• Jugular veins pulsation→ transmitted from
the Rt atrium to the jugular vein (jugular
venous pulse).
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine
THANKS
Dr abdelaziz Hussein, Mnasoura
Faculty of Medicine