صدق الله العظيم الاسراء 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

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

DefinitionDefinition: it is the pressure inside veins c) Peripheral venous pressure (PVP): b) Central venous pressure (CVP): a) Hydrostatic indifferent point (HIP): 3. Factors affecting 1.Value at different levels 2. Measurement 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: 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. and vice versa. Dr abdelaziz Hussein, Mnasoura Faculty of Medicine

b) Peripheral venous pressure 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 - 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 below the Rt atrium and vice versa. Dr abdelaziz Hussein, Mnasoura Faculty of Medicine

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:◊ Measurement of the CVP: a) Direct method: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:◊ Measurement of the CVP: b) Indirect method: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

◊ Measurement of the PVP:◊ Measurement of the PVP: a) Direct method: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:◊ Measurement of the PVP: b) Indirect method (hand to heart method):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

a) CVP is ↑ed inb) CVP is ↓ed in +ve intrathoracic pressure e.g. straining. -ve intrathoracic pressure during breathing. Congestive heart failure (CHF). Standing (CVP decreases to 2 mmHg). Hypervolemia (blood transfusion). Hypovolaemia (haemorrhage). Sympathomimetic due to venoconstriction and ↑ the VR. Sympatholytic due to venodilatation and ↓ the VR. Dr abdelaziz Hussein, Mnasoura 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

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 of big veins and regurgitation of blood in veins. Dr abdelaziz Hussein, Mnasoura Faculty of Medicine

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: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: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: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: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:6) Muscular exercise: - Contracting skeletal ms press on veins, ↑ing the VP. - Arteriolar VD of active ms, ↑ing the VP. 7) Respiratory movement: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: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: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:8) Acceleration force: a) Blacking out: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:8) Acceleration force: b) Reddening out: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