Archive for the ‘ L2-CVP & JVP ’ Category

L2- Central Venous Pressure (CVP) Jugular Venous Pulse (JVP)

Central Venous Pressure (CVP) & Jugular Venous Pulse (JVP)

You Know

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•Venules & Veins are the reservoirs of blood (capacitance vessels of the body)

•Change in venous blood volume & venous pressure can alter CO by affecting right atrial & ventricular preload

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Veins

•Veins are more distensible than arteries (thinner muscle layer)

•Many veins have one way valves directing blood towards heart

•The venous blood flow from lower part of the body to abdominal veins is aided by contraction of lower limbs muscles (skeletal muscle pump)

•The venous flow from big abdominal veins to thoracic veins (then to heart) is aided by inspiration (which increases intrathoracic negativity & compress abdominal veins)

Venous Pressure

•Venous Pressure generally refers to the average pressure within venous compartment of circulation

•The mean venous pressure is ~2mm Hg compared to a mean arterial pressure of ~ 90-100 mm Hg

•This low pressure is due to:

-drop of pressure from arterioles to capillaries

-The highly compliant character of veins (can accommodate large volume without great change in pressure)

Normal values of Venous Pressure at Different Body Points

Hydrostatic Indifferent Point (HIP):

a point about 5-7 cm below diaphragm where venous pressure is ~ 10 mm Hg either on standing or recumbence.

Normal Values of VP

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1) Central Venous Pressure (CVP)

•CVP: is the pressure in the thoracic vena cava near the right atrium

•It is important because it determines the filling pressure of right ventricle & consequently the ventricular stroke volume; thus reflecting cardiac function

•Normally, ranges from 2mm Hg (standing) to 4.6 mm Hg (recumbent)

Factors Affecting CVP

•Cardiac output

•Respiratory Activity

•Contraction of Skeletal muscles (esp. leg & abdominal muscles).

•Sympathetic Vasoconstrictor tone

•Gravity

– All these affect CVP by either changing venous blood volume or venous compliance

-Thus, CVP α ∆Vv/ ∆Cv

CVP is increased by:

1. A decrease in CO:

e.g. ventricular failure

will lead to stagnation of blood in venous circulation (↑venous volume)

2. An increase in total blood volume:

e.g. renal failure leading to activation of ANG-Renin-Aldosterone

3. Venous constriction:

either caused by sympathetic activity or circulating vasoconstrictors (adrenaline or ANG II)

4. A shift of blood into thoracic veins:

e.g. change of position from standing to sitting or recumbent position

5. Arterial dilatation:

by vasodilator drugs or decreased sympathetic tone → increase blood flow from arterial to venous side

6. Forced Expiration (against resistance= straining):

increases intrapleural pressure → increases pressure on thoracic vena cava

7. Muscle Contraction:

rhythmic contraction of limbs & abdominal muscles increases venous return

CVP is increased by either:

-Increasing Venous Volume

-Decreasing Venous Compliance

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How to Measure CVP?

•Direct: by catheter introduced into large thoracic veins

•Indirect: Is estimated from Jugular venous pressure

2) Jugular Venous Pulse (JVP)

•Pressure changes transmitted from right atrium

•The right internal jugular is the best neck vein to inspect

•Provides information about haemodynamic changes in right atrium & ventricle

Why Internal Jugular Vein?

•The internal jugular is preferred more than external jugular because valves between external jugular & SVC interfere with transmission of pressure waves

•The Right internal jugular is preferred than the left because the Right is in a direct line with SVC leading to better transmission of pressure & pulse waves

•The internal jugular vein is lateral to carotid artery & deep to sternomastoid muscle.

•External jugular is superficial to sternomastoid

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JV Pressure & CVP

•JVP is a reliable means for estimating CVP

•The sternal angle (junction between manubrium sterni and body of sternum) is the external reference point (right atrium is below sternal angle by 5cm)

•Thus, CVP equals the distance between an imaginary line below sternal angle by 5 cm to the highest point of visible jugular pulsation

Examining JVP for Estimating CVP

In normal adults: CVP ranges from 2-9 cm H2O

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•If the jugular pulsations are visible in a patient sitting in an upright position, then the CVP is at least 10 cm H2O with no need to measure it.

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Record of JVP (JVP Trace)

•JVP trace reflects phasic pressure changes in Rh atrium

•Composed of 3 positive waves; a, c & v

•2 negative waves: x & y

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Relation of Timing of JVP to Carotid pulse & ECG

•“a” wave precedes carotid pulsation

•“v” wave synchronous with late diastole

•“a” wave follows P wave of ECG

•a-c interval corresponds to P-R interval

Wave Abnormalities in JVP

•Variation in shape of JVP trace can help in diagnosis of some diseases;

•Huge or large a wave; in tricuspid stenosis or pulmonary hypertension

• Canon a wave; in complete heart block where Rh atrium & ventricle contract at the same time or in ventricular tachycardia

•Absent a wave in atrial fibrillation

•Huge v wave in tricuspid regurgitation

Clinical Significance of JVP Trace

•Atrial fibrillation: absent a wave (no effective atrial contraction)

•Tricuspid stenosis: Canon a wave

•1st degree heart block: a-c interval is prolonged

•Complete heart block: normal number of a waves but has no relation to cxv waves, cannon a waves appear (atrium contracts with ventricle at the same time

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