Phasic blood flow

Phasic blood flow

Comparison of phasic blood flow velocity characteristics of arterial and venous coronary artery bypass conduits.

BACKGROUND:

Coronary artery bypass conduits derived from internal mammary arteries show relative resistance to atherosclerosis and significantly improved long-term patency compared with saphenous vein grafts. Atherothrombotic occlusion of venous conduits has previously been correlated with lower flow rates measured intraoperatively. To quantitate coronary bypass conduit flow velocity, we examined the phasic blood flow velocity patterns by intravascular Doppler spectral analysis in patients during cardiac catheterization to test the hypothesis that resting systolic and diastolic phasic blood flow velocity patterns differ significantly between arterial and venous bypass conduits.

METHODS AND RESULTS:

Spectral phasic blood flow velocity was measured using an intravascular Doppler-tipped angioplasty guidewire in the proximal, mid, and distal segments of 18 internal mammary artery conduits and 11 saphenous vein grafts in 27 patients at a mean of 4 years (range, 1 to 11) postoperatively. In situ internal mammary artery conduits demonstrated a gradual longitudinal transition in the phasic flow pattern from predominantly systolic velocity proximally (diastolic/systolic peak velocity ratio, 0.6 +/- 0.2) to predominantly diastolic velocity distally (diastolic/systolic peak velocity ratio, 1.4 +/- 0.3; P < .001).

Phasic blood flow

Saphenous vein graft flow velocity pattern, however, showed a consistently diastolic predominance, both proximally and distally (diastolic/systolic peak ratios, 1.4 +/- 0.6 and 1.5 +/- 0.7, respectively; P = NS). Mean flow velocities, total velocity integral, and calculated maximal shear rates were significantly higher in all segments of internal mammary arteries compared with values in saphenous vein grafts.

CONCLUSIONS:

Patterns of resting phasic blood flow, as well as mean velocity and total velocity integral, differ significantly between internal mammary artery and saphenous vein bypass conduits. These differences may have implications regarding blood-vessel wall interactions, the development of degenerative graft disease, and long-term conduit patency.


Cerebral Circulation

Cerebral Circulation
What is cerebral circulation?

Cerebral circulation is the blood flow in your brain. It’s important for healthy brain function. Circulating blood supplies your brain with the oxygen and nutrients it needs to function properly.

Blood delivers oxygen and glucose to your brain. Although your brain is a small part of your body’s total weight, it requires a lot of energy to function. According to the Davis Lab at the University of Arizona, your brain needs about 15 percent of your heart’s cardiac output to get the oxygen and glucose it needs. In other words, it needs a lot of blood circulating through it to stay healthy.

When this circulation is impaired, your brain can become damaged. Many conditions and disabilities related to neurological function can occur as a result.

How does blood flow through your brain?

The four main arteries that supply blood to your brain are the left and right internal carotid arteries and the left and right vertebral arteries. These arteries connect and form a circle at the base of your brain. This is called the circle of Willis. Smaller blood vessels also branch off from these arteries to nourish different sections of your brain.

Your brain also has venous sinuses. These types of veins carry blood containing carbon dioxide and other waste products away from your cranium. Some of them connect with the veins of your scalp and face.

Nutrient and waste exchange occurs across the blood-brain barrier. This barrier helps protect your brain.

What happens when your cerebral circulation is impaired?

When your cerebral circulation is impaired, less oxygen and glucose reach your brain. This can cause brain damage and neurological problems. Some conditions related to impaired cerebral circulation include:

  • stroke
  • cerebral hemorrhage
  • cerebral hypoxia
  • cerebral edema

Stroke

When a blood clot blocks the flow of blood in your cranial artery, a stroke can occur. As a result, the brain tissue in that area can die. When that tissue dies, it can impair the functions that part of your brain normally controls. For example, it can affect your speech, movement, and memory.

The degree of impairment you experience after a stroke depends on how much damage has occurred, as well as how quickly you get treatment. Some people fully recover from a stroke. But many people have lasting disabilities or even die from strokes. According to the American Stroke Association, stroke is the fifth leading cause of death among Americans.

Cerebral Circulation

Cerebral hypoxia

Cerebral hypoxia occurs when part of your brain doesn’t get enough oxygen. This happens when you don’t have enough oxygen in your blood even if there’s enough blood flow. Causes of cerebral hypoxia include:

  • drowning
  • choking
  • suffocation
  • high altitudes
  • pulmonary diseases
  • anemia

If you experience it, it’s likely you’ll appear confused or lethargic. If you address the underlying cause quickly enough, your brain tissue probably won’t become damaged. But if you don’t address it quickly enough, coma and death can occur.

Cerebral hemorrhage

A cerebral hemorrhage is internal bleeding in your cranial cavity. It can occur when your arterial walls are weakened and burst. This forces blood into your cranial cavity. In turn, this can put pressure on your cranial cavity and cause you to lose consciousness. Other possible causes of cerebral hemorrhage include abnormally formed blood vessels, bleeding disorders, and head injuries.

A cerebral hemorrhage can potentially cause brain damage and death. It’s a medical emergency.

Cerebral edema

Edema is a type of swelling that occurs due to the collection of watery fluids. Cerebral edema is swelling that occurs due to an increase of water in your cranial cavity. Disturbances in the blood flow in your brain can also cause it.

Cerebral edema can put pressure on your brain. This can eventually crush or damage your brain if it’s not relieved in time.

What are the risk factors for poor cerebral circulation?

Anyone at any age can have problems with cerebral circulation. You’re at an increased risk of having these problems if you:

  • have high blood pressure
  • have high cholesterol
  • have heart disease
  • have atherosclerosis
  • have a family history of heart disease
  • have diabetes
  • are overweight
  • smoke
  • drink alcohol
The takeaway

You need good cerebral circulation to supply your brain with oxygen- and nutrient-rich blood. Cerebral circulation also helps remove carbon dioxide and other waste products from your brain. If your cerebral circulation becomes impaired, it can lead to serious health issues, including:

  • a stroke
  • cerebral hypoxia
  • cerebral hemorrhage
  • cerebral edema
  • brain damage
  • disability

It can even lead to death in some cases.

Some causes of impaired cerebral circulation may be hard to prevent. But you can lower your risk of stroke and some other conditions by practicing healthy habits and following these tips:

  • Maintain a healthy weight.
  • Eat a well-balanced diet.
  • Exercise regularly.
  • Avoid smoking.
  • Limit alcohol.

Objectives of ECG

Objectives of ECG

Electrocardiogram (ECG) deals with the study of electrical activity of the heart. The instrument used to record the activity is called electrocardiograph. It was developed by a Dutch physiologist Einthoven in the year 1903. The recording was known as electrokardiogram (EKG). Both ECG and EKG are valid terms that can be used for the recording. The study of ECG, tells us the heart rate, rhythm, conduction in the heart and presence of any abnormalities in them known as arrhythmias. It is also useful to know the presence of infarction in the myocardium and the effect of drugs, electrolytes on the heart.
The ECG waves represent the sum total of tiny action potentials developed from the cardiac muscle. The electrical activity is spread to the surface of the body through the body fluid, which acts as a volume conductor. These electrical potentials from the surface of the body can be recorded by placing surface electrodes or leads, on certain conventional positions in the body. They are amplified and connected to a string galvanometer, which records them on a moving strip of paper or displayed on the screen in cathode ray oscilloscope.

There are 12 leads used in the recording of ECG. Einthoven recorded the electrical activity of the heart by using bipolar limb leads. He considered right arm, left arm and left leg as the regions for surface recording and showed that, when these points are joined, an equilateral triangle could be obtained. In the center of this triangle, the heart is situated. The equilateral triangle obtained by this method is called Einthoven’s triangle. The bipolar limb leads record the potential difference between two limbs. Accordingly, there are three types of leads present.
They are:

  • Lead I (between right arm and left arm)
  • Lead II (between right arm and left leg)
  • Lead III (between left arm and left leg).

Objectives of ECG
In the bipolar limb leads, if we know the potentials in any two leads, the potential in the third lead can be determined. According to Einthoven’s law, the sum of the potentials in lead II.
Lead I + Lead III = Lead II

In Unipolar augmented limb leads method, there is an indifferent electrode (V), which is obtained by connecting the three limb leads and passing through 5000 ohms resistance to get 0 potential (Wilson’s terminal). Recording between one limb and the other two limbs increases the size of the potential by 50%. The two limbs are connected through electrical resistance to the negative terminal and the other limb is connected to the positive terminal. There are three types of leads such as aVR, aVL and aVF present in this category.
There is an indifferent electrode (V) and exploring electrode is placed on the anterior chest wall in six positions. They are given numerical numbers from 1 to 6. The leads are V1, V2, V3, V4, V5 and V6. In ECG recording, positive deflection is recorded, when the wave of excitation moves towards the positive or exploring electrode. If the depolarization wave moves away from the exploring electrode, a negative deflection is recorded. In aVR lead, the exploring electrode is facing the cavity of the ventricles and the wave of excitation moves away from the recording electrode and hence in this lead, all the deflections of ECG are negative.


ECG waves

ECG waves

What is an ECG?

ECG is short for electrocardiogram.

It is used to record the electrical activity of the heart from different angles to identify and locate pathology.

Electrodes are placed on different parts of a patient’s limbs and chest to record the electrical activity.

Parts of the ECG explained

P-waves

P-waves represent atrial depolarisation.

In sinus rhythm, there should be a P-wave preceding each QRS complex.

 

PR interval

The PR-interval is from the start of the P-wave to the start of the Q wave.

It represents the time taken for electrical activity to move between the atria and ventricles.

QRS complex

The QRS-complex represents depolarisation of the ventricles.

It is seen as three closely related waves on the ECG  (Q,R and S wave).

ST segment

The ST-segment starts at the end of the S-wave and finishes at the start of the T-wave.

The ST segment is an isoelectric line that represents the time between depolarization and repolarization of the ventricles (i.e. contraction).

T-wave

The T-wave represents ventricular repolarisation.

It is seen as a small wave after the QRS complex.

 

RR-interval

The RR-interval starts at the peak of one R wave and ends at the peak of the next R wave.

It represents the time between two QRS complexes.

QT-interval

The QT-interval starts at the beginning of the QRS complex and finishes at the end of the T-wave.

It represents the time taken for the ventricles to depolarise and then repolarise.

 

The 12 lead ECG: how it all works

The first thing to clear up is the definition of the word “lead” in an ECG context.

Lead refers to an imaginary line between two ECG electrodes.

The electrical activity of this lead is measured and recorded as part of the ECG.

A 12-lead ECG records 12 of these “leads” producing 12 separate graphs on the ECG paper.

However you only actually attach 10 physical electrodes to the patient.

Electrodes

The electrodes are wires that you attach to the patient to record the ECG.

These electrodes allow leads to be calculated.

For example Lead I is calculated using the electrodes on the right and left arm.

Below are the electrodes used in a 12 lead ECG.

Chest electrodes positions 

V1 – 4th intercostal space right sternal edge

V2 – 4th intercostal spaceleft sternal edge

V3 – midway between V2 and V4

V4 – 5th intercostal space midclavicular line

V5 – left anterior axillary line same horizontal level as V4

V6 – left mid-axillary line same horizontal level as V4 & V5

Limb electrodes

LA – left arm

RA right arm

LL – left leg

RL – right leg – neutral – not used in measurements

Leads

Lead refers to an imaginary line between two ECG electrodes.

There are 12 leads measured in a 12-lead ECG.

Chest leads

V1 – Septal view of heart

V2 – Septal view of heart

V3 – Anterior view of heart

V4 – Anterior view of heart

V5 – Lateral view of heart

V6 – Lateral view of heart

Chest electrode positions

Other leads

Lead I Lateral view (RA-LA)

Lead II – Inferior view (RA-LL)

Lead III – Inferior view (LA-LL)

aVR – Lateral view (LA+LL – RA)

aVL – Lateral view (RA+LL – LA)

aVF – Inferior view (RA+LA – LL )

This diagram is a useful way of understanding the relationships between the leads

Hexaxial

Lead viewpoints


Viewpoints of the heart

It’s important to understand which leads represent which part of the heart.

This allows you to localise pathology to a particular heart region.

For example if there is ST elevation in leads V3 and V4 it suggests an anterior myocardial infarction (MI).

You can then combine this with some anatomical knowledge of the heart’s blood supply, to allow you to work out which artery is likely to be affected (e.g left anterior descending artery).


How to read ECG paper

The paper which ECGs are recorded upon is standardised across all hospitals (usually):

  • Each small square represents 0.04 seconds
  • Each large square on the paper represents 0.2 seconds
  • 5 large squares therefore = 1 second
  • 300 large squares = 1 minute


The shape of the ECG waveform

Each individual leads ECG recording is slightly different in shape.

This is due to each lead recording the electrical activity from different directions.

When the electrical activity of the heart travels towards a lead you get a positive deflection.

When the electrical activity travels away from a lead you get a negative deflection.

Electrical activity in the heart flows in many directions at once.

The wave seen on the ECG paper represents the average direction.

The height of the deflection also represents the amount of electricity flowing in that direction.

The lead with the most positive deflection is closest to the direction the heart’s electricity is flowing.

If the R-wave is greater than the S-wave it suggests depolarisation is moving towards that lead.

If the S-wave is greater than the R-waves it  suggests depolarisation is moving away from that lead.

If the R and S-waves are of equal size it means depolarisation is travelling at exactly 90° to that lead.


Cardiac axis explained

The electrical activity of the heart starts at the sinoatrial node then spreads to the atrioventricular (AV) node.

It then spreads down the bundle of His and then Purkinje fibres to cause ventricular contraction.

Whenever the direction of electrical activity is towards a lead you get a positive deflection in that lead.

Whenever the direction of electrical activity is away from a lead you get a negative deflection in that lead.

The cardiac axis gives us an idea of the overall direction of electrical activity when the ventricles are contracting.

Normal cardiac axis

In healthy individuals you would expect the axis to lie between -30° and +90º.

The overall direction of electrical activity is towards leads I,II and III (the yellow arrow below).

As a result you see a positive deflection in all these leads, with lead II showing the most positive deflection as it is the most closely aligned to the overall direction of electrical spread. You would expect to see the most negative deflection in aVR. This is due to aVR looking at the heart in the opposite direction to the overall electrical activity.

Normal Cardiac Axis

Right axis deviation

Right axis deviation (RAD) is usually caused by right ventricular hypertrophy.

In right axis deviation the overall direction of electrical activity is distorted to the right (between +90º and +180º).

Extra heart muscle causes a stronger positive signal to be be picked up by leads looking at the right side of the heart.

This causes the deflection in lead I to become more negative and the deflection in III to be more positive.

RAD is associated with pulmonary conditions as they put strain on the right side of the heart.

It can also be a normal finding in very tall individuals.

Right axis deviation

Left axis deviation

In left axis deviation (LAD) the direction of overall electrical activity becomes distorted to the left (between -30° and -90°).

This causes the deflection in lead I to become more positive and the deflection in III to be more negative.

LAD is usually caused by conduction defects and not by increased mass of the left ventricle.

Left axis deviation