Electrocardiogram

-

 

 ELECTROCARDIOGRAM

     An electrocardiogram records the electrical signals in the heart. It's a common and painless test used to quickly detect heart problems and monitor the heart's health.

     Electrical signals from the heart characteristically precede the normal mechanical function and monitoring of these signals has great clinical significance.

    ECG provides valuable information about wide range of cardiac disorders such as the presence of an inactive part(infarction) or an enlargement (cardiac hypertrophy) of the heart muscle.


ECG WAVEFORM






P Wave: Atrial depolarization

 

       T Wave: Ventricular repolarization

 

                                     QRS Complex: Ventricular depolarization

 

ECG BLOCK DIAGRAM


 

     Lead selector

 In the lead selector, the electrodes are selected two by two according to the lead program.

 By means of capacitive coupling to the differential preamplifier.

·      Preamplifier

 The preamplifier is usually a three or four stage differential  amplifier.

 Preamplifier are having large negative current feedback from end stage to first stage which gives a stabilizing effect.

·     Power amplifier

 Push-pull differential type

 The base of one input transistor of this amplifier is driven by pre amplified signal.

 The base of the others transistor is driven by the feedback signal resulting from the pen position and connected via frequency selective network.

·     Frequency selective network

 R-C network

 Which provides necessary damping of the pen motor and is preset by the manufacturer.

·    Auxiliary circuits

              Provides a 1mv calibration signal and automatic blocking of the amplifier of the lead switch.

             It may include a speed control circuit for the chart drive motor.

 

Comments

Post a Comment

Popular posts from this blog

Short wave diathermy

-
Image
       The diathermy means, 'through heating' or producing deep heating directly in the tissues of the body.          Externally applied sources of heat like hot towels, infrared lamps and electric heating pads often produce discomfort and skin burns long before adequate heat has penetrated to the deeper tissues.          But with the diathermy technique, the subject's body becomes a part of the electrical circuit and the heat is produced within the body and not transferred through the skin.          The heating of the tissues is carried out by high frequency alternating current which generally has a frequency of 27.12 MHz and wavelength of 11m. The short wave diathermy machine consists of 2 main circuits.                       * Oscillating circuit - which produces a high frequency current.              ...
Read more

History of Artificial limb

-
Image
  Artificial limb (c. 550 B.C.E)         The earliest written reference to an artificial limb occurs in an epic Indian poem"Rig-Veda", which was compiled between 35000 and 1800 B.C.E written in Sanskrit the poem includes a description of the amputation of the warrior Queen vishpla's leg during battle. Later fitted with an iron prosthesis by the Ashvins (celestial physicians),she returned to combat.        Most authorities doubt the story of Queen Vishpla, and turn to the Histories of Herodotus for the first plausible reference to a prosthetic limb. Herodotus describes how, in the mid sixth century B.C.E.,Hegesistratus of Eli's, a Persian soldier and seer imprisoned by the Spartans, was sentenced to death, and cut off part of his foot to escape from the stocks. Hegesistratus fashioned a wooden prosthesis to help walk the 30 miles (48 km) to Tregea, but unfortunately was captured by Zaccynthius and beheaded.          ...
Read more