An eleceroxcardiograph records the tracing standard speed of 2S mmiecond. This a

Question

An eleceroxcardiograph records the tracing standard speed of 2S mmiecond. This allows us to determine peecisely the heart rate and the duration of the intervals we discussed. As you can see in Figure 19 small box on the ECG tracing measures 0.04s, and eas large box measures 0.20s. Five large boxes together measure I second. Determining the duration of mon E19.5 Normal Values for ECG Periods .7,cach Heart rate 0.12-0.20s 042-044 Q-T interval and add the seconds together. Cakulating the heart rane is equally simplei count the number of large boxes, and QRS complex duration Less than or equal to 0.12s divide 300 by this number For example, if you count 4.2 boxes: 3004.2 71 beats per minute. The normal valoes for the periods we discussed are given in Table 19.5 Procedure 1 ldentifying Waves of an ECG Let's start by correlating the waves on the ECG with the electrical activity occurring in the heart electrical events taking place in cardiac cells at each of the six points in the ECG in Figure . Identify the 19.8, and explain not mechanical the events in the answer lines provided. Do remember though that the ECG shows only electrical events, events. A heart can have electrical activity but not be beating FIGURE 19.8 ECG tracing. 1 Cocuu e depolaned 4 5 6 ropoarR tom& Physiology in the Laboratory

Explanation / Answer

The heart can respond to the electrical changes which is processed in myocardium and we can detect these changes by an ECG graph. So in the graph the 1 wave represent the repolarization of the atria or atrial depolarization which occurby atria through pacemaker or sino atrial node .this wave can rremain as long as 70 to 100 Milli sec in normal heart.

The second point corresponds time delayed in the atria and ventricle beginning.It shows the conduction time of atria to the ventricle or atrial ventricle time .this time is decreased in the case of excessive exercise ,running and this time increasesin the case of lower heart rates like when we sleep or at the time of thinking.

The 3 points correspond to the points when our ventricles get depolarization or ventricular depolarization means the ventricles will respond to the electrical changes occur in heart

The 4 point corresponds to the the point all those changes in the myocardium starts the depolarization of atria begins before these points the heart starts responding to these electrical changes.

The 5 segment corresponds to the starting of the electrical activity of cell in the cardiac when it returns to the normal resting state after it gets activated. This segments shows the neutrality or no net charges in the phase of ECG.

The 6 segment corresponds to the point when the electrical activity get associated in the cell . The cardiac ventricle start relaxing of ventricle walls.its the longer segment because at this segment the relaxation of ventricle is less tightly than contraction of the same ventricles.

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