I am using the Electrocardiogram (ECG ) in my lab and I get these results and I

Question

I am using the Electrocardiogram (ECG ) in my lab and I get these results and I want to know the reasons for these cases :

1) When I fists his right hand, the baseline voltage increases initially (for ECG reading), then decrease when I lets go. (the frequency increases < why ?

2) when I tapped on one electrode, the amplitude increases extremely (for ECG reading) < why ??

3) when I took deep breaths, the baseline moves down/there’s a gap between spikes((for ECG reading) . When I inhale it drops when I exhale it goes back to normal.< Why ??

Explanation / Answer

1. The frequency increases because in normal physiologic states the PR interval may vary with heart rate due to any form of physical activity which increases the tone and therefore results in increased conduction through the AV node at faster heart rates.

2. The applied stimulus can disturb the surrounding of the electrode and the artifact thus, resulting in change of amplitude of the ecg signal.

3. The quantum of electrical energy that reaches the surface of the chest wall depends largely on myocardial mass, proximity and thickness of chest wall. This is known as Brody's effect. For example, in case of a dilated Left ventricle, due to a regurgitant lesion, the LVEDV is increased . This is due to the very good electric conductivity of blood , it amplifies the transmural activation front and therefore, results in high voltage QRS complex.

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