Impedance is a term that is commonly used in the world of #electrophysiology and #BiomechanicalEngineering.

The chance of getting an electric shock is high when you have wet hands because the impedance of the skin is lower than when it is dry.

Thoracic impedance increases during inspiration.

When applying electric current to the chest during #defibrillation, less energy may reach the heart during the inspiratory phase than during the expiratory phase because of this phenomenon, thereby decreasing the possible success of defibrillation.

So better to attempt defibrillation during the expiratory phase of mechanical ventilation.

Where the #resistance of a circuit is dependent on the frequency of the current through it, the term impedance is used.

The unit of impedance is therefore the same as that of resistance (the ohm), but the symbol Z is used to differentiate it from the symbol used for resistance (Ω).

In case of a capacitor, as the frequency of the current increases, the current passes through the circuit more easily, i.e. the resistance of the capacitor falls with increasing current frequency.

In contrast, the resistance of an inductor rises as the frequency of the current increases.

#PhysicsForAnesthesiologist , #anesthesiologist , #anesthesia , #biomedical

Davis PD, Kenny GNC. Basic Physics and Measurement in Anaesthesia, 5th edn. Oxford: Butterworth–Heinemann, 2003; pp. 149–64 . Ewy GA, Hellman DA, McClung S, Taren D. Influence of ventilation phase on transthoracic impedance and defibrillation effectiveness. Crit Care Med 1980; 8: 164–6