Calculating Energy Delivered by a Pacemaker to the Heart

[Sloan650]

A pacemaker stimulates heart tissue with R of 100ohms.
Pulse amplitude is 1.2 Volts & pulse duration is 0.5ms.
Stimulates at 70bpm
Current drain = 2microamps

Calculate energy delivered to heart from pacemaker at each pulse.

i got

P=V^2/R = 0.0144

Then Energy = Power*time = 0.0144*0.5x10-3 = 7.2x10-6 J

But do i not need to take into account the current drain?

 

[Sloan650]

Please help?! its for an exam tomorrow!

 

[gneill]

A pacemaker stimulates heart tissue with R of 100ohms.
Pulse amplitude is 1.2 Volts & pulse duration is 0.5ms.
Stimulates at 70bpm
Current drain = 2microamps

Calculate energy delivered to heart from pacemaker at each pulse.

i got

P=V^2/R = 0.0144

Then Energy = Power*time = 0.0144*0.5x10-3 = 7.2x10-6 J

But do i not need to take into account the current drain?

It would appear that the current drain and the 70bpm figures are superfluous information.

 

[NascentOxygen]

A pacemaker stimulates heart tissue with R of 100ohms.
Pulse amplitude is 1.2 Volts & pulse duration is 0.5ms.
Stimulates at 70bpm

If the pacemaker electronics is 100% efficient (unrealistic, but let's consider it to be ideal for sake of argument), then the above information will account for a drain on the battery averaging 7 μA.

Current drain = 2microamps

So I'm puzzled by their figure of just 2 μA. I say it has to be more than 7 μA.

Then Energy = Power*time = 0.0144*0.5x10-3 = 7.2x10-6 J

I agree with this figure, and it has units of Joules.

But do i not need to take into account the current drain?

No. But the person who set the question does need to explain the anomaly.

 

[gneill]

If the pacemaker electronics is 100% efficient (unrealistic, but let's consider it to be ideal for sake of argument), then the above information will account for a drain on the battery averaging 7 μA.


So I'm puzzled by their figure of just 2 μA. I say it has to be more than 7 μA.


I agree with this figure, and it has units of Joules.


No. But the person who set the question does need to explain the anomaly.

The problem doesn't say that the stated current drain is measured at the output of the pacemaker, or that the pacemaker's battery must be 1.2V. For all we know the pacemaker could be running on a 12V battery (okay that's unlikely but you get the idea) and its circuitry is designed to deliver the required pulses via suitable transformation. The concern would be with energy conservation (power drawn >= power delivered), or I*V, rather than just I.

 

[NascentOxygen]

The only interpretation of "current drain" is current drawn from the battery. But you are right that the battery need not be 1.2 volts. What it would realistically be, though, I don't know.

Good save.