Battery operated ECG recorders are well known here (Europe). In principle you could use a DC/AC converter (thinking about 'driving' == "car"), but there is really no need to do that: ECG recording does not require much power, so using batteries (preferably rechargeable) are well suited.

Why you do not use a transformer?

As far as i understand that you are thinking to use your laboratory setup in measured location i.e. in 'car'. Due to this you are worried about 230V power supply is it? if so, i recommend you NI 6009 USB based data acquisition card (http://www.ni.com/datasheet/pdf/en/ds-218). It is simply driven by usb power (operating vol. +5V DC). For accruing ECG data, connect ECG signal conditioning output to the various port of USB 6009 and connect this module with your laptop USB port. Thus, you can easily store & monitoring the ECG signal by using LabVIEW software. 

If you don not wish to use your laptop then you have another option by using NI myRio device, which required only 12V Dc supply and it can store data without any high end device. For generating 12V DC you have to use a DC to DC converter with the car battery.     

 Thanks Subir, 

We have some NI DAQ like SB RIO, PXI X series, but they all need 230 V supply. We may use third party "Arduino" but  it will give analog inputs voltage not in TDMS format and not  will not match with exact values as ECG magnitudes are in mV.

You have good device but i don't know about your SB RIO model. If it is sbRIO-9626 then it will operate in 9 - 30V DC input supply.

I don't have SB RIO, but i see the specification of SB RIO and i am sure that every module have an adapter which converts the 230V into 9-30V Dc. if so, it will be easily replace with any 9-30v battery supply.    

I am not aware of any Ni Daq device, which indeed requires 230V. Usually its just power supply which you source from AC 230V mains, but it produces DC 5V, 12V,  or 24V voltages to power particular device. Those are easily obtainable from car's 12V battery.

I have two suggestions for you:

1. Use portable device with own battery and choose daq which can be powered from USB

2. Use DC/DC converter to power a device running on voltage other than 12V. Please put a special emphasis on filtering of output stage, as most DC-DC converters are switching mode devices which operate at high frequencies, which may alter your measurements!

Thanks Michal.

If you are looking for hardware soltions from NI - contct your local sles office and state your needs. They are very helpful with matching hardware to user/researcher needs.