Hi,
Please check out the following link which is an example of the functions in Matlab that need to be called in order to send and retrieve data from LabVIEW. In particular, note that it is using "vi.run=1;" to run the vi.
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3DF7356A4E034080020E74861&p_node=DZ52053&p_source=External
Regards,
Ankita A.
Applications Engineer
National Instruments