3. Intangible assets

During the year ended December 31, 2008, the Company acquired Comfort Life Medical, LLC (Comfort Life). The acquisition resulted in recording an intangible asset in the amount of $92 related to the Medicare license held by the acquired company. The Company amortizes this intangible asset over its estimated useful life of ten years. As of June 30, 2014 and December 31, 2013, there were no impairments recorded related to this intangible asset. On April 1, 2009, Comfort Life Medical, LLC merged with Inogen, Inc., and was simultaneously dissolved. During the year ended December 31, 2009, the Company was assigned four patents previously held as an exclusive license from Air Products & Chemicals (APC) in exchange for an increase in a long-term liability due to APC of $250. The acquisition of these patents resulted in an intangible asset of $250. During the year ended December 31, 2011, the Company purchased additional patents from APC for a total value of $650. The Company amortizes these intangible assets over an estimated useful life of five years. There were no impairments recorded related to these intangible assets for the three and six months ended June 30, 2014 and June 30, 2013.  The Company recalculated interest and amortization of the period based on adjusted asset and debt.

During the year ended December 31, 2011, the Company acquired Breathe Oxygen Services, LLC. The acquisition resulted in recording an intangible asset in the amount of $66 related to the Medicare license held by the acquired Breathe Oxygen Services that allowed them to operate in the state of Tennessee as well as other assets. On August 29, 2011, Breathe Oxygen Services, LLC merged with Inogen, Inc., and was simultaneously dissolved.  The Company amortizes this intangible asset over its estimated useful life of ten years. During the three months and six months ended June 30, 2014 and June 30, 2013, there were no impairments recorded related to this intangible asset. The Company also capitalizes costs incurred for the production of direct response advertising commercials and amortizes these intangible assets over a useful life of two years. During the three months and six months ended June 30, 2014, the Company paid $11 and $180 for its patient setup video, website development and redesign and production of commercials.  The Company did not capitalize any intangible assets during the three and six months ended June 30, 2013.

Amortization expense for intangible assets for the three months ended June 30, 2014 and June 30, 2013 was $41 and $67, respectively, and for the six months ended June 30, 2014 and June 30, 2013 was $80 and $135, respectively.

The following tables represent the changes in net carrying values of the intangibles as of the respective dates: