Goleta-based medical equipment maker Inogen has set the pricing range for its IPO, saying in a filing with the SEC that it expects its stock to price at between $16.00 and $18.00 per share. The company is offering up 3,529,411 shares of its stock, and plans to trade on the NASDAQ Global Market as INGN. Inogen is a maker of oxygen concentrators and equipment used by patients with COPD and other respiratory ailments. Inogen's portable oxygen concentrators are used as an alternative to bulky and inconvenient oxygen canisters. Inogen is venture backed by Novo AS, Versant Ventures, Arborteum Ventures, Avalon Ventures, and Accuitive Medical Ventures.