An improved pulse oximeter provides for simultaneous, noninvasive oxygen status and photoplethysmograph measurements at both single and multiple sites. In particular, this multiple-site, multiple-parameter pulse oximeter, or "stereo pulse oximeter" simultaneously measures both arterial and venous oxygen...http://www.google.com.au/patents/US6714804?utm_source=gb-gplus-sharePatent US6714804 - Stereo pulse oximeter
