The concentration (and thus the partial pressure) of certain gases, such as carbon dioxide and oxygen and the pH (hydrogen ion concentration) in arterial blood are determined without the need for contacting the blood by first stripping off the top dry skin layer forming a "window" of small size. A small...http://www.google.de/patents/US4041932?utm_source=gb-gplus-sharePatent US4041932 - Method for monitoring blood gas tension and pH from outside the body
