A method and apparatus are disclosed for using photoplethysmography to obtain physiological parameter information related to respiration or the autonomic nervous system. In one implementation, the process involves obtaining (602) a pleth, filtering (604) the pleth to remove unwanted components, identifying...http://www.google.com.au/patents/US6896661?utm_source=gb-gplus-sharePatent US6896661 - Monitoring physiological parameters based on variations in a photoplethysmographic baseline signal
