Optical sensors for heart- and respiratory rate measurements. Academic prototypes and clinical evaluation

The authors have developed two new sensor principles for heart- and respiratory rate monitoring. One sensor (Hjartrud) is based on skin microcirculatory fluctuations in blood flow, synchronous with the heart- and respiratory rates. A second sensor (Optovent) is based on condensation of humidity from the airways at the end of an optical fibre, the properties of which change with condensation of water. Both sensor principles have been evaluated. The accuracy's are comparable with sensors more established in clinical work. By using optical fibres one can obtain electromagnetic noise immunity of great value in MR-monitoring and during surgical diathermy. The Hjartrud sensor utilises digital signal processing techniques to extract and separate the heart- and respiratory signals from noise. Both instruments are in an industrial preproduction evaluation phase.