Creare engineers have developed a way to better characterize the cause and onset of decompression sickness (DCS). Caused by the formation of small bubbles in the bloodstream and tissues, DCS has long been a major concern in any activity requiring significant change in the ambient environmental pressure. Divers returning from significant depths require regimented decompression stops on the way up. Likewise, astronauts preparing for extra-vehicular activity (EVA) in spacesuits pressurized to only a third of an atmosphere must undergo two or more hours of oxygen pre-breathe prior to suiting up. Both activities significantly decrease work efficiency in their respective environments. Despite over a century of dealing with DCS, tabular decompression tables remain statistical and experiential – and in fact, the appropriate decompression time can vary from person to person, and from time to time within a given individual.

With funding from NASA, NSBRI, and the Navy, Creare engineers have developed an approach to monitor and measure noninvasively the formation of nitrogen bubbles both in the bloodstream and in tissue, for the purpose of generating data to better characterize and understand the physical etiology of DCS. The instrument is able to detect and size intravascular gas bubbles in the range of 30 to 200 microns, and extravascular bubbles on the order of 1 micron in diameter. These extravascular bubbles and their precursors are thought to play an important role in DCS, but there previously has been no way to detect them. 

The theoretical basis for operation of the instrument developed by Creare is the exploitation of the nonlinear resonant properties of bubbles, which are strongly correlated to bubble size. Ultrasonic energy at two frequencies is used to resonate the bubbles, and the reflected signal is processed to detect and size the bubbles. Tissue is insonified with a combination of carefully selected frequencies – a lower “pump” frequency and a higher “image” frequency – and a frequency analysis of the return signal is performed. Bubbles act as nonlinear mixers such that if a bubble that resonates at the lower pump frequency is contained in the measurement volume there will be energy in the return signal at both the sum and difference of the two frequencies. Without a resonant bubble present, there will be no significant energy at these sidebands. The efficacy of this method has been demonstrated by Creare with in vivo testing.