Real time single-fiber optic sensor for physiological parameters

In situations of acute trauma or longer-term critical care, physiological parameters such as temperature and partial pressure of oxygen in blood are very important to monitor every 10 to 20 secs. The combined excited state phosphorescence lifetimes of an alexandrite crystal and platinum tetraphenylporphyrin Pt(TPP) in a single-fiber sensor are used to monitor temperature and oxygen concentration in the physiological range from 15-45{dollar}spcirc{dollar}C and 0-50% O{dollar}sb2{dollar} with precision of 0.046{dollar}spcirc{dollar}C & 0.021% O{dollar}sb2{dollar} and accuracy of 0.3{dollar}spcirc{dollar}C & 0.2% O{dollar}sb2{dollar}. A 500{dollar}mu{dollar}m cubic alexandrite crystal bound to the distal end of a 750{dollar}mu{dollar}m diameter optical fiber core and the Pt(TPP) coated circumferentially with length 1cm from the end of the same fiber are excited with pulsed super bright blue LED light. This apparatus uses a 125 KHz sampler for data acquisition and frequency domain methods for signal processing. The instrument amplifies both the dc and ac components of the photomultiplier output and band limits the signal to 20 KHz. The fundamental frequency of the excitation is set to 488.3 Hz. This band limited signal is sampled and averaged over a few hundred cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic are then computed. At least four log spaced harmonic phases or modulations are averaged before decoding the two lifetimes of temperature and oxygen phosphorescent sensors. A component of zero lifetime is introduced to account for the excitation backscatter leakage through optical interference filters seen by the photodetector. Linear and second order empirical polynomials are employed to compute the temperatures and oxygen concentrations from the inverse lifetimes. In the situation of constant oxygen concentration, the lifetime of Pt(TPP) will change with temperature but can be compensated immediately with the measured lifetime of alexandrite crystal. The system drift is 0.65{dollar}spcirc{dollar}C for the temperature measurement and 0.32% for the oxygen concentration measurement over 6 hours of continuous operation. The instrumentation and methods allow for 6-s update times and 90-s full response times. The individual of an alexandrite, a ruby crystal fiber optic temperature sensor and Pt(TPP) fiber optic oxygen sensor are preliminary tested for monitoring temperature and oxygen concentration in the physiological range with satisfied performance.