RECORDINGS OF MUCOCILIARY ACTIVITY IN-VIVO - BENEFIT OF FAST FOURIER TRANSFORMATION OF THE PHOTOELECTRIC SIGNAL

Investigations of mucociliary activity in vivo are based on photoelect ric recordings of light reflections from the mucosa. The alterations i n light intensity produced by the beating cilia are picked up by a pho todetector and converted to photoelectric signals. The optimal process ing of these signals is not known, but in vitro recordings have been r eported to benefit from fast Fourier transformation (FFT) of the signa l. The aim of the investigation was to study the effect of FFT for fre quency analysis of photoelectric signals originating from an artificia l light source simulating mucociliary activity or from sinus or nasal mucosa in vivo, as compared to a conventional method of calculating mu cociliary wave frequency, in which each peak in the signal is interpre ted as a beat (old method). In the experiments with the artificial lig ht source, the FFT system was superior to the conventional method by a factor of 50 in detecting weak signals. By using FFT signal processin g, frequency could be correctly calculated in experiments with a compo und signal. In experiments in the rabbit maxillary sinus, the spontane ous variations were greater when signals were processed by FFT. The co rrelation between the two methods was excellent: r=.92. The increase i n mucociliary activity in response to the ciliary stimulant methacholi ne at a dosage of 0.5 mu g/kg was greater measured with the FFT than w ith the old method (55.3%+/-8.3% versus 43.0%+/-8.2%, p <.05, N=8), an d only with the FFT system could a significant effect of a threshold d ose (0.05 mu g/kg) of methacholine be detected. In the human nose, rec ordings from aluminum foil placed on the nasal dorsum and from the nas al septa mucosa displayed some similarities in the lower frequency spe ctrum (<5Hz) attributable to artifacts. The predominant cause of these artifacts was the pulse beat, whereas in the frequency spectrum above 5 Hz, results differed for the two sources of reflected light, the me an frequency in seven healthy volunteers being 7.8+/-1.6 Hz for the hu man nasal mucosa. It is concluded that the FFT system has greater sens itivity in detecting photoelectric signals derived from the mucociliar y system, and that it is also a useful tool for analyzing the contribu tions of artifacts to the signal.