Oscillations in the human cutaneous blood perfusion signal modified by endothelium-dependent and endothelium-independent vasodilators

The purpose of the present study was to compare the effects of endothelium- dependent [acetylcholine (ACh)] and endothelium-independent [sodium nitropr usside (SNP)] vasodilators on the oscillatory components of the cutaneous b lood perfusion signals in humans. The unstimulated basal blood perfusion an d the blood perfusion during iontophoretically delivered ACh and SNP were m easured using laser Doppler flowmetry (LDF). The wavelet transform was calc ulated before spectral analysis of the measured signals. In the frequency i nterval from 0.0095 to 1.6 Hz the LDF signal consists of oscillations with five different characteristic frequencies. In addition to the cardiac (1 Hz ) and respiratory (0.3 Hz) rhythms, three other oscillations in the regions around 0.1, 0.04, and 0.01 Hz were detected. The oscillations with the dif ferent frequencies were observed in unstimulated blood now and also during stimulation with ACh and SNP. Compared to the unstimulated blood now, both ACh and SNP increased the mean amplitude of the total spectrum (P < 0.005 f or both substances). The only significant difference between the effects of ACh and SNP was observed in the amplitude of oscillations with the frequen cy of around 0.01 Hz. ACh increased the absolute amplitude of this frequenc y to a greater extent than SNP in athletes (P = 0.03), whereas only a trend was observed in controls (P = 0.2). The relative amplitude, defined as the ratio between the absolute amplitude of a particular frequency interval an d the mean amplitude of the total spectrum, was also higher for ACh compare d to SNP both in controls (P = 0.008) and in athletes (P = 0.004), only for oscillations with the frequency of around 0.01 Hz. We conclude that ACh se lectively influences the oscillatory component of around 0.01 Hz in the cut aneous blood perfusion signal to a greater extent than SNP. This finding in dicates that endothelium-mediated vasodilatation is manifested as oscillati ons with a repetition time of approximately 1 min. The mechanisms for the e ndothelial dependency of this frequency remain to be elucidated Our data in dicate that spectral analysis based on wavelet transform of the cutaneous p erfusion signal can be used clinically to investigate endothelial function. The described noninvasive method might be used to evaluate endothelial fun ction for research, for diagnostic purposes, and maybe also to assess effec ts of therapy in cardiovascular diseases. (C) 1999 Academic Press.