A signal processing approach to the invetiation of the effects of age and smoking history on microvascular function

We have used laser Doppler fluximetry [LDF] and signal processing to investigate the effects of smoking on microvascular function. Skin bloodflux was measured using a pin-head probe [Moor Instruments, UK] mounted in a 1 cm heating block before and during mild thermal warming to 43 °C, in 8 heavy smokers [mean 50 y; 19 cigarettes/day, 30pack years], 20 light smokers [23 y; 11/day, 4 pack years] and their age, sex and BMI matched non-smoking controls. Basal LDF analysed in the time domain was similar in all 4 groups [10–15 AU]. The increase in blood flux during the initial 10 min heating was attenuated in both light and heavy smokers vs controls [P<0.005]. Total hyperaemic response [AUC to 10 min] was also significantly attenuated in the heavy smokers [4 ± 2 vs 6 ± 2 x10⁴ AU·sec] but not in the light smokers [8 ± 2 vs 10 ±4]. The LDF trace was analysed in the frequency domain using a fast Fourier transform and total spectral power together with the contribution of the frequency intervals between 0.01 and 2 Hz, calculated. Attenuation of the hyperaemic response in the heavy smokers was associated with a reduction in total spectral power of >40%, attributable to a reduction in spectral power around 0.01 Hz and 0.1 Hz [P<0.05]. These data suggest that the attenuation of the sustained hyperaemic response to thermal warming in long-term smokers is associated with a reduction in vasomotion and that this is in part the result of a reduced endothelial and smooth muscle cell activity. These changes are also evident in younger smokers with a shorter smoking history, suggesting that the vasodilatory response is impaired even at this early stage.