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The pulse oximeter waveform (POW) is derived from variation in intensity of transmitted light through tissues. It may be used to provide a non-invasive surrogate for the intra-arterial waveform, and represents an accessible measure of cardiovascular status. We examined the effects of age, blood pressure and smoking on the waveform patterns. These factors are known to decrease arterial compliance, increase peripheral wave reflection and alter the contour of the pulse pressure waveform. Supine and standing POW recordings were taken from 200 healthy volunteers. The resting waveform patterns were categorised into four distinct classes as described by Murgo and Nichols for intra-arterial pressure waveforms, and compared to age and systolic blood pressure. Post hoc ANOVA revealed a significant relationship between waveform class and age (P < 0.001), blood pressure (P < 0.001), and smoking status (P = 0.021. These effects appear to represent changes in the peripheral arterial system resulting from altered wave reflection. We also analysed the POW in both time and frequency domains. On standing, time domain analysis showed a decrease in total variability, as measured by standard deviation and variance. Frequency domain analysis demonstrated an increase in power at a frequency (0.1 Hz) associated with sympathetic nervous system output. These results are consistent with changes in the microcirculation related to autonomic control mechanisms. These patterns of change, however, were only apparent in a proportion of the subjects. We believe that the responses elicited are dependent on factors affecting the long-term compliance of the arterial tree, and are thus related to the pulse oximeter waveform classification described. We have shown that POW analysis yields consistent and reproducible patterns. Further research may lead to the use of these techniques as a measure of peripheral vascular responsiveness, with potential utility in the evaluation of cardiovascular disease. |
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