LETTER TO THE EDITOR
Reply
Christian Binggeli, MD
Cardiovascular Center, Division of Cardiology, University Hospital, CH-8091 Zürich, Switzerland
Georg Noll, MD, FESC
christian.binggeli{at}usz.ch
Drs. Minson and Wong support our findings that the hyperemic skin blood flow is not nitric oxide (NO) dependent. They showed that NO is responsible neither for the development nor the maintenance of the hyperemic response after arterial occlusion. This is true for reactive hyperemia after short occlusion as well as after more prolonged arterial occlusion of 15 min (1).
We also believe that normalization of the laser-Doppler-flux is important to minimize the influence of the number of blood vessels under the probe. The data of Wong et al. (1) and our data were normalized in a slightly different way. Normalization to the maximum level achieved during infusion of sodium nitroprusside and local heating as done by Wong et al. (1) assumes that the maximum vasodilatory effect is not largely affected by cardiovascular risk factors as shown in conductance arteries using different techniques. Our method normalizes to baseline. In the microvasculature, baseline as well as peak laser-Doppler-flux are at least in part dependent on the presence of risk factors (2,3). Therefore, both of the approaches have some advantages and disadvantages. We are aware that despite correcting for different sites, the intra-individual variability is considerably high. However, the decreased hyperemic responses of smokers and patients with hypercholesterinemia are in line with endothelial dysfunction measured using more invasive techniques, suggesting a common phenomenon. A better reproducibility of the method would allow one to detect smaller differences and, therefore, local heating as nicely investigated by Minson et al. (4) may be advantageous. The advantage of this simple and noninvasive method may allow screening of a large number of patients at risk. Prospective evaluation of data may demonstrate a correlation of vascular dysfunction in the skin microcirculation with cardiovascular events.
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References
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1. Wong BJ, Wilkins BW, Holowatz LA, Minson CT. Nitric oxide synthase inhibition does not alter the reactive hyperemic response in the cutaneous circulation. J Appl Physiol. 2003;95:504–510[Abstract/Free Full Text]
2. Orlandi C, Rossi M, Finardi G. Evaluation of the dilator capacity of skin blood vessels of hypertensive patients by laser Doppler flowmetry. Microvasc Res. 1988;35:21–26[CrossRef][Medline]
3. Tur E, Yosipovitch G, Bar-On Y. Skin reactive hyperemia in diabetic patients. A study by laser Doppler flowmetry. Diabetes Care. 1991;14:958–962[Abstract]
4. Minson CT, Berry LT, Joyner MJ. Nitric oxide and neurally mediated regulation of skin blood flow during local heating. J Appl Physiol. 2001;91:1619–1626[Abstract/Free Full Text]
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