1. Vasoconstrictor responses to inspiratory gasp were determined in fingertip skin by laser Doppler flowmetry in relation to age and gender of healthy adults. Variations of the responses were examined together with variations in body mass index and vital capacity.

2. In the absence of any significant difference in the baseline blood flow, the index of vasoconstrictor response (per cent change) induced by inspiratory gasp was higher in young males than in young females (71.4% versus 59.4%; P<0.05), and in the same direction as the change in vital capacity determined in the same laboratory setting. Similar parallel differences in the indexes of vasoconstrictor response and vital capacity existed between young and middle-aged males, suggesting that the differences observed were not due to gender or age per se.

3. Strong positive correlations between the index of the vasoconstrictor response and vital capacity in the same subject were found when young males and females were pooled together and when young and middle-aged males were pooled together. Furthermore, after graded inspiratory gasp, graded vasoconstrictor response was observed in the same subject, indicating a close relationship between the depth of inspiration (magnitude of stimulus) and the index of the vasoconstrictor response (reactivity).

4. We concluded that the index of the vasoconstrictor response induced by inspiratory gasp depends significantly on the magnitude of the vital capacity. These results provide a new approach for quantifying dynamic changes in skin blood flow and raise caveats about comparing differences in neurovascular functions using single measurements of vasoconstrictor response induced by inspiratory gasp as an index.

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