Cluster headache: the peripheral chemosensitivity as indicated by the single-breath CO2 test.

A single-breath CO2 test was carried out in cluster headache patients both during bout and remission, and in matched healthy individuals (n = 10 for each group) to assess peripheral chemosensitivity. The test subjects inhaled one tidal breath of 13% CO2 in air. The response was expressed as the maximal increase in inspiratory minute ventilation (Vi) within 20 seconds from the exposure to CO2, divided by the increase in end-tidal PCO2 (PETCO2) (the difference in PCO2 between the test breath and the preceding control breaths): delta Vi/delta PETCO2. Under the initial resting condition, cluster headache patients within the bout showed a slight hyperventilation in that there was a significantly reduced PETCO2 (P < 0.05, Student's paired t-test), and during remission, higher Vi, and a lower PETCO2 (P < 0.05, Wilcoxon signed rank test), in comparison with the controls. There was no statistically significant difference as regards the peripheral chemosensitivity between cluster headache and control groups. These results indicate that cluster headache patients have an intact and properly-functioning carotid body.