A single-breath CO2 test was carried out in cluster headache patients both during bout and remission, and in matchedhealthy individuals (n = 10 for each group) to assess peripheral chemosensitivity. The test subjects inhaled one tidal breath of13% CO2 in air. The response was expressed as the maximal increase in inspiratory minute ventilation (VI) within 20 secondsfrom the exposure to CO2, divided by the increase in end-tidal PCO2 (PETCO2) (the difference in PCO2 between the testbreath and the preceding control breaths): DVI/DPETCO2.
Under the initial resting condition, cluster headache patients within the bout showed a slight hyperventilation in that therewas 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 significantdifference as regards the peripheral chemosensitivity between cluster headache and control groups. These results indicatethat cluster headache patients have an intact and properly-functioning carotid body.