Introduction: The Breath Holding Index (BHI) is a non-invasive method for evaluation of cerebrovascular reactivity, the results of which correlate with those obtained by using intravenous acetazolomide and CO2 inhalation, so that it can be used as an alternative method to these in cooperative patients. However, the technique is not completely defined. Therefore Markus et al make a second measurement of the BHI 2-3 minutes later and take the arithmetical mean of the two readings as the final result.
Objectives: To assess the intra-observer concordance between two BHI obtained with less than two minutes difference, and therefore whether the second index obtained may be used as an indicator of cerebrovascular reactivity.
Patients and methods: Our study included 18 patients (7 men and 11 women; average age: 28.8 years; limits 17-50 years) with primary headache and no known cerebrovascular disease, diabetes mellitus or arterial hypertension. Using transcranial Doppler 28 measurements of the BHI (BHI1) were made in the middle cerebral arteries (right and/or left) in a similar way to that described by Markus. Once the average arterial velocity returned to basal levels the procedure was repeated in the first two minutes (BHI2) after the first index. Statistical analysis was done using the Student's t test and the kappa index between the two BHI after taking 0.8 as the cut-off point.
Results: The BHI2 (average +/- DT: 0.79 +/- 0.34) was significantly lower than that of BHI1 (average +/- DT: 1.04 +/- 0.44) (p < 0.005, t = 3.683). The kappa index between the two indices was very low: 0.058 +/- 0.158.
Conclusion: The BHI2 is not a reliable index of cerebrovascular reactivity since it under-estimates it in relation to the previous index, even when the average arterial velocity has returned to basal levels.