Regarding “No evidence of a gender difference in carotid blood velocities across stenoses”

Abstract

Comerota et al 1 reported significantly higher blood flow velocities in women across stenoses of 55% to 75% of the internal carotid artery (ICA) than in men. Given the law of conservation of mass, it is difficult to understand how a given percentage of luminal narrowing can cause a different increase in velocity across genders. Comerota et al used a small sample size (Ͻ40 in each group), neglected to use an appropriate correction for multiple comparisons, such as the Bonferroni correction, and did not report statistics for age (a potential confound) in the groups where the significant differences were found.The John Hunter Hospital Cardiovascular Unit database was queried for all carotid duplex studies since the inception of the database in 1991. The analysis included 6,165 studies comprising 3,287 men and 2,878 women. Student's t test for independent samples was used to determine if there was an effect of gender on carotid artery blood flow velocities in both ICA and common carotid artery (CCA) on the left and right. Because of the number of comparisons being made, a Bonferroni correction was used, and a result of P Ͻ .004 was considered significant. With this sample size, assuming a statistical power of 0.8, a mean difference of 0.06 m/s in the ICA would be detectable at the level of P Ͻ 0.004. Comerota et al found a mean difference of 0.49 m/s.In our dataset, women had significantly lower CCA velocities than men (left side: t ϭ 5.327, df[6163], P Ͻ .0001; right side: t ϭ 4.646, df[6179], P Ͻ .0001). Furthermore, females were an average of 2 years older than their male counterparts (t ϭ -6.583, df[6228], P Ͻ .0001). Age was significantly correlated with velocities of the CCA (r ϭ -.295, P Ͻ .0001) and the ICA (r ϭ -.048, P Ͻ .0001). This confound may account for the 0.03-m/s difference found in both the right and left CCA velocities between men and women.Comerota et al found a gender difference at 50% and 60% stenosis. The arteries where a 50% to 79% stenosis was found on duplex were extracted from the group as a whole and compared across genders for both the right and left sides. This gave a sample size of 202 men and 174 women with right-sided stenoses and 382 men and 336 women with left-sided stenoses. No significant differences in velocities were found for either the left or the right common or internal carotid arteries in this group.A 2 analysis, performed using gender and category of stenosis, found that men are significantly more likely to have moderate and severe disease than women (right side: 2 ϭ 12.134, P Ͻ .001; left side: 2 ϭ 13.235, P Ͻ .001.In conclusion, there is no evidence of a gender difference in blood flow velocities across stenoses in our relatively large dataset. The findings of Comerota et al may be confounded by an effect of age differences.

Regarding “No evidence of a gender difference in carotid blood velocities across stenoses”

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