Baroreceptor reflex sensitivity index derived from phase 4 of the Valsalva maneuver

Abstract

The purpose of this study was to find a method to assess the sensitivity of the baroreceptor reflex avoiding the use of a pressor amine. Following the release of the Valsalva maneuver (VM), there is usually a pressor rise similar to the one obtained by phenylephrine administration. We were able to assess the baroreceptor reflex sensitivity index (BRSI) using this phase of the VM. Included in this study were nine healthy subjects, 25 patients with chronic Chagas' disease, and 10 hypertensive patients. The brachial artery and the antecubital vein were cannulated. VM was then performed during 20 seconds, and later 50 to 200 /ig of phenylephrine were administered intravenously (i.v.). During Phase 4 of the VM, multiple correlations between systolic pressure and cycle length were obtained. The best correlations were observed when initial beats after the release were disregarded. During this period, changes in pressure were not followed by changes in cycle length. The following results were obtained: rise in systolic pressure by VM: 60 ± 28 mm Hg and by phenylephrine: 30 ± 26 mm Hg. The Valsalva BRSI (BRSI val) was 9.52 ± 5.4 msec/mm Hg, with a mean r of 0.92 ± 0.08; the phenylephrine BRSI (BRSI ph) was 9.91 ± 5.4 msec/mm Hg, with a mean r of 0.86 ± 0.11. The correlation between both BRSI was: Y = 0.06 + 0.94X; r - 0.91. These results indicate that the BRSI obtained by both methods is similar. We conclude that during the initial beats following the release of the VM there is a total inhibition of the baroreceptor reflex; and that following this brief inhibition period it is possible to measure the BRSI without use of a pressor amine such as phenylepbrine. © 1981 American Heart Association, Inc.