Assessment of chemoreflex sensitivity in free breathing young subjects by correction for respiratory influence

Background: The assessment of autonomic function is an important tool for r isk stratification in critically in patients. Peripheral cardiac chemorefle x sensitivity has been considered a marker for increased risk of sudden car diac death. In normals, the evaluation of peripheral cardiac chemoreflex se nsitivity is performed under controlled breathing conditions during inhalat ion of hypoxic gas. Since this is poorly tolerated by patients, they are co mmonly studied under hyperoxic conditions, which are not physiological. Met hods: We studied 20 healthy volunteers who underwent free and controlled br eathing of a hypoxic gas mixture (10% O-2 in N-2) over 5 min. Values of per ipheral cardiac chemoreflex sensitivity, corrected for respiratory influenc e, were compared with the results obtained experimentally under controlled breathing conditions in the same subjects. Results: We found a substantial difference between values obtained during free and controlled breathing (3. 64 +/-0.81 vs. 1.53 +/-0.32 ms/mmHg, respectively: P <0.05). After applicat ion of a respiratory correction, described and validated in this article, n o significant difference was seen for these values (0.89 +/-0.91 vs. 1.53 /-0.32 ms/mmHg, P = 0.46), Conclusions: This approach allows the evaluation of peripheral cardiac chemoreflex sensitivity in free breathing subjects. This correction could improve the assessment of cardiac chemoreflex sensiti vity in patients with cardiorespiratory disorders. who find it difficult to control their breathing according to an experimental protocol. (C) 2001 El sevier Science Ireland Ltd. All rights reserved.