Respiratory modulation of cardiovagal baroreflex sensitivity.

Emerging evidence has suggested that with minimal prerequisite training, slow deep breathing around 0.10 Hz can acutely enhance cardiovagal baroreflex sensitivity (BRS) in humans. Such reports have led to the speculation that behavioral interventions designed to reduce breathing frequency may serve a therapeutic role in ameliorating depressed baroreflex function in conditions such as chronic heart failure, essential hypertension, and obstructive airway disease. This study sought to test the hypothesis that slow controlled breathing acutely enhances cardiovagal baroreflex function in young healthy volunteers. Distinct from earlier studies, however, baroreflex function was examined (n = 30) using the classical pharmacological modified Oxford method, which enabled the assessment of cardiovagal BRS through experimentally driven baroreceptor stimulation across a wide range of blood pressures. For a comparison against existing evidence, spontaneous cardiovagal BRS was also assessed using the alpha-index and sequence method. Compared with fast breathing (0.25 Hz), slow breathing (0.10 Hz) was associated with an increase in the alpha-index (8.1 +/- 14 ms/mmHg, P < 0.01) and spontaneous up-sequence BRS (10 +/- 11 ms/mmHg, P < 0.01). In contrast, BRS derived from spontaneous down sequences and the modified Oxford method were unaltered by slow breathing. The lack of change in BRS derived from the modified Oxford method challenges the concept that slow breathing acutely augments arterial baroreflex function in otherwise healthy humans. Our results also provide further evidence that spontaneous BRS may not reflect the BRS determined by experimentally driven baroreceptor stimulation.