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(Hypertension. 2006;47:51.)
© 2006 American Heart Association, Inc.

Original Articles

Sympathetic Neural Outflow and Chemoreflex Sensitivity Are Related to Spontaneous Breathing Rate in Normal Men

Krzysztof Narkiewicz; Philippe van de Borne; Nicola Montano; Dagmara Hering; Tomas Kara; Virend K. Somers

From the Hypertension Unit (K.N., D.H.), Department of Hypertension and Diabetology, Medical University of Gdansk, Gdansk, Poland; Hypertension Clinic (P.v.d.B.), Erasme Hospital, Brussels, Belgium; Medicina Interna II (N.M.), Ospedale L. Sacco, Universita degli Studi di Milano, Milan, Italy; and Divisions of Cardiovascular Disease and Hypertension (T.K., V.K.S.), Mayo Clinic, Rochester, Minn.

Correspondence to Krzysztof Narkiewicz, Department of Hypertension and Diabetology, Akademia Medyczna w Gdansku, Debinki 7c, 80-952 Gdansk, Poland. E-mail knark{at}amg.gda.pl

Respiration contributes importantly to short-term modulation of sympathetic nerve activity. However, the relationship between spontaneous breathing rate, chemoreflex function, and direct measures of sympathetic traffic in healthy humans has not been studied previously. We tested the hypothesis that muscle sympathetic nerve activity and chemoreflex sensitivity are linked independently to respiratory rate in normal subjects. We studied 69 normal male subjects aged 29.6±8.1 years. Subjects were subdivided according to the tertiles of respiratory rate distributions. Mean respiration rate was 10.6 breaths/min in the first tertile, 14.8 breaths/min in the second tertile, and 18.0 breaths/min in the third tertile. Subjects from the third tertile (faster respiratory rate) had greater sympathetic activity than subjects from the first tertile (slower respiratory rate; 29±3 versus 17±2 bursts/min; P<0.001). Stepwise multiple linear regression analysis revealed that only respiratory rate was linked independently to sympathetic activity (r=0.42; P<0.001). In comparison to subjects with slow respiratory rate, subjects with fast respiratory rate had greater increases in minute ventilation during both hypercapnia (7.3±0.8 versus 3.2±1.0 L/min; P=0.005) and hypoxia (5.7±0.8 versus 2.4±0.7 L/min; P=0.007). Muscle sympathetic nerve activity and chemoreflex sensitivity are linked to spontaneous respiratory rate in normal humans. Faster respiratory rate is associated with higher levels of sympathetic traffic and potentiated responses to hypoxia and hypercapnia. Spontaneous breathing frequency, central sympathetic outflow, and chemoreflex sensitivity exhibit significant and hitherto unrecognized interactions in the modulation of neural circulatory control.

Key Words: autonomic nervous system • sympathetic nervous system • blood pressure • heart rate

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