• R K Vesalainen, E M Ekholm, T T Jartti, K U Tahvanainen, T J Kaila, and R U Erkkola.
• Department of Medicine, Turku University Central Hospital, Finland.
• Br J Obstet Gynaecol. 1999 Mar 1; 106 (3): 238-43.

ObjectiveTo study the acute effects of tocolytic treatment with intravenous ritodrine on cardiovascular autonomic regulation.DesignValidated methods to assess cardiovascular autonomic nervous function-heart rate and blood pressure variability and vagal cardiac baroreflex sensitivity-were measured before and during ritodrine infusion.SettingTurku University Central Hospital, Turku, Finland.SampleTwelve pregnant women admitted to hospital for threatened preterm labour.MethodsElectrocardiogram and continuous noninvasive finger blood pressure signals were recorded in each woman, resting in a supine position. Autoregressive spectrum analysis was used to quantify short term heart rate and blood pressure variability. Vagal cardiac baroreflex sensitivity was measured as the bradycardia response to an intravenous bolus injection of phenylephrine.Main Outcome MeasuresVagal cardiac baroreflex sensitivity and spectrum analysis indices of short term heart rate and blood pressure variability.ResultsRitodrine significantly decreased vagal cardiac baroreflex sensitivity as well as total (0.00-0.40 Hz), low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz) power bands of the heart rate variability spectrum. Ritodrine significantly increased mean heart rate and the low frequency power band of the systolic blood pressure variability spectrum.ConclusionsIn pregnant women with threatened preterm labour intravenous administration of ritodrine decreases vagal cardiac baroreflex sensitivity and vagal modulation of heart rate, and increases sympathetically mediated blood pressure variability. Decreased baroreflex sensitivity and heart rate variability are known to be associated with a poor prognosis in some patient groups, so the effects of ritodrine tocolysis may be unfavourable in women with impaired circulatory homeostasis.

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