Acute cardiovascular responses to slow and deep breathing in normotensive non-pregnant and pregnant women.

Abstract

Objective: To compare the acute cardiovascular responses of non-pregnant and pregnant women to slow and deep breathing (SDB) at a range of breathing frequencies. Participants: Forty-one women (23 non-pregnant and 18 pregnant).Methods: Participants completed five different breathing conditions in a randomised order (5-min duration); spontaneous breathing (Sfr), dynamic SDB breathing frequency (Dfr), and three fixed breathing frequencies of 4 breaths. min−1 (4Ffr), 6 breaths. min−1 (6Ffr), and 8 breaths. min−1 (8Ffr). Main Outcome Measures: Non-invasive beat-to-beat arterial blood pressure, heart rate and respired airflow were monitored continuously.Results: The maximum amplitude of respiratory sinus arrhythmia (RSA) during SDB was 2.1 times higher than during spontaneous breathing (Sfr) for both groups, maximising at 6 breaths. min−1 (0.25s ± 0.1 non-pregnant, 0.15s ± 0.1 pregnant). Although absolute RSA was significantly lower in pregnant women during spontaneous breathing (Sfr; 0.07s vs. 0.12s non-pregnant), SDB increased RSA to the same level as non-pregnant women’s spontaneous breathing levels. In both groups, the amplitude of blood pressure oscillations (both systolic and diastolic blood pressure) increased as breathing frequency declined, reaching a peak at 4 breaths. min−1 (4Ffr), which was up to 4.5 times higher (14.3%, 10 mmHg) than during spontaneous breathing (Sfr).Conclusion: Cardiovascular responses maximised at ≤6 breaths. min−1 and acute haemodynamic responses to SDB are similar in pregnant and non-pregnant women, despite absolute differences under spontaneous breathing conditions. If blood pressure oscillations underpin the anti-hypertensive effect of SDB, the data indicate that these can be amplified in pregnant women at frequencies between 4 and 6 breaths. min−1.