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

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 (S f r ), dynamic SDB breathing frequency (D f r ), and three fixed breathing frequencies of 4 breaths . min −1 (4F f r ), 6 breaths. min −1 (6F f r ), and 8 breaths. min −1 (8F f r ). 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 (S f r ) 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 (S f r ; 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 (4F f r ), which was up to 4.5 times higher (14.3%, 10 mmHg) than during spontaneous breathing (S f r ). 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 .