Breathing exercises during late pregnancy in a microgravity-like environment

Background. Breathing exercises are commonly used as a relaxation technique during pregnancy and to help in labour, but whether the burden of the fetus may cause a cardiovascular reflex activation during deep breathing is poorly known. Water immersion (WI), which mimic a microgravity condition, may relieve breath discomfort during deep breathing in late pregnancy. Nevertheless, body position may play a role, as during WI the hydrostatic drive is directed toward the diaphragm in sitting but not in supine position. Aims. To compare the cardiovascular activation due to deep low-frequency breathing exercises in a gym (DRY) and during water immersion (WI) in different positions (supine and sitting) in late pregnant women. Methods. We collected in 11 pregnant women (age 31±2 [m±SD] yrs; gestational age 29±6 wks) RR interval series by a heart rate monitor at baseline, while sitting comfortably, and during deep and slow ventilation (about 0.05 Hz), in both DRY and WI conditions, either in supine and sitting position (10 min each). The following parameters were calculated for each series: Low Frequency (LFnu, 0.06-0.15 Hz) and High Frequency (HFnu, 0.15-0.4 Hz) power (FFT method), LF/HF ratio. Results. Compared to baseline (86±8 bpm), heart rate significantly increased during breathing while sitting in both conditions (DRY: 95±3 bpm, p<0.01; WI: 93±11 bpm, p<0.01 vs baseline) but more slightly in WI (p<0.05 vs DRY). Conversely, heart rate did not change during breathing in supine position in DRY (81±9 bpm) and WI (84±10 bpm) state. Baseline LF/HF ratio was 2.0±1.2. Breathing while sitting significantly increased LF/HF ratio vs baseline in both DRY (3.9±0.9, p<0.01) and WI condition (3.7±2.5, p<0.05). During breathing supine LF/HF increased significantly in DRY only (4.4±3.1, p<0.04) but not in WI (2.1±1.5) condition. The observed modifications in LF/HF ratio were due to a significant shift in normalized LF (+34%, +28% and +26% in sitting DRY, supine DRY and sitting WI, respectively) and HF (-40%, -30% and –27%, respectively) power compared to baseline, but this effect was significantly reversed in WI (LF: -4%; HF: +10%, p=0.08 vs DRY) supine condition. Conclusions. Deep slow breathing seems to activate a significant autonomic response in sitting position. WI tends to mitigate such reactions, partially in sitting and completely in supine position. Therefore, in late pregnant women WI may alleviate the fetal burden on respiration, but exercise position is relevant.