Table 2.
Spectral power values for the R–R interval and SBP series, and low-frequency transfer function
| PMA 28–32 (n = 16) | PMA 32–37 (n = 10) | PMA 37–42 (n = 6) | |
|---|---|---|---|
| Respiratory rate (Hz) | 0.82 ± 0.20 | 0.88 ± 0.23 | 0.77 ± 0.20 |
| R–R interval series | |||
| R–R interval (ms) | 423 ± 27 | 426 ± 30 | 492 ± 48†, ‡ |
| LF power | 18 (9–36) | 28 (12–94) | 65 (34–262)† |
| HF power | 1 (1–2) | 3 (1–19) | 24 (6–45)† |
| Total power | 26 (10–45) | 36 (15–150) | 96 (83–384)† |
| SBP series | |||
| SBP (mmHg) | 55 ± 4 | 56 ± 4 | 59 ± 6 |
| LF power | 0.9 (0.4–1.6) | 0.6 (0.4–1.4) | 0.4 (0.1–0.9) |
| HF power | 0.3 (0.2–0.3) | 0.4 (0.2–0.5) | 0.1 (0.1–0.2)‡ |
| Total power | 1.2 (0.8–2.2) | 1.3 (1.0–2.4) | 0.7 (0.3–1.1)‡ |
| Transfer function parameters | |||
| LF frequency (Hz) | 0.07 (0.06–0.10) | 0.08 (0.06–0.10) | 0.08 (0.08–0.11) |
| LF Coherence | 0.67 (0.60–0.73) | 0.60 (0.53–0.75) | 0.66 (0.58–0.78) |
| LF gain (ms mmHg−1) | 4.6 (3.1–5.4) | 7.5 (5.2–10.1)§ | 15.0 (11.8–19.7)‡, † |
| LF phase (s) | −2.8 (−3.6 to −1.5) | −2.6 (−5.5 to −2.0) | −2.6 (−3.9 to −2.2) |
(Cross-)spectral power analysis of the study groups with postmenstrual age (PMA) of 28–32 weeks, 32–37 weeks and 37–42 weeks. The spectral power values for the R–R interval and SBP series are presented in units of ms2 and mmHg2, respectively. The low-frequency (LF) band was defined between 0.04 and 0.15 Hz. The high-frequency (HF) band was defined as the frequency range between the p-10 and p-90 centile of the individual respiratory frequency. The total power was computed for the frequency band between 0.04 and 1.5 Hz. The coherence value within the LF band is shown with the corresponding frequency, gain and phase. The LF transfer gain was considered to be an estimate for baroreceptor reflex sensitivity. Negative phase values indicate SBP fluctuations lead R–R interval changes. Parametric data are expressed as the mean ±s.d. and comparisons between groups were statistically evaluated with ANOVA and the post hoc Scheffé test. Non-parametric data are expressed as median (IQR) and comparisons between groups evaluated with Kruskal-Wallis H test and Mann-Whitney U test.
P < 0.01 (PMA 37–42 versus 28–32);
P < 0.01 (PMA 37–42 versus 32–37);
P < 0.01 (PMA 32–37 versus 28–32).