Table 2.
Heart rate variability of healthy volunteers during sham ventilation (SV) and Bilevel ventilation (BV)
| SV N= 20 | BV of 8–15 cmH2O N= 20 | BV of 13–20 cmH2O N= 20 | |
|---|---|---|---|
| Time domain | |||
| Mean RR (ms) | 919.2±109.2 | 866.4±102.7 * | 826.9±99.4 †‡ |
| SDNN (ms) | 54.1±23.4 | 56.5±26.6 | 49.3±20.6 |
| rMSSD (ms) | 50.2±32.5 | 45.6±29.4 | 38.9±18.9 † |
| NN50 (ms) | 81±71.2 | 68.2±60.2 | 51.1±40.1 † |
| pNN50 (%) | 26.2±22.9 | 21.7±19.5 | 17.1±13.3 † |
| Nonlinear | |||
| SD1 (ms) | 35.8±23.1 | 32.6±20.9 | 27.9±13.5 † |
| SD2 (ms) | 85.4±32.7 | 93.1±40.3 | 85.7±31.8 |
| Frequency Domain | |||
| LF (nu) | 60.1±20.5 | 72.5±21.7 * | 68.1±21.4 |
| HF (nu) | 39.9±20.5 | 27.5±21.7 * | 31.9±21.4 |
| LF/HF | 3.7±7.5 | 5.2±4.3 | 4.2±4 |
Mean RR= the mean of R-R intervals, in ms; SDNN= standard deviation of all R-R intervals, in ms; rMSSD= root mean square of the squares of the differences between successive R-Ri, in ms; NN50= number of successive R-Ri interval pairs that differ by more than 50 ms; pNN50= percentage of successive R-Ri pairs that differ by more than 50 ms; SD1= the standard deviation of the Poincaré plot perpendicular to the line-of-identity, in ms; SD2= the standard deviation of the Poincaré plot along the line-of-identity, in ms; LF= low frequency, in normalized units; HF= high frequency, in normalized units; LF/HF= ratio of low frequency to high frequency.
Bilevel of 8–15 cmH 2O versus SV;
Bilevel of 13–20 cmH2O versus SV;
Bilevel of 13–20 cmH2O versus Bilevel of 8–15 cmH2O. Repeated-measures analysis of variance (ANOVA) with the Tukey post-test. Data expressed in mean and standard deviation.