Characterization of neural breathing pattern in spontaneously breathing preterm infants

Abstract

The aim was to characterize the neural breathing pattern in nonintubated preterm infants. The diaphragm electrical activity (EAdi) and heart rate were simultaneously measured repeatedly for 1 h over several days using a modified feeding tube equipped with miniaturized sensors. The EAdi waveform was quantified for phasic and tonic activity, neural timings, and prevalence of recurring patterns, including central apnea. Ten infants with mean age 7 d (range, 3-13 d) were studied. Their birth weight was 1512 g (1158-1800 g) and GA at birth 31 wk (28-36 wk). Neural inspiratory and expiratory times were 278 ms (195-450 ms) and 867 ms (668-1436 ms) and correlated with GA (p < 0.001). Tonic EAdi represented 29.5% of phasic EAdi (16-40%) and was related to GA (r = 0.61, p < 0.001). For the group, 68% of the time was regular phasic breathing (without tonic activity) and 29% of the time with elevated tonic activity. Central apneas >5 s occurred on average 10 times per hour (2-29). Heart rate reductions were correlated to central apnea duration. In conclusion, esophageal recordings of the EAdi waveform demonstrate that neural breathing pattern is variable, with regards to timing, amplitude, and pattern with a distinct amount of tonic diaphragm activity.

Figures

Figure 1. Experimental set-up

A modified nasal or orogastric feeding tube for feeding and measuring EAdi was inserted and connected to a computer for data acquisition.

Figure 2. Breath-by-breath analysis method

A: Raw signals from all eight electrode pairs. B: Processed EAdi waveform. Cursors were manually placed at the onset, peak, and subsequent onset of the processed EAdi waveform for calculation of neural timings, and signal strength.

Figure 3. 5-second epoch analysis method

Data was divided into 5 second-epochs, and a minimum EAdi, short dashed lines (EAdimin5), and maximum EAdi, long dashed lines (EAdimax5), were identified. The noise level is indicated by the grey horizontal bar.

Figure 4. Representative tracings of the different neural breathing patterns on the same day

Each panel demonstrates the EAdi waveform obtained in one subject on the same recording day, and demonstrates examples of the different breathing pattern types (1–7, see Methods).

Figure 5. Representative tracings of the different neural breathing patterns on different days

Each panel demonstrates the EAdi waveform obtained in one subject on the different recording days. A= Day 1 AM, B= Day 1 PM, C= Day 2 AM, D= Day 3 AM, E = Day 4 AM

Figure 6. Representative tracings of EAdi and ECG in one subject

Time sequence is Figure 6A to 6D. Each panel demonstrates the EAdi waveform (bottom in each panel) and the ECG. A = thirty seconds prior to the apnea, heart rate was 153, and saturation 98%. B = slowing in heart rate at the same time as the central apnea. C= Heart rate 66, saturation 82%, and the nurse aroused the baby (D). Three minultes later, HR = heart rate 159, saturation 99%.

Figure 7. Relationship between central apnea duration and heart rate

Group data demonstrating that longer apneas are associated with greater reductions in heart rate. * indicates statistical significance from beginning to end of apnea.