Non-Nutritive Suck Parameters Measurements Using a Custom Pressure Transducer System

Summary

The non-nutritive suck (NNS) device can easily collect and quantify NNS features using a pacifier connected to a pressure transducer and recorded through a data acquisition system and laptop. Quantification of NNS parameters can provide valuable insight into a child's current and future neurodevelopment.

Abstract

The non-nutritive suck (NNS) device is a transportable, user-friendly pressure transducer system that quantifies infants' NNS behavior on a pacifier. Recording and analysis of the NNS signal using our system can provide measures of an infant's NNS burst duration (s), amplitude (cmH₂O), and frequency (Hz). Accurate, reliable, and quantitative assessment of NNS has immense value in serving as a biomarker for future feeding, speech-language, cognitive, and motor development. The NNS device has been used in numerous research lines, some of which have included measuring NNS features to investigate the effects of feeding-related interventions, characterizing NNS development across populations, and correlating sucking behaviors with subsequent neurodevelopment. The device has also been used in environmental health research to examine how exposures in utero can influence infant NNS development. Thus, the overarching goal in research and clinical utilization of the NNS device is to correlate NNS parameters with neurodevelopmental outcomes to identify children at risk for developmental delays and provide rapid early intervention.

Introduction

Non-nutritive suck (NNS) is one of the first occurring behaviors that an infant can perform with their mouth soon after birth and therefore has the potential to provide meaningful insights into brain development¹. NNS refers to sucking movements without nutritional intake (e.g., sucking on a pacifier) and is characterized by a series of rhythmic expressions and suction movements of the jaw and tongue with pause breaks for breathing. Common parameters of NNS have been noted to include an average NNS burst (series of suck cycles) of 6-12 suck cycles with an intra-burst frequency of two sucks per second²; however, NNS features vary among clinical populations^3,4 and dynamically change during the first year of life⁵. These changes are attributed to the growth of the oral cavity and associated anatomy, maturation of feeding skills and neurodevelopment, and experiences. The neural bases of NNS mainly include the suck central pattern generator in the central gray of the brainstem, comprising an intricate network of interneurons and the facial and trigeminal motor neuron nuclei⁶. A coordinated NNS also relies on intact neural pathways among cortical and brainstem regions to modulate its performance to sensory stimuli^7,8, which makes NNS a viable indicator of early neural function and development.

NNS measures are linked to feeding success in premature infants^9,10, and both sucking and feeding outcomes have been linked to subsequent motor, communication, and cognitive development^11,12,13. In a retrospective study that characterized 23 preschool-aged children with language and motor impairments, 87% had a history of early feeding issues, which included difficulties in sucking¹¹. Nutritive sucking performance immediately following birth and caregiver reports of feeding difficulties were significantly associated with multiple domains of neurodevelopment in children 18 months of age^12,14. Interestingly, the sensitivity and specificity of feeding performance were higher than ultrasound assessment of the brain on neurodevelopmental outcome measures¹². In another study, sucking/oral motor performance scores assessed via the neonatal oral-motor assessment scale¹⁵ in early infancy were associated with motor skills, language, and measures of intelligence at 2 and 5 years of age in a cohort of children born prematurely^13,16.

Given that sucking and feeding can be sensitive indicators of neurodevelopmental outcomes throughout childhood, there is a critical need for accessible, accurate, and quantitative assessment of NNS to help identify children at risk for delayed and disordered development to provide early intervention. This need led to the design and research utilization of the Speech & Neurodevelopment Lab's (SNL) NNS device. This portable device includes a pacifier attached to the end of an easy-to-hold handle, connected to a customized pressure transducer designed in-house, and connected to a data acquisition center (DAC). The DAC connects to a laptop, and the data is recorded via data acquisition and analysis software. The pressure transducer measures pressure changes inside the pacifier and converts it into a voltage signal. The DAC contains converters that change the analog voltage signal to digital values in cmH₂O that are visualized and recorded via the data acquisition and analysis software. NNS outcome measures that can be analyzed from the suck signal waveform include NNS duration (how long a suck burst lasts measured in s), amplitude (measured as peak height subtracted by peak-trough in cmH₂O), cycles/burst (number of suck cycles within a burst), frequency (intra-burst frequency measured in Hz), cycles (number of suck cycles that occur in a min), and bursts (number of suck bursts that occur in a min).

Protocol

Northeastern University's institutional review board has approved studies using the NNS device with human subjects (15-06-29; 16-04-06; 17-08-19). Informed consent was obtained from the children's caregivers. All research personnel have completed human subject training prior to collecting any data with the NNS device. The SNL team has generated several training resources and protocols for new research personnel to complete prior to data collection using the NNS device. These training sessions include reviewing the following protocol.

1. NNS device setup

1. Open the transportable case (Figure 1) and remove the following device components: DAC and its power cord, customized pressure transducer box (NNS box) with pacifier receiver handle and gray cable attached, laptop computer and the USB cord that connects it to the DAC, and pacifier.
2. Plug in the following components: the power cord into the DAC and a three-pronged power outlet, a grey cable connected to the NNS box into the first front round port of the DAC, and a USB cord into the laptop computer and DAC (Figure 2).
3. Turn on the DAC using the power switch in its back and log onto the laptop/computer.

2. NNS device calibration

1. Remove the pressure calibrator and 1 mL syringe from the case.
2. Unscrew the black pacifier receiver from the handle. Screw the handle onto the pressure calibrator so that the handle is horizontal with the pressure calibrator (Figure 3A-C).
3. Draw the syringe plunger fully out and then screw it into the upper position on the pressure calibrator. The syringe should be perpendicular to the pressure calibrator (Figure 3D).
4. On the laptop computer, open the spreadsheet labeled SNL Suck Analyzer Calibration File.
   NOTE: This file contains formulas that assess pressure variability between the data acquisition and analysis application and pressure calibrator device measured in psi. There is a box in the upper left corner for data entry, which is used to enter data readings from the pressure calibrator and the LabChart Calibration File (described below).
   1. Right-click the tab that reads Duplicate and Rename as Date and select Move or Copy.
   2. In the Move or Copy pop-up window, click the box Create a Copy within the SNL Suck Analyzer Calibration File and then click Ok.
   3. Double-click the tab that was just copied and rename it as the current date.
5. Open the data acquisition and analysis file on the laptop computer's desktop labeled Calibration File.
   NOTE: Ensure the spreadsheet is still viewable on the laptop computer screen, which may require minimizing and re-arranging the spreadsheet and data acquisition and analysis application windows.
6. Press the Power button on the pressure calibrator device to turn it on.
7. On the laptop computer, select Start on the Calibration File while the NNS box gear is at Zero. Check the waveform sampling across time on the file.
   NOTE: The NNS box has two setting options: Zero and Sample. Ensure that it is set to Zero before starting calibration. The file's Start button will only activate when the file is opened after the DAC has been powered on. If the file is opened and the Start button cannot be clicked, close the file, power on the DAC, and reopen the file.
8. In their respective cells in the spreadsheet (i.e., under the DAC Program and Red Calibrator columns), record the value at the top right corner of the Calibration File and the value on the pressure calibrator device while psi is at 0.00 (Figure 4A).
9. Turn the gear from Zero to Sample on the NNS box. Wait approximately 15 s to allow adequate time for the pressure transducer to change recording functions.
10. Slowly depress the syringe plunger until the pressure calibrator reaches a value as close to 0.2 psi as possible, and then fill in the Calibration File with the pressure calibrator values in their respective cells in the spreadsheet.
11. Repeat step 2.10. for the following psi values: 0.4, 0.6, and 0.8 (Figure 4A).
12. Once all values are inputted into the spreadsheet, click Stop in the Calibration File. In the spreadsheet, check the Slope and Goodness of Fit cells located to the right of the table that was used to plug in the psi values from the data acquisition and analysis application and the calibration device (Figure 4B). If both cells are highlighted in green, the calibration was successful; proceed to step 2.13.
    NOTE: If one or both cells are red, clear the values in the psi measurement cells in the spreadsheet, turn the NNS box from Sample to Zero, close out the Calibration File, turn off the pressure calibrator by pressing the Power button, fully unscrew the syringe off the pressure calibrator, and pull the syringe plunger fully out before screwing it back on. Repeat steps 2.5. - 2.12.
13. Close the Calibration File without saving, turn the gear on the NNS box to Zero, and turn the pressure calibrator off by pressing the Power button.
14. Unscrew the syringe off the pressure calibrator. Pull the syringe plunger fully out again and then screw it back on the pressure calibrator.
15. On the computer's desktop, select and open the file labeled Master Settings File. On the top channel in the file, click the arrow for drop-down options on Suck Pressure and select Arithmetic.
    NOTE: Ensure the spreadsheet is still viewable on the laptop/computer screen, which may require minimizing and re-arranging the spreadsheet and data acquisition and analysis application windows.
16. Within the parentheses of the Formula text box in the data acquisition and analysis file, type in the values from the spreadsheet that are located in the blue cells above the Slope and Goodness of Fit cells (Figure 4C). Click OK on the file.
17. Turn the pressure calibrator back on using the Power button. Press Start on the Master Settings File. Turn the NNS box back to Sample and wait for 15 s.
18. Depress the syringe plunger as close to 0.5 psi as read on the pressure calibrator.
19. Scroll to the right within the spreadsheet and record the Master Settings File value under the cell labeled DAC and the pressure calibrator's value under the cell labeled Calibrator (Figure 4D). If the percentage error cell is highlighted in green, the calibration is successfully completed. If it is red, clear the data entered in this step and restart the calibration process from step 2.13.
20. Click Stop on the Master Settings File. Turn the NNS box to Zero. Save the Master Settings File by selecting File, then Save as Settings. Name the file as the date of successful calibration.
21. In the spreadsheet, select File > Save and then File > Close.
22. Turn off the pressure calibrator by pressing the Power button. Unscrew the handle and syringe from the pressure calibrator and screw the black receiver back on the handle. Turn off, unplug, and pack up device components back in the case.

3. Collecting non-nutritive suck data

1. Complete steps 1.1. - 1.3. for NNS device setup.
2. Wash hands, put on latex gloves, and attach a newly opened pacifier to the pacifier receiver (Figure 5).
3. Open the data acquisition and analysis file on the laptop computer's desktop with the latest calibration date. Once the file is opened, select Start.
4. Turn the NNS box gear from Zero to Sample. Wait approximately 15 s to allow adequate time for the pressure transducer to change recording functions.
5. Offer the pacifier to the child in a comfortable position and hold it for them to suck on for 2-5 min (or however long is tolerable for the child and comfortable with their caregiver).
   NOTE: Preferable positions to measure NNS in children would be optimal feeding positions for their age. The researcher or a caregiver can offer the child the pacifier (Figure 6).
6. When the child is finished or 5 min has passed, retrieve the pacifier handle from whoever was holding it for the child and press Stop on the file. Change the NNS box gear from Sample to Zero.
7. Remove the pacifier from the receiver and safely dispose of it following any institutional sanitary protocols. Safely remove and dispose of gloves and wash hands.
8. Save the file by selecting Save as and name the file with the participant's ID number and the date of data collection. Save the file to the desktop of the laptop computer.
9. Turn off, unplug, and pack up device components back in the case.

4. Analyzing non-nutritive sucks amples

1. Using a desktop or laptop that has the data acquisition and analysis software, open up the participant's NNS data file on the desktop by double-clicking on it.
2. Manually identify suck bursts using the following criteria: NNS bursts having more than one suck cycle, each suck cycle having an amplitude of at least 1 cmH₂O, and waveforms within 1000 ms of each other being considered as part of the same suck burst (Figure 7).
   NOTE: It is helpful to modify the view of the waveform (click the Set horizontal scaling box on the bottom right of the screen to have zoom-in and out options) to better identify NNS cycles from noise. The analysis is completed in a 50:1 view. It is important to note as we explore NNS across populations, these criteria may change as various populations exhibit altered NNS patterns.
3. To set peak analysis settings, select Peak Analysis, then Settings, then Table Options. Check the T Start, T End, Height, Peak Area, and Period boxes. All other boxes should be unchecked.
4. Use the cursor to click and drag a box around the first NNS burst identified with the criteria described in step 4.2.
5. Click Analyze (as part of peak analysis options in the top toolbar), which will identify peaks with parameters specified in step 4.3.
6. Click the Burst Analysis Macro button, which will generate a pop-up data pad menu.
7. In the data pad, insert a row in the column above the data by right clicking that column, selecting Insert Row for the first NNS burst, and typing Min 0-1 (or whichever minute the first burst occurs in).
8. Continue steps 4.4. - 4.6. until all NNS bursts have been selected. Continue to keep track of the minute in which bursts occur by characterizing the specific minute (e.g., Min 1-2, Min 2-3) in the data pad.
9. Once the analysis is complete, select File > Save As, and save the analyzed NNS file as the participant ID, date, and researcher initials. Additionally, select File > Export > Data Pad Only as Text File > Save to save the data pad file separately.
   NOTE: It is important to save the raw NNS file, analyzed NNS file, and text file.
10. Process the text file through a custom NNS burst macro. This produces an analyzed text file that contains the following burst variables: duration, frequency, height (amplitude), burst count, cycles/burst, and cycles/minute for each NNS burst. It also contains an average for the two consecutive minutes of NNS with the highest cycle count, which is often used for final analyses. Adjust depending on what analysis window needs to be analyzed.

Results

The NNS device has been used in numerous published studies that incorporate NNS outcome measures^17,18,19. In the example data shown in Figure 7, bursts have been manually identified with the following criteria: more than one suck cycle per burst, cycles having at least an amplitude of 1 cmH₂O, and suck waveforms within 1000 ms of each other. Once bursts are identified, the custom Macro ou...

Discussion

The NNS device has several limitations that are important to acknowledge. Although NNS provides critical insight into feeding⁹, there is a considerable amount of extrapolation from NNS to feeding performance. Solutions to this limitation have included research teams pairing NNS results with actual feeding observations and comprehensive feeding-related questionnaires for caregivers to more fully capture how NNS relates to feeding¹⁸. In addition, an infant can have a well-pat...

Materials

Name	Company	Catalog Number	Comments
Case	Pelican	1560
Data Acquisition and Analysis Software/LabChart	ADInstruments	8.1.25
Data Acquisition Center (PowerLab 2/26)	ADInstruments	ML826
Laptop	Dell	Latitude 5480
Pressure Calibrator	Meriam Process Technologies	M101
Soothie Pacifier	Phillips Avent	SCF190/01
Syringe	CareTouch	CTSLL1