Table 3.

Overview of the measuring systems used to monitor sucking process: measurands, sensors and measurement procedures.

	Measurand	Measuring Transducer	Measurement Procedure	Ref.
Suction	Intraoral Pressure	PT	PT embedded into a catheter and placed at the tip of the nipple	[28,29,32,34,48]
			PT connected to a catheter, whose opposite tip ends into the oral cavity lumen	[10,14,16,25,35, 41,44,49–51]
			PT placed between the nipple and a flow limiting device (restriction orifice or a capillary tube)	[37,39]
	Throat movements	Videocamera and markers (DLT)	Digital video camera at 1 m from the infant's face; markers placed on the lateral angle of the eye and on the throat	[44]
Expression	Expression Pressure	PT	PT connected to a polyethylene catheter, connected to a catheter of compressible silicone rubber, placed on the nipple	[27,29,32,34,48]
			PT connected to the lumen of the nipple by means of a silicone catheter; one-way valve placed between the nipple chamber and the nutrient reservoir.	[14,35,49]
	Jaw movements	Videocamera and markers (DLT)	Digital video camera at 1 m from the infant's face; markers placed on the lateral angle of the eye and on the tip of the jaw.	[44]
		Strain gauge Transducer	Strain gauge transducer attached between the infant's forehead and the chin	[10]
Sucking events (no S/E distinction)	Intranipple pressure	PT	PT connected to the lumen of the nipple by means of a silicone catheter	[30,33,40,51,52]
	Chin movements	Strain-gauge	Stretch-sensitive strain gauge placed under the infant's chin and secured over the zygomatic bones; its wire connector inserted into a plethysmograph	[31,53]