Med. & Biol. Eng. & Comput. 1979, 17, 742-750 Breathing ratemeter fop neonatal intensive cape S. Ben-Yaakov A. Cohen Electrical Engineering Department, Ben-Gurion University of the Negev, Beer-Sheva 84 120, P0 Box 653, Israel Abstract--A new bit-to-bit ratemeter based on rate multiplication is described. The ratemeter is part of a signal monitoring and processing system used to analyse respiratory signals of neonates that are characterised by low and unstable rates. The advantages of the new ratemeter are discussed and a comparison is made with other meters. The response of the ratemeters is demonstrated by means of simulated signals as well as actual neonatal respiratory signals. Keywords--Apnoea, Breathing, Ratemeters, Respiration rate 1 Introduction NEONATAL intensive-care units have recently received much attention in terms of monitoring and process- ing equipment. The availability of microprocessors and new noninvasive techniques, such as the trans- cutaneous pO2 measurement (EBERHARD et aL, 1975), allows the continuous monitoring and processing of various physiological signals from infants (RoLFE, 1975). In contrast with intensive- care units for adults, neonatal intensive care requires an extensive monitoring and processing of respiratory signals. The respiratory system undergoes a complex transition between intra- and extra-uterine states during the birth process. Even after the first breaths of life have established independent respiration, the neonatal respiratory system remains, for a time, a system that may be inherently unstable in its ability to maintain a constant lung volume (NELSON, 1976). Infants, and especially premature infants, may develop respiratory problems that require monitor- ing, and, often, intervension. A common type of breathing for such infants is the 'periodic breathing', where short nonbleathing periods (apnoeas) exist. The effects of the duration and frequency of these apnoeic attacks are not exactly known. It is generally recognised, however, that a long-duration apnoea (of the order of 20 s) reflects a clinical abnormality often requiring intervension. The most common respiration monitoring device in neonatal intensive- care units is, therefore, the apnoea detector. This device detects long nonbreathing periods and activates an alarm. Recently, several investigators have suggested that multiple apnoeas of shorter duration may also have clinical implications. The cumulative affect of such apnoeas on the pulmonary arterial pressure and right ventricular failure was First received 4th January and in final form 23rd March 1979 0140-0118/79/060742-09 $01-50/0 @ IFMBE: 1979 stressed, for example, by COCCAGNA et al. (1972). Several reports linking the high incidence of apnoeas with the sudden infant death syndrome have been reported (STE1NSCHNErDER, 1972). The monitoring and processing of the respiratory signal is also important for the determination of the state of consciousness of the newborn, and especially the preterm infant. The sleep cycle, namely the total amount of sleep and the distribution of quiet and active sleep, may be important for the early develop- ment of the immature brain (GABmEL,1977; HOPPEN- BROUWERS, 1977; PRECriTL et aL, 1973). Many types of respiration monitoring devices have been used. These ate divided into two major groups. The contactless systems include the air-filled-mattress device (LEwIN, 1969), under-mattress pressure- sensing devices (Health Devices, 1974), magneto- meter devices (ROLFE, 1971), capacitance-change detectors (BARROWand COLGAN, 1973) and radar reflection systems (LIN, 1977). The contact systems include whole-body plethysmography (CRoss, 1949), pneumotachography (BLUMFIELD et al., I973), impedance pneumography (I-IILL et al., 1967) and thermistor anemometry. A comprehensive discussion of these systems, their advantages and disadvantages, is given elsewhere (Health Devices, 1974; ROLFE, 1975; FRANKS et al., 1976). Modern neonatal intensive-care units call for more sophisticated respiration signal processing than the common apnoea detectors (Health Devices, 1974). Factors such as the respiratory rate, distribu- tion of apnoeas and analysis of breathing modes are required. This paper describes an analogue breathing ratemeter that is used as a stand-alone monitoring device or as a part of a larger sophisticated system. The breathing signal is provided by a nasal thermistor. This sensor was chosen because of its simplicity and because most of the wolk was per- formed on premature newborns where breathing is said to be predominantly through the nose (PRECHTL 742 Medical & Biological Engineering & Computing November 1979