Multivariate autoregressive model in the study of interrelations between cardiorespiratory signals in neonatal lambs

288 nation and its accuracy has been established, no normative BP values for this device are available for the newborn. We measured BPS in the right upper arm (Arm) and the calf in 219 normal full-term newborns l-3 days of age by the Dinamap Monitor, in order (1) to establish normative BPS and, (2) to help detect infants with coarctation of the aorta (COA). The width of the BP cuff was selected to be 0.4-0.5 times the circumference of the extremities. The Neonatal #4 (4.6 cm) or Infant cuff (5.4 cm) met the selection criterion for all neonates. The circumference of the Arm and calf was almost identical; 10.7 f 0.8 and 11.1 + 0.8 cm, respectively. Three readings of BPS and heart rate (HR) were obtained, from each site, in the supine position and were statistically analyzed using the SPSS computer program. Arm BP values ( f S.D.) of quiet neonates were 64.7 f 8.1 systolic, 40.6 f 6.3 diastolic, 49.8 f 7.0 mean pressures. The 90th percentile values were 75/50(60). The HR was 134.1 f 15.1 per min. BP values in the calf using the same-sized cuff were almost identical to those of the Arm. Active neonates had values 5-9 mmHg higher than quite neonates. The HR of active neonates was lO/min faster than that of quite neonates. Five neonates with COA (4 preductal, 1 postductal) had either a) hypertension in the arm with BP 90th percentile values or greater, (4/5 patients) and/or (b) calf BP which was lower than Arm BP by 1 SD (6-9 mmHg) (5/5 patients). Other positive findings seen in all patients with preductal COA included (1) differential pulses in the arm and leg, (2) unequivocal right ventricular hypertrophy on ECG, (3) large dimensions of the right ventricle and pulmonary artery (with relatively small left ventricular dimension) and direct visualization of COA by 2D echocardiography and (4) Doppler evidence of COA. These results show that (a) Arm BPS and calf BPS using the same-sized cuff are almost identical with mean values of 65/41(50) in quiet neonates, and 2) Arm BP 75/50(60) or greater and/or calf BPS lower than Arm BPS by 6-9 mmHg in quite neonates suggest COA in the newborn l-3 days old.

Multivariate autoregressive model neonatal lambs. J. Griinlund, S. Cardiorespiratory Research Unit, Research Centre of Finland and Technology, Finland

in the study of interrelations between cardiorespiratory signals in Kallib, H. Ihalainen’, A. Siimes”, K. Antila’ and I. Valimiikiki’. University of Turku, bMedical Engineering Laboratory, Technical cMeasurement Engineering Laboratory, Tampere University of

Cardiorespiratory control is mediated by the autonomic nervous system. Respiration modulates heart rate and blood pressure. Baroreflex links blood pressure and heart rate together. The influence of the autonomic control on complex cardiovascular and respiratory interactions has been relatively little studied quantitatively in the neonatal period. The reason for this may be the lack of sufficiently advanced signal analysis methods. The purpose of our study was to examine interrelations between heart rate (HR), respiratory transthoracic impedance (resp) and arterial blood pressure (BP) as well as the influence of sympathetic control on these variables by multivariate autoregressive (MAR) modelling. The MAR model developed describes a system where all three simultaneous signals are related to each other. Each signal is a linear combination of its own past values and the past values of the other signals plus a predictive modelling term. The magnitudes of interrelations between the signals are assessed by source contribution analysis. HR, BP and resp were recorded in 8 neonatal lambs. To examine the influence of sympathetic control system the animals were given propranolol 1.Omg/kg i.v. The recordings were made 60 min before and 10 after the administration of the drug. Signals were digitized, low-pass filtered and the MAR-model was computed (VAX 1l/750 computer). The comparison between the signal variabilities was performed by signal source contribution ratios of the MAR-model. The frequency-areas of interest were 0.02-G.08 Hz (thermoregulation, renin-angiotension), 0.08-0.25 (natural frequency of baroreflex) and 0.40-0.75 (respiratory rate). Both the HR and BP had large autocontributions at each frequency area. The cross-contribution of BP to HR and vice versa was higher at the low-frequency area than in the frequencies > 0.08 Hz. The respiratory cross-contribution on HR and BP was greatest at the frequencies corresponding to the respiratory rate. The signal source contributions to resp and BP signals were not significantly affected by the beta blockade. The beta blockade decreased respiratory cross-contribution to HR significantly at 0.020.25 Hz.

289 The results show that the cardiorespiratory signals have strong interactions and that the magnitudes of the cross-contributions are frequency selective. The magnitudes of these interactions may be estimated by the MAR modelling but the technique is computationally demanding. A great advantage of the MAR model is that the interrelations between numerous (> 2) signals can be examined at the same time. We can conclude that the low-frequency components of respiratory heart rate variability are in part mediated by beta-adrenergic system in the newborn lamb. Acknowledgement: The Academy of Finland has supported this project. The effect of hypoxia and hyperoxia on breathing pattern and ventilation in three-day old infants during sleep. D. Andersson., G. Gennserb and P. Johnson’, “Department of Paediatrics, and bObstetrics and Gynecology, University Hospital, Malmii, Sweden & ‘Nuffield Department of Obstetrics and Gynecology, John Radcliffe Hospital, Headington, Oxford, U.K. The biphasic response of the newborn infant to hypoxia remain unclear. We have attempted to combine the use of non invasive, direct and indirect, measurements suitable for investigating in both sleep states the following factors that influence respiratory control in healthy sleeping infants, at 3 days of postnatal age: (1) the influence of peripheral chemoreceptor drive; (2) in response to hypoxia the possible contribution of an altered metabolism and/or an altered strategy of breathing. Data were obtained during air breathing, and during the first 10 min of exposure to 15010oxygen in 21 infants sleeping in prone position in a thermoneutral environment (32“C). Fourteen other infants were exposed to 1 min of 100% oxygen. It was found that while sleep state, at 3 days of age, did significantly influence the pattern of breathing (and therefore needs to be identified), it did not alter the magnitude of the ventilatory response to hypoxia. There was no biphasic ventilatory response but an immediate decrease (within 1 min) in ventilation, which was sustained throughout the hypoxic period. It was found that higher basal Ptcco, and heart rate, together with lowtr Ptco, and minute volume, distinguished a minority of infants who developed periodic breathing and lower oxygen tensions during hypoxia, compared with the majority of infants, who developed active retardation of expiratory air flow and maintained higher oxygen tensions during hypoxic challenge. Arousals during hypoxia were common in the latter group but rare in the former. A ventilatory response to hyperoxia was also absent, supporting the lack of peripheral chemoreceptor activity at this age. A novel finding is the link between basal ventilation (but not breathing frequency) and respiratory pattern and CNS arousability during hypoxia. The results suggest an active inhibition of ventilation and basal metabolism during hypoxia. Interaction of heart rate and respiration in newborn babies. T. &irimaa,

V&limki, Department of Pediatrics and Cardiorespiratory Finland.

R. Oja, K. Antila and I. Research Unit, University of Turku, Turku,

Spectral analysis allows a quantitative method to study periodic functions in frequency domain. Thus e.g. periodic components of heart rate variability (HRV) can be displayed and their relative densities quantified using this method. HRV can also be examined against respiratory activity by cross-correlation. Respiratory sinus arrhythmia (RSA) is one example of interaction of heart rate (HR) and respiration. The modulation of HR by respiration is probably rather complex and mediated by multiple mechanisms. The autospectral and cross-spectral densities of HRV and impedance respirogram (TEZ) were studied in three groups of neonates: healthy term babies (22), healthy preterm babies (21) and preterm babies with respiratory distress syndrome (11). The peak activity of HRV was at < 0.2 Hz (low frequency, LF) area but the evolution of postnatal spectral patterns in the three groups displayed differences which probably reflect maturational and disease prone differences in the cardiac control system. The cross-spectral activity of HRV and TEZ spectra was more prominent in both groups of preterm babies in whom the LF regulation of HRV seems to be more firmly connected with regulation and mechanics of respiration. RSA was minimal at frequency areas > 0.2 Hz in all the neonates studied. Acknowledgements: ported this study.

The Academy of Finland and Turku University Foundation have economically sup-