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Cotside measurement of cerebral blood flow in sick newborn infants by near infrared spectroscopy
292
We have therefore demonstrated that complete plethysmographic measurements can be performed in infants without the need for airway occlusion. 1 I. Dab and F. Alexander (1978): Pediat. Res., 12: 878. Grant CPBR, Poland No 11.7.14.1.
Conventional
statistical indices for neonatal heart rate variability are not reliable -
what to do? Hannu
Anttila, Department of Pediatrics, University of Turku, Turku, Finland. Irregularities in the rate of the beating heart are caused by cardioregulatory mechanisms which are necessary for the adjustment of circulation to respond to changing demands of the body. A considerable decrease in HRV has been detected in critically ill newborn infants like those suffering from respiratory distress. Clinical computing of simple HRV indices is still rather uncommon. This may be because no conventional statistical indices of HRV alone give sufficient and stable information about the cardiac control of the neonate and they are extremely vulnerable for sudden irregularities caused by ectopic heart beats and other non-stationarities. To produce more reliable representation of the HRV a moving window technique was developed. Seventeen newborn infants, 10 fullterm (2900-4830 g) and 7 newborns with RDS (1470-2880 g) were studied by recording 1000 successive R-R intervals from bipolar chest leads. The values of RMSM and RMSSD were calculated for a window of 50 successive R-R intervals. This computing window was moved forward by steps of one R-R interval and values of RMSM and RMSSD were computed and plotted as function of time of the center point of the window. The computation was repeated and the HRV index was updated for each window. This method produces time-related HRV-indices called here instantaneous RMSM (IRMSM) and instantaneous RMSSD (IRMSSD). The plot of simultaneous instantaneous HR, IRMSM and IRMSSD tracings displayed time-related changes in the HR and HRV. Frequency densities of IRMSM and IRMSSD helped to feature the variability of HR and detect the commonest (modal) HRV level. The vulnerability of the used conventional statistical indices for sudden non-stationarities was displayed by simulation. To a simple of 1000 R-R intervals with no irregularities 1, 2 and 3 extrasystoles were added and the values of RMSM, RMSSD and modal values of IRMSM and IRMSSD were studied. The effect of these extrasystoles on the statistical indices of HRV showed a three-fold rise in RMSSD and CVS; from 2.06 to 6.19 ms and 0.47 to 1.40, respectively. The values of RMSM and CV changed much less (16.50 to 16.83 ms and 3.74 to 3.81, respectively). There was practically no influence on the modal values of instantaneous HRV indices (IRMSM 4 and IRMSSD 2 ms constantly in spite of the added extrasystoles). For the control group the conventional HRV indices, RMSM and RMSSD were 15.8 ms and 5.4 ms and the mean respiratory rate was 456/min. For the group with RDS RMSM was 10.6 (NS) and RMSSD 2.6 (P < 0.05) and mean respiratory rate was 6O/min. The modal values for IRMSM and IRMSSD were in the control group 6.9 ms and 4.0 ms and in the group with RDS 3.7 and 2.5 (P< 0.05 for both), respectively. The mean modal values of IRMSM and IRMSSD were found superior in distinguishing the small groups of healthy infants from a group of infants with RDS. Acknowledgement: This study has been supported by the Turku University Foundation. Cotslde measurement of cerebral blood flow in sick newborn infants by near infrared spectroscopy. A.D.
Edwards, J.S. Wyatt, C.E. Richardson, D.T. Delpy, M. Cope and E.O.R. Reynolds, Departments of Paediatrics, and Medical Physics and Bioengineering, University College and Middlesex School of Medicine, London, U.K. We describe a new non-invasive method for quantifying cerebral blood flow (CBF) derived from the Fick Principle. If a small sudden change occurs in arterial oxygen saturation (Saod then, provided cerebral
293 oxygen extraction remains constant, the resulting increase in arterial oxyhaemoglobin (HboJ concentration can be used as an intravascular tracer. The increase in cerebral Hbo, (A[Hbo,]) at a time t following the change can be quantified by near infrared spectroscopy (NIRS). If r is less than the cerebral transit time then A[Hbo,] measures the accumulation of tracer in the brain. The quantity of tracer introduced is given by the time-integrated product of ASao, and the arterial total haemoglobin concentration (fHb). Thus: CBF(ml - 100 g-l - min-‘) = (K - A [Hbo,])/[tHb]
S’o(ASao,)dt
where K is a constant reflecting cerebral/large vessel haematocrit ratio, molecular weight of haemoglobin and cerebral tissue density. CBF was measured on 31 occasions in nine ill infants born at 26-44 weeks’ gestation and aged l-10 days. All infants were receiving supplementary oxygen, and baseline Sao, was 80-95%. Changes in cerebral [HboJ were measured every l-2 s by NIRS while Sao, was measured by a modified pulse oximeter sited on an ear. Following a period when recordings were stable a sudden increment of 5-10% was induced by Sao* by increasing the inspired oxygen concentration. CBF normally ranged from 14 to 33 ml * 100 g-l . mm-l, but was much lower, 7 ml - 100 g-’- min-’in one infant following indomethacin. Supported by the MRC, the Wellcome Trust, and Hamamatsu Photonics KK.
The relationship between environmental temperature, metabolic rate and sleep state in infants from birth to two months. Yehu Azax, Peter Fleming, Michael Levine and Rosemary McCabe, Institute of Child Health, University of Bristol, U.K. The lower end of the thermoneutral range is slightly lower at 3 weeks of age than at 1 day but little information is available on the effect of sleep state on metabolic rate beyond the first week. We have investigated the effect of sleep state on metabolic rate at temperatures within and below the thermoneutral range in a longitudinal study of fifteen lightly clothed term infants from 2 days to 3 months. Polygraphic recordings of sleep state were performed in a modified barometric plethysmograph in which temperature could be controlled whilst recording oxygen consumption (%,), CO2 production (VCCII),and the infants skin and axillary temperatures. Wz and .Woz rose as environmental temperatures fell below 23% at all ages. At temperatures of 23-27’W, WJ~was higher at one month than at two days in both Rapid Eye Movement (REM) sleep (increase = 34%) and Quiet Sleep (QS) (increase = IS%), and remained at this level at two months. %.zo*showed similar changes. At each age and all temperatures ib, and Vcoco2 were higher in REM than in QS. Thus there is little change in the lower end of the thermoneutral range between two days and two months. The rise in metabolic rate at one month parallels the previously described increases in heart rate and respiratory rate [I]. Carseet al. (1981): J. Dev. Physiol., 3,85--100.
Cerebral haemodynamics
during the development
of secondary energy failure following birth asphyxia.
J.S. Wyatt, D. Axxopardi, M. Cope, E.B. Cady, C.E. Richardson, D.T. Delpy, A.D. Edwards and E.O.R. Reynolds, Departments of Paediatrics, and Medical Physics and Bioengineering, University College and Middlesex School of Medicine, London, U.K. Changes in cerebral blood volume (CBV) and vascular response to changes in arterial carbon dioxide tension (Pace,) during the development of secondary energy failure following severe birth asphyxia were investigated by near infrared spectroscopy (NIRS). Nine infants born at 36-44 weeks’ gestation who had sustained severe birth asphyxia were studied
We have therefore demonstrated that complete plethysmographic measurements can be performed in infants without the need for airway occlusion. 1 I. Dab and F. Alexander (1978): Pediat. Res., 12: 878. Grant CPBR, Poland No 11.7.14.1.
Conventional
statistical indices for neonatal heart rate variability are not reliable -
what to do? Hannu
Anttila, Department of Pediatrics, University of Turku, Turku, Finland. Irregularities in the rate of the beating heart are caused by cardioregulatory mechanisms which are necessary for the adjustment of circulation to respond to changing demands of the body. A considerable decrease in HRV has been detected in critically ill newborn infants like those suffering from respiratory distress. Clinical computing of simple HRV indices is still rather uncommon. This may be because no conventional statistical indices of HRV alone give sufficient and stable information about the cardiac control of the neonate and they are extremely vulnerable for sudden irregularities caused by ectopic heart beats and other non-stationarities. To produce more reliable representation of the HRV a moving window technique was developed. Seventeen newborn infants, 10 fullterm (2900-4830 g) and 7 newborns with RDS (1470-2880 g) were studied by recording 1000 successive R-R intervals from bipolar chest leads. The values of RMSM and RMSSD were calculated for a window of 50 successive R-R intervals. This computing window was moved forward by steps of one R-R interval and values of RMSM and RMSSD were computed and plotted as function of time of the center point of the window. The computation was repeated and the HRV index was updated for each window. This method produces time-related HRV-indices called here instantaneous RMSM (IRMSM) and instantaneous RMSSD (IRMSSD). The plot of simultaneous instantaneous HR, IRMSM and IRMSSD tracings displayed time-related changes in the HR and HRV. Frequency densities of IRMSM and IRMSSD helped to feature the variability of HR and detect the commonest (modal) HRV level. The vulnerability of the used conventional statistical indices for sudden non-stationarities was displayed by simulation. To a simple of 1000 R-R intervals with no irregularities 1, 2 and 3 extrasystoles were added and the values of RMSM, RMSSD and modal values of IRMSM and IRMSSD were studied. The effect of these extrasystoles on the statistical indices of HRV showed a three-fold rise in RMSSD and CVS; from 2.06 to 6.19 ms and 0.47 to 1.40, respectively. The values of RMSM and CV changed much less (16.50 to 16.83 ms and 3.74 to 3.81, respectively). There was practically no influence on the modal values of instantaneous HRV indices (IRMSM 4 and IRMSSD 2 ms constantly in spite of the added extrasystoles). For the control group the conventional HRV indices, RMSM and RMSSD were 15.8 ms and 5.4 ms and the mean respiratory rate was 456/min. For the group with RDS RMSM was 10.6 (NS) and RMSSD 2.6 (P < 0.05) and mean respiratory rate was 6O/min. The modal values for IRMSM and IRMSSD were in the control group 6.9 ms and 4.0 ms and in the group with RDS 3.7 and 2.5 (P< 0.05 for both), respectively. The mean modal values of IRMSM and IRMSSD were found superior in distinguishing the small groups of healthy infants from a group of infants with RDS. Acknowledgement: This study has been supported by the Turku University Foundation. Cotslde measurement of cerebral blood flow in sick newborn infants by near infrared spectroscopy. A.D.
Edwards, J.S. Wyatt, C.E. Richardson, D.T. Delpy, M. Cope and E.O.R. Reynolds, Departments of Paediatrics, and Medical Physics and Bioengineering, University College and Middlesex School of Medicine, London, U.K. We describe a new non-invasive method for quantifying cerebral blood flow (CBF) derived from the Fick Principle. If a small sudden change occurs in arterial oxygen saturation (Saod then, provided cerebral
293 oxygen extraction remains constant, the resulting increase in arterial oxyhaemoglobin (HboJ concentration can be used as an intravascular tracer. The increase in cerebral Hbo, (A[Hbo,]) at a time t following the change can be quantified by near infrared spectroscopy (NIRS). If r is less than the cerebral transit time then A[Hbo,] measures the accumulation of tracer in the brain. The quantity of tracer introduced is given by the time-integrated product of ASao, and the arterial total haemoglobin concentration (fHb). Thus: CBF(ml - 100 g-l - min-‘) = (K - A [Hbo,])/[tHb]
S’o(ASao,)dt
where K is a constant reflecting cerebral/large vessel haematocrit ratio, molecular weight of haemoglobin and cerebral tissue density. CBF was measured on 31 occasions in nine ill infants born at 26-44 weeks’ gestation and aged l-10 days. All infants were receiving supplementary oxygen, and baseline Sao, was 80-95%. Changes in cerebral [HboJ were measured every l-2 s by NIRS while Sao, was measured by a modified pulse oximeter sited on an ear. Following a period when recordings were stable a sudden increment of 5-10% was induced by Sao* by increasing the inspired oxygen concentration. CBF normally ranged from 14 to 33 ml * 100 g-l . mm-l, but was much lower, 7 ml - 100 g-’- min-’in one infant following indomethacin. Supported by the MRC, the Wellcome Trust, and Hamamatsu Photonics KK.
The relationship between environmental temperature, metabolic rate and sleep state in infants from birth to two months. Yehu Azax, Peter Fleming, Michael Levine and Rosemary McCabe, Institute of Child Health, University of Bristol, U.K. The lower end of the thermoneutral range is slightly lower at 3 weeks of age than at 1 day but little information is available on the effect of sleep state on metabolic rate beyond the first week. We have investigated the effect of sleep state on metabolic rate at temperatures within and below the thermoneutral range in a longitudinal study of fifteen lightly clothed term infants from 2 days to 3 months. Polygraphic recordings of sleep state were performed in a modified barometric plethysmograph in which temperature could be controlled whilst recording oxygen consumption (%,), CO2 production (VCCII),and the infants skin and axillary temperatures. Wz and .Woz rose as environmental temperatures fell below 23% at all ages. At temperatures of 23-27’W, WJ~was higher at one month than at two days in both Rapid Eye Movement (REM) sleep (increase = 34%) and Quiet Sleep (QS) (increase = IS%), and remained at this level at two months. %.zo*showed similar changes. At each age and all temperatures ib, and Vcoco2 were higher in REM than in QS. Thus there is little change in the lower end of the thermoneutral range between two days and two months. The rise in metabolic rate at one month parallels the previously described increases in heart rate and respiratory rate [I]. Carseet al. (1981): J. Dev. Physiol., 3,85--100.
Cerebral haemodynamics
during the development
of secondary energy failure following birth asphyxia.
J.S. Wyatt, D. Axxopardi, M. Cope, E.B. Cady, C.E. Richardson, D.T. Delpy, A.D. Edwards and E.O.R. Reynolds, Departments of Paediatrics, and Medical Physics and Bioengineering, University College and Middlesex School of Medicine, London, U.K. Changes in cerebral blood volume (CBV) and vascular response to changes in arterial carbon dioxide tension (Pace,) during the development of secondary energy failure following severe birth asphyxia were investigated by near infrared spectroscopy (NIRS). Nine infants born at 36-44 weeks’ gestation who had sustained severe birth asphyxia were studied