Night-to-night variability of apnea indices M.M.R. VERHELST, R.J. SCHIMSHEIMER, C. KLUFT, A.W. DE WEERD CENTRE FOR SLEEP AND WAKE DISORDERS, MCH, WESTEINDE HOSPITAL, THE HAGUE In our centre, the diagnosis of OSAS is made by 2x24 hours ambulatory polysomnography. This approach has the advantage that it provides insight not only in respiratory parameters but also in sleep quality and excessive daytime sleepiness. In view of financial restrictions by the government, the question arose if a single night screening might be sufficient. The answer to this question is also important for another reason : CPAP treatment is given when the apnea-index (AI) is 15. Can such an important therapeutical decision be taken on the basis of a single night recording? On the other hand little is known about night-to-night variability of apnea indices in ambulatory polysomnography. This study therefore investigates the night to night variability of apnea indices. Methods The polysomnographic records of 50 patients with an apnea index 5 in at least one of the two nights were retrospectively screened (45 men and 5 women). We compared the mean duration of the apneas, the maximum duration of the apneas, the AI in the total sleep time (TST) and the AI in the total sleep period (TSP) in both nights. The intra subject apnea variability between night1 and night 2 was calculated as a relative percentage by the following formula : (AI TST 1 AI TST 2) : (AI TST 1 + AI TST 2) x 100. Results Table 1 lists the mean values with standard deviations of the analysed characteristics in both the first and second night and the absolute difference between first and second night. 175
Night 1 Night 2 Night 2 Night 1 Mean duration 22 ± 7 23 ± 8 0.5 ± 5 Maximum duration 50 ± 26 52 ± 32 2 ± 20 AI TST 21 ± 21 24 ± 27 10 ± 15 AI TSP 16 ± 15 17 ± 16 1.3 ± 7 Table 1 Absolute differences where analysed by Student s t-test. There was no significant difference for all parameters even if individual differences were quite substantial. Figure 1 shows the relative difference of apnea indices in TST between the two nights. Most patients differed in the range 10-30 %. For example: a patient with an apnea index of 15 (TST) in one night may have an index of 10 or 20 in the following night. The cut-off point for CPAP treatment was reached by 23 patients in the first night. From the other 27 patients only 3 reached this criterium in the second night. Figure 1 Conclusion Night-to-night intra subject variability of the apnea index was small for this group. As substantial individual variability does exist, single night recording induces a certain risk. For the decision to treat a patient with CPAP (at a cutoff point AI=15) the risk is 13-17%. This means for example that a patient with clear clinical syptoms of OSAS but with an apnea index of only 10 in the first night a second polysomnography is strongly recommended. 176
The transition from neonatal to infantile sleep A.W.DE WEERD, R.J.SCHIMSHEIMER, B.KEMP JULIANA CHILDREN HOSPITAL AND CENTRE FOR SLEEP AND WAKE DISORDERS, MCH, WESTEINDE HOSPITAL, THE HAGUE The electro-encephalogram (EEG) of the full term born baby is well developed, but has many features that disappear in the first three months of life. On the other hand new elements emerge in this period that represent the transition to the infantile EEG. During sleep, spindles are example of new EEG phenomena. Features from the record during sleep that disappear are REM sleep onset (mostly called Active Sleep onset, AS, at this age), background patterns consisting of short periods with alternating high and low amplitude activity (Tracé Alternant, TA) and triangular slow waves with highest amplitude over frontal regions (Encoches Frontales, EF). Elements from the EEG that are seen in the prematurely born child and are sometimes still present at term in a normal baby, disappear completely during these first months. Examples are so called delta brushes (DB) and short runs of rhythmic 4-6 Hz activity over temporal regions (Premature Temporal Theta activity, PTT). For more details, see 1. The elements mentioned are well described, but knowledge about the time course of the transition from the neonatal sleep EEG to that characteristic for the two to three month old child is far less detailed. The EEG is an important tool in the assessment of cerebral function in the first months of life. Sleep spindles (SS), a continuous background pattern (instead of TA) and no sleep onset AS are not only characteristic for the somewhat older infant, but are the first manifestations of human sleep as seen in the older child and adult as well. Thus, more details on the development of the sleep EEG in this period of life is of interest from a scientific point of view as well as for daily practice in pediatric medicine. Up to now this course in time of important aspects of the neonatal and infantile EEG has been studied in small groups of children only (for example 2, 3, 4), leading to sometimes conflicting results. The results presented in this report are taken from a large study of the EEG in babies with a Conceptional Age (CA, i.e. the age in weeks after conception; for example CA at term birth is 38-42 weeks) in the range between 30 and 53 weeks. Except for prematurity in the children born before CA 37 weeks, all were normal at clinical examination at the time of recording of the EEG and all had a good long-term outcome. The group of children with a CA in which the transition from neonatal to infantile sleep could be expected (CA 43-53 weeks) was studied in detail for the features of sleep mentioned above. 177
Patients and Methods Eighty-one children (44 boys) from the database met the criteria for inclusion in the study. They had a CA between 43 and 53 weeks, slept at least part of the recording time and were normal at clinical examination at the time of EEG recording and during follow-up. Admittedly, they underwent EEG registration for clinical reasons (short lasting asphyxia during birth: 2; unexplained breathing disturbances, so called ALTE s: 54; febrile convulsion: 1; slight head trauma: 1; and miscellaneous, mostly movements that might be interpreted as of epileptic origin, but never proven so: 23). The children studied were not completely normal in the strict sense of the word, but they represented the group encountered in daily practice that can be considered as very low risk and defacto normal. Seven children had a second EEG registration, resulting in 88 records for analysis. Differentiation for CA resulted in the following categories and numbers of patients: CA 43-44 weeks: N=24; CA 45-46 weeks: N=20; 47-48 weeks: N=15; 49-50 weeks: N=19 and CA 51 weeks or more: N=10. The EEG and accompanying polygraphy of ECG, respiration, eye movements and muscular tone was recorded and assessed according to internationally standardized criteria (5). In addition to this basic evaluation the EEG features relevant in the transition from neonatal to infantile sleep were studied in detail. From the 88 records 1287 minutes of sleep EEG were available for analysis (range: 90-2290 s.; median: 925 s. per recording). For the EEG in the waking condition these figures were 1713 minutes total recording time; range: 270-3460 s.; median 1055 s. per registration Results Discontinuity in background activity, the TA pattern, was seen up to the age of CA 47 weeks and was not encountered in the EEGs recorded after that age. TA is characterized by alternating periods of activation and relative suppression of background activity. When TA was present, mean and maximal duration of the suppression and the ratio between amplitudes during activation and suppression were independent from the age of the child. REM (AS) sleep onset occurred in only nine of the EEGs, in all cases before the age of CA 49 weeks. In seventy recordings NREM was the mode of first sleep. For the remaining eleven differentiation in sleep onset was not certain, but rapid eye movements, which are the hallmark of AS, were not seen at all. Frontal sharp waves, EF, occurred up to the age of 49 weeks. In particular bilateral EF, which is the main variant of this EEG phenomenon in the young child, gradually disappeared with age. EEG transients (DB and PTT) that are seen mostly in the prematurely born child and are still sometimes present at CA around 40 weeks did not occur in the study group. 178
From the age of CA 43 weeks on, there were recordings containing sleep spindles. In the youngest age category of CA 43-44 weeks this EEG phenomenon was seen in 6 out of 24 records (25%) with maximum duration of the spindles of three seconds. For the children with CA of 49 and more weeks (who all had periods of NREM sleep, see above) these figures were 25 out of 29 recordings (86%) and duration up to 12 seconds. From the age of CA 52 weeks all recordings contained sleep spindles. Conclusion. See the figure. Figure Development of sleep patterns Conceptional Age (weeks) 43 44 45 46 47 48 49 50 51 52 53 Disappearing patterns (no recording contains the pattern) Trace Alternant [ Active Sleep onset [ Encoches Frontales [ Emerging patterns (all recordings show the pattern) Sleep spindles [ References 1 de Weerd AW. Atlas of EEG in the first months of life. Amsterdam, Elsevier Scientific Publishers 1995. 2 Ellingson RJ, Peters JF. Development of EEG and daytime sleep in normal full-term infants during the first 3 months of life: longitudinal observations. Electroenceph clin Neurophysiol 1980;49:112-124. 3 Jankel WR, Niedermeyer E. Sleep spindles. J Clin Neurophysiol 1985;2:1-35. 179
4 Statz A, Dumermuth G. Transient EEG patterns during sleep in healthy newborns. Neuropediatrics 1982;13:115-122. 5 de Weerd AW, Despland PA, Plouin P. Neonatal EEG. In: G. Deuschl, A.Eisen eds. Recommendations for the practice of Clinical Neurophysiology. International Federation for Clinical Neurophysiology 1999 (ter perse en verschijnt begin september 1999; de exakte beschrijving volgt). Acknowledgement: The EEGs were recorded by I. Keyzers, J. Vreeburg and E. Dijkstra. 180