The Character Of MLS Brainstem Auditory Evoked Potential In Preterm Infants And The Effect Of Hypoxia On It

Conventional brainstem auditory evoked potential (BAEP) has been widely used to detect the function of brainstem auditory pathway in preterm infants. Because the click rate has been limited, there may be some false-negative results in conventional BAEP. A relatively new technique, the maximum length sequence (MLS) BAEP, allows presentation of stimuli at much higher rates than possible with conventional methods, but there are only few reports about its application in preterm infants. Perinatal hypoxia could make brain injury and probably affect brianstem auditory pathway. It is very important to study the character of MLS BAEP in preterm infants and the effect of perinatal hypoxia on it.Objectives: To study the character of MLS BAEP waveform in preterm infants and the correlation between MLS BAEP and the click rate, gestational age, birth weight, head circumference and sex. To study the effect of hypoxia on MLS BAEP, the sensitive variables which could reflect the change of brainstem auditory function and if MLS BAEP is better for early detection of brain damage than the conventional BAEP.Methods: Normal preterm group included 89 preterm babies (gestation 29w-36⁺³w) without any perinatal complication and risk factor of auditory injury. They also were divided into preterm group A (gestation 29w-31⁺⁶w), preterm group B (gestation 32w-33⁺⁶w) and preterm group C (gestation 34w-36⁺⁶w) according to their gestational age. Hypoxia preterm group included 87 preterm babies with perinatal hypoxia. They were divided into severe hypoxia group (51 babies) and mild hypoxia group (36 babies) according to their perinatal hypoxic history. Most of babies in severe hypoxia group were divided into severe brain injury group (19 babies) and mild brain injury group (25 babies). Normal term group included 38 healthy term babies. The recording of conventional and MLS BAEP was performed on 3-7 day after birth, at 37-42 week and 3 month of postconceptional age. MLS BAEP was recorded at threeclick rates, 91/s, 227/s and 455/s, and the conventional BAEP was recorded at 21/s as control. Latencies and amplitudes of wave I, III and V and interpeak intervals of I-III, III-V and I-V were measured.Results: CDWave I, III and V were more clear and identifiable than other waves in both conventional and MLS BAEP in normal preterm group. All these three waves were clear at 91/s, 227/s and 455/s, while they might be difficult to be identified at 910/s. ?The latencies and interpeak intervals of all MLS BAEP components in normal preterm group were correlated positively with the click rate, while all wave amplitudes were correlated negatively with it. Wave V latency (r=0.558), III-V interval (r=0.528), I-V interval (r=0.525), wave III amplitude (r=-0.635) and wave V amplitude (r=-0.633) were more closely correlated with the click rate than other variables. (3) The latencies, interpeak intervals and amplitudes of all MLS BAEP components were correlated with the gestational age in normal preterm group on 3-7 day. The latencies and interpeak intervals were correlated negatively while the amplitudes were correlated positively with the gestational age. Most variables were correlated with the birth weight and the head circumference, while there was no obvious correlation between variables and the sex. In the correlation between all variables and the gestational age, wave V latency and amplitude and I-V interpeak interval were more closely correlated with it than other components at all click rates (455/s, r=-0.645, 0.372 and -0.592 respectively). ?The results of comparison among preterm group A, B and C and normal term group showed that all wave latencies and interpeak intervals decreased while amplitudes increased with the increase of the gestational age at all click rates (P<0.05⁰.001), and the latencies and interpeak intervals increased while amplitudes decreased with the increase of click rate in the same group (P<0.01⁰.001). ?At 37-42 week of postconceptional age, no statistically significant differences were found between normal preterm group and term group in wave I, III and V latencies and amplitudes. I-V interpeak interval of preterm neonates tended to increase slightly but did not differ significantly from the term ones. The I-III interval decreased significantly (PO.05) whereas the III-V interval increased significantly (P<0.05⁰.01) at all 91/s, 227/s and particularly 455/s (I-III interval is 3.09ms+0.16ms in preterm group and 3.19ms±0.21ms in term group, PO.05. III-V interval is 2.98ms±0.16ms in preterm group and 2.86ms ±0.18ms in term group,P<0.01). ?In hypoxia preterm group, wave V latency, III-V and I-V interpeak intervals increased while wave V amplitude decreased comparing with those in normal preterm group, which becamemore significant at 455/s and at the same time wave III latency (6.6 lms + 0.56ms) and I-III interval (3.65ms±0.47ms) also increased while wave III amplitude (0.03 nvi 0.02 n v) decreased. Comparing variables in mild hypoxia group with those in normal preterm group, no differences were found in all latencies, interpeak intervals and amplitudes at conventional 21/s, while at 227/s and 455/s of MLS BAEP, wave III and V latencies, all interpeak intervals increased (P<0.05⁰.01) and some amplitudes reduced. Comparing variables in severe hypoxia group with those in mild hypoxia group, the main differences were the increase of wave V latency, III-V and I-V intervals and the decrease of wave V amplitude, which became more significant when comparing with those in normal preterm group (PO.01⁰.001), and at the same time the latency and amplitude of wave III and I-III interval all became abnormal. It was more significant that the increase of latencies and intervals and the decrease of amplitudes in severe brain injury group than those in mild brain injury group. ?At 37-42 week of postconceptional age, I-III and I-V intervals in mild hypoxia group were similar to those in normal term group. In severe hypoxia group, wave V latency, III-V and I-V intervals still increased and wave V amplitude decreased than those in normal group, which was more significant at 455/s (9.45ms ± 0.44ms, 3.28ms± 0.24ms, 6.53ms ± 0.24ms and 0.05 u v± 0.02 u v respectively). (8)At 3 month, no major differences were found in the latencies, interpeak intervals and amplitudes between severe hypoxia group and normal term group at conventional 21/s. Only III-V and I-V interpeak intervals and wave V amplitude in severe hypoxia group differed slightly from those in normal term group (PO.05).Conclusions: ?MLS BAEP can be used to detect the brainstem auditory function in preterm infants, and 91/s, 227/s and 455/s are relatively proper click rates for preterm neonates. ?There is correlation between all wave latencies, interpeak intervals and amplitudes and the click rate in MLS BAEP. All variables are correlated with the gestational age, and most of them are correlated with the birth weight and the head circumference. No significant correlation is found between the variables and the sex. (3)On 3-7 day after birth, the brainstem auditory function of normal preterm neonates is more immature than that of term babies but similar to it at term. The preterm babies have a relatively advanced peripheral development of the brainstem auditory pathway, which is probably related to the earlier exposure to sound enviroment ex utero. ?Perinatal hypoxia can injury the brainstem auditory pathway, and more severe hypoxia, more extensive and severe damage. The brainstem auditory...