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- Fetal
yawning: all
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- Both nurse clinicians and
researchers use specific infant behaviors to
indicate preterm infant responses to
stimulation. For example, changes in preterm
behaviors have been used to identify acute
medical complications, such as cold stress and
sepsis (Holditch-Davis & Hudson, 1995), and
pain (Walden et al., 2001). Researchers also
used behaviors to show preterm infant responses
to interventions that modified neonatal care so
that it would be more developmentally
appropriate (Chang, Anderson, & Lin, 2002).
Infant behaviors have also been used by
clinicians to indicate stress. However, there is
little research validation for this. "Stress"
behaviors did not differ between times when
preterms were receiving routine and painful care
(Grunau, Holsti, Whitfield, & Ling, 2000;
Walden et al., 2001) and only occasionally
differentiated the responses of preterm infants
with and without chronic lung disease to
handling (Medoff-Cooper, 1988).
-
- Thus, a greater
understanding of infant behaviors could
strengthen the nursing care of preterm infants.
According to the developmental science
perspective (Cairns, Elder, & Costello,
1996), the infant and the environment form a
complex system, in which every behavior of the
infant is a function of the entire system
(Thoman et al., 1983). Sub-systems within the
infant, including maturation, physiological
processes, such as sleeping and waking, and
illnesses, affect the overall system and in turn
are affected by it. Thus, the biological factors
affecting infant behaviors as well as the
environmental context of behaviors need to be
examined. The purpose of this study, therefore,
was to examine biological factors affecting
eight preterm infant behaviors, specifically
development, sleeping and waking, infant
characteristics, and illness severity.
- The amounts of infant
behaviors are known to change over age (Cioni
& Prechtl, 1990). Sighs were less common in
fullterm infants than in preterm infants (Hoch,
Bernhard, & Hinsch, 1998). The likelihood of
having hiccups decreased and mouth movements
increased with age over the third trimester in
fetuses (D'Elia, Pighetti, Moccia, &
Santangelo, 2001; Pillai & James, 1990). The
amount of large body movements did not show
developmental changes over the preterm period in
infants (Giganti et al., 2001; Hayes, Plante,
Kumar, & Delivoria-Papadopoulos, 1992) but
did decrease in fetuses, possibly due to
decreased room to move in utero late in
gestation (D'Elia et al., 2001; Kisilevsky,
Hains, & Low, 1999). The development of
other behaviors, including startles, jitters,
and negative facial expressions, has not been
examined. Moreover, most studies compared
incidence of behaviors in individuals of
different ages; only one examined developmental
changes longitudinally (D'Elia et al., 2001).
Also, Only one study examined development in
preterm infants (D'Elia et al., 2001; Hoch et
al., 1998). Thus, little is known about
developmental changes in infant behaviors over
the preterm period, the time period of greatest
interest to neonatal nurses.
-
- In both preterm and fullterm
infants, sleeping and waking is known to affect
infant behaviors. Each behavior occurs primarily
in a specific sleep-wake states. Sighs were more
frequent in active sleep than quiet sleep in
both fullterm and preterm infants (Hoch et al.,
1998). yawns and negative facial
expressions were less common in quiet sleep than
active sleep or waking states in near term
fetuses and preterm infants (Giganti,
Hayes, Akilesh, & Salzardo,
2002; van Woerden et
al., 1988). In fullterm neonates, body movements
occurred primarily in waking (Weggeman, Brown,
Fulford, & Minns, 1987). Fullterm infants
showed mouth movements and startles primarily in
active sleep with rapid eye movements (REMs)
(Korner, 1968), and startles were more common in
sleeping, especially quiet sleep, than in waking
states (Emory & Mapp, 1988; Huntington,
Zeskind, & Weiseman, 1985; Korner, 1969). On
the other hand, hiccups were not related to any
particular state in near term fetuses (van
Woerden, 1989). The relationship between
behaviors and sleep-wake states is strong enough
that a number of behaviors are used to define
sleep. However, not until at least 36 weeks'
post-conceptional age, do preterm infants show
the same degree of correlation among these
behaviors as fullterm infants (Curzi-Dascalova,
Peirano, & Morel-Kahn, 1988). This suggests
that both the amount of specific behaviors and
the degree to which they are associated with
particular sleep-wake states change with
age.
- The infant characteristics
of gender and race have biological bases in the
preterm period through prenatal hormones and the
greater incidence of perinatal complications in
minority infants (Johnson, 2000) and, thus, may
affect infant behaviors. Although some
researchers found no gender differences in
fullterms in the amounts of large body
movements, startles, and negative facial
expressions (Korner, 1968; Weggemann et al.,
1987), others have found that boys show more
startles (Korner, 1969). African American
preterm infants had more jitters than Caucasians
(Pressler & Hepworth, 2002), but racial
effects on other infant behaviors have not been
studied.
-
- Likewise, illness may affect
infant behaviors. Even mild perinatal
complications were related to more jitteriness
and changes in the incidence of startles in
different states in fullterm and preterm infants
(Emory & Mapp, 1988; Huntington et al.,
1985; Parker et al., 1990). Preterms with
chronic lung disease had more sighs and jitters
than other preterms (Holditch-Davis & Lee,
1993). High-risk fetuses have fewer large body
movements than low-risk fetuses (Kisilevsky et
al., 1999). At 41 weeks post-conceptional age,
preterm infants had more large movements in
active and quiet sleep and more facial movements
in active sleep than fullterms (Booth, Leonard,
& Thoman, 1980).
- However, infant
characteristics and illness severity effects on
preterm infant behaviors have only rarely been
studied along with development and sleep-wake
states. Thus, how these factors jointly relate
to preterm infant behaviors is unknown. The
objectives of this study were 1) to examine the
development of eight infant behaviors over the
preterm period, 2) to determine how these
behaviors relate to infant characteristics and
illness severity, 3) to examine the development
of these behaviors within different sleep-wake
states, 4) to determine whether the
relationships of these behaviors to infant
characteristics and illness severity is
different in different sleep-wake states, and 5)
to determine whether the amounts of the
behaviors are different in different sleep-wake
states. Eight specific behaviors often observed
by nurses were studied: yawn, sigh,
negative facial expressions, startle/jerk,
jitter, large body movements, mouth movements,
and hiccups. These behaviors were related to
four sleeping and waking states, to two infant
characteristics (gender and race), and to
illness severity indicators (birthweight, length
of mechanical ventilation, and theophylline
treatment). Birthweight and length of mechanical
ventilation are known to be related to the
neurological status and developmental outcomes
of preterm infants (Bhutta, Cleves, Casey,
Cradock, & Anand, 2002; McCarton, Wallace,
Divon, & Vaughm, 1996); whereas theophylline
is a common medication that is known to affect
sleeping and waking (Thoman et al.,
1985).
-
- Methods
- Participants
- A convenience sample of 71
preterm infants, born at less than 35 weeks
gestational age and at high risk for later
developmental problems due to either a
birthweight less than 1500 grams or a need for
mechanical ventilation or continuous positive
airway pressure, took part in this study; 56
infants were both smaller than 1500 gm and
mechanically ventilated. They were patients in a
neonatal intensive care unit of a regional
perinatal center in the Southeast and
participants in a larger study on the
relationship between preterm behavior and
developmental outcomes conducted in the late
1980s (Holditch-Davis & Edwards, 1998). This
hospital did not use developmental care, other
than for positioning and comforting infants.
Infants with congenital problems associated with
neurological or developmental problems (such as
congenital hydrocephalus or Down Syndrome) were
excluded. All other infants, including those
with intraventricular hemorrhage, were eligible
so that the sample would be representative of
preterm infants in intensive care units.
-
- Although neonatal nursing
and medical care and the incidence of specific
illnesses have changed since the time these
infants were studied, the relation of biological
factors, such as maturation, sleeping and
waking, and illness severity, to infant
behaviors should be unaffected by changes in
treatment practices. To confirm that there were
no changes over time in these relationships, we
divided the sample into two cohorts. The only
difference between the cohorts was that the 37
infants in the first cohort were recruited and
studied before the 34 infants in the second
cohort. There were no obvious changes between
the cohorts in the nursing and medical care.
- The demographic
characteristics of the two cohorts are given in
Table 1. The cohorts were compared using t-tests
for continuous variables and Chi square analyses
for categorical variables in Holditch-Davis and
Edwards (1998). The only differences between the
cohorts was that the mothers of cohort 2 infants
were somewhat older than the first cohort
mothers and that the infants in the second
cohort were observed more often.
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- Variables Used for Data
Analyses
- Infant behaviors. Eight
infant behaviors commonly observed by nurses
were studied. Seven behaviors--yawn,
sigh, negative facial expression, startle/jerk,
jitter, large body movement, and hiccups--have
been suggested to be signs of infant stress (Als
et al., 1986). The eighth behavior, mouth
movements, may be used by infants for
self-comforting:
- yawn--The infant
yawns.
- Sigh-- A deep audible
respiration of the infant.
- Negative facial
expression--The infant makes a cry face or a
frown, in isolation or with crying.
- Startle/Jerk--A sudden
infant movement involving at least one whole
extremity, as in a Moro reflex.
- Jitter-- A rhythmic infant
twitch of at least three cycles and involving
part or all of the body.
- Large body movement--A
movement involving the extremities and the
trunk.
- Mouth
movementsÑDefinite movements of the
infant's mouth, including sucking.
- Hiccup--The infant
hiccups.
- Sleeping and waking states.
The two sleep states were scored by direct
observation of the infants, as defined in
Holditch-Davis and Edwards (1998):
- Active sleep--The infant's
eyes are closed. Respiration is uneven and
primarily costal in nature. Sporadic motor
movements occur, but muscle tone is low between
these movements. Rapid eye movements (REMs)
occur intermittently.
- Quiet sleep--The infant's
eyes are closed, and respiration is relatively
regular and abdominal in nature. A tonic level
of motor tone is maintained, and motor activity
is limited to occasional startles, sighs, or
other brief discharges.
- Periods when the infant
showed mixed signs of active and quiet sleep
were scored as quiet sleep if they were
transitional either into or out of quiet sleep.
Otherwise they were scored as active sleep.
Active sleep was sub-divided into periods of
active sleep with REMs and active sleep without
REMs because the literature on fullterm infants
suggests that neurological activity and infant
behaviors may be different during phasic periods
(active sleep with REMs) (Kohyama, 1996; Korner,
1968). The periods that infants were not in
active or quiet sleep because they were awake or
in transition between sleeping and waking were
scored as non-sleeping.
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- Measures. For this
report, the eight infant behaviors were measured
as percentages of the total observation and of
the four sleeping and waking states. These
percentages were calculating by dividing the
number of 10-second periods in which a behavior
occurred by the number of 10-second periods in
the total observation or each sleep-wake
state.
- Infant Characteristics.
Information on seven infant characteristics and
illness severity variables (post-conceptional
age, cohort, birthweight, race, gender, days of
mechanical ventilation, and theophylline
treatment) was obtained form the medical record.
Post-conceptional age at each observation was
the number of weeks since birth added to
gestational age at birth, which was calculated
from the obstetric estimated date of
confinement, determined either by the date of
the mother's last menstrual period or by an
ultrasound examination. If this gestational age
did not agree within 2 weeks with the results of
a gestational age examination (Ballard, Novak,
& Driver, 1979) conducted by nursery staff
on admission to intensive care, the age
calculated using just the physical criteria on
the assessment was used. Whether or not the
infant was receiving theophylline was determined
at each observation because theophylline is
known to affect sleeping and waking (Thoman et
al., 1985). Theophylline has a 30-hour half-life
in the preterm period (Aranda & Turmen,
1979), so infants were scored as receiving
theophylline if they had received a therapeutic
dose (more than 2 mg per kg) of the drug in the
24 hours before the observation. Cohort 1 was
scored as 0, and cohort 2 as 1. Race was scored
as either white or minority. (There were 22
African American and 1 Native American infants
in cohort 1 and 14 African American and 2 Native
American infants in cohort 2.) Days of
mechanical ventilation was a highly skewed
variable (mean 10.3, standard deviation 13.0,
median 5). Thus, infants with 1 day or less of
mechanical ventilation were scored as receiving
1 day, and the natural log of each subject's
score was used in analyses.
-
- Procedures
- Procedures for this study
have been previously reported (Holditch-Davis
& Edwards, 1998, Holditch-Davis & Lee,
1993). Briefly, the study was approved by the
institutional committee for protection of human
subjects. Infants were enrolled as soon as their
medical conditions were no longer critical if an
additional hospital stay of at least 1 week was
anticipated and informed consent was obtained
from the parents. They left the study on
discharge or on reaching 40 weeks
post-conceptional age. Thus, the ages at which
subjects were in the study varied, but 27 weeks
was the earliest study age for any infant, and
39 weeks was the oldest.
- Infant behaviors and
sleeping and waking states were observed once a
week from about 7 to 11 pm. Because the purpose
of the study was to examine the development of
infant behaviors in the hospital environment,
nursing and medical care and parental visiting
continued during the observation period as
though the observer were not there. During the
observations, the occurrences of behaviors and
sleeping and waking states were recorded every
10 seconds. The end of each 10-second period was
signaled audibly through an earphone from a
small electronic timer on a Tandy 100 portable
computer used as an event recorder. At this
signal, the observer recorded all behaviors that
occurred during the period and the sleep-wake
state lasting the greatest portion of the
10-second period. Multiple occurrences of the
same behavior in the same epoch were not
recorded, but these behaviors rarely occurred
more than once every 10 seconds. Each
observation was conducted by one of two
observers, who observed the entire 4-hours
without taking breaks but was able to sit down
or move around the incubator to maintain a clear
view of the infant even when visitors or nurses
were at the bedside. Correlations between
observers, calculated by having the observers
score 45 minutes of observations together, were
.99 for active and quiet sleep, .79 for the
presence of REMs, and ranged from .79 (sigh) to
1.00 (hiccups) for the infant behaviors.
-
- Data
Analysis
- The primary analysis for
this study was the general linear mixed model,
or mixed model, in the form of a random
coefficients model (Fairclough & Helms,
1986; Holditch-Davis, Edwards, & Helms,
1998). The general linear mixed model (mixed
model) is a flexible statistical procedure that
is widely used for analyzing continuous
longitudinal data and easily accommodates
missing values and mistimed data. This approach
models a curve across time, where time is
included in the model as a continuous
explanatory variable. It accounts for the
correlation present across the repeated measures
within each subject, as well as treating as
random effects the subject-specific deviations
from the overall curve for both the intercept
and the slope. In this manner, a regression
curve is computed for each subject, in addition
to the overall mean curve. Parameterization of
the mixed model includes population (fixed)
effects while simultaneously calculating
individual (random) effects. The fixed effects
can be interpreted the same way as the effects
in a multiple regression.
- A generalized estimating
equation (GEE) approach was used for hiccups due
to its skewed distribution. The hiccups variable
was converted into a dichotomous variable:
either present or not present during an
observation. Analyses examined the likelihood of
having hiccups at each age. GEE is like the
mixed model in its ability to accommodate
missing values and mistimed observations (Zeger,
Liang, & Albert, 1988). However,
parameterization of the GEE only includes
population (fixed) effects. Here, it was
utilized to model time as a continuous
explanatory variable, and the repeated measures
within a subject were treated as being
correlated.
- To address objectives 1-4,
infant behaviors as percentages of the total
observation and of each sleep-wake state were
regressed over post-conceptional age using
either the mixed general linear model (for all
behaviors except hiccups) or the GEE (for
hiccups). Birthweight, race, gender, days of
mechanical ventilation, theophylline treatment,
and cohort were used as covariates in the fixed
effects component of the model. Only intercept
and post-conceptional age effects were included
as random (individual subject) effects. Cohort
was also used as a covariate. Prior to analysis,
post-conceptional age was "centered" so that 34
weeks, roughly the mean value for
post-conceptional age, equaled 0. An elimination
(or model reduction) procedure was followed
whereby each variable, except intercept and the
linear effect of post-conceptional age, had to
reach p < 0.05 in a preliminary mixed model.
The variables remaining after this screening
procedure were used in a final mixed model. This
procedure simplified the model and led to
inferences that some effects were either zero or
not large enough to be detected. Valid
covariance matrices were not obtained for the
models with both random intercepts and slopes
for two behaviors in non-sleeping (sigh and
startle/jerk) so only random intercepts (but not
random slopes) were included in the
model.
- To address objective 5 and
determine whether infant behaviors differed
between sleep-wake states, the difference in the
percentage of each behavior in each pair of
sleep-wake states was calculated. A mixed model
was used to calculate the developmental pattern
of the difference scores for all behaviors
except hiccups. A significant intercept
indicated the percentage of the behavior
differed between the two states. A significant
post-conceptional age effect indicated that the
difference between the states changed over age.
For hiccups, a record was formed for each pair
of states at each age for each subject. A GEE
model was then specified with the binomial
distribution and logit link for main effects of
age and state, as well as their interaction; an
exchangeable correlation matrix was further
specified. This provided a logistic regression
line for each of the states, while accounting
for the dependency due to the correlated effects
within each subject. The main effect of state
then corresponded to the difference in the
intercepts of the lines, and the interaction
provided the difference in the
slopes.
-
- Results
- The infants in cohort 1 had
132 weekly observations, and 157 weekly
observations were obtained for cohort 2. The
number of observations for each infant ranged
from 1 to 11, with 5 infants having only 1
observation. Infants averaged 39 minutes out the
4-hour observation with caregivers, including
gavage feedings were left hanging after the
nurse left the bedside and interruptions in
caregiving lasting less than 2 minutes. Parents
visited during only 36 observations.
- Development of Infant
Behaviors over the Entire
Observation
- Table 2 shows the analyses
of the development of behaviors as percentages
of the entire observation. Five behaviors showed
development over the preterm period: the
percentage of negative facial expressions
increased, and sighs, startle/jerks, jitters,
and the likelihood of having hiccups decreased.
The developmental patterns of these five
variables are shown in Figures 1 and
2.
- The covariates had minor
effects. Boys had more negative facial
expressions. Length of mechanical ventilation
was related to sighs and jitters, such that
longer mechanical ventilation was associated
with more sighs and jitters. Cohort 1 had more
yawns, negative facial expressions, and
large movements and greater likelihood of
hiccups but fewer sighs. Birthweight, race, and
theophylline treatment did not significantly
affect the amount of any infant
behavior.
- Development of the Sleeping
and Waking States
- The percentage of three of
the four sleeping and waking states changed
significantly over age (see Table 3).
Non-sleeping and quiet sleep increased, and
active sleep without REM decreased over the
preterm period. Active sleep with REM did not
show significant developmental changes.
-
- Development of Infant
Behaviors within Sleeping and Waking
States
- Table 4 shows the analyses
of the development of infant behaviors as
percentages of the four sleeping and waking
states. Every behavior showed significant
development in at least one state, but only
negative facial expressions, startle/jerks, and
jitters showed significant development in all
four states. yawns decreased over age in
non-sleeping and active sleep with REMs. Sighs
decreased in all sleep states. Startle/jerks and
jitters decreased in all states. Negative facial
expression decreased in non-sleeping, active
sleep with REM, and quiet sleep but increased in
active sleep without REMs. Large body movements
decreased in active sleep with REMs and quiet
sleep but increased in active sleep without REM.
Mouth movements increased in active sleep
without REMs. The likelihood of hiccups
decreased in both active sleep
states.
-
- Covariates had inconsistent
effects. Only the few covariates with the same
effects on a given behavior in more than one
sleeping and waking state are likely to
represent real effects, rather than chance
findings. Cohort 1 had fewer sighs and more
negative facial expressions in all sleep states
and fewer jitters in active sleep without REMs
and non-sleeping. Mechanical ventilation was
related to more jitters in all states. Girls had
fewer startle/jerks in active sleep without REMs
and quiet sleep and fewer large movements in
non-sleeping and quiet sleep. Minority infants
had more jitters in non-sleeping and active
sleep without REMs.
-
- Relationship of the Sleeping
and Waking States to the Percentages of Infant
Behaviors
- To determine whether state
affected the percentages of variables, general
linear mixed models (or GEEs) were conducted on
the differences between each pair of states for
each behavior (see Table 5). yawns,
negative facial expressions, and large movements
were most frequent in non-sleeping, more
frequent in the active sleep states than quiet
sleep, and more frequent in active sleep without
REM than in active sleep with REM. Mouth
movements showed a similar pattern except that
the active sleep states and non-sleeping did not
differ. Jitters also showed a similar pattern,
but the percentage of jitters did not differ
between the two active sleep states.
Startle/jerks occurred most frequently in active
sleep without REMs, more frequently in both
active sleep states than in quiet sleep, and
least frequently in non-sleeping. Sighs occurred
most frequently in quiet sleep, more frequently
in active sleep states than in non-sleeping, and
more frequently in active sleep without REMs
than active sleep with REMs. The probability of
having hiccups was lower in quiet sleep than in
either active sleep state or non-sleeping.
-
- A few state-related
differences changed over age. The differences
between non-sleeping and the sleep states for
yawns became smaller with age. The
difference in sighs between non-sleeping and
quiet sleep and active sleep without REMS and
between active sleep with and without REMs also
became smaller with age. The differences in the
percent of negative facial expressions between
quiet sleep and active sleep without REM and
between active sleep with and without REMs
increased over age. For startle/jerk, the
difference between quiet sleep and the two
active sleep states became smaller with age. The
difference between jitters in quiet sleep and
active sleep with REM decreased over age, and
although the two active sleep states did not
differ significantly for jitters, the difference
between them was larger at older ages. The
differences in the percent of large movements
between quiet sleep and active sleep without
REMs and between the two active sleep states
increased over age. The differences in the
percent of mouth movements between quiet sleep
and non-sleeping decreased over age, and the
differences between the two active sleep states
increased over age. Although the probability of
having hiccups did not differ between
non-sleeping and the active sleep states, the
difference was greater between active sleep with
REMs and non-sleeping at younger ages and
between active sleep without REMs and
non-sleeping at older ages.
-
- Discussion
- Clearly, development of
infant behaviors occurs over the preterm period.
The percentage of one behavior increased
(negative facial expressions), and four
decreased (sighs, startle/jerks, jitters, and
the likelihood of having hiccups) over time. The
development of behaviors was related to sleeping
and waking. All behaviors showed state-related
differences in frequency, and every behavior
showed development in at least one sleep-wake
state. However, only startle/jerks and jitters
showed the same developmental patterns in all
four states. Two behaviors showed opposite
development in different states: negative facial
expression decreased in four states and
increased in the other, and large body movements
decreased in two state but increased in a third.
-
- Consistent with the findings
of other studies, we found that infant behaviors
exhibited developmental changes. Like other
studies, we found that sighs and the likelihood
of having hiccups decreased over age (Hoch et
al., 1998; Pillai & James, 1990) and that
large body movements did not show developmental
changes (Giganti et al., 2001; Hayes et al.,
1993). However, unlike D'Elia et al. (2001), we
did not find any developmental changes in mouth
movements. We also found developmental changes
in startle/jerks, jitters, and negative facial
expressions even though other studies have not
examined the development of these behaviors. Our
study examined development longitudinally over
the preterm period so our findings are more
likely than those of previous studies to be
applicable to preterm infants in neonatal
intensive care units.
- Moreover, like other
studies, we found that the frequency of infant
behaviors differed in different sleeping and
waking states. Similar to previous studies, we
found that yawns, negative facial
expressions, and large body movements were less
common in quiet sleep than active sleep or
waking states (Giganti et al., 2002; Weggeman et
al., 1987; van Woerden et al., 1988) and that.
mouth movements were most frequent in the active
sleep states (Korner, 1968). Our finding that
startle/jerks were most common in active sleep
without REMs is similar to that of Huntington et
al. (1985) but differed from studies finding
more startles in quiet sleep (Emory & Mapp,
1988; Korner 1969). We found that sighs were
more common in quiet sleep than active sleep,
whereas other researchers found the opposite
(Hoch et al., 1998), possibly because the other
studies were limited to healthy infants without
residual lung disease. We also found that the
likelihood of having hiccups was lower in quiet
sleep than either active sleep state or
non-sleeping despite findings that hiccups in
fetuses were not related to any particular state
(van Woerden et al., 1989).
-
- Since the amounts of the
sleep-wake states changed over the preterm
period and the amounts of behaviors differed
among states, the development of sleeping and
waking probably has a major impact on the
development of most infant behaviors.
Developmental patterns of behaviors reflect
changes in both the absolute amounts of the
behaviors and the amounts of the sleep-wake
states in which they occurred. For example, an
overall increase in negative facial expressions
occurred despite a developmental decrease in
three of four states because the state in which
it was most common, non-sleeping, was increasing
more rapidly over age than the rate at which
negative facial expression was decreasing within
this state. Thus, infant behaviors are not only
a response to environmental stimulation but also
reflect the sleeping and waking states in which
they occur.
- Compared to sleeping and
waking, infant characteristics and illness
severity had only minor effects on behaviors.
Race, birthweight, and theophylline treatment
had no effect on any behavior over the total
observation although a previous study found that
African American preterms had more jitters than
whites (Pressler & Hepworth, 2002).
Likewise, the only gender effects in this study
were that boys had more negative expressions
over the total observation, more startle/jerks
in active sleep without REMs and quiet sleep,
and more large movements in non-sleeping and
quiet sleep. Some previous studies have found
gender effects on behaviors (Korner, 1969), but
others have not found any gender effects
(Korner, 1968; Weggemann et al., 1987). Like
other studies (Parker et al., 1990), we found
that longer mechanical ventilation was related
to more sighs and jitters. Unlike many studies,
we did not find any effects of illness severity
on body movements, facial movements, or startles
(Booth et al., 1980; Emory & Mapp, 1988;
Kisilevsky et al., 1999).
-
- In fact, the covariate with
the greatest effect on infant behaviors was
cohort: infants from cohort 1 had more
yawns, negative facial expressions, large
movements, and likelihood of having hiccups but
fewer sighs than cohort 2 infants. These cohort
differences were not due to slight differences
in the illness severity of the two cohorts since
the illness differences were not significant and
three covariates reflecting illness severity
were included in every analysis. However, they
may have reflected changes in the medical and
nursing care of preterms, in the prenatal care
of their mothers, and in the population of
infants in the nursery between December 1985 to
June 1988 when the first cohort was studied and
July 1988 to September 1990 when the second
cohort was studied. Contrary to expectations,
historical changes probably affected the
relation of infant behaviors to development, but
these effects were small, ranging from 0.36% for
yawns to 4% for large movements. Thus,
the general relationships described in this
study probably hold over time even though the
absolute amounts of behaviors varied somewhat.
- Altogether, our findings
indicate that the factors affecting the
frequency and development of infant behaviors in
the preterm period are complex. Since sleeping
and waking affected both frequency and
development, future studies of behaviors need to
include state. Research is also needed to
determine the nature of the relationships
between behaviors and sleeping and waking.
Behaviors may be indicators of particular
states, responses to other state-related changes
such as apnea, or reflections of underlying
neural activation (Hoch et al., 1998; Huntington
et al., 1985; van Woerden et al., 1988). In
other cases, behaviors may be signs of arousals
or imminent state changes (Giganti et al.,
2002); or the behaviors, such as hiccups, might
actually cause state changes.
-
- More research is also needed
on the underlying causes and consequences of
behaviors in preterms. Preterm infants have
limited behavioral repertoires so the same
behavior may have different meanings in
different situations. We found that all eight
infant behaviors occurred in all four sleep-wake
states. Yet infants usually arouse and change
state in response to stress or pain (Zahr &
Balian, 1995). Behaviors are not always
responses to external stimulation, but rather
sometimes they may be the result of endogenous
processes that contribute to the development of
the nervous system (e.g., Korner, 1969) or only
reflect changes in the underlying sleep-wake
state. Therefore, to make clinically useful
interpretations of infant behaviors, more
empirical data is needed about how the
co-occurrence of infant behaviors and sleeping
and waking is affected by different stimuli,
including nursing care and painful procedures,
and how these co-occurrences are affected by
differing levels of illness severity or
differing post-conceptional ages.
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