Fetal Breathing Activity Research Articles

Fetal cardiac autonomic control during breathing and non-breathing epochs: The effect of maternal exercise

We explored whether maternal exercise during pregnancy moderates the effect of fetal breathing movements on fetal cardiac autonomic control assessed by metrics of heart rate (HR) and heart rate variability (HRV). Thirty women were assigned to Exercise or Control group (n=15/group) based on the modifiable physical activity questionnaire (MPAQ). Magnetocardiograms (MCG) were recorded using a dedicated fetal biomagnetometer. Periods of fetal breathing activity and apnea were identified using the fetal diaphragmatic magnetomyogram (dMMG) as a marker. MCG R-waves were marked. Metrics of fetal HR and HRV were compared using 1 breathing and1 apneic epoch/fetus. The main effects of group (Exercise vs. Control) and condition (Apnea vs. Breathing) and their interactions were explored. Fetal breathing resulted in significantly lower fetal HR and higher vagally-mediated HRV. Maternal exercise resulted in significantly lower fetal HR, higher total HRV and vagally-mediated HRV with no difference in frequency band ratios. Significant interactions between maternal exercise and fetal breathing were found for metrics summarizing total HRV and a parasympathetic metric. Post hoc comparison showed no group difference during fetal apnea. Fetal breathing was associated with a loss of Total HRV in the Control group and no difference in the Exercise group. Both groups show enhanced vagal function during fetal breathing; greater in the Exercise group. During in utero breathing movements, the fetus of the exercising mother has enhanced cardiac autonomic function that may give the offspring an adaptive advantage.

Characterization of the fetal diaphragmatic magnetomyogram and the effect of breathing movements on cardiac metrics of rate and variability

Breathing movements are one of the earliest fetal motor behaviors to emerge and are a hallmark of fetal well-being. Fetal respiratory sinus arrhythmia (RSA) has been documented but efforts to quantify the influence of breathing on heart rate (HR) and heart rate variability (HRV) are difficult due to the episodic nature of fetal breathing activity. We used a dedicated fetal biomagnetometer to acquire the magnetocardiogram (MCG) between 36 and 38 weeks gestational age (GA). We identified and characterized a waveform observed in the raw data and independent component decomposition that we attribute to fetal diaphragmatic movements during breathing episodes. RSA and increased high frequency power in a time-frequency analysis of the IBI time-series was observed during fetal breathing periods. Using the diaphragmatic magnetomyogram (dMMG) as a marker, we compared time and frequency domain metrics of heart rate and heart rate variability between breathing and non-breathing epochs. Fetal breathing activity resulted in significantly lower HR, increased high frequency power, greater sympathovagal balance, increased short-term HRV and greater parasympathetic input relative to non-breathing episodes confirming the specificity of fetal breathing movements on parasympathetic cardiac influence. No significant differences between breathing and non-breathing epochs were found in two metrics reflecting total HRV or very low, low and intermediate frequency bands. Using the fetal dMMG as a marker, biomagnetometry can help to elucidate the electrophysiologic mechanisms associated with diaphragmatic motor function and may be used to study the longitudinal development of human fetal cardiac autonomic control and breathing activity.

Fetal breathing is associated with increased umbilical blood flow

In humans, fetal breathing movements affect blood velocities in the umbilical vein and artery, but it is not known whether fetal respiratory activity is associated with increased fetal blood flow through the placenta. We therefore tested this hypothesis in the present study. One-hundred and ten women with low-risk singleton pregnancies were each examined three times by ultrasound during the second half of pregnancy. Fetal heart rate, umbilical artery blood velocity, umbilical vein diameter and blood velocity, and umbilical blood flow at the placental end were determined during fetal rest and fetal respiratory movements. Based on 330 observations obtained during fetal rest or breathing activity, no difference was found in the mean fetal heart rate (beats per minute (bpm)) during rest compared with breathing (142 bpm vs. 142 bpm, respectively). Although fetal breathing affected the umbilical artery waveform, there was no difference in the mean time-averaged maximum velocity between rest and breathing: 26.6 (95% CI, 25.1-28.3) cm/s vs. 28.9 (95% CI, 27.2-30.7) cm/s, respectively. The umbilical vein was 27% greater in cross-sectional area and the blood velocity 9% higher during breathing, resulting in a 42% increase in mean umbilical blood flow: 121.8 (95% CI, 109.5-135.0) mL/min at rest vs. 173.0 (95% CI, 158.0-188.6) mL/min during breathing. Venous velocity was calculated from recordings of mean duration 3.7 s at rest and 6.2 s of respiratory activity. Gestational age did not influence the relationship. Fetal breathing is associated with increased umbilical blood flow during the second half of pregnancy. Umbilical vein distension during breathing suggests active endocrine regulation.

Effects of fetal behavioral states on renal sympathetic nerve activity and arterial pressure of unanesthetized fetal sheep.

Fetal behavior, renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP), and heart rate (HR) were studied 1-3 days after surgery in seven fetal sheep (aged 127-136 days). Five behavioral states were defined from chart recordings of electrocortical (electrocorticographic; ECoG) activity and eye, limb, and breathing movements. Most records were of high-voltage ECoG (HV) or low-voltage (LV) ECoG with breathing (LVB); 6.7 +/- 1.7% were LV ECoG with no breathing (LV0). RSNA was lower in LV0 (P < 0.001) and greater in LVB than in HV (P < 0.05). MAP was lower in both LV states than in HV and when the fetuses went from LV to HV (P < 0.001 to P < 0.03). HR was highest in HV (P < 0.001). In HV and LVB and when the fetus went from LV to HV, MAP and HR were inversely related (P = 0.012-0.003). In LVB and from LV to HV there were direct relationships between MAP and RSNA (P = 0.0014, P = 0.08), and when the fetus went from LV to HV there was also an inverse relationship between HR and RSNA (P = 0.02). Thus fetal RSNA, MAP, and HR are affected by behavioral state as is fetal cardiovascular control. The increase in RSNA during fetal breathing showed that there was an altered level of fetal RSNA associated with fetal breathing activity.

Role of Adenosine in Regulating Fetal Sleep States and Breathing Activity

A review of: Koos BJ, Maeda T, and Jan C 2001 Adenosine A1 and A2A receptors modulate sleep state and breathing in fetal sheep. J Appl Physiol 91:343–350; and Koos BJ, Maeda T 2001 Adenosine A2A receptors mediate cardiovascular responses to hypoxia in fetal sheep. Am J Physiol Heart Circ Physiol 280:H83–H89

Fetal breathing: a clinically useful paradox

Purpose: To examine fetal breathing movements in fetuses with congenital diaphragmatic hernia and compare this to unaffected fetuses and with their outcome after birth.Methods: Twenty women with normal singleton pregnancies and four cases of congenital diaphragmatic hernia were studied. All fetuses were observed for 60 min at 36 weeks of gestation. Fetal breathing movements were observed by scan taking a cross‐sectional view across the abdomen. The scan was recorded and breathing movements analyzed off‐line. All sessions occurred at the same time of the day and two hours after a light meal. No patients were cigarette smokers. Bouts of fetal breathing activity were defined as the length in seconds of each series of successive individual breathing movements bracketed by periods of apnea. The absence of fetal breathing movements for more than 3 s was called the apnea period. Total duration of breathing was the sum of all bouts.Results: The normal fetuses exhibited a breath to breath interval of 1.3 s and displayed breathing movements for around 30–35% of the observation period. Of the four fetuses with congenital diaphragmatic hernia, three died during the neonatal period due to lung hypoplasia, one survived following surgical repair. All four fetuses exhibited a similar breath to breath interval as unaffected fetuses but the three fetuses who died spent 80% (range 70–90%) of the time breathing whereas the fetus that survived spent 32% of its time breathing. Increased yawning was also observed in the fetuses who died.Conclusions: It has been speculated that the inhibition of fetal breathing movements may result in pulmonary hypoplasia, yet fetuses with lung hypoplasia spend more time breathing than those without lung hypoplasia. The relationship between breathing movements and lung development requires further study. Breathing movements may provide important information on fetal health and outcome.

Intermittent umbilical cord occlusion in the ovine fetus near term: Effects on behavioral state activity

Objective: The purpose of this study was to determine the effects on fetal behavioral state activity of intermittent umbilical cord occlusion resulting in repetitive severe short-term hypoxemia. Study Design: Fifteen near-term fetal sheep (experimental group, n = 8; control group, n = 7) were studied during 4 days while behavioral and cardiovascular parameters were monitored. Each day after a 2-hour control period, cord occlusions were performed in the experimental group animals by complete inflation of an occluder cuff (duration, 90 seconds) every 30 minutes for 3 to 5 hours. Results are presented as group mean ± SEM. Results: During umbilical cord occlusions fetal arterial PO2 (change of 12 mm Hg), oxygen saturation (change of 40%), and glucose concentration (change of 0.3 mmol/L) fell and PCO2 (change of 7 mm Hg) rose, but all returned toward control values after release of occlusion. Fetal behavioral state activity was markedly disrupted by 90 seconds of cord occlusion, with animals showing an abrupt flattening of the electrocorticogram. In >90% of instances the first identifiable state after cord release was the high-voltage non–rapid-eye-movement state. There was no apparent change in this response through the 4 days of the study. For experimental group animals the mean percentages of time spent in low-voltage electrocortical state (from 53 ± 2 to 36 ± 2), electro-ocular state (from 45 ± 3 to 28 ± 3), and fetal breathing activity (22 ± 4 to 12 ± 3) were significantly decreased (P < .001) during occlusion hours with respect to nonocclusion hours. Conclusion: Intermittent umbilical cord occlusion with severe but limited hypoxemia and no cumulative acidosis in the near-term ovine fetus disrupts behavioral state activity, with a flattening of the electrocortical activity during occlusions and an overall decrease in the prominence of the low-voltage rapid-eye-movement state. If such insults are frequent and severe enough, they might have an effect on growth and development of the brain during the perinatal period. (Am J Obstet Gynecol 1999;181:1520-9.)

Acute maternal alcohol consumption disrupts behavioral state organization in the near-term fetus.

Disturbed sleep regulation is often observed in neonates of women who drank heavily during pregnancy. It is unknown if (and how) an occasional drink affects fetal sleeping behavior. In 28 near-term pregnant women we examined the effects on fetal behavioral state organization of two glasses of wine (0.25 g of ethanol/kg of maternal body weight). Simultaneous 2-h recordings of fetal heart rate and body, eye, and breathing movements were made on two successive days, once without alcohol exposure and once during maternal alcohol consumption. The study was standardized for time of day and fetal sleep state, i.e., the start of recording was either during quiet sleep (n = 16) or during active sleep (n = 12). Alcohol intake reduced fetal eye movements, disorganized behavioral state organization (rapid eye movement sleep was affected in particular), and suppressed fetal breathing activity almost completely. Modest maternal alcohol intake affects fetal behavioral state organization, which reflects an immediate effect on fetal brain function.

Doppler assessment of tracheal fluid flow during fetal breathing movements in cases of congenital diaphragmatic hernia.

The purpose of this investigation was to examine the characteristics of breathing-related fluid flow in the trachea of human fetuses with congenital diaphragmatic hernia in the hopes of developing a standard for the prenatal diagnosis of the degree of severity of the resulting pulmonary hypoplasia. Our ultimate goal is the prediction of postnatal mortality in fetuses with congenital diaphragmatic hernia. The study comprised six cases of isolated congenital diaphragmatic hernia (one on the right side; five on the left) varying in gestational age from 26 to 36 weeks. Four of the patients survived after surgical repair and two died during the neonatal period owing to lung hypoplasia. Color Doppler was used to visualize the fluid displacement in the trachea generated by fetal breathing movements. Spectral Doppler was then used to analyze the fluid flow velocity waveforms. More than 40 continuous breathing cycles (inspiration + expiration) were recorded for each case. We distinguished between regular and irregular patterns. Only the regular breathing phases, defined as five or more consecutive cycles of symmetric appearance, were considered for analysis. The inspiration and expiration times, the peak velocity of inspired and expired fluid and the volume obtained by integration of the tracheal fluid flow displaced during fetal breathing were compared with those of five healthy fetuses for each gestational age. Only the tracheal volume flow was helpful in predicting outcome. In normal pregnancies this parameter increased from 0.21 +/- 0.10 ml/breath (mean +/- SD) at 26 weeks to 1.37 +/- 0.48 ml/breath at 36 weeks of gestation. A significantly low (p < 0.05) volume flow was found only in the fetuses with congenital diaphragmatic hernia with a lethal postnatal outcome, whereas this parameter was normal in all survivors. Our preliminary observations suggest that the tracheal volume flow during fetal breathing activity is related to lung growth. In fetuses with severe lung hypoplasia one would expect a significant reduction in this parameter as an expression of deficient fetal lung growth. The displaced fluid volume per breath in the trachea of human fetuses as assessed by Doppler ultrasound may be a useful predictor of outcome in cases of isolated congenital diaphragmatic hernia.

Diurnal Rhythm of Fetal Behavioral State

To test for the presence in utero of diurnal periodicity in the amount of time spent in organized behavioral states, seven records of 24-hour duration were obtained from each of five chronically instrumented fetal baboons between 144 and 158 days gestation (term = 175 days). Concordance of fetal breathing activity, heart-period variability, and electroencephalographic parameters were used to define two distinctive patterns of fetal physiological activities. One pattern was characterized as EEG activity dominated by tracé alternant, reduced heart-period variability, and fewer breaths in epochs of fetal breathing. This fetal behavioral state (1FB) is analogous to quiet sleep in infants. A second pattern was characterized by the relative absence of tracé alternant, increased heart-period variability, and fetal breathing activity. This fetal behavioral state (2FB) is analogous to active sleep. Cycles of these states were present 29% of time, with a duration of approximately 26 minutes and a 1.7:1 predominance of 2FB/1FB. Cosinor analysis across fetuses revealed a significant (p < .01) 24-hour periodicity of the time spent by the fetus in organized behavioral states, with a peak around 1400 (lights-on 0700 to 1900) and a peak-nadir fluctuation of 15%. These periodicities in the incidence of organized state were significant (p < .01) in three fetuses, and approached significance (< .09) in the two others. Data demonstrate a diurnal rhythmicity in fetal behavioral states, with less time spent in organized state at night than during the day.

The effects of maternal exercise on fetal heart rate and movement patterns.

The aim of this study was to investigate the effects of maternal exercise on fetal movement and heart rate patterns. Twelve healthy women at 29-32 weeks of pregnancy performed a (sub)maximal bicycle exercise test, reaching 53-99% (median 82%) of their maximal increase in heart rate (MIHR). Fetal heart rate (FHR) and its variation and fetal body and breathing movements were recorded for 1 h before and after the exercise and also on a control day. After exercise, FHR was higher for 30 min and FHR variation reduced for 20 min as compared with pre-exercise levels (P < 0.01). Fetal body movements were reduced for the first 5 min following exercise (P < 0.05). In two cases, fetal bradycardia was observed (at 89 and 99% MIHR) followed by a considerable reduction in FHR variation and absence of body and breathing movements for 20 min. In the other 10 fetuses fetal breathing activity was increased for the first 5 min after exercise (P < 0.05). FHR (and to a lesser extent breathing movements) increased with increasing level of maternal exercise, but decreased when the % MIHR exceeded approximately 90%. Body movements were negatively correlated with the % MIHR (P < 0.05). In conclusion, moderate to heavy maternal exercise clearly affects the human fetus with signs of transient fetal impairment after heavy exercise.

Low dose indomethacin via fetal vein or cerebral ventricle stimulates breathing movements in fetal sheep

Indomethacin, a prostaglandin synthesis inhibitor, transforms normally intermittent fetal breathing into nearly continuous breathing. If indomethacin acts in brain, we hypothesized that indomethacin would stimulate breathing at a lower dose when given via the lateral cerebral ventricle (i.c.v) than via the fetal jugular vein (i.v.). Chronically catheterized fetal sheep were studied at 0.88 of gestation (128 days). A 2-h control period was followed by an indomethacin infusion at 7 micrograms.kg-1 fetal body weight over the first 10 min of each hour for 3 h then at 28 micrograms.kg-1 over the first 10 min of each hour for the next 3 h, either i.c.v. (n = 7) or i.v. (n = 6). Plasma prostaglandin E2 concentrations decreased similarly by both routes, although the decrease was only significant for the i.c.v. route. Indomethacin at 7 micrograms.kg-1.h-1 did not change fetal breathing activity by either route within 3 h. During the 2nd and 3rd h at 28 micrograms.kg-1.h-1, breathing incidence increased (from approximately 35 to approximately 80% time), breath amplitude and rate increased, and arterial O2 content decreased slightly (all changes significant). ANOVA revealed no significant differences in responses evoked by the two routes. Fetal arterial pressure, heart rate, Pco2, and pH were unchanged (both doses, both routes). The indomethacin dose (105 micrograms.kg-1 over 6 h) was > or = 10-fold lower than that used in previous studies on breathing in fetal sheep but similar to that used clinically to treat patent ductus arteriosus. We conclude that site(s) mediating effects of indomethacin on breathing respond to a low dose and are equally accessible by i.c.v. and i.v. routes.

Diurnal rhythms in cardiorespiratory function of the fetal baboon.

Diurnal periodicities of cardiorespiratory function were monitored between 144 and 156 days of gestation (term = 175 days) in six chronically instrumented fetal baboons. For each fetus, 5-11 days of electrocardiographic and tracheal fluid pressure data were summarized as hourly means of fetal heart rate (FHR), standard deviation of FHR, breath-to-breath interval (B-Bi) and percent time spent in fetal breathing activity (PFB). Summaries were evaluated by cosinor analysis to determine the least squares fit to a 24-h cycle. For all fetuses, FHR had a significant (P < 0.001) diurnal rhythm with peak to nadir fluctuations of 17.4 beats/min around a 24-h mean of 163.2 beats/min. The time of the peak FHR was similar across animals occurring in the mid-day between 10:49 h and 14:45 h. For each fetus, standard deviation of FHR also had a significant (P < 0.01) diurnal periodicity with highest values at night between 20:15 h and 02:04 h. The times of the acrophase for these heart rate parameters were correlated (R = 0.88, P < 0.02) across fetuses. Significant (P < 0.001) 24-h rhythms were found in four of six fetuses for B-Bi and five of six for PFB. These PFB rhythms accounted for a fluctuation of 14.4% around a mean of 36.9 +/- 4.5%. In contrast to heart rate, the acrophases of fetal breathing parameters were distributed throughout the entire 24-h cycle and not significantly correlated across fetuses. It is concluded that diurnal rhythms of fetal heart rate, which are synchronized with light/dark conditions in the environment, are evidence for a passive response or entrainment of fetal systems to maternal circadian influences. Alternately, the absence of synchronization across fetuses in daily rhythms of fetal breathing activity provides evidence for a functioning fetal pacemaker, and not simply the imposition of maternal rhythms on her fetus. This differential in the cardiac and breathing activity of the developing primate indicates that pathways for entrainment of fetal pacemaker function are subject to important maturational influences during late gestation.

Oxygen consumption, acid-base status, and behavior during and after acute, severe hemorrhage in fetal lambs.

The metabolic and behavioral effects of 40-45% hemorrhage (at approximately 1%/min) were studied in nine fetal lambs in utero (130-135 days of gestation) until 2 days posthemorrhage. Umbilical blood flow (Qum) fell from 192 +/- 14 to 100 +/- 9 ml.min-1.kg-1 at the end of blood loss, and on the day of hemorrhage it was linearly related to blood volume. However, on the posthemorrhage days, Qum was restored even though blood volume was still reduced. Fetal O2 delivery (DO2) fell with the decrease in Qum and later due to anemia (decrease in hematocrit from 33.4 +/- 1.2 to 23.6 +/- 1.2%), from 946 +/- 81 to 494 +/- 47 mumol.min-1.kg-1, but the decrease was lessened because of a rise in umbilical venous PO2 (31.7 +/- 2.6 to 45.9 +/- 2.8 mmHg). Fetal O2 consumption was reduced during and for 2 h after hemorrhage (262 +/- 17 to 190 +/- 16 mumol.min-1.kg-1), and this was associated with modest lactic acidemia (1.25 +/- 0.11 to 2.91 +/- 0.43 mM). There was also a temporary reduction in fetal breathing activity, low voltage electrocortical state, and rapid eye movements, but this was not associated with hypoxemia. It is concluded that reductions in fetal DO2 achieved via fetal blood loss are better tolerated than during hypoxemia and that the associated depression in fetal biophysical activities involves mechanisms other than systemic hypoxia.

Fetal breathing characteristics and postnatal outcome in cases of congenital diaphragmatic hernia

Objective: Our purpose was to determine characteristics of fetal breathing activity by recording fetal nasal fluid flow velocity in cases of congenital diaphragmatic hernia.Study Design: Fetal breathing-related nasal fluid flow was studied in 47 patients at 34 to 41 weeks of gestation, 16 cases of antenatally diagnosed congenital diaphragmatic hernia and 31 cases of uncomplicated pregnancy. The examination was performed by ultrasonography combined with color-flow and spectral Doppler analysis. An average of 25 breath cycles from each case was determined for each of the following timing parameters: breath-to-breath interval, time of inspiration, time of expiration, and ratio of time of inspiration and time of expiration.Results: In all cases with uncomplicated pregnancy fetal breathing-related nasal fluid flow was seen at the level of the nose, and the timing components of this flow were determined as control values. In two cases with diaphragmatic hernia no perinasal flow was demonstrated, although fetal breathing movements observed as chest wall movements were present. The other 14 cases with congenital diaphragmatic hernia who demonstrated perinasal flow had the following postnatal outcome: one stillbirth, five neonatal deaths (group I), and eight survived and were discharged (group II). The study revealed that the time of expiration (in milliseconds) in group II (493.2 ± 34.3 SEM) was significantly (p = 0.0030) shorter than in group I (653.4 ± 38.4) and in cases of uncomplicated pregnancy (633.6 ± 18.5). The value of the time of inspiration/time of expiration ratio in group II was approximately 15% higher than in group I and approximately 30% higher than in cases of uncomplicated pregnancies.Conclusions: Observation of fetal breathing-related nasal fluid flow velocity in cases of antenatally diagnosed congenital diaphragmatic hernia provides a rationale for the hypothesis that time of expiration and the time of inspiration/time of expiration ratio may be useful in the prediction of postnatal outcome. We speculate that the changes in the group of survivors may represent a compensatory phenomenon by causing intermittent changes in the volume of fluid within the lungs.

Patterns of fetal breathing in the baboon vary with EEG sleep state

This report examines the hypothesis that the characteristics of breathing activity of the fetal baboon are modulated with respect to sleep state in a fashion similar to that observed in the human fetus. The pattern of fetal breathing activity was examined in relationship to electroencephalographic (EEG) sleep state in studies of six fetuses of chronically monitored pregnant baboons at 143–148 days of gestation (term, 175–180 days). Fetal breaths were defined by fluctuations of tracheal fluid pressure. EEG sleep states were defined with an automated method for discrimination of EEG patterns that are standard indices of quiet and active sleep in immature primates. During more than 250 h of recorded data, the fetuses spent on average 33.3 ± 3.9% of time in EEG quiet sleep. In comparisons across state the fetuses spent significantly ( P = 0.001) less time breathing during quiet than active sleep (49.5 ± 6.8 vs. 69.0 ± 3.8%). The inspiratory and expiratory time intervals of fetal breaths were not differentiated by EEG state but, the mean breath to breath interval was significantly ( P < 0.001) longer in EEG quiet sleep. In addition to these differences in incidence and time interval of breaths, during epochs of breathing, there was a significantly slower rate, lower amplitude, and lower variability of rate of breathing in quiet sleep (all P-values < 0.02). Thus, periodic breathing activity in the fetal baboon is present in both quiet and active EEG sleep states. Sleep states have a powerful influence on patterns of fetal breathing in the non-human primate, directly comparable to the human fetus.

Patterns of breathing movements in the near-term human fetus: relationship to behavioural states

The occurrence of fetal breathing movements was studied in relation to fetal behavioural states 1F and 2F, as recognized by the heart rate patterns A and B, respectively. Simultaneous recordings of fetal heart rate and body, eye and breathing movements were available for analysis ( n = 88). These recordings, lasting ≥ 2 h, had been made in healthy near-term fetuses during the afternoon or evening, starting about 1 h after the maternal meal. In the majority of recordings fetal breathing activity was lower during heart rate pattern A than during pattern B, but as the opposite occurred in 29/88 recordings (33%), the interstate difference was not significant ( P = 0.052). Detailed analysis revealed that breathing movements were more numerous during pattern B than during pattern A if the incidence of breathing during a particular time period was low (30–40% of time). At a high overall breathing incidence (>40%), however, breathing movements were more often present during pattern A than during pattern B. The latter occurred especially in the first hour of recording, i.e. less distant in time from maternal meals. We conclude that fetal breathing activity is generally higher during state 2F than during state IF, but a clear-cut state-dependency is absent. Secondly, the relationship between the incidences of breathing during states 1F and 2F depends on the ‘drive’ or motivation (presumably the blood glucose content) to breathe.

Fetal Breathing Activity in WelLControlled Dietary-Treated Gestational Diabetes Mellitus

The purpose of our study was to assess fetal breathing activity in well-controlled gestational diabetic women. The study group included 20 dietary-treated well-controlled gestational diabetic women in their third trimester. During a 20-min observation period, the number and length of breathing episodes and the number of breathing movements in each episode were recorded, and the percentage of time spent in breathing activity and the frequency of fetal breathing movements were calculated. The control group included 20 women with uncomplicated pregnancies, matched for gestational age. The fetuses of the study group spent more time in breathing activity (65% vs. 26%, P 30s (8.25 vs. 2.4, P < 0.0001). This occurred despite similar blood glucose levels in the two groups, sampled just before the recordings. No differences were found in either the number of short breathing episodes or the rate of breathing movements per minute. Fetal brea...

Maturation of fetal breathing activity.

Spontaneous breathing movements are present during fetal life and they are important for normal development of the lung. Early in gestation they seem to represent free-running activity of the respiratory centers, not controlled by peripheral mechanisms but probably dependent on a tonic CO2 drive. Maturation of sleep states brings into play powerful brainstem inhibitory mechanisms which control FBM. At birth these mechanisms must be overridden to allow the establishment of continuous breathing.

Fetal breathing—related nasal fluid flow velocity in uncomplicated pregnancies

Our purpose was to determine the Doppler ultrasonographic characteristics of fetal breathing-related nasal fluid flow velocity in uncomplicated pregnancies. Fetal nasal flow velocity was studied in 52 uncomplicated pregnancies at gestational ages ranging from 22 to 41 weeks. The evaluation of fetal breathing-related nasal fluid flow velocity was performed with ultrasonography combined with color flow and spectral Doppler analysis. The study revealed that the breath-to-breath interval and duration of the inspiratory phase of the fetal breathing-related nasal flow increased from 22 to 35 weeks and decreased thereafter. The breath-to-breath interval (milliseconds) at 33 to 35 weeks (1203.9 +/- 295.7 SD) was approximately twice what it was in the earliest age group (22 to 25 weeks); subsequently it decreased by approximately 25% in the term group (38 to 41 weeks). A positive correlation existed between the mean breathing-related nasal peak inspiratory flow velocity and advancing gestational age (r = 0.56, p = 0.0008), and between the inspiratory flow velocity acceleration and advancing gestational age (r = 0.53, p = 0.0076). Changes in fetal breathing activity during uncomplicated pregnancies can be determined by measurement of fetal breathing-related nasal fluid flow velocity. Our observations in uncomplicated pregnancies may be useful in future studies of these parameters in complicated pregnancies such as those at risk for pulmonary hypoplasia.