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PubMed1975

Effects on breathing mechanics and gas exchange of different inspiratory gas flow patterns in patients undergoing respirator treatment.

In order to investigate the importance of different inspiratory gas flow patterns in respirator treatment, eight intensive care patients were studied with breathing mechanics and five patients also with gas exchange studies. Three different inspiratory gas flow patterns were tested in randomized sequences namely, accelerating, constant and decelerating flow. All three flow patterns were generated by the same respirator. No end-inspiratory pause was used. The results point to a favourable effect on breathing mechanics of a decelerating and a constant flow when compared with an accelerating flow type. However, when the total effects on gas distribution and lung perfusion were evaluated in the gas exchange studies, no significant differences were seen between the three flow patterns.

Aged↗
PubMed2004

Pulmonary gas distribution during ventilation with different inspiratory flow patterns in experimental lung injury -- a computed tomography study.

BACKGROUND: There is still controversy about the optimal inspiratory flow pattern for ventilation of patients with acute lung injury. The aim of this study was to compare the effects of pressure-controlled ventilation (PCV) with a decelerating inspiratory flow with volume-controlled ventilation (VCV) with constant inspiratory flow on pulmonary gas distribution (PGD) in experimentally induced ARDS. METHODS: Sixteen adult sheep were randomized to be ventilated with PCV or VCV after surfactant depletion by repeated bronchoalveolar lavage. Positive end-expiratory pressure (PEEP) was increased in a stepwise manner from zero end-expiratory pressure (ZEEP) to 7, 14 and 21 cm H(2)O in hourly intervals. Respiratory rate, inspiration-to-expiration ratio and tidal volume were kept constant. Central hemodynamics, gas exchange and airway pressures were measured. Electron beam computed tomographic (EBCT) scans of the entire lungs were performed at baseline (preinjury) and each level of end-expiratory pressure during an inspiratory and expiratory hold maneuver. The lungs were three-dimensionally reconstructed and volumetric assessments were made separating the lungs into four subvolumes classified as overinflated, normally aerated, poorly aerated and nonaerated. RESULTS: Pressure-controlled ventilation led to a decrease in peak airway pressure and an increase in mean airway pressure. No differences between groups were found regarding plateau pressures, hemodynamics and gas exchange. Recruitment, defined as a decrease in expiratory lung volume classified as nonaerated, was similar in both groups and predominantly associated with PEEP. Overinflated lung volumes were increased with PCV. CONCLUSIONS: In this model of acute lung injury, ventilation with decelerating inspiratory flow had no beneficial effects on PGD when compared with ventilation with constant inspiratory flow, while the increase in overinflated lung volumes may raise concerns regarding potential ventilator-associated lung injury.

Animals↗
PubMed1998

Admission test: a predictive test for fetal distress in high risk labour.

OBJECTIVE: To study predictive utility of admission test (AT) for perinatal outcome in high risk labours. METHOD: A hundred patients at risk of fetal jeopardy due to uteroplacental insufficiency were screened by admission test. The traces were classified as per the criteria suggested by Ingemarsson and Arulkumaran (1986). The perinatal outcome was correlated with the initial FHR pattern and Chi square test was applied to the results. RESULTS: Fifty-eight patients had reactive, 35 had equivocal and 7 had ominous tracing. The incidence of operative delivery for fetal distress showed a progressive rise from reactive (5.17%) to ominous (28.5%) pattern group. The perinatal morbidity also showed a rise from 6.89% in the reactive to 31.42% in the equivocal (p < 0.01) and 85.71% in the ominous group (p < 0.02). The reactive pattern was assuring of the fetal well being for next 5 hours. Presence of late decelerations and decelerations of 60 beats or more below the baseline were additional ominous characteristics, associated with a significant increase in perinatal morbidity. CONCLUSION: Reactive AT appears to be predictive of fetal well being in high risk labours also. Repeat tracing 4 to 5 hours apart may improve the predictive accuracy. Equivocal and ominous patterns require vigilant monitoring.

Apgar Score↗
PubMed2000

The role of gravity in human walking: pendular energy exchange, external work and optimal speed.

During walking on Earth, at 1.0 g of gravity, the work done by the muscles to maintain the motion of the centre of mass of the body (W(ext)) is reduced by a pendulum-like exchange between gravitational potential energy and kinetic energy. The weight-specific W(ext) per unit distance attains a minimum of 0.3 J x kg(-1) x m(-1) at about 4.5 km x h(-1) in adults. The effect of a gravity change has been studied during walking on a force platform fixed to the floor of an aircraft undergoing flight profiles which resulted in a simulated gravity of 0.4 and 1.5 times that on Earth. At 0.4 g, such as on Mars, the minimum W(ext) was 0.15 J x kg(-1) x m(-1), half that on Earth and occurred at a slower speed, about 2.5 km x h(-1). The range of walking speeds is about half that on Earth. At 1.5 g, the lowest value of W(ext) was 0.60 J x kg(-1) x m(-1), twice that on Earth; it was nearly constant up to about 4.3 km x h(-1) and then increased with speed. The range of walking speeds is probably greater than that on Earth. A model is presented in which the speed for an optimum exchange between potential and kinetic energy, the 'optimal speed', is predicted by the balance between the forward deceleration due to the lift of the body against gravity and the forward deceleration due to the impact against the ground. In conclusion, over the range studied, gravity increases the work required to walk, but it also increases the range of walking speeds.

Energy Metabolism↗
PubMed1989

Development and stability in visual sustained attention in 14, 20, and 26 week old infants.

Infants were studied at 14, 20, and 26 weeks of age in a longitudinal design. They were presented with varying and complex patterns on a TV screen. Two-thirds of the presentations were accompanied by a stimulus in the periphery delayed in time from the onset of fixation on the central stimulus. As in previous research, the infants were not as easily distracted by the interrupting stimulus when the presentation occurred at the point of maximal heart rate deceleration as when the presentation occurred at the end of the heart rate response. Infants with large amounts of respiratory sinus arrhythmia (i.e., heart rate variability) in a baseline recording were less distractible during the deceleration-defined trials than were infants with low amounts of respiratory sinus arrhythmia. Intra-individual patterns of development in respiratory sinus arrhythmia over the testing ages were closely paralleled by patterns of heart rate responding during sustained attention. Individual differences in baseline levels of heart rate and respiratory sinus arrhythmia were more stable than individual differences in sustained attention. The stability of attention responses over age may be mediated by the stability of the physiological system (e.g., heart rate, respiratory sinus arrhythmia, etc.), and by the within-age relation of attention to heart rate variability.

Arousal↗
PubMed1992

Event-related potentials and autonomic responses to a change in unattended auditory stimuli.

Event-related brain potentials (ERPs) and autonomic nervous system (ANS) responses to occasional pitch and rise-time changes in a task-irrelevant auditory stimulus repeating at short intervals were measured while the subject performed a difficult intellectual task (Raven Matrices). It was found that deviant stimuli elicited the mismatch negativity (MMN) component of the ERP even when they elicited no ANS response. There was no significant difference in the mismatch negativity between trials in which the skin conductance response was or was not elicited. The pitch deviant tone also elicited heart rate deceleration, whereas the rise-time deviant tone tended to elicit a later heart rate acceleration. Neither heart rate change correlated with the mismatch negativity. The pattern of results obtained suggests that the mismatch negativity is generated by an automatic discrimination process associated with the cerebral events initiating the orienting response to stimulus change, but does not necessarily lead to the orienting response elicitation. Longer-latency ERP components tended to show slight covariation with ANS responses. The P3 was larger when a skin conductance response was elicited than when it was not elicited. Further, heart rate change trials tended to be accompanied by larger slow waves than trials with no heart rate response. Heart rate acceleration trials were accompanied by a larger slow parietal positivity and a smaller frontal negativity than were heart rate deceleration trials.

Adolescent↗
PubMed1992

Concomitant heart rate and eyeblink Pavlovian conditioning in human subjects as a function of interstimulus interval.

Pavlovian heart rate and eyeblink conditioning were simultaneously assessed in human subjects. Tone durations of 0.6, 1.1, and 2.1 s were employed in separate groups of subjects as the conditioned stimulus. A 100-ms corneal airpuff, which served as the unconditioned stimulus, overlapped the last 100 ms of the tone in each group, thus producing interstimulus intervals of 0.5, 1.0, and 2.0 s. Other groups of pseudoconditioning subjects received explicitly unpaired tone and airpuff presentations of identical durations but in a pseudorandom sequence so that they never occurred together. The best eyeblink conditioning was observed in the group with the .5-s interstimulus interval, although the 1.0-s group also demonstrated some evidence of eyeblink conditioning. The group with the 2.0-s interstimulus interval showed a lower overall rate of conditioned response occurrence and the highest rate of pseudoconditioned responding. The conditioned heart rate response in all three conditioning groups consisted of cardiac decelerations, but tone-evoked cardiac accelerations were observed in the pseudoconditioning groups. The magnitude of the cardiac deceleration was comparable in all three conditioning groups.

Adult↗
PubMed1994

Heart rate and sustained attention during childhood: age changes in anticipatory heart rate, primary bradycardia, and respiratory sinus arrhythmia.

This study examined age changes in three aspects of heart rate responsivity elicited in an auditory oddball task; anticipatory heart rate change, primary bradycardia, and respiratory sinus arrhythmia. Three age groups (5-, 7-, and 9-year-old boys) were presented with series of target (15%) and standard (85%) tones. The results were consistent with the findings reported previously in the adult literature. Heart rate decreased in anticipation of the target tone. The morphology of anticipatory deceleration was somewhat different for the 5-year-olds compared to the older children. Stimuli presented during the early part of the cardiac cycle induced added deceleration, but this primary bradycardia did not differ between age groups. Respiratory sinus arrhythmia did not discriminate between age groups but was suppressed during the performance of the oddball task relative to base level. It was concluded that these three aspects of heart rate responsivity show developmental constancy rather than change.

Arousal↗
PubMed1996

Anticipatory EMG responses of pericranial muscles in relation to heart rate during a warned simple reaction time task.

Obrist's cardiac-somatic coupling hypothesis predicts a widespread inhibition of heart rate and task-irrelevant muscle activity during expectancy situations. This hypothesis was tested by measuring heart rate and pericranial electromyographic (EMG) activity during a warned simple reaction time task with visual or auditory reaction signals and hand or foot responses. In each of three groups of 24 participants, EMG activity of three different facial, masticatory, or neck muscles was recorded. During the warning interval preceding the presentation of the reaction signal, masticatory and lower facial muscles predominantly showed a gradual inhibition in activity concomitant with heart rate deceleration. In contrast, two upper facial muscles showed increasing activity. Pericranial EMG responses were little affected by reaction signal modality and were independent of responding limb. Greater heart rate deceleration was associated with greater inhibition and weaker facilitation of EMG responses. The results suggest a functional role of inhibitory EMG responses in increasing the perceptual sensitivity to expected signals.

Adult↗
PubMed2005

A freezing-like posture to pictures of mutilation.

Postural sway and heart rate were recorded in young men viewing emotionally engaging pictures. It was hypothesized that they would show a human analog of "freezing" behavior (i.e., immobility and heart rate deceleration) when confronted with a sustained block of unpleasant (mutilation) images, relative to their response to pleasant/arousing (sport action) or neutral (objects) pictures. Volunteers stood on a stabilometric platform during picture viewing. Significantly reduced body sway was recorded during the unpleasant pictures, along with increased mean power frequency (indexing muscle stiffness). Heart rate during unpleasant pictures also showed the expected greater deceleration. This pattern resembles the "freezing" and "fear bradycardia" seen in many species when confronted with threatening stimuli, mediated by neural circuits that promote defensive survival.

Adult↗
PubMed1975

The analysis of continuous fetal heart rate traces in the first and second stages of labour.

In the search for a simplified method of fetal heart rate trace assessment 50 traces recorded during the first stage of labour and those recorded in the last hour of each of a further 50 labours have been analysed intensively. The importance of baseline variability in predicting possible fetal distress in both the first stage and the last hour of labour is shown and the possible use of an objective measurement of baseline variability in the further screening for fetal acidosis is described. The importance of lag time measurement in the first stage of labour is demonstrated and the relationships between fetal scalp blood pH and other heart rate parameters is discussed. Significant inverse correlations between one-minute Apgar score and maximum amplitude of deceleration and total deceleration area in the last hour of labour are also shown. Temporal relationships between intrauterine pressure rises and transient changes of fetal heart rate failed to give significant correlations in the last hour. These findings in the last hour of labour are compared with those obtained in the first stage of labour and the differences are discussed.

Acidosis↗
PubMed1977

Fetal heart rate patterns and uterine activity after segmental epidural analgesia.

The effects of low-dose segmental epidural analgesia on fetal heart rate (FHR) patterns, uterine activity, and some clinical features were examined in a series of 105 normal parturients. The aim of the analgesic technique was to relieve pain during the first stage of labour by blocking the sensory nerve fibres at the spinal level of T 10 to T12, with either 0-5 per cent bupivacaine or bupivacaine with adrenaline 1 : 200 000, the dose varying from 10 to 25 mg. Obvious pathological changes (late decelerations, prolonged fetal bradycardia, variable deceleration, or loss of beat to beat variation) in FHR patterns within the first 30 minutes after the beginning of analgesia were noted in 9 per cent of the patients. Addition of adrenaline to the analgesic agent seemed to reduce uterine activity for 60 minutes after the analgesia and this was reflected in a longer interval between the block and delivery. A 25 per cent fall in systolic blood pressure was recorded in 11 per cent of the patients. Nine patients required vacuum extractions. Our results show that the epidural technique employed has distinct advantages over the previous methods, which require larger doses of the analgesic, agent, and is therefore safer for the fetus; the addition of adrenaline to the analgesic agent is contraindicated.

Anesthesia, Epidural↗
PubMed1982

Pattern of the normal human fetal heart rate.

With an improved method for fitting baselines to human fetal heart-rate traces, the patterns of episodic variations, accelerations and decelerations were similar in 215 64-min records from normal pregnancies and in 95 with mild hypertension and normal outcome. The change in signal loss with gestational age, by Doppler ultrasound for recording heart rate, was entirely due to the greater loss in episodes of high heart-rate variation. The changes in the numbers and sizes of accelerations and decelerations with gestational age were described. There were many records which had only one or no acceleration at 28-33 weeks gestation (16.2%) or 34-41 weeks (7.3%). However, only two (0.7%) had episodes of high heart-rate variation lasting less than 10 min from 28 weeks onwards. The presence of these episodes, with clusters of fetal movements, is therefore likely to be a better numerical index of normality.

Female↗
PubMed1982

Characteristics and management of intrapartum prolonged fetal bradycardia.

Twenty-five patients had intrapartum prolonged fetal bradycardia, defined as a drop of the fetal heart rate (FHR) by greater than or equal to 50 beats/min maintained for greater than or equal to 3 min; 10 were delivered by caesarean section and 15 vaginally. The only neonatal death occurred in the group delivered abdominally. Statistical analysis showed no difference in amplitude or duration of deceleration in the two groups but the 1 and 5 min Apgar scores were higher in the group delivered vaginally (P less than 0.01), whereas the onset of deceleration to delivery interval was shorter in the group delivered by caesarean section (p less than 0.005). Appropriate management of prolonged bradycardia is outlined and the characteristics of the FHR tracings are identified that are of prognostic value in determining whether or not immediate delivery is indicated.

Adolescent↗
PubMed1997

The intrapartum CTG prior to neonatal encephalopathy at term: a case-control study.

OBJECTIVE: To compare cardiotocograph (CTG) records during labour in cases of neonatal encephalopathy and matched controls. DESIGN: Case-control study. SETTING: Metropolitan area of Perth, Western Australia. SUBJECTS: Term deliveries complicated by neonatal encephalopathy and controls matched for sex, hospital, time of birth, day of week of birth and maternal health insurance. MAIN OUTCOME MEASURES: Low fetal heart rate (FHR) variability, FHR accelerations, late decelerations, total Kreb's score and FIGO classification of CTG records. RESULTS: The neonatal encephalopathy group had significantly more abnormal CTG records (89%) classified according to FIGO, although 52% of control CTG records were also abnormal. CTG records from cases developed significant differences in terms of absence of FHR accelerations and low FHR variability, but not late decelerations, prior to delivery. CONCLUSION: Given the low incidence of neonatal encephalopathy in this study (7 per 1000) the predictive value of an abnormal CTG record is clinically unhelpful. However, the changes in the FHR in such cases suggest a greater disturbance of fetal (rest-activity) behaviour during labour.

Brain Diseases↗
PubMed1999

Fetal heart rate variability changes during brief repeated umbilical cord occlusion in near term fetal sheep.

OBJECTIVE: To determine whether changes in fetal heart rate variation during repeated umbilical cord occlusions reflect evolving cardiovascular compromise in near term fetal sheep. DESIGN: Fetal heart rate variation, fetal mean arterial pressure, electroencephalogram (EEG) and acid-base status were measured during one minute umbilical cord occlusions, repeated either every five minutes (1:5 group) or every 2.5 minutes (1:2.5 group) for four hours or until mean arterial pressure fell below 20 mmHg for two successive occlusions. SAMPLE: Fourteen chronically instrumented fetal sheep, mean gestation 126.3 (2.6) days. RESULTS: Cord occlusion caused variable decelerations with initial sustained hypertension. In the 1:5 occlusion group mean arterial pressure remained elevated throughout, with little change in acid-base status (pH = 7.34 (0.07), base deficit = 1.3 (3.9) after 4 hours) and no significant change in fetal heart rate variation. In contrast, in the 1:2.5 group from the third occlusion there was progressive hypotension during occlusions, severe progressive metabolic acidaemia (pH 6.92 (0.1), base deficit 17.0 mmol/L (4.7) after the last occlusion) and marked EEG suppression (P < 0.01). Fetal heart rate variation increased with the onset of occlusions (P < 0.05) and then progressively fell with continued occlusions. During the last 30 minutes of occlusions, fetal heart rate variation was severely suppressed in four, but increased in two fetuses, while all six fetuses developed overshoot-instability of fetal heart rate and mean arterial pressure following each occlusion. CONCLUSIONS: Acute progressive asphyxia was typically associated with an immediate, transient increase in fetal heart rate variation. Subsequently variation became suppressed in only two-thirds of fetuses during terminal acidaemia and hypotension. Fetal heart rate overshoot-instability may be a useful marker of fetal decompensation following variable decelerations.

Acidosis↗
PubMed2001

Computerised analysis of the fetal heart rate and relation to acidaemia at delivery.

OBJECTIVE: To identify the individual features of the computerised analysis of the cardiotocograph that relate to arterial pH and base deficit at delivery. DESIGN: Retrospective observational study. SETTING: Teaching hospital labour wards. PARTICIPANTS: 679 women requiring continuous intrapartum fetal monitoring. METHODS: Fetal heart and uterine contraction data were obtained using the Nottingham Fetal ECG monitor. Fetal heart rate patterns for the last half-hour preceding delivery were analysed using a computer algorithm developed for intrapartum application. The significance of the areas under receiver operator characteristic curves were calculated. MAIN OUTCOME MEASURES: Umbilical arterial pH and base deficit at delivery. RESULTS: Three parameters, fetal bradycardia, total deceleration area and the deceleration area after a contraction had receiver operator characteristic curves that significantly predict a low umbilical arterial pH and base deficit at delivery (areas under receiver-operator characteristic curves = 0.53, SD 0.01 P = 0.03; 0.60, SD 0.03 P = 0.002; 0.62 SD 0.04 P < 0.001, respectively). Tachycardia, accelerations and variability did not. CONCLUSIONS: The individual components of the computerised analysis of the fetal heart rate that predict acidaemia at delivery are identified.

Acidosis↗
PubMed2004

The effects of intrapartum hypoxia on the fetal QT interval.

BACKGROUND: The morphology of the fetal ECG complex provides information on the fetal condition during labour, such as the ST segment and T-wave configuration. We hypothesised that the intrapartum fetal QT interval may provide additional information on the condition of the fetus, as it is known that the QT interval reacts to situations of stress and exercise. DESIGN: Retrospective study. SETTING: Data were substracted from a European community multicentre trial. METHODS: The intrapartum QT interval was measured in 68 fetuses who were acidemic at birth (pH <7.05 and BD (ecf) >12 mmol/L) and in a control group of similar size. All of these cases were monitored by STAN S21. Measurements were performed at the start of the recording at baseline heart rate, during variable decelerations and at the end of the recording. The QTc was calculated using Bazett's formula: QT/ radical RR. The intervals were compared using the Wilcoxon signed ranks test. MAIN OUTCOME MEASURES: Fetal QT interval, and the corrected QT interval: QTc. RESULTS: In the acidemic fetuses, there was a significant shortening of the QTc interval at the end of the recording compared with the start of the recording (397 ms at the end vs 359.3 ms at start; P < 0.001), in association with a significantly lowered heart rate (136.3 vs 110.9 bpm, P < 0.001). Measurements of QT and QTc during variable decelerations at the start and end of the recording also showed a shortening of the QT interval (301.9 vs 273.3 ms, P< or = 0.001) and QTc interval (381.6 vs 340.3, P < 0.001), and this was not dependent on heart rate. In the control cases, no differences in FHR, QT and QTc intervals were present. CONCLUSIONS: In intrapartum hypoxia, resulting in metabolic acidosis, a significant shortening of the fetal QT and QTc is present, irrespective of changes in heart rate. In control cases, this shortening does not occur. The intrapartum fetal QT interval may therefore provide additional information on the condition of the fetus.

Cardiotocography↗