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Biomedical subjects

I E Hopkin

Publications and source records attributed to I E Hopkin.

At least 19 recordsLinked to original sources
PubMed1992

Dynamic lung inflation during high frequency oscillation in neonates.

The effects of high frequency oscillation (HFO) on dynamic lung inflation were examined in 22 neonates ventilated for respiratory disease. HFO was combined with conventional ventilation and a series of frequencies from 2-25 Hz was tested. Dynamic lung inflation was measured using a jacket plethysmograph which was converted to a measure of alveolar pressure using the compliance of the respiratory system obtained during conventional ventilation. The results showed an increase in dynamic lung inflation with frequency such that volume increased by 0.4 ml for each increase of 10 Hz. Alveolar pressure increased by 1.2 cm H2O for each increase of 10 Hz. Dynamic lung inflation also increased with increased volumes of oscillation.

High-Frequency Ventilation↗
PubMed1992

The effects of mid-trimester amniocentesis on lung function in the neonatal period.

Lung function tests were carried out on 39 healthy full term babies born after pregnancies subjected to mid-trimester amniocentesis. The results were compared to 42 babies born after normal pregnancies. There were no significant differences in gestational age, birth weight, thoracic gas volume or crying vital capacity. Babies subjected to amniocentesis had a significantly lower dynamic compliance (6.96 ml/cm H2O vs. 8.60 ml/cm H2O) and tended to have higher resistance compared to controls (52.8 cm H2O/l/s vs. 37.3 cm H2O/l/s). This provides further evidence that mid-trimester amniocentesis does have an adverse effect on lung growth and development.

Adolescent↗
PubMed1992

Measurement of tidal lung volumes in neonates during high-frequency oscillation.

High-frequency oscillation (HFO) has been used clinically to ventilate infants with respiratory distress. However, there are problems in monitoring the effects on the respiratory system and in particular in measuring the volumes delivered; this is important information in terms of safety and mechanisms of action of HFO. We have validated two sizes of respiratory jacket for measuring oscillatory volume changes of 0.25-5 ml at frequencies of 2-25 Hz, the volume delivered from a purpose-built oscillator having first been validated. Different combinations of volume and frequencies were then oscillated into each jacket, while it was being worn by a well preterm baby. Studies were performed with each jacket on five babies with weights between 0.82 and 1.86 kg. The results showed that at any given frequency there was a linear relationship between the pressure oscillations measured from a side port of the jacket and the delivered volume. Both jackets showed the same pattern of frequency response, overreading at less than 10 Hz and underreading at 10-25 Hz. When appropriately calibrated, the respiratory jacket can be used as a non-invasive method of measuring volumes delivered by HFO.

Calibration↗
PubMed1991

Combined conventional ventilation with high frequency oscillation in neonates.

Combined high frequency oscillation (HFO) with conventional ventilation was used on a group of 12 ventilator dependent neonates in order to investigate the frequency response of the respiratory system to HFO. Pressure oscillations were measured at the airway opening with a transducer and volume oscillations at the chest wall using a calibrated respiratory jacket. Pressure oscillations increased with increasing frequency but the oscillating volumes showed a variable pattern with maximum oscillating volumes of up to 4 ml/kg. Three babies showed no change in volume between 2-25 Hz, 3 babies showed increasing volumes up to 25 Hz and the remainder showed a maximum volume (or resonant frequency) at 15-20 Hz. Oscillating volumes were higher when the conventional ventilator was in the expiratory phase. The differences in frequency response were unrelated to severity of lung disease, birth weight, age at testing, or size of the endotracheal (ET) tube. Local factors in the ET tube and large airways may account for some of the observed differences.

Combined Modality Therapy↗
PubMed1989

Inspiratory-to-expiratory ratio during ventilation for idiopathic respiratory distress syndrome.

We have studied the effects of changes in inspiratory-to-expiratory ratios (I/E ratios) on transcutaneous blood gases in a group of 30 infants receiving respiratory support for the idiopathic respiratory distress syndrome (IRDS). Following the use of a reversed I/E ratio (inspiration exceeding expiration), changes in oxygenation were very variable but improvements were seen most consistently in babies weighing greater than 1,750 g and less than 850 g. The use of reversed I/E ratios seemed less efficient than positive end-expiratory pressure in raising TcPO2 for the same increase in mean airway pressure. Changes from a 1:1 ratio to a normal I/E ratio, in which expiratory time exceeded inspiratory time by 50-100%, led to more marked and consistent falls in TcPO2. We conclude that a flexible attitude toward the use of I/E ratios should be adopted to avoid raising mean airway pressure needlessly.

Animals↗
PubMed1987

A simple method of face mask resuscitation at birth.

Twenty two infants were resuscitated at birth using a face mask connected to an oxygen supply from a conventional resuscitaire. Intermittent finger occlusion provided the positive pressure within the mask. This method was apparently at least as effective as the best bag and mask systems and was convenient to use.

Female↗
PubMed1987

Endotracheal resuscitation of preterm infants at birth.

The adequacy of initial ventilation in 21 preterm babies (25-36 weeks' gestation), who required endotracheal intubation and positive pressure ventilation, were studied. Pressure and flow were measured at the proximal end of the endotracheal intubation tube and expiratory volume calculated from the flow trace. The results were compared with those from a group of 26 term infants who also required resuscitation. Five of 21 preterm babies (24%) had adequate tidal ventilation with the first inflation. This rose to seven of 21 (33%) by the third inflation. This was significantly less than the results in the term infants (chi 2 = 4.38 p less than 0.05). Respiratory reflex responses to resuscitation were seen in 41% of inflations in preterm and 56% of inflations in term infants. There was a significant correlation between reflex activity and adequate ventilation in the preterm group (chi 2 = 11.83, p less than 0.001) but not in the term group (chi 2 = 0.212, p = NS). No correlation was seen between initial ventilation and outcome.

Humans↗
PubMed1987

Validity of forced expiratory flow volume loops in neonates.

It is claimed that suddenly squeezing a newborn baby's trunk with a pressure of 3-4 kPa produces a flow volume curve that can be used to measure the function of the small airways. If the squeeze is applied during expiration rather than at the end of inspiration, however, anomalous results may be obtained. One possible explanation is that the babies are limiting expiratory flow by making inspiratory efforts in response to the applied external pressure. The response of 10 healthy term neonates to forced expiration was studied by using an oesophageal balloon. The squeeze was provided by an inflatable jacket, and measurements of oesophageal pressure and jacket pressure were recorded, as well as flow and volume changes at the mouth. Two hundred and twenty one squeezes were performed at different points in the respiratory cycle. In 188 squeezes an inspiratory effort was evident before the oesophageal pressure reached a plateau (mean time to peak pressure = 155 ms). For the remaining squeezes a plateau pressure was associated with closure or narrowing of the upper airway in most of the babies. When the squeeze was applied at low lung volumes the inspiratory effort was significantly earlier and stronger than around end inspiration. Thus a baby makes a reflex inspiratory response to chest compression that may interfere with the measurement of airway function when this technique is used.

Esophagus↗
PubMed1986

Efficiency of manual resuscitators at birth.

The effectiveness of five neonatal/paediatric manual resuscitators was assessed in a group of babies born by caesarean section. Results showed that devices incorporating a large volume reservoir produced the greatest tidal volume, while those with smaller volume reservoirs could not be considered satisfactory for routine use during neonatal resuscitation.

Apnea↗
PubMed1985

Changing overall workload in neonatal units.

An epidemiological study was carried out in the current Nottingham health district to determine changes in both neonatal unit workload and in the infants requiring neonatal care during two study periods. All admissions for 1977 and again for the 12 months 1 April 1983 to 31 March 1984 were reviewed. Total numbers of admissions have shown roughly a 50% reduction because of a more rigorous admission policy locally. The admissions of infants of 33 weeks' gestation or less have shown a significant increase, while the overall survival of infants less than 33 weeks' gestation has improved.

Birth Weight↗
PubMed1985

Continuous positive airway pressure via a single nasal catheter in preterm infants.

We present the results of giving continuous positive airway pressure (CPAP) via a single nasal catheter to 20 preterm infants. A beneficial effect in terms of reduced work of breathing (P less than or equal to 0.01) and improved pattern of respiration (P less than or equal to 0.05) are demonstrated. CPAP via a single nasal catheter does not seem to mediate effects inside the thorax unlike CPAP delivered by a tight fitting face mask. Gross variations in CPAP level may result from altering the infant's position.

Apnea↗
PubMed1985

Manipulation of ventilator settings to prevent active expiration against positive pressure inflation.

Recent publications have suggested that in infants receiving artificial ventilatory support a particular pattern of interaction between spontaneous breaths and ventilator inflations (active expiration against each ventilator inflation) may be important in the production of pneumothoraces. We have looked at patterns of interaction from 47 preterm infants studied on 51 occasions. We found that active expiration against the ventilator occurred on a total of 16 occasions. This pattern was prevented on 14 occasions by altering the ventilator settings. In two other babies, the pattern persisted but neither baby developed a pneumothorax.

Carbon Dioxide↗
PubMed1985

Inspiratory time and tidal volume during intermittent positive pressure ventilation.

We measured the tidal volume achieved during intermittent positive pressure ventilation using various inspiratory times with a minimum of 0.2 seconds. Results indicate that tidal volume shows no reduction with inspiratory times down to 0.4 seconds. An inspiratory time of 0.3 seconds, however, is likely to reduce tidal volume by 8%, and at 0.2 seconds a 22% fall may be anticipated.

Humans↗
PubMed1985

Effects of positive end expiratory pressure during ventilation of the preterm infant.

Twenty two babies receiving artificial ventilator support were studied on 29 occasions to determine the effects of low levels of positive end expiratory pressure. Mean positive end expiratory pressure during these studies was 2.6 cm H2O. Changes in tidal volume, minute volume, compliance, and transcutaneous gas trends produced by the use of positive end expiratory pressure were investigated. Positive end expiratory pressure consistently caused a rise in transcutaneous oxygen tension. Changes in transcutaneous carbon dioxide tension after the introduction of positive end expiratory pressure were less consistent and not of the same magnitude as the observed reduction in minute ventilation. Compliance values fell with the use of positive end expiratory pressure.

Apnea↗
PubMed1984

Efficacy of facemask resuscitation at birth.

The efficacy of facemask resuscitation was assessed by measuring the expiratory tidal volume during the first three inflations in nine babies with birth asphyxia and comparing the results with those obtained in a further nine babies resuscitated after endotracheal intubation. The facemask system was relatively inefficient, with tidal exchange less than one third of that seen after intubation and rarely sufficient to produce adequate alveolar ventilation. Successful resuscitation depended on stimulating the baby to make his own respiratory efforts.

Asphyxia Neonatorum↗
PubMed1984

High and conventional rates of positive pressure ventilation.

We compared high frequency positive pressure ventilation with conventional rate ventilation in 23 preterm infants with the idiopathic respiratory distress syndrome. Nine infants (10 studies) were making spontaneous respiratory efforts during conventional ventilation that abated at 100 breaths per minute. Six of these showed an increase in TcPo2 of at least 10% at the higher rate (mean 18.5%). Two babies showed no change during high frequency positive pressure ventilation, and in one baby (the largest) the TcPo2 fell. Eight infants were apnoeic at both ventilator rates: five suffered a fall in TcPo2 of at least 10% at 100 breaths per minute (mean 19%) and three were unchanged. A further six infants (seven studies) would not tolerate a reduction in rate from 100 breaths per minute without an increase in FIO2. Failure to tolerate a conventional ventilator rate in these circumstances seemed related to the onset or a noticeable increase in spontaneous respiratory efforts.

Carbon Dioxide↗