Search PubMed⌕ Search

Biomedical subjects

M F Hird

Publications and source records attributed to M F Hird.

23 records · Page 2Linked to original sources
PubMed1991

Airway pressure triggered ventilation for preterm neonates.

The usefulness of airway pressure triggered ventilation for the preterm newborn has been assessed using a new patient triggered valveless ventilator, the SLE 2000 infant ventilator (SLE 2000). This ventilator performs well at fast rates with no inadvertent positive end expiratory pressure (PEEP) even at rates of 150 breaths per minute (bpm). The ventilator is triggered by a change in airway pressure equal to or exceeding 0.5 cmH2O. If the infant fails to achieve the change in airway pressure which will trigger the ventilator the infant is ventilated at the back-up rate which is predetermined in conventional mode prior to commencing PTV. Infants were ventilated for one hour on a conventional neonatal ventilator, then for one hour on the SLE 2000 in conventional mode without changing the ventilator settings and finally for one hour on the SLE 2000 in patient triggered mode. Arterial blood gases were checked at the end of each hour. During patient triggered ventilation (PTV) the peak pressure, inspiratory time and inspired oxygen concentration were the same as those used during conventional mode. Simultaneous recordings were made of flow, volume, ventilator and oesophageal pressure change, from this recording the trigger delay during PTV was calculated. The trigger delay, being the time lag from the start of spontaneous inspiration, indicated by the negative deflection in the oesophageal pressure trace, and the onset of the ventilator breath. Thirteen infants were included in the study, median gestational age 32 weeks (range 25-35) and birthweight 1640 g (range 838-3038). All were being ventilated for respiratory distress syndrome (RDS) and were 4 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation Studies as Topic↗
PubMed1990

Causes of failure of neonatal patient triggered ventilation.

Causes of failure of patient triggered ventilation (PTV) in neonates have been determined. In particular we have investigated the importance of the timing of ventilator inflation in the spontaneous respiratory cycle and hence the respiratory interaction provoked during PTV. Fifty-six infants (median gestational age 29 weeks) were studied on 63 occasions using two different trigger systems, changes in airway pressure and airflow. After one hour of PTV, only 26 infants were synchronous (inflation coinciding with and occurring only in inspiration), 8 were apnoeic. In the remaining 29 infants, inflation extended into expiration, five of whom were actively expiring. The timing of inflation in the spontaneous respiratory cycle and the interaction provoked was significantly related to the trigger delay, but not the inflation time or type of trigger used. Oxygenation after one hour of PTV improved in infants in whom inflation occurred in inspiration only and in some when it extended beyond. Failure of long term PTV was more common, however, in infants in whom inflation extended beyond inspiration (i.e. asynchronous), but this did not relate to the type of trigger used. Failure was also associated with a long trigger delay (P less than 0.01), a very short inflation time (P less than 0.01) and commencement of PTV early in the infant's illness (P less than 0.05). We conclude that synchrony is the most beneficial respiratory interaction during PTV. Our data suggest that this interaction would be more consistently provoked by the use of a sensitive triggering system which ensured a short trigger delay.

Apnea↗
PubMed1990

Gestational age: an important influence on the success of patient triggered ventilation.

We have evaluated a new patient triggered (PT) ventilator which has been produced as suitable for neonatal use. This ventilator, the Draeger Babylog 8000, is triggered by airflow changes detected by a hot wire anemometer. Laboratory assessment demonstrated maintenance of tidal volume and absence of inadvertent PEEP at flow rates up to 20 l min-1 and rates of 120 breaths min-1. The ventilator was then used in both conventional and trigger mode in 14 pre-term infants. The results were compared with PT ventilation delivered by the SLE ventilator. At all inflation times studied, using the Draeger ventilator 100% of respiratory efforts were detected in the majority of infants. The trigger delay varied from a median of 80-100 ms and was significantly shorter than the trigger delay of the SLE system (P less than 0.05). Oxygenation improved on Draeger PT compared with conventional ventilation, however, only in infants more mature than 27 weeks gestation. We conclude the Draeger Babylog 8000 is an important advance in patient triggered ventilation, particularly at fast frequencies, but PT ventilation should still be restricted to relatively mature infants.

Gestational Age↗
PubMed1980

The effects of some dopamine antagonists on cholinergic mechanisms in the guinea-pig ileum.

1. Activation of prejunctional muscarinic and opiate receptors on cholinergic neurones of the guinea-pig ileum by acetylcholine (ACh) or morphine was seen as an inhibition of twitch responses to transmural electrical stimulation. These inhibitory responses were antagonised by metoclopramide and DL308-IT but no other antagonist used blocked the morphine responses apart from sulpiride in very high concentrations (100 muM and above). 2 Prejunctional and postjunctional responses to ACh on the guinea-pig ileum were measured in the presence of increasing concentrations of some muscarinic and dopamine antagonists. Atropine, hyoscine, chlorpromazine, cis-flupenthixol and thioridazine showed no selectivity in their antagonism of either response to ACh. Benzhexol selectivity antagonised the postjunctional response whereas metoclopramide and DL308-IT showed greater selectivity for the prejunctional effect which they antagonised competitively. Sulpiride, a compound chemically related to metoclopramide, blocked neither the prejunctional nor postjunctional ACh responses. Clozapine antagonised the postjunctional ACh responses whilst apparently potentiating the prejunctional inhibition by ACh. 3 It was concluded that pharmacological differences may exist between prejunctional and postjunctional muscarinic receptors for ACh and that the antipsychotic actions of dopamine antagonists are unlikely to involve blockade of prejunctional ACh or opiate receptors.

Acetylcholine↗