PubMed · 2392368
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D A Stringer, S H Ein. 1990. Pneumatic reduction: advantages, risks and indications.. https://doi.org/10.1007/bf02075214
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The cellular mechanisms underlying the effect of high pressure on synaptic transmission were studied in the opener muscle of the lobster walking leg. Excitatory postsynaptic currents (EPSCs) were recorded using a loose macropatch-clamp technique at normal pressure and 3.5, 6.9 MPa helium pressure. Responses of the single excitatory axon could be grouped into two types: low-yield (L) synapses exhibiting small EPSCs with a considerable number of failures, and high-yield (H) synapses having larger EPSCs with very few failures. High pressure reduced the average EPSC amplitude in all synapses and shifted their amplitude histograms to the left by decreasing the quantal content (m) without changing their quantum current (q). A binomial distribution fit of EPSC amplitudes revealed that high pressure greatly decreased n, the number of available active zones, but the effect on p, the probability of release for each zone, was not consistent. Many of the spontaneous miniature EPSCs (mEPSCs), observed only in L-type synapses, were "giant" (size = 2-5 q). High pressure increased the frequency of the giant mEPSCs but had little effect on their amplitude histogram. High pressure depressed evoked synaptic transmission by modulating the presynaptic quantal release parameters, but concomitantly enhanced spontaneous quantal release by an unknown mechanism.
Pressure- and flow-triggering are available in the Puritan Bennett 7200ae and Siemens SV 300. Using a mechanical lung model, we described the characteristics of the pressure- and flow-triggered continuous positive airway pressure (CPAP) of both ventilators. In the Puritan Bennett 7200ae, the pressure-triggered CPAP is characterized by the relatively insufficient flow delivery after the triggering, resulting in a greater lung pressure-time product (total PTP) than the flow-triggered CPAP. Pressure support of 5 cmH2O results in total PTP less than that with flow-triggered CPAP. In the Siemens SV 300, total PTP with pressure- or flow-triggered CPAP is comparable. Total PTP is less with pressure- or flow-triggered CPAP of the Siemens SV 300 than that of the Puritan Bennett 7200ae, respectively. The application of small pressure- or flow-triggered pressure support in the Puritan Bennett 7200ae eliminates the difference. The impact of these differences on patient inspiratory muscle work remains to be determined.
High-frequency ventilation techniques have been applied for a number of years for laryngeal surgery in order to ventilate patients without endotracheal tubes or catheters. A further development of high-frequency jet ventilation (HFJV) is the technique of superimposed HFJV (SHFJV), which was achieved by combining low- and high-frequency jet streams. Although good clinical results were observed, which have been published in the past, the clinical details of development of SHFJV have not been previously published. METHODS. In order to understand and study the mechanism of superimposition of a high-frequency jet stream, extensive experiments on a lung simulator at defined measuring points, which represented the operating field in microlaryngeal surgery and the trachea, were conducted prior to the clinical application of SHFJV. RESULTS. The measurements demonstrated that superposition of the two jet streams led to greater velocity during inspiration, and therefore produced an increase in tidal volume and entrainment of inspiratory gas. This demonstrates that it is possible to apply a HFJV technique in patients even with an open system. During expiration, the velocity of the low-frequency gas stream is decreased by the opposing flow of the high-frequency jet stream, leading to the buildup of positive end-expiratory pressure. The pulsations of the high-frequency jet stream induce continuous alveolar ventilation. The positioning of the jet nozzles in the jet laryngoscopy has the result that the velocities are already decreased at the tip of the laryngoscope and decrease further with distance from the nozzles. This prevents possible damage to the laryngeal mucosa.