ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

We found that the transport of gases in oscillating gas columns was proportional to oscillation frequency and the square of oscillation amplitude. When these results were applied to high-frequency oscillation and high-frequency jet ventilation in dogs, alveolar ventilation was proportional to frequency and to the square of tidal volume, and inversely proportional to anatomic dead space.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

A pneumatic-to-electrical circuit anàlog is used to describe 2 separate mechanisms by which high-frequency jet ventilators sustain ventilation and oxygenation in the presence of large airway disruptions. The frequency-dependent mechanism is based on variations in the pneumatic equivalent to capacitive reactance. The pressure-dependent mechanism models lung defects on a voltage-controlled resistor. The electrical circuit model is also used to explain the factors leading to gas trapping and inadvertent positive end-expiratory pressure during high-frequency jet ventilation.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Traditional concepts of gas transport in the lung cannot explain the adequate alveolar ventilation observed during high-frequency ventilation (HFV) with tidal volumes (VT) less than the anatomic dead space (VD). Different physical mechanisms enhance and limit gas exchange during HFV. Mechanisms enhancing transport include: (a) diffusion, the spontaneous intermingling of the molecules of 2 gases due to Brownian motion; (b) convective mechanisms which depend on bulk flow, such as direct alveolar ventilation, pendelluft, and streaming; and (c) the combined effects of convection and diffusion, often termed augmented transport. Equations describing some of these mechanisms have been incorporated into theoretical models of gas transport which predict that the efficiency of HFV is proportional to faVTb, where f is frequency and b is greater than a. These predictions generally agree with experimental results obtained in healthy animals and humans. However, experimental results in subjects with lung disease show that, at a fixed VT, gas transport efficiency plateaus as f increases. One explanation for this plateau is that in subjects with increased peripheral airway resistance, the upper airways act as a shunt compliance, absorbing a fraction of the delivered VT. Experimental results to date have not confirmed or refuted any specific theory, but it seems likely that gas mixing during HFV is enhanced by a number of the mechanisms mentioned above and that the mechanical properties of the lungs might limit gas transport, especially in patients with peripheral airway obstruction.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

A variety of technical decisions are required for the proper selection and safe and efficacious application of high-frequency jet ventilation (HFJV). Criteria for analyzing the performance of an HFJV system are presented, along with discussions of some of the more common respiratory measurements and their applicability to HFJV.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

High-frequency oscillation (HFO) minimizes tidal volume. To investigate whether ventilation can proceed when tidal movement (volume) is eliminated, a nondis-tensible physical model of interconnected chambers was constructed. During HFO, ventilation was related to pressure waveform characteristics recorded within the separate chambers. Ventilation increased up to a critical frequency related to the time constant of the system. Beyond this frequency, ventilation dropped off rapidly.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

A high-frequency (HF) unit which can be used in combination with a volume-cycled ventilator was tested in an oxygen-consuming lung model. Alveolar O2and CO2concentrations were not related to superimposed HF pulsations. With constant alveolar ventilation each basal frequency resulted in identical alveolar fractions of O2and CO2. Addition of HF pulsations did not change the volume of CO2or O2exchanged between alveolar and dead-space compartments. Superimposed HF pulsations may affect gas exchange, but the verification of this hypothesis requires further studies.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Amplitude modulation of the waveforms of several cardiovascular variables was investigated during high-frequency (1.3 to 3.3 Hz) positive-pressure ventilation (HFPPV). The amplitude modulation of the pulmonary artery pressure wave was most prominent and its beat frequency (BF) was equal to the difference between the heart rate and the ventilation rate. Spectral analysis of the pulmonary artery pressure demonstrated well-defined peaks associated with the BF. No significant physiologic changes in either cardiovascular or pulmonary function were attributable to the presence of the beat phenomenon.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Positive-pressure ventilation can increase dead space by trapping gas, especially at high frequencies. Under conditions of high airway resistance and high pulmonary compliance, gas trapping can increase alveolar pressure without affecting proximal airway pressure, due to impedance to expiratory gas flow. The difference between alveolar pressure and proximal airway pressure at end-expiration has been called auto-PEEP. Using a mechanical test lung, we altered compliance and resistance under a variety of high-frequency jet ventilator settings to evaluate the generation of auto-PEEP. High driving pressures and prolonged inspiratory times significantly increased gas trapping. This effect was most pronounced when both airway resistance and pulmonary compliance were elevated. These findings support the concept that high-frequency jet ventilation (HFJV) may have deleterious side-effects in patients with chronic obstructive pulmonary disease.

ISSN:0090-3493    

出版商:OVID    

年代:1984

数据来源: OVID