Biomedical subjects

R Leuthold

Publications and source records attributed to R Leuthold.

5 recordsLinked to original sources

PubMed1994

High-frequency ventilation: oscillatory dynamics.

OBJECTIVES: To determine the influence of the dynamic properties of the oscillator on the oscillatory volume delivered through the endotracheal tube to the lung or lung surrogate (delivered volume) under conditions of high-frequency ventilation. In particular, the relation between the tidal volume of the pump (oscillator) and the delivered volume was analyzed. PaCO2 was measured further as a function of the delivered volume in a number of experiments performed with healthy dogs. DESIGN: Laboratory study. SETTING: Engineering and animal laboratory. SUBJECTS: Lung surrogates and healthy dogs. INTERVENTIONS: An experimental oscillatory system was connected to various lung surrogates. In addition, six beagle dogs received high-frequency ventilation with different delivered volumes during the study. Control of the mean airway pressure was achieved by a peripheral pressure chamber located at the exhaust port of the bias flow tube. RESULTS: The delivered volume, which is the quantity of interest from a physiologic point of view, can deviate considerably from the tidal volume of the pump due to dynamic (particularly resonance) effects. Because the delivered volume and the mean airway pressure have to be controlled independently, two independent quantities are necessary for control purposes (e.g., the tidal volume of the pump and the mean pressure at the exhaust port). Furthermore, it was found that a minimal condition for adequate gas exchange is a delivered volume that exceeds the machine-related deadspace. For this reason, and in order to maximize the CO2 gradient, the exhaust tube must be as short as possible. CONCLUSIONS: a) The delivered volume has to be monitored under clinical conditions; b) however, because the impedance of the endotracheal tube in general considerably exceeds the impedance of the lung, the influence of the impedance of the lung on the delivered volume is generally small, and thus an in vitro calibration may serve as a useful approximation; c) at least two independent quantities are needed for an adequate oscillatory control; d) a necessary (not necessarily sufficient) condition for adequate CO2 removal is that the delivered volume must exceed the machine-related deadspace; e) in a clinical environment involving extremely pathologic lung conditions, e.g., adult respiratory distress syndrome, mechanical lung characteristics may deviate substantially from those characteristics used in this study (i.e., the results obtained may not necessarily be applicable under all clinical situations).

Animals↗

PubMed1992

Gas transport during high-frequency ventilation: the significance of direct wash-out.

Gas transport during high-frequency oscillation was investigated in vitro using CO2 elimination from the lung surrogate as a measure of gas transport efficiency. The length of the connecting tube between the piston pump and the three-port connector did not affect gas transport efficiency if the oscillatory volume (VDEL) was constant; inserting an additional tube between the three-port connector and the endotracheal tube decreased gas transport efficiency dramatically. In contradistinction, increasing VDEL caused a steep rise in gas transport efficiency as soon as VDEL surpassed the volume of the tubes connecting the lung surrogate with its surroundings. As gas transport efficiency was found to be very sensitive to the net oscillatory volume, i.e. VDEL minus the volume of the tubes connecting the lung and the surroundings, direct wash-out was considered to be an effective gas transport mechanism during high frequency oscillation. Two preliminary experiments on dogs allowed us to substantiate this hypothesis in vivo.

Animals↗

PubMed1991

Significance of bulk convection during high-frequency oscillation.

In 7 anesthetized supine dogs with an anatomic dead space of 115-162 ml, gas transport during high-frequency oscillation (HFO) was investigated at an oscillatory frequency of 15 Hz. Starting with an oscillatory volume effectively delivered to the lungs (VDEL) of 60 ml, measured on line with an ultrasonic airflow meter, VDEL was reduced in steps of 10 ml, down to a VDEL of 30 ml, whereby fresh gas flow rate, airway occlusion pressure and lung volume above functional residual capacity were kept constant. An HFO-circuit without bias tube was used. The volume of endotracheal tube and three port connector, designated as HFO-circuit related rebreathing volume, was 35 ml. PaCO2 continuously increased, when VDEL was reduced from 60 ml to 40 ml and the data fit perfectly to a reciprocal regression (1/PaCO2 = a + b.VDEL), r2 ranging from 0.95 to 1.00. Measured PaCO2 values at a VDEL of 30 ml (8.26 +/- 1.77 kPa), however, were significantly (P less than 0.025) higher than PaCO2 values predicted by the individual reciprocal regression equations (6.25 +/- 1.46 kPa). This overproportionate increase in PaCO2 due to a reduction of VDEL from 40 ml to 30 ml may be explained by the sudden drop out of bulk convection as a gas transport mechanism between central airways and the surrounding because bulk convection is only possible as long as VDEL exceeds the HFO-circuit related rebreathing volume. Bulk convection therefore is considered an essential gas transport mechanism during HFO and the efficiency of CO2 elimination during HFO is critically dependent on the net oscillatory volume, i.e. VDEL minus the HFO-circuit related rebreathing volume and not on the relationship between VDEL and anatomic dead space.

Animals↗

PubMed1990

Gas transport enhancement in high-frequency oscillation.

Gas transport during high-frequency oscillation (HFO) with (HFO+BT) and without bias tube (HFO-BT) was investigated in 10 anesthetized supine dogs. The oscillatory volume effectively delivered to the lungs, airway occlusion pressure and lung volume above functional residual capacity (FRC), regulated by a newly deviced pressure control system, as well as the oscillatory frequency (20 Hz) were adjusted to equal levels in HFO+BT and HFO-BT. At a fresh gas flow rate (fgf) of 3 L/min (room air), arterial CO2 partial pressures (PaCO2) decreased from 49.9 +/- 6.5 mm Hg (mean +/- SD) to 40.2 +/- 6.3 mm Hg (P less than 0.01) i.e. by 19.2 +/- 8.7%, and arterial O2 partial pressures (PaO2) increased from 71.5 +/- 13.1 mm Hg to 85.6 +/- 14.6 mm Hg (P less than 0.01) or by 20.5 +/- 12.0% in HFO-BT as compared to HFO+BT. At a fgf of 6 L/min, PaCO2 decreased less but still significantly (P less than 0.025) from 42.1 +/- 6.5 mm Hg to 37.8 +/- 6.8 mm Hg (10.4 +/- 5.6%) and PaO2 increased from 78.1 +/- 12.9 mm Hg to 84.6 +/- 16.4 mm Hg i.e. by 8.1 +/- 6.4% (P less than 0.05) in HFO-BT. The higher gas transport efficiency after removing the bias tube can be explained by two mechanisms: (1) By removing the bias tube, the volume of the bias system decreased from 54 ml in HFO+BT to 1 ml in HFO-BT and rebreathing of exhaust gas from the bias system is therefore eliminated in HFO-BT.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Augmentation of CO2 elimination during high frequency oscillation by removing the bias tube--an in vitro study.

In clinical applications of high frequency oscillation (HFO), sufficient CO2 elimination (VCO2) may represent a problem mainly at higher oscillation frequencies. With the intention of examining how to increase VCO2 a modified bias flow system was investigated in vitro with wash-out experiments. In bias flow systems, long tubes have been used in order to minimize the loss of oscillatory volume; however, a distinct increase of VCO2 was achieved in the present study by removing the bias tube. This improvement occurred over the whole frequency range of 2-60 Hz, although the oscillatory volume, effectively delivered to the lungs was smaller with the HFO circuit without bias tube (HFO-BT) as compared to the arrangement with bias tube (HFO + BT). A long bias tube flattens the CO2 concentration gradient from the alveoli to the atmosphere. Removing the bias tube results in a steeper CO2 concentration gradient and in a correspondingly enhanced VCO2. Furthermore, the large oscillatory volume at the exit of the bias flow system in HFO-BT supports VCO2 as an additional wash-out mechanism. Based upon longitudinal tracer gas concentration measurements between the alveoli and the atmosphere during HFO16,17, an increase of gas transport up to 20% can be expected for in vivo applications by removing the bias tube.

Carbon Dioxide↗