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F Bristow

Publications and source records attributed to F Bristow.

6 recordsLinked to original sources
PubMed1997

Variation of nitric oxide concentration during inspiration.

OBJECTIVE: To evaluate the pattern of inspiratory nitric oxide concentration in a simple, constant flow delivery system during the use of two phasic-flow ventilatory modes. DESIGN: Laboratory study in a lung model. SETTING: University experimental laboratory. SUBJECT: Nitric oxide (800 ppm in nitrogen) was administered continuously into the inspiratory circuit to deliver a nitric oxide concentration of 10 and 40 ppm to a test lung during volume-controlled (constant flow) and pressure-controlled (decelerating flow) ventilation, with an FIO2 of 1.0. INTERVENTIONS: In each mode, minute ventilation of 7, 14, and 21 L/min and installation of mixing chambers (none, 1-L, 2-L, and 3.2-L turbulence boxes) were studied, respectively. Nitric oxide and nitric dioxide were monitored by chemiluminescence. Since the nitric oxide/nitrogen gas is the only nitrogen source in the system during ventilation with an FIO2 of 1.0, we evaluated the fluctuation in the inspiratory nitric oxide (NOx) concentration by measuring nitrogen with a fast-response analyzer. To test the effect of the measurement site, we measured nitric oxide concentrations using chemiluminescence at different positions in the inspiratory and expiratory limbs, with and without the mixing chambers, with a minute ventilation of 14 L/min and a nitric oxide concentration of 40 ppm. MEASUREMENTS AND MAIN RESULTS: Nitrogen dioxide production was not influenced by the flow pattern. During a nitric oxide concentration of 10 ppm, nitrogen dioxide was always < 0.6 ppm. During a nitric oxide concentration of 40 ppm, the highest nitrogen dioxide (4.47 ppm) concentration was found at the lowest minute ventilation and the largest inspiratory circuit volume. Nitric oxide values displayed by chemiluminescence indicated stable concentrations at all settings. However, without mixing chambers, NOx concentration calculated from nitrogen measurements demonstrated marked inspiratory fluctuations and was highest with a minute ventilation of 21 L/min and higher during pressure-controlled ventilation compared with volume-controlled ventilation (nitric oxide concentration of 40 ppm, pressure-controlled ventilation: 14.5 to 130.5 ppm; volume-controlled ventilation: 21.6 to 104.7 ppm; nitric oxide concentration of 10 ppm, pressure-controlled ventilation: 3.2 to 30.9 ppm; volume-controlled ventilation: 4.5 to 27.1 ppm). NOx concentration fluctuation decreased with an increasing mixing chamber, and was negligible at all settings with the 3.2-L turbulence box. Nitric oxide concentration fluctuation influenced chemiluminescence measurements. The displayed nitric oxide values varied, depending on the sampling site, and did not accurately reflect mean inspiratory nitric oxide concentration. Incorporation of a mixing chamber eradicated this sampling site influence. CONCLUSIONS: Continuous flow delivery of nitric oxide into the circuit of a phasic-flow ventilator results in marked inspiratory nitric oxide concentration fluctuation that is not detected by a slow-response chemiluminescence analyzer. Moreover, nitric oxide concentration fluctuation can influence the accuracy of the chemiluminescence measurements. These effects can be diminished by using additional mixing chambers to facilitate a stable gas concentration. As these mixing volumes increase the contact time of nitric oxide with oxygen, an increase of nitrogen dioxide has to be taken into account.

Lung↗
PubMed1997

Flow-proportional administration of nitric oxide with a new delivery system: inspiratory nitric oxide concentration fluctuation during different flow conditions.

OBJECTIVE: To evaluate the accuracy of a flow-proportional delivery system and the pattern of inspiratory nitric oxide (NO) concentration during different flow conditions. DESIGN: Laboratory study in a lung model. SETTING: University experimental laboratory. SUBJECT: With a new delivery system, NO was administered proportional to the inspiratory flow into the inspiratory circuit to deliver a NO concentration of 10 and 30 ppm to a test lung during different ventilatory modes (volume-controlled ventilation [VCV], pressure-controlled ventilation [PCV], and airway pressure release ventilation [APRV]) with a fraction of inspired oxygen (FIO2) of 1.0. INTERVENTIONS: During VCV and PCV, the flow pattern was varied to achieve tidal volumes of 300, 600, and 900 mL, respectively, with inspiratory to expiratory time ratios of 1:3, 1:2, and 1:1. APRV was studied at a minute volume of 6, 12, and 18 L. Nitric oxides (NOx [NO+NO2]) and nitric dioxide (NO2) were monitored by chemiluminescence and electrochemical analysis. As the NO/N2 gas mixture is the only nitrogen source during ventilation with an FIO2 analyzer. RESULTS: During all flow conditions, NOx concentration was stable but slightly higher than expected. Measured and expected mean concentrations differed <9% (mean, <4%). Inspiratory NOx concentration fluctuation derived from N2 concentration was significantly higher than expected at higher flow rates, but this difference was not detected by chemiluminescence or electrochemical analysis. The NO2 production was not affected by the flow rate and was always < or =0.2 ppm (NO, 10 ppm) and < or =1.9 ppm (NO, 30 ppm). CONCLUSION: The tested NO delivery module administered stable mean inspiratory NO concentrations. Although inspiratory NO concentration fluctuates depending on the inspiratory flow rate, this delivery device allows stable NO administration without requiring adjustments when ventilator settings are changed.

Equipment Design↗
PubMed1996

Intratracheal pulmonary ventilation provides effective ventilation in a near-drowning model.

Overdistension of the lungs from high inspiratory pressure is increasingly recognized as a major contributor to lung injury and worsening respiratory failure in the child who requires prolonged mechanical ventilation. Many modes of ventilation (such as high-frequency ventilation) have been introduced in an attempt to decrease this lung injury. Recently, a new mode of tracheal ventilation, intratracheal pulmonary ventilation (ITPV), has been described. By using a catheter positioned at the carina with continuous gas flow, it is possible to achieve effective ventilation at very low pressures. The purpose of this study was to evaluate the usefulness of ITPV in a near-drowning model. Ten domestic Yorkshire swine underwent arterial, venous, and pulmonary arterial catheter as well as tracheotomy placement. All animals received 13 mL/kg of fresh water intratracheally to induce a pulmonary injury. Six pigs were ventilated for 4 hours using ITPV; the other four pigs received conventional mechanical ventilation (CMV). Circulatory and ventilatory pressures, hemodynamic variables, arterial blood gases, and end-tidal CO2 were measured before lung injury and every 30 minutes thereafter. Both proximal and distal peak and mean airway pressures were measured. The animals were ventilated as needed to maintain the arterial blood gases in the normal range. The authors found the expected changes in pulmonary compliance, oxygen requirement, and airway pressure after inducement of lung injury. The six animals treated with ITPV had significantly lower airway pressures than those of controls. Peak inspiratory pressures with ITPV were 8.2 +/- 1.9 cm H2O versus 17.8 +/- 3.7 with CMV (P < .001). Distal mean airway pressures using ITPV were 2.3 +/- 0.1 cm H2O versus 9.0 +/- 3.2 with CMV (P < .01). With respect to hemodynamic variables, there were no differences between experimental and control animals. In conclusion, ITPV can afford effective ventilation in a near-drowning model of lung injury at airway pressures significantly lower than those required with CMV. ITPV could be a very valuable addition to the currently available methods of mechanical ventilation.

Animals↗
PubMed1996

Evaluation of a new thin-walled endotracheal tube for use in children.

Conventional endotracheal tubes have high intrinsic resistive properties due to their high outer-to-inner diameter ratio. This has significant disadvantages in the treatment of the small neonatal or pediatric patient as work of breathing increases with decreasing internal radius. Diagnostic and therapeutic procedures, including suctioning, may be very difficult in patients with small endotracheal tubes. We therefore measured airway resistance and pressure differential during simulated mechanical ventilation using proximal and distal endotracheal tube flow transducers. Conventional and new, ultrathin-walled endotracheal tubes reinforced with flat stainless steel or a novel, crush-proof nickel-titanium alloy were compared using fixed ventilator settings. Ventilation through the ultrathin-walled tubes resulted in a significantly reduced airway resistance (p < or = 0.01). These new ultrathin-walled endotracheal tubes showed flow characteristics typical of much larger conventional endotracheal tubes: the 3.2-mm internal diameter had an airway resistance (Raw) of 36, while a standard 2.5-mm internal diameter endotracheal tube had a Raw of 146. Both endotracheal tubes have identical external diameters of 3.6 mm. We conclude that ultrathin-walled endotracheal tubes could have a significant role in the treatment of the ventilated child by facilitating interactive ventilation and maintenance of airway patency and may make procedures such as fiberoptic endoscopy and intrapulmonary ventilation using reverse-thrust catheters possible in the small child.

Airway Resistance↗