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Biomedical subjects

G T Ozaki

Publications and source records attributed to G T Ozaki.

16 recordsLinked to original sources
PubMed1997

Characterization of variables defining hindpaw withdrawal latency evoked by radiant thermal stimuli.

We have examined the stability and sources of variation within the nociceptive model of rat hind paw withdrawal from an under-glass radiant stimulus (Hargreaves et al., 1988) using a system where stimulus intensity and floor temperature can be controlled and reproducibly changed. The current study demonstrates that: (i) increased stimulus intensity with a fixed surface temperature is associated with a monotonic decrease in mean response latency and its variance; (ii) for a fixed stimulus intensity, the mean paw withdrawal latency and variance increased as the glass floor temperature is lowered from 30 degrees C to room temperature (25 degrees C). Using subcutaneously-implanted thermocouples and a 30 degrees C glass surface, the subcutaneous paw temperature observed at an interval corresponding to the time at which the animal displayed a paw withdrawal did not differ across multiple heating rates (41-42.5 degrees C). This finding is in agreement with human studies of pain thresholds and C-fiber activity. These studies emphasize the importance of maintaining a fixed surface temperature to reduce experimental variability and the utility of this apparatus across multiple stimulus intensities to define agonist efficacy.

Analysis of Variance↗
PubMed1995

Confirmation of endotracheal intubation over a jet stylet: in vitro studies.

An accepted method of tracheal reintubation is to pass an endotracheal tube (ETT) over a jet stylet (JS). It is desirable to confirm tracheal reintubation prior to removing the JS from its known intratracheal location. The purpose of this study was to determine the functional size equivalent of the annular space between the JS and ETT for all combinations of variously sized ETTs and JSs and to determine whether this annular space will permit detection of exhaled carbon dioxide (CO2). Our experiment consisted of two parts. One model measured the airflow resistance of variously sized test catheters (14- to 18-gauge intravenous catheters and ETT sizes 2.5-9.0 mm inside diameter (ID)) and all of the possible combinations of small, medium, and large Sheridan JSs within 4.9-9.0-mm ID ETTs (ETT/JS) by determining pressure versus annular space flow curves. The other model measured the times to first detection of CO2, to 70% maximum (max) [CO2] detection, and from first detection to 70% max [CO2] through empty 4.0- to 9.0-mm ID ETTs and through the annular space between all possible ETT/JS combinations at lung driving pressures of 5-10 mm Hg. The resistance of the catheters and ETT/JS combinations increased as the flow rate increased and/or the net conducting area of the conduit decreased. Some ETT/JS had an annular space < a 4.0 mm ID ETT. All three CO2 detection times increased with decreasing size of the net conducting area and with decreasing driving pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1994

Spinal and systemic action of the alpha 2 receptor agonist dexmedetomidine in dogs. Antinociception and carbon dioxide response.

BACKGROUND: alpha 2 Agonists are powerful analgesics after spinal delivery. The current work characterizes the dose-dependent antinociception and effects upon respiratory function of dexmedetomidine after intrathecal, epidural, intravenous, and intracisternal delivery in chronically prepared dogs. METHODS: Dogs were prepared with chronic tracheostomies and trained to perform rebreathing studies. These animals were then prepared with chronic lumbar intrathecal, epidural, or intracisternal catheters. RESULTS: A rapid dose-dependent increase in the thermal skin twitch response latency and paw withdrawal to mechanical pinch was observed after intrathecal, epidural, and intravenous dexmedetomidine (dose required to reach 50% of maximal effect for skin twitch = 1.8, 10, and 15 micrograms, respectively) but not after intracisternal dexmedetomidine (> 15 microgram), with the maximally effective dose lasting approximately 90 min. The spinal effect was unaccompanied by effects upon behavioral alertness, motor function, or changes in CO2 response. In contrast, intravenous dexmedetomidine (1-10 micrograms/kg) resulted in a dose-dependent sedation and a significant reduction in heart rate and respiratory rate and a diminished response to increased CO2, these effects lasting approximately 2 h. Intracisternal administration of up to 15 micrograms had no effect upon the nociceptive threshold, and CO2 response, and failed to result in a significant reduction in alertness. All of the effects of dexmedetomidine were antagonized by the alpha 2-antagonist atipamezole (30-300 micrograms/kg, intravenous), but not by the opioid antagonist naloxone (30 micrograms/kg, intravenous), while atipamezole did not reverse the antinociceptive or respiratory depressant actions of intravenous sufentanil (50 micrograms), effects which were reversible by naloxone. CONCLUSIONS: Dexmedetomidine, acting through an alpha 2-receptor, produces a powerful antinociceptive effect, mediated at the spinal level, while systemic redistribution of the drug leads to a hypnotic state with significant cardiorespiratory effects.

Adrenergic alpha-Agonists↗
PubMed1994

Evaluation of the Bullard laryngoscope using the new intubating stylet: comparison with conventional laryngoscopy.

The Bullard laryngoscope (BL) is a new device for managing the difficult airway. Previous publications on the BL are primarily descriptive, and fail to use internal controls (i.e., determine the best intubating mechanism) or external controls (i.e., compare the BL to a known standard such as conventional laryngoscopy). Therefore, we attempted to determine the best of four intubating mechanisms described for the BL (independently styletted endotracheal tube [ETT], the Bullard intubating forceps, an ETT with a directional tip or the new dedicated intubating stylet) and to determine whether time to successful intubation with the BL using the best intubating mechanism correlates with conventional grade of laryngoscopic view. The new intubating stylet provided the optimal intubating method; fewer attempts were required (1.1 vs 1.7, P = 0.005), and it took less time to successful tracheal intubation (39 +/- 34 s vs 83 +/- 74 s, P = 0.004) compared to the three other intubating mechanisms. Our results also suggest that the time to successful intubation with the BL using the intubating stylet was not affected by the conventional laryngoscopic grade; it was just as easy (and difficult) to intubate a conventional Grade I laryngoscopic view patient (full glottic view) as it was to intubate a conventional Grade III laryngoscopic view patient (visualization of just the epiglottis) with the BL. There were two failed intubations with the BL (3%) due to an inability to trap the epiglottis.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1993

Can an anesthesia machine flush valve provide for effective jet ventilation?

Transtracheal jet ventilation (TTJV) using a percutaneously inserted intravenous (IV) catheter for the patient who cannot be ventilated or tracheally intubated or, using a jet stylet for changing endotracheal tubes (ETT) in patients for whom subsequent ventilation and/or tracheal reintubation may be difficult, are extremely valuable therapeutic options. The jet ventilation system must have a sufficiently high pressure-oxygen source to drive oxygen through noncompliant tubing and through relatively small IV catheters and/or jet stylets in order to achieve adequate ventilation and oxygenation. There is no evidence that using the common gas outlet of an anesthesia machine by activating the flush valve can provide enough flow (V) and tidal volume (VT) for effective jet ventilation. This in vitro study utilized a mechanical lung model that had a varying lung compliance [Cset (10-100 mL/cm H2O)] to determine the VT (measured by integrating a pneumotachograph flow signal) and corresponding minute ventilation (VE) through 14-, 16-, and 18-gauge IV catheters and small, medium, and large jet stylets. The flow of O2 was generated by activating the flush valve of Dräger Narkomed 2 and 2A and Ohmeda Modulus II and II Plus anesthesia machines at an inspiratory:expiratory (I:E) ratio = 1:1 (unit of time = 1 s). We found that the largest VT and resultant VE were consistently obtained by activating the flush valve of the Ohmeda Modulus II and Dräger Narkomed 2 anesthesia machines. The smallest VT and VE were produced using the Ohmeda Modulus II Plus anesthesia machine.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1992

A comparison in a lung model of low- and high-flow regulators for transtracheal jet ventilation.

There is widespread agreement that transtracheal jet ventilation (TTJV) using a percutaneously inserted intravenous (iv) catheter through the cricothyroid membrane is a simple, quick, relatively safe, and extremely effective treatment for the situation in which neither ventilation nor intubation can be achieved. No study has reported whether a low-flow pressure-reducing regulator (LFR) can provide enough driving pressure and flow under a variety of clinical circumstances for adequate TTJV. We determined, using a high-flow regulator (HFR) as our control, the tidal volume (VT) (measured by integrating a pneumotachograph signal) that a LFR could deliver via a Carden jet injector through 14- and 20-G iv catheters initially at an inspiratory:expiratory ratio (I:E) = 1:1 (unit of time = 1 s) in a mechanical model that had varying lung compliance (Cset, 10-100 ml/cmH2O) and airway diameters (proximal trachea 15.0, 4.5, or 3.0 mm ID and distal mainstem bronchi 9.0 or 4.5 mm ID). The lowest Cset (10 ml/cmH2O) and smallest airway diameter (tracheal diameter = 3.0 mm, bronchial diameter = 9.0 mm) resulted in the lowest VT (220 and 320 ml for the 20- and 14-G iv catheters, respectively, with the LFR), and the highest Cset (100 ml/cmH2O) and largest airway diameter (tracheal diameter = 15 mm, bronchial diameter = 9.0 mm) resulted in the highest VT (780 and 1040 ml for the 20- and 14-G iv catheters, respectively, with the LFR). The VT produced during TTJV was greatly dependent on air entrainment (measured by a second pneumotachograph), with the contribution to total VT ranging from 15 to 74%; the amount of air entrainment was independently confirmed by excellent agreement between measured and calculated alveolar oxygen concentrations. Decreasing Cset (with the largest airway diameter) and decreasing airway diameter (at Cset = 50 ml/cmH2O) over the full range studied resulted in approximately a 45-80% decrease in VT for all iv catheter/regulator combinations. Increasing Cset and narrowing airway diameter over the full range studied resulted in a progressive increase in end-expiratory volume (EEV) for all iv catheter/regulator combinations. The I:E ratio was also varied from 1:3 to 3:1 (unit of time = 1 s) using the 14-G catheter at Cset = 50 ml/cmH2O with both regulators at the extremes of the proximal tracheal diameters (15.0 and 3.0 mm ID), and we found that jet ventilation through a proximal tracheal diameter of 3.0 mm with the HFR at I:E ratios = 1:1 and 3:1, EEV exceeded the capacity of the mechanical lung (4,000 ml).(ABSTRACT TRUNCATED AT 400 WORDS)

Catheterization, Peripheral↗
PubMed1992

Operative lung constant positive airway pressure with the Univent bronchial blocker tube.

Constant positive airway pressure (CPAP) to the operative lung during one-lung ventilation (1-LV) with a double-lumen tube increases PaO2; there have been no reports of application of CPAP to the operative lung during 1-LV with the Univent bronchial blocker (BB) tube. This study determined the method of administration and the effect on PaO2 of 10 cm H2O of CPAP to the operative lung during 1-LV (1-LV + 10 CPAP) produced by the Univent BB system. We designed our CPAP system for the Univent BB using an in vitro lung model so that low O2 flow rates (2-4 L/min) yielded clinically relevant levels of CPAP (5-20 cm H2O) over a wide range of lung compliance. The CPAP system simply consisted of placing a resistance to a variable oxygen flow distal to the operative lung. Seven consenting patients who required thoracotomy and 1-LV were anesthetized and their tracheas were intubated with the Univent BB tube; the BB was inserted into the appropriate mainstem bronchus until the proximal surface of the BB cuff was just distal to the tracheal carina. PaO2 was measured in the seven patients during 12 sequences of two-lung ventilation (2-LV), one-lung ventilation (1-LV), and 1-LV with 10 cm H2O CPAP (1-LV + 10 CPAP). 1-LV + 10 CPAP was always instituted on the deflation phase of a previous single tidal inhalation. We found in our patients with a lung compliance of 32 +/- 4 mL/cm H2O that 2.4 +/- 0.2 L/min of oxygen flow produced 1-LV + 10 CPAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Quantification of the jet function of a jet stylet.

The concept and use of a jet stylet as an additional safety measure during tracheal extubation of patients in whom subsequent ventilation and/or reintubation of the trachea may be difficult has recently been described. If jet ventilation through a jet stylet could provide for effective gas exchange, it would allow additional time to assess the need for reintubation of the trachea. We determined the tidal volumes (measured by integrating a pneumotachograph flow signal) that 50-psi jet ventilation, at an inspiratory to expiratory time ratio of 1:1 (unit of time = 1 s), could deliver through small, medium, and large Sheridan tube exchangers into an in vitro lung model that had lung compliances of 50 and 30 mL/cm H2O (six experimental permutations). The tidal volume (VT) produced during jet ventilation was moderately dependent on air entrainment (measured by a volume spirometer), with the contribution to total VT ranging from 0% to 31%; the amount of air entrainment was confirmed by excellent correlation between the alveolar oxygen concentration (FAO2) measured by an oxygen analyzer and the FAO2 calculated from entrained and total VT. Decreased lung compliance caused decreased VT and end-expiratory volume for all six experimental conditions. The largest VT and minute ventilation (VE) generated were 1680 mL and 51.6 L/min (large tube exchanger, high lung compliance) and the lowest VT and VE were 440 mL and 13.2 L/min (small tube exchanger, low lung compliance), respectively. These findings validate the term "jet stylet" for all three tube exchangers as even the smallest tube exchanger, coupled with a low lung compliance, can provide a VE consistent with total ventilatory support for most clinical situations.

Evaluation Studies as Topic↗
PubMed1991

IPPV plus low-flow intermittent oxygen insufflation (end-exhalation to beginning inhalation) does not improve CO2 elimination.

It has been previously reported that continuous insufflation of low-flow O2 (0.05 to 0.20 L/kg/min), both supracarinally and subcarinally, in addition to intermittent positive-pressure ventilation (IPPV) (IPPV + O2 at a specific flow rate) caused progressive hemodynamic deterioration in patients. As demonstrated in a subsequent mechanical lung model, the hemodynamic deterioration was most probably due to lung hyperexpansion. The purpose of this study was to test the hypothesis that the O2 retarded the outflow of gas from the lung during exhalation and that if the insufflation were limited to the period of time from the end of tidal exhalation (EE) to the beginning of the next IPPV tidal inspiration (BI), lung hyperexpansion would not occur. The use of intermittent O2 in addition to IPPV was studied in both a mechanical lung model and in patients under general anesthesia; the mechanical lung model permitted direct examination of lung volume, and the patient study allowed determination of gas exchange effects. In the mechanical lung model and in the patients, a wide range of EE-BI O2 flow rates were used; respectively, 1 to 40 L/min and 0.05 to 0.20 L/kg/min. In the mechanical lung model, lung pressure and volume at EE and end-inspiration did not increase as long as the O2 flow was kept at or below 10 L/min. In the patients, airway pressure and hemodynamics did not change appreciably, but there was also no increase in CO2 elimination.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Depth of placement of left double-lumen endobronchial tubes.

Data on the normal depth of insertion of double-lumen tubes have not been published. We studied 101 adult patients undergoing thoracic operations whose tracheas were intubated with a left double-lumen tube. A fiberoptic bronchoscope was introduced into the tracheal lumen, and the tube position was adjusted until the cephalad surface of the bronchial cuff was immediately below the carinal bifurcation. The average depth of insertion for both male and female patients 170 cm tall was 29 cm, and for each 10-cm increase or decrease in height, average placement depth was increased or decreased 1 cm. The correlation between depth of insertion and height was highly significant (P less than 0.0001) for both male and female patients. As depth of DLT insertion at any given height was normally distributed, a technique to confirm correct double-lumen tube position always should be used after initial placement.

Adult↗
PubMed1989

Pressure-augmented fluid administration: modified system and general results.

Rapid fluid infusion is generally augmented by compression devices (pumps) that take advantage of compressibility of modern plastic fluid containers. The most commonly used pumps are not the most effective pressure sources for driving pressure. This paper describes the experience at a Level I trauma hospital with a relatively new device that serves as a more efficient source of pressure for rapid fluid administration. This device, commercially manufactured but locally modified, increases capability with minimal expense and additional training.

Equipment Design↗
PubMedDate not supplied

It is not necessary to remove a jet stylet to determine tracheal tube location.

A jet stylet is a small internal diameter (ID), semirigid hollow catheter that is inserted into an in situ tracheal tube prior to extubation of a patient who may be difficult to reintubate. After the tracheal tube is withdrawn over the jet stylet, the hollow catheter can be used for jet ventilation or as an intratracheal stylet for reintubation with a new tracheal tube. It was previously thought that after the new tracheal tube was inserted over the jet stylet, the stylet would have to be removed to allow connection of the new tube to the breathing circuit and confirmation of intratracheal placement of the tube. We describe a method for preserving the intratracheal location of the jet stylet while confirming intratracheal placement of the new tracheal tube.

Anesthesia, Inhalation↗