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Changes in blood flow in the tracheal mucosa of the dog caused by the pressure exerted by high volume, low-pressure cuffs were measured with the hydrogen clearance method. Before inflating the cuffs, the blood flow of the tracheal mucosa was measured as a control for 12 h in order to confirm that the procedures of the hydrogen clearance method itself had little or no influence on the blood flow in the tracheal mucosa. After inflating the cuffs to create a tracheal wall pressure (TWP) of 1.3 kPa (10 mmHg), 2.6 kPa (20 mmHg), 3.9 kPa (30 mmHg) or 6.0 kPa (45 mmHg), local blood flows of tracheal mucosa (TBF) corresponding to each TWP were measured every hour for 12 h. No significant changes in blood flow were observed in the tracheal mucosa with the hydrogen clearance method before inflating the cuffs. In the groups with TWP of 1.3 and 2.6 kPa, the TBF rose 1 h after inflation of the cuffs, and then returned to the baseline values. In the group with TWP of 6.0 kPa, the TBF decreased markedly already 1 h after inflation of the cuffs, and continued to decrease severely thereafter. In the group with TWP of 3.9 kPa, the TBF followed an intermediate course between the groups with TWP of 2.6 kPa and 6.0 kPa. From the results of the present study, it was found that TBF was significantly impaired by a TWP of more than 3.9 kPa. Therefore, in prolonged intubation, TWP should be kept at or below 2.6 kPa.

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REPLY Ventilation in patients with tracheal obstruction can create serious problems, particularly when the cross-sectional diameter of the trachea is narrowed to 5-6 mmHg. That is why the anaesthetic management and method of ventilation in our patient followed a step-by-step algorithm to ensure safety. The anaesthetic plan started by awake tracheal intubation, to be followed by spontaneous inhalation anaesthesia in 100% oxygen. Neuromuscular blockade and controlled ventilation were initiated after ensuring adequate jet ventilation. In his letter, Dr. Agarwal shouM have agreed with us, rather than disagreed, since we shifted to controlled ventilation as soon as we ensured its safety.

All nucleotides examined (AMP, GMP, TMP and CMP) quench the fluorescence or 10methylacridinium chloride (10-MEAC). The fluorescence spectrum of 10-MEAC-nucleotide system is identical with that of 10-MEAC itself, and the fluorescence decay kinetics follow a single-exponential decay law. The dependence of fluorescence quantum yields and fluorescence lifetimes upon the concentration of nucleotides indicates that the fluorescence of 10-MEAC is greatly quenched in both dynamic and static processes by nucleotides. The quenching constants increase in the order: A M P c GMP > TMP c CMP. The results of 10-MEAC are compared with those of other acridine dyes (proflavine, 9-aminoacridine and acridine orange).

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The fluorescence properties (spectrum, lifetime and quantum yield) of 9-aminoacridine cation in aqueous solutions of nucleotides have been examined. It was found that the fluorescence of the dye is quenched by adenosine-5′-monophosphate and guanosine-5′-monophosphate. Quantitative analysis of the results shows that the quenching of fluorescence is caused by dynamic and static quenching processes.