Category Archives: Pulmonary Function : Part 10

The Control of Breathing during Weaning from Mechanical Ventilation (2)

Based on this comparison, we tested the hypothesis that patients with weaning-induced dyspnea and/or tachypnea retain C02 relative to the unloaded state before overt pump failure in the form of respiratory acidosis becomes manifest. C02RT was also compared with the arterial C02 tension measured during mechanical ventilation (C02MV) at machine settings determined by the primary physician. This comparison served to test the hypothesis that C02MV is ventilator setting dependent and, therefore, serves as a poor predictor of the ventilatory requirement during spontaneous breathing.
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The Control of Breathing during Weaning from Mechanical Ventilation (1)

The Control of Breathing during Weaning from Mechanical Ventilation (1)Respiratory pump failure results from an imbalance between the ventilatory load and the strength of the respiratory muscles. The intrinsic load of the respiratory muscles depends largely on the impedance of the respiratory system and the minute volume (Vk) that must be maintained to satisfy the ventilatory requirement. The determinants of Vk include the rate of C02 production by the tissues (Vc;o2), the dead space to tidal volume ratio (ViWr), and the arterial C02 tension (PaC02). These variables, although easily measurable during mechanical ventilation, often provide limited insight into the ability of a patient to wean from the ventilator because the ventilatory requirement during spontaneous breathing is not known. A rise in C02 during weaning relative to the PaC02 during mechanical ventilation either means that the patient had been hyperventilated or reflects the respiratory pumps response to a large load.
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (11)

A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (11)In both of these cases the FEV, values obtained prior to delivery of any active agent show a high degree of variability. Some investigators reported that these challenges would not be acceptable to them, but they still calculated and reported a PDaoFEV, value. It clearly has been shown that with induced bronchoconstriction the greater the degree of constriction, the greater the difference in FE V| noted between the first and the second spirogram. For this reason, we feel that it is not appropriate to discard the results of a spirogram obtained after histamine delivery solely on the basis of a lack of reproducibility in FEV, between paired spirograms. In the pre-drug delivery spirograms, however, a lack of reproducibility would suggest that the spirograms should be repeated. The results of previous studies would suggest that during such challenge procedures only one spirogram should be performed at each level of bronchoconstriction. buy birth control online
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (10)

The reported results given for our histamine challenges (Table 6) reveal the wide divergence in the methods used to calculate an end result. These results were calculated irrespective of the type of solutions or method of delivery used in our procedure. In two of the examples there was a clear cut difference of opinion about whether any result should be reported. In challenge 3, clearly a large number thought that the test was inadequate and that the concentration of the first dose of histamine administered should have been lower. In challenge 9, it was believed by the majority that the challenge was incomplete and should have been continued until a 20 percent drop in FEVi had been achieved. However, 12 investigators calculated a PDaoFEVi or a PCjoFEVi, either by extrapolation or because they felt that a 20 percent drop in baseline FEV! had been achieved. Cheap Diskus Advair
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (9)

A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (9)Specifically, there was a difference of opinion regarding the need for buffering each concentration used, whether a preservative could or should be added, and if there was a need for each concentration to be isotonic. The pH and osmolar-ity of inhaled solutions have been shown to affect the degree of bronchospasm induced. The effects of inhalation of dilute solutions of phenol are not clear. One investigator strongly questioned the rationale for using a preservative in the histamine solutions, stating that this would add yet another variable. However, 44 percent of those using methacholine challenges reported that a preservative had been added to the solutions that they used. The commercially available preparation currendy approved for use in this country (Roche Provocholine) contains methacholine chloride reconstituted with 0.9 percent sodium chloride, 0.4 percent phenol (pH 7.0) as a preservative. flovent inhaler
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (8)

Discussion
Guidelines for the performance of bronchial provocation tests have been established by several groups. The methodology recently has been comprehensively reviewed by Eiser. Many of the numerous factors that have been shown potentially to affect the results of such challenges have been identified and discussed in these studies. It was not the purpose of this survey to determine which is the “correct” technique, but rather to ascertain those which are currently in common usage, and to determine if the difference in methods of analysis used would result in widely varying results. The role of bronchodilatation in the assessment of airway reactivity was not addressed in this study. ampicillin antibiotic
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (7)

A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (7)The most common method used was that of linear interpolation from a dose-response curve, either reporting a PD or the PC, 57.5 and 20 percent, respectively. Other methods are less commonly employed. buy cipro
For histamine and methacholine inhalation challenges, the parameter and units that were reported as being representative of airway hyperreactivity are shown in Table 5. With regard to measurement of the time to recovery following a challenge procedure and the slope of the recovery curve, only one investigator reported that this was of any value.
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (6)

Most respondents reported using the FEVj to measure a response to bronchoprovocation (78 percent), discontinuing the study when a fall of 20 percent had been recorded. However 12 percent (five of 40) reported that they routinely measured SGaw, looking for a fall of 35 percent from baseline. Other measures of response to bronchoconstriction included SRaw, Rrs and MEFV from partial flow volume curves (10 percent). None reported a routine use of the PEFR as a measure of response. Two respondents stated that in certain well defined research projects they would continue the challenge until the response had reached a “plateau,” but that in their laboratory this was not a common procedure. antibiotic levaquin
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (5)

A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (5)The number of patient beds in the hospital in which the investigators worked ranged from 70 to 1,400 (775 ± 68, mean ± SEM). The challenge procedures were reported as being routinely performed by a research assistant or research fellow (45 percent), a pulmonary function laboratory technician (30 percent), or by the investigator (25 percent). ventolin 100 mcg
The type of bronchoprovocational challenges currently employed by the respondents are shown in Table 1. Methacholine was the most commonly used inhalation agent, with histamine being relatively infrequently utilized by this group as were exercise challenges. Only one respondent reported that he never found reason to use methacholine for inhalation challenges. The characteristics of the solutions of histamine and methacholine used in inhalation challenges are shown in Table 2.
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A Survey of the Current Use and Methods of Analysis of Bronchoprovocational Challenges (4)

Each histamine solution had been buffered with phosphate-buffered saline to a pH of 7.4 and rendered isotonic by the addition of sodium chloride equivalent. We reported that with use of our technique one breath unit, which was defined as one inhalation of a histamine solution of 1 mg/ml concentration, corresponds to delivery at the mouth of 12 |ig of histamine diphosphate (MW of 307), or 4.3 \l% of histamine base (MW of 111).
Each investigator was asked to complete the questionnaire. From the available information each also was asked to calculate the results of each of the histamine challenges and to report them in whichever units they most commonly used.
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