Posted in Pulmonary Function | 03/03/2015
In the present study, Vo2resp was estimated as the difference between Vo2tot during spontaneous respiration and that during controlled ventilation. Two points should be emphasized. First, for the estimation of Vo2resp, we used a mass spectrometer system which has the advantage of giving an accurate continuous measurement of Vo2, in contrast with the Fick method, or the Douglas bag method2 which have the limitation of intermittent data availability. Secondly, during CV, particular attention was paid to ensure that ventilation was entirely passive, without any inspiratory, or expiratory effort. To obtain this complete relaxation, it was most often necessary to induce a certain degree of hyperventilation, leading to a decrease in H+ concentration. It has been shown that Vo2 is pH dependent, and that respiratory alkalosis is associated with an increase in Vo2. So, in our study, Vo2 might have been slightly over-estimated during CV, and thus, Vo2 resp might have…
Posted in Pulmonary Function | 02/03/2015
Measurements and Calculations Pa02, PaC02 and H+ concentration were measured using standard electrodes. For the measurements of pressures and flow in patient 7, we used pressure transducers, a pneumotachograph (Could), and a four-channel recorder (Could). Esophageal and gastric pressures were measured by two balloon-catheters joined to each other. The esophageal balloon was positioned 10 cm above the cardia. The balloons were 5 cm long and were filled with 0.5 ml air. Pulmonary gas exchange was measured with our mass-spectrometer-microcom-puter system. Details of this procedure and thorough validation have been given in a previous report. The system can be briefly described as follows. Gas samples were drawn from the Y piece of the patients breathing circuit to the mass-spectrometer and analyzed for inspired 02 concentration and C02 wave-form recognition.
Posted in Pulmonary Function | 01/03/2015
Pressure Support Ventilation vs Continuous Positive Airway Pressure During weaning from artificial ventilation, changing from a controlled to a spontaneous mode of respiration is associated with an increase in whole-body oxygen consumption (Vo2tot). This increase, called oxygen cost of breathing (Vo2resp), is less than 5 percent ofVo2tot in normal subjects breathing quietly. In critically ill or postoperative patients, whose tra-cheas were intubated, Vo2resp has been found to be in the order of 20 percent of Vo2tot. Recently, inspiratory pressure support ventilation (IPSV) has been proposed to decrease the work of breathing in spontaneously breathing patients. We hypothesized that IPSV can reduce significantly Vo2 resp in the weaning period of artificial ventilation. We therefore investigated Vo2resp in postoperative patients breathing alternatively with IPSV and with continuous positive pressure ventilation (CPAP).
Posted in Airway | 25/02/2015
Subjects Work and Pressure Support To determine the usefulness of the relationship of pressure support and Vt/Ti derived from the mechanical model, trans-pulmonary inspiratory work was measured in four normal subjects. Each subject was trained to breathe at a Vt of500 ml at rates of 15,25, and 35 breaths per minute with I:E ratios of approximately 1:2. Throughout the study, subjects monitored volume using an oscilloscope (Tectronix 5113) which displayed the integrated flow signal. Respiratory rate and I:E ratio were held constant with the aid of a metronome. Each subject breathed through the same circuit as was used as in the first part of the study (Fig 1B). In addition, esophageal pressure (Pes) was measured using an esophageal balloon. A 10-cm latex balloon attached to a perforated polyethylene catheter was positioned transnasally into the esophagus and filled with the appropriate volume of air. Subjects were seated in an upright position…
Posted in Airway | 24/02/2015
Pressure Support Compensation for Added Inspiratory Work Three different Puritan-Bennett 7200 ventilators were tested. All were calibrated to the manufacturers specification, equipped with a standard patients circuit and humidifier (Cascade I, Puritan Bennett Co.), and set in the CPAP = 0 mode with a sensitivity of 0.5 cmHsO (fractional concentration of oxygen in the inspired gas [FIoJ = 0.21). Shiley low-pressure cuffed endotracheal tubes (length, 30 cm) with internal diameters of 7, 8, and 9 mm were used.
Posted in Airway | 23/02/2015
Then an intubated patient breathes spontaneously through an intermittent mandatory ventilation (IMV) or demand continuous positive airway pressure (CPAP) ventilator circuit, both the resistance of the endotracheal tube and the ventilator circuit can contribute to the inspiratory work of breathing. The level of this additional work increases as the diameter of the endotracheal tube decreases and minute ventilation increases. Increased inspiratory work can contribute to respiratory muscle fatigue and interfere with successful weaning from mechanical ventilation.
Posted in Myocardial Infarction | 22/02/2015
Limitations of Study Selection of patients for this kind of study is extremely difficult. We have excluded patients with predisposing factors whose role and relevance to the clinical situation studied is not well determined and are of uncertain clinical connection; for example, this study may well be hampered by removal of patients with hypokalemia; however, we believe that in this way a clear distinction may be obtained between delayed repolarization ventricular arrhythmias (a term adopted by Schweitzer and Mark) and VF with the multiform QRS configuration. This concept could be further consolidated by the relative lack of spontaneous conversion, the unlimited course, and the relatively good response to cardioversion of the multiform variety of VF, in contrast to what would be expected, respectively, concerning the clinical course of “torsade de pointes.” In our opinion, these observations may justify this approach to selection, which is particularly essential in patients with AMI….