The aim of this study was to determine what the influence of different designs of face masks and different noninvasive ventilator modes would be upon total dynamic dead space.Using a spontaneous breathing model, total dynamic dead space was measured when using 19 commercially available face masks and a range of ventilators in various ventilation modes.Total dynamic dead space during spontaneous ventilation was increased above physiological dead space from 32% to 42% of tidal volume by using face masks. The use of noninvasive ventilation modes such as bilevel and continuous positive airway pressure, with continuous pressure throughout the expiratory phase, reduced total dynamic dead space to approach physiological dead space with most face masks. Pressure assist and pressure support ventilation decreased total dynamic dead space to a lesser degree, from 42% to 39% of tidal volume. Face masks with expiratory ports over the nasal bridge resulted in beneficial flow characteristics within the face mask and nasal cavity, so as to decrease total dynamic dead space to less than physiological dead space from 42% to 28.5% of tidal volume.Exhaust ports over the nasal bridge in face masks effect important decreases in dynamic dead space provided positive pressure throughout the expiratory phase is used.
To be most effective, noninvasive ventilation (NIV) ventilators should synchronize well with patients' breathing. However, the speed with which different ventilators can respond to the transitions between inspiration and expiration may vary, and abnormal respiratory mechanics and mask leaks may exacerbate this problem. This study explored synchronization using a new test lung model designed to simulate acute exacerbations of chronic obstructive pulmonary disease (COPD). Thirteen ventilators were tested against different combinations of tidal volume (VT), airways resistance (Raw), FRC, and mask leak. These combinations ranged from those of a severe exacerbation of COPD, to a mild condition reflecting the optimal triggering conditions a ventilator is likely to encounter. The triggering delays from the beginning and end of "inspiration" of the test lung, to the appropriate responses from the ventilators were measured. Three of the ventilators had trigger delays less than approximately 120 ms at both the beginning and end of expiration under all conditions. Trigger delays of other ventilators were mainly in the range of 120 to 300 ms, although exceptionally as long as 500 ms. Varying the conditions had a variable but generally small effect on triggering times, suggesting that there is a largely unavoidable element to the triggering delays intrinsic to the design of the ventilators.
In patients with septic bursitis the indications for admission and surgical intervention remain unclear, and practice has varied widely. The effectiveness of a conservative outpatient based approach was assessed by an outcome study in a prospective case series. Consecutive patients attending an emergency department with acute swelling of the olecranon or prepatellar bursa were managed according to a structured approach, subjective and objective outcomes being assessed after two to three days, and subsequently as required until clinical discharge. Long-term outcomes were assessed by telephone follow-up for up to eighteen months. 47 patients were included in the study: 22 had septic bursitis, 15 of the olecranon bursa and 7 of the prepatellar bursa. The mean visual analogue pain scores of those with septic bursitis improved from 4.8 at presentation to 1.7 at first follow-up for olecranon bursitis, and from 3.8 to 2.7 for prepatellar bursitis. Symptoms improved more slowly for patients with non-septic bursitis. No patients were admitted initially, but 2 were admitted (two days each) after the first follow-up appointment. One patient had incision and drainage on the third attendance, and 3 patients developed discharging sinuses, which all healed spontaneously. All patients made a good long-term symptomatic recovery and all could lean on the elbow or kneel by the end of the follow-up period. The management protocol, with specific criteria for admission and surgical intervention, thus produced good results with little need for operation or admission.
An in vivo comparison of a catheter mounted pressure transducer system with conventional balloon catheters. I.M. Stell, S. Tompkins, A.T. Lovell, J.C. Goldstone, J. Moxham. #ERS Journals Ltd 1999. ABSTRACT: In the assessment of respiratory muscle function balloon catheters have been widely used for pressure measurements. However, this type of investigation is poorly tolerated by acutely ill patients. This study assessed the performance of a possible alternative, a catheter-mounted miniature pressure transducer (CMT).The assessment consisted of a laboratory study of the linearity, frequency response, and stability of gain and baseline of the CMT system, and an in vivo study directly comparing the CMT and balloon catheter systems in seven normal subjects for a range of respiratory manoeuvres. These were: 1) maximal inspiratory and expiratory pressures against a closed airway, 2) twitch transdiaphragmatic pressure elicited by cervical magnetic phrenic nerve stimulation, and 3) tidal breathing, sniffs and coughs in five body positions. The agreement of the two systems was analysed for measurements of 1) absolute pressures, 2) magnitude of changes in pressure, and 3) rate of change of pressure (maximum relaxation rate after sniff manoeuvres).The CMT system was linear, with a high frequency response and stable gain, but showed baseline drift. The two systems agreed well for measurements of change and rate of change of pressure, but less well for measurements of absolute pressure.The CMT system tested is potentially useful for studies of acute changes in respiratory pressures, or studies of respiratory muscle strength, but would be less useful where accurate measurements of absolute pressures are required.
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