Measurement of Spirometry, Respiratory Muscle Strength, and Arterial Blood Gases
Characterization of the patients’ physiologic status was conducted by measuring spirometry, respiratory muscle strength, and gas exchange. FVC and FEV1 were measured using a spirometer (Gould 2400 Spirometer; Gould Inc; Dayton, OH) according to American Thoracic Society guidelines. Respiratory muscle strength was evaluated by measuring maximal inspiratory mouth pressure (Plmax) and maximal expiratory mouth pressure (PEmax), as previously described. Arterial blood gas analysis was performed using a gas analyzer (model BG3; Instrumentation Laboratory, Inc; Lexington, MA).
Assessment of Functional Status
Functional status of all patients was measured using a 7-point functional scale, where 1 = impaired cognition; 2 = awake, alert, oriented; 3 = chairbound; 4 = independent in activities of daily living; 5 = ambulatory, but homebound; 6 = performs all selfcare activities at home (housework, cooking, etc.); and 7 = performs activities outside the house. Functional scores are recorded in arbitrary units (AUs). Reading here
All patients were evaluated for NPPV via a bilevel positive pressure ventilatory support device (BiPAP; Respironics, Inc; Monroeville, PA) or a portable volume ventilator (PLV-102 Volume Ventilator, Lifecare Inc, Boulder, CO). A description of the BiPAP ventilatory support device has been previously described. Appropriate settings of inspiratory and expiratory pressures, volumes, and ventilatory modes (ie, BiPAP vs portable volume ventilator) were chosen while monitoring airway pressure, inspiratory and expiratory airflow and changes in tidal volume (Vt). Airway pressures were measured at the mask pressure port by an in-line pressure transducer (range, ± 100 cm H2O; Validyne; Northridge, CA). Changes in airflow were measured by an in-line pneumotachograph (Hans Rudolph, Inc; Kansas City, MO), which was placed between the mask and the exhalation valve. Inspiratory and expiratory volumes were recorded by integration of the airflow signal and recorded on a multichannel strip chart recorder (model ES 1000; Gould Inc). Inspiratory and expiratory pressures, and ventilator-delivered Vt for patients using BiPAP or volume ventilator, respectively, were titrated until expired minute ventilation increased > 20% above baseline values while simultaneously improving gas exchange (ie, increased Pao2/Flo2 and lower Paco2) and ensuring patient-ventilator synchrony. The choice of ventilator (ie, BiPAP or portable volume ventilator) was determined by each patient’s degree of comfort with each source of ventilation, coupled with the ability to increase minute ventilation, improve gas exchange, and diminish the patient’s work of breathing. After initial evaluation, 34 patients received NPPV via BiPAP and 6 patients required NPPV via the portable volume ventilator.
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