Respiratory Care

Test the hypothesis that automated rotational therapy reduces the incidence of respiratory complications associated with mechanical ventilation.

A prospective, randomized, multicenter trial.

Intubated mechanically ventilated patients who were free of respiratory infection were eligible. Patients were randomized to use either a standard intensive care unit bed or an automated rotational bed that could turn the patient up to 32 degrees from the horizontal 8 times per hour. Patients were followed until successful extubation, death, or the development of a lower respiratory tract inflammatory syndrome (LRIS). The development of other clinically important events (ie, cardiac, urinary, gastrointestinal, neuropsychiatric) were also recorded.

There was no significant difference in the incidence of LRIS in the group that used automated rotational beds as compared to the control group (17% vs 26%, p = 0.15). There was a significantly lower incidence of urinary tract infection (11% vs 27%, p < 0.05) in the patients treated with automated rotational beds. Nurses noted the development of anxiety in 8 patients on the automated rotational beds. No other significant differences in the development of other clinical events were observed.

In this study, the automated lateral rotational bed and the turning strategy employed with that bed showed no statistically significant advantage over standard ICU patient-turning procedures in the prevention of lower respiratory tract inflammation. [Respir Care 1999;44(12):1447-1451]

The diagnosis of asthma is made difficult by the overlap of asthma symptoms with those of other disorders and by the limitations of the specificity of bronchoprovocation tests and symptoms. The purpose of this study was to assess the utility of demographic, medical, and psychiatric variables in predicting airway hyperresponsiveness defined by methacholine inhalation challenge (MIC) test results among patients presumed to have asthma.

Sixty-eight patients with clinical diagnoses of asthma underwent MIC and provided information about demographic variables, psychiatric symptoms, and medical utilization related to asthma. Logistic regression was used to identify clinical predictors of positive versus negative MIC results.

Negative MIC results were associated with being older, being a life-long nonsmoker, having better air flow, and with having full or subsyndromal symptoms of social phobia. Among persons with clinical diagnoses of mild-to-moderate asthma, 31% had negative MIC tests. Anxiety symptoms related to social circumstances were powerful predictors of the absence of bronchial hyperresponsiveness.

Anxiety symptoms may be mislabeled as a respiratory condition, leading to unnecessary medical utilization.

(1) To describe the pulmonary findings in severely obese individuals and (2) to describe the changes in resting pulmonary function and exercise performance after clinically significant weight loss.

We performed flow-loop spirometry, lung volumes, diffusing capacity for carbon monoxide (DL_co), and cycle ergometry with expired and blood gas analysis in 16 (14 women, 2 men) very obese (body-mass index > 40 kg/mβ) subjects before and immediately after 6 months of treatment including a very-low-calorie diet. Patients with a smoking history, hypoventilation and/or sleep apnea syndromes, or other cardiac or lung disease were carefully excluded.

Patients lost 23 ± 9.0 kg. There were significant increases in thoracic gas volume (2.3 ± 0.54 L versus 2.7 ± 1.1 L, p < 0.025) and expiratory reserve volume (0.89 ± 0.21 L versus 1.46 ± 0.72 L, p < 0.01), a decrease in the inspiratory capacity (2.8 ± 0.56 L versus 2.5 ± 0.49 L, p < 0.01), and a change in the relationship between thoracic gas volume and total lung capacity. There were no significant changes in other lung volumes, expiratory flow rates (peak flow or forced expiratory flow rate during the middle 50% of the forced vital capacity), airway resistance, or DL_co. Resting oxygen consumption did not change, but at peak exercise the oxygen consumption per kilogram weight increased, as did the ventilatory equivalent for the level of oxygen consumption.

Our results among carefully-selected patients accurately reflect the pulmonary function changes in uncomplicated ("healthy"), severely obese women. When changes in other lung volumes, airway resistance, DL_co, or blood gas tensions are found, evaluation for other causes of pulmonary disease should be undertaken. Weight loss leads to clinically important increase in lung volume and modest improvement in maximum aerobic capacity, even when normal weight is not attained. [Respir Care 1999;44(12):1458-1464]

Portable spirometry offers many potential advantages over conventional lung function measurements obtained in a pulmonary function laboratory.

We compared the performance characteristics of the MicroPlus portable spirometer with the SensorMedics Vmax22 diagnostic spirometer used in our pulmonary function laboratory. Lung function measurements (forced expiratory volume [FVC], forced expiratory volume in the first second [FEV₁], and peak expiratory flow [PEF]) were obtained from both instruments simultaneously, during the same forced expiratory maneuver. The study group consisted of 20 normal subjects, 20 asthmatics with mildly reduced lung function, and 20 severely obstructed chronic obstructive pulmonary disease (COPD) patients.

The difference between instruments (SensorMedics minus MicroPlus) was statistically significant for FVC in all 3 groups (0.31 L ± 0.57 in favor of the SensorMedics) and was also significant for FEV₁ (0.09 L ± 0.39) and PEF (0.33L/s ± 0.77) in the asthma and COPD groups. Between-group comparison of bias was highly significant (p = 0.0001) for PEF when comparing normal subjects with both obstructive lung disease groups. We also conducted a bench study in which we compared lung function from 3 additional MicroPlus units with the SensorMedics, measuring FVC from a 3-L syringe at several flow rates. A tendency to underestimate lung function, particularly at low expiratory flows, was noted in all 4 MicroPlus units tested.

We conclude that the MicroPlus underestimates lung function and, thus, the results obtained with the MicroPlus and the desktop SensorMedics Vmax22 diagnostic spirometer should not be considered equivalent or interchangeable. [Respir Care 1999;44(12):1465-1473]

Many studies have reported that users of metered dose inhalers (MDIS) have difficulty in coordinating inhalation with actuation of the MDI canister. The purpose of this study was to determine how a lack of coordination affects the respirable dose delivered to the patient's lungs when an MDI spacer or chamber is used. Measuring respirable dose (the dose in the 1-5 µm particle size range) requires the use of a cascade impactor or other particle sizer. However, a cascade impactor requires a constant flow rate. This would appear to be incompatible with a study of coordination, which requires a variable flow rate to simulate the patient's breathing through the MDI device.

We describe herein a new variable flow rate technique for measuring particle sizes and dose output with a cascade impactor (with a constant flow rate), while simulta-neously using a breathing machine to regulate the flow of aerosol medication through an MDI device and throat model. Using this technique, we tested 4 hand-held MDI devices: the Airlife Hand-Held MediSpacer, the Aerosol Cloud Enhancer (ACE), the OptiHaler, and the AeroCham-ber. Each device was tested under two different conditions: (a) in-phase, in which the MDI drug canister (Ventolin) is actuated at the start of inhalation, and (b) out-of-phase, in which the MDI canister is actuated at the start of exhalation and some portion of the drug plume may be retained until the following inhalation.

For all 4 devices the respirable dose was significantly less in the out-of-phase case than in the in-phase case. At the same time, the devices varied widely in the percentage of the usable aerosol plume that was retained in the out-of-phase case. The percentages retained until the following inhalation (as compared with the amount of drug delivered in the in-phase case) are as follows: MediSpacer 67%, ACE 23%, OptiHaler 9%, and AeroChamber 46%.

Timing greatly affects the amount of drug delivered by an MDI device, even one equipped with a valve. Also, device design has a large influence on the amount of drug delivered and the percentage of the drug plume retained when inhalation is delayed. The variable flow rate technique made this study possible, and this technique may also have applications in studying the effects of unusual breathing patterns.