Michael Sherman

Pulmonary dysfunction and reduced exercise capacity in patients with myelomeningocele

OBJECTIVE To evaluate pulmonary function and exercise capacity in children with myelomeningocele. STUDY DESIGN Prospective evaluation in a randomly selected cohort of 12 subjects (10 to 17 years of age) with myelomeningocele and 12 control subjects matched for age, sex, and arm span. METHODS Spirometry, lung volumes, maximum respiratory pressures, maximum oxygen expenditure during arm ergometry, and anaerobic threshold were measured. RESULTS Mean total lung capacity and fractional lung volumes were significantly lower in case subjects than control subjects. Eleven subjects (92%) had a reduced forced vital capacity; seven (58%) had restrictive disease as evidenced by reductions in total lung capacity with normal or increased forced expiratory volume in 1 second/forced vital capacity ratio. Nine subjects (75%) had respiratory muscle weakness as evidenced by reduced maximum respiratory pressures or a low maximum voluntary ventilation. Exercise capacity was reduced as evidenced by a lower maximum oxygen consumption at peak exercise (13.8 +/- 4.8 vs 21.3 +/- 7.5 ml/min per kilogram of body weight; p < 0.02) and a lower anaerobic threshold (12.4 +/- 5.1 vs 17.3 +/- 4.2 ml/min per kilogram; p < 0.01) than the control group. Though the majority of subjects with myelomeningocele had a significant degree of restrictive disease, respiratory muscle weakness, or both, only one subject had pulmonary symptoms during exercise. CONCLUSIONS Though most subjects with myelomeningocele had a significant degree of restrictive lung disease, respiratory muscle weakness, or both, exercise capacity was mostly limited by arm weakness. Skeletal muscle weakness may mask the symptoms of an underlying pulmonary abnormality, which may not be evident unless a pathologic cause of increased ventilation is present. Pulmonary function testing is suggested to screen for these abnormalities.

Systemic Steroids for the Treatment of Acute Asthma: Where Do We Stand?

Despite over 50 years of clinical experience, many uncertainties persist with respect to the onset of action, dose–response characteristics, duration of treatment, and optimal route of administration of systemic steroids when used in the treatment of severe acute asthma. Studies show that treating severe acute asthma with systemic corticosteroids within 1 hour of presentation to the emergency department lowers hospitalization rates and improves pulmonary function. The onset of action may be seen in as little as 2 hours in studies using peak flow, but may be delayed as much as 6 hours in studies using forced expiratory volume in 1 second as the pulmonary function outcome measure. A clear dose–response is seen at doses below 40 mg per day of methylprednisolone or equivalent; however, there is limited evidence for any added efficacy when doses above 60 to 80 mg per day are administered. There is no clear benefit of intravenous systemic steroids over oral steroids for treatment of severe acute asthma. High-dose inhaled corticosteroids may have a potential role, but further studies are needed to confirm efficacy. There is good evidence that a short course of oral systemic steroids for 3 to 7 days after initial steroid therapy prevents rebound asthma symptoms; no steroid taper is required if the patient was receiving inhaled steroids. Intramuscular steroids are at least equally effective and may be useful in patients who poorly adhere to their medication regimens; however, they are associated with more side effects than oral therapy.

Practice patterns for maintaining airway stents deployed for malignant central airway obstruction.

Although significant experience exists in placing airway stents, and knowledge of stent-related complications is widespread, information is lacking regarding methods of surveillance and maintaining patency of these stents. The purpose of this investigation was to determine the actual practice patterns used by interventional pulmonologists for airway stent maintenance. We prospectively surveyed members of the American Association of Bronchology and Interventional Pulmonology or attendees at their annual meeting during Chest 2008. Sixty-two respondents returned the completed surveys and were included in the analysis. Practice settings included university (50%), single specialty (27%), community academic (11%), and multispecialty (11%) settings. Annual placement of stents was ≤10 (31%); 11 to 30 (45%); and >30 (24%). Considerable variability existed in both medications used for maintenance and surveillance schedules, and less than 50% protocolized postplacement management. Although stent placement is common among experienced interventional pulmonologists, half have no protocol for surveillance or maintenance. Similarly, there is no discernable consistency or standard practice pattern to monitor for or prevent stent failure. Further study is required to determine the best practices for postdeployment surveillance and maintenance of airway stents.

A method for estimating respiratory muscle efficiency using an automated metabolic cart.

We measured respiratory muscle efficiency (RME) in twelve healthy human subjects by dividing the added energy cost of breathing against a threshold resistance load by the associated increase in caloric expenditure. Caloric expenditure was calculated using steady-state measurements of oxygen consumption and carbon dioxide production during loaded and unloaded breathing. Calculated RME ranged from 1.7% to 5.5% (mean 3.5%). The coefficient of variation in six subjects averaged 13%. We compared these calculations with a previously described oxygen consumption-based method that did not incorporate carbon dioxide production measurements. We found that changes in the respiratory quotient during resistive breathing could cause significant errors in oxygen consumption-based calculations of RME. Limits of agreement of 95% suggest that the oxygen-consumption-based calculations could potentially overestimate efficiency by as much as 5.0% or underestimate by up to 3.4%. We recommend that carbon dioxide production be measured when this technique for estimation of RME is used. This can be easily accomplished through the use of an automated metabolic cart.