Malnutrition and hyperinflation may both lead to respiratory muscle weakness. To assess separately the effects of chronic hyperinflation and malnutrition on respiratory muscle strength (RMS), 22 subjects with cystic fibrosis (CF) with both hyperinflation and malnutrition were compared to 10 asthmatic patients, a group with hyperinflation without malnutrition, 9 subjects with anorexia nervosa (AN), a group with malnutrition without lung disease, and 14(6 males and 8 females) control subjects with neither compromise. Nutritional status was assessed by body mass percentile (BMP) and percentage ideal weight (PIWT). RMS was diminished in the AN and CF groups (PImax 90 +/- 27, 88 +/- 31 versus 124 +/- 40 cm H2O, p less than 0.05; PEmax 87 +/- 12, 93 +/- 39 versus 121 +/- 32 cm H2O, p less than 0.05), but no difference was found when the AN group was compared with only the female controls. The decrease in PImax in the CF group was primarily due to the mechanical disadvantage placed on the diaphragm by their marked hyperinflation, a mean RV/TLC ratio of 50 +/- 23%. As older CF subjects had previously been shown to have decreased RMS when malnourished, a CF subgroup in the same age range as the controls was evaluated. RMS in this group did not differ from controls despite the presence of malnutrition and hyperinflation. RMS is mildly influenced by nutritional status as assessed by BMP and PIWT but not to any degree of clinical significance.

In order for an individual FVC maneuver to be considered acceptable according to the 1994 American Thoracic Society (ATS) standards it must meet end of test (EOT) criteria of a minimum expiration time of 6 s with minimal volume change (0.03 L) over 1 s. We have found that while these criteria are often not met in children, most of the tests do meet the ATS criteria for reproducibility with repeated efforts. We, therefore, sought to develop new EOT criteria that would be more appropriate for children and in keeping with the findings for reproducibility. Using an exponential curve fitting of the volume time tracing, we determined a theoretical curve that closely approximated the actual curve (mean difference between actual and derived FEV1 0.01 +/- 0.04 L). The theoretical FVC (FVCFULL) at the point where the curve reached its asymptote was then determined using the fitted curve. Since this point could be difficult to reach for some patients, 95% of FVCFULL (FVC95) was proposed as the new EOT in children. Data from 382 patients were reviewed. Their ages ranged from 5 to 18 yr and their FEV1s from 21 to 120% of predicted. Only 19% of the patients met current ATS EOT requirements despite the fact that 91% met the reproducibility criteria for both FEV1 and FVC. However, 90% of them reached their FVC95. When this was broken down by age, 37% of those < or = 7 yr failed to reach FVC95 whereas only 4% of the older children failed to do so. It is proposed that patients be coached to obtain maximal effort and that the curves be individually fitted to an exponential equation to determine whether the patient has achieved EOT as defined by FVC95.

The American Thoracic Society (ATS) recommendations to establish reproducibility of the forced expiratory volume in one second (FEV1) are that the value come from "at least 3 acceptable forced expiratory curves" where "the largest forced vital capacity maneuver (FVC) and the second largest FVC should not vary by more than 5%." It has been suggested that there is a "negative effort dependence" of the FEV1 and, alternatively, that the magnitude of the FVC influences the FEV1. We examined the relationship between FEV1 and a direct measurement of effort, or work, defined as the area under the alveolar pressure-volume curve in 1 s. Thirteen normal individuals and 17 patients with cystic fibrosis or asthma were instructed to make a series of maximal efforts, as in routine testing. Comparing the maneuver that resulted in the greatest work to that with the lowest work, all with FVCs within 5% of one another, there was no correlation between change in work and change in FEV1 (delta FEV1). There was a significant relationship between delta FEV1 and changes in FVC (r = 0.49, p < 0.01). The delta FEV1 did not correlate with the degree of hyperinflation (the FRC) or degree of airflow limitation (the initial FEV1). The magnitude of changes in FEV1 was small and almost always within acceptable limits for reproducibility. Because a larger FVC is due either to an increased inspiration, which could affect the FEV1, or to an increased expiratory reserve volume, which occurs only after the first second, these results emphasize the importance of a maximal inspiration at the start of the test.