CF & Exercise article

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Role of Exercise and Lung Function in Predicting Work Status in Cystic

Fibrosis

Frangolias DD, Holloway CL, Vedal S, Wilcox PG

American Journal of Respiratory and Critical Care Medicine.

2003;167(2):150-157

Introduction

More patients with cystic fibrosis (CF) are surviving into adulthood and

entering the workforce. Issues of impairment and disability will

necessarily increase. The current study evaluated a cohort of adult CF

patients to determine the proportion who are limited in employment or

education based on American Thoracic Society (ATS) impairment

criteria,[1] to determine the utility of different resting and exercise

measurements to determine impairment in CF patients, and to determine

the energy cost of patients' work as a fraction of their maximal oxygen

uptake VO2max in relation to ATS impairment criteria.[1]

Methods

Stable patients underwent spirometry[2] and VO2max tests[3] and had the

Shwachman-Kulczycki (S-K)[4] and Brasfield scores[5] calculated. The

number of days treated for infection over the past 2 years was counted.

Demographic and clinical information was obtained by means of

questionnaire. Patients were grouped based on whether they were

full-time, part-time, or not employed or in school; ATS impairment

criteria; and impact of CF on work/school status. The energy costs of

subjects' jobs[6] and the percentage of job energy cost of VO2max were

calculated.

Results

The study sample (n = 73) was compared with the remaining clinic

population (n = 57). The study population was similar to the clinic

population as a whole except for an earlier age at diagnosis (6.2 ±

1.1 vs 12.7 ± 2.4 years, P = .005) and lower forced expiratory volume

in 1 second (FEV1) %predicted (53.4 ± 2.7 vs 64.7 ± 4.4%, P = .02)

in the study vs general population, respectively. There was no

difference in employment status or disability grouping (P = 0.23).

There were 11, 14, 23, and 25 patients classified as normal, mildly

impaired, moderately impaired, or severely impaired, respectively, based

on FEV1 %predicted criteria. There were 37, 25, and 11 patients

categorized as employed, employed-limited, or unemployed-limited,

respectively, indicating level of impact of CF on their work/school

status. Mean FEV1 %predicted was significantly greater in the employed

vs the other 2 groups, which were similar. Change in FEV1 and resting

peripheral oxygen saturation (SpO2) did not predict the disability

group. Similarly, there was no statistically significant change in SpO2

with maximal exercise between groups. Based on VO2max criteria, there

were 57 patients capable of heavy labor, 15 patients capable of work

loads of less than 40% VO2max, and 1 patient who was classified as

limited. With ordered logistic regression analysis, only FEV1 %predicted

and S-K scores were independently predictive of disability group.

There was a higher energy cost of work for the employed-limited vs

employed group and an association between more severe pulmonary disease

as reflected in FEV1 %predicted and higher energy cost of work (r =

-.44, P = .0001) and energy cost of work and hospital days for pulmonary

infection (r = .32, P = .009).

Discussion

The authors discussed the limited utility of pulmonary function and

exercise capacity measures in predicting work/school status. Whereas

FEV1 was identified as a factor in predicting work-related disability,

there was limited clinical utility as the group means were comparable

for the group unable to work and those working part time. Similarly, a

threshold of FEV1 %predicted of less than 40[1] was a poor discriminator

of those unable to work with 5 of 11, 8 of 37, and 12 of 25 patients

unable to work or working full-time or part-time, respectively, having

an FEV1 %predicted in this range. Other clinical variables were of

similar limited utility, including VO2max and energy cost of work.

The authors indicated that the poor predictive capacity of specific

thresholds of lung function and exercise capacity for CF patients is not

surprising. The generally younger age of CF patients as well as the

multifactorial nature of disability, including psychological factors,

are not addressed by the ATS criteria. Additionally, in CF patients,

other organ dysfunction may contribute to disability. Previous studies

have found age, adult CF diagnosis, female sex, and single marital

status predictive for disability after controlling for disease

severity.[7] These variables were generally not seen in the current

study to be statistically significant. Others have noted that

socioeconomic status is an important predictor of clinical outcome.[8]

The authors discussed several potential limitations in their study,

including the effort-dependent nature of exercise and pulmonary function

testing. In addition, the findings are only pertinent to adult patients

with CF.

They noted that patients with CF attempt to live as normal a life as

possible. Their CF cohort had a higher high school graduation rate than

the general population (95.9% vs 84.5%). However, several patients with

CF indicated that they modified their educational and career goals and

objectives secondary to their underlying disease. Approximately 25% of

the cohort indicated their belief that they had been denied employment

at some point in their life due to their disease.

In summary, the authors concluded that pulmonary function testing alone

does not give an accurate assessment of a patient's capabilities and

that exercise testing provides additional information. They suggested

that both measures be considered when assessing impairment and

predicting disability. S-K scores should be calculated for an overall

presentation of clinical status, and also the frequency of pulmonary

infections should be considered.

References

American Thoracic Society. Evaluation of impairment/disability secondary

to respiratory disorders. Am Rev Respir Dis. 1986;133:1205-1209.

American Thoracic Society. Standardization of spirometry, 1994 update.

Am J Respir Crit Care Med. 1995;152:1107-1136.

Frangolias DD, Wilcox PG. Predictability of oxygen desaturation during

sleep in patients with cystic fibrosis: clinical, spirometric, and

exercise parameters. Chest. 2001;119:434-441.

Shwachman H, Kulczycki L. Long-term study of one hundred five patients

with cystic fibrosis. Am J Dis Child. 1958;96:6-15.

Brasfield D, Hicks G, Soong S, Tiller RE. The chest roentgenogram in

cystic fibrosis: a new scoring system. Pediatrics. 1979;63:24-29.

PW, Paffenbarger RS Jr, JN, Havlik RJ. Assessment methods

for physical activity and physical fitness in population studies: report

of an NHLBI workshop. Am Heart J. 1986;111:1177-1192.

Gillen M, Lallas D, Brown C, Yelin E, Blanc P. Work disability in adults

with cystic fibrosis. Am J Respir Crit Care Med. 1995;152:153-156.

Schechter MS, Shelton BJ, Margolis PA, Fitzsimmons SC. The association

of socioeconomic status with outcomes in cystic fibrosis patients in the

United States. Am J Respir Crit Care Med. 2001;163:1331-1337.

Becki

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