Chest
Volume 116, Issue 3, September 1999, Pages 647-654
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Clinical Investigations
Cystic Fibrosis
Hypoxemia and Hypercapnia During Exercise and Sleep in Patients With Cystic Fibrosis

https://doi.org/10.1378/chest.116.3.647Get rights and content

Background

In patients with cystic fibrosis (CF), it has been proposed that hypoxemia and hypercapnia occur during episodes of stress, such as exercise and sleep, and that respiratory muscle weakness because of malnutrition may be responsible.

Methods

Pulmonary function, respiratory muscle strength, and nutrition were assessed and correlated with the degree of hypoxemia and hypercapnia during exercise and sleep in 14 patients with CF and 8 control subjects.

Results

Despite no differences in maximum static inspiratory pressure (Pimax) between the two groups, the CF group developed more severe hypoxemia (minimum oxyhemoglobin saturation [Spo2], 89 ± 5% vs 96 ± 2%; p < 0.001) and hypercapnia (maximum transcutaneous CO2 tension [Ptcco2], 43 ± 6 vs 33 ± 7 mm Hg; p < 0.01) during exercise. Similarly, during sleep, the CF group developed greater hypoxemia (minimum Spo2, 82 ± 8% vs 91 ± 2%; p < 0.005), although CO2 levels were not significantly different (maximum Ptcco2, 48 ± 7 vs 50 ± 2 mm Hg). Within the CF group, exercise-related hypoxemia and hypercapnia did not correlate with FEV1, residual volume/total lung capacity ratio (RV/TLC), Pimax, or body mass index (BMI). Hypoxemia and hypercapnia during sleep correlated with markers of gas trapping (RV vs minimum arterial oxygen saturation [r = −0.654; p < 0.05]), RV vs maximum Ptcco2 (r = 0.878; p < 0.001), and RV/TLC vs maximum Ptcco2 (r = 0.790; p < 0.01) but not with Pimax or BMI.

Conclusion

Patients with moderately severe CF develop hypoxemia and hypercapnia during exercise and sleep to a greater extent than healthy subjects with similar respiratory muscle strength and nutritional status. Neither respiratory muscle weakness nor malnutrition are necessary to develop hypoxemia or hypercapnia during exercise or sleep.

Section snippets

Subjects

Patients attending the Alfred Hospital Adult Cystic Fibrosis Service and healthy control subjects were invited to participate in the study. Patients with CF of either sex were eligible for inclusion in the study if they were ≥ 18 years of age, with FEV1 < 60% of predicted normal, Pao2 > 55 mm Hg at rest, not receiving domiciliary oxygen, and in a clinically stable condition as indicated by no hospital admission or change in medications for ≥ 4 weeks. The healthy subjects recruited were matched

Subject Characteristics

Fourteen patients with CF (9 men and 5 women), and 8 control subjects (4 men and 4 women) participated in the study (Table 1). Pao2 was significantly lower in the CF group (67 ± 8 vs 99 ± 4 mm Hg; p < 0.0001); however, there were no significant differences in Paco2 or pH (Table 1). Compared with control subjects, the patients with CF had significantly lower FEV1, FVC, and FEV1/FVC, and significantly greater RV (Table 1). Neither TLC nor Dlco were significantly different between groups. The

Discussion

The major findings of the current study were fourfold. First, hypoxemia and hypercapnia occurred during exercise and sleep to a greater degree in stable, nonhypoxic adult patients with CF, despite normal respiratory muscle strength, than in control subjects. Second, in the CF group, pulmonary function, respiratory muscle strength, and nutritional status correlated with maximum workload during exercise but not with levels of hypoxemia or hypercapnia that occurred during exercise. Third, in the

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    Dr. Solin is a recipient of an Australian National Health and Medical Research Council scholarship. Matthew Naughton is a recipient of an Astra/Australian Lung Foundation Career Development Award and Viertal Clinical Investigatorship.

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