Chest

Chest

Volume 114, Issue 2, August 1998, Pages 521-525
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Clinical Investigations: Pulmonary Function
Long-term Within-Subject Variability of Inspiratory Neural Drive Response to Hypoxia

https://doi.org/10.1378/chest.114.2.521Get rights and content

Study objective

We analyze the within-subject variation of mouth occlusion pressure (P0.1) response to progressive isocapnic hypoxic stimulation over long time periods in normal subjects.

Patients and interventions

We studied 21 healthy subjects (14 male and 7 female; aged 40±12 yrs) (mean±SD). Lung volumes, basal P0.1, and P0.1 response to hypoxia were measured on two separate occasions 2 months apart, under similar ambient and clinical conditions.

Results

There was no significant change in clinical condition, FVC, FEV1, arterial oxygenation saturation, end-tidal and mixed venous Pco2 levels, or P0.1 between the two visits. The mean P0.1 responses to hypoxia in the two explorations were 0.032±0.022 and 0.034±0.022 kPa/%, respectively. There was a moderate intrasubject variability of P0.1 response to hypoxia, with a coefficient of reproducibility of 0.01 kPa/%. Power calculations to establish the optimal sample size required for hypoxic stimulation are presented.

Conclusion

Long term within-subject variability of P0.1 response to hypoxia is moderate. This intrinsic variability needs to be emphasized when interpreting the effects of experimental interventions on hypoxic sensitivity.

Section snippets

Subjects

Twenty-one normal subjects, 14 male and 7 female (40 ±12 years), gave their informed consent to be studied. They were judged healthy by history, physical examination, ECG, basal spirometry, and chest fluoroscopy. Their mean height was 170 ±9 cm and their mean weight was 73 ±13 kg. Eight volunteers were current smokers and none were taking medication (including oral contraceptives). The women were studied during the estrogenic portion of their menstrual cycles.

Study Design

Two pulmonary function studies were

Results

There were no significant differences in the anthropometric and spirometric characteristics between the two explorations (Table 1). Basal SaO2, mixed venous Pco2 levels at which the hypoxic response was tested, and baseline end-tidal Pco2 levels before testing was begun on two visits are also shown in Table 1. None of these parameters changed significantly between the two explorations. No changes in basal P0.1 (0.130±0.029 vs 0.139±0.03 kPa) or in P0.1 response to hypoxia (0.032±0.022 vs

Discussion

Our study indicates that P0.1 response of healthy subjects to progressive isocapnic hypoxic stimulation presents a moderate intrasubject variation over long time periods.

Data describing variability of respiratory response to hypoxia are scanty.9, 10, 11, 12, 20 Moreover, several methodologic differences limit the comparison of results. Previous studies have only measured the ventilatory response to hypoxia. Different methods of stimulation (steady-state,20 rebreathing,9, 10, 11 or rebreathing

Acknowledgments

The authors gratefully acknowledge the continuous technical assistance of A. Alvárez, P. Librán, and C. Suárez.

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    Copyright © 1998 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.