We hypothesized that patients with Cheyne-Stokes respiration exhibit periodic increases in end-expiratory lung volume, mediated by changes in breath components, postinspiratory inspiratory muscle activity, or both. Calibrated inductive plethysmography revealed that 12 of 12 patients with Cheyne-Stokes respiration experienced increases in end-expiratory volume during hyperpnea: maximum 412 +/- 112 (SE) ml (range 75-1,543 ml). Compared with quiet breathing, the breath with largest increase in end-expiratory volume had larger tidal volume (867 +/- 107 vs. 567 +/- 38 ml, p < 0.01) and shorter expiratory time (1.25 +/- 0.11 vs. 1.66 +/- 0.15 seconds, p < 0.05). During decrescendo, the breath with largest decrease in end-expiratory volume had smaller tidal volume (p < 0.01) and longer expiratory time (p < 0.01). Cross-correlation of time series revealed that end-expiratory volume was related to both breath components (p < 0.0001). Bipolar needle electrodes revealed that scalene muscle activity at end-expiration was 50.7 +/- 14.0% higher at highest increase in lung volume than during preceding apnea (p < 0.05). Time series for scalene activity and end-expiratory volume were cross-correlated (p < 0.008). Increase in tonic scalene activity at end-expiration, however, was equivalent during crescendo and decrescendo phases: 50.6 +/- 22.1 versus 42.0 +/- 12.9% (p = 0.48). In conclusion, patients with Cheyne-Stokes respiration exhibit fluctuations in end-expiratory lung volume, primarily because of alterations in tidal volume and expiratory time rather than postinspiratory inspiratory muscle activity.