RESPIRATORY MUSCLE-ACTIVITY DURING SLEEP-INDUCED PERIODIC BREATHING IN THE ELDERLY

During spontaneous sleep-induced periodic breathing in elderly subject s, we have found that tidal volume oscillations are related to recipro cal oscillations in upper airway resistance. The purpose of this study was to address the mechanism of the relationship between oscillations in tidal volume and upper airway resistance in elderly subjects with sleep-induced periodic breathing. We hypothesized that the spontaneous periodic breathing observed in non-rapid-eye-movement (NREM) sleep in elderly subjects would be closely related to fluctuations in upper ai rway resistance and not to changes in central motor drive to ventilato ry pump muscles. Therefore, in eight healthy elderly subjects, we meas ured costal margin chest wall peak moving time average electrical insp iratory activity (CW EMG), ventilation variables, and upper airway res istance during sleep. Five of eight subjects had significant sine wave oscillations in upper airway resistance and tidal volume. For these f ive subjects, there was a reciprocal exponential relationship between peak upper airway inspiratory resistance and tidal volume or minute ve ntilation [r = -0.60 +/- 0.20 (SD) (P < 0.05) and -0.55 +/- 0.26 (P < 0.05), respectively], such that as resistance increased, ventilation d ecreased. The relationship between CW EMG and tidal volume or minute v entilation was quite low (r = 0.12 +/- 0.32 and -0.07 +/- 0.27, respec tively). This study demonstrated that oscillations in ventilation duri ng NREM sleep in elderly subjects were significantly related to fluctu ations in upper airway resistance but were not related to changes in c hest wall muscle electrical activity. Therefore, changes in upper airw ay caliber likely contribute to oscillations in ventilation seen durin g sleep-induced periodic breathing in the elderly.