Instability of nocturnal parasympathetic nerve function in patients with chronic lung disease with or without nocturnal desaturation

Abstract

Objective/background: This study was performed to evaluate the association of nocturnal autonomic nerve (AN) dysfunction, especially parasympathetic nerve (PN) function instability, and nocturnal oxygen desaturation (NOD) in patients with chronic lung diseases (CLD).

Patients and methods: Twenty-nine stable CLD patients with irreversible pulmonary dysfunction and mild-to-moderate daytime hypoxemia, 13 CLD patients receiving long-term oxygen therapy (LTOT) with maintained SpO₂ >90%, and 17 senior healthy volunteers underwent two-night examinations of nocturnal AN function by pulse rate variability (PRV) instead of heart rate variation using a photoelectrical plethysmograph simultaneously monitoring SpO₂ and the presence of sleep disordered breathing at home. AN function was examined by instantaneous time-frequency analysis of PRV using a complex demodulation method.

Results: There were no significant differences in mean low frequency/high frequency (HF) ratio (index of sympathetic nerve activity) or mean HF amplitude (index of PN activity) among controls and CLD patients with and without NOD (defined as SpO₂ <90% for at least 3% of total recording time at night). However, the relative times over which the same main HF peak was sustained for at least 20 seconds (%HF_20sec) and 5 minutes in total recording time, indexes of PN function stability, were significantly reduced in CLD patients compared with controls, and further decreased in CLD patients with NOD compared with non-NOD. %HF_20sec was significantly higher in the LTOT group than the NOD group. Furthermore, PaO₂ at rest and nocturnal hypoxia were significantly correlated with PN function instability in CLD patients.

Conclusion: PN function is unstable at night associated with nocturnal hypoxemia in CLD patients, which may reflect poor quality of sleep.

Keywords: autonomic nerve function; heart rate variability; long-term oxygen therapy; photoelectric plethysmography; sleep disordered breathing.

Figure 1

Comparison of sympathetic (A) and parasympathetic (B) activity among healthy elderly subjects (control), CLD patients with NOD and without NOD (non-NOD), and CLD patients treated with LTOT. Note: **P<0.01 vs control. Abbreviations: LF, low frequency; HF, high frequency; LF/HF ratio, an index of sympathetic nerve activity; HF amplitude, an index of parasympathetic nerve activity; NOD, nocturnal oxygen desaturation; LTOT, long-term oxygen therapy; CLD, chronic lung disease.

Figure 2

Comparison of indexes of stability of parasympathetic nerve function, %HF_20sec (A) and %HF_5min (B), among healthy elderly subjects (control), CLD patients with NOD and without NOD (non-NOD), and CLD patients treated with LTOT. Notes: **P<0.01 vs control; ^##P<0.01 vs non-NOD; ^§§P<0.01 vs NOD. Abbreviations: %HF_20sec and %HF_5min, the relative times over which the same main high-frequency peak was sustained for at least 20 seconds and 5 minutes in total recording time (markers of stability of parasympathetic nerve function); CLD, chronic lung disease with irreversible pulmonary dysfunction and mild-to-moderate daytime hypoxemia; NOD, nocturnal oxygen desaturation defined as CT90 ≥3%; CT90, cumulative time with SpO₂ <90%; LTOT, long-term oxygen therapy.

Figure 3

Relationship between %HF_20sec, an index of stability of parasympathetic nerve function, and CT90 (A) or PaO₂ (B). Abbreviations: CT90, cumulative time with SpO₂ <90%; %HF_20sec, the relative time over which the same main HF peak was sustained for at least 20 seconds in total recording time (an index of stability of parasympathetic nerve function); HF, high frequency.