Nocturnal Respiratory Rate and Variability Predict Long-term Mortality in Stable Outpatients with Cardiovascular Disease
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Background
Respiratory rate (RR) predicts short-term mortality in acute care settings, yet its prognostic significance in clinically stable outpatients remains poorly defined.
Objectives
To determine whether the median and variability of nocturnal respiratory rate (NRR) are independently associated with long-term cardiovascular and all-cause mortality in outpatients with cardiovascular disease.
Methods
We analyzed overnight chest belt waveforms from elective polysomnography in 5,679 older adults with cardiovascular disease enrolled in the Sleep Heart Health Study (SHHS). NRR was quantified at 30-second resolution, and per-subject median NRR and within-night variability (standard deviation) were derived. Kaplan-Meier survival analysis and Cox proportional hazards models were used to evaluate associations with cardiovascular and all-cause mortality over 3-year and 15-year follow-up periods, adjusting for demographic characteristics, cardiopulmonary comorbidities, and sleep apnea severity.
Results
Higher median NRR and greater NRR variability were each associated with increased cardiovascular and all-cause mortality. Combining these metrics identified a high-risk group characterized by high median and high variability of NRR, with nearly five-fold higher 3-year all-cause mortality compared with a low-risk group (unadjusted HR: 2.61; 95% CI: 1.65, 4.14; p <0.001; adjusted HR: 2.15; 95% CI: 1.30, 3.55; p =0.003).
Conclusions
Both the baseline level and variability of NRR independently predict morttality in clinically stable outpatients with cardiovascular disease. Densely profiled NRR represents a promising, underutilized biomarker for long-term risk stratification.
Condensed Abstract
Nocturnal respiratory rate (NRR) is an underutilized biomarker whose prognostic significance in stable cardiovascular outpatients is unknown. In 5,679 participants from the Sleep Heart Health Study, median NRR and within-night variability derived from overnight polysomnography independently predicted cardiovascular and all-cause mortality. Stratification based on these metrics identified a high-risk group with nearly five-fold higher 3-year mortality compared with a low-risk group (adjusted HR: 2.15; 95% CI: 1.30-3.55; p =0.003).
