Patients with chronic obstructive pulmonary disease (COPD) exhibit increases in lung volume due to expiratory airflow limitation. Increases in lung volumes may affect upper airway patency and compensatory responses to inspiratory flow limitation (IFL) during sleep. We hypothesized that COPD patients have less collapsible airways inversely proportional to their lung volumes, and that the presence of expiratory airflow limitation limits duty cycle responses to defend ventilation in the presence of IFL. We enrolled 18 COPD patients and 18 controls, matched by age, body mass index, sex, and obstructive sleep apnea disease severity. Sleep studies, including quantitative assessment of airflow at various nasal pressure levels, were conducted to determine upper airway mechanical properties [passive critical closing pressure (Pcrit)] and for quantifying respiratory timing responses to experimentally induced IFL. COPD patients had lower passive Pcrit than their matched controls (COPD: -2.8 ± 0.9 cmH2O; controls: -0.5 ± 0.5 cmH2O, P = 0.03), and there was an inverse relationship of subject's functional residual capacity and passive Pcrit (-1.7 cmH2O/l increase in functional residual capacity, r(2) = 0.27, P = 0.002). In response to IFL, inspiratory duty cycle increased more (P = 0.03) in COPD patients (0.40 to 0.54) than in controls (0.41 to 0.51) and led to a marked reduction in expiratory time from 2.5 to 1.5 s (P < 0.01). COPD patients have a less collapsible airway and a greater, not reduced, compensatory timing response during upper airway obstruction. While these timing responses may reduce hypoventilation, it may also increase the risk for developing dynamic hyperinflation due to a marked reduction in expiratory time.
The critical closing pressure (PCRIT), a quantitative assessment of upper airway collapsibility, is derived from pressure flow relationship during sleep. The analytic generation of the pressure flow relationships are non-standardized due to various regression models (linear, spline, median), breath characteristics (flow limited, non-flow limited) or known covariates (sleep stage, body position). We propose a GUI based PCRIT Analysis Software (PAS) to streamline PCRIT analysis and validate its reliability and accuracy compared to current analysis procedures.
Methods
Seventeen subjects underwent a physiology sleep study in which the PCRIT was determined during NREM sleep. Data analysis was performed independently using three paradigms: 1) PAS (Igor Pro; median regression), 2) non-graphic statistics application (SAS; spline regression), and 3) manual spreadsheet calculations (Excel; linear regression). The reliability and accuracy of the PAS was examined through the agreement between each approach using Bland-Altman plots of the mean difference and within-individual variation using intra-class correlation (ICC).
Results
There was no difference in the group mean values for PCRIT using the PAS (−1.7±0.7 cm H2O) compared to spline regression (−1.6±0.7 cm H2O; p=0.69) or linear regression (−2.1±0.7 cm H2O; p=0.92). The Bland-Altman analysis did not demonstrate a systematic bias between the PAS and either approach. There was a mean difference of 0.39±0.2 cm H2O between the PAS and linear regression approaches, with upper and lower limits of agreement of 1.81 and −1.02 cm H2O, respectively. The PAS and spline analysis demonstrated an even smaller mean difference of −0.10 ± 0.1 cm H2O, with upper and lower limits of 0.90 and −1.08 cm H2O, respectively.
Conclusion
PAS preserves the reliability and accuracy of the original PCRIT analysis methods while vastly improving their efficiency through graphic user interface and automation of analytic processes. Providing a standardized platform for physiologic data processing offers the ability to implement quality assurance and control procedures for multicenter studies as well as cost saving by improving the efficiency of complex repetitive tasks.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.