We sought to develop procedures for computerized analysis of long-term, high-resolution activity monitoring data that allow accurate assessment of the time course of activity levels suitable for use in chronic obstructive pulmonary disease (COPD) patients. Twenty-two COPD patients utilizing long-term oxygen recruited from 5 sites of the COPD Clinical Research Network wore a triaxial accelerometer (RT3, Stayhealthy, Monrovia, CA) during waking hours over a14 day period. Computerized algorithms were composed allowing minute-by-minute activity data to be analyzed to determine, for each minute, whether the monitor was being worn. Temporal alignment allowed determination of average time course of activity level, expressed as average vector magnitude units (VMU, the vectorial sum of activity counts in three orthogonal directions) per minute, for each hour of the day. Mid-day activity was quantified as average VMU/minute between 10AM and 4PM for minutes the monitor was worn. Over the 14 day monitoring period, subjects wore the monitor an average of 11.4±3.0 hours·day−1. During midday hours, subjects wore the monitor 76.3% of the time and generated an average activity level of 112±55 VMU·min−1. Increase in precision of activity estimates with longer monitoring periods was demonstrated. This analysis scheme allows a detailed temporal pattern of activity to be defined from triaxial accelerometer recordings and has the potential to facilitate comparisons among subjects and between subject groups. This trial is registered at ClinicalTrials.gov (NCT00325754).

During heavy exercise in chronic obstructive pulmonary disease (COPD), dynamic airways compression leads to a progressive fall in intrabreath flow. This is manifested by concavity in the spontaneous expiratory flow-volume (SEFV) curve. We developed a method to quantify the SEFV curve configuration breath-by-breath during incremental exercise utilizing a computerized analysis. The flow signal was digitized at 100Hz. For each breath's SEFV curve, points of highest flow (V (max)) and end-expiration (V (EE)) were identified to define a rectangle's diagonal. Fractional area within the rectangle below the SEFV curve was defined as the "rectangular area ratio" (RAR); RAR <0.5 signifies concavity of the SEFV. To illustrate the utility of this method, time courses of RAR during incremental exercise in 12 healthy and 17 COPD individuals (FEV(1) %Pred.=39+/-12) were compared. SEFV in healthy individuals manifested progressively more convex SEFV curves throughout exercise (RAR=0.56+/-0.08 at rest and 0.61+/-0.05 at peak exercise), but became progressively more concave in COPD patients (RAR=0.52+/-0.08 at rest and 0.46+/-0.06 at peak exercise). In conclusion, breath-by-breath quantification of SEFV curve concavity describes progressive shape changes denoting expiratory flow limitation during incremental exercise in COPD patients. Further studies are warranted to establish whether this novel method can be a reliable indicator of expiratory flow limitation during exercise and to examine the relationship of RAR time course to the development of dynamic hyperinflation.

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