Discussion
This study describes the validation and use of an LVR counter, retrofitted onto a commercially available LVR kit, to objectively quantify an individual’s concordance with prescribed LVR therapy. The minimum pressure required to trigger the LVR counter’s pressure switches under conditions of zero leak was 1.9 cm H2O, suggesting that it is extremely sensitive in detecting usage (Experiment 1). The LVR counter is accurate at detecting single compressions of the LVR bag in a controlled setting, with the LVR counter recording 98% of all compressions at low pressure (Experiment 2). The in-series design of the LVR counter ensured that both a compression of the bag and adequate participant seal must simultaneously occur for use to be recorded (Experiment 3).
Although the LVR counter overestimated the count of individual compressions delivered to the test lung under high-pressure bench test conditions (up to 100 cm H2O) by 15%, it demonstrated 100% accuracy in counting all 40 repetitions. Arguably, the ‘overcounting’ of compressions is of little clinical importance because compressions are simply the mechanism by which one achieves the clinically important outcome; the attainment of the therapeutically targeted maximal tolerated insufflation capacity (MIC or LIC); and the repetition, sets and sessions that sum to provide the daily dose of LVR therapy (figure 2). Physiological control testing (Experiment 4) similarly demonstrated 100% accuracy between repetitions and sets of LVR therapy conducted and recorded, regardless of the speed at which the technique was performed. Increasing the LVR counter’s sampling rate to 4 Hz recorded compressions precisely, and therefore, if required perhaps for research applications, both compressions and repetitions may be recorded with higher fidelity.
The use of this LVR counter in the community appeared feasible; data were obtained for 92% participant days (880 out of a possible 960). Of the 853 sets of paired data, there was absolute agreement regarding the daily dose between the LVR counter and self-report diary 77% of the time (653 instances). Greater discordance in the direction of the diary suggests overestimation of self-reported LVR usage, a common finding in other chronic conditions when self-report measures have been compared with objective measures of use.26 27 In one study, 47% of people with cystic fibrosis reported performing more airway clearance therapy sessions than objectively recorded data would suggest across a 5-week period.26 In contrast, medication adherence literature would indicate better concordance, with 72% of studies reporting ‘high’ concordance; high concordance is defined as <10% difference between self-reported diary and other measures of adherence.27 Differences in concordance rates between self-reported and objective measures may be related to the type of intervention (eg, ease and time required to perform), duration of follow-up period and participant awareness of monitoring.
A limitation of the way the LVR counter was used in our field testing was that it needed it to be manually switched ‘on’ before each therapy session. This approach was taken to ensure adequate battery life as the LVR counters’ data were downloaded only once a month. As such, forgetting to start the counter before each therapy session would lead to an under-recording of LVR usage and could partially explain the apparent overestimation on the diary. Anecdotal participant reports confirmed this, but there was no suggestion this accounted for all discordant data. In 5% of cases, we identified a therapy session had been recorded on the LVR counter and not documented in the diary. Given the LVR counter’s design, we suggest that when discordance favours the LVR counter, this represents actual usage and a conservative but accurate representation of ‘at least’ delivered dose.
The ability to objectively monitor therapy use, dosage or concordance with recommended prescription is much needed; examining dose–response is vital to assess the efficacy of LVR therapy and establish empirically derived optimal dose recommendations. Moreover, monitoring of treatment data including therapy use has been shown to improve adherence to continuous positive airway pressure treatment, when part of a multimodal intervention strategy in people with obstructive sleep apnoea.30 To date, evidence of effectiveness of LVR is largely limited to retrospective cohort design or prospective studies with only participant self-report of use. In other conditions, this has been shown to be inaccurate, and hence, translation of these studies into practice and policy is compromised. Reports of little or no therapeutic benefit may reflect non-performance of treatment or a true lack of effect, but without objective usage data, it is not possible to know. The ability to correlate clinically important outcomes with a specific threshold of utilisation will assist in clinical prescription so as not to overburden or undertreat individuals. The requirement for both pressure switches to be triggered during the manoeuvre is a strength of the design of this LVR counter. This guards against usage being recorded when the LVR bag is compressed but not connected to the person (ie, simulating usage or demonstrating the equipment). Similarly, ineffective therapy due to interface leak is not counted as demonstrated by the lack of any recorded compressions in conditions with substantial leak.
Limitations
There was no recording of the flow or volume delivered during LVR nor any external criterion measure of use during field testing (Experiment 5); we were comparing the new LVR counter to self-report. While the performance of the LVR counter in the preceding bench tests strongly suggests that the LVR counter accurately records repetitions, sets and thus sessions and daily dose, there is a possibility that the self-report data were ‘more true’ than the LVR counter. As noted, previous literature in other self-report versus objective measurement conditions would make this possibility unlikely.26 27 The LVR counter used in this project is an in-house-developed prototype and as such does not provide a clear pathway to commercial and clinical translation of our findings; however, we suggest that this paper illustrates clear translational opportunities. Clinically, objective data provide opportunities for home monitoring of therapy, may suggest poor usage and may prompt clinicians to identify barriers to treatment, and similarly, patterns of use may provide important information about users’ beliefs and treatment choices, both positive and negative. As with continuous positive airway pressure therapy for sleep apnoea,31 demonstrating sufficient LVR use could be linked to funding of LVR therapy, potentially providing a commercialisation pathway for device development.