The annual asthma review is central to primary care respiratory management. A nurse or clinician assesses symptom frequency, rescue inhaler use, exacerbation history, and current medication, performs spirometry when indicated, and updates the treatment plan. This is a sensible process that provides useful information. Its limitation is that it captures a ten-minute snapshot of a condition that can change markedly from day to day, week to week, and season to season. Using that review to judge asthma control is like assessing cardiovascular risk from one casual blood pressure reading: useful, but potentially very misleading.
This article examines asthma control between reviews, why that interval matters clinically, and what home monitoring may and may not provide as an additional lens.
The Variability Challenge
Variability is intrinsic to asthma. Airway inflammation waxes and wanes with allergen exposure, viral triggers, air quality, physical exertion, and seasonal factors. Someone reporting good control at an October review may have had two to three poorly controlled episodes during the previous summer pollen season without seeking care. Conversely, someone appearing poorly controlled at review may simply have had an unusually difficult week before the appointment, with their underlying control better than the snapshot suggests.
The tools used between reviews are mainly retrospective and patient reported. The Asthma Control Test (ACT) asks patients to recall symptoms over the past four weeks. The Royal College of Physicians Three Questions address sleep disturbance, activity limitation, and daytime symptoms. Both tools are validated and useful, but both depend on recall and on an individual's threshold for reporting symptoms, which can differ considerably. Patients who have lived with poorly controlled asthma for years may describe acceptable control because their subjective baseline has adapted to chronic underperformance.
What Asthma Acoustics Add
In asthma, the main acoustic change associated with poor control is expiratory wheeze. It arises as air moves through narrowed, oedematous airways, and wheeze during resting tidal breathing indicates clinically significant bronchospasm. Patients may not hear it themselves, especially when it occurs above the audible range or only in the lower lobes. It can also be intermittent, emerging at night or in the early morning when circadian changes in airway tone produce peak bronchoconstriction.
Clinical review commonly misses nocturnal and early morning wheeze. Patients may be asleep when it occurs, or may not associate disrupted sleep with airway narrowing. Nonetheless, it is measurable and detectable airway dysfunction that correlates with overall control.
A home continuous acoustic monitoring system can capture this signal. In our pilot work with asthma patients, wheeze index values from early morning resting recordings, roughly 4 to 7 a.m., correlate with self-reported control scores, but do not always agree. A subset reporting acceptable questionnaire control has measurable nocturnal wheeze on acoustic monitoring. The important question is whether that difference can guide care, and the answer depends on the clinical context.
When Monitoring Helps, and When It Does Not
For patients with well-controlled asthma who adhere to preventer therapy and have no exacerbation history, continuous monitoring is likely to add little clinical value. Their acoustic profile is stable and their control is good, so monitoring would mainly confirm the findings of clinical review. Applying it across an entire asthma register would be expensive without a proportionate clinical benefit.
Monitoring is most likely to alter management for patients with frequent exacerbations, for those whose reported control may not reflect their physiological status, and for those considering a step-down in therapy when it is genuinely uncertain whether control will persist. In these groups, acoustic data from the four to six weeks before a medication change can provide objective information unavailable from clinical review alone.
We also see possible value for occupational asthma and environmental triggers. Monitoring may show how wheeze episodes relate to workdays and rest days. This timing pattern can help assess whether a workplace trigger contributes to poor control, but interpretation requires clinical judgement and the pattern is not diagnostic by itself.
What Monitoring Can Sustain
Any monitoring method requiring active participation is likely to see adherence decline over time. Patients who are well most of the time may have little motivation to continue a daily routine. Every monitoring programme therefore needs to consider the effort required and whether patients can sustain it long enough to generate useful data.
The home acoustic monitoring we have designed is passive: during a defined overnight window, the sensor operates without patient action beyond wearing it. This differs substantially from peak flow diary programmes, which ask patients to make an effort twice daily and are notoriously difficult to maintain in real-world settings. Passive monitoring largely avoids adherence problems during overnight windows. The remaining challenge is correct, consistent sensor use, a simpler request than asking someone to perform a calibrated manoeuvre and record a reading every morning and evening.
Passive monitoring still involves some effort. Devices need maintenance and battery charging, and occasional troubleshooting is expected. For digitally engaged and motivated patients, this is minor friction. Older patients and those with limited digital literacy may need additional clinical team support during initial set-up.
The Appointment Still Matters: A Clarification
The title is intentionally provocative. We are not proposing that clinic appointments be abandoned, nor that clinical review is the wrong approach. The appointment is an essential, irreplaceable point for clinical assessment, medication review, and the therapeutic relationship. Our point is that treating it as the sole measurement point creates a sampling problem. A continuously varying condition cannot be fully characterised by intermittent snapshots, however carefully those snapshots are taken.
The appointment and continuous monitoring serve complementary purposes. The appointment supplies clinical context, the diagnostic framework, and the treatment decision. Monitoring supplies longitudinal information between appointments, helping to inform that decision. Neither replaces the other. With four weeks of acoustic data, a clinician can judge more precisely whether the current regimen is achieving adequate physiological control than with a questionnaire score alone. That added precision is what we offer, and we believe it is useful without overstating its role.
What Remains Unknown
We are clear about the current evidence gaps in asthma monitoring. Our enrolled asthma cohort in the pilot is smaller than our COPD cohort, and asthma is more heterogeneous, with more variable phenotypes. The acoustic features we track are biologically plausible, and pilot data is directionally encouraging. However, we have not established the relationship between acoustic findings and clinical outcomes in asthma with the same confidence we have in COPD. We are building that evidence base and will report findings as they mature. Clinicians considering monitoring for asthma patients should know that this application is at an earlier stage of evidence development than our COPD application.