The aim of this study is to collect capnometric (tidal breathing CO2) data using TidalSense's N-Tidal C Data Collector Device. The data collected will be examined for correlation with currently accepted assessment techniques for COPD (spirometry, vital signs and pulse oximetry) and the patient's clinical condition (stable, worsening, improving). The patient numbers and study duration have been determined by power calculations to provide a statistically significant sample size, based on expected number of exacerbations (mild, moderate and severe) from the patient cohort. The data will also be examined to assess the predictive possibility of a non-invasive self-care personal CO2 monitoring device to identify COPD exacerbations.

Study Design: This is an uncontrolled, non-randomised, un-blinded longitudinal observational data collection study with the N-Tidal C Data Collector Device in patients with COPD.

Patients will be identified from the Cambridge COPD Centre. This unit sees patients following emergency admissions, GP referrals and has a regional referral base for complex COPD. Patients' medical records will be reviewed and classified according to GOLD criteria. Those patients who are classified as COPD with appropriate inclusion criteria (below) will be invited to participate. Patients who give informed consent will be screened for the study.

The N-Tidal C Data Collector Device will be explained to the patients and they will be trained how to use it. All patients will complete a short daily diary record.

Patients will undergo a clinical assessment of COPD during screening at Addenbrooke's Hospital. All patients will be assessed five times: at the start, 2 weeks, 10 weeks, 18 weeks and at the end of the 26 week study period. A brief follow-up telephone review will be conducted approximately 2 weeks after the end of the monitoring period. At each assessment, capnometry measurements will be taken in addition to vital signs and pulse oximetry. The study will not interfere with routine management of the patient's condition.

Inclusion Criteria:

1. Aged 40 years and over.
2. Diagnosis of COPD (Primary) and at least one moderate exacerbation within 12 months of the start of the study period.
3. Able to provide signed informed consent.

Exclusion Criteria:

1. Patients who, in the opinion of the investigator, are unlikely to comply with the requirements of the study, use the device correctly or keep the diary records;
2. Diagnosis of neuromuscular disorders or Kyphoscoliosis;
3. Diagnosis of other Respiratory disorders that, in the opinion of the investigator, would impact the conduct of the study e.g. clinically significant bronchiectasis, asthma;
4. Patients who have experienced an exacerbation of their COPD that has required treatment with antibiotics and/or oral corticosteroids within 2 weeks prior to the study start.

Patients with moderate-to-severe chronic obstructive pulmonary disease (COPD) will be identified from the Cambridge COPD Centre.

Those patients with COPD satisfying the inclusion criteria will be invited to participate.

The majority of these will be GOLD D.