The study involves a new device, called 'N-Tidal C', which uses a method that has the potential to predict when asthma attacks are about to happen. The device works by accurately measuring an individual's exhaled CO2 waveform. A person has to breathe in and out through the mouthpiece at their normal relaxed rate of breathing. It does not need any extra effort and therefore has considerable benefits over current breathing tests which require significant patient effort.

People with more severe asthma suffer from frequent asthma attacks that require regular hospital admissions. These attacks are difficult to predict and can devastate the lives of patients. A new tool is needed that can help to predict when an asthma attack is going to happen. This would help people recognise an attack earlier and allow treatment to be started sooner. This study will evaluate a new breathing monitor, to see whether it can detect asthma attacks. The study tests a new device, called 'N-Tidal C', which uses a method that has the potential to predict when attacks are about to happen. The investigators have found that people with asthma breathe out a gas, called carbon dioxide (CO2), in a different way to healthy people. The pattern of breathing out CO2 (the waveform) changes further when patients are having an attack of their disease. If patients could monitor their CO2, they may recognise when their asthma is getting worse, and take earlier action to avoid attacks getting out of hand and going to hospital.

Inclusion Criteria:

1. Male or Female, aged ≥7 years.
2. Confirmed clinician diagnosis of asthma by examination of medical records, and based on accepted national and/or international criteria e.g. BTS/SIGN, or GINA.
3. Moderate or Severe asthma (defined as BTS stage 2-5)
4. Poorly controlled asthma (defined as an ACQ score of ≥1)
5. Exacerbation prone asthma (defined as at least 1 asthma exacerbation requiring oral corticosteroid treatment in the last 12 months).
6. Providing written informed consent, or parental/guardian consent and participant assent in the case of a child

Exclusion Criteria:

1. Inability to understand or comply with study procedures and/or inability to give fully informed consent.
2. Known other lung, chest wall, neuromuscular, cardiac or other comorbidity or abnormality that would affect spirometry and/or other measures of lung function or TBCO2 measurements (including Breathing Pattern Disorder or Chronic Obstructive Pulmonary Disease).
3. Smokers (current or ex-smokers) with a >10 pack year history.
4. In the opinion of the clinical investigator, the participant would have difficulty completing the study procedures consistently (for example, difficulty holding the device, or long periods of absence/travel) throughout the study period.

Patients with poorly controlled asthma