To assess patients with hypercapnic respiratory failure using echocardiography,cardiac output measurements and markers of neural respiratory drive (EMGpara) prior to, during and after non-invasive ventilation (NIV) initiation, and to follow the patients for 3 months. The investigators hypothesize that the improvement in cardiac function and/or respiratory mechanics over time are associated with ongoing improvements in oxygenation, quality of life and exercise capacity.

Respiratory failure is characterized by the incapacity of the respiratory system to maintain the normal arterial blood gas homeostasis. Specifically, the overlap of hypoxaemia and hypercapnia (PaCO2 >6 kPa) is referred to as Hypercapnic Respiratory Failure (HRF). HRF is one of the most common causes for hospital admission with high re-admission rates, therefore constitute a major burden on healthcare systems. Non Invasive Ventilation (NIV) is a well established treatment in patients with hypercapnic respiratory failure who frequently suffer with associated pulmonary hypertension (PH). NIV helps to increase arterial oxygenation and reduces hypercapnia. It is used in patients with hypercapnic respiratory failure caused by Obesity Hypoventilation Syndrome (OHS). The associated degree of PH can lead to an increased afterload of the right ventricle (RV) that causes progressive remodelling of the right heart. RV dysfunction is correlated with a reduced long term prognosis in respiratory conditions. In literature NIV is shown as effective method to treat acute hypercapnic respiratory failure in OHS.

It has not been described how NIV impacts on cardiac function and NRD in OHS.

Inclusion Criteria:

• Confirmed diagnosis of OHS and Overlap Syndrome
• Hypercapnic respiratory failure with the need to commence NIV
• Expected to remain an inpatient for ≥ 24 hours
• Age ≥ 18 and <80 years
• BMI >30 kg/m2
• Confirmed sleep-disordered breathing
• Able to give informed consent to participation in the evaluation study
• Clinically stable without exacerbations for ≥ 6 weeks

Exclusion Criteria:

• Patients established on NIV
• Inability to tolerate NIV (< 4 hours usage at during hospital titration)
• Contraindication to NIV
• Requirement for immediate invasive mechanical ventilation at admission or any other acute critical illness
• Acute infective exacerbation
• Presence of other acute pathology or critical illness (such as pulmonary embolism)
• Presence of acute or chronic Left ventricular Cardiac Failure
• Significant Kidney or Liver disease
• Significant Anaemia
• History of Pulmonary Embolism in the previous 2 years
• Presence of cardiac congenital disease
• Presence of Primary Pulmonary Hypertension
• Presence of other severe medical problem, e.g. cancer and systemic connective tissue disease and vasculitides
• Pregnancy
• Psychological and social factors that would impair compliance with the evaluation

Patients presenting with a confirmed diagnosis of OHS and Overlap Syndrome and hypercapnic respiratory failure with the clinical intervention to commence on NIV will be invited to participate in the trial.