Impact of Non-invasive Positive Pressure Ventilation on Cardiac Function and Echocardiographic Parameters
Condition: Heart Function Tests; Hemodynamics; Noninvasive Ventilation; Circulatory and Respiratory Physiological Phenomena
Study type: Interventional

Summary: 
      Cardiologists and intensive care specialists are confronted daily with mechanically
      ventilated patients exhibiting cardiac failure. It is of paramount importance to understand
      the effect of mechanical ventilation on cardiac function and to interpret echocardiographic
      findings correctly in order to provide the patient with the best possible treatment to
      support cardiac and circulatory function. Currently physicians interpret echocardiographic
      findings based on studies that were performed in spontaneously breathing patients. With this
      study, the investigators intend to contribute to the understanding of cardiac physiology in
      patients needing ventilatory support, especially they aim to provide the physiological basis
      for the interpretation of echocardiographic findings in order to improve medical support
      (e.g. fluid resuscitation, vasoactive drugs, ventilation strategy) of ventilated patients
      with impaired cardiovascular function.
    

Detailed description: 
      Background

      Mechanical ventilation (MV) is commonly used in intensive care units (ICU) to improve gas
      exchange and to reduce breathing effort. The need for MV is the single most prominent reason
      for admission to an intensive care unit, either for acute cardiac or respiratory failure,
      postoperative ventilation or other reasons. Its usefulness is not limited to critically ill
      patients but has also gained recognition in treating sleep-related breathing disorders. Soon
      after the introduction of MV to clinical practice its adverse hemodynamic effects were noted
      and have been studied ever since. It is now well accepted that MV, by applying external
      positive pressure in order to achieve tidal breathing, affects lung volume and intrathoracic
      pressure which in turn influence cardiac loading and function.

      Echocardiography is increasingly used in intensive care to evaluate hemodynamics and
      especially Doppler assessments of mitral inflow and annular tissue velocity to describe left
      ventricular (LV) diastolic function. There is a growing body of evidence stating that
      diastolic dysfunction is a key factor for weaning failure from MV, a clinical issue affecting
      up to one third of patients. Worsened diastolic LV filling under MV may decisively lower
      cardiac performance and cause hemodynamic instability especially in case of pre-existing
      diastolic dysfunction in patients with arterial hypertension, a disease with a high
      prevalence of 30-45% in the general population. So far, despite the extensive use of
      echocardiography in ventilated patients, the causative pathophysiological mechanisms
      underlying ventilation-induced changes of echocardiographic parameters used to determine
      diastolic LV function have never been thoroughly evaluated. Assessing diastolic function
      during MV is complex since Doppler derived surrogate parameters all depend on cardiac loading
      conditions and loading itself is inevitably coupled to MV. The question therefore arises
      whether echocardiography allows for detection of deteriorating LV diastolic function in terms
      of impaired intrinsic ventricular relaxation or LV stiffness or whether it primarily mirrors
      MV-induced loading alterations. It is important to differentiate if echocardiographic signs
      of diastolic dysfunction in the patient under MV are caused by changes in loading or a LV
      filling restraint since in case of hemodynamic instability the two scenarios would ask for
      different therapeutic measures. In case of a loading problem, pre- and afterload can be
      targeted using drugs or fluid resuscitation. If a MV-induced filling restraint is the
      predominant problem one may consider special ventilatory modes or even deep sedation and the
      use of muscle relaxants to minimize Pit.

      The basic concepts of heart-lung interactions under positive pressure ventilation make it
      conceivable that extrinsic pressure applied to the thorax and therefore, as explained later
      in more detail, to the heart may mimic diastolic dysfunction even in a totally healthy heart
      if assessed by echocardiography. Echocardiographic parameters to assess diastolic function
      have been evaluated against the gold standard - invasive LV pressure and volume measurements
      - in spontaneously breathing patients. Such an evaluation is lacking for the patient with
      ventilatory support and therefore the value of echocardiography for assessment of diastolic
      function under MV needs further clarification. The investigators intend to comparatively
      study cardiac and particularly left ventricular diastolic function in ventilated patients
      using both invasive and ultrasound methods.

      Objective

      The presented study will elucidate the influence of positive pressure ventilation on cardiac
      function in humans. Furthermore, the investigators aim to describe the changes of
      echocardiographic parameters under different levels of positive pressure ventilation and link
      these changes to the underlying pathophysiological alterations in hemodynamics induced by
      positive pressure ventilation.

      Methods

      Prospective single-centre study at the University Hospital Berne. 30 patients scheduled for
      an elective coronary angiogram will be included. During spontaneous breathing and two
      different levels of non-invasive PPV transthoracic echocardiography is performed while
      recording LV-pressure-volume loops using an impedance catheter. Simultaneously the pulmonary
      artery occlusion pressure, the right atrial pressure and the intrathoracic pressure are
      recorded using a pulmonary artery catheter and an oesophageal balloon respectively.
    

Intervention name(s): Non-invasive positive pressure ventilation
Intervention type(s): Other
Intervention description(s): Ventilatory support to alter intrathoracic pressure
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Cardiac Catheterization; Echocardiography; Noninvasive Ventilation; Positive-Pressure Respiration; Ventricular Function