It can be seen that the HEV reacts in less than 100 ms, meaning that the patient will feel imperceptible delay. For optimum patient comfort it is important that the ventilator has a rapid response to the patient effort, followed by a sharp and precise pressure rise. For each patient a more detailed view is shown of the start of inspiration. It can be seen that the ventilator responds to the patient demand, keeping very good synchronicity.

In this mode the inspiration is triggered by the patient and the expiration is patient cycled the expiration is triggered when the flow drops to a fraction of the peak value, where this fraction is defined by the clinician. Three different sets of curves are shown, in the case where the patient is breathing with a weak, normal, or strong effort. The second image shows the performance in Pressure Support Mode. HEV ventilator performance in Pressure Control Mode The quality of the patient treatment, especially for sedated modes, depends on a sharp and precise pressure rise, exactly as provided by HEV. The variations in the shapes of the curves in the patient lungs are the consequence of the different resistance and compliance. For each patient the target pressure is rapidly attained and the flow and volume show the expected shapes. For each patient the pressure is shown as measured inside the ventilator, at the patient airway, and inside the patient lung, the air flow is shown, and the volume of air entering the lung. The breathing curves are shown for three different patients, highlighting high and low lung compliance and high and low resistance. In this mode the start of breath can be triggered by machine or by the patient and the end of the inspiration is controlled by the ventilator, using parameters entered by the clinician. Combining perfusion lung scanning with clinical assessment helps to restrict the need for angiography to a minority of patients with suspected PE.We show first the performance in Pressure Control Mode. Results of a recent prospective study indicate that accurate diagnosis or exclusion of PE is possible with perfusion lung scanning alone (without ventilation imaging).

However, a single negative venous study result does not permit to rule out PE in patients with non-diagnostic ventilation/perfusion scans. Under these circumstances, documentation of deep vein thrombosis by non-invasive leg testing warrants anticoagulation without the need for angiography. Ventilation/perfusion abnormalities other than those of the high probability scan should be regarded as non-diagnostic. Yet, only a minority of patients with confirmed PE have high probability ventilation/perfusion scans. A high probability ventilation/perfusion scan (segmental or greater perfusion defects with normal ventilation) warrants the institution of anticoagulant therapy especially when paired with high clinical suspicion of PE. Ventilation/perfusion lung scanning is, at present, the most widely used non-invasive diagnostic test for PE. Non-invasive diagnostic strategies have therefore been developed to forego pulmonary angiography in patients suspected of having PE. Pulmonary angiography is still the reference standard for diagnosing PE but it is costly, invasive and not readily available. Pulmonary embolism (PE) remains a challenging diagnostic problem because it mimics other cardiopulmonary disorders.

Diagnostic ventilation cenon