Ventilator Trigger Sensing — Biomedical Instrumentation & Clinical Sensing

Abstract — Ventilator Trigger Sensing

Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/ ). The choice of a ventilator model for a single patient is usually based on parameters such as size (portability), presence or absence of battery and ventilatory modes. However, there are many details within each ventilator model about triggering, pressurisation or autotitration algorithms that may go unnoticed, but may be important or may justify some drawbacks that may occur during their use in individual patients. This review is intended to emphasize these differences. Guidance is also provided on the operation of autotitration algorithms, in which the ventilator is able to take decisions based on a measured or estimated parameter. It is important to know how they work and their potential sources of error. Current evidence on their use is also provided.

Sensor Interfacing & Analog Front-End Conditioning

Keywords: trigger, pressurization, ventilatory modes, hybrid modes, upper airway obstruction, expiratory flow limitation Figure 2: Diagnostic Medical Waveform & Bio-Potential Clinical Trace for Ventilator Trigger Sensing The precursors of home NIV date back to the polio epidemics in the 1950s, which gave rise to the first devices, mainly ventilators, using negative extrathoracic pressure as a method of rib cage expansion (iron lung) . However, these early models presented some important problems, such as the difficulty of transport and the possibility of side effects during their use, such as upper airway obstructive events. Later, in 1984, intermittent positive pressure was introduced for patients with muscular dystrophies and, since then, it has become the treatment of choice for both acute and chronic respiratory failure secondary to various diseases [ 2 , 3 ].

Bio-Signal Waveform Analysis & Simulation Findings

Over the last two decades, the performance and improvements of NIV devices have progressively evolved in available ventilatory modes, range of set parameters and monitoring capabilities. Classically, older devices were able to work in a single ventilation mode (volumetric or barometric) and were not equipped with monitoring capabilities beyond a rudimentary counter to control compliance. All positive pressure devices can be classified according to different criteria, as each country has its own legislation, which classifies ventilators according to the situation in which they are indicated for NIV (life support, need for a battery, etc.) . From a more generic perspective, the most agreed classification classifies them as bi-level, intermediate respiratory care ventilators and ICU ventilators. Bi-level ventilators operate with a turbine system, single limb circuit and intentional leakage. They are usually transportable, have a good number of alarms and some have an internal battery. They are mainly used in chronic ventilation. ICU ventilators were primarily intended for invasive ventilation, although more modern ventilators have added “NIV modes”, which include a leak compensation system. They are usually operated with dual-limb systems and the operating mechanism can be either piston or compressor driven. They are equipped with a sophisticated alarm system and their use is restricted to critical care units. Finally, intermediate-care ventilators fall between the two categories mentioned above. They are usually equipped with an internal battery and are multifunctional, being used from the patient’s home to medical transport or emergency units [ 5 , 6 ].

Scope & Clinical Applications

• Real-time multi-parameter vital signs telemetry (ECG, Heart Rate, SpO2, Temperature, Respiration)
• Low-noise Analog Front-End (AFE) conditioning with active Driven Right Leg (DRL) 50 Hz cancellation
• Digital signal processing in MATLAB: Pan-Tompkins QRS detection, FIR/IIR notch, and Continuous Wavelet Transforms
• Finite element tissue bio-electromagnetics and orthopedic mechanical simulations in COMSOL & ANSYS
• Complete Arduino firmware .INO sketches, circuit schematics, and university dissertation reports