Airflow mechanical ventilation

Chow, W. K., and W. Y. Fung. 1997. Experimental studies on the airflow characreri.stics of spaces with mechanical ventilation. ASHRAE Transactions, p. 1. 

The airflow rate infiltrating and exfiltrating through each air leakage pass, Q , due to the combined effect of wind, stack, and mechanical ventilation system perfotmance can be calculated ftom the mass balance equation... 

The airflow rate Q, for each air leakage path is expressed with Eqs. (7.237), (7.242), and (7.243) using the infotmation on effective leakage area, CjA, and a pressure difference across the path. The total pressure acting on an opening from the outside is the sum of the pressure due to wind, gravity forces, and mechanical ventilation performance, and the static pressure inside the building results from Eq. (7.244). 

Assume the use of mechanical ventilation with full mixing ventilation in the room, and calculate a rough estimate of ventilation airflow found by assuming dilution of contaminants released to the room air to one-third of the TLV level given for the substance in question. 

Proper design and construction of a local ventilation system must account for hood flow rate, contaminant generation process and rate, and the generated flow rate of contaminated air. Thus, knowledge about airflow mechanics, process performance, and the contaminant source is essential. The descriptions of different sources are included in Chapter 7 and here only short descripiions are included as necessary to identify different processes and source types. 

When air flows at a certain rate through the space, energy is transported in relation to the difference between supply and extract air temperature. Such airflow can be induced by natural or mechanical ventilation. See Section 11.5 on the interaction between naturally induced airflows and the thermal behav ior of the room. 

Noninvasive positive-pressure ventilation (NPPV) provides ventilatory support with oxygen and pressurized airflow using a face or nasal mask with a tight seal but without endotracheal intubation. In patients with acute respiratory failure due to COPD exacerbations, NPPV was associated with lower mortality, lower intubation rates, shorter hospital stays, and greater improvements in serum pH in 1 hour compared with usual care. Use of NPPV reduces the complications that often arise with invasive mechanical ventilation. NPPV is not appropriate for patients with altered mental status, severe acidosis, respiratory arrest, or cardiovascular instability. 

Natural ventilation can be adequate provided there are sufficient vents or louvers at the ceiling or floor level. An effective design will ensure that the airflow either sweeps across the floor or ceiling continuously and adequate outside make-up air is provided. The discharge should be directed outside and away from any air inlets, other openings, and equipment such as compressors. If adequate natural ventilation cannot be provided a mechanical ventilation system should be used. Mechanical ventilation systems for applications involving transfer of flammable liquids typically have a capacity of 0.25 to 2 cfm/ft2 (0.075-0.60 m3/min/m2) and higher in trenches, sumps, or other collection areas. 

Main fan A mechanical ventilator installed at the surface operates by either exhausting or blowing to induce airflow through the mine roadways and workings. 

Pepe PE, Marini JJ. Occult positive end-expiratory pressure in mechanically ventilated patients with airflow obstruction the auto-PEEP effect. Am Rev Respir Dis 1982 126 166-170. 

Three usually seen airflow, including sinusoidal, square, and descending wave, in mechanical ventilation are modeled as the inspiratory flow pattern during CMV mode and volume-targeted mechanical ventilation in this paper. Instead of optimizing the pressure profile, the airflows waveforms will be optimized in current study through the optimal respiratory control model. 

In some cases, the ventilation process in the room can be simplified and mechanisms of air and contaminant movement under the influence of each of the above factors can be described using simplified theoretical principles of fluid mechanics, empirical data, and observations from numerous research studies. In general, the ventilation process in a room is complex and different factors have a joint effect on airflow patterns and characteristics, in continued spaces and in industrial buildings particularly. 

By definition, a powered ventilation system includes a mechanical means of inducing airflow using an external... 

In advanced COPD, airflow obstruction, damaged bronchioles and alveoli, and pulmonary vascular abnormalities lead to impaired gas exchange. This results in hypoxemia and eventually hypercapnia. Hypoxemia is initially present only during exercise but occurs at rest as the disease progresses. Inequality in the ventilation/perfusion ratio (VAQ) is the major mechanism behind hypoxemia in COPD. 

Ventilation-perfusion mismatch leads to hypoxemia. Reduced ventilation caused by obstructed airflow or reduced perfusion caused by obstructed blood flow leads to impaired gas exchange. Interestingly, each of these conditions is minimized by local control mechanisms that attempt to match airflow and blood flow in a given lung unit. 

Secretion clearance is addressed in detail elsewhere in the text. However, physical therapy and careful hydration are the cornerstones of management. Mucupurulent secretions are often noted in acute respiratory failure. Administration of acetylcysteine 600 mg/day will decrease sputum viscosity hut its value in NIV patients has been less well studied. In patients with NMD, manually assisted coughing, air stacking, and mechanical devices can all be used in patients with a facial mask. On rare occasions, bronchial lavage under local anesthesia can be carried out during NIV. Secretion clearance reduces the ventilation pressures required to overcome the impedance to airflow. 

Keywords— Ventilator airflow, optimization respiratory mechanics. 

Comparative Studies of the Optimal Airflow Waveforms and Ventilation Settings under Respiratory Mechanical Loadings... 

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