Mean inspiratory flow

Several lines of evidence support the likelihood that increased mechanical load contributes to LTMV dependence. First, mechanical load is greater in ventilator-dependent patients than in non-ventilator-dependent patients (41,43). Second, progression to successful weaning has been associated with improvement in work of breathing per liter of minute ventilation, which is a function of compliance, resistance, tidal volume, and minute ventilation (48). Third, the mean inspiratory flow produced for a given level of neuromuscular inspiratory drive is lower in LTMV-dependent patients than in patients who are successfully weaned after a period of PMV (Fig. 3) (41,43). Lastly, effective inspiratory impedance correlates with inspiratory pressure output (41). This correlation suggests worse load-capacity balance in patients who are dependent on LTMV than in patients who are successfully weaned after a period of PMV (41). 

Mean airstream velocity diminishes as inspiratory flow moves toward the lung parenchyma because of the rapid increase in total cross-sectional area. The largest increases in area occur in the distal bronchioles and pulmonary airways, causing u to approach zero because... 

Deposition experiments were carried out in replicate hollow casts of the upper airways or a human tracheobronchial tree using 0.2, 0.15 and 0.04 ym diameter particles and cyclic inspiratory flow rates of approximately 1 8 and 34 liters per minute (L/min) (see Table I). The replicates were produced from a single solid master airway cast prepared from the lungs of 34 year old male. The airway dimensions of the cast corresponded closely with the population mean of eight adult males as reported by Nikiforov and Schlesinger (1985). The airway diameters are somewhat larger and... 

Air-pressure-driven active devices. Air-pressure-driven aerosolization is the concept employed in a number of devices currently in different stages of development with drugs for local or systemic action. These devices rely on a small patient-operated air pump. Air is compressed by mechanical means (piston or bellows) and is released on the external trigger given by the patient s inspiratory cycle. Because of the use of this air pump, these devices have an active aerosolization mechanism and are assumed to be less flow-rate-dependent than passive DPI devices. 

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