This study demonstrates that the efficiency of nasal oxygen therapy is improved by early delivery of the inspiratory pulse; the Sa02 increases progressively as the delay between the inspiratory signal and the delivery of the pulse is shortened. In contrast, delays in delivery of transtracheal pulses up to 164 ms has no effect on Sa02. The Sa02 achieved with the 164 ms delay is not different from the Sa02 derived from pre- inspiratory triggered pulse.
The discrepancy in the effect of pulse delay between transtracheal and nasal delivery can be analyzed using the volume-time curve of the breath cycle (Fig 3). The volume-time curve (I:E = 1:2) is an approximation of the breath cycle of a COPD patient and is typical of Respitrace patterns in this study. A patient with a breath rate of 20 per minute will have a 3-s respiratory cycle comprised of a 1-s inspiration and a 2-s expiration. Approximately the first two thirds of the inspired volume will reach the alveoli and potentially contribute to gas exchange, while the end-inspiratory one third will fill the anatomic dead space. Since the end- inspiratory portion of the curve flattens, approximately one half of inspiratory time is devoted to dead space filling, leaving the remaining half (0.5 s) available for alveolar filling. cialis super active
FIGURE 3. The volume-time curve. This is an approximation of the respiratory cycle of a patient with COPD. From this model, it is estimated that a patient breathing a 3-s breath cycle may benefit only during the first 0.5 s of inspiration.
In the Oxymatic, the delay between the onset of inspiration and the delivery pulse is about 30 ms. With a pulse duration of 150 ms, the fastest pulse delivery time is about 180 ms. This interval is well within the inspiratory “window” of 500 ms. Considering that the longest delay setting was 164 ms, the longest interval between the beginning of inhalation and the end of the oxygen pulse would be about 344 ms. Even this rather lengthy delay is well within the 500 ms of non- dead space inhalation. However, oxygen delivered into the nasal vestibule must mix with the gas already occupying the upper airway and the tracheobronchial tree; moreover there is some oxygen loss into the atmosphere through the nose and mouth. Thus, the rapid response times are important in nasal oxygen therapy.
In contrast, transtracheal delivery occurs earlier than nasal delivery as the dead space of the upper airway is bypassed. Furthermore, oxygen loss is minimized because the oxygen pulse is delivered directly into the trachea. In pulsed transtracheal oxygen therapy, delays of 164 ms do not decrease efficiency.
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There are several commercially available oxygen pulsing devices, most of which have reported oxygen savings of between 2:1 and 3:1 over continuous flow oxygen delivery. The Oxymatic has been demonstrated to have a 7:1 savings when compared with continuous flow during both rest and exercise, with some data covering longer time spans. The short 150-ms pulse duration and a rapid response of 30 ms might explain its greater efficiency. However, this study suggests that pulsed devices, which are less efficient for nasal oxygen delivery, may be just as efficacious when delivered transtracheally. In fact, we previously determined that there was little difference in the efficiency of pulsed TTO therapy when the Oxymatic was compared with the Pulsair (Cry02 Corp, Florida).