Biomedical Engineering Reference
In-Depth Information
TABLE 9-2
Specifications of Five Negative-Pressure Pumps
Variable
NEV-100
Negavent
Maxivent
Newmarket
CCP-001
Breaths/min
4 to 60
1 to 50
5.6 to 25
6 to 30
10 to 30
Inspire: Expire ratio
1:29 to 1:0.6
1:99 to 1:0.2
1:1.2 fixed
1:1.5 to 1:0.7
1:1.5 to 1:0.7
−
94 cmH
2
O
Max negative pressure
−
89 cmH
2
O
-74 cmH
2
O
-49 cmH
2
O
-38 cmH
2
O
Max positive pressure
30 cmH
2
O
—
70 cmH
2
O
51 cmH
2
O
41 cmH
2
O
Max flow
845 L/min
944 L/min
630 L/min
780 L/min
660 L/min
Weight
14.5 kg
14.5 kg
16.5 kg
34.8 kg
14.7 kg
FIGURE 9-35
Experimental setup
to measure
negative-pressure
pump
characteristics.
[Adapted from
(Smith, King et al.,
1995).]
In an interesting paper, the performances of five different pumps were compared using
a mechanical lung simulator and pressure and flow measurement sensors (Smith, King
et al., 1995). The five pumps were the NEV-100, Negavent respirator DA-1, Thompson
Maxivent, the CCP-001, and Newmarket device, and their specifications are listed in
Table 9-2.
In the experimental setup shown in Figure 9-35, a sealed chamber with an adjustable
leak houses the lung simulator. A pressure sensor connected to the chamber monitors
the internal pressure. The output of the lung simulator (the mouth) was open to the at-
mosphere and was instrumented using a pneumotachograph to measure air flow. The
negative-pressure pumps in the comparison were fitted to the chamber in turn, and their
characteristics were logged and later analyzed.
Analysis showed that the selected inspire:expire ratio was within 1% for all of the
pumps but that the variation in peak negative pressure was larger, with the NEV-100 being
the most accurate at -29.8 to -31.2 cmH
2
O for a 30 cmH
2
O set point and the Maxivent
the least accurate at -29.7 to -32.8 cmH
2
O.
Most interesting, however, was the variation in the pressure during the pump cycle.
The NEV-100 and Negavent produced square waves over the inspiratory time of 1.33 s,
whereas the CCP-01 and Newmarket pumps approximated a half-sine wave, as shown in
Figure 9-36.
Because the total inspired volume is proportional to the time integral of the negative
pressure if the inspiratory time is reasonably short, the pumps that produced half-sine
waveforms would generate a smaller tidal volume. This effect is illustrated in Figure 9-37.
