We have previously reported (Am Rev Respir Dis 1988;138:675-678) that the resistance characteristics of six commonly used artificial noses (five hygroscopic condenser humidifiers HCH and one heat-moisture exchanger HME) can be best described by the power function: P = aV b , where P = pressure, V = flow, and a and b are constants determined by the characteristics of the device. The report also demonstrated that the resistance of the artificial noses increases with increasing weight caused by moisture accumulation in the inserts. We now provide tables that show the pressure drop measured across each of the six devices after periods of simulated use at various flowrates. The specification of drops in pressure allows the clinician to estimate the increased resistance that the patient may encounter. Such increases in resistance may cause clinically important increases in patient work during periods of spontaneous breathing as during intermittent mandatory ventilation or weaning trials.
Ploysongsang et al. (Sun,) studied this question.
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