Table 3.

Comparison of temperature (T) and absolute humidity (AH) of Heat and Moisture Exchanger (HME) performance indicators between laboratory values as declared by the manufacturer and in vivo measured values. All values are expressed as laboratory values minus in vivo values and were measured at a tidal volume of 500 ml.

HME performance indicators and ventilatory parameters	Laboratory – in vivo t0	Laboratory – in vivo t1	Laboratory – in vivo t2	Laboratory values [15, 16, 19, 20]
Load T (°C)	+ 3.4	+ 3.7	+ 3.7	37.0
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Load AH (mg/l)	+ 6.9	+ 7.4	+ 7.6	43.8
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Return T (efficacy) (°C)	+ 0.8	+ 1.2	+ 1.3	32.3
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Return AH (efficacy) (mg/l)	+ 1.3	+ 2.0	+ 2.2	33.6
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Thermal differential (efficiency) (°C)	+ 2.5	+ 2.5	+ 2.4	4.7
	(p < 0.01)	(p < 0.01)	(p < 0.01)
AH yield (efficiency)	- 0.12	- 0.12	- 0.12	0.77
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Input T (°C)	- 2.9	- 2.2	- 2.5	23.0
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Input AH (mg/l)	- 0.2	- 0.3	- 0.2	1.0
	(p = 0.03)	(p < 0.01)	(p = 0.049)
Loss T (°C)	- 3.0	- 2.3	- 2.5	23.0
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Loss AH (mg/l)	- 0.3	- 0.9	- 0.6	6.0
	(p = 0.10)	(p <0.01)	(p =0.16)
Tidal volume (ml)	+ 57	+ 69	+ 75	500
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Respiratory rate (min−1)	- 3	- 3	- 3	15
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Minute ventilation (l/min)	+ 0.04	- 0.02	+ 0.08	7.5
	(p = 0.91)	(p = 0.96)	(p = 0.84)
I:E ratio	+ 0.47	+ 0.41	+ 0.42	1
	(p < 0.01)	(p < 0.01)	(p < 0.01)
Room temperature (°C)	- 1.0	- 0.3	- 0.7	23.0
	(p < 0.01)	(p = 0.63)	(p < 0.01)
Patient temperature (°C)	+ 0.4	+ 0.1	+ 0.3	37.0
	(p < 0.01)	(p = 0.12)	(p < 0.01)