Comparison of pulsed versus continuous oxygen delivery using realistic adult nasal airway replicas

Figures & data

Table 1 Airway replica volumes and surface areas for 15 adult nasal airway replicas

Subject	Sex	Age (years)	Volume (cm^3)	Surface area (cm^2)
MRI2	F	–	44.6	287
MRI5	F	–	35.9	235
MRI6	M	–	50.1	313
MRI8	M	–	47.3	289
MRI9	M	–	45.3	250
CT1	M	60	60.0	343
CT2	F	50	73.1	315
CT3	M	57	59.2	320
CT4	M	54	71.9	349
CT5	M	60	50.1	280
CT6	F	72	59.1	321
CT7	M	62	56.3	308
CT8	M	63	61.9	326
CT9	M	27	48.1	276
CT10	F	56	53.2	265

Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging; M, male; F, female.

Figure 1 Solid 3D nose–throat airways of the 15 replicas tested in the present study.

Note: The top row displays airways derived from MRI, while the bottom two rows display airways derived from CT images.
Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging.

Figure 2 Schematic of experimental apparatus.

Note: Arrows indicate direction of oxygen flow.

Table 2 Breathing parameters of representative breathing profiles for COPD patients at rest, doing light exercise, and while asleep

	Rest	Exercise	Sleep
Tidal volume, VT (mL)	640	800	520
Inspiratory time, TI (s)	1.20	0.96	1.79
Expiratory time, TE (s)	2.33	1.77	2.93
Breathing frequency, f (breaths/min)	17	22	13

Abbreviation: COPD, chronic obstructive pulmonary disease.

Table 3 SimplyGo oxygen pulse characteristics at pulse flow setting numbers of 2.0 and 6.0 using various breathing frequencies

Breath frequency	f=13 breaths/min			f=17 breaths/min			f=22 breaths/min
Pulse setting	Pulse volume (mL)	Pulse delay (ms)	Pulse duration (ms)	Pulse volume (mL)	Pulse delay (ms)	Pulse duration (ms)	Pulse volume (mL)	Pulse delay (ms)	Pulse duration (ms)
Pulse mode 2.0	23.8	110	291	23.8	114	290	22.7	111	320
Pulse mode 6.0	68.7	110	479	68.8	113	480	66.8	109	613
Sleep mode 2.0	28.9	109	582	22.2	110	449	38.2	109	764
Sleep mode 6.0	85.7	108	613	66.5	103	479	112.5	104	793

Figure 3 Example of oxygen mole fraction and flow rate waveforms indicating (A) steady flow oxygen delivery, (B) complete pulse delivery, and (C) incomplete pulse delivery.

Notes: Waveforms were selected from experiments conducted using subject CT7 with the sleep breathing pattern (A) and (C), and using subject CT9 with the rest breathing pattern (B). Positive flow rates indicate inspiration; negative flow rates indicate expiration. Numbers indicate points of interest in the oxygen waveform: (1) maximum inspiratory oxygen fraction; (2) minimum inspiratory oxygen fraction; (3) oxygen fraction changing through onset of exhalation; (4) oxygen fraction rising/falling to end-expiratory value.

Table 4 Number of breathing replicas indicating incomplete pulse delivery out of the total number of replicas used to calculate volume-averaged fraction of inspired oxygen (F_iO₂) at each setting/breathing pattern combination

POC setting	Rest	Exercise	Sleep
Pulse mode 2.0	0/15	0/15	2/12
Pulse mode 6.0	1/15	2/15	3/11
Sleep mode 2.0	N/A	N/A	5/14
Sleep mode 6.0	N/A	N/A	5/14

Abbreviations: N/A, not applicable; POC, portable oxygen concentrator.

Figure 4 Comparison of volume-averaged F_iO₂ at SF 2.0 L/min and PF setting number 2.0, averaged over n different airway replicas, measured using five successive breaths per replica.

Notes: For exercise and rest breathing patterns, n=15. For the sleep breathing pattern combined with pulse mode, n=12; with sleep mode, n=14. Error bars indicate one standard deviation.

Abbreviations: F_iO₂, fraction of inspired oxygen; SF, steady flow; PF, pulse flow.

Figure 5 Comparison of volume-averaged F_iO₂ at SF 6.0 L/min and PF setting number 6.0, averaged over n different airway replicas, measured using five successive breaths per replica.

Notes: For exercise and rest breathing patterns, n=15. For the sleep breathing pattern combined with pulse mode, n=11; with sleep mode, n=14. Error bars indicate one standard deviation.
Abbreviations: F_iO₂, fraction of inspired oxygen; SF, steady flow; PF, pulse flow.

Figure 6 Pressure drop measured at the cannula as a function of inspiratory flow rate, averaged over three measurements for all 5 MRI subjects.

Note: Error bars represent one standard deviation.
Abbreviations: CT, computed tomography; MRI, magnetic resonance imaging.

Figure 7 Comparison of volume-averaged F_iO₂ estimated from airway experiments and F_iO₂ predicted using pulse characteristics.

Notes: Airway experiment F_iO₂ values were averaged over n airway replicas, measured using five successive breaths per replica. For all experiments with exercise and rest breathing patterns, n=15. For the sleep breathing pattern combined with pulse mode setting number 2.0, n=12; with pulse mode setting number 6.0, n=11; with sleep mode setting numbers 2.0 and 6.0, n=14. Error bars indicate one standard deviation.
Abbreviation: F_iO₂, fraction of inspired oxygen.