Table 2. Indirect evidence study characteristics and findings.

L, left; R, right

Author, year, country	Study design	Population	Intervention	Control	Outcome	Findings on our outcomes, as presented in the article
Ozturk et al., 2014, Turkey [20]	Observational	15 patients (mean age=28.8; 9 female) at least 18 years of age with no nasal symptoms within 3 weeks, and not pregnant.	Nasal dorsal skin cooling using two ice packs applied to left (L) and right (R) side of nose for 10 minutes (n=15).	No application, baseline	Cross-sectional area (cm2) and nasal cavity volume (cm3) via acoustic rhinometry	Mean values for the sum of the L and R first minimal cross-sectional area and second minimal cross-sectional area revealed no statistical differences, for either parameter at any between any intervals. Means values for nasal cavity volume revealed no statistical differences, for any parameter, between any intervals.
Porter et al., 1991, United Kingdom [21]	Cross-over, Randomized	16 healthy subjects (mean age=32, range 25-40) with no history of the nasal disease, previous nasal surgery or symptoms, and a normal rheoscopic examination.	Ice contained with a surgical glove applied to forehead or mouth for 3 minutes each (n=16).	Same, but at body temperature for 3 minutes each.	Nasal mucosal blood flow, measured in flux (velocity and concentration of the moving blood cells)	Oral ice packs produced a significant decrease in nasal mucosal blood flow (p<0.05, average decrease=23% {standard error=5.9}) compared to control (average decrease=5%; standard error not calculated/provided). Oral ice packs produced a fall in flux in 9 of 16 (56%) subjects, a rise in 1 (6%), and 6 (37%) experienced no change. Ice packs to the forehead produced a fall in flux in 1 of 16 (6%) subjects, a rise in 1 (6%).
Porter, 1991, United Kingdom [22]	Cross-over, Randomized	13 healthy subjects (mean age=30, range 25-40) with no nasal disease or treatment.	(a) Ice pack wrapped in paper toweling held to the forehead by subject for 15 minutes. (b) Ice cubes sucked into the mouth for 15 minutes. (c) Combination of (a) and (b) for 15 minutes.	No application, baseline	Nasal submucosal temperature (°C)	A significant difference between the nasal submucosal temperature ice pack to the forehead (a) compared to ice cubs in the mouth (b) (p=.0.026), favoring ice cubes alone. A significant difference between nasal submucosal temperature in the ice pack to the forehead compared to the combined stimulus (c) (p=.0.006), favoring combined stimulus. In all subjects (n=13, 100%) ice cubes in the mouth (b) produced a lower nasal submucosal temperature. The ice pack to the forehead (a) produced a decrease in nasal mucosal temperature in 7 of 13 (53%) subjects.
Scheibe et al., 2006, Germany [23]	Cross-over	15 healthy subjects (range 25-40, 7 female) with no reported breathing difficulties, acute nasal allergies, or acute rhinitis; nasal endoscopy by an ENT specialist revealed no pathology.	Ice collar (4°C) placed onto neck region for 10 minutes.	No application, baseline	Nasal blood volume via optical rhinometry (measured in nm) for the whole nose and at the septum, randomized.	A significant (p<0.01) decrease in nasal blood volume for regional measurements at the septum. Decrease in nasal blood volume at nasal septum was, on average, observed after approximately 2 minutes t1=111 sec ± 73 sec); decrease reached its maximum after approximately 6 minutes (t2=337 sec ± 119 sec).
Teymoortash et al., 2003, Germany [24]	Cross-over	56 healthy subjects (mean age=30, range 17-48) with normal rhinoscopy and no history of nasal allergy or acute or recurrent symptoms of rhinitis.	Ice pack applied all-round the neck for 5 minutes.	No application, baseline	Nasal mucosal microcirculatory blood flow via laser Doppler flowmetry, nasal mucosal blood content (indirectly via conventional computer-aided anterior rhinomanometry by measuring alternations in nasal airflow and airway patency).	Following cold application, nasal mucosal blood flow decreased from 1368.8 ± 927.9 to 1130.5 ± 792.2), (p=0.11). Total nasal inspiratory airflow before the application was 513.9±190.4 cm3/s, after exposure to cold 471.5±164.6 cm3/s (p=0.08). Total nasal expiratory airflow before the application was 474.2±211.7 cm3/s, after exposure to cold 443.1±162.4 cm3/s (p=0.30).
Yamagiwa et al., 1990, Denmark [25]	Cross-over	10 healthy subjects (mean age=21±11.0, range 24-54) with no significant complaints or rhinoscopically overt nasal abnormalities.	(a) Feet cooling (both) in large tub (0-4°C) immersed 30 cm from heel for 5 minutes, (n=10). (b) One hand and forearm cooling in a bucket (0-4°C) immersed to around 23 cm from the middle fingertip for 5 minutes (n=9).	No application, baseline	Nasal cavity volume (mL) rhinometry for L and R cavities.	Foot cooling arm. In the exposure period, nasal airway volume was significantly higher than preexposure values in 4 of 10 (40%) subjects, none showed significantly lower values. Hand cooling arm. In the exposure period, nasal airway volume was significantly higher than preexposure values in 1 of 9 (11%) of subjects, lower in 2 of 9 (22%), and no difference in 6 of 9 (66%)