Table 1.

Descriptive characteristics of experimental studies on air ions and respiratory outcome measures

Study author and year	Study objective	Study design	Study population	Sample size	Primary outcomes of interest
Infants
[8]	Measure effects of ion exposure to bronchial asthma subjects and comparison to conventional treatment.	Double-blind	Infant patients aged 2–12 months with bronchial asthma.	19 (13 with bronchial asthma and 6 without asthma); 19 additional subjects at different hospital with same diagnosis.	Respiratory rate and scored degree of bronchospasm severity.
Child-adolescent (up to 20)
[6]	Measure therapeutic effect of negative air ions on exercise-or inhaled histamine-induced asthma.	Double-blind randomized	Asthmatic children aged 10–20 yrs recruited from patient population.	11 (for exercise challenge); 9 (for histamine challenge)	FEV1
[15]	Measure efficacy of negative ion treatment for asthma patients.	Double-blind	Asthmatic male students aged 8.8 to 12.6 years at a special school for asthmatics	24	Lung function (whole-body plethysmorgraph and nitrogen washout)
[16]	Measure respiratory effects of positive ions on asthmatic children under physical exertion; follow-up study from [6].	Double-blind randomized	Asthmatic children aged 9–15 yrs recruited from patient population.	12; 7 M and 5 F	Lung function (FEV1 and minute ventilation), oxygen consumption, heart rate, and respiratory heat loss.
[14]	Measure effects of air ions on concentration of airborne dust mite allergen in air and asthmatics	Double-blind crossover	Asthmatic children aged 3–11 yrs recruited from clinic's patient population who's home environments have elevated dust mite allergen air concentration.	20	Peak expiratory flow rate (PEFR) morning and night; self-reported symptom scores; self-medication scores; air concentration of Der p I allergen.
Overlapping child-adult
[7]	Measure efficacy of negative ion treatment for asthma patients.	Subject-blind	Asthma patients aged 10–54 yrs; Male=6, Female=1.	7	Peak expiratory flow rate (PEFR); self-reported symptoms.
[17]	Measure efficacy of negative ion treatment for patients suffering from respiratory symptoms	N.S.	Patients male and female aged 7 to 59 years	27	Relief from hay fever, bronchial asthma, neurogenic asthma, acute rhinitis, allergic rhinitis, subacute rhinitis, urticaria, neurodermatitis
[18]	Measure effects of positive and negative ions on hay fever symptoms	N.S.	Patients male and female aged 4 to 59	123	Relief from hay fever and asthma
[10]	Measure physiological and subject effects of breathing ionized air.	N.S.	60 subjects, 25 F and 35 M, aged 10–68 yrs. 45 were normal, 15 had arthritis, 1 had pulmonary tuberculosis, 1 had hypertension, 2 with extreme nervousness, 1 with anemia, and 2 with undernutrition.	60	Pulse rate, blood pressure, respiration rate, mouth temperature, metabolism (oxygen consumption), arterial and finger blood, subjective sensation, subjective impression
[19]	Measure therapeutic effects of negative ions on asthmatics	Double-blind	Chronic asthma patients from hospital aged 15–53 yrs	16	Severity (scored from mild, moderate, or severe) of wheezing, dyspnea, coughing, and septum, and side effects in nose and throat
[20]	Measure pulmonary effects of negative and positive ions.	Subject-blind	Patients (7 F & 8 M) aged 16 to 48 yrs with bronchial asthma who were hospitalized for an extended allergy testing.	15	Lung function (FEV1), histamine threshold for 25% reduction in FEV1, and subjective scoring (air quality, breathing comfort, temperature).
Adult
[21]	Measure physiological effects of negative and positive ions.	Subject-blind	Experiment 1: Six healthy women (age range: 20 to 30 years) chosen at random and Experiment 2: 5 women and 7 men (age range: 19 to 45 years) selected from 125 subjects because they appeared to be most sensitive to ionization	Experiment 1: 6 women Experiment 2: 5 women and 7 men	Experiment 1: skin temperature, rectal temperature, comfort temperature, pulse rate, respiratory rate, mental performance, and subjective feelings of comfort Experiment 2: same as in Experiment 1 except for comfort temperature
[22]	Measure pulmonary, biochemical, emotional, and physical symptom effects of positive and negative ions on asthma.	Double-blind controlled	Asthmatic patients aged 35–64 (8 female and 1 male).	9	Pulmonary (FEV1), pulse and blood pressure, serum theophylline, urinary serotonin metabolite (5HIAA), symptom, response to three questionnaires designed to elicit somatic response and mood changes (Sharav #1 and 2, Adjective check)
[23]	Measure perception of environment, personal comfort, and physical symptom effects of negative ions on workers in a "sick-building" office setting	Subject-blind	Workers in five rooms of office building	26	Linear analogue scores on environment and personal comfort; physical symptom.
[3]	Measure effects on physiological parameter and subjective state from exposure to positive and negative ions.	Subject-blind	Male medical student paid volunteers aged 18–25 yrs; "morning" group N = 6 and "afternoon" group N = 5 to represent different metabolic states during the day.	11	Basal or total metabolism/oxygen consumption (depending on morning or afternoon group), blood pressure, pulse rate, respiratory rate, oral temperature, urine volume, and self-reported subjective state.
[24]	Measure effects of negative ion on physiological parameters and circadian rhythm at rest and during exercise.	Subject-blind cross-over	Male aged 19–25 yrs experienced in physical training and without respiratory ailments.	8	Rectal temperature, heart rate, oxygen uptake (VO2) and minute ventilation (VE), state anxiety per Spielberger (1970), and perception of effort per Borg (1970).
[25]	Measure effects of weather-related positive ions on pulmonary functions of asthmatics	N.S.	6 F and 6 M aged 41–69 yrs recruited from advertisement for subjects with weather-related asthmatic condition	12	Mean peak flow at four times a day measured by subjects using Mini Wright Peak Flow Meter
[26]	Measure physiologic effects and subjective impressions after exposure to light positive and negative air ions.	Subject- blind	17 M and 8 F, aged 22–51 yrs recruited from University research students, lab technicians, and faculty members. Secondary experiments among arthritic patients and infants.	25	Physiological observations such as, heart rate, blood pressure, metabolic rate, respiration; subjective sensations
Unspecified adult populations
[2]	Measure adverse effect of positive air ions and beneficial effect of negative air ions on respiratory allergies.	Double-blind randomized	"Reversible" condition (e.g., hay fever), "partially-reversible" condition (e.g., asthma), and "Irreversible" condition (e.g., pulmonary emphysema) patients; N = 12, 10, and 4, respectively.	26	Six pulmonary functions (VC, total VC1, total VC3, MEFR, MBCR, SBT)
[27]	Measure effects of positive and negative ions on asthmatic, bronchitis, and hay fever patients	N.S.	Patients with mild to moderate asthma, mild bronchitis, or hay fever	24	Lung function (FVC, FEV1, and MMFR)
[28]	Measure pulmonary effects of negative and positive ions.	Not blinded nor randomized	Subjects with severe emphysema/chronic pulmonary disease and/or fibrosis	46; 26; 79	VC, FEV0.5, FEV1, FEV3, MBC, MPFR
[13]	Measure efficacy of negative ion treatment for asthma patients.	Double-blind crossover	Men and women with asthma; 1/20 subject dropped out.	20	Peak expiratory flow rate (PEFR); self-reported symptoms; self medication.
[9]	Measure whether the body is a collector of air ions and biological effects of air ions.	N.S.	77 individuals (half had cardiovascular disease. Various experiments conducted	77	Body as ion collector experiment: electrical current developed between body and ionizer; biological effects study: clinical symptoms (headache, nasal obstruction, husky voice, sore throat, itchy nose, dizziness, congested throat), maximum breathing capacity, and feeling of exhilaration.

N.S.-not specified, FEV-forced expiratory volume, VC-vital capacity, PEFR-peak expiratory flow rate, MBC-Maximum breathing capacity, MPFR-Maximum peak flow rate, MMFR-maximum midexpiratory flow rate; 5HIAA-5-hydroxyindole acetic acid.