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Background: Cold exposure is associated with increased morbidity and mortality. Elite cross-country skiers are regularly exposed to cold, dry air and have a high prevalence of asthma compared to the Swedish population. However, evidence is limited regarding how a combination of sub-zero temperatures and physical activity affects the airways of healthy individuals.

Aims: The aims of this thesis were to study the prevalence of self-reported asthma, age at asthma onset, and predictors of asthma in Swedish endurance athletes, with a focus on cross-country skiers. This thesis also aimed to assess the effects of subzero temperature and physical activity on healthy human airways.

Methods: Study 1 (papers I-II) consisted of an annual postal questionnaire investigating asthma prevalence and predictors of asthma that was sent to invited athletes in 2011–2015. Invited athletes were Swedish elite cross-country skiers, biathletes, ski orienteers, and orienteers from Swedish National Elite Sport Schools, national teams, and Swedish Ski Universities, or top orienteers according to national ranking. Former Swedish Olympic skiers and an adolescent reference group were invited in 2013. Paper I included cross-sectional data from 2011 for adolescents/adults and from 2013 for former skiers (n=491). Paper II included adolescent elite skiers (n=253) from the Swedish National Elite Sport Schools invited during 2011-2013, as well as a reference group (n=500) aged 16-20 years that was matched for school municipalities and invited in 2013. Study 2 (papers III-IV) comprised whole-body experimental exposure of healthy adults to sub-zero temperatures and exercise in an environmental chamber. Lung function and biochemical markers in plasma and urine were measured before and after exposure. Symptoms were investigated before, during, and after exposure. In both trials, study subjects were exposed for 50 min on two separate occasions in randomized order. Paper III comprised 31 subjects and moderate-intensity exercise (30 min running at 62-78% of VO2max), at 10°C vs. -10°C. Paper IV included 29 subjects and hard-intensity exercise (30 min of running at 85% of VO2max) vs. rest, both at a temperature of -15°C.

Results: In paper I, the overall response rate was 82%. Athletes reporting asthma in the different age categories were: 29% of skiers (38% of the female skiers) and 17% of orienteers (p=0.071) among 15 to 19-year-olds; 35% of skiers and 16% of orienteers (p=0.029) among 20 to 34-year-olds; and 22% of the skiers aged 40–94 years. Asthma onset occurred in adolescence among the active athletes. Increasing age, female sex, allergy, family history of allergy/asthma, and being a skier were predictors of self-reported physician-diagnosed asthma. In paper II, the response rate was 96% for skiers and 48% for the reference group. Skiers reported a higher prevalence of self-reported physician-diagnosed asthma than the reference population (27% vs. 19%, p=0.046). Physician-diagnosed asthma was more frequently reported by female skiers than male skiers (34% vs. 20%, p=0.021). Median age at asthma onset was higher among skiers than in the reference population (12.0 vs. 8.0 years; p<0.001). Female sex, family history of asthma, nasal allergy, and being a skier were risk factors associated with self-reported physician-diagnosed asthma. In paper III, exercise at -10°C decreased FEV1 (p=0.002) and FEV1/FVC (p<0.001) and increased resistance at 20 Hz (p=0.016) to similar magnitudes as exercise at 10°C. Exercise at 10°C increased reactance (p=0.005), which differed (p=0.042) from a less pronounced response after exercise at -10°C. Plasma CC16 increased similarly after both exposures, without significant differences. More intense symptoms from the upper airways were reported after exercise at -10°C than at 10°C. Symptoms from the lower airways were few and mild. In paper IV, FEV1 decreased from baseline after both rest (p<0.001) and exercise (p=0.012) at -15°C, with no differences between exposures. Compared to rest, exercise at -15°C induced greater increases in reactance (p=0.023), plasma CC16 (p<0.001), and plasma IL-8 (p<0.001). Exercise gave rise to more intense symptoms from the lower airways, whereas rest induced more general symptoms.

Conclusions: In the 1990s, a high prevalence of physician-diagnosed asthma was reported among Swedish elite cross-country skiers, and our studies show that this has not changed. Asthma onset commonly occurs in early adolescence among skiers, in the beginning of their career. Being an elite skier is an independent risk factor associated with asthma. Targeted preventive measures should be introduced at an early age to avoid the development of asthma in endurance athletes. Healthy individuals performing short-duration moderate- and hard-intensity exercise in sub-zero temperatures responded with lung function changes and an increased airway permeability. These findings warrant further research on airway responses to sub-zero temperatures in vulnerable individuals such as elite endurance athletes.

Purpose: Exposure to cold air may harm the airways. It is unclear to what extent heavy exercise adds to the cold-induced effects on peripheral airways, airway epithelium, and systemic immunity among healthy individuals. We investigated acute effects of heavy exercise in sub-zero temperatures on the healthy airways.

Methods: Twenty-nine healthy individuals underwent whole body exposures to cold air in an environmental chamber at − 15 °C for 50 min on two occasions; a 35-min exercise protocol consisting of a 5-min warm-up followed by 2 × 15 min of running at 85% of VO2max vs. 50 min at rest. Lung function was measured by impulse oscillometry (IOS) and spirometry before and immediately after exposures. CC16 in plasma and urine, and cytokines in plasma were measured before and 60 min after exposures. Symptoms were surveyed pre-, during and post-trials.

Results: FEV1 decreased after rest (− 0.10 ± 0.03 L, p < 0.001) and after exercise (− 0.06 ± 0.02 L, p = 0.012), with no difference between trials. Exercise in − 15 °C induced greater increases in lung reactance (X5; p = 0.023), plasma CC16 (p < 0.001) as well as plasma IL-8 (p < 0.001), compared to rest. Exercise induced more intense symptoms from the lower airways, whereas rest gave rise to more general symptoms.

Conclusion: Heavy exercise during cold air exposure at − 15 °C induced signs of an airway constriction to a similar extent as rest in the same environment. However, biochemical signs of airway epithelial stress, cytokine responses, and symptoms from the lower airways were more pronounced after the exercise trial.

Training in cold climates is an established risk factor for development of exercise-induced bronchoconstriction and asthma. Inhalation of large volumes of cold and dry air challenges the airways’ capacity to condition inspired air, leading to acute airway injury, and over time, bronchial hyperresponsiveness. We lack evidence-informed guidelines regarding ‘safe’ thresholds for exercise in cold climates, i.e., temperatures (as well as exercise intensities/durations) that do not substantially increase the risk for healthy individuals to develop asthma. This study aimed to investigate the effect of temperature on systemic asthma- and exercise-associated cytokine responses to moderate-intensity exercise among healthy individuals. 31 healthy participants provided written, informed consent to participate in this randomised, crossover trial. On separate days, participants completed a 5 min warm up followed by 30 min running exercise (62-78% VO2peak) in a climate chamber at 10 or -10°C. Blood samples were taken pre and 1 h post-exercise and analysed for 10 cytokines (GM-CSF, IL-10, IL-13, IL-17E, IL-1β, IL-4, IL-5, IL-6, IL-8 and TNF-α) using multiplex ELISA. Values below the lower limit of detection for the assay were excluded. Data from 21 participants were analysed using two-way repeated measures ANOVA. IL-6 and IL-8 increased post-exercise (IL-6: log2 fold change: 0.47±0.67, p=0.001; IL-8: log2 fold change: 0.16±0.27, p=0.001). There were no differences in the response magnitude of any cytokine to exercise in -10 versus 10°C. We conclude that exposure to -10°C does not exacerbate inflammatory responses to moderate-intensity exercise, including for cytokines associated with exercise-induced asthma.

This article was presented at the 2022 ERS Lung Science Conference, in session “Poster Session 2”.This is an ERS Lung Science Conference abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).

Exposure to a cold climate is associated with an increased morbidity and mortality, but the specific mechanisms are largely unknown. People with cardiopulmonary disease and winter endurance athletes are particularly vulnerable. This study aimed to map multiple domains of airway responses to exercise in subzero temperature in healthy individuals.

Thirty-one healthy subjects underwent whole-body exposures for 50 minutes on two occasions in an environmental chamber with intermittent moderate-intensity exercise in +10 °C and -10 °C. Lung function, plasma/urine CC16 , and symptoms were investigated before and after exposures.

Compared to baseline, exercise in -10 °C decreased FEV1 (p=0.002), FEV1/FVC (p<0.001), and increased R20Hz (p=0.016), with no differences between exposures. Reactance increased after +10 °C (p=0.005), which differed (p=0.042) from a blunted response after exercise in -10 °C. Plasma CC16 increased significantly within exposures, without differences between exposures. Exercise in -10 °C elicited more intense symptoms from the upper airways, compared to +10 °C. Symptoms from the lower airways were few and mild. 

Short-duration moderate-intensity exercise in -10 °C induces mild symptoms from the lower airways, no lung function decrements or enhanced leakage of biomarkers of airway epithelial injury, and no peripheral bronchodilatation, compared to exercise in +10 °C. 

The objective of the study was to compare the prevalence of self-reported physician-diagnosed asthma and age at asthma onset between Swedish adolescent elite skiers and a reference group and to assess risk factors associated with asthma. Postal questionnaires were sent to 253 pupils at the Swedish National Elite Sport Schools for cross-country skiing, biathlon, and ski-orienteering (skiers) and a random sample of 500 adolescents aged 16-20, matched for sport school municipalities (reference). The response rate was 96% among the skiers and 48% in the reference group. The proportion of participants with self-reported physician-diagnosed asthma was higher among skiers than in the reference group (27 vs 19%, P=.046). Female skiers reported a higher prevalence of physician-diagnosed asthma compared to male skiers (34 vs 20%, P=.021). The median age at asthma onset was higher among skiers (12.0 vs 8.0years; P<.001). Female sex, family history of asthma, nasal allergy, and being a skier were risk factors associated with self-reported physician-diagnosed asthma. Swedish adolescent elite cross-country skiers have a higher asthma prevalence and later age at asthma onset compared to a reference population. Being an adolescent, elite skier is an independent risk factor associated with asthma.

Humans react to cold with various symptoms. Previous studies enquiring about symptoms during cold exposure have for the most part been population based studies using questionnaries and have focused on a narrow spectrum of symptoms. The purpose of this study was to study the effect of cold air and physical exercise on a wide range of symptoms in healthy individuals.

A total of 31 healthy subjects were experimentally exposed to +10 °C and -10 °C in an environmental chamber for one hour, on two separate occasions. During each exposure, subjects performed an intermittent moderate-intensity running protocol between 62-78% of maximal oxygen consumption (VO2 max). At five timepoints, before, during and after the exposures, subjects were asked about 18 symptoms and their intensity. The Borg CR10 scale was used to rate the intensity from 0 to 11, where 0 meant "none" and 11 meant "maximal". The sum of all five Borg CR10-scores were added together to form a single score for each exposure. Paired Wilcoxon signed-rank test was used for analysis. Data are presented as medians.

Symptoms of cough, eye irritation, physical discomfort, and cold extremities were present only at -10 °C. Compared to exercise in +10 °C, exercise in -10 °C induced significantly higher summed symptom scores for eye irritation 2.0 vs 0.5 (p=0.011), rhinitis 12.0 vs 8.0 (p=0.000), nasal irritation 3.5 vs 0.5 (p=0.001), cold face 7.0 vs 1.0 (p=0.000), physical discomfort 6.5 vs 0.0 (p=0.000), and cold extremities 10.0 vs 0.5 (p=0.000).

In healthy subjects, moderate-intensity exercise in -10 °C can induce and enhance the intensity of a wide range of symptoms. Symptoms of the lower airways were infrequent and mild.

OBJECTIVE: Asthma is common among elite endurance athletes. Since the first published Swedish studies in 1993, awareness of "skiers' asthma" has increased. The current prevalence of asthma among Swedish skiers is unknown. This paper aims to present the design of a 5-year prospective annual questionnaire study on asthma among Swedish current and former elite endurance athletes, the first cross-sectional results on prevalence, age of onset, and predictors of self-reported physician-diagnosed asthma in the study population.

METHODS: An annual postal questionnaire is sent to Swedish elite skiers and orienteers during 2011-2015. In 2013, former Swedish Olympic skiers were similarly invited. We present cross-sectional data obtained in 2011 from the adolescents and adults and in 2013 from former skiers. A total of 491 athletes were invited. The results are presented by age, sex and sport. Chi-square test was used for group comparisons. Predictors of asthma were identified using logistic regression.

RESULTS: Response rate was 82%. Among athletes aged 15-19, 29% of the skiers (38% of the female skiers), and 17% of the orienteers reported asthma (p = 0.071). Among the athletes aged 20-34, 35% of the skiers and 16% of the orienteers reported asthma (p = 0.029). Among the former skiers aged 40-94, 22% reported asthma. Among the active athletes, the onset of asthma was in early adolescence. Logistic regression found increasing age, female sex, allergy, family history of allergy/asthma and being skier predictors of self-reported physician-diagnosed asthma.

CONCLUSIONS: The prevalence of physician-diagnosed asthma is high among Swedish endurance athletes, especially female adolescent skiers.