A group of patients with severe asthma (Group S) and a gender-, age- and body mass index-matched group of asthmatic patients with mild-moderate asthma (Group M), diagnosed according to GINA guidelines (1) who attended the Asthma Clinic of the NHS Department of Respiratory Medicine, G Papanikolaou Hospital between September 2019 and December 2019 constituted the study population. Mild asthma was defined as asthma that was well controlled with Step 1 or Step 2 treatment, that is, with as needed inhaled corticosteroid (ICS)/formoterol alone, or with low intensity maintenance controller treatment. Moderate asthma was defined as asthma that was well controlled with Step 3 treatment, e.g., low dose ICS / long-acting beta agonist (LABA) and severe asthma was defined as asthma that required Step 4 or Step 5 treatment (e.g., high dose ICS /LABA) to prevent it from becoming “uncontrolled, or asthma that remained “uncontrolled”, despite this treatment [1]. All patients were stable without any exacerbations or hospitalizations due to asthma or other causes or changes in asthma-specific medication in the last three months prior to study entry. Patients with a) uncontrolled asthma, b) serious musculoskeletal disorders that interfered with normal physical activity, c) mental disorders that did not allow comprehending and consenting to the protocol, d) arterial oxygen saturation (SpO₂) at rest <92%, e) other concomitant respiratory disorders, f) smoking history (current smokers or ex-smokers with smoking history ≥10 pack/years or smoking cessation within less than 12 months) were excluded from study entry. All patients provided informed, written consent for study participation, the principles of the Declaration of Helsinki (http://www.wma.net/en/30publications/10policies /b3/ index.html) were followed, and the Scientific Review Board Committee of General Hospital “G. Papanikolaou” approved the study protocol (138/2019).

In more detail, the patient matching was conducted as follows: All asthmatic patients aged 18-80 years old with asthma diagnosis of at least one year, that had participated in clinical trials regarding asthma in the previous 3 years, and were, so, recorded in a clinical database of the Department for Respiratory Medicine, were theoretically eligible for study recruitment. The database included 42 patients and selection was done according to the following procedure: patients were first separated according to severity. For every patient with severe asthma, we tried to match another patient with mild-moderate asthma and similar BMI, gender and age. Thus, following a procedure of 1:1 matching, we created two groups of 10 patients each. These patients were called and asked to participate in the study and given a new informed consent. However, 2 female patients in group M decided to withdraw their consent, so a group of 8 mild-moderate and a group of 10 severe asthma patients were eventually included in the study protocol.

This is a pilot case-control study. All study data were prospectively collected. Study patients arrived at the clinic in the morning after receiving their regular medication and undergoing a detailed clinical evaluation. To continue with further testing, patients had to have a priori heart rate <100 beats/min and systolic blood pressure <180 mmHg at the day of evaluation, at rest, or else they were asked to repeat the visit within 3-5 days. All participants then completed:

(a) The International Physical Activity Questionnaire (IPAQ, short form): it is a 9-item, self-completed instrument used for the evaluation of PA, by summing up vigorous, moderate and walking PAs over the previous seven-day period and generating a total physical activity score (PAscore), expressed in MET-minutes per week (MET.min/wk) [8]. A Greek version of IPAQ-short has been previously used in the Eurobarometer survey conducted by the European Union [9].

(b) The Asthma Control Test (ACT): It is a 5-item, self-completed tool with 4-week recall (on symptoms and daily functioning) for identifying those with poorly controlled asthma [10]. Each item is scored with a 5-point scale (1=not controlled at all; 5=totally controlled) and the higher the scores, the greater the asthma control. The scores range from 5 (poor control of asthma) to 25 (complete control of asthma); an ACT score >19 indicates well-controlled asthma. ACT has been translated and validated for the Greek population [11].

(c) The Asthma Control Questionnaire (ACQ): It is a self-completed tool with a 7-day recall of symptoms; the 5-item questionnaire was used in this study (ACQ-5). Each item is scored on a 7-point scale (0=no impairment; 6=maximum impairment) and scores range between 0 (totally controlled) and 6 (severely uncontrolled) [12]. Based on the average values, asthma is well controlled when ACQ <0.75. The ACQ has been previously translated and validated for the Greek population [13].

Following, participants underwent lung function measurement (Omnia Pulmonary Function Testing Lab by COSMED^@, Rome, Italy), according to American Thoracic Society (ATS)/ European Respiratory Society (ERS) guidelines [14] including post-bronchodilation Forced Expiratory Volume in 1 second (FEV₁), Forced Vital Capacity (FVC), Total Lung Capacity (TLC), Residual Volume (RV), Inspiratory Capacity (IC), Peak Expiratory Flow (PEF), Forced Expiratory Flow 25-75 (FEF_25-75) and lung diffusion (Diffusion Capacity of lung for carbon monoxide; DLCO and carbon monoxide transfer coefficient; KCO). The reference values applied were Global Lung Function Initiative (GLI) 2012 [15]. After at least 30 minutes rest, all patients completed a 6-minute walking test (6MWT) on a flat 33m corridor, followed by 3 minutes of recovery, according to ATS guidelines [16]; the distance walked (6MWD, m) was recorded. SpO₂, vs pulse oxymetry, and systolic and diastolic blood pressure, vs cuff manometer, were measured at rest, at the end of exercise test and at the end of recovery. Heart rate was measured at rest, at the end of the test and at 1, 2 and 3 minutes of recovery. The 0-10 Borg Dyspnea (BorgD) [17] and the 0-10 Borg Rating of Perceived Excursion (RPE) [18] were assessed before and at the end of the 6MWT. Double product was calculated as the product of systolic blood pressure and heart rate before 6MWT (rest), at the end of the exercise test and at the end of recovery (3^rd minute).

The entire analysis was conducted using the IBM SPSS Statistics 20 (CA, USA). Continuous variables were expressed as mean ± standard deviation (mean ± SD) or median [interquartile range] depending on the normality of distribution, while categorical variables as % percentages. The predicted 6MWD was also calculated based on the equation: predicted 6MWD= 1.250 X height – 2.816 X age -39.07 X gender + 518.853 (where female=1 and male=0) [19]. The %predicted 6MWD was then calculated as (6MWD X 100)/predicted 6MWD. The 6-minute walk distance work (6MWork) was calculated as the product of 6MWD X Bodyweight (m X kg) [20]. The Shapiro-Wilk test was applied to exam the normality of distribution for quantitative variables. The Student’s t-test for Independent Samples or the Mann -Whitney U test was used for group comparisons of continuous variables, depending on their distribution of values and the Chi Square was applied for group comparisons of categorical variables. The Pearson r or the Spearman rho were utilized to indicate correlations between continuous variables. P <0.05 was considered significant for all comparisons.

Eighteen subjects (14 male, 4 female; age: 53.9±14.9 years) were included in the study. Ten subjects (age range 39-72 years old) presented with severe asthma (Group S) and the rest 8 gender- age- and BMI- matched patients (age range 40-78 years old) presented with mild-moderate asthma (Group M). The baseline characteristics of the study population are presented in Table 1. Patients’ regular treatment were as follow: ICS/LABA (33.3%), ICS/LABA + long-acting muscarinic agonist (LAMA) (33.3%), ICS/LABA + monoclonal antibody (16.7%), ICS/LABA + leukotriene antagonist (11.1%) and leukotriene antagonist (5.6%). No patient received extra short-acting beta agonist (SABA) before visiting the clinic.

Based on ACT, 61.1% of patients had good and 38.9% had poor asthma control. Of those with good asthma control, 63.6% had mild-moderate, while 36.4% had severe asthma, while among those with poor asthma control, 14.3% had mild-moderate, while 85.7% had severe asthma (p=0.04). Based on ACQ, 44.4% had good, 27.8% had poor asthma control, while another 27.8% were in an intermediate condition. Among patients with mild-moderate asthma most had well-controlled asthma (87.5% based on ACT and 62.5% based on ACQ) and normal spirometry (75%). In the S group, 40% according to ACT or 30% according to ACQ had controlled asthma, while no patient had normal spirometry (that is normal FEV₁, normal FVC and normal FEV₁/FVC).

Average METs/week were 2916.9±2737.7 and only 4 subjects (22.4%) were complied to physical activity levels, as suggested by WHO for subjects >18 years old. Only three subjects presented high PA, 12 (66.7%) moderate PA and the rest 16.7% PA. Exercise capacity, Borg dyspnea, RPE score and double product are presented in Table 2.

Double-product at exercise end was significantly lower in Group S, compared to Group M (18594.8±3984.4 vs. 16412.2±4732.1 mmHgXbpm; p=0.041), while BorgD was significantly higher (Table 3). Although total METs were similar between the groups, group S had significantly lower moderate intensity physical activity, compared to Group M. However, 6MWD (both absolute and %predicted), 6MWWork, ACT score, ACQ and RPE were similar between the groups (Table 2). Moreover, the values of HR during the 1^st, 2^nd and 3^rd minutes of recovery between the groups were also similar. Table 3 presents the absolute and the %predicted values of HR at the end of 6MWT for each patient. In M group the HR% predicted was 62.7±11.3%, while in the S group it was 66.8±10.9% (p>0.05), indicating similar exercise intensity between the groups.

When subjects were compared according to asthma control based on ACT, none of the above parameters were found to be different (data not shown).

Double product at the end of 6MWT was significantly and positively correlated to 6MWD %predicted (r=0.592; p=0.010) (Fig. 1).

Fig. (1). The positive, linear association between double product and 6-minute walking distance (% predicted).