Assessing the Consequences of Smoking Tobacco Products with Consideration of the Forced Oscillation Technique

Introduction

Tobacco addiction kills more than 8 million people each year, including 1.2 million due to exposure to second-hand smoke. All forms of tobacco intake are harmful, and there is no safe dose [1].

Smoking can cause or significantly increase the risk of respiratory diseases. In addition to lung cancer, smokers most commonly develop chronic obstructive pulmonary disease (COPD), emphysema, interstitial lung disease, and idiopathic pulmonary fibrosis. The effects of smoking are not limited to the respiratory system but extend to the circulatory system, increasing the risk of heart failure, venous thromboembolism, arrhythmia, coronary heart disease, and even stroke [2–4]. With the likelihood of more people becoming addicted to nicotine, this could pose a significant public health problem [5–8].

Currently, popular forms of nicotine intake are substitutes for conventional cigarettes, including nicotine water pipes, chewing tobacco, snuff, kretek, bidi, and the increasingly popular electronic (e-)cigarettes and heated tobacco products [9]. E-cigarettes, or electronic nicotine delivery systems, are devices that heat a liquid, known as e-liquid, to approximately 100 to 250°C, producing an aerosol typically containing nicotine and other additives [1,10,11]. E-cigarettes are not pharmacologically controlled. Therefore, the amount of nicotine and additives in the liquid varies from manufacturer to manufacturer. Moreover, the amount of nicotine is not the same among other available liquids for a specific type of e-cigarette. The presence of some of the chemicals found in cigarette smoke, such as acetone, formaldehyde, acrolein, and butanol, as well as acetaldehyde, has also been demonstrated in the aerosol formed during e-cigarette use [12]. In contrast to the thousands of compounds identified in cigarette smoke, between 94 and 139 compounds were detected in the aerosol of flavored e-cigarettes, including 9 substances recognized by the World Health Organization as toxic, with levels around 99% lower than those measured in a traditional cigarette [13].

Heat-not-burn (HNB) tobacco heating systems are some of the newer alternatives to conventional cigarettes. These devices are electronic, heating the processed tobacco to approximately 250 to 350°C. During their use, the combustion process does not occur, and the aerosol produced when heated emits much lower levels of harmful substances than that of conventional cigarettes [12,14–15]. The disposable cartridges are designed so that the duration of use and number of inhalations is similar to that of a traditional cigarette. The amount of nicotine per gram of tobacco in a heat stick is approximately 15.2 mg [16]. HNB products produce 50% less tar and 99% less carbon monoxide during use than do conventional cigarettes [17]. Farsalinos et al showed that tobacco warmers generate much less formaldehyde, croton, acetal and propionic aldehyde, and acrolein than do conventional cigarettes. In contrast, when compared with e-cigarettes, a higher content of these carbonyls was recorded in the aerosol composition, with the exception of crotonaldehyde and propionaldehyde, which were not present during e-cigarette use [18]. Analysis of the aerosol produced by the HNB device revealed the presence of 529 compounds at concentrations ≥100 ng/item, excluding water, nicotine, and glycerine. All 529 compounds were also present in cigarette smoke, but only a few exceeded the levels tested in smoke from the reference cigarette. These included propylene glycol, 1-hydroxy-2-propanone/1,2-propenediol, hexadecanoic acid, ethyl ester, and 2(5H)-furanone [19].

Despite the varied forms of research on oxidative stress, the results are clear: any of the given alternative forms of nicotine delivery can induce oxidative stress [20,21]. The key is the level of exposure, from 120 inhalations in the case of an e-cigarette, to 12 puffs using an HNB, to just 1 puff in the case of smoking a traditional cigarette [20].

E-cigarettes and heated tobacco products are gaining popularity despite the lack of sufficient scientific evidence to determine their potential harmfulness. This study is a response to the observed trend, and its results may significantly contribute to increasing the awareness of current or future users of these alternative forms of nicotine intake. The aim of the study was to assess the effects of smoking traditional cigarettes and using alternative forms of nicotine intake on the functional state of the respiratory system of smokers and non-smokers.

Material and Methods

CHARACTERISTICS OF THE STUDY MATERIAL:

Sixty participants were included in the study. The pre-test and direct qualifying part of the study was a self-constructed questionnaire, which was completed by a total of 278 respondents. These individuals volunteered to participate in the study based on an advertisement in social media and a local newspaper. Eventually, based on the questionnaire, 143 respondents were qualified for the study, and the remaining 135 were excluded. The respondents were between 19 and 29 years old, were of Polish nationality, lived in Wrocław, and had student or working status. The respondents had a high school education. The 143 individuals who underwent the qualification process were divided into 3 groups on the basis of information in the questionnaire, resulting in 48 non-smokers, 42 traditional cigarette smokers, and 53 users of nicotine alternatives. From each group, 20 participants were drawn and qualified for the study into 1 of 3 groups: control (non-smokers), cigarette smokers, and users of nicotine alternatives (Table 1). Of the participants, 68.33% were women and 31.67% were men.

The only necessary inclusion criterion for the study was that participants were between 19 and 29 years of age. In contrast, the exclusion criteria were inhalant allergies, diagnosed respiratory disease (asthma, COPD, cystic fibrosis, and others), chest deformity, practicing competitive physical activity, previous smoking cessation, or being in the process of quitting nicotine addiction. The study received approval from the Senate Committee on Research Ethics at the Wrocław University of Health and Sport Sciences.

TEST METHODS:

Respiratory function testing was performed in all study participants with a Jaeger FlowScreen instrument (models 780 and 578, version 1.3, Jaeger, Germany). Spirometric tests were conducted in accordance with the American Thoracic Society/European Respiratory Society criteria [22]. Spirometric tests resulted in a flow-volume curve, and the procedure was repeated 3 times, with an expiration time of at least 6 s. Measurements in at least 2 of the 3 trials had to be reproducible [22].

The following parameters were analyzed: vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), ratio of FEV1 to vital capacity as a percentage of VC (FEV1%/VC), peak expiratory flow (PEF), and maximum expiratory flow at half vital capacity (MEF50) [22,23]. The results obtained were related to the predicted values, considering values above 80% as a correct result [24].

According to the guidelines for conducting the study by the American Thoracic Society/European Respiratory Society, calibration of the spirometer must be performed at least once a day using a 3-L syringe at least 3 times to achieve a flow range of 0.5 to 12 L/s (with a 3-L injection time of 0.5 to 6 s).

Another method used in the study was assessment of respiratory muscle strength using a specialized FlowScreen attachment. Maximum inspiratory pressure (PImax, expressed in kPa) and maximum expiratory pressure (PEmax, express in kPa) exerted through the mouth were measured during the study [25,26]. The study was performed in accordance with the American Thoracic Society/European Respiratory Society guidelines. Each participant took between 5 to 10 valid measurements. The acceptable difference between measurements could not be higher than 5% or 5 cmH2O [22].

The forced oscillation technique (FOT) was used to investigate the clinical mechanical properties of the respiratory system. The instrument used for these purposes was the Resmon Pro V3 from MGC Diagnostics, which produces a type of pseudo-random, relative prime number signal. The frequencies used during the study were 5, 11, and 19 Hz [27].

The oscillatory waves were set to a multi-frequency mode (5, 11, and 19 Hz) to correspond to small, medium, and large airways, respectively [28].

Factory calibration was done according to international recommendations, with auto-zeroing of the sensors before each measurement. Calibration check was conducted with a test object (supplied with the device) and with a 3-L calibration syringe.

PROCEDURE:

Smokers of traditional cigarettes or those using alternative forms of nicotine intake were asked to not use the previously mentioned stimulants (smoking and/or vaping and/or water pipe) on the day of the study, or at least 2 to 3 h before participating.

The coefficient of variation for all accepted trials was ≤10%, thus maintaining an “A” category [27]. The coefficient of variation for all accepted samples was obtained from a multivariate regression model, which included the following explanatory variables: age, sex, weight, and height. To maintain sanitary-epidemiological safety, each participant received new mouthpieces, with a viral-bacterial filter for the FOT and spirometer.

FOT was performed with participants in a seated position on a chair with an adjustable seat height in order to ensure proper positioning of the lower limbs, namely flexion at the hip, knee, and ankle joints of 90°. This allowed for optimal positioning of the torso in an upright position and the head in an intermediate position. The adjustable stand allowed the height of the device to be adjusted to suit the study participant. During the study, the participants did not lean against the back of a chair. Immediately prior to commencement, the study participants placed a nose clip on themselves. The operator held the participants’ cheeks each time the trial began to most effectively nullify the effects of upper airway artifacts during measurement [29]. The test itself did not require the participants to perform forced breathing maneuvers. They were required to perform 5 trials. One consisted of 8 breaths, of which the first 3 were test breaths. Once these were completed, the device selected 3 of the 5 repetitions that were most similar to each other and then generated the final results.

Spirometry and measurement of respiratory muscle strength were performed in an analogous position of the participants, who had a nose clip on also during these tests. The test position differed only in the chair, which had a fixed seat height, and the device that performed the measurement was held by the participants themselves. The operator, seated next to the participant, informed participants each time about the course of the study. Once the examination started, the operator set the rhythm and instructed the participant on the activities they were to perform. Everyone performed the spirometry twice (the better of the 2 attempts was used). In contrast, respiratory muscle strength was measured only once, and this consisted of a p0 and a test proper: 5 tests relating to the inspiratory muscles and 5 tests measuring the strength of the expiratory muscles (the highest values achieved by the participants for the inspiratory and expiratory muscles were the results of this test).

All the above respiratory function tests were performed in accordance with European Respiratory Society and American Thoracic Society recommendations [22].

STATISTICAL ANALYSIS:

The first step of the statistical analysis was to check the normality of the distribution of the evaluated characteristics. The Shapiro-Wilk test was used for this purpose. All analyzed parameters had a normal distribution. Basic descriptive statistics were calculated. ANOVA and NIR post hoc tests were used to demonstrate the significance of differences, and for qualitative characteristics, the chi-square test was used. The Spearman rank correlation and Pearson simple correlation were used to assess the relationship between respiratory functional parameters and respiratory muscle strength and forced oscillation parameters. The classification according to Guilford was used to determine the strength of the relationship. The sample size was 52. Distribution of participants into groups was purposive according to smoking status. Significant values were considered to be P values less than or equal to 0.05.

Results

The analysis of the study results started with an assessment of the homogeneity of the study groups and found that, based on the chi-square test, the groups did not differ significantly in terms of size, sex, age, weight, height, and body mass index values (Table 1).

The assessment of lung ventilation parameters and respiratory muscle strength in the evaluated 3 groups with statistical characteristics and P value obtained from ANOVA analysis of variance are shown in Table 2. On this basis, the NIR post hoc test was applied to show detailed significant differences.

Few significant differences in functional parameters of the respiratory system were found between the groups evaluated. Significantly lower values were recorded for the first second of expiratory volume% vital capacity (expressed as%, FEV1%VC in%, at P=0.03) between the alternative nicotine intake smoking group and the control group, which can indicate a greater tendency toward obstructive-type ventilation disorders.

Also, maximal expiratory flow at 25% of vital capacity (MEF25) showed significantly lower values in the group of smokers of alternative forms of nicotine intake than in the control group (P=0.02) and the group of cigarette smokers (P=0.03), which can indicate a greater tendency to develop fine bronchial obstruction.

Using the criteria for assessing pulmonary ventilation disorders, a reduction in values below 80% of the predicted VC or FVC can suggest the presence of restrictive lung disorders, while a reduction below 80% of the predicted value of FEV1, as well PEF, can indicate obstructive disorders. On the other hand, MEF25, assessing the condition of small bronchi, and MEF50, assessing the condition of medium bronchi, are indicative of small bronchial obstruction.

The assessment of lung ventilation parameters in terms of the presence of obstructive and restrictive abnormalities showed that no abnormalities were recorded in any of the groups assessed: values of VC, FEV1, and forced expiratory volume in 1 s% of vital capacity, Tiffeneau (FEV1%VC) parameters expressed as% of predicted values were within physiological norms, ranging from 75% to as high as 136%.

Assessment of inspiratory muscle strength values measured by PImax parameters sensitive to% of normal values confirmed the absence of abnormalities in the study groups. In contrast, the assessment of expiratory muscle strength based on the PEmax parameter in relation to norms showed the occurrence of reduced strength in 21.4% of women and 100% of men.

For adults under 65 years of age, the PImax lower limit of normal should be 90 cmH2O or 8.82 kPa in men and 70 cmH2O or 6.86 kPa in women. In contrast, PEmax should be 140 cmH2O or 13.73 kPa in men and 70 cm H20 or 6.87 kPa in women. Weakening of the expiratory muscles can cause dyspnea and exertion intolerance.

A PEmax parameter of less than 60 cmH2O (5.88 kPa) predicts poor coughing efficiency and expectoration problems [24]. Table 2 shows the characteristics of spirometric parameters and respiratory muscle strength of the study groups. Table 3 shows the statistical characteristics and P value obtained from ANOVA of the FOT parameters of all study groups. On this basis, the NIR post hoc test was applied to show detailed significant differences.

Significant parameter differences were shown for inspiratory resistance at 5 Hz% (Rrs 5 Hz Rinsp%), total respiratory resistance at 5 Hz% (Rrs 5 Hz Rtot%), inspiratory resistance at 11 Hz% (Rrs 11 Hz Rinsp%), and total respiratory resistance at 11 Hz% (Rrs 11 Hz Rtot%).

The NIR post hoc analysis showed significantly higher values for the parameter Rrs 5 Hz Rinsp% in the nicotine alternative users (P=0.05) and cigarette smokers (P=0.05) groups than in the control group. The value of the parameter Rrs 11 Hz Rinsp% in the cigarette smokers group was the highest and was significant in relation to the control group (P=0.05) and the nicotine alternative users group (P=0.05). Also, the value of this parameter in the nicotine alternatives users group was significantly higher than the value in the control group (P=0.05). Evaluated frequency ranges used in the FOT study allowed assessment of the proximal and peripheral airways, where the lower frequency (Rrs 5 Hz) penetrated down through the proximal airways into the peripheral airways, giving a measure of total airway resistance. Resistance at lower frequencies (5 Hz) is more useful in differentiating smoking-related airway abnormalities than are higher resistance frequencies (Tables 3, 4).

Pearson correlation analysis showed a significant moderate to strong negative correlation of total respiratory resistance at 5Hz% (Rrs 5 Hz Rtot%) and total respiratory resistance at 11 Hz% (Rrs 11 Hz Rtot%), with all respiratory functional parameters expressed in absolute values in the nicotine alternative users group. The same significant negative correlations were found for total reactance at 5 Hz% (Xrs 5 Hz Xtot%), with parameters VC in% (VC%), FVC in% (FVC%), FEV1 in % (FEV1%), MEF50, and MEF25 only in the nicotine alternative users group. In addition, a significant negative correlation of the area under inspiratory reactance curve% (AX insp%) with FEV1% and MEF25 was observed in the nicotine alternative users group, while a negative correlation was seen only with MEF25 parameter in the cigarette smokers group. Although the 2 techniques measure different pathophysiological aspects of the airway during different breathing maneuvers, both can be used to assess airflow obstruction; therefore, the above analysis can point out their detailed relationship.

Table 4 shows the Pearson simple correlation coefficients of the parameters of forced oscillation technique and time of use of tobacco products and alternative forms of nicotine use with functional parameters of the respiratory system and respiratory muscle strength.

Pearson correlation analysis showed a significant moderate to strong negative correlation of total respiratory resistance at 5Hz% (Rrs 5 Hz Rtot%) and total respiratory resistance at 11 Hz% (Rrs 11 Hz Rtot%), with all respiratory functional parameters expressed in absolute values in the nicotine alternative users group. The same significant negative correlations were found for total reactance at 5Hz% (Xrs 5 Hz Xtot%) with parameters VC%, FVC%, FEV1%, MEF50, and MEF25 only in the nicotine alternative users group. In addition, a significant negative correlation of the area under inspiratory reactance curve% (AX insp%) with FEV1% and MEF25 was observed in the nicotine alternative users group, while a negative correlation was seen only with MEF25 in the cigarette smokers group. Although the 2 techniques measure different pathophysiological aspects of the airway during different breathing maneuvers, both can be used to assess airflow obstruction; therefore, the above analysis can point out their detailed relationship.

Discussion

Our study shows smokers and users of alternative forms of nicotine are characterized by decreased flow through the small bronchi, as evidenced by reduced values of flow parameters (MEF25) in the pulmonary function test as well as at the test level of the forced oscillation technique (Rrs 5 and 11 Hz). In contrast, there were no changes in respiratory muscle strength in our study groups. This represents an important part of the study, which points to the possibility of using oscillatory diagnostics as one of the first methods to confirm the negative effects of cigarette smoking and alternative forms of nicotine intake on human health.

Own research indicates a reduction in fine bronchial flow in smokers and users of alternative forms of nicotine intake. Studies by other authors confirm this trend. These data indicate that vaping and smoking can cause a similar degree of airway obstruction. Alternative forms of nicotine intake have similar harmful effects of altering airflow through the airways as smoking cigarettes and, therefore, may not be a healthier alternative to smoking [30]. Other authors recognized that using an e-cigarette for 5 min causes an increase in peripheral airway resistance, increased impedance, and oxidative stress and considered it an important clinical effect [31].

In our study, significantly lower values of the MEF25 parameter were observed in people smoking traditional cigarettes and using alternative forms of nicotine intake, which may indicate a greater tendency to develop obstructive disorders of small bronchi.

Similarly, the values of the resonance frequency, which maintained an increasing trend, respectively higher for cigarette smokers and alternative nicotine users, may show a tendency to narrow the airways.

The available literature has found few epidemiological studies examining the long-term effects of e-cigarette use, both in young people who start smoking e-cigarettes and in smokers who switch to exclusive use of e-cigarettes. Meo et al conducted a study comparing 30 healthy daily e-cigarette users with 30 people from the control group. The groups were homogeneous and met the American Thoracic Society smoking criteria prior to the study. They found that e-cigarette users had lower FEV1 (4.6 [SD 0.7] L vs 5.2 [0.8] L; P=0.007) and FEV1/FVC (77.4 [7.2] vs 83.4 [5.6]; P=0.001), compared with the control group [31].

Similar results to ours regarding a decrease in the values of the MEF25, FEV1%, and FVC parameters and an increase in the resonance frequency in people smoking traditional cigarettes were obtained by Borrill et al. They included 18 smokers and 10 non-smokers. The groups were homogeneous in terms of age. The authors measured FEV1, FVC, and MMEF 3 times and showed significantly lower predicted%MMEF and FEV1/FVC in the smoking group, as well as a higher resonance frequency [32].

Schivinski et al confirmed the influence of passive smoking on the reduction of flow parameters tested both in spirometry and forced oscillation techniques. They conducted cross-sectional studies among children aged 6 to 14 years. Their aim was to identify changes in forced and quiet breathing parameters in lung function in healthy children and adolescents exposed to passive smoking. A total of 78 children were enrolled in the study and divided into 2 equal groups, also, in terms of the number of boys and girls. Impulse oscillometry (at 5 and 20 Hz) and spirometry were used to analyze quiet breathing. Evaluation of the data after spirometry showed that the group that was exposed to passive smoking had lower absolute average values for all variables. Statistically significant differences between groups occurred only in PEF values. Smaller values were obtained by the group of children exposed to passive smoking. On the other hand, oscillometry results showed significantly higher absolute values for the area under reactance curve (AX) and a higher average percentage of predicted resistance values at 20 Hz, AX%, and resonance frequency in the group of children exposed to secondhand smoke [33].

Despite the fact that resonance frequency and AX are considered to be sensitive markers of respiratory changes in active as well as passive smokers [34], in our study, we observed an increasing trend only in the parameter AX insp% for the nicotine alternative users group and a decrease in the average value of the parameter AX insp% in the cigarette smokers group than in the control group. On the other hand, the resistance value of 5 and 11 Hz insp% differed significantly between the groups, being the highest in the cigarette smokers group and correspondingly lower in the control group. There were no significant differences between the groups with respect to peak expiratory flow, with a tendency toward lower average values only for the surveyed smokers.

Research similar to ours, confirming the indicated trends, was conducted by Sakaguchi et al, who conducted a study looking at the impact of biomarkers of potential harm that can be associated with tobacco-related diseases in exclusive users of new vapor products, compared with those of traditional smokers and non-smokers, under real-world conditions. A total of 459 participants were studied: 100 conventional cigarette smokers, 100 non-smokers, and 259 users of novel tobacco vapor. In addition to biomarker analysis, a functional respiratory test was performed, and spirometric parameters were measured. The FVC levels of never-smokers were significantly higher than those achieved by the traditional cigarette smoking group. In turn, they were not significantly different compared with those of users of novel tobacco vapor. FEV1 and FEF values 25–75 achieved by the non-smokers and users of novel tobacco vapor group were significantly higher than those of the conventional cigarette group. The results of FEV1% and PEF parameters were not significantly different between the groups [35]. In our study, only a similar trend in FVC results was found, but this was not a significant relationship, as in the above studies. On the other hand, the values of FEV1 and FEV1% did not differ significantly among the groups, and the PEF and PEF% parameters were higher in the group of non-smokers than in the group of smokers and those using alternative forms of nicotine intake. However, these were not statistically significant differences.

In the available literature, we found a study that also assessed the parameters of respiratory muscle strength. The authors conducted research on 376 participants, aged between 18 and 25 years. They divided the participants into 3 groups: (1) never smokers (control group); (2) smokers of less than 15 cigarettes per day; and (3) smokers of more than 15 cigarettes per day. The average number of cigarettes smoked was 8.7 in group 2 and 19.8 in group 3. The authors assessed the effect of smoking habit on respiratory muscle strength in a group of young Saudi Arabian participants. Therefore, they measured respiratory muscle strength with maximal inspiratory pressure, maximal expiratory pressure, and maximum voluntary ventilation. They also measured spirometric parameters. Smokers with up to 15 cigarettes per day showed a reduction in FEF 25–75 and an increase in FEV1/FVC, compared with non-smokers. In contrast, both parameters were reduced in the group of smokers smoking more than 15 cigarettes per day. In the results of maximum inspiratory pressure, no significant differences were observed between the control group and mild and compulsive smokers. On the other hand, the results of maximum pressure were significantly lower in the group of heavy smokers [36]. Our study showed no statistically significant differences for the parameters PImax and PEmax. It can only be concluded that there is an increasing trend for the PImax and PEmax parameter for the group using alternative forms of nicotine intake, compared with non-smokers and conventional cigarette smokers.

In view of the adverse effects of cigarette smoking on health and, in particular, the increased risk of many lung diseases, it seems important to compare the values of functional parameters obtained by FOT and spirometry in groups of patients, smokers, and users of alternative forms of nicotine intake. FOT measures both resistance and reactance, allowing assessment of the mechanical properties of the airways and lung parenchyma [37]. Therefore, our own research was extended to analyze the correlation of functional parameters of the respiratory system and the strength of respiratory muscles with the forced oscillation technique and the duration of use of tobacco products and their alternative forms.

Another study using the FOT method was conducted by Paredi et al, who examined 34 patients with asthma, 48 with COPD, and 18 healthy people. Their aim was to compare inspiratory and expiratory resistance and reactance in patients with asthma and COPD. An impulse oscillometer was used for this purpose. A whole-breath analysis was performed, which showed no significant differences between the patient groups. However, the authors noted that in the COPD group, the expiratory phase reactance at 5 Hz was greater than the inspiratory phase. Such observations, however, did not occur in patients with asthma [38].

The conclusions drawn by the authors of the above paper regarding patients with COPD are also not supported by our research. No significant differences in expiratory phase reactance values at 5 Hz were observed between non-smokers, users of alternative forms of nicotine intake, and smokers of traditional cigarettes.

In our own research, strong negative correlations were observed in the group of users of alternative forms of nicotine use between the parameters resistance at 5 Hz, 11 Hz, 19 Hz and reactance at 5 Hz and the values of VC, FVC, FEV1, PEF, MEF50, and MEF25. Negative correlations were also observed between FEV1% in the nicotine alternative users group and MEF25 in the cigarette smokers group. Strong negative correlations were also observed between the Rrs 5–19 insp coefficient of variation and VC parameters in the group of traditional cigarette smokers and FEV1%VC in% in the group of people using alternative nicotine.

A similar analysis of respiratory function tests and FOT testing was performed by Mori et al, who examined 97 patients diagnosed with idiopathic pulmonary fibrosis. They tested whether the reactance values obtained after FOT reflected the severity of the disease. Respiratory impedance was measured using a broadband FOT device called MostGraph-01. Data were also collected and some of the parameters analyzed were Rrs 5 Hz (R5) and 20 Hz (R20), as well as the difference between R5 and R20 (R5-R20) and the reactance at 5 Hz, along with the resonance frequency and the low-frequency reactance area. This was followed by spirometry measurements with a focus on VC, FVC, and FEV1. The participants were divided into 2 groups, the allocation depending on the stage of the disease. Group 1 consisted of those in stage I, and group 2 consisted of those in stage II/III GAP. Negative correlations were shown between the reactance at 5 Hz, 20 Hz, and the difference between them, and VC, FVC, and FEV1. In contrast, the reactance at 5 Hz showed strong positive correlations with the parameters VC,%VC, FVC,%FVC, and FEV1. Negative correlations were also observed between the resonant frequency and low-frequency reactance area and VC,%VC, FVC,%FVC, and FEV1. The participants in group 2 achieved significantly lower reactance values at 5 Hz and higher resonance frequencies and low-frequency reactance areas. It was observed that expiratory-phase reactance at 5 Hz predicted reduced future lung capacity and disease severity in patients diagnosed with idiopathic pulmonary fibrosis [39]. The correlations in the work of Mori et al were largely similar to those obtained in our study. The only significant difference was the correlation of reactance at 5 Hz, which was strongly positive in their 2020 study and negative in our study [39].

The significant correlations shown indicate that the 2 types of testing are related. FOT measures airway resistance and reactivity during breathing, just as spirometry measures airflow limitation during forced expiration. FOT measures both resistance and reactance, thus allowing us to assess the mechanical properties of the airways and lung parenchyma [40]. Although the 2 techniques measure different pathophysiological aspects of the airway during different breathing maneuvers, both can be used to assess airflow obstruction.

The conclusions drawn by the authors of the above paper regarding patients with COPD are also not supported by our research. No significant differences in expiratory phase reactance values at 5 Hz were observed between non-smokers, users of alternative forms of nicotine intake, and smokers of traditional cigarettes.

The results of our study showed a trend toward decreased airway flow measured by spirometry and by forced oscillation technique testing. A greater reduction in spirometric parameters was observed in cigarette smokers, whereas a greater reduction in flow assessed by FOT parameters was observed in users of alternative forms of nicotine. It should be emphasized that the self-reported study was conducted in young people, which underlines its validity. Confirmation of the indication of the existence of a problem of frequent use of such forms of nicotine in young people is provided by the study by Jankowski et al [41], who studied 1090 Polish adults. Their aim was to assess the current prevalence and patterns of e-cigarette and tobacco use, as well as to identify the socio-economic factors associated with smoking among adults in Poland. For that purpose, a survey questionnaire developed for the study was used, which was conducted online. In total, 28.8% of respondents declared that they smoked cigarettes every day, and 4.2% indicated that they smoked cigarettes occasionally. Regular use of e-cigarettes was reported by 4.8% of respondents, and HNB by 4.0%. E-cigarettes were most commonly used among 18 to 29 year olds; the percentage of use in this age group was 6.8%. HNB products were most popular in 40 to 49 year olds, with their users accounting for 7.0% of the total age group. In contrast, among 18 to 29 year olds, 3.6% used HNB products [41]. The self-report questionnaire also provided information on the prevalence of smoking and the use of e-cigarettes and HNB products among 19 to 29 year olds. Of the 278 respondents, 153 were non-smokers, representing 55.03% of the total group. Smoking traditional cigarettes was indicated by 43 people, 15.47% of respondents. In the survey, the use of e-cigarettes and HNB products was indicated by a total of 82 people, 29.5% of all respondents. These results may indicate an upward trend in the number of e-cigarette and HNB product users among young adults and traditional cigarette smokers in this age group. In this case, it would be the first such a high jump in the number of people smoking or using alternative forms of nicotine intake in several years. It seems that the current situation may have been influenced by the Covid-19 pandemic, or more precisely, the lockdowns introduced in most countries. Already in 2022, Bandi et al, after conducting research on a group of over 788 000 adult smokers in the United States, showed a reduction in the frequency of attempts to quit the addiction, which was recorded for the first time since 2011. At the same time, there was a decline in expected sales of nicotine replacement therapy [42].

To summarize, it should be emphasized that the demonstrated tendencies to reduce airway patency resulting from the use of especially alternative forms of nicotine have health consequences. According to Lappas et al, the cause of airway obstruction can be the propylene glycol liquid added to e-cigarettes, which causes irritation and even inflammation of the respiratory tract. Interestingly, mild airway obstruction can occur even in people without asthma [43]. In turn, other authors emphasize the increase in the percentage of young people using e-cigarettes [43]. At the same time, there is a high incidence of asthma among teenagers. Health education for young people is particularly important, especially for those who experience symptoms of wheezing.

Limitations of the present study are the relatively small number of respondents in each group and the age of the respondents. The study focused on young people, and it would be advisable to extend the study to different periods of ontogeny. We did not consider the size of the “dose” of nicotine intake. We included a priori in the exclusion criterion people with coexisting bronchial asthma. This was an important criterion for the homogeneity of the group. However, after an in-depth analysis of the literature, it seems important to conduct research in the near future on the use of nicotine in young people with diagnosed bronchial asthma and to continue the research.

Conclusions

Smokers and users of alternative forms of nicotine have reduced flow through the small bronchioles, as evidenced by a reduction in the MEF25 parameter. Smokers and users of alternative forms of nicotine have higher values of resistance at the level of the small and medium bronchioles, which is indicative of reduced flow through the airways and may therefore exacerbate symptoms of inflammation. The forced oscillation technique is a sensitive diagnostic tool for detecting early respiratory changes in smokers. Multiple frequencies and the frequency dependence of resistance and reactance can provide valuable and early information on smoking-induced airway changes. A relationship analysis showed a significant correlation between age of smoking initiation/use of alternative forms of nicotine, and changes in medium bronchial resistance. This is part of a new strand of research that indicates the importance of assessing these parameters.