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ORIGINAL ARTICLE
Year : 2012  |  Volume : 1  |  Issue : 3  |  Page : 166-171

A study of reduction in breath-holding time in smokers and recovery among ex-smokers in bus depot workers


1 Department of Physiology, JSS Medical College (A constituent college of JSS University), Mysore, India
2 Department of Statistics, Manipal University, Level 6, Health Sciences Library Building, Manipal, India

Date of Web Publication26-Dec-2012

Correspondence Address:
Bakthavathsalam Sreenivas Sudha
Department of Physiology, JSS Medical College (A constituent college of JSS University), Mysore
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2278-344X.105080

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  Abstract 

Background: Smoking has deleterious effects on breath-holding time (BHT), which has been used in respiratory physiology as a measure of ventilatory response. Evidences regarding assessment of the reversibility of the impact of smoking on BHT and recovery in ex-smokers are ambiguous. Hence, this study was conducted to quantify the reduction in BHT and to assess the reversibility of the same. Materials and Methods: A cross-sectional study was conducted on 84 bus-depot workers consisting of equal number of smokers, ex-smokers, and non-smokers. Breath-holding time was recorded using the mouth piece attached to the mercury manometer where the subjects were advised to blow through the mouth piece after full inspiration as long as possible till the breaking point following standard methods and precautions. Comparisons among 3 groups were performed employing one-way ANOVA and post-hoc tests. The significance of difference in BHT between the 2 categories of frequency and duration of smoking was tested using Student's t-test for independent samples. Results: BHT was found to be significantly reduced among smokers compared to non-smokers. Almost complete recovery of BHT was observed in ex-smokers. There was deterioration in BHT with increase in BMI, and a statistically significant negative correlation was observed when BHT was correlated with age, especially in smokers. Conclusion: Present study has demonstrated considerable reduction of BHT in smokers and indications of recovery in ex-smokers. Further detailed study with larger sample size, stricter definition of ex-smokers, and considering physical activity is recommended.

Keywords: Breath-holding time, bus depot workers, Mysore, recovery, smoking


How to cite this article:
Sudha BS, Sunitha MS, Nataraj SM, Dhar M. A study of reduction in breath-holding time in smokers and recovery among ex-smokers in bus depot workers. Int J Health Allied Sci 2012;1:166-71

How to cite this URL:
Sudha BS, Sunitha MS, Nataraj SM, Dhar M. A study of reduction in breath-holding time in smokers and recovery among ex-smokers in bus depot workers. Int J Health Allied Sci [serial online] 2012 [cited 2019 Sep 20];1:166-71. Available from: http://www.ijhas.in/text.asp?2012/1/3/166/105080


  Introduction Top


Life is absolutely dependent upon the act of breathing. Breathing is considered the most important of all the functions of the body as all other functions depend upon it. Breath-holding time (BHT) may be considered as one of indicators of efficiency of breathing function. BHT is defined as the time taken by the subject to hold his breath as long as he can. Normal voluntary breath-holding time is 45-55 seconds. Respiration can be voluntarily inhibited for some time, but eventually, the voluntary control is overridden. During voluntary breath-holding, tissues continue to use oxygen and produce carbon dioxide. Therefore, during breath-holding, arterial PO 2 falls and PCO 2 rises, resulting in a state of asphyxia. Since both these factors are powerful respiratory stimulants, a point is reached where the respiratory drive becomes so strong that the person cannot hold the breath any longer. The point at which breathing can no longer be voluntarily inhibited is called the breaking point. Thus, BHT is the time duration from the time of inhibition of breathing till the breaking point. The breaking point is generally reached when alveolar PO 2 is 56 mmHg and alveolar PCO 2 is 49 mmHg. Either an increase in PCO 2 or a decrease in PO 2 can affect respiration through respiratory centers, thus influencing BHT. [1] The maximal breath-holding time (BHT) has been used in respiratory physiology as a measure of ventilatory response. [2],[3],[4] The unpleasant bursting sensation in the lower chest and abdomen and the onset of irregular inspiratory muscle activity have been well documented at the breakpoint of the breath-holding maneuver. [5]

Respiratory efficiency can be increased by training. Respiratory efficiency tests facilitate the increase in the strength of the respiratory muscles. Age and sex also affect the breath-holding time. [6]

Smoking and obesity are leading global causes of death. More than 2000 potentially noxious constituents have been identified in tobacco smoke, many of which are potential carcinogens. [2] It is a well-established fact that smoking causes inflammation of the air ways and impairment of the lung functions. It is also a major risk factor for developing COPD.

Smoking causes multidimensional health hazards. Its carcinogenic effects and adverse effects on cardio-pulmonary fitness have been established beyond doubt. There are sporadic reports of these effects being reversible. In our earlier research paper, we reported the effects of smoking on PFT parameters and its reversibility. [7]

Present study was conducted with the aim of assessing the role of smoking in BHT. To achieve the same, the specific objectives of the study were; (a) to estimate the BHT among asymptomatic smokers and ex-smokers and to compare the same with that of non-smokers, (b) to assess the reversibility of the impact of smoking on BHT, and (c) to study the relationship of BHT with age and BMI.


  Materials and Methods Top


Workers of KSRTC bus depot Mysore who were in the age group of 30-50 years participated in this study. Sample size was estimated to be enough to detect a clinically relevant difference of 15% in BHT at 5% level of significance and 90% power. Based on this, the required sample size of 28 in each group was arrived at. Group 1 (smokers) included those who smoked more than 5 pack years and were currently smoking. Group 2 (ex-smokers) included those who had smoked more than 5 pack years and had quit smoking at least 1 year before the study. Group 3 (non-smokers) consisted of non-smokers. Thus, 28 subjects in each group satisfying the age criteria were included in the study.

Inclusion criteria

For smokers: Current smokers in the age group of 30-50 years who have smoked at least 5 pack years.

For ex-smokers: Persons in the same age group who had smoked at least 5 pack years and had quit smoking for a minimum period of 1 year before the study.

For non-smokers: Bus depot workers between 30-50 years who had not smoked at all.

All the 3 groups were exposed to the same occupational environment.

Exclusion criteria

For all the 3 groups:
Subjects with respiratory and cardiac illness
Occasional smokers.

Collection of data

The purpose, procedure, and importance of the study were thoroughly explained to the bus depot workers, and their informed consent was obtained. Data on age, sex, smoking status, and the history of respiratory or cardiac illness was collected to decide the eligibility of the subjects for inclusion in 1 of the 3 groups. Subsequently, the data on height, weight, frequency, and duration of smoking were recorded. Body mass index (BMI) was derived by dividing the weight in kgs by the square of height in meters. Smoking history was calculated in pack-years as the product of tobacco use in (years) and the average number of cigarettes smoked per day and dividing the product by 20 (years x cigarettes per day/20). [8] This study was approved by the ethical committee of JSS medical college, Mysore.

After explaining the procedure, breath-holding time was recorded using the mouth piece attached to the mercury manometer. [9] The subjects were advised to blow through the mouth piece after full inspiration until pressure in mercury manometer up to 40 mmHg [10],[11] and maintained as long as possible till the breaking point when the subject was unable to hold the breath voluntarily. The time taken for this procedure was considered as BHT. The respiratory maneuvers were demonstrated to each subject before the test. Three reproducible tests were carried out for each measurement, and the best result was selected for statistical analysis.

Statistical analysis

Mean and standard deviation was worked out to assess the level of BHT in the 3 groups. In order to compare the level of BHT in the 3 groups (smokers, ex-smokers, and non-smokers), analysis of variance (ANOVA) was applied at 5% level of significance. The significance of difference in BHT between the 2 categories of frequency and duration of smoking was tested using Student's t-test for independent samples. Data entry and statistical analysis were performed using MS-excel and SYSTAT 13 package, respectively.


  Results Top


Basic characteristics of the subjects [Table 1]

In order to assess the comparability of 3 groups, we compared basic parameters, namely, age, height, and weight, with main focus on age, which is an independent predictor in any biological phenomena. Average age of the subjects in the 3 groups varied between 43-48 years with no statistically significant difference among the groups. Similarly, average height (163-166 cms) did not depict any significant difference among 3 groups. In case of weight, there was significant difference between smokers and non-smokers. However, ex-smokers did not differ significantly from any of other 2 groups. Consequently, BMI of non-smokers was higher than that of smokers but not significantly different for ex-smokers.
Table 1: Mean and standard deviation of various anthropometric parameters among the 3 groups (each 28) along with the results of ANOVA and post-hoc tests

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Effect of smoking on BHT and its reversibility [Table 2]a and b and [Figure 1]

A clear impact of smoking on BHT was observed. BHT was found to be significantly reduced among smokers compared to non-smokers (P < 0.001). The reduction in BHT was to the extent of about half. There was a significant increase in mean values of BHT of ex-smokers compared to smokers, indicating the improvement in respiratory strength and reserve after the person quits smoking. As far as ex-smokers and non-smokers are concerned, there was no significant difference in BHT, indicating an almost complete recovery of BHT on quitting the habit. We did a relative comparison of BHT also. It was found to be reduced to 54% among smokers, and recovery was seen up to 89% among ex-smokers.
Figure 1: Relative quantum of BHT in smokers and exsmokers compared to non-smokers

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Table 2:

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To look into the role of frequency of smoking, we classified the same into 2 classes; ≤12 cigarettes per day and >12 cigarettes per day. However, no statistically significant difference was found between these 2 groups. Similarly, duration of smoking was also classified into 2 classes, and no significant difference was observed between the 2 groups.

Relationship of BHT with AGE and BMI [Table 3] and [Table 4]

First, we compared BHT among different categories of age and BMI. Impact of age on BHT was found in non-smokers. In smokers and ex-smokers, there was a reduction in BHT with an increase in age. The differences, however, were not statistically significant. As far as BMI is concerned, there was deterioration in BHT with increase in BMI. However, the same were not statistically significant.
Table 3: Mean and standard deviation (SD) of BHT according to age and BMI among the three groups under study

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Table 4: Pearson's coefficient of Correlation of BHT with age, BMI, frequency, and duration of smoking

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Subsequently, we also estimated Pearson's correlation coefficient to quantify the linear relationship of BHT with age and BMI. A statistically significant negative correlation was observed when BHT was correlated with age, especially in smokers. Though there was a negative correlation between BMI and BHT, it was not statistically significant. A paradoxical correlation was noted when BHT was correlated with smoking frequency, especially in smokers, but it was not statistically significant. Smoking duration also showed a negative correlation indicating that as the duration of smoking increases, BHT values reduced.


  Discussion Top


Breath-holding time (BHT) has been used in respiratory physiology as a measure of ventilatory response. It is directly proportional to the lung volume at the onset of breath-holding, partly because this has a major influence on oxygen stores. [2] When one holds one's breath at rest, a total of about 600 mL of O 2 is available and can be utilized. "Normal" maximal BHT is 30 to 60 seconds. The arterial PO 2 then drops to about 75 to 50 mmHg, and the PCO 2 rises from 45 to 50 mmHg. This elevated CO 2 pressure plays a greater role in forcing the individual to discontinue the breath-holding than does the reduced O 2 pressure. [12]

The simplest objective measure of breath-holding is its duration, which is highly variable. Breath-holding is a voluntary act, but normal subjects appear unable to breath-hold to unconsciousness. A powerful involuntary mechanism normally overrides voluntary breath-holding and causes the breath that defines the breakpoint. The central respiratory rhythm is present throughout breath-holding. Humans cannot, therefore, stop their central respiratory rhythm voluntarily. The breath hold test is one of the many methods used in order to induce a sensation of dyspnea and provide information regarding the onset of and resistance to the sensation of dyspnea, [13] thus deriving that smoking reduces the capacity to endure physical discomfort. [14] It is a psycho- physiological phenomenon and is thus influenced by many factors.

Smoking has an impact on BHT, and the resultant deterioration may be due to the carbon monoxide, tar, and other toxic contents of tobacco smoke adversely affecting the alveoli. [15] Cigarette smoking decreases the breathing capacity of the lungs. Smoking accelerates the decline in forced expiratory volume in 1 second, which strongly indicates that important inflammatory and/or remodeling processes are positively affected. In individuals who smoke, are obese, or both, the breath hold test reveals pulmonary abnormalities, even in case in which spirometry results are normal. [13] Even asymptomatic smoking is associated with impaired mucociliary clearance function and significant mucosal damage in major bronchi and causes central and peripheral airway inflammation. Tobacco promotes release of superoxide anion, a factor, thought to be involved in the pathogenesis of emphysema and of smoking-related small airway disease. [16]

BHT was found to be substantially reduced among smokers, and recovery was seen among ex-smokers in our study. This reduction in BHT indicates that prolonged and intense smoking may lead to one of the major morbid complications that is chronic obstructive pulmonary disease (COPD) as low BHT values have been recorded in COPD patients. [17] The lower values of BHT in smokers when compared with non-smokers were also observed in a study conducted on workers exposed to dust and fumes. [18] Respiratory disorders develop much earlier and, therefore, respiratory morbidity is also higher in smokers. It was also observed that the earlier the person quits smoking, the better the lung function improvements are. Thus, this study goes on to suggest that BHT improves if the person quits smoking earlier.

Similar to our study, another study also stated that breath-holding ability was greater in ex-smokers than in current or non-smokers. A behavioral mechanism whereby longer breath holders smoke less because of a greater tolerance for the physical discomfort associated with intervals between cigarettes is consistent with these findings. [18] Another similar study also observed a difference in breath-holding ability whereby sustained quitters held their breaths for longer. [19] Though some studies have suggested that ex-smokers still show lung damage and the negative effect remains even after a smoker quits, [20] our study revealed recovery of BHT in ex-smokers.

Contrary to a study, which suggested that the sex and age of the patient had no significant effect on breath-holding performance, [21] our study showed that there was a reduction in BHT with increase in age. A weak inverse relationship between patient's age and BHT indicates that older patients tend to hold their breath for a shorter period than do younger patients as respiratory functions may influence the BHT.

This study has substantiated the deterioration of BHT with increase in BMI. This correlates well with other studies that showed that BHT was shorter in obese subjects compared with normal subjects, and another study done on obese females showed significant differences in the mean of the breath-holding time between the normal and the obese female subjects. A high but inverse relationship was found between estimated body fat and breath-holding time. [22] We also know that if there is any correlation between BMI and BHT, it is negative as suggested by a similar study, which states that the extent of lung function loss tended to be higher among those who reported greater BMI values. [23] Thus, higher BMI may result in reduction in the values of BHT. BHT is also a measure of endurance for physical discomfort. This was studied by determining the breath-holding ability and correlating this with grip-holding ability, thus serving as a marker of endurance for physical discomfort. [24]

Conservatism is an important issue in any study related to smoking. Generally, the smokers are expected to be conservative in reporting the duration and frequency of smoking. This is more so in case of ex-smokers. There is a possibility that a person claiming to have quit the habit, smokes occasionally. This might have had an impact on the findings about the reversibility of the deterioration in BHT. Therefore, the estimate of quantum of reversibility reported by present study may be the conservative one. More stringent criteria in selecting ex-smokers may resolve the issue of conservatism in reporting.

Cigarette smokers who attempt to quit often relapse. [25] Recovery from smoking depends on many factors, such as, duration, frequency, and type of smoking before quitting and the resultant deterioration, duration since quitting and many other life style-related factors. It was not possible to consider these factors in the present study given the sample size, which was estimated to be enough to detect the difference in different groups. Therefore, a further study with the larger sample size incorporating associated factors may be recommended. It may be noted that behavior of tobacco use is a habit very difficult to change, even with medicinal aids for cessation. [26] Only a small proportion of smokers stop smoking successfully on their own. Therefore, once established, the facts about recovery after quitting the habit may be important information useful for counseling the smokers for quitting the habit.

As stated earlier, BHT is an indicator of efficiency of breathing function and is a measure of ventilatory response. The commonest complication seen in chronic smokers is chronic bronchitis, which paralyzes the cilia lining the bronchi. This, along with mucus accumulation, serves as a nidus for infection and inflammation, leading to edema and blockage of airways restricting the entry of oxygen into the alveoli. Though the direct patho-physiological mechanisms of smoking affecting BHT is not clear, smokers show a reduction in lung volumes, their respiratory muscle strength and their capacity to endure physical discomfort is limited. The reduced BHT observed in smokers could be explained better by considering the levels of PCO 2 and PO 2 chemical changes in their blood. It is a known fact that smoking raises the CO 2 levels in blood. The CO present in cigarette smoke is more than 600 times the concentration of CO in automobile exhaust. This causes potentially hazardous levels of CO in smoker's blood (4-15 times higher than that of a non-smoker), which avidly binds with the hemoglobin forming carboxy hemoglobin, thus effectively reducing the transport of oxygen in blood. Hence, a smoker already has an elevated threshold for hypoxia and hypercapnia compared to a non-smoker causing the rapid attainment of the break point, ultimately reducing the BHT.

Regular physical exercise may be associated with BHT of an individual and, therefore, may act as a potential confounder in this type of studies. However, with the given socio-demographic and economic status and nature of work of the study subjects, regular physical exercise among them is expected to be not considerable. Therefore, it may have a negligible effect on the results of this study.

To conclude, this study has demonstrated the substantial deterioration of BHT in smokers and the indications of recovery among ex-smokers. However, in view of the limitations and potential biases, there is a possibility of conservatism in the estimates of deterioration and recovery. Therefore, we recommend further active research with larger sample size taking into account the quantum of exposure, duration of quitting, and regular physical exercise. This may possibly establish the recovery of BHT among ex-smokers, a very important fact from public health policy point of view.

 
  References Top

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