Relationship between peak expiratory flow and impaired functional capacity in obese individuals

Introduction: Obesity, characterized by the accumulation of excess body fat, can alter respiratory mechanics and compromise functional capacity. Given its increasing prevalence and the significant morbidity associated with the condition, it is important to investigate techniques that enable rapid, easy measurement of lung function and the possible correlation between obesity and functional capacity. Objective: To assess lung function and functional capacity in obese adults and determine whether there is a correlation between reduced peak expiratory flow and impaired functional capacity. Methods: 30 participants, distributed into two groups: obese (36 ± 13 years) and normal weight (31 ± 9 years) were evaluated based on anthropometric measurements, the six-minute walk test (6MWT) and peak expiratory flow (PEF). Results: The obese individuals showed reduced PEF (382 ± 99 vs. 497 ± 104 L/min, p < 0.01), walked shorter distances in the 6MWT (453 ± 37 vs. 617 ± 50 m, p < 0.01), had higher blood pressure and perceived exertion (p < 0.05) when compared to normal weight participants. Additionally, there was a positive significant association between expiratory flow and distance walked in the 6MWT (r = 0.635 and p < 0.001). Conclusion: Obese individuals exhibited lower PEF and walked shorter distances in the 6MWT, indicating a positive correlation between these two variables. In light of this outcome, the assessment methods used could contribute to improving analysis of respiratory and functional status in this population and aid in exercise prescription.


Introduction
Obesity, a chronic condition characterized by the accumulation of excess body fat, is a major global public health problem. 1,2 The World Health Organization (WHO) estimates that one billion people worldwide are overweight and 300 million of these are obese.Projections are that 40% of the population in the USA, 30% in England and 20% in Brazil will be obese by 2025. 3 Different anthropometric indices can be used to identify obesity. The body mass index (BMI) is considered the international standard for obesity classification, while the abdominal circumference (AC) and waist-hip ratio (WHR) characterize increased cardiovascular risk. 4 According to the WHO, individuals with BMI between 18.5 and 24.9 kg/m² are considered normal weight and those with values above 30 kg/m² are considered obese. 5 For AC and WHR, respective measures for men and women of more than 102 and 88 cm and 0.95 and 0.85 increase the risk of cardiovascular dysfunction. 6 Studies show that obesity can compromise respiratory system mechanics. 7 Obese adults tend to experience respiratory problems, with reduced aerobic capacity and lung compliance as well as increased airway resistance, leading to a decline in functional residual capacity (FRC), forced vital capacity (FVC), residual volume (RV) and forced expiratory volume in one second (FEV 1 ). 8,9 Changes in respiratory function can be identified using a peak flow meter, which evaluates peak expiratory flow (PEF), that is, the maximum flow generated during a forced expiration. 10 This is a simple, non-invasive, lowcost technique that exhibits good reliability because of its

Results
The results obtained indicate similar age, height and sex ratio between the groups. However, as expected, anthropometric variables, weight, BMI, AC, WC, HC and WHR differed significantly between groups, with higher values recorded in obese individuals (Table 1).
With respect to predicted PEF, scores in the normal weight group were within the predicted range, whereas obese individuals obtained low values (p1). The obese group obtained significantly lower PEF scores than their normal weight counterparts (p2) ( Table 2).
The obese group performed worse in the 6MWT, walking shorter distances than the normal weight participants. These results are presented in Table 3.
The behavior of cardiorespiratory variables differed between groups during the 6MWT, as shown in Figure   1.    these physiologically expected responses are shown in Figure 1.
Indeed, a positive significant correlation was observed between PEF and distance walked in the 6MWT (r = 0.635 and p < 0.001), as shown in Figure 2. Corroborating these findings, Retory et al. 25 also found that obese adults walked shorter distances in the 6MWT.
Bautista et al. 26 reported that obese participants walked approximately 100 meters less than their normal weight counterparts. Even among the severely obese, Santarém et al. 27 reported that individuals with a BMI between 40 and 49.9kg/m² walked further than those who BMI was 50 to 60 kg/m² .
Although poor lung function can compromise functional capacity, obese individuals do not always exhibit reduced lung volumes and capacities. 23  Increased SBP and HR are directly related, since a rise in the latter alters cardiac output. Respiratory rate and perceived exertion increase due to the rise in oxygen consumption and carbon dioxide production, resulting in greater pulmonary ventilation and dyspnea. 30,31 With respect to these cardiovascular variables, analyzed during the 6MWT, the positive pressure and chronotropic response can be justified by sympathetic activation. Trevizani et al. 32 found that HR tends to increase linearly with exertion and that SaO 2 remains unchanged when the oxygen supply to the body is satisfactory, however, SaO 2 declined in the present study. In this context, Retory et al. 25 reported that obese individuals displayed a higher rate of dyspnea during the 6MWT. This result is similar to that of the present study, whereby perceived exertion was greater among the obese participants.
Sympathetic activation may be hyperactive in cardiometabolic diseases due to the respiratory muscle metaboreflex. In these cases, prioritized perfusion to ventilatory muscles such as the diaphragm could explain

Discussion
The main finding of the present study is that obese

Conclusion
Obese individuals exhibited reduced peak expiratory flow and walked shorter distances in the sixminute walk test. Low peak expiratory flow is directly correlated with decreased functional capacity. In light of this outcome, the assessment methods used could contribute to improving analysis of respiratory and functional status in this population and aid in exercise prescription. The results support an easy-to-perform assessment of the health status of obese individuals that could suggest, at least in part, greater risk of morbidity.

Author´s contributions
GMSM and AMR participated in all stages of the study, from its conception to writing the manuscript, and were responsible for choosing the topic, planning and carrying out the research, data collection in the field, as well as data analysis and interpretation.
PMMC provided support in study planning, revised data interpretation and corroborated in writing the manuscript. PACM assisted in the statistical design, revised data analysis and interpretation and corroborated in writing the manuscript. IMGF was the study advisor, responsible for guiding the research and the statistical design, assisted in defining the topic and methods used for respiratory and functional assessment, monitored data collection in the field, performed data analysis and interpretation, reviewed the reports and corroborated in writing the manuscript.
All the authors contributed to compiling the manuscript.