Restrictive spirometric pattern (RSP), characterized by reduced forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) with a preserved FEV1/FVC ratio, is associated with various conditions like interstitial lung diseases, pleural effusions, and neuromuscular disorders. Recent research indicates a higher prevalence of RSP in the general population, and studies using the US National Health and Nutrition Examination Survey (NHANES) have linked RSP to functional impairment, poor health, respiratory symptoms, multiple comorbidities, and reduced quality of life. However, the relationship between RSP severity and the decline in health status remains unclear. This study aims to investigate this relationship, focusing on the impact of RSP severity on physical activity, nutrition, and quality of life using a large, nationally representative dataset from the Korea National Health and Nutrition Examination Survey (KNHANES). The study's importance lies in potentially improving the understanding of the health burden associated with RSP and informing more tailored clinical interventions based on the severity of the condition. Understanding this correlation allows for more effective strategies for prevention and management of RSP-related health issues. The use of KNHANES data offers a strong foundation for generalizability of findings to the broader Korean population.

Existing literature extensively demonstrates the association between restrictive spirometric pattern (RSP) and a range of health problems. Studies using NHANES data have shown that individuals with RSP report higher rates of functional limitations and self-reported poor health compared to those with normal lung function. Furthermore, RSP is linked to increased respiratory symptoms and multiple comorbidities. Guerra et al. (2010) demonstrated the association between RSP and mortality in a longitudinal study. Other research highlights connections between RSP and reduced quality of life. However, a significant gap exists in understanding how the severity of RSP influences the extent of these adverse health outcomes. Previous studies have largely focused on the presence or absence of RSP without adequately considering its severity. This research aims to fill this gap by examining the graded impact of RSP severity on key health indicators.

This cross-sectional study utilized data from the Korea National Health and Nutrition Examination Survey (KNHANES) conducted between 2007 and 2016. The study population consisted of non-institutionalized South Koreans, sampled using a stratified, multistage clustered probability sampling design. From the initial 81,503 participants, individuals with missing weight variables or pulmonary function test (PFT) results were excluded, as were those with obstructive spirometric patterns. The final cohort included 23,615 participants categorized into three groups: normal spirometry, mild-to-moderate RSP, and severe RSP, based on pre-bronchodilator FEV1/FVC and FVC values. Demographic information, smoking status, income, medical history, and comorbidities were collected through self-reported questionnaires. Physical activity was assessed based on self-reported moderate and high-intensity activity. Quality of life was measured using the EuroQoL five dimensions (EQ-5D) questionnaire, with a cut-off value of 0.9 used to define poor quality of life. Statistical analyses, accounting for the complex sampling design, employed univariable and multivariable linear and logistic regression to analyze the associations between RSP severity and nutritional intake (total calories), physical activity (high-intensity), and quality of life (EQ-5D index). Multivariable analysis adjusted for age, sex, smoking status, BMI, education, income, and number of comorbidities.

The study revealed significant differences in various health indicators across the three RSP severity groups. Subjects with severe RSP were older, had a higher proportion of males, larger waist circumferences, lower education levels, and a greater prevalence of comorbidities (including diabetes, hypertension, cardiovascular disease, and others) compared to those with normal spirometry. Critically, individuals with severe RSP exhibited significantly lower total daily caloric intake (1661.1 ± 76.4 kcal) compared to the normal (2001.4 ± 8.7 kcal) and mild-to-moderate (1935.9 ± 22.6 kcal) RSP groups. They also demonstrated significantly reduced high-intensity physical activity (6.8% vs. 16.8% in normal and 14.5% in mild-to-moderate). The severe RSP group had a significantly lower EQ-5D index (0.88) indicating poorer quality of life compared to the normal (0.95) and mild-to-moderate (0.92) groups. Multivariable analysis showed that both mild-to-moderate and severe RSP groups had significantly lower caloric intake compared to the normal group (-56.6 kcal and -286.7 kcal, respectively). Mild-to-moderate and severe RSP groups were also associated with increased odds of having poor quality of life (adjusted OR 1.26 and 1.96, respectively). The impact of RSP severity on quality of life was particularly notable in males. Supplementary analysis on EQ-5D components showed severe RSP was associated with greater impairment in self-care and usual activities.

This study's findings strongly support the hypothesis that the severity of RSP is directly linked to declines in nutrition, physical activity, and quality of life. The observed reduction in caloric intake in individuals with RSP, despite often having higher BMIs, suggests a complex interplay of factors. The lower caloric intake may be a consequence of reduced physical activity and the increased prevalence of comorbidities, such as diabetes, leading to decreased appetite or metabolic changes. The disproportionate impact on males warrants further investigation into potential sex-specific mechanisms underlying this association. The significant reduction in quality of life, particularly in self-care and usual activities, emphasizes the broad impact of severe RSP. These findings highlight the importance of incorporating RSP severity into clinical assessments and management strategies. Modifying factors like physical inactivity and obesity may play a significant role in improving outcomes for individuals with RSP. However, due to the cross-sectional nature of the study, conclusions regarding causality should be cautious.

This study, using a large nationally representative dataset, demonstrates a strong correlation between the severity of restrictive spirometric pattern and reductions in nutrition, physical activity, and quality of life. The findings highlight the importance of considering RSP severity in clinical practice and suggest that interventions targeting modifiable factors like physical activity and obesity may be beneficial. Future prospective studies are needed to confirm these findings and elucidate the underlying mechanisms and potential interventions.

As a cross-sectional study, this research is limited in establishing causal relationships. The observed associations may be influenced by reverse causality; individuals with severe RSP might already have reduced caloric intake and physical activity. The study's focus on the Korean population limits the generalizability of findings to other populations. Self-reported data may introduce information bias, and the use of pre-bronchodilator spirometry might have led to misclassification of some individuals.