Normative reference values for maximum inspiratory and expiratory pressures in healthy Singaporean adults aged 21 to 80 years

This study aims to: (1) establish the NRV of MIP and MEP, and (2) explore the correlation of demographic and anthropometric variables that could affect MIP and MEP in the healthy Singaporean adult population aged 21 to 80 years.

This cross-sectional study was conducted between February 2023 and August 2024. Healthy Singaporean adults aged 21-80 years with body mass index (BMI) below 27.5 kg/m² were recruited via convenience sampling. Participants were excluded if they were pregnant or had any unresolved cardiopulmonary or musculoskeletal issues, and/or other difficulties such as cognitive impairment that would interfere with their participation in the MIP and MEP measurements. Age and gender were obtained. Height, weight, waist, and hip circumferences were measured, with BMI and waist-hip ratio (WHR) calculated using standard formulae. Chest expansion circumferences at the level of the axilla and xiphoid process were measured. MIP and MEP were measured using a portable spirometer for a minimum of 2 attempts, with the best attempt used for data analysis. Normality testing was conducted to ascertain the parametric properties of the dataset, before applying non-parametric descriptive statistical analyses to establish the NRV. Spearman’s rank correlations were used to establish the agreement between the demographic and anthropometric variables with MIP and MEP. Statistical significance was accepted if p 0.05.

364 Singaporean adults (178 males, 186 females) completed this study. The average MIP and MEP, expressed as median (interquartile range), were 95 (73-122) and 74 (61-88) cmH₂O, respectively. Males had higher MIP and MEP [112 (88-134); 85 (72-105) cmH₂O] than females [85 (66-103); 64 (56-76) cmH₂O]. Gender (Spearman rho r_s = -0.391), age (r_s = -0.108), height (r_s = 0.316), weight (r_s = 0.416), BMI (r_s = 0.349), WHR (r_s = 0.246), chest expansion circumferences at axilla (r_s = 0.196) and xiphoid process levels (r_s = 0.207) correlated significantly (p 0.05) with MIP. Gender (r_s = -0.529), height (r_s = 0.376), weight (r_s = 0.462), BMI (r_s = 0.362), WHR (r_s = 0.317) and chest expansion circumference at xiphoid process level (r_s = 0.144) correlated significantly (p 0.05) with MEP. 

This study updated the NRV of MIP and MEP in healthy Singaporean adults. Gender, height, weight, BMI, WHR and chest expansion circumference at xiphoid process level correlated significantly with both MIP and MEP.

This study has determined the normative values for MIP and MEP, allowing for the approximation of normal respiratory muscle strength. It also provides benchmarks to indicate suboptimal respiratory pressure, and therefore guides the prescriptions for interventions such as inspiratory muscle training.