Preserved Ratio Impaired Spirometry in Low- and Middle-Income Countries: An Emerging Cardiopulmonary Phenotype and Cardiovascular Risk-A Narrative Review.

Preserved ratio impaired spirometry (PRISm) is increasingly recognized as a clinically important non-obstructive spirometric phenotype associated with excess all-cause, respiratory, and cardiovascular mortality. PRISm is variably defined across studies and should be distinguished from pre-COPD and restrictive spirometric pattern, particularly in LMIC settings where diagnostic context may differ. Although most evidence has been generated in high-income settings, PRISm may be especially relevant in low- and middle-income countries (LMICs), where the phenotype appears to arise within a markedly different exposure environment. Rather than reflecting predominantly the smoking-obesity-metabolic profile commonly described in wealthier populations, PRISm in LMICs may more often emerge from the cumulative effects of tuberculosis, household biomass smoke, ambient particulate air pollution, poverty-related undernutrition, impaired lung growth, and other adverse life-course exposures. These factors may contribute both to low-volume lung-function impairment and to increased cardiovascular risk through shared pathways of chronic low-grade inflammation, immune activation, oxidative stress, endothelial dysfunction, and metabolic dysregulation. In this context, PRISm may represent a measurable interface between environmental and infectious lung injury, social disadvantage, and systemic vascular vulnerability. The emerging literature further suggests that PRISm in LMICs may include distinct leaner, poverty-related, and infection-linked phenotypes that differ from the obesity-associated patterns more often described in high-income cohorts. This perspective has important clinical implications, as PRISm may identify individuals at elevated risk of cardiometabolic comorbidity, heart failure, stroke, and cardiovascular death who may otherwise remain unrecognized within current respiratory care pathways. Although direct causal evidence remains limited, the convergence of epidemiological, mechanistic, and clinical data supports the view that PRISm in LMICs should be considered a meaningful cardiopulmonary risk state rather than a benign spirometric abnormality. Further LMIC-focused longitudinal, mechanistic, and implementation research is needed to refine phenotyping, clarify causal pathways, and inform integrated prevention strategies.