Respiratory Physiology and Clinical Manifestations of Obstructive Sleep Apnea: Pathophysiological Mechanisms and Cardiovascular Consequences

Background: Obstructive sleep apnea (OSA) is a highly prevalent sleep-related breathing disorder characterized by recurrent upper airway collapse, intermittent hypoxemia, and sleep fragmentation. Beyond sleep disruption, OSA is increasingly recognized as a systemic condition with strong associations with cardiovascular morbidity and mortality. Objectives: The purpose of this study was to examine the link between OSA severity, respiratory physiology, clinical symptoms, and cardiovascular implications in adult patients with suspected OSA. Methods: A prospective study was carried out at two tertiary care hospital in Lahore, Pakistan, between March 2023 and March 2024. Ninety patients aged 30-70 years performed a standardized clinical examination, including the Epworth Sleepiness Scale (ESS), anthropometry, nighttime polysomnography (PSG), arterial blood gas measurement, and cardiovascular evaluations such as blood pressure, electrocardiography, echocardiography, and biomarker testing. The severity of OSA was determined using the apnea-hypopnea index (AHI). The data was analyzed using SPSS v26.0, with a significance level of p <0.05. Results: The average age was 49.6 ± 10.8 years, and 64.4% were men. Patients with severe OSA exhibited substantially greater BMI, neck circumference, and ESS ratings compared to moderate OSA (p < 0.001). PSG results showed a decline in mean nocturnal SpO₂ (92.4% in moderate vs. 87.2% in severe, p < 0.001), oxygen desaturation index, and alertness index. Severe OSA was associated with higher rates of cardiovascular problems, including as hypertension (78.1%), resistant hypertension (21.9%), atrial fibrillation (18.8%), diastolic dysfunction (46.9%), pulmonary hypertension (28.1%), and increased hs-CRP (6.9 ± 2.2 mg/L). Conclusion: OSA severity strongly correlates with respiratory impairment, systemic inflammation, and cardiovascular dysfunction. Early recognition and comprehensive management are essential to reduce long-term cardiovascular risk and improve patient outcomes.