Sleep apnea syndrome refers to a constellation of findings deriving from frequent episodes of apnea (i.e., non-breathing) and hypopnea (i.e., ineffective breathing) during sleep.1 There are two forms of sleep apnea: central and obstructive. Central sleep apnea is caused by a defect in brain signaling, resulting in episodes of apnea and hypopnea. Meanwhile, obstructive sleep apnea (OSA) – the more common counterpart – refers to the presence of apneic and hypopneic episodes due to the relaxation of oral, soft palatal musculature, causing complete (i.e., apnea) or incomplete (i.e., hypopnea) obstruction of airflow during sleep.2 Sleep apnea can result in a number of adverse health effects, both short-term and long-term.
While sleep apnea represents a syndrome, there are many adverse sequelae resulting from these periods of apnea and hypopnea that lead to hypoxemia (i.e., low blood oxygen tension and saturation); hypoxemia leads to reduced oxygen delivery to tissues, causing tissue damage.2 Sleep apnea also increases the risk of long-term cardiovascular disease. It not only leads to decreased oxygen delivery to tissues, but it also results in a stress response by the body and increased pressure on the walls of the heart. This, in turn, leads to organ dysfunction, increased heart rate, and predisposes the heart to irregular rhythms (i.e., arrhythmias).3 OSA increases one’s risk of stroke (odds ratio [OR] 3.8), death in severe OSA (hazard ratio 3.8), hypertension (OR 2.9), motor vehicle accidents (relative risk [RR] 2.4), heart failure (RR 2.4), occupational accidents (RR 2.2) and type 2 diabetes (OR 1.6) according to a 2015 literature review.4
More recently, OSA has been found to have high prevalent comorbidity for other respiratory diseases. The amalgamation of OSA with another respiratory disorder is referred to as an overlap syndrome.5 OSA has been found to be in overlap with chronic obstructive pulmonary disease, asthma, and interstitial lung disease.5 Another pulmonary pathology which can arise with or from OSA is pulmonary hypertension. Chronic, or long-term, sleep apnea can lead to increased pressures against which the right ventricle must overcome in order to send de-oxygenated blood through the pulmonary circulation to oxygenate the red blood cells. This increased pressure, referred to as pulmonary hypertension, is caused by areas of the lung being deventilated by apnea or hypopnea. In response to the decreased oxygen delivery to the alveoli – the functional, oxygen-carbon dioxide exchange unit of the lung – the capillaries supplying these non-ventilated or hypo-ventilated alveoli constrict, raising the blood pressure within the pulmonary circuit. This can eventually lead to what is known as pulmonary hypertension.6
In short, sleep apnea is a syndrome caused by periodic and prolonged episodes of apnea and hypopnea. OSA, rather than central sleep apnea, is the most common form. When untreated, undertreated, or prolonged, this can lead to a slew of adverse health effects in the long term. Cardiovascular disease is one of the more concerning and highly documented adverse outcomes. However, the manifestation of pulmonary disease, such as overlap syndromes and pulmonary hypertension, can ensue as well. If one is diagnosed with, or suspects that they have, sleep apnea syndrome, they should be evaluated by a medical provider.
References
1. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med. 1993;328(17):1230-1235. doi:10.1056/NEJM199304293281704
2. Cumpston E, Chen P. Sleep Apnea Syndrome. In: StatPearls. StatPearls Publishing; 2025. Accessed January 18, 2025. http://www.ncbi.nlm.nih.gov/books/NBK564431/
3. Javaheri S, Barbe F, Campos-Rodriguez F, et al. Sleep Apnea: Types, Mechanisms, and Clinical Cardiovascular Consequences. J Am Coll Cardiol. 2017;69(7):841-858. doi:10.1016/j.jacc.2016.11.069
4. Knauert M, Naik S, Gillespie MB, Kryger M. Clinical consequences and economic costs of untreated obstructive sleep apnea syndrome. World J Otorhinolaryngol – Head Neck Surg. 2015;1(1):17-27. doi:10.1016/j.wjorl.2015.08.001
5. Bouloukaki I, Fanaridis M, Testelmans D, Pataka A, Schiza S. Overlaps between obstructive sleep apnoea and other respiratory diseases, including COPD, asthma and interstitial lung disease. Breathe Sheff Engl. 2022;18(3):220073. doi:10.1183/20734735.0073-2022
6. Kholdani C, Fares WH, Mohsenin V. Pulmonary hypertension in obstructive sleep apnea: is it clinically significant? A critical analysis of the association and pathophysiology. Pulm Circ. 2015;5(2):220-227. doi:10.1086/679995