NUR 315 Module 5 Milestone Two example

Milestone Two: The Pathophysiology of Obstructive Sleep Apnea Behind Resistant Hypertension and Atrial Fibrillation

[Student Name]

Southern New Hampshire University

NUR 315: Pathophysiology for Nurses

Final Project Milestone Two

[Instructor Name]

[Date]

The organization, setting and figures below are a composite written as a model document. No real employer, client, colleague or patient is described.

Milestone Two: The Pathophysiology of Obstructive Sleep Apnea Behind Resistant Hypertension and Atrial Fibrillation

Case Recap

The case selected in Milestone One is a 57-year-old restaurant manager whose body mass index is 34 and whose neck circumference measures of 45 centimeters. His blood pressure averages 152/94 mmHg despite adherence to three antihypertensive medications, including a diuretic, which meets the definition of resistant hypertension. Two months ago he went to the emergency department with palpitations and was found to be in atrial fibrillation, which converted to sinus rhythm with medication. His wife reports loud snoring with pauses in breathing, and he falls asleep while reading in the afternoon. An overnight sleep study showed an apnea-hypopnea index of 38 events per hour, with oxygen saturation falling as low as 79 percent, consistent with severe obstructive sleep apnea.

This milestone explains the mechanism of obstructive sleep apnea and how it produces the findings in this case. The central claim is that the disease is not only a problem of sleep but a nightly cardiovascular stress that can raise blood pressure and remodel the atria.

The Airway in Normal Sleep

The upper airway behind the tongue and soft palate has no rigid support. It stays open during wakefulness because dilator muscles, particularly the genioglossus, keep a steady tone that resists the negative pressure created when air is drawn into the lungs. At sleep onset, the tone of these muscles falls, and the airway narrows slightly in everyone. In most people the narrowing is small enough that breathing continues normally (Jordan et al., 2014).

During rapid eye movement sleep, muscle tone falls further, which is why obstructive events are often longest and oxygen drops deepest in that stage. Lying on the back also allows the tongue and soft palate to fall backward under gravity, narrowing the airway more than in side-lying positions. These normal features of sleep explain why the disorder appears only at night and why its severity can change with sleep stage and body position.

What Goes Wrong in Obstructive Sleep Apnea

In obstructive sleep apnea, the airway is anatomically narrow, easily collapsible or both. In this patient, fat deposited around the pharynx and in the tongue reduces the space available, and a large neck circumference is a marker of that crowding. When muscle tone falls during sleep, the narrowed airway partly or completely collapses. A complete collapse with continued effort to breathe is an apnea; a partial collapse with reduced airflow is a hypopnea. His index of 38 events per hour means that his airway closed or nearly closed, on average, more than once every two minutes throughout the night.

Each event ends only when the brain briefly arouses from sleep. The arousal restores muscle tone, the airway opens, and the patient takes several large breaths before falling back to sleep, often without any memory of waking. Anatomy is not the only factor. Research has also identified variations in how responsive the dilator muscles are, how easily a person arouses and how stable breathing control is, which help explain why people with similar anatomy differ in severity (Jordan et al., 2014).

Three Nightly Stresses

Each obstructive event produces three stresses that repeat hundreds of times a night. The first is intermittent hypoxia. During the pause in airflow, oxygen saturation falls and carbon dioxide rises, and when breathing resumes, oxygen returns quickly. This cycle of low and restored oxygen resembles repeated small episodes of ischemia and reperfusion, which generate oxidative stress and inflammation in the vessel wall. His lowest saturation of 79 percent shows how deep those drops can be.

The second stress is sympathetic activation. Low oxygen stimulates chemoreceptors in the carotid bodies, which increase sympathetic nerve activity, and each arousal adds a further surge. Heart rate and blood pressure rise sharply at the end of each event. Over time, sympathetic activity remains elevated even during the day, which is thought to contribute to sustained hypertension (Yeghiazarians et al., 2021).

The third stress is mechanical. When the patient tries to breathe against a closed airway, the pressure inside his chest becomes strongly negative. That negative pressure pulls on the heart and great vessels, increases the load on the left ventricle and stretches the thin-walled atria. Repeated stretching of the atria is one of the proposed links between obstructive sleep apnea and atrial fibrillation.

From Nightly Stress to Cardiovascular Disease

The resistant hypertension in this case follows from the combination of persistent sympathetic activation, endothelial dysfunction from oxidative stress, and a hormonal push toward sodium retention through renin, angiotensin and aldosterone, which increases sodium and fluid retention (Rogers, 2023). Because these effects continue while the airway remains untreated, medications that act on one pathway may not be enough to control blood pressure. Obstructive sleep apnea is among the most common identifiable causes of resistant hypertension, which is why current guidance recommends considering it in patients whose blood pressure remains uncontrolled (Yeghiazarians et al., 2021).

Atrial fibrillation can be explained by the same processes acting on the atria. Repeated stretching from negative chest pressure, surges of sympathetic activity, hypoxia and inflammation can alter the electrical properties of atrial cells and promote fibrosis, creating the substrate in which the arrhythmia starts and persists. People with untreated obstructive sleep apnea also have a higher rate of recurrent atrial fibrillation after treatment such as cardioversion, which supports a causal contribution.

Linking Findings to Mechanisms

The table below summarizes how each finding in the case is explained.

Table 1

Clinical Findings and Their Mechanisms in the Case

Next Steps for the Final Analysis

The final case analysis will build on this mechanism by adding risk factors, including obesity, male sex and age, and by explaining how treatment acts on the chain described here. Continuous positive airway pressure works by splinting the airway open, which removes the obstruction that starts each cycle of hypoxia, arousal and pressure swings. The analysis will also address nursing implications, including screening questions, support for adherence to positive airway pressure, and monitoring of blood pressure and heart rhythm once treatment begins.

References

Jordan, A. S., McSharry, D. G., & Malhotra, A. (2014). Adult obstructive sleep apnoea. The Lancet, 383(9918), 736-747. https://doi.org/10.1016/S0140-6736(13)60734-5

Rogers, J. L. (Ed.). (2023). McCance & Huether's pathophysiology: The biologic basis for disease in adults and children (9th ed.). Elsevier.

Yeghiazarians, Y., Jneid, H., Tietjens, J. R., Redline, S., Brown, D. L., El-Sherif, N., Mehra, R., Bozkurt, B., Ndumele, C. E., & Somers, V. K. (2021). Obstructive sleep apnea and cardiovascular disease: A scientific statement from the American Heart Association. Circulation, 144(3), e56-e67. https://doi.org/10.1161/CIR.0000000000000988