A 63-year-old man presents to his primary care physician complaining of excessive daytime sleepiness. He explains that this problem has worsened slowly over the past few years but is now interfering with his ability to play with his grandchildren. He worked previously as an overnight train conductor, but he has been retired for the past 3 years. He sleeps approximately 8-9 hours per night and believes his sleep quality is good; however, his wife notes that he often snores loudly during sleep. He has never experienced muscle weakness or hallucinations. He has also been experiencing headaches in the morning and endorses a depressed mood. His physical exam is most notable for his large body habitus, with a BMI of 34. What is the best description of the underlying mechanism for this patient's excessive daytime sleepiness?

Circadian rhythm sleep-wake disorder

Deficiency of the neuropeptides, orexin-A and orexin-B

A 54-year-old man comes to the physician because of excessive daytime sleepiness for 5 months. He wakes up frequently at night, and his wife says his snoring has become louder. He is 180 cm (5 ft 10 in) tall and weighs 104 kg (230 lb); his BMI is 33 kg/m2. His pulse is 80/min and his respiratory rate is 11/min. His jugular venous pressure is 7 cm H2O. He has 2+ pitting edema of the lower legs and ankles. Arterial blood gas analysis on room air shows a pH of 7.42 and a PCO2 of 41 mm Hg. An x-ray of the chest shows normal findings. Which of the following is the most likely underlying cause of this patient's condition?

Intermittent collapse of the oropharynx

Daytime alveolar hypoventilation

Decreased levels of hypocretin-1

Increased medullary ventilatory responsiveness

A 68-year-old man presents with shortness of breath, particularly when walking up stairs and when lying down to go to sleep at night. He also complains of a chronic cough and states that he now uses 2 extra pillows at night. The patient has a history of type 2 diabetes that is well-managed with metformin. He also takes Prozac for a long-standing history of depression. The patient has a 60-pack-year smoking history. He also has a history significant for alcohol abuse, but he quit cold turkey 15 years ago when his brother was killed in a drunk driving accident. Both he and his brother were adopted, and he does not know other members of his biological family. Despite repeated efforts of patient counseling, the patient is not interested in quitting smoking. The physical exam is significant for an obese male using accessory muscles of respiration. The vital signs include: temperature 36.8°C (98.2°F), heart rate 95/min, respiratory rate 16/min, and blood pressure 130/85 mm Hg. The oxygen saturation is 90% on room air. Additional physical exam findings include cyanotic lips, peripheral edema, hepatomegaly, and ascites. The cardiovascular exam is significant for an S3 heart sound and elevated JVP. The pulmonary exam is significant for expiratory wheezing, diffuse rhonchi, and hyperresonance on percussion. The laboratory test results are as follows: BUN 15 mg/dL pCO2 60 mm Hg Bicarbonate (HCO3) 32 mmol/L Creatinine 0.8 mg/dL Glucose 95 mg/dL Serum chloride 103 mmol/L Serum potassium 3.9 mEq/L Serum sodium 140 mEq/L Total calcium 2.3 mmol/L Hemoglobin 26 g/dL Bilirubin total 0.9 mg/dL Bilirubin indirect 0.4 mg/dL Iron 100 Ferritin 70 TIBC 300 The posterior-anterior chest X-ray is shown in the image. Which of the following interventions is indicated for decreasing the mortality of this patient?

Both smoking cessation and oxygen administration

A 65-year-old male with multiple comorbidities presents to your office complaining of difficulty falling asleep. Specifically, he says he has been having trouble breathing while lying flat very shortly after going to bed. He notes it only gets better when he adds several pillows, but that sitting up straight is an uncomfortable position for him in which to fall asleep. What is the most likely etiology of this man's sleeping troubles?

Amyotrophic lateral sclerosis (ALS)

A 56-year-old man presents to the physician for the evaluation of excess snoring over the past year. He has no history of a serious illness and takes no medications. He does not smoke. His blood pressure is 155/95 mm Hg. BMI is 49 kg/m2. Oropharyngeal examination shows an enlarged uvula. Examination of the nasal cavity shows no septal deviation or polyps. Examination of the lungs and heart shows no abnormalities. Polysomnography shows an apnea-hypopnea index of 2 episodes/h with a PCO2 of 51 mm Hg during REM sleep. Arterial blood gas analysis in room air shows: pH 7.33 PCO2 50 mm Hg PO2 92 mm Hg HCO3− 26 mEq/L Which of the following best explains these findings?

Obesity hypoventilation syndrome

Obesity hypoventilation syndrome with obstructive sleep apnea

Central hypoventilation syndrome with obstructive sleep apnea

Central hypoventilation syndrome

Obstructive sleep apnea-hypopnea syndrome

A 37-year-old man presents to his primary care physician because he has been experiencing episodes where he wakes up at night gasping for breath. His past medical history is significant for morbid obesity as well as hypertension for which he takes lisinopril. He is diagnosed with sleep apnea and prescribed a continuous positive airway pressure apparatus. In addition, the physician discusses making lifestyle and behavioral changes such as dietary modifications and exercise. The patient agrees to attempt these behavioral changes. Which of the following is most likely to result in improving patient adherence to this plan?

Provide follow-up appointments to assess progress in attaining goals

Refer the patient to a peer support group addressing lifestyle changes

Ask the patient to bring a family member to next appointment

Provide appropriate publications for the patient's educational level

Inform the patient of the health consequences of not intervening

A 49-year-old woman comes to the physician because of a 4-month history of a dry cough and shortness of breath on exertion. She also reports recurrent episodes of pain, stiffness, and swelling in her wrist and her left knee over the past 6 months. She had two miscarriages at age 24 and 28. Physical examination shows pallor, ulcerations on the palate, and annular hyperpigmented plaques on the arms and neck. Fine inspiratory crackles are heard over bilateral lower lung fields on auscultation. Which of the following additional findings is most likely in this patient?

Decreased right atrial pressure

A 35-year-old woman who was recently ill with an upper respiratory infection presents to the emergency department with weakness in her lower limbs and difficulty breathing. Her symptoms began with a burning sensation in her toes along with numbness. She claims that the weakness has been getting worse over the last few days and now involving her arms and face. Currently, she is unable to get up from the chair without some assistance. Her temperature is 37.0°C (98.6°F), the blood pressure is 145/89 mm Hg, the heart rate is 99/min, the respiratory rate is 12/min, and the oxygen saturation is 95% on room air. On physical examination, she has diminished breath sounds on auscultation of bilateral lung fields with noticeably poor inspiratory effort. Palpation of the lower abdomen reveals a palpable bladder. Strength is 3 out of 5 symmetrically in the lower extremities bilaterally. The sensation is intact. What is the most likely diagnosis?

Acute disseminated encephalomyelitis

Sleep-disordered breathing for USMLE Step 3: High-Yield Internal Medicine Lessons

Sleep-Disordered Breathing - The Nightly Choke

Obstructive Sleep Apnea (OSA): Repetitive pharyngeal collapse during sleep leading to intermittent hypoxia.
- Risk Factors: Obesity (neck circumference >17" men, >16" women), craniofacial abnormalities, alcohol/sedative use.
- Symptoms: Daytime somnolence, non-restorative sleep, morning headaches, loud snoring with witnessed apneas.
- 📌 Screening: STOP-BANG questionnaire.
Diagnosis: In-lab polysomnography (PSG) is the gold standard.
- Apnea-Hypopnea Index (AHI) defines severity: Mild (5-15/hr), Moderate (15-30/hr), Severe (>30/hr).
Management:
- Primary: CPAP, weight loss, positional therapy.

Normal vs. Obstructed Airway in Sleep Apnea

⭐ OSA is an independent risk factor for systemic hypertension, pulmonary hypertension, and atrial fibrillation due to chronic intermittent hypoxia and sympathetic surges.

Central Sleep Apnea (CSA): Impaired respiratory drive from CNS (e.g., heart failure, stroke); characterized by absent respiratory effort.

OSA vs. CSA - Airway vs. Brainstem

Obstructive Sleep Apnea (OSA): An "airway" problem. Repetitive upper airway collapse during sleep despite persistent respiratory effort.
Central Sleep Apnea (CSA): A "brainstem" problem. Periodic absence of respiratory effort and airflow from a transient loss of central drive to breathe.

Feature	Obstructive Sleep Apnea (OSA)	Central Sleep Apnea (CSA)
Pathophysiology	Physical obstruction (e.g., obesity, tonsillar hypertrophy)	Impaired central chemoreceptors; neurologic dysfunction
Effort	Present & often paradoxical (chest/abdomen move opposite)	Absent; no signal from the brain to breathe
Polysomnography	Continued respiratory effort despite absent airflow	No airflow & no respiratory effort
Key Associations	Loud snoring, daytime somnolence, hypertension	Heart failure (Cheyne-Stokes), stroke, opioids

⭐ Cheyne-Stokes respirations, a crescendo-decrescendo breathing pattern followed by apnea, is a hallmark of CSA in patients with advanced congestive heart failure.

Diagnosis - The Sleep Study

Polysomnography (PSG): In-lab, attended overnight study. Gold standard. Monitors EEG, EOG, EMG, ECG, respiratory effort, airflow, and O₂ saturation.
Home Sleep Apnea Test (HSAT): Unattended, portable monitor. For high-probability patients without significant comorbidities (e.g., CHF, COPD, neuromuscular disease).
Apnea-Hypopnea Index (AHI): Key diagnostic metric. Calculated as $AHI = (Total Apneas + Hypopneas) / Hours of Sleep$.
- Mild: 5-15 events/hr
- Moderate: 15-30 events/hr
- Severe: >30 events/hr

⭐ Hypopnea Definition: A reduction in airflow by ≥30% for ≥10 seconds, associated with ≥3% oxygen desaturation or an arousal from sleep.

Polysomnography setup for sleep-disordered breathing

Management - Pressurize & Stabilize

Positive Airway Pressure (PAP): First-line therapy for moderate-to-severe OSA.
- CPAP (Continuous): Constant pressure splinting the airway open. Initial choice for most OSA.
- BiPAP (Bilevel): Higher inspiratory (IPAP) and lower expiratory (EPAP) pressures. Used for CPAP intolerance, obesity hypoventilation syndrome (OHS), or COPD overlap.
- ASV (Adaptive Servo-Ventilation): Auto-adjusting pressure for central or complex sleep apnea.

CPAP machine with nasal pillow mask

⭐ SERVE-HF Trial: ASV is contraindicated in patients with chronic, symptomatic heart failure (HFrEF) and an LVEF ≤ 45% due to increased mortality risk.

Obstructive Sleep Apnea (OSA) is caused by recurrent upper airway collapse during sleep, strongly associated with obesity and increased neck circumference.

Key symptoms include excessive daytime somnolence, loud snoring, and witnessed apneas.

Polysomnography is the gold-standard diagnostic test; an AHI ≥ 15/hour is diagnostic.

Major complications include systemic hypertension, pulmonary hypertension, and increased risk of cardiovascular events.

CPAP is the first-line treatment. Weight loss is a critical adjunctive therapy.

Central Sleep Apnea is defined by a lack of respiratory effort, often seen in heart failure.

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