Sleep Apnea: OSA Pathophysiology, Diagnosis, and Treatment

Introduction

Sleep-disordered breathing encompasses a spectrum of conditions characterized by abnormal respiration during sleep. Obstructive sleep apnea (OSA) is the most common form, affecting approximately 15-30% of men and 10-20% of women in the United States. OSA is characterized by repeated episodes of complete (apnea) or partial (hypopnea) upper airway collapse during sleep, resulting in intermittent hypoxia, sleep fragmentation, and daytime symptoms.

Classification of Sleep-Disordered Breathing

Type	Description	Mechanism
Obstructive sleep apnea (OSA)	Repetitive pharyngeal collapse with continued respiratory effort	Anatomic narrowing + neuromuscular factors
Central sleep apnea (CSA)	Absence of respiratory effort due to loss of central drive	Cheyne-Stokes respiration (heart failure), high-altitude, opioid-induced
Mixed/complex apnea	Combination of OSA and CSA (often emerges on CPAP treatment)	Treatment-emergent central apnea
Upper airway resistance syndrome (UARS)	Increased respiratory effort without frank apnea or hypopnea	Mild airway resistance causing sleep fragmentation

Pathophysiology of OSA

Pharyngeal Collapse Mechanism

Factor	Contribution	Mechanism
Anatomic narrowing	Major	Obesity (fat deposition in lateral pharyngeal walls), large tongue, small mandible, enlarged tonsils, soft palate elongation
Pharyngeal dilator muscle dysfunction	Major	Reduced genioglossus (tongue) and tensor palatini activity during sleep; impaired neuromuscular compensation
Lung volume effect	Moderate	Decreased lung volume (especially supine and in obesity) reduces tracheal traction on pharynx
Instability of ventilatory control	Minor	High loop gain (ventilatory response to CO2) promotes cycling
Arousal threshold	Minor	Low arousal threshold causes frequent arousals that destabilize breathing

Obesity and OSA

Relationship	Detail
Prevalence	60-90% of OSA patients are overweight or obese
Relative risk	BMI >30: 5-7x increased risk of OSA
Mechanism	Adipose tissue in lateral pharyngeal walls narrows airway; visceral fat reduces lung volumes
Weight loss effect	10-15% weight loss reduces AHI by 50% in many patients
Weight loss targets	10% of body weight as initial goal

Anatomic Risk Factors

Feature	Significance
Neck circumference	Men >17 inches (43 cm); Women >16 inches (41 cm) - strong predictor
Mallampati score (III-IV)	Higher score indicates narrower oral airway
Retrognathia/micrognathia	Posteriorly positioned mandible reduces pharyngeal space
Tonsillar hypertrophy	Common cause in children; may contribute in adults
Macroglossia	Large tongue (obesity, acromegaly, Down syndrome)
Nasal obstruction	Increases negative pressure driving pharyngeal collapse

Risk Factors

Modifiable Risk Factors

Risk Factor	Odds Ratio	Mechanism
Obesity (BMI >30)	7-10x	Pharyngeal fat deposition, reduced lung volume
Alcohol before sleep	2-3x	Reduces pharyngeal dilator muscle tone
Smoking	2-4x	Upper airway inflammation, edema
Supine sleep position	2x (supine-predominant OSA)	Gravity-dependent pharyngeal collapse
Sedative medications	2-3x	Reduced pharyngeal dilator tone

Non-Modifiable Risk Factors

Risk Factor	Mechanism
Male sex	2-3x higher prevalence (fat distribution, hormonal factors)
Age	Increased prevalence (peak 50-70 years); pharyngeal compliance increases
Menopause	Increased risk (3x) due to hormonal changes affecting airway and fat distribution
Family history	Genetic factors: craniofacial structure, obesity predisposition, ventilatory control
Race/ethnicity	Higher risk in African Americans, Asians (craniofacial differences)
Medical conditions	PCOS, hypothyroidism, acromegaly, Down syndrome, Marfan syndrome

Clinical Presentation

Symptoms

Category	Symptom	Frequency in OSA
Nocturnal	Snoring (loud, habitual)	90-95%
Nocturnal	Witnessed apneas	70-80%
Nocturnal	Gasping/choking episodes	50-70%
Nocturnal	Nocturia (2+ episodes/night)	50-70%
Nocturnal	Restless sleep	60-80%
Nocturnal	Diaphoresis (night sweats)	30-50%
Nocturnal	GERD exacerbation	30-40%
Daytime	Excessive daytime sleepiness (Epworth >10)	70-80%
Daytime	Morning headache	30-50%
Daytime	Fatigue, low energy	80-90%
Daytime	Cognitive impairment (memory, concentration)	50-70%
Daytime	Irritability, mood changes	40-60%
Daytime	Decreased libido, erectile dysfunction	30-50%

Epworth Sleepiness Scale (ESS)

Activity	Chance of Dozing (0-3)
Sitting and reading
Watching TV
Sitting inactive in a public place (theater, meeting)
As a passenger in a car for 1 hour without a break
Lying down to rest in the afternoon
Sitting and talking to someone
Sitting quietly after lunch without alcohol
In a car, while stopped for a few minutes in traffic
Total Score

ESS Interpretation

Score	Interpretation
0-10	Normal
11-14	Mild sleepiness
15-18	Moderate sleepiness
19-24	Severe sleepiness

Diagnosis

Polysomnography (PSG)

Parameter	Monitored For	Significance
EEG	Sleep stages, arousals	Determines sleep architecture
EOG	Eye movements	REM vs NREM
EMG (chin)	Muscle tone	Identifies REM
EMG (legs)	Periodic limb movements	Comorbid PLMD
Nasal pressure	Airflow	Detects apneas/hypopneas
Thermistor	Oronasal airflow	Confirms apnea
Chest and abdominal belts	Respiratory effort	Distinguishes OSA (effort) from CSA (no effort)
Pulse oximetry	Oxygen saturation	Desaturation magnitude and duration
ECG	Heart rate, arrhythmias	Detects bradycardia, PACs/PVCs, AFib
Snore microphone	Snoring intensity and pattern	Corroborative
Body position	Supine vs non-supine	Positional component

Home Sleep Apnea Test (HSAT)

Type	Channels Recorded	Sensitivity	Specificity
Type II	7+ channels (EEG, EOG, EMG, airflow, effort, oximetry, ECG)	High	High (but requires manual scoring)
Type III	4-7 channels (airflow, effort, oximetry, +/- ECG)	Moderate-high	Moderate-high
Type IV	1-3 channels (typically oximetry only or airflow + oximetry)	Low-moderate	Low

Apnea-Hypopnea Index (AHI) and Severity

Severity	AHI (events/hour)	Oxygen Desaturation Nadir	Clinical Significance
Normal	<5	None or mild	No OSA diagnosis
Mild	5-14	Typically >85%	May cause mild symptoms
Moderate	15-29	80-85%	Increasing cardiovascular risk
Severe	30+	Typically <80%	High cardiovascular risk, significant symptoms

RDI vs AHI

Index	Definition
AHI	(Apneas + Hypopneas) / Total sleep time (hours)
RDI	(Apneas + Hypopneas + RERAs) / Total sleep time (hours)
RERA	Respiratory effort-related arousal: increasing respiratory effort that causes arousal but does not meet criteria for apnea or hypopnea
RDI is always equal to or higher than AHI

OSA Diagnostic Algorithm

Step	Action
1	Clinical suspicion (snoring, witnessed apneas, daytime sleepiness, risk factors)
2	STOP-BANG screening questionnaire
3	If high risk (STOP-BANG 5-8): polysomnography or home sleep apnea test
4	If low-intermediate risk: use clinical judgment for testing
5	AHI 5-14 + symptoms = OSA diagnosis; AHI 15+ = OSA diagnosis regardless of symptoms
6	Determine severity, contributing factors, and treatment plan

STOP-BANG Questionnaire

Question	Yes/No
S (Snoring)	Do you snore loudly (louder than talking or can be heard through closed door)?
T (Tired)	Do you often feel tired, fatigued, or sleepy during daytime?
O (Observed)	Has anyone observed you stop breathing or choke/gasp during sleep?
P (Pressure)	Do you have or are you being treated for high blood pressure?
B (BMI)	BMI >35 kg/m2?
A (Age)	Age >50 years?
N (Neck)	Neck circumference >40 cm (16 inches)?
G (Gender)	Male gender?

Score	Risk of OSA	Recommendation
0-2	Low	Consider other causes if symptoms
3-4	Intermediate	Further evaluation
5-8	High	Polysomnography or HSAT strongly indicated

Complications of Untreated OSA

Cardiovascular

Complication	Relative Risk	Mechanism
Hypertension	2-3x	Sympathetic activation, RAAS activation, endothelial dysfunction
Coronary artery disease	1.5-2x	Intermittent hypoxia, oxidative stress, inflammation
Heart failure	2-3x	Left ventricular hypertrophy, diastolic dysfunction, pulmonary hypertension
Atrial fibrillation	2-4x	Apnea-induced autonomic surges, atrial remodeling
Stroke	2-3x	Prothrombotic state, hypertension, AFib
Pulmonary hypertension	1.5-2x	Hypoxic pulmonary vasoconstriction
Sudden cardiac death	2-3x (especially nocturnal)	Arrhythmia, sympathetic surge, hypoxia

Metabolic

Complication	Risk
Type 2 diabetes	2-3x independent of obesity
Insulin resistance	Present in 40-80% of OSA patients
Nonalcoholic fatty liver disease	Increased risk and severity
Dyslipidemia	Increased triglycerides, decreased HDL

Neuropsychiatric

Complication	Impact
Excessive daytime sleepiness	70-80% of patients
Cognitive impairment	Reduced executive function, memory, attention
Mood disorders (depression)	2-3x increased risk
Decreased quality of life	SF-36 scores reduced across multiple domains
Motor vehicle accidents	2-3x increased crash risk (equivalent to alcohol impairment)

Treatment

Continuous Positive Airway Pressure (CPAP)

Aspect	Details
Mechanism	Pneumatic splint that maintains upper airway patency by delivering positive pressure
Pressure range	4-20 cm H2O (determined by titration study or auto-titration)
Modes	CPAP (fixed), Auto-CPAP (APAP), BiPAP, ASV
Efficacy	AHI reduction from 30-60/hr to <5/hr
Symptom improvement	Sleepiness, snoring, nocturia, morning headache, cognition
Blood pressure reduction	Average 3-10 mmHg (dose-dependent on adherence)
Adherence rate	30-60% long-term (more than 4 hours/night, 70% of nights)

CPAP Masks

Mask Type	Surface Coverage	Advantages	Disadvantages
Nasal pillow (Prongs)	Nostrils only	Minimal contact, no claustrophobia, good for reading	Mouth leaks, nasal congestion
Nasal mask	Nose only	Good seal, less intrusive than full face	Mouth leaks, nasal issues
Full face mask	Nose and mouth	No mouth leak, good for mouth breathers	Claustrophobia, more leak potential
Hybrid	Nose + under mouth	Less claustrophobic than full face	Less stable seal

CPAP Side Effects and Troubleshooting

Side Effect	Cause	Solution
Nasal congestion	Pressure, dry air	Heated humidifier, nasal steroids, change from full face to nasal pillows
Dry mouth	Mouth leak	Full face mask, chin strap, heated humidifier, increase pressure
Claustrophobia	Mask sensation	Nasal pillows, mask desensitization (wear while awake)
Aerophagia	Swallowing air	Lower pressure, BiPAP with pressure relief, avoid supine
Skin breakdown	Mask pressure	Mask liner, alternate mask type, proper fitting
Noise	Mask or machine	Machine at floor level, proper mask seal, earplugs for partner
Pressure intolerance	Pressure too high	Ramp feature, pressure relief (EPR), BiPAP, auto-CPAP

BiPAP (Bilevel Positive Airway Pressure)

Aspect	Description
Indications	CPAP intolerance (high pressure), obesity hypoventilation syndrome, neuromuscular disease, central apnea
Mechanism	Different pressures for inhalation (IPAP) and exhalation (EPAP)
Pressure support	IPAP - EPAP = support for ventilation
Settings	IPAP, EPAP, rate (S, S/T, T, PC modes)

Oral Appliances

Type	Mechanism	Efficacy	Indications
Mandibular advancement device (MAD)	Protrudes mandible forward, advancing the tongue and soft palate	AHI reduction: 40-60% overall; 60-70% achieve AHI <10	Mild-moderate OSA or severe OSA intolerant to CPAP
Tongue retaining device	Holds tongue forward with suction	Less effective than MAD	Limited use
Custom vs prefabricated	Custom-fit (dental fabrication) far superior to boil-and-bite	Custom essential
Side effects	Dental discomfort, TMJ pain, salivation changes, bite changes	Limit: 40% have long-term changes in bite

Positional Therapy

Aspect	Details
Indication	Supine-predominant OSA (AHI supine 2x non-supine AHI)
Methods	Tennis ball technique, positional belts, vibrating devices (NightShift, Philips)
Efficacy	Variable; often insufficient alone for moderate-severe OSA
Combination	Often used with CPAP or oral appliance

Weight Management

Intervention	Impact on AHI
Lifestyle modification (diet + exercise)	AHI reduction 30-50% with 10-15% weight loss
Bariatric surgery	AHI reduction 50-80%; OSA resolution in 40-60% (but may recur with weight regain)
Very low-calorie diet	Rapid AHI improvement before significant weight loss
Target	10% or more of body weight reduction

Surgery

Procedure	Indication	Success Rate	Notes
Uvulopalatopharyngoplasty (UPPP)	Palatal obstruction (tonsils, soft palate)	40-60% (variable)	Most common sleep surgery; limited efficacy in non-selected patients
Maxillomandibular advancement (MMA)	Maxillary/mandibular hypoplasia	80-95%	Major surgery; high efficacy in selected patients
Hypoglossal nerve stimulation (Inspire)	Moderate-severe OSA, failure of CPAP	70-80% responder rate	Implanted device; requires specific anatomy
Nasal surgery (septoplasty, turbinate reduction)	Nasal obstruction	Low efficacy as sole therapy	Usually adjunctive to other treatments
Bariatric surgery	Obesity-related OSA	50-60% resolution	Effect mediated by weight loss

Hypoglossal Nerve Stimulation (Inspire)

Aspect	Details
Mechanism	Implanted stimulator activates genioglossus (tongue protrusion) during inspiration
Indications	AHI 15-65, failed CPAP, no complete concentric palatal collapse
Efficacy	70-80% achieve AHI <20; 50-60% achieve AHI <5
Components	Implanted pulse generator (chest), stimulation lead (hypoglossal nerve), sensing lead (intercostal)
Side effects	Tongue abrasion, device discomfort, infection

Pediatric OSA

Aspect	Details
Prevalence	1-5% of children
Peak age	2-8 years (tonsillar hypertrophy peak)
Common cause	Adenotonsillar hypertrophy (70-80% of cases)
Presenting symptoms	Mouth breathing, restless sleep, bedwetting, daytime hyperactivity (not sleepiness)
Screening	Ask about snoring, mouth breathing, witnessed apneas; STOP-BANG not validated in children
Diagnosis	Polysomnography (recommended before adenotonsillectomy)
Treatment	Adenotonsillectomy (first-line; 70-80% cure rate), CPAP (if not surgical candidate or residual OSA), anti-inflammatory (montelukast, nasal steroids for mild)
Complications	Growth impairment, cognitive/behavioral issues, cardiovascular strain (pulmonary hypertension)

Follow-up and Monitoring

Interval	Action
1-3 months after CPAP initiation	Download adherence data, assess symptom response, address side effects
6-12 months	Clinical follow-up, weight check, reassess symptoms
Annually	CPAP adherence download, mask condition check, device filter check
2-5 years	Consider repeat PSG if significant weight change, symptom change, or new cardiovascular event
After weight loss (10%+ body weight)	Repeat PSG to reassess severity and need for CPAP pressure adjustment