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Table 2 Similarities and differences between overlap syndrome and obesity hypoventilation

From: Respiratory mechanics and ventilatory control in overlap syndrome and obesity hypoventilation

 

Overlap

Obesity hypoventilation syndrome

Coexistent OSA

No causal relationship

Causal relationship in 90% of the cases

Hypoventilation (PaCO 2 ≥ 45 mmHg)

Occasionally

Always (by definition)

Obesity (BMI ≥ 30 kg/m 2 )

Often (but not obligatory)

Always (by definition)

Coexistent COPD

Always (by definition)

Never (exclusion by definition)

Coexistent restrictive pulmonary disease

Occasionally mixed pattern

Often present

FRC

Decreased

Decreased

Chemosensitivity (HCVR)

Normal, enhanced or decreased

Decreased

Leptine resistance

Present

Present

Hypoxemia pattern

Intermittent (intermittent and chronic in severe cases)

Intermittent and chronic (90%), or chronic (10%)

Level of hypoxemia

Absent to very severe disturbance

Moderate to very severe disturbance

Prevalence in general population

1-4%

0.37%

Prevalence in OSA

10%

14%

Pulmonary hypertension

+ to ++

++ to +++

Health care consumption

Increased

Increased

Mortality

80% in 12 years

23% in 1.5 years

90% in 8 years in LTOT

  1. +: mild increase; ++ moderate increase; +++severe increase.