Table 2.
Similarities and differences between 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 |
+: mild increase; ++ moderate increase; +++severe increase.