Respiratory mechanics and ventilatory control in overlap syndrome and obesity hypoventilation

Respiratory Research

Table 1 Similarities and differences in lung function characteristics between morbid obesity without or with hypoventilation

	Normocapnic morbid obesity	Obesity hypoventilation syndrome
Lung volumes:
FRC	↓	↓
ERV	↓	↓↓
TLC	Normal	Normal or ↓
Respiratory compliance	↓	↓↓
Respiratory impedance	↑↑	↑↑↑
PaCO ₂ (awake)	Normal	↑ or ↑↑
PaO ₂ (awake)	Normal or ↓	↓ or ↓↓
HCO ₃ -	Normal	↑ or ↑↑
Respiratory drive	↑↑	Normal
HVR	Normal to ↑	↓↓
HCVR	Normal to ↑	↓↓
P 0.1	↑	↓↓
MVV	↓	↓↓
Pimax	Normal or ↓	↓ or ↓↓
Work of breathing	Sitting – normal to ↑	Sitting - ↑↑
	Supine - ↑↑	Supine - ↑↑↑
	Sleep - sitting - ↑↑
	Supine - ↑↑
Upper airway resistance	Sitting - normal	Sitting - ↑
Upper airway resistance	Supine - ↑	Supine - ↑↑↑

FRC: functional residual capacity, ERV: expiratory reserve volume; TLC: total lung capacity; HVR: hypoxic ventilatory response; HCVR: hypercapnic ventilatory response; MVV: maximal minute ventilation. ↑: mild increase; ↑↑: moderate increase; ↑↑↑: strong increase; ↓: mild decrease; ↓↓: moderate decrease.

ISSN: 1465-993X