Table 4. Actions of continuous positive airway pressure in CHF.

Scenario	Acute pulmonary oedema	OSA	CSA-CSR
Upper airway
Pneumatic splinting	+	+++	+
Pulmonary
Overcome negative ITP	+	+++	+
Increase lung volume	++	++	++
Prevent alveolar collapse	+++	+	++
Improve VQ matching	+++	+	++
Reduce pulmonary vasoconstriction	+++	+	++
Assist inspiratory muscles	+++	+	++
Cardiac
Afterload reduction
Less negative ITP	+	+++	+
Fall in systemic BP	+	++	++
Reduced LV diameter	+	++	++
Preload reduction	++	+	+

Three common scenarios: +, a slight effect; ++, a moderate effect; +++, a major effect. CHF, congestive heart failure; OSA, obstructive sleep apnea; CSA-CSR, central sleep apnoea with cheyne stokes respiration; ITP, intrathoracic pressure; VQ, ventilation perfusion.