Regulation of plasma volume during obstructive sleep apnoea

Area of Science:

• Cardiology
• Nephrology
• Pulmonology

Background:

• Obstructive sleep apnea (OSA) is associated with indirect evidence of altered plasma volume.
• Observations include paradoxical resolution of peripheral edema and decreased hematocrit with continuous positive airway pressure (CPAP) treatment.

Purpose of the Study:

• To interpret the observed fluid distribution alterations in untreated OSA.
• To elucidate the mechanisms behind fluid shifts in OSA patients.

Main Methods:

• Indirect evidence from clinical observations during CPAP treatment.
• Analysis of fluid and electrolyte excretion patterns.
• Assessment of hormonal and vasoactive substance levels.

Main Results:

• Untreated OSA may cause increased renal sodium excretion and vascular permeability, leading to fluid shifts, nocturnal polyuria, edema, and hemoconcentration.
• CPAP treatment reverses increased membrane permeability and urine excretion, resolving edema and decreasing hematocrit.
• Hormonal changes like increased atrial natriuretic peptide and decreased renin-angiotensin-aldosterone activity, plus elevated thromboxane and endothelin, are implicated.

Conclusions:

• Fluid distribution abnormalities in OSA are likely driven by increased renal sodium excretion and vascular permeability.
• CPAP therapy effectively reverses these pathological fluid shifts.
• Specific hormonal and vasoactive mediators play a crucial role in OSA-related fluid dysregulation.