title: Impact of nephrotic edema of the lower limbs on obstructive sleep apnea: gathering a unifying concept for the pathogenetic role of nocturnal rostral fluid shift.
abstract: BACKGROUND
  Nocturnal rostral fluid shift has been suggested to be a risk factor for obstructive sleep apnea (OSA) in healthy subjects after lower body positive pressurization. It remains unclear whether this may apply to subjects with nephrotic lower limb edema and, if so, whether disease remission may reverse the accompanying OSA.
  
  
  METHODS
  Patients who presented with steroid-responsive primary nephrotic syndrome with lower limb edema as the predominant presenting clinical feature were recruited. They underwent one overnight polysomnography (PSG) before treatment and a repeat testing after achieving remission of the nephrotic edema.
  
  
  RESULTS
  Among 23 consecutive nephrotic subjects, 11 (48%) had polysomnographic evidence of sleep apnea [apnea-hypopnea index (AHI)≥5] upon presentation. After steroid-based treatment, there was remission of proteinuria associated with complete disappearance of lower limb edema, significant reduction of body mass index, waist, hip and calf circumferences and total body water mainly in the extracellular compartment. Repeat PSG, performed 8.1±2.6 months later, showed that the overall (N=23) respiratory disturbance index (RDI) and AHI fell from 17.3±5.0 to 8.7±2.5 (P<0.05) and from 16.3±5.1 to 7.8±2.3 (P=0.057), respectively. Among the 11 subjects with sleep apnea detected at baseline, their AHI and RDI fell from 33.4±7.8 to 15.0±3.7 (P<0.05) and from 34.8±7.6 to 16.5±4.0 (P<0.05), respectively. There was also concomitant improvement in sleep efficiency, mean nocturnal oxygen saturation, shorter duration during sleep with oxygen saturation<95 and <90% and reduced desaturation index. There was also subjective improvement in self-reported daytime sleepiness.
  
  
  CONCLUSIONS
  Nephrotic lower limb edema is associated with disturbed respiratory breathing and increased propensity to OSA, which was reversed upon remission of the nephrosis. This gathers a unifying concept for the role of nocturnal rostral fluid shift in the pathogenesis of OSA.
authors.affiliation: Division of Nephrology, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
authors.forename: Sydney C W
authors.initials: SC
authors.lastname: Tang
authors.forename: Bing
authors.initials: B
authors.lastname: Lam
authors.forename: Jamie C M
authors.initials: JC
authors.lastname: Lam
authors.forename: Ching Kit
authors.initials: CK
authors.lastname: Chan
authors.forename: Chik Cheung
authors.initials: CC
authors.lastname: Chow
authors.forename: Yiu Wing
authors.initials: YW
authors.lastname: Ho
authors.forename: Mary S M
authors.initials: MS
authors.lastname: Ip
authors.forename: Kar Neng
authors.initials: KN
authors.lastname: Lai
mesh_terms: D000328:Adult; D000368:Aged; D004487:Edema / Q000150:complications* / Q000503:physiopathology*; D017097:Electric Impedance; D005260:Female; D018495:Fluid Shifts; D005500:Follow-Up Studies; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009404:Nephrotic Syndrome / Q000503:physiopathology*; D010101:Oxygen Consumption; D017286:Polysomnography; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D020181:Sleep Apnea, Obstructive / Q000209:etiology* / Q000473:pathology; D012894:Sleep Stages / Q000502:physiology; D055815:Young Adult