Effect of below-the-knee compression stockings on severity of obstructive sleep apnea.

BACKGROUND: Overnight fluid shift from the legs to the neck may narrow the upper airway and contribute to obstructive sleep apnea (OSA) pathogenesis. We hypothesized that below-the-knee compression stockings will decrease OSA severity in a general OSA population by decreasing daytime leg fluid accumulation and overnight fluid shift and increasing upper-airway size. METHODS: Patients with OSA (apnea-hypopnea index ≥ 10) were randomized to wear compression stockings during the daytime or to a control group for 2 weeks. Overnight polysomnography with measurement of leg and neck fluid volumes and upper-airway cross-sectional area before and after sleep was performed at baseline and follow-up. The primary outcome was change in the apnea-hypopnea index. RESULTS: Twenty-two patients randomized to compression stockings and 23 to control completed the study. The apnea-hypopnea index decreased significantly more in the compression stockings than in the control group (from 32.4 ± 20.0 to 23.8 ± 15.5 vs. from 31.2 ± 25.0 to 30.3 ± 23.8, p = 0.042), in association with a significantly greater reduction in the overnight decrease in leg fluid volume (p = 0.028), and a significantly greater increase in morning upper-airway cross-sectional area (p = 0.006). Overnight change in neck fluid volume was unchanged. CONCLUSION: These observations suggest that in, a general OSA population, below-the-knee compression stockings decrease OSA severity modestly via attenuation of overnight fluid shift and consequent upper-airway dilatation.

Night-to-night variability in obstructive sleep apnea severity: relationship to overnight rostral fluid shift.

STUDY OBJECTIVES: Overnight rostral fluid shift from the legs to the neck may narrow the pharynx and contribute to obstructive sleep apnea (OSA) pathogenesis. We hypothesized that night-to-night changes in the apnea-hypopnea index (AHI) would be associated with changes in overnight rostral fluid shift. METHODS: Twenty-six patients with OSA (AHI ≥10) underwent two polysomnograms 14 days apart with measurement of neck and leg fluid volumes (LFV), neck circumference and upper-airway cross-sectional area before and after sleep. RESULTS: Although mean AHI did not differ between polysomnograms, 35% of patients had a difference in AHI >10, indicating significant intra-individual variability. There were direct correlations between change in non-rapid-eye movement (NREM), but not REM AHI and change in evening LFV between polysomnograms (r = 0.440, p = 0.036 and r = 0.005, p = 0.982, respectively) and between change in supine, but not non-supine AHI and change in evening LFV (r = 0.483, p = 0.020 and r = 0.269, p = 0.280, respectively). An increase in evening LFV between polysomnograms was associated with a greater overnight decrease in LFV (r = 0.560, p = 0.005) and a greater overnight increase in neck fluid volume (r = 0.498, p = 0.016). Additionally, a greater overnight increase in neck circumference was associated with a greater overnight increase in neck fluid volume between polysomnograms (r = 0.453, p = 0.020) and a greater overnight decrease in upper-airway cross-sectional area (r = -0.587, p = 0.005). CONCLUSION: Intra-individual variability in OSA severity may be partly explained by day-to-day changes in evening leg fluid volume and overnight rostral fluid shift, which may be most important in the pathogenesis of OSA during NREM and supine sleep.

A randomized, double crossover study to investigate the influence of saline infusion on sleep apnea severity in men.

STUDY OBJECTIVES: Obstructive sleep apnea (OSA) is commoner in patients with fluid-retaining states than in those without fluid retention, in men than in women, and worsens with aging. In men, OSA severity is related to the amount of fluid shifting out of the legs overnight, but a cause-effect relationship is not established. Our objective was to test the hypothesis that mimicking fluid overload during sleep would increase severity of OSA more in older (≥ 40 years) than in younger men (< 40 years). DESIGN: Randomized, single-blind, double crossover study. SETTING: Research sleep laboratory. PATIENTS OR PARTICIPANTS: Seven older and 10 younger men with non-severe or no sleep apnea, matched for body mass index. INTERVENTIONS: During the control arm, normal saline was infused to keep the vein open. During intervention, subjects received an intravenous bolus of normal saline (22 mL/kg body weight) after sleep onset while they were wearing compression stockings to prevent fluid accumulation in the legs. MEASUREMENTS AND RESULTS: Compared to younger men, infusion of similar amounts of saline in older men caused a greater increase in neck circumference (P < 0.05) and in the AHI (32.2 ± 22.1 vs. 2.2 ± 7.1, P = 0.002). CONCLUSIONS: Older men are more susceptible to the adverse effects of intravenous fluid loading on obstructive sleep apnea severity than younger men. This may be due to age-related differences in the amount of fluid accumulating in the neck or upper airway collapsibility in response to intravenous fluid loading. These possibilities remain to be tested in future studies.

Relationship of circadian pattern of urine sodium excretion to hypertension and obstructive sleep apnoea.

OBJECTIVES: Obstructive sleep apnoea (OSA) and hypertension frequently coexist, and both are associated with higher night-time than daytime urine sodium excretion rate (UNaV). However, the relative contribution of each condition is unknown. We compared the circadian pattern of UNaV in hypertensive and normotensive patients with and without OSA. METHODS: Hypertensive [blood pressure (BP) >140/90 or on antihypertensive medications, excluding diuretics] and normotensive (BP <135/85) patients underwent overnight polysomnography to determine the presence or absence of OSA (apnoea-hypopnoea index ≥10 or <10, respectively), same-day 24-h urine collection divided into day and night-time samples and automated evening BP measurement. RESULTS: Twenty-six hypertensive (9 without and 17 with OSA) and 26 normotensive (15 without and 11 with OSA) patients were studied. Night-time UNaV was higher in the hypertensive than the normotensive patients. Whereas in the normotensive patients night-time UNaV was unaffected by OSA, in the hypertensive patients, it was higher in those with than without OSA (P = 0.009 for OSA × hypertension interaction). Night : day UNaV ratio was higher in hypertensive than normotensive patients, but was not significantly affected by OSA in either group. On multivariate analysis, SBP and apnoea-hypopnoea index were independent predictors of night-time UNaV (model r = 0.574, P < 0.001) and night : day UNaV ratio (model r = 0.397, P < 0.001). However, SBP was the strongest independent predictor. CONCLUSIONS: In hypertensive patients, OSA exacerbates the reversal of the normal circadian sodium excretion pattern by elevating nocturnal UNaV, possibly via its BP-elevating effects. However, OSA does not affect nocturnal UNaV in normotensive patients.

Effect of rostral fluid shift on pharyngeal resistance in men with and without obstructive sleep apnea.

BACKGROUND: Obstructive sleep apnea (OSA) relates to overnight rostral fluid shift, possibly because fluid accumulation around the pharynx increases pharyngeal resistance (Rph). We hypothesised that Rph will increase more in men with than without OSA in response to rostral fluid redistribution. METHODS: Seventeen men with, and 12 without OSA were randomized to lower body positive pressure (LBPP) for 15min or control, then crossed over. Leg fluid volume (LFV) and Rph were measured before and after each period. RESULTS: LBPP displaced similar amounts of fluid from the legs in both groups. However, compared to the non-OSA group, Rph increased significantly more during LBPP in the OSA group (-0.38±2.87 vs. 2.52±2.94cmH2O/l/s, p=0.016). Change in Rph during LBPP correlated directly with baseline Rph in the OSA group, but inversely in the non-OSA group. CONCLUSION: OSA patients have increased susceptibility to pharyngeal obstruction in response to rostral fluid redistribution, which could predispose to pharyngeal collapse during sleep.

Role of nocturnal rostral fluid shift in the pathogenesis of obstructive and central sleep apnoea.

Obstructive sleep apnoea (OSA) is common in the general population and increases the risk of motor vehicle accidents due to hypersomnolence from sleep disruption, and risk of cardiovascular diseases owing to repetitive hypoxia, sympathetic nervous system activation, and systemic inflammation. In contrast, central sleep apnoea (CSA) is rare in the general population. Although their pathogenesis is multifactorial, the prevalence of both OSA and CSA is increased in patients with fluid retaining states, especially heart failure, where they are associated with increased mortality risk. This observation suggests that fluid retention may contribute to the pathogenesis of both OSA and CSA. According to this hypothesis, during the day fluid accumulates in the intravascular and interstitial spaces of the legs due to gravity, and upon lying down at night redistributes rostrally, again owing to gravity. Some of this fluid may accumulate in the neck, increasing tissue pressure and causing the upper airway to narrow, thereby increasing its collapsibility and predisposing to OSA. In heart failure patients, with increased rostral fluid shift, fluid may additionally accumulate in the lungs, provoking hyperventilation and hypocapnia, driving below the apnoea threshold, leading to CSA. This review article will explore mechanisms by which overnight rostral fluid shift, and its prevention, can contribute to the pathogenesis and therapy of sleep apnoea.

BK virus nephropathy in renal transplant patients in London.

BACKGROUND: BK nephropathy (BKN) is an important cause of renal transplant dysfunction, believed to be associated with higher levels of immunosuppression. We assessed the experience of BKN in renal transplant patients in the London region. METHODS: All six London transplant centers participated and case notes of patients with BKN in 2004 to 2005 were reviewed. RESULTS: There were 17 cases of BKN, giving an incidence of 2.1%. Median time to diagnosis was 9 months. Median baseline creatinine rose from 150 to 196 mumol/L. At diagnosis, 16 patients were on tacrolimus, 15 on mycophenolate mofetil, and 10 on triple therapy with tacrolimus, mycophenolate mofetil, and prednisolone. Management of BKN involved reducing immunosuppression; cidofovir was used in two patients and methylprednisolone in five for acute rejection. Median follow-up time was 29.2 months. Creatinine returned to baseline in four patients, remained elevated in 12 and one patient lost his graft. The new median baseline creatinine was 216 mumol/L. Eight patients underwent repeat biopsies of which four became negative for BKV and three subsequently cleared the virus on blood and urine polymerase chain reaction and urine decoy cells. Overall, eight patients cleared the virus. None of age, sex, viral load, or biopsy characteristics (Banff ct score, Drachenberg grade, and number of BKV positive cells) were associated with poorer outcome when patients with increase in creatinine of less than 30% (n=7) or more than 30% (n=10) from baseline were compared. CONCLUSION: The incidence of BKN in this study is comparable with previous studies, with more favorable outcomes. It supports the association of BKN with potent immunosuppression.