Leg Fluid Volume Research Articles

A pilot study to assess the effects of preventing fluid retention in the legs by wearing compression stockings on overnight airway narrowing in mild asthma.

Nocturnal asthma is a sign of asthma worsening and could be partially due to more fluid drawn into the thorax during sleep by gravitational force and/or pharyngeal collapse in those with obstructive sleep apnea. Wearing compression stockings during the day reduces fluid shift from the legs to the neck overnight. However, the potential effect of wearing compression stockings to reduce fluid accumulation in the leg and to improve nocturnal small airway narrowing in patients with asthma has not been investigated. This study investigates whether reducing leg fluid volume by wearing compression stockings during the day would attenuate small airway narrowing in patients with asthma before and after sleep. We enrolled 11 participants with asthma. All participants underwent overnight polysomnography with or without wearing compression stockings for 2weeks. Before and after sleep, leg fluid volume (LFV) was measured by bioelectrical impedance, and airway narrowing was primarily assessed by respiratory system resistance and reactance at 5Hz (R5 and X5 respectively) using oscillometry. After 2weeks of wearing compression stockings, the LFV measured in the evening was reduced (∆ = - 192.6 ± 248.3ml, p = 0.02), and R5 and X5 improved (∆ = - 0.7 ± 0.9 cmH2O/L/s, p = 0.03 and 0.2 ± 1.4 cmH2O/L/s, p = 0.05 respectively). No changes were observed in the morning. Preventing fluid retention in the legs by wearing compression stockings for 2weeks during the day, reduced LFV and airway narrowing in the evening in all participants with asthma, but not in the morning after sleep.

Effect of lateral position on rostral fluid shift and relationship to severity of Cheyne-Stokes respiration in heart failure patients.

Lateral sleep position has a significant beneficial effect on the severity of Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) in patients with heart failure (HF). We hypothesized that a reduction in rostral fluid shift from the legs in this position compared with the supine position may contribute to this effect. In patients with CSR-CSA and an apnea-hypopnea index (AHI) ≥ 15/h (by standard polysomnography), uncalibrated leg fluid volume was measured in the supine, left lateral decubitus, and right lateral decubitus positions (in-laboratory assessment). The correlation between postural changes in fluid volume and corresponding changes in AHI was evaluated. Since there was no difference in both leg fluid volume and AHI between the right and left positions, measurements in these two conditions were combined into a single lateral position. In 18 patients with CSR-CSA,leg fluid volume increased by 2.7 ± 3.1% (p = 0.002) in the lateral position compared to the supine position, while AHI decreased by 46 ± 20% (p < 0.0001) with the same postural change. The correlation between postural changes in AHI and leg fluid volume was 0.22 (p = 0.42). Changes in leg fluid volume were a slow phenomenon, whereas changes in CSR-CSA severity were almost synchronous with changes in posture. Lateral position causes a reduction in rostral fluid shift compared to the supine position, but this change does not correlate with the corresponding change in CSR-CSA severity. The two changes occur on different time scales. These findings question the role of postural changes in rostral fluid shift as a determinant of corresponding changes in CSR-CSA severity.

Overnight Rostral Fluid Shifts Exacerbate Obstructive Sleep Apnea After Stroke.

Overnight shifts of fluid from lower to upper compartments exacerbate obstructive sleep apnea (OSA) in some OSA populations. Given the high prevalence of OSA after stroke, decreased mobility and use of IV fluids among hospitalized patients with stroke, and improvement in OSA in the months after stroke, we hypothesized that overnight fluid shifts occur and are associated with OSA among patients with subacute ischemic stroke. Within a population-based project, we performed overnight sleep apnea tests (ApneaLink Plus) during ischemic stroke hospitalizations. Before sleep that evening, and the following morning before rising from bed, we assessed neck and calf circumference, and leg fluid volume (bioimpedance spectroscopy). The average per subject overnight change in the 3 fluid shift measurements was calculated and compared with zero. Linear regression was used to test the crude association between each of the 3 fluid shift measurements and the respiratory event index (REI). Among the 292 participants, mean REI was 24 (SD=18). Within individuals, calf circumference decreased on average by 0.66 cm (SD=0.75 cm, P<0.001), leg fluid volume decreased by a mean of 135.6 mL (SD=132.8 mL, P<0.001), and neck circumference increased by 0.20 cm (SD=1.71 cm, P=0.07). In men, when the overnight change of calf circumference was negative, an interquartile range (0.8 cm) decrease in calf circumference overnight was significantly associated with a 25.1% increase in REI (P=0.02); the association was not significant in women. The relationship between overnight change in leg fluid volume and REI was U shaped. This population-based, multicenter, cross-sectional study showed that in hospitalized patients with ischemic stroke, nocturnal rostral fluid shifts occurred, and 2 of the 3 measures were associated with greater OSA severity. Interventions that limit overnight fluid shifts should be tested as potential treatments for OSA among patients with subacute ischemic stroke.

Effect of compression stockings on overnight rostral fluid shift and obstructive sleep apnea: A meta-analysis

ObjectiveThe overnight rostral fluid shift from the lower limbs is one of the causes of obstructive sleep apnea (OSA). Compression stockings (CS) prevent lower limb fluid retention and have been reported to decrease nighttime fluid shift. The aim of this study is to evaluate the effect of CS on fluid shift and the severity of OSA. MethodsA systematic literature search was performed in the PubMed, EMBASE and Cochrane Library databases. The data were analyzed using Comprehensive Meta-Analysis software (Version 3; Biostat, Englewood, NJ). Studies evaluating the effect of CS on the overnight fluid shift and OSA severity were included in the analysis. ResultsA total of 4 studies were included in this meta-analysis. The pooled analysis showed that the apnea-hypopnea index (AHI) of the overall study group was significantly lower after using CS (SMD, -1.08; 95% CI, -1.49 to -0.67). Decreases in the AHI were also observed in the normal fluid status (SMD, -1.05; 95% CI, -1.73 to -0.37) and fluid overload status (SMD, -1.17; 95% CI, -1.76 to -0.58) populations. The overall study group had significant decreases in overnight changes in neck circumference (SMD, -1.05; 95% CI, -2.06 to -0.03) and leg fluid volume (SMD, -1.14; 95% CI, -1.88 to -0.41) after using CS. However, no significant differences in overnight changes in neck circumference and leg fluid volume were observed in normal fluid status patients. ConclusionCS may help decrease overnight fluid shift and could be a treatment option for OSA.

0684 Overnight Fluid Shift In Apnea And Stroke: Does Being Physically Active Matter

Abstract Introduction Obstructive sleep apnea (OSA) and physical inactivity are frequent in patients with stroke. Overnight fluid shift may increase the propensity to pharyngeal obstruction and thus predispose to OSA. Also, physical inactivity can lead to consequent edema in the hemiparetic side. Methods In 7 patients at 3 months following post-first-ever ischemic stroke, we measured change in AHI (PSG), neck circumference, and arms and legs fluid volume (bioelectric impedance), before and after PSG in two conditions during the day before PSG: (1) inactive (sitting/lying), and (2) physically active (standing, walking, climbing stairs and mild exercise for 30 mins/hour). Results Being physically active for one day decreased mean AHI (inactive: 17.9/h; active: 12.6/h). Mean neck circumference increased overnight in both conditions (active and inactive) but increased more when the participants were physically active (inactive: 38 to 38.5cm; active: 38.43 to 39.5cm). Mean paretic arm fluid volume increased after inactive condition and did not change after physically active condition (inactive: 1.33L to 1.45L; active: 1.82L). Mean non-paretic arm fluid volume increased after active and inactive conditions (inactive: 1.34L to 1.45L; active: 1.74 to 1.78L). In both conditions and for paretic and non-paretic arms, being physically active for one day increased arm fluid volume between pre- and post-sleep comparisons. Mean paretic leg fluid volume increased after both conditions but increased more when the participants were inactive (inactive: 6.08L to 6.52L; active: 6.12 to 6.24L). Mean non-paretic leg fluid volume increased after inactive condition and decreased after being physically active (inactive: 6.01L to 6.45L; active: 6.15 to 6.06L). Conclusion Being physically active for one day decreased AHI, despite the increased fluid accumulation in the neck, and contributed to leaving no edema in the hemiparetic side. Breaking up inactivity and increasing physical activity in patients following stroke may be a promising intervention to reduce edema and OSA. Support São Paulo Research Foundation (FAPESP, grant #2018/18952-1 to CF).

A pilot study in men to show the effects of postural fluid shifts on the severity of obstructive sleep apnea.

Studies reveal that rostral fluid shifts due to body posture changes from standing to lying down may narrow the upper airway. However, without credible and direct experimental evidence, it remains unclear what the role of natural fluid redistribution in the neck is in affecting obstructive sleep apnea (OSA) severity. Our aim is using direct experimental evidence to determine whether or not postural fluid shifts affect OSA severity. We performed overnight polysomnography on two consecutive nights for 22 men. The bed was set horizontally on the control night, while its tail part was lowered by 30° on the experimental night to reduce the amount of fluid shifted into the neck. We measured sleep and anthropometric parameters on each night. The mean (95% CI) apnea-hypopnea index (AHI) in the supine head and trunk position decreased from 66.6 events per hour (57.6-75.6) to 61.2 (52.0-70.4) (t = 4.507, p <0.001), and the oxygen desaturation index from 69.5 events per hour (56.4-82.6) to 61.6 (50.5-72.6) (t = 3.293, p = 0.004), from the control to the experimental night with a decrease in the change of leg fluid volume from 17.7% (15.7-19.8) to 4.7% (1.9-7.5) (t = 11.659, p < 0.001). Our findings provide direct experimental evidence to show that natural fluid shift caused by the day-to-night posture change does contribute to OSA pathogenesis and severity. It is likely that the neck fluid increase from an actual day-to-night position change, with 90° change in posture, would produce a much larger AHI increase than the 11.2% found in this study, which contains only a 30° change in posture. These findings suggest that reducing the amount of fluid in the neck region may relieve airway obstructions for patients with moderate and severe OSA.

Corticomotor control of airway calibre in obstructive sleep apnoea syndrome.

Corticomotor control of airway calibre in obstructive sleep apnoea syndrome.

Abstract 106: The Association Between Overnight Rostral Fluid Shift and Sleep Disordered Breathing in Patients With Treatment Resistant Hypertension

Background: Sleep disordered breathing (SDB) is an important modifiable risk factor of treatment resistant hypertension (TRH). Overnight rostral fluid shift from lower extremities is associated with the severity of SDB in patients prone to fluid accumulation (e.g. TRH, heart failure, and end-stage renal disease). However, the association between overnight rostral fluid shift and SDB in Japanese patients with TRH remains unclear. Methods: All patients with TRH underwent polysomnography. Neck circumference (NC) and leg fluid volume (LFV) were measured by tape measure and bioelectrical impedance just before sleep and after waking up. Correlation between apnea-hypopnea index (AHI), overnight change of LFV (ΔLFV), and overnight change of NC (ΔNC) were assessed by regression analysis. Results: Total 11 patients were examined (7 men [63%], Age: 62.6±13.4 years, body mass index: 28.1±4.2 kg/m 2 ). Mean AHI, ΔLFV, and ΔNC were 30.5±24.1/h. -267.5±156.1 ml, and 0.4±0.5 cm, respectively. ΔLFV correlated significantly with ΔNC (r=-0.63; P=0.04). Besides, both ΔLFV and ΔNC were significantly associated AHI respectively (ΔLFV, r=-0.92; P&lt;0.01, ΔNC, r=0.67; P=0.02). In the stepwise regression analysis including estimated glomerular filtration rate, B-type natriuretic peptide along with ΔNC and ΔLFV, onlyΔLFV was the significant independent correlate with AHI, Conclusion: In Japanese patients with TRH, overnight rostral fluid shift contributes to the worsening of SDB, in association with the increase in NC.

Effect of Mitral Valve Surgery on Overnight Fluid Shift and Sleep Apnea in Patients With Moderate to Severe Mitral Valve Regurgitation and Preserved Ejection Fraction

SESSION TITLE: Sleep 2 SESSION TYPE: Original Investigation Poster PRESENTED ON: Wednesday, November 1, 2017 at 01:30 PM - 02:30 PM PURPOSE: Rostral fluid shift from the legs is strongly associated with sleep apnea (SA) in heart failure (HF) patients with reduced left ventricular ejection fraction (LVEF) accompanied by pulmonary congestion and/or pharyngeal edema. It is also known that sleep apnea is common among patients for cardiac surgery. Recent report showed that rheumatic valvular heart disease patients with obstructive SA had an increased incidence of perioperative complications, however the etiologies are unknown. Since MR contributes to pulmonary congestion and often have fluid retention in their legs, overnight fluid shift from the legs to the lungs or peripharyngeal area may play important roles in the pathogenesis of SA in patients with MR. Therefore, elucidating the relationship between fluid shift, SA, and effect of mitral valve (MV) surgery in patients with MR may provide some solutions. Purpose of this study is to investigate whether relationship between overnight fluid shit and severity of SA exists, and whether MV surgery affects either severity of SA and/or fluid shift, in patients with moderate-to-severe MR and preserved LVEF. METHODS: Patients with moderate-to-severe MR and preserved LVEF performed overnight polysomnography before and after the MV surgery. At the same time, leg fluid volume (LFV) was measured by bio-electrical impedance device before and after polysomnography. Relationship between overnight changes (△) of LFV and severity of SA as assessed by apnea-hypopnea index (AHI) was analyzed. RESULTS: Among 20 patients (mean age; 67±11 years, mean LVEF; 66±11%) enrolled, significant inverse relationship between △LFV and the AHI in univariable analysis (r=-0.78; P<0.001) was observed. Even in the multivariable regression analysis including other correlates to the AHI which showed P<0.1 in the univariable analyses, such as 24-hour urine volume (r=-0.46; P=0.041), regurgitant volume by PISA (r=0.46; P=0.049), use of diuretics (r=0.47; P=0.035) and beta blockers (r=054; P=0.014), △LFV was the significant correlates to the AHI (r=-0.72; P<0.001). 17 patients among them have done polysomnography after the surgery. Although body weight significantly decreased from 59.4±13.5 to 58.9±13.0 kg (P=0.004) following MV surgery, the AHI and △LFV did not change (AHI, from 27.9±18.5 to 31.4±18.0; P=0.463 and △LFV, from -397±188 to -401±202 ml; P=0.723). However, there were significant correlation between change in the AHI and change in △LFV, even after adjustment of change in the body weight (r=-0.58; P=0.035). CONCLUSIONS: Significant independent relationship between overnight fluid shift and SA severity were found in patients with moderate-to-severe MR and preserved LVEF. Despite no changes in AHI and LFV following MV surgery, there was a significant correlation between change in the AHI and change in △LFV. CLINICAL IMPLICATIONS: These findings suggest that in patients with moderate-to-severe MR and preserved LVEF, overnight rostral fluid displacement from the legs contributes to the pathogenesis of SA. Further investigation may contribute to reveal mechanisms. DISCLOSURE: Takatoshi Kasai: Grant monies (from industry related sources): affiliated with a department endowed by Philips Respironics, ResMed, and Fukuda Denshi The following authors have nothing to disclose: Azusa Murata, Shoichiro Yatsu, Hiroki Matsumoto, Takao Kato, Shoko Suda, Masaru Hiki, Kan Kajimoto, Taira Yamamoto, Atsushi Amano No Product/Research Disclosure Information

Increased Urine Production Due to Leg Fluid Displacement Reduces Hours of Undisturbed Sleep.

To investigate whether or not the leg fluid displacement observed when moving from the standing to recumbent position at bedtime reduces the hours of undisturbed sleep (HUS). Men aged 50 years or older who were hospitalized for urological diseases were investigated. Body water evaluation was performed three times with a bioelectric impedance method: (i) 17:00, (ii) 30 min after (short-term), and (iii) waking up (long-term). A frequency volume chart was used to evaluate the status of nocturnal urine production, and the factors affecting HUS were investigated. A total of 50 patients (mean age: 68 years) were enrolled. Short-term changes in extracellular fluid (ECF in the legs showed a significant positive correlation with urine production per unit of time at the first nocturnal voiding (UFN/HUS) (r = 0.45, P = 0.01). In the comparison between patients who had <3 HUS vs. those who had ≥3 HUS, the <3 HUS group showed significantly greater short-term changes in leg fluid volume, night-time water intake (17:00-06:00), and UFN/HUS. Multivariate analysis to assess the risk factors for <3 HUS indicated UFN/HUS as a risk factor in the overall model, and short-term changes in leg ECF and night-time water intake as risk factors in the model that only considered factors before sleep. Nocturnal leg fluid displacement may increase urine production leading up to first voiding after going to bed, and consequently, induce early awakening after falling asleep.

The effect of fluid overload on sleep apnoea severity in haemodialysis patients.

As in heart failure, obstructive and central sleep apnoea (OSA and CSA, respectively) are common in end-stage renal disease. Fluid overload characterises end-stage renal disease and heart failure, and in heart failure plays a role in the pathogenesis of OSA and CSA. We postulated that in end-stage renal disease patients, those with sleep apnoea would have greater fluid volume overload than those without.End-stage renal disease patients on thrice-weekly haemodialysis underwent overnight polysomnography on a nondialysis day to determine their apnoea-hypopnoea index (AHI). Extracellular fluid volume of the total body, neck, thorax and right leg were measured using bioelectrical impedance.28 patients had an AHI ≥15 (sleep apnoea group; OSA:CSA 21:7) and 12 had an AHI <15 (no sleep apnoea group). Total body extracellular fluid volume was 2.6 L greater in the sleep apnoea group than in the no sleep apnoea group (p=0.006). Neck, thorax, and leg fluid volumes were also greater in the sleep apnoea than the no sleep apnoea group (p<0.05), despite no difference in body mass index (p=0.165).These findings support a role for fluid overload in the pathogenesis of both OSA and CSA in end-stage renal disease.

The effect of sitting and calf activity on leg fluid and snoring

Prolonged sitting may promote leg fluid retention that redistributes to the neck during sleep and contributes to snoring. This could be attenuated by calf activity while sitting. In 16 healthy non-obese subjects we measured leg fluid volume (LFV) below the knees using bioelectrical impedance while sitting for 4h, snoring using a portable BresoDx™ device, and Mallampati grade. Using a double cross-over study design, subjects were randomized to one of two arms and crossed-over one week later: control arm – no calf exercise while sitting; intervention arm – calf contraction against a pedal resistance while sitting. The effects of sitting±calf activity on LFV and snoring were compared. We found that LFV increased by 216±101.0ml (p<0.0001) after sitting. Calf activity while sitting attenuated LFV by 53.8ml (p<0.0001) and, in all five subjects with severe upper airway narrowing (Mallampati grade IV), reduced snoring duration (from 357±132.9 to 116.2±72.1s/h, p=0.02) suggesting reduced overnight rostral fluid shift to the neck.

Effects of exercise training on sleep apnoea in patients with coronary artery disease: a randomised trial.

Overnight fluid shift from the legs to the neck and lungs may contribute to the pathogenesis of obstructive sleep apnoea (OSA) and central sleep apnoea (CSA). We hypothesised that exercise training will decrease the severity of OSA and CSA in patients with coronary artery disease (CAD) by decreasing daytime leg fluid accumulation and overnight rostral fluid shift.Patients with CAD and OSA or CSA (apnoea-hypopnoea index >15 events per h) were randomised to 4 weeks of aerobic exercise training or to a control group. Polysomnography, with measurement of leg, thoracic and neck fluid volumes and upper-airway cross-sectional area (UA-XSA) before and after sleep, was performed at baseline and follow-up.17 patients per group completed the study. Apnoea-hypopnoea index decreased significantly more in the exercise group than in the control group (31.1±12.9 to 20.5±9.4 versus 28.1±13.5 to 27.0±15.1 events per h, p=0.047), in association with a greater reduction in the overnight change in leg fluid volume (579±222 to 466±163 versus 453±164 to 434±141 mL, p=0.04) and by a significantly greater increase in the overnight change in UA-XSA in the exercise group (p=0.04).In patients with CAD and sleep apnoea, exercise training decreases sleep apnoea severity via attenuation of overnight fluid shift and an increase in UA-XSA.

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

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. 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. 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). 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.

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

BackgroundOvernight 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. MethodsPatients 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. ResultsTwenty-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. ConclusionThese 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.

Influence of rostral fluid shift on upper airway size and mucosal water content.

Fluid displacement from the legs during recumbency while in bed might narrow the upper airway (UA) in association with nuchal fluid accumulation that may contribute to the pathogenesis of obstructive sleep apnea (OSA). The aim of this study was to test the hypothesis that rostral fluid displacement from the legs causes a greater decrease in UA cross-sectional area (UA-XSA) and a greater increase in UA mucosal water content (UA-MWC) and internal jugular venous volume (IJVVol) in subjects with OSA than in those without OSA. Subjects underwent baseline assessment of leg fluid volume (LFV) measured by bio-electrical impedance, as well as UA-XSA and UA-MWC by magnetic resonance imaging. They were then randomly assigned to a 20-min period either with or without application of lower body positive pressure (LBPP) of 40 mm Hg, followed by a 15-min washout period, after which they crossed over to the other arm of the study. Measurements of LFV, UA-MWC, and UA-XSA were repeated after each arm of the study. In 12 subjects without sleep apnea, UA-XSA increased and UA-MWC decreased significantly, whereas in 12 subjects with OSA, UA-XSA decreased and UA-MWC increased significantly in response to LBPP. The changes in UA-XSA and UA-MWC in response to LBPP differed significantly between the 2 groups (p = 0.006 and p < 0.001, respectively), despite similar changes in LFV and IJVVol. Our results suggest that rostral fluid shift may contribute to the pathogenesis of OSA at least partly through narrowing of the UA due to transudation of fluid into the UA mucosa.

Modelling fluid accumulation in the neck using simple baseline fluid metrics: implications for sleep apnea.

Obstructive sleep apnea (OSA) is a common respiratory disorder among adults. Recently we have shown that sedentary lifestyle causes an increase in diurnal leg fluid volume (LFV), which can shift into the neck at night when lying down to sleep and increase OSA severity. The purpose of this work was to investigate various metrics that represent baseline fluid retention in the legs and examine their correlation with neck fluid volume (NFV) and to develop a robust model for predicting fluid accumulation in the neck. In 13 healthy awake non-obese men, LFV and NFV were recorded continuously and simultaneously while standing for 5 minutes and then lying supine for 90 minutes. Simple regression was used to examine correlations between baseline LFV, baseline neck circumference (NC) and change in LFV with the outcome variables: change in NC (ΔNC) and in NFV (ΔNFV90) after lying supine for 90 minutes. An exhaustive grid search was implemented to find combinations of input variables which best modeled outcomes. We found strong positive correlations between baseline LFV (supine and standing) and ΔNFV90. Models developed for predicting ΔNFV90 included baseline standing LFV, baseline NC combined with change in LFV after lying supine for 90 minutes. These correlations and the developed models suggest that a greater baseline LFV might contribute to increased fluid accumulation in the neck. These results give more evidence that sedentary lifestyle might play a role in the pathogenesis of OSA by increasing the baseline LFV. The best models for predicting ΔNC include baseline LFV and NC; they improved accuracies of estimating ΔNC over individual predictors, suggesting that a combination of baseline fluid metrics is a good predictor of the change in NC while lying supine. Future work is aimed at adding additional baseline demographic features to improve model accuracy and eventually use it as a screening tool to predict severity of OSA prior to sleep.

Relationship of left atrial size to obstructive sleep apnea severity in end-stage renal disease

BackgroundIncreased left atrial (LA) size is linked to elevated mortality in end-stage renal disease (ESRD). In addition, the degree of overnight rostral fluid shift from the legs is associated with severity of obstructive sleep apnea (OSA). As rostral fluid shift might distend the left atrium and increase fluid accumulation in the neck, we postulated that LA size would be related to the degree of overnight rostral fluid shift and OSA severity in ESRD patients. MethodsPatients with ESRD underwent echocardiography and polysomnography. Leg fluid volume (LFV) was measured by bioelectrical impedance before and after the overnight sleep study in a subset of 21 patients. ResultsForty patients (22 men), with a mean apnea–hypopnea index (AHI) of 25.1 ± 23.4/h of sleep, had echocardiography and polysomnography performed. In men, there was a correlation between the AHI and LA size indexed for body surface area (r = 0.743, p < 0.001) that was not observed in women. Strong relationships were seen, again in men only, between LA size indexed to body surface area and the overnight change in leg fluid volume (ΔLFV) (r = −0.739, p = 0.02) and between AHI and ΔLFV (r = −0.863, p = 0.003). ConclusionsIn ESRD patients, there are relationships between ΔLFV and both LA size and OSA severity. These findings suggest that the relationship between LA size and mortality in ESRD may be related to ΔLFV and severity of OSA.

Effect of intensified diuretic therapy on overnight rostral fluid shift and obstructive sleep apnoea in patients with uncontrolled hypertension

Fluid displacement from the lower extremities to the upper body during sleep is strongly associated with obstructive sleep apnoea in hypertensive patients. The present pathophysiological study tests the hypothesis that intensified diuretic therapy will reduce the apnoea-hypopnoea index and blood pressure of uncontrolled hypertensive patients with obstructive sleep apnoea in proportion to the reduction in overnight change in leg fluid volume. Uncontrolled treated hypertensive patients underwent overnight polysomnography and measurement of overnight changes in leg fluid volume and neck circumference. Those with an apnoea-hypopnoea index at least 20 events per hour (n=16) received metolazone 2.5 mg and spironolactone 25 mg daily for 7 days after which the daily dose was doubled for 7 additional days. Baseline testing was again repeated. Intensified diuretic therapy reduced the apnoea-hypopnoea index from 57.7 ± 33.0 to 48.5 ± 28.2 events per hour (P=0.005), overnight change in leg fluid volume from -418.1 ± 177.5 to -307.5 ± 161.9 ml (P<0.001) and overnight change in neck circumference from 1.2 ± 0.6 to 0.7 ± 0.4 cm (P<0.001). There was an inverse correlation between the reduction in overnight change in leg fluid volume and decrease in apnoea-hypopnoea index (r=-0.734, P=0.001). The reduction in overnight change in leg fluid volume was also significantly correlated with the change in morning blood pressure (r=0.708, P=0.002 for SBP; r=0.512, P=0.043 for DBP). The findings provide further evidence that fluid redistribution from the legs to the neck during sleep contributes to the severity of obstructive sleep apnoea in hypertension and may be an important link between these two conditions.

Is intensified diuretic therapy an effective new treatment strategy in obstructive sleep apnoea patients with uncontrolled hypertension?

There is evidence of an important mutual interaction between sleep disorders and cardiovascular problems. Patients with cardiovascular diseases often complain of several sleep disturbances such as sleep fragmentation, insomnia and breathing disorders during sleep. On the contrary, patients with sleep disorders are more frequently affected by cardiovascular problems. Such a reciprocal interaction makes it often difficult to determine which is the cause and which is the effect between these conditions. Sleep-related breathing disorders, particularly obstructive sleep apnoea syndrome (OSAS), formerly named Pickwickian syndrome, are highly prevalent in the general population, OSAS affecting at least 4% of middle-aged men and 2% of middle-aged women in the developed world, with its prevalence increasing in parallel with the growing prevalence of obesity. Individuals with OSAS are also characterized by a worsened quality of life and by excessive daytime somnolence, and are at an increased risk of road traffic and workplace accidents when compared with nonapnoeic individuals [1–3]. From a public health viewpoint, also the reported increased risk of cardiovascular morbidity and mortality associated with a diagnosis of obstructive sleep apnoea (OSA) is of particular importance [4,5]. OSA is associated with a higher prevalence of hypertension, in particular resistant hypertension, myocardial infarction, cardiac arrhythmias, congestive heart failure and stroke. Indeed, untreated severe OSA confers a three-fold increased risk of death from cardiovascular causes [1,2,6]. Prevalence of hypertension in OSA patients ranges from 35 to 80% and appears to be influenced by OSA severity. In fact, more than 60% of individuals with respiratory disturbance index greater than 30 were found to be hypertensive. Conversely, approximately 40% of hypertensive patients are diagnosed with OSA. Finally, when focussing on patients with resistant hypertension, OSA prevalence is significantly higher, reaching 83% [7]. Given this background, and the relevant interaction between OSA and cardiovascular disorders, it is evident that strategies for OSA treatment also play a key role in cardiovascular diseases prevention.