Influence of Lower Body Positive Pressure on Upper Airway Cross-Sectional Area in Drug-Resistant Hypertension

Abstract

Abstract-We previously showed that in hypertensive patients the amount of fluid displaced from the legs overnight is directly related to the severity of obstructive sleep apnea and that the rostral fluid shift was greater in drug-resistant hypertensive patients. The findings suggested that this fluid redistribution increases upper airway collapsibility, yet more direct evidence is lacking. The present study examines the effects of graded lower body positive pressure on leg fluid volume, upper airway cross-sectional area, and neck circumference in patients with drug-resistant hypertension (n=25) and controlled hypertension (n=15). In both groups, the reduction in mean upper airway cross-sectional area and oropharyngeal junction area, assessed by acoustic pharyngometry, and the increase in neck circumference, determined by mercury strain gauge plethysmography, were related to the amount of fluid displaced from the legs (R 2 =0.41, P<0.0001; R 2 =0.42, P<0.0001; and R 2 =0.47, P<0.0001, respectively). Displacement of leg fluid volume was significantly greater in patients with drug-resistant hypertension than in controlled hypertension (P<0.0001), and as a consequence, the former experienced greater reductions in mean upper airway cross-sectional area and oropharyngeal junction area (P=0.001 and P<0.0001, respectively). The findings support the concept that in hypertensive subjects, rostral fluid displacement may participate in the pathogenesis of obstructive sleep apnea by narrowing the upper airway and making it more susceptible to collapse during sleep. The exaggerated fluid volume displacement from the legs and upper airway response to lower body positive pressure in patients with drug-resistant hypertension provide additional evidence of an important link between drug-resistant hypertension and obstructive sleep apnea. 112.203547/-/DC1Correspondence to Alexander G. Friedman et al Lower Body Positive Pressure in Hypertension 241increases pharyngeal resistance and upper airway collapsibility in healthy subjects. [14][15][16] In this study, we examined the effects of LBPP on the upper airway cross-sectional area of patients with DRH and controlled hypertension (CH). We hypothesized that the degree of upper airway narrowing would be related to the amount of fluid shifted from the legs and the extent of narrowing would be greater in patients with DRH than those with CH. Methods Study DesignThe study was carried in a human physiology laboratory during the daytime. The human subjects review committee of Mount Sinai Hospital, University Health Network, and Toronto Rehabilitation Institute, all in Toronto, approved the study. All subjects provided written informed consent before participation. Study SubjectsPatients with CH and DRH were recruited from the Hypertension Clinic at the Mount Sinai Hospital in Toronto. DRH was defined as uncontrolled hypertension on optimal doses of a diuretic and 2 additional antihypertensive medications or normal blood pressure (BP) on ≥4 drugs and CH as normal BP on ≤3 agents.1 In deter...

Night-to-night Variability in Obstructive Sleep Apnea Severity: Relationship to Overnight Rostral Fluid Shift

“…Application of LBPP to healthy subjects and hypertensive patients decreased UA-XSA in association with an increase in neck circumference. 22,23 Furthermore, in the hypertensive patients the decrease in UA-XSA and increase in neck circumference were both directly related to the decrease in LFV. 23 In OSA patients, LBPP increased upper airway resistance in association with increased neck circumference.…”

“…22,23 Furthermore, in the hypertensive patients the decrease in UA-XSA and increase in neck circumference were both directly related to the decrease in LFV. 23 In OSA patients, LBPP increased upper airway resistance in association with increased neck circumference. 24 Finally, in healthy subjects, LBPP increased upper airway collapsibility in proportion to the decrease in LFV and the increase in neck circumference.…”

Longitudinal Effect of CPAP on BP in Resistant and Nonresistant Hypertension in a Large Clinic-Based Cohort

“…19 We, therefore, considered the impact of substituting neck size for BMI in the multivariable model to examine for superiority of fit. We noted changes in model coefficients and significance and compared model fit using Akaike Information Criteria (AIC) with a better fitting model defined as two or more units lower than the comparison model.…”

“…[12][13][14][15] Additionally, increased sympathetic activity, changes in autonomic cardiovascular modulation, increased systemic inflammation and increased chemo reflex drive, and increased rostral edema contribute to increases in BP, including rises that are refractory to standard medication treatment. [16][17][18][19] Randomized clinical trials have demonstrated modest antihypertensive benefits of treatment of SDB with CPAP, with mild reductions in BP of 3 to 5 mm Hg 20,21 compared with more substantive reductions in RHTN, namely 7 to 10 mm Hg. 22 Notwithstanding the vast interventional trial data published on SDB and HTN, relatively fewer randomized studies [23][24][25] have investigated the effect of CPAP on control of BP in patients with OSA and RHTN, and none have examined the effect of CPAP in real-world clinical practice settings.…”

“…We hypothesize that CPAP use in SDB will reduce BP significantly in RHTN and non-RHTN, and the effect will be more pronounced in RHTN, even after consideration of confounders. Additionally, given data implicating the preferential role of rostral neck edema specifically in RHTN compared with HTN, 19 we anticipate that neck circumference used in place of BMI will more accurately characterize the anthropometric risk in RHTN.…”