Sleep apnea and hypertension: Pathophysiologic mechanisms

Sleep Health and Road Safety: Continuation of Asia-Pacific Economic Cooperation Sleep Technology Agenda

In 2017, the Asia-Pacific Economic Cooperation Sleep Technology Agenda emphasized the impacts of sleep health on road safety. An official meeting between the Department of Transportation of United States and the International Sleep Science and Technology Association took place in Washington, DC, on February 3, 2020. This was followed by several meetings in Taiwan advocated by the International Sleep Science and Technology Association Taiwan Chapter. We hope to raise the awareness in the government sectors, and to provide the scientific evidence of verified sleep and fatigue-monitoring technologies to avoid numerous tragedies on the road from its root cause.

Role of melanocortin 4 receptor in hypertension induced by chronic intermittent hypoxia

AIM

We previously demonstrated that central nervous system (CNS) melanocortin 4 receptors (MC4R) play a key role in regulating blood pressure (BP) in some conditions associated with increased SNS activity, including obesity. In this study, we examined whether activation of CNS MC4R contributes to chronic intermittent hypoxia (CIH)-induced hypertension and ventilatory responses to hypercapnia.

METHODS

Rats were instrumented with an intracerebroventricular (ICV) cannula in the lateral cerebral ventricle for continuous infusion of MC4R antagonist (SHU-9119) and telemetry probes for measuring mean arterial pressure (MAP) and heart rate (HR). Untreated and SHU-9119-treated rats as well as obese and lean MC4R-deficient rats were exposed to CIH for 7-18 consecutive days.

RESULTS

Chronic intermittent hypoxia reduced cumulative food intake by 18 ± 5 g while MAP and HR increased by 10 ± 3 mm Hg and 9 ± 5 bpm in untreated rats. SHU-9119 increased food intake (from 15 ± 1 to 46 ± 3 g) and prevented CIH-induced reduction in food intake. CIH-induced hypertension was not attenuated by MC4R antagonism (average increase of 10 ± 1 vs 9 ± 1 mm Hg for untreated and SHU-9119 treated rats). In obese MC4R-deficient rats, CIH for 7 days raised BP by 11 ± 4 mm Hg. However, when MC4R-deficient rats were food restricted to prevent obesity, CIH-induced hypertension was attenuated by 32%. We also found that MC4R deficiency was associated with impaired ventilatory responses to hypercapnia independently of obesity.

CONCLUSION

These results show that obesity and the CNS melanocortin system interact in complex ways to elevate BP during CIH and that MC4R may be important in the ventilatory responses to hypercapnia.

Relationship between head posture and the severity of obstructive sleep apnea

INTRODUCTION

The objective of this study was to compare the head posture of patients with obstructive sleep apnea (OSA) having different levels of severity with that of control subjects.

METHODS

One hundred subjects participated in this study. Seventy-five subjects underwent overnight polysomnography in a sleep laboratory and were allocated into "mild," "moderate," or "severe" OSA groups, and 25 subjects with no complaints regarding OSA were allocated into 1 group and served as the controls. Cephalometric radiographs were obtained from all participants in natural head position. Craniocervical, craniovertical, and cervicovertical angles were measured in the groups. Data were analyzed using the least significant difference.

RESULTS

The results showed significant differences between the OSA groups and the control group, and among the test groups, in all craniocervical, craniovertical, and cervicovertical angles (P <0.05), except for 1 craniovertical measurement (P >0.05). There were no significant differences in this measurement among the test groups and in any measurement between the mild and moderate OSA groups (P >0.05).

CONCLUSIONS

Head posture showed significant differences in patients with OSA. In general, the more severe the OSA, the more extended the natural head position as indicated by increases in the craniocervical angles. The cervical posture parameters may indicate existing OSA.

Pharyngeal airway analysis in obese and non-obese patients with obstructive sleep apnea syndrome

BACKGROUND

Sleep disorders are a group of disorders characterized by abnormalities of respiration during sleep. OSA (Obstructive Sleep Apnea) is characterized by the repetitive episodes of complete or partial collapse of the upper airway during sleep, causing a cessation or a significant reduction of airflow.

METHOD

The study population consisted of 30 control patients (AHI ≤ 5) events per hour, 74 patients with OSAS, including 34 Obese (BMI ≥ 27) and 40 non-obese (BMI ≤ 27). Polysomnography and measurements of 21 cephalometric variables were carried out for all patients with OSAS.

RESULTS

Obese patient with OSAS showed significant difference in following cephalometric parameters: (1) PAS (2) MPT (3) MPH (4) PNS-P (5) SAS. In addition, obese patient had longer tongue (TGL), more anteriorly displaced hyoid bones (H-VL) and more anterior displacement of mandible (G-VL) when compared with control groups. The findings of non-obese patients when compared to controls showed all the findings of obese patients and in addition to that narrow bony oropharynx were significant. Step wise regression analysis showed the significant predictors for all patients were MPH, PNS-P, bony nasopharynx (PNSBa), MPT, and palatal length (ANS-PNS) for AHI. The significant predictors for obese OSA (obstructive sleep apnea) group were MAS while for non-obese OSA group ANS-PNS was significant predictor for AHI (apnea-hypopnea index).

CONCLUSION

Craniofacial landmarks such as increase in hyoid distance, longer tongue and soft palate with increased thickness and narrowing of superior pharyngeal, oropharyngeal and hypopharyngeal airway space may be important risk factors for development of OSAS.

Obstructive sleep apnoea and anaesthesia

Obstructive sleep apnoea (OSA) correlates positively with obesity and age, both of which are becoming increasingly prevalent. Obstructive sleep apnoea occurs much more frequently in clinical practice than formerly diagnosed, and that this condition represents complex challenges for difficulty in mask ventilation, laryngoscopic intubation, accelerated arterial desaturation, postoperative monitoring and discharge status. In this review article pathophysiology, diagnosis, and perioperative management of this group of patients have been discussed in detail.

Snoring and daytime sleepiness as risk factors for hypertension and diabetes in women--a population-based study

The aim of this study was to analyze whether snoring and excessive daytime sleepiness (EDS), the main symptoms of obstructive sleep apnea syndrome (OSAS), are associated with hypertension and diabetes in women. A random sample of 6779 women aged 20-99 years answered questionnaires on sleep disturbances, daytime symptoms and somatic diseases. The women were categorized into four groups: "no EDS or snoring" (reference group), "snoring but no EDS", "EDS but no snoring" and "snoring and EDS". Prevalences of hypertension and diabetes were lowest in the reference group (8.7% and 1.6%, respectively) and highest among women with both snoring and EDS (hypertension: 26.3%, diabetes: 5.8%). In a multivariate model adjusting for age, body mass index, smoking, physical activity and alcohol dependency, "snoring and EDS" was a risk factor for hypertension (adjusted OR 1.82 (95% CI 1.30-2.55)) while isolated snoring or EDS was not. "Snoring and EDS" was more closely related to hypertension among women aged <50 years (adj. OR 3.41 (1.78-6.54) vs. 1.50 (1.02-2.19), P=0.01). For diabetes, both "EDS but no snoring" and "snoring and EDS" were risk factors and the associations were most pronounced in women aged >50 years (adj. OR 2.33 (1.28-4.26) for "EDS but no snoring" and 2.00 (1.05-3.84) for "snoring and EDS"). We conclude that the combination of snoring and EDS is a risk factor for hypertension and diabetes in women. For hypertension, the risk is partly age dependent and, for diabetes, EDS without snoring is a risk factor of similar magnitude. These differences might indicate differences in pathophysiologic mechanisms underlying the association between sleep-disordered breathing and hypertension and diabetes respectively.

Pathophysiology of obstructive sleep apnea

This article explores the physiologic basis and symptoms of obstructive sleep apnea--a general term encompassing central sleep apnea and obstructive sleep apnea. The former is relatively uncommon while the latter is much more common. Episodic collapse and blockage of the upper airway occur during sleep despite continuous respiratory effort. Three types of sleep obstructive breathing--apnea, hypopnea, and airway resistance--are associated with respiratory-related arousals from sleep.

Obstructive sleep apnea

BACKGROUND

Patients with undiagnosed obstructive sleep apnea (OSA) represent a major public health problem, and studies suggest that the incidence of OSA may be even higher than estimated.

TYPES OF STUDIES REVIEWED

The authors reviewed current literature describing comorbidities of patients with OSA.

RESULTS

Sleep medicine is a relatively new field. Dental practitioners may lack educational exposure and, as a result, feel uncomfortable asking their patients sleep-related questions. While patients with well-controlled OSA present few difficulties for routine dental treatment, it is imperative that health care professionals understand the comorbidities associated with OSA and that untreated OSA may contribute to increased morbidity and mortality.

CLINICAL IMPLICATIONS

Dental professionals have a unique doctor-patient relationship that affords them a role in recognizing sleep disorders by exploring the history of patients who are sleepy.

Sleep disorders and the failure to lower nocturnal blood pressure

PURPOSE OF REVIEW

The failure to lower systolic blood pressure at night (called non-dipping) and sleep apnea are both associated with adverse cardiovascular outcomes. Sleep apnea is a common cause of non-dipping blood pressure.

RECENT FINDINGS

Sleep apnea increases night time blood pressure through enhanced cardiac pre-load, sleep disturbance and hypoxia. Hypoxia elicits increased levels of norepinephrine, endothelin and erythropoetin. Patients with sleep apnea tend to be elderly and obese, so they have poor endothelial nitric oxide release and blunted baroreflexes. They thus have several stimuli for high blood pressure and poor compensatory mechanisms to lower blood pressure.

SUMMARY

Non-dipping patients without sleep apnea have evidence of volume overload and correct their blood pressure pattern in response to diuretics. Individuals with sleep apnea have evidence of increased cardiac pre-load from episodes of negative intrathoracic pressure. Their daytime blood pressure responds poorly to many drugs, but beta blockers may be effective. Their night time blood pressure responds only slightly to therapy of their sleep apnea with continuous positive airway pressure, even though continuous positive airway pressure decreases their norepinephrine, erythropoetin and endothelin levels.

Subcortical ischaemic vascular dementia

Vascular dementia is the second most common type of dementia. The subcortical ischaemic form (SIVD) frequently causes cognitive impairment and dementia in elderly people. SIVD results from small-vessel disease, which produces either arteriolar occlusion and lacunes or widespread incomplete infarction of white matter due to critical stenosis of medullary arterioles and hypoperfusion (Binswanger's disease). Symptoms include motor and cognitive dysexecutive slowing, forgetfulness, dysarthria, mood changes, urinary symptoms, and short-stepped gait. These manifestations probably result from ischaemic interruption of parallel circuits from the prefrontal cortex to the basal ganglia and corresponding thalamocortical connections. Brain imaging (computed tomography and magnetic resonance imaging) is essential for correct diagnosis. The main risk factors are advanced age, hypertension, diabetes, smoking, hyperhomocysteinaemia, hyperfibrinogenaemia, and other conditions that can cause brain hypoperfusion such as obstructive sleep apnoea, congestive heart failure, cardiac arrhythmias, and orthostatic hypotension. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL)and some forms of cerebral amyloid angiopathy have a genetic basis. Treatment is symptomatic and prevention requires control of treatable risk factors.