Treatment of obstructive sleep apnoea leads to enhanced pulmonary vascular nitric oxide release

Positive Airway Pressure Therapy for Pediatric Obstructive Sleep Apnea

Pediatric obstructive sleep apnea syndrome (OSAS) is a disorder of breathing during sleep, characterized by intermittent or prolonged upper airway obstruction that can disrupt normal ventilation and/or sleep patterns. It can affect an estimated 2–4% of children worldwide. Untreated OSAS can have far reaching consequences on a child’s health, including low mood and concentration as well as metabolic derangements and pulmonary vascular disease. Most children are treated with surgical intervention (e.g., first-line therapy, adenotonsillectomy); however, for those for whom surgery is not indicated or desired, or for those with postoperative residual OSAS, positive airway pressure (PAP) therapy is often employed. PAP therapy can be used to relieve upper airway obstruction as well as aid in ventilation. PAP therapy is effective in treatment of OSAS in children and adults, although with pediatric patients, additional considerations and limitations exist. Active management and care for various considerations important to pediatric patients with OSAS can allow PAP to be an effective and safe therapy in this population.

Effects of Normoxic Recovery on Intima-Media Thickness of Aorta and Pulmonary Artery Following Intermittent Hypoxia in Mice

Obstructive sleep apnea (OSA) patients are at risk for increased blood pressure and carotid intima-media thickness (IMT), with pulmonary hypertension and right-sided heart failure potentially developing as well. Chronic intermittent hypoxia (IH) has been used as an OSA model in animals, but its effects on vascular beds have not been evaluated using objective unbiased tools. Previously published and current experimental data in mice exposed to IH were evaluated for IMT in aorta and pulmonary artery (PA) after IH with or without normoxic recovery using software for meta-analysis, Review Manager 5. Because IMT data reports on PA were extremely scarce, atherosclerotic area percentage from lumen data was also evaluated. IH significantly increased IMT parameters in both aorta and PA as illustrated by Forest plots (P < 0.01), which also confirmed that IMT values after normoxic recovery were within the normal range in both vascular beds. One-sided scarce lower areas in Funnel Plots were seen for both aorta and PA indicating the likelihood of significant publication bias. Forest and Funnel plots, which provide unbiased assessments of published and current data, suggest that IH exposures may induce IMT thickening that may be reversed by normoxic recovery in both aorta and PA. In light of the potential likelihood of publication bias, future studies are needed to confirm or refute the findings. In conclusion, OSA may induce IMT thickening (e.g., aorta and/or PA), but the treatment (e.g., nasal continuous positive airway pressure) will likely lead to improvements in such findings.

Sleep disordered breathing and enlargement of the right heart after myocardial infarction

Structural and functional integrity of the right heart is important in the prognosis after acute myocardial infarction (AMI). The objective of this study was to assess the impact of sleep disordered breathing (SDB) on structure and function of the right heart early after AMI.

54 patients underwent cardiovascular magnetic resonance 3–5 days and 12 weeks after AMI, and were stratified according to the presence of SDB, defined as an apnoea–hypopnoea index of ≥15 events·h−1.

12 weeks after AMI, end-diastolic volume of the right ventricle had increased significantly in patients with SDB (n=27)versusthose without (n=25) (mean±sd14±23%versus0±17%, p=0.020). Multivariable linear regression analysis accounting for age, sex, body mass index, smoking, left ventricular mass and left ventricular end-systolic volume showed that the apnoea–hypopnoea index was significantly associated with right ventricular end-diastolic volume (B-coefficient 0.315 (95% CI 0.013–0.617); p=0.041). From baseline to 12 weeks, right atrial diastolic area increased more in patients with SDB (2.9±3.7 cm2versus1.0±2.4 cm2, p=0.038; when adjusted for left ventricular end systolic volume, p=0.166).

SDB diagnosed shortly after AMI predicts an increase of right ventricular end-diastolic volume and possibly right atrial area within the following 12 weeks. Thus, SDB may contribute to enlargement of the right heart after AMI.

Use of pulmonary arterial hypertension-specific therapy in overweight or obese patients with obstructive sleep apnea and pulmonary hypertension

Pulmonary hypertension (PH) in overweight or obese patients with obstructive sleep apnea (OSA) may be multifactorial. The effect of pulmonary artery hypertension (PAH)-specific drugs on PH and exercise capacity in such patients is unknown. We performed a retrospective review of overweight or obese patients with OSA and PH who were treated with PAH-specific therapy in our PH clinic. We identified 9 female and 2 male patients. The mean age ± SD was 54.9 ± 9.3 years. The mean pulmonary artery pressure at the time of diagnosis of PH was 39.8 ± 16.1 mmHg. The right atrial pressure was 11.1 ± 4.5 mmHg, the pulmonary artery wedge pressure was 14.1 ± 2.9 mmHg, the cardiac index was 2.6 ± 0.5 L/min/m(2), and the pulmonary vascular resistance index was 10.6 ± 7.1 Wood units/m(2). The indications for use of PAH-specific therapy were dyspnea in association with right heart failure (n = 4), persistent PH despite compliance with nocturnal positive airway pressure (PAP) therapy (n = 4), or inability to tolerate PAP therapy (n = 3). PH was treated with an endothelin receptor antagonist (n = 8) or a phosphodiesterase-5 inhibitor (n = 3). The 6-minute walk distance (6MWD) improved significantly, from 234 ± 49.7 to 258 ± 54.6 m (24 m [95% confidence interval (CI): 6.5-341.5 m]; P = 0.014) over a period of 4.4 ± 1.8 months (n = 8) and from 241.7 ± 48.5 to 289.9 ± 91 m (48 m [95% CI: 5.5-90.8 m]; P = 0.033) in those with a longer follow-up period of 12.1 ± 6.4 months (n = 7). The systolic pulmonary artery pressure dropped significantly, from 64 ± 25.2 to 42 ± 10.4 mmHg (22 mmHg [95% CI: 4-40 mmHg]; P = 0.024) over a period of 6.1 ± 4.1 months (n = 7). In conclusion, PAH-specific therapy resulted in significant improvement in both PH and 6MWD.

Pathophysiology of sleep apnea

Sleep-induced apnea and disordered breathing refers to intermittent, cyclical cessations or reductions of airflow, with or without obstructions of the upper airway (OSA). In the presence of an anatomically compromised, collapsible airway, the sleep-induced loss of compensatory tonic input to the upper airway dilator muscle motor neurons leads to collapse of the pharyngeal airway. In turn, the ability of the sleeping subject to compensate for this airway obstruction will determine the degree of cycling of these events. Several of the classic neurotransmitters and a growing list of neuromodulators have now been identified that contribute to neurochemical regulation of pharyngeal motor neuron activity and airway patency. Limited progress has been made in developing pharmacotherapies with acceptable specificity for the treatment of sleep-induced airway obstruction. We review three types of major long-term sequelae to severe OSA that have been assessed in humans through use of continuous positive airway pressure (CPAP) treatment and in animal models via long-term intermittent hypoxemia (IH): 1) cardiovascular. The evidence is strongest to support daytime systemic hypertension as a consequence of severe OSA, with less conclusive effects on pulmonary hypertension, stroke, coronary artery disease, and cardiac arrhythmias. The underlying mechanisms mediating hypertension include enhanced chemoreceptor sensitivity causing excessive daytime sympathetic vasoconstrictor activity, combined with overproduction of superoxide ion and inflammatory effects on resistance vessels. 2) Insulin sensitivity and homeostasis of glucose regulation are negatively impacted by both intermittent hypoxemia and sleep disruption, but whether these influences of OSA are sufficient, independent of obesity, to contribute significantly to the "metabolic syndrome" remains unsettled. 3) Neurocognitive effects include daytime sleepiness and impaired memory and concentration. These effects reflect hypoxic-induced "neural injury." We discuss future research into understanding the pathophysiology of sleep apnea as a basis for uncovering newer forms of treatment of both the ventilatory disorder and its multiple sequelae.

Nitric oxide: new evidence for novel therapeutic indications

BACKGROUND

Nitric oxide (NO) deficiency is implicated in many pathophysiological processes in mammals. NO is a ubiquitous molecule involved in multiple cellular functions. Uncontrolled or inappropriate production of NO may lead to several disease states including septic shock, rheumatoid and inflammatory arthropathies, and expansion of cerebral damage after stroke. However, to date, there are no therapeutic agents available that can overcome these conditions. Similarly, underproduction of NO by NO synthase or enhanced breakdown of NO also leads to diseases such as hypertension, ischemic conditions, pre-eclampsia, premature delivery, among others. NO donor therapies are indicated in these conditions.

RESULTS

Nitroglycerin and nitrates (NO donors) have been used as therapeutic agents for the past century, particularly to treat vascular disease, and the only significant adverse effects are headaches. NO donors are highly cost-effective and have beneficial effects in multiple body systems. When the body cannot generate NO via NO synthase or due to rapid turnover leading to inadequate amounts of NO available for biological homeostasis, administration of exogenous NO, or prolongation of the actions of endogenous NO, are practical ways to supplement NO.

CONCLUSION

Recipients of such therapy include patients with angina pectoris, coronary artery disease, hypertension, osteoporosis, gastrointestinal motility disorders, pregnancy-related disorders including premature delivery, pre-eclampsia, vulvodynia, and erectile dysfunction in men. Postmenopausal NO deficiency is rectified with hormone replacement therapy, which enhances local production of NO. Declining local NO production secondary to estrogen deficiency in postmenopausal women and perhaps in older men could be one of the reasons for age-related increased incidences of cardiovascular events and sexual dysfunction. Thus, in addition to supplementation of NO compounds in acute situations like alleviating angina and erectile dysfunction, chronic NO therapy is cost-effective in decreasing cardiovascular events, and improving the urogenital system and skeletal health.

Cardiovascular morbidity in obstructive sleep apnea: oxidative stress, inflammation, and much more

Sleep-disordered breathing and obstructive sleep apnea (OSA) are highly prevalent disorders throughout the lifespan, which may affect up to 2-10% of the population, and have now been firmly associated with an increased risk for cardiovascular and neurobehavioral complications. Nevertheless, the overall pathophysiologic mechanisms mediating end-organ injury in OSA remain undefined, particularly due to the very frequent coexistence of other disease states, such as obesity, that clearly complicate the potential cause-effect relationships. Two major, and to some extent overlapping, mechanisms have been proposed to explain the morbid consequences of OSA, namely increased generation and propagation of reactive oxygen species and initiation and amplification of inflammatory processes. The evidence supporting the validity of these concepts as well as that detracting from such mechanisms will be critically reviewed in the context of clinical and laboratory-based approaches. In addition, some of the contradictory issues raised by such evaluation of the literature will be interpreted in the context of putative modifications of the individual responses to OSA, as determined by genetic variants among susceptibility-related genes, and also by potential environmental modulators of the phenotypic expression of any particular end-organ morbidity associated with OSA.