Continuous Positive Airway Pressure Pressure Level Research Articles

Real-time multislice MRI during continuous positive airway pressure reveals upper airway response to pressure change.

To determine if a real-time magnetic resonance imaging (RT-MRI) method during continuous positive airway pressure (CPAP) can be used to measure neuromuscular reflex and/or passive collapsibility of the upper airway in individual obstructive sleep apnea (OSA) subjects. We conducted experiments on four adolescents with OSA and three healthy controls, during natural sleep and during wakefulness. Data were acquired on a clinical 3T scanner using simultaneous multislice (SMS) RT-MRI during CPAP. CPAP pressure level was alternated between therapeutic and subtherapeutic levels. Segmented airway area changes in response to rapid CPAP pressure drop and restoration were used to estimate 1) upper airway loop gain (UALG), and 2) anatomical risk factors, including fluctuation of airway area (FAA). FAA significantly differed between OSA patients (2-4× larger) and healthy controls (Student's t-test, P < 0.05). UALG and FAA measurements indicate that neuromuscular reflex and passive collapsibility varied among the OSA patients, suggesting the presence of different OSA phenotypes. Measurements had high intrasubject reproducibility (intraclass correlation coefficient r > 0.7). SMS RT-MRI during CPAP can reproducibly identify physiological traits and anatomical risk factors that are valuable in the assessment of OSA. This technique can potentially locate the most collapsible airway sites. Both UALG and FAA possess large variation among OSA patients. 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1400-1408.

Clinical predictors of effective continuous positive airway pressure in patients with obstructive sleep apnea/hypopnea syndrome.

To identify standard clinical parameters that may predict the optimal level of continuous positive airway pressure (CPAP) in adult patients with obstructive sleep apnea/hypopnea syndrome (OSAHS). This is a retrospective study in a tertiary academic medical center that included 129 adult patients (117 males and 12 females) with OSAHS confirmed by diagnostic polysomnography (PSG). All OSAHS patients underwent successful full-night manual titration to determine the optimal CPAP pressure level for OSAHS treatment. The PSG parameters and completed physical examination, including body mass index, tonsil size grading, modified Mallampati grade (also known as updated Friedman's tongue position [uFTP]), uvular length, neck circumference, waist circumference, hip circumference, thyroid-mental distance, and hyoid-mental distance (HMD) were recorded. When the physical examination variables and OSAHS disease were correlated singly with the optimal CPAP pressure, we found that uFTP, HMD, and apnea/hypopnea index (AHI) were reliable predictors of CPAP pressures (P = .013, P = .002, and P < .001, respectively, by multiple regression). When all important factors were considered in a stepwise multiple linear regression analysis, a significant correlation with optimal CPAP pressure was formulated by factoring the uFTP, HMD, and AHI (optimal CPAP pressure = 1.01 uFTP + 0.74 HMD + 0.059 AHI - 1.603). This study distinguished the correlation between uFTP, HMD, and AHI with the optimal CPAP pressure. The structure of the upper airway (especially tongue base obstruction) and disease severity may predict the effective level of CPAP pressure. 4.

Humidification during CPAP titration: an unresolved issue

AbbreviationsAHI Apnea–hypopnea indexCPAP Continuous positive airway pressureHH Heated humidifierOSA Obstructive sleep apneaDear Editor,Thereisstillacontroversyovertheroleandpositiveeffectsofheated humidifier (HH) on nasopharyngeal symptoms andobjective measures during continuous positive airway pres-sure(CPAP)titration[1,2].WereadwithinterestthearticlebyYu et al. [3] who analyzed the effects of HH during CPAPtitration in subjects with and without nasopharyngeal symp-toms. The investigators randomly assigned 52 patients withobstructive sleep apnea (OSA) during CPAP titration underpolysomnographic monitoring into HH and non-HH groups.The authorsassessedsymptomatology (nasalcavity, pharynx,and nasopharynx) before and after CPAP titration, and evalu-ated leak, AHI reduction, and optimal CPAP pressure level inthe two groups. They concluded that HH does not improveany of the objective measures during CPAP titration and didnot recommend the use of HH during CPAP titration. Webelieve that the conclusion is overstated based on the pre-sented data. The results cannot be generalized to all OSApatients undergoing CPAP titration. The need for humidifica-tion during positive airway pressure therapy through a nonin-vasive route is influenced by several factors such as air leaks,interface, room temperature, temperature of inhaled gas, air-flow, and pressure used [4].External humidification will have no added benefits inpatients who can maintain adequate physiological levels ofhumidity. As the pressure needed to overcome the obstruc-tive respiratory events in the studied group was relativelylow, it seems that the studied subjects were able to maintainadequate airway humidity without HH. The conclusions ofthe study of Yu et al. [3] cannot be generalized to OSApatients who require high positive airway pressure to over-come airway obstruction. Another important issue to con-sider when assessing the need for humidification is thepresence of mouth breathing and mouth leaks. Mouthbreathing may generate unidirectional nasal air flow andresults in significant increase in nasal airway resistanceand hence mouth leaks [5]. The nasal mucosa has a consid-erable ability for heating and humidifying inspired air; how-ever, it can be overwhelmed at high flow rates with CPAPand when there is unidirectional flow caused by mouthleaks. The potential effects of mouth breathing were notevaluated in the paper of Yu et al. [3].Therefore, we think that the role of humidificationduring CPAP titration cannot be discarded. Humidifica-tion may be beneficial in selected OSA patients duringCPAP titration such as patients with mouth breathingand patients requiring high positive airway pressure toeliminate airway obstruction. Future studies should as-sess the role of humidification during CPAP titration inpatients with mouth breathing and patients requiringhigh positive airway pressure.

The effects of heated humidifier in continuous positive airway pressure titration

BackgroundPrevious studies have shown that routine heated humidifier (HH) do not provide any benefit during continuous positive airway pressure (CPAP) titration if there are no significant naso-pharyngeal symptoms. In clinical practice, nasal diseases and upper airway symptoms are very common. This study investigates the effects of HH during CPAP titration in subjects with or without naso-pharyngeal symptoms.MethodsFifty-two patients who received polysomnography with CPAP titration were randomly assigned to HH and non-HH groups. Their nasal cavity, pharynx, and naso-pharynx were evaluated before CPAP titration, and a questionnaire on subjective sensation, including naso-pharyngeal symptoms, willingness to further use CPAP, and sleep improvement, was used. Objective (e.g., leak, apnea–hypopnea index (AHI) reduction, and optimal CPAP pressure level) and subjective data were analyzed between the two groups.ResultsIn subjective sensation, the HH group did not have any benefit in further willingness to use CPAP and in sleep improvement, but had improved naso-pharyngeal symptoms (p = 0.043). There were no significant differences in leak, AHI reduction, and optimal CPAP pressure, even in patients with significant naso-pharyngeal symptoms.ConclusionRoutine use of HH is not necessary during CPAP titration regardless of naso-pharyngeal symptoms.

Central sleep apnea, upper airway resistance and sleep

The question of why ‘central’ apnea is seen is a recurring theme. The term ‘diaphragmatic’ apnea is a better term than ‘central’ apnea as the latter indicates a dysfunction in the medulla, which is rare. The short response to the question raised is: ‘because the upper airway is not completely open’. This is a very common consequence when dental appliances are used to treat sleep-disordered breathing, but the response needs an explanation. Long-term studies on the outcome of dental appliances have mostly been poor. We reviewed 25 obstructive sleep apnea (OSA) patients monitored between 4 and 12 months post-fitting with commercially available dental appliances (unpublished observations). All subjects presented at least one standard deviation higher amount of cyclic alternating pattern (CAP), with higher CAP rate and higher amount of phase A2 [1]) and A3 [1]) than their ageand gender-matched controls, indicating persistence of some degree of sleep disturbance and instability of non-rapid eye movement (NREM) sleep in these patients. The reasons why dental appliances may not completely relieve a patient are multiple, from problems involving soft tissues attached to the maxilla and advancing the mandible, to a narrow airway at the base of the tongue and difficulty shifting the hyoid bone forward even with nasal continuous positive airway pressure (CPAP). The more interesting question is why we see persistence of diaphragmatic apneas with dental appliances, a similar finding sometimes when CPAP pressure level is not high enough when performing CPAP titration. During wakefulness, chemosensitivity plays little role in quiet breathing due to the non-specific stimuli that

Optimal continuous positive airway pressure for the treatment of obstructive sleep apnea/hypopnea.

The obstructive sleep apnea/hypopnea syndrome (OSA/H) is characterised by repetitive obstruction of the upper airway during sleep. The consequences of OSA/H include excessive daytime sleepiness, reduced perceived health quality and an increased risk of driving accidents. There is evidence that treatment with nasal continuous positive airway pressure (CPAP) is effective in eliminating these consequences. In addition, OSA/H may also be associated with hypertension and an increased risk of vascular disease, and although there is no clear evidence in this regard, CPAP may be effective alleviating these consequences as well. Nasal CPAP is considered the treatment of choice for clinically significant OSA/H. The optimal CPAP prescription is that which is most effective in eliminating the adverse consequences of OSA/H. Patients should be initially treated with standard CPAP. For those in whom standard CPAP is unsuccessful or intolerable bi-level or self-adjusting modes may be attempted. The nasal CPAP pressure level can be titrated to eliminate apnea, hypopnea, snoring, respiratory arousal and inspiratory flow limitation as a means of predicting successful long-term therapy. The reliability of these physiologic parameters in predicting the optimal long-term CPAP pressure is eroded by the tendency of CPAP pressure-level requirement to decrease with chronic CPAP use, and by other factors that may increase the CPAP pressure requirement. The split-night polysomnogram and unattended auto-CPAP titration have been proposed as efficient means of determining the optimal CPAP pressure, but for patients with subtle OSA/H, underlying cardiopulmonary disease or other forms of sleep-disordered breathing a full-night polysomnogram may be required. The CPAP prescription must include a comfortable well-fitting interface. When CPAP is prescribed it is essential that the patient undergo clinical re-evaluation to ensure that treatment goals are being met.