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Volume 14 No. 04
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Accepted Papers





Scientific Investigations

Integrating the Divided Nasal Cannula Into Routine Polysomnography to Assess Nasal Cycle: Feasibility and Effect on Outcomes

Marcelo Scapuccin, MD1,2; Logan Schneider, MD3; Nur Rashid, MD1,4; Soroush Zaghi, MD1; Talita Rosa, MD1; Yung-an Tsou, MD1,5; Stanley Liu, MD1; Paulo Lazarini, MD2; Robson Capasso, MD1; Chad Ruoff, MD3
1Division of Sleep Surgery, Department of Otolaryngology – Head and Neck Surgery at Stanford University School of Medicine, Stanford, California; 2Department of Otolaryngology – Head and Neck Surgery at Santa Casa School of Medicine, Santa Casa de Misericórida de São Paulo, São Paulo, SP, Brazil; 3Division of Sleep Medicine, Department of Psychiatry and Behavioral Sciences, Stanford University, School of Medicine, Stanford, California; 4Department of Otolaryngology – Head and Neck Surgery at University Putra Malaysia, Serdang, Selangor, Malaysia; 5Department of Otolaryngology, China Medical University Hospital, Taichung, Taiwan

ABSTRACT

Study Objectives:

Patients suspected to have sleep-disordered breathing underwent an overnight polysomnography using a divided nasal cannula to gain additional information about the nasal cycle during sleep.

Methods:

This was a prospective, observational cohort study replacing the undivided nasal cannula with a divided nasal cannula during routine polysomnography (n = 28).

Results:

Integration of the divided nasal cannula pressure transducer system into routine polysomnography was easy and affordable. Most patients (89%) demonstrated nasal cycle changes during the test. Nasal cycle changes tended to occur during body position changes (62%) and transitions from non-rapid eye movement sleep to rapid eye movement sleep (41%). The mean nasal cycle duration was 2.5 ± 2.1 hours. Other sleep study metrics did not reveal statistically significant findings in relation to the nasal cycle.

Conclusions:

Replacing an undivided nasal cannula with a divided nasal cannula is easy to implement, adding another physiologic measure to polysomnography. Although the divided nasal cannula did not significantly affect traditional polysomnographic metrics such as the apnea-hypopnea index or periodic limb movement index based on this small pilot study, we were able to replicate past nasal cycle findings that may be of interest to sleep clinicians and researchers. Given the ease with which the divided nasal cannula can be integrated, we encourage other sleep researchers to investigate the utility of using a divided nasal cannula during polysomnography.

Citation:

Scapuccin M, Schneider L, Rashid N, Zaghi S, Rosa T, Tsou Y, Liu S, Lazarini P, Capasso R, Ruoff C. Integrating the divided nasal cannula into routine polysomnography to assess nasal cycle: feasibility and effect on outcomes. J Clin Sleep Med. 2018;14(4):641–650.


BRIEF SUMMARY

Current Knowledge/Study Rationale: The phenomenon that underlies the alternation of congestion and decongestion of nasal airways, producing a relative change in resistance between one side of the nasal passage and the other, is called the nasal cycle. It is well known that body position can influence nasal airway resistance and respiratory events.

Study Impact: In our study, we replaced the undivided nasal cannula with a divided nasal cannula during polysomnography, allowing us to replicate past nasal cycle findings and search for other associations between the nasal cycle and traditional polysomnographic measures.

INTRODUCTION

Advances in polysomnography (PSG), dating back to the first paper-based PSG, have been made possible largely by integrating new technologies into the test. Upper airway resistance syndrome was first confirmed with the use of an esophageal pressure monitor.1 Additionally, although the nasal-oral thermistors aided in evaluation of sleep-disordered breathing, their poor performance with hypopnea detection2 prompted Norman et al.3 to measure nasal airflow more directly with a simple pneumotachograph, consisting of a standard nasal cannula connected to a 2-cmH2O pressure transducer. In 2002, O'Malley et al.4 reported that the addition of frontal electroencephalographic leads significantly improved the detection of respiratory-related arousals, highlighting the fact that some arousal waveforms can only be seen in leads that are spatially distinct from the conventional PSG montage.4 Moreover, advancements in digital signal collection and processing have resulted in improved ability to analyze these complex biological signals.5,6 Ultimately, the improvements in the PSG over time have led to a better understanding of sleep disorders and their pathophysiologic consequences.

Although much effort has gone into moving sleep evaluations into the home with small and portable technologies, the PSG has remained largely the same test for more than a decade. Although home sleep apnea tests will improve access for diagnosis of sleep apnea, they will not advance our understanding of sleep and sleep apnea, nor its treatment. Moving to a more streamlined diagnosis and treatment pathway under our current paradigm may not be sufficient for better care, as seen in a number of recent studies focused on the treatment of obstructive sleep apnea (OSA).7,8 One of the primary concerns echoed by many experts in the field is the lack of discernment afforded by current metrics used to define OSA.9,10 The PSG may provide an opportunity to both diagnose and treat and also an opportunity to phenotype OSA through sophisticated physiologic analyses allowing for more a personalized physiologic approach to treatment.1113 The “nasal cycle” was described as early as 1895 as periodic cycles of congestion and decongestion alternating between the right and left nasal passages, producing changes in resistance.14,15 The sympathetic nervous system, hypothalamus, and brainstem are thought to regulate the nasal cycle by changing the resistance in the venous sinusoids lining the nasal mucosa.1619 Comparatively, parasympathetic inner-vation plays a minor role in the nasal cycle.1619

Two dynamic features of sleep—body position and sleep stage—have demonstrated the most significant impact on nocturnal nasal cycle activity. Rohrmeier et al.19 reported an association between changes in body position and nasal cycle, describing an increase in resistance in the “down” side nostril in the lateral position.19 This phenomenon is referred to as the corporonasal reflex, which can also occur without a change in body position if pressure is simply applied to the shoulder, lateral thorax, or pelvis.2022 A relationship between changes in sleep stages and nasal resistance has also been described in the literature.23 Kimura et al. described how spontaneous nasal cycle transitions occur during transitions into rapid eye movement (REM) sleep, perhaps in relation to changes in the sympathetic nervous system.23 The use of sympathomimetic medications causes nasal decongestion with the effect lasting for more than 6 hours.22,23 Using rhinomanometry, Tatar et al. determined that radiofrequency of the inferior turbinates changes nasal physiology but not the nasal cycle.24 Changes in age, temperature, airflow, and nasal infections, but not race, sex, height, nor weight, have been shown to influence the nasal cycle.25 Other findings from the PSG may also bear a relationship to the nasal cycle such as periodic limb movements of sleep (PLMS). Not only have periodic limb movements been associated with airway resistance,26 but the autonomic changes associated with PLMS may also influence the nasal cycle. Given the autonomic regulation of the nasal cycle and PLMS, these two phenomena, when both present, may be associated.27

Nasal airflow can be different in each nostril for different reasons and may have an influence on sleep quality that may not be apparent through the current methods by which standard PSG is performed. Therefore, a divided nasal cannula could potentially add important information to PSG results in relation to the nasal cycle and could potentially aid in our understanding of this currently ambiguous phenomenon. Therefore, our first aim was to evaluate the feasibility of adopting and integrating the divided nasal cannula into the routine PSG. We also aimed to replicate past findings of how nasal anatomy, body position, and sleep stage influence the nasal cycle. Last, we aimed to study the nasal cycle in relation to other selected PSG variables including the apnea-hypopnea index (AHI), arousal index, oxygen-desaturation index (ODI), and PLMS.

METHODS

Patients

The study protocol was approved by the Institutional Review Board of Stanford University (IRB no. 32109). All patients were informed about the study protocol, and provided their informed consent. This study enrolled 28 adult patients (18 years or older) from the Stanford sleep clinic suspected to have sleep-disordered breathing. Exclusion criteria included the following: (1) pulmonary and cardiovascular comorbidities; (2) severe nasal septum deviation, or nasal surgery in the past 6 months; (3) psychiatric disorders; (4) engaged in shift work or traveled across time zones within 1 month prior to the experiment; and (5) use of sympathomimetic medication or topical corticosteroids.

Nasal Evaluation

The nasal evaluation included both an objective and subjective component (ie, physical examination and patient report including a survey). The physical examination was performed to define anatomic patency by two otolaryngologists. The findings of the physical examination, using nasal speculum and endoscope, documented the presence or absence of nasal septal deviation to left/right. The patients' subjective report of the most frequently obstructed nasal passageway (ie, symptomatic side) was also recorded at time of interview. Of note, the otolaryngologists were not blinded to patients' subjective reports. In addition, we administered the Nasal Obstruction Symptom Evaluation (NOSE) survey, which is a well-validated measure of symptomatic nasal obstruction, to differentiate patients presenting with and without subjective nasal obstruction.28 Patients were categorized as having mild (5–25), moderate (30–50), severe (55–75), or extreme (80–100) nasal obstruction, based on commonly accepted cutoffs on the NOSE survey.29

Polysomnography

PSG was performed in a temperature-controlled room according to American Academy of Sleep Medicine (AASM) standards, except that a divided nasal cannula replaced the standard undivided nasal cannula30 (Figure 1). The evaluation of nasal flow was assessed using a divided nasal cannula (Pediatric CO2 divided cannula, Salter Labs, Lake Forest, Illinois, United States) connected to a dual-channel pressure transducer (Kit Model 0580, Braebon Medical Corporation, Proctor Avenue, Ogdensburg, New York, United States). The signal was sampled at the AASM-recommended industry standard of 25 Hz. We applied a nasal-oral thermistor on top of the divided nasal cannula, allowing measurement of airflow from each nostril. Each PSG was manually reviewed in 2-minute increments to assign working and resting phase. The working phase was assigned to the nostril side with the predominant airflow; whereas the resting phase was assigned to the nostril side with less flow. More specifically, the working phase was defined as the side with ≥ 20% airflow amplitude compared to the other side for at least 20 minutes (Figure 2). In order to define a nasal cycle transition, a working phase had to persist for at least 20 consecutive minutes. Side-to-side amplitude differences of less than 20% were defined as an equal nasal cycle. All events that happened during an equal cycle nasal cycle period were excluded from the data analysis in this study. This resulted in the exclusion of 20 equal cycle periods, with a mean time of 18 ± 36 minutes.

Divided nasal cannula and dual pressure transducer.

The dual pressure transducer used to analyze the nasal cycle using the divided nasal cannula.

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Figure 1

Divided nasal cannula and dual pressure transducer.

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A nasal cycle transition.

A 10-minute epoch from an overnight polysomnogram using a divided nasal cannula demonstrating a transition from left working phase to right working phase.

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Figure 2

A nasal cycle transition.

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Changes in sleep stage (ie, non-REM sleep to REM sleep transitions) and body position were, by definition, associated with a change in the nasal cycle if nasal cycle and sleep stage/ body position changed within 5 minutes of each other. If both sleep stage and body position changed within 5 minutes of each other, then the change in nasal cycle was associated with both sleep stage transition and body position change.

Board-certified sleep technologists manually scored the electronic raw data in accordance with 2012 AASM criteria, except hypopneas were determined using a divided rather than undivided nasal cannula. A board-certified sleep medicine physician reviewed all scored PSG tests for accuracy. Hypopneas were scored if there was a 30% to 90% reduction in the amplitude of the nasal cannula from the working phase lasting at least 10 seconds and associated with a ≥ 3% oxyhemoglobin desaturation and/or cortical arousal. The oronasal thermistor was used to evaluate for apneas.

Body Position

Each PSG video recording was reviewed in 2-minute increments in order to assign change in body and head position. A new head and/or body position was marked only if the position was maintained for 5 minutes or longer. Body positions were designated as left, right, supine, and prone. Head positions were designated as left side (0–45 degrees), neutral (45–135 degrees), and right side (135–180 degrees). Head movements, relative to the neutral plane of the head, occurring in the supine position, were also marked as a positional shift. Time spent in left and right lateral decubitus body positions was considered in analyses. Time spent in the supine position with head position to the left or right side was considered in analyses as well. Time spent in the left lateral decubitus and supine body position with the head to the left side was summed together. Time spent in the right lateral decubitus and supine position with head to right side was added together. Time spent in the prone position was excluded from the analyses.

For analyses of body position and nasal cycle, a categorization scheme was adopted using working phase and body/ head position. For example, if the working phase was on the left nasal cannula/passage (ie, “LW”) and the patient's body/ head was on the left (ie, “LS”) then this scenario was designated as “LWLS.” In addition, we specified whether the working phase was “up” or “down” relative to body/head position (ie, working phase orientation). For example, if the patient was in the left lateral decubitus position and the working phase of the nasal cycle was on the right, we defined the working phase orientation as “up”; however, if the patient was in the left lateral decubitus position and the working phase was on the left side, we termed this as “down.” Specific PSG findings including arousals, apneas, hypopneas, oxygen desaturations, and periodic limb movements were tallied and indices determined using total time spent in different scenarios (eg, “LWLS”) and nasal cycle “up” or “down.”

Statistical Analysis

First, demographic data were reported using descriptive statistics, using mean ± standard deviation for continuous variables and number (percent) for categorical variables. For comparison of means across multiple categories (eg, nasal cycle and body position), a two-way analysis of variance was performed; when only two means were being compared, a t test was used. For comparisons of categorical data proportions, Fisher exact test was used, as all circumstances resulted in at least one category with fewer than five observations. Correlations between continuous variables were analyzed using Spearman correlation coefficients; whereas, significant categorical associations had correlation effect sizes assessed by Cramér V. The statistical analysis was performed using R v3.3.3 (The R Foundation, Vienna, Austria) and associated packages: car, agricolae, and corrplot. The standard alpha threshold of .05 was Bonferroni adjusted, to account for multiple comparisons.

RESULTS

The study included 18 males (64.28%) and 10 females (35.71%) with the mean age of 40.3 ± 12.7 years (range, 19–57 years). The mean body mass index was 27.09 ± 4.64 kg/m2 (range, 19–37 kg/m2). All patients tolerated usage of the divided nasal cannula without incident, allowing for completion of all studies per standard clinical protocol.

Clinical Assessment and Symptomatic Reports

Septal deviation was present in 75% (21/28) of patients. The mean NOSE score of our study population was 4.16 ± 2.5. Agreement between patients' symptomatic side and septal deviation was high (Fisher exact test P = .004, Cramér V/φ: 0.51) (Table S1 in the supplemental material). No significant associations were found between septal deviation and working phases (Table 1) or septal deviation and body positions (Table S2 in the supplemental material). As expected, given the high correlation between septal deviation and symptomatic side, no significant associations were found between symptomatic side and working phases or symptomatic side and body positions (data not shown). No significant associations were found between side of septal deviation and any of the features of interest (Table 2).

Association between septal deviation and working phases.

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Table 1

Association between septal deviation and working phases.

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Relationship of septal deviation to variables of interest.

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Table 2

Relationship of septal deviation to variables of interest.

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Nasal Cycle

A classic nasal cycle change was present in 89.2% of the participants (25/28). There were a total of 69 nasal cycles evaluated in the patients with an average of 2.8 nasal cycles per night. Average nasal cycle length was 2.5 ± 2.1 hours, ranging from 1.0 to 7.5 hours. A change to REM sleep was associated with 41% of the nasal cycle transitions ([11 + 17] / 69) (Figure 3). In all cases, stage R sleep began either on the same epoch, or one epoch before the nasal cycle transition (Figure 4). Positional shifts were associated with 62% of the nasal cycle transitions ([11 + 32] / 69). The positional shifts that were associated with nasal cycle transitions happened on average 1.8 minutes before the nasal cycle transition (Figure 4). Nasal cycle transitions were associated with both a body position change and the onset of REM sleep in 16% of the nasal cycles observed in this study (11/69), yet 13% (9/69) did not have an association with either a body position change or the onset of REM sleep.

Nasal cycle transition associations.

Nasal cycle transitions expressed as count (%), based on association with position, REM sleep, both, or neither. REM = rapid eye movement.

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Figure 3

Nasal cycle transition associations.

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A hypnogram with the nasal cycle.

(A) Change in the working phase of the nasal cycle associated with onset of REM sleep depicted on a hypnogram. (B) Change in the working phase of the nasal cycle associated with change in body position depicted on a hypnogram. REM = rapid eye movement.

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Figure 4

A hypnogram with the nasal cycle.

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Changes in body position preceded 62% of the nasal cycle transitions ([11 + 32] / 69). These changes in body position and nasal cycles were in opposition 61% of the time. For example, if the patient shifted body position to the right side, the working phase of the nasal cycle would transition to the left nostril, and vice versa. There was no statistically significant categorical association between the working phase and body position predominance (Fisher exact test P = .48) (Table S3 in the supplemental material). In addition, the correlations between the duration of time spent in a working phase relative to a body position were weak (range of Pearson ρ was −0.13 to 0.22) (Table S4 in the supplemental material).

When we factored in working-phase orientation (ie, “up” or “down” working phases as described in the Methods section), none of the assessed indices were noted to be significantly different based on working phase position category (Table 3). However, we were able to replicate past findings of a statistically significant higher AHI in the supine versus nonsupine body positions (25.5 ± 17.8 versus 13.9 ± 10.2 events/h, P < .01). With regard to PLMS, we did not find any statistically significant differences (P = .83) in the periodic limb movement index occurring with the working phase up (6.72 ± 12.62 events/h) versus working phase down (7.77 ± 9.59 events/h). Even, with post hoc pairwise comparisons (data not shown), there were no group-to-group differences in any of the measures. Analyses then explored whether just having the nasal cycle in the up (versus down) position influenced any of the sleep measures (Table 4). Individuals spent a similar amount of time with the working phase up versus down (3.46 ± 1.33 versus 3.43 ± 4.15 hours, P = .97) on average. Despite a well-balanced duration of comparison between these states, none of the outcome measures of interest differed significantly between working phase being up or down.

Associations between variables of interest with nasal cycle and body position.

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Table 3

Associations between variables of interest with nasal cycle and body position.

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Associations between variables of interest with time spent with working phase orientation “up” and “down.”

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Table 4

Associations between variables of interest with time spent with working phase orientation “up” and “down.”

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DISCUSSION

Although the nasal cycle is considered to be present in approximately 80% of the adult population, findings vary considerably within individual studies, with the nasal cycle being reported in frequencies that range from 21% to 100%.31 Kimura et al. described the increase of nasal cycle duration during sleep.23 We found a classic nasal cycle in 89.2% of the patients in this study (25/28). This phenomenon has been attributed to fewer effects of environmental factors or physical activity, traditionally encountered during wakefulness. We found the nasal cycle duration to last 2.5 ± 2.1 hours, ranging from 1.0 to 7.5 hours. These results are similar to those reported by Hasegawa and Kern, a mean nasal cycle duration of 2.9 hours (range, 1 to 6 hours).15

The functional significance of the nasal cycle in health and disease remains undefined, although an attractive hypothesis is the idea that the nasal cycle may act to share the burden of air conditioning between the two nasal passages.32,33 Eccles proposes that it plays a major part in respiratory defense.16 Nonetheless, there is reason to suspect that the nasal cycle, through an interaction with anatomy (eg, septal deviation), body position, and associated fluid shifts, may affect sleep phenomena and, thereby, pathophysiology. However, we acknowledge that the negative results from this pilot study may be the consequence of a number of potential factors, the most obvious of which include: (1) the number of nasal cycles and duration spent in a given cycle and/or given body position were insufficient to meet our prespecified power estimates; (2) the prevalence and severity of the explored phenomena (eg, PLMS) were too low to make meaningful comparisons; (3) there may, in fact, be no pathophysiologic association of nasal cycle with any of the sleep phenomena explored (eg, sleep-disordered breathing, limb movements, spontaneous arousals, etc.). Fortunately, this study demonstrates the ease with which a divided nasal cannula can be incorporated into the PSG without diminishing performance, while also providing a statistical basis to power future studies in order to enroll sufficient numbers of participants to account for the prevalence of sleep phenomena and number/duration of nasal cycles.

Associations Between Nasal Cycle, Septum Deviation, and Symptoms

Although nasal obstruction has not been demonstrated in the literature to serve as a major determinant of disease severity among patients with moderate to severe OSA, it has been shown to significantly increase event frequency and severity in patients with mild OSA.34 In our study, patient subjective report of the most frequently obstructed nasal passageway (ie, symptomatic side) was highly concordant with septal deviation (Fisher exact test P = .004, Cramér V/φ: 0.51). However, neither septal deviation (Table 1 and Table S2) nor symptomatic side (data not shown) demonstrated a significant relationship with the predominant working phase of the nasal cycle or predominant body position. In other words, the finding of a left septal deviation or symptomatic left side in a patient does not necessarily lead to more time spent with the working phase on the right. Further, if a patient spends most of the night on his/her right side, this does not necessarily mean that more time will be spent with the working phase of the nasal cycle on the left side.

Although nasal surgery widens the nasal airway, it has not been shown to significantly help sleep apnea, with some studies showing reduction of OSA severity measures by as little as 16.7% after nasal surgery.35,36 This may be because surgical procedures have not shown an effect on the nasal cycle, which is concordant with the findings of this study demonstrating a lack of association between signs or symptoms of nasal obstruction and working phase or body position predominance (Table 1 and Table S2). Regardless of procedure used (eg, radiofrequency of nasal turbinate or functional endoscopic sinus surgery), patients still demonstrate nasal cycle physiology after the procedure.24,29 However, nasal surgery usually improves the quality of life for patients with OSA, and it may be possible that nasal surgeries contribute to a more balanced amount of time in the working phase of each side of the nasal passages within the nasal cycle. Targeting surgical interventions to result in more effective balancing of airflow based on nasal cycle data from the nocturnal PSG, which has less environmental noise and physical activity, may help to improve surgical outcomes. For example, in our study, each subject without a classic nasal cycle in this study (n = 3) had a septal deviation. The absence of nasal cycle during sleep in these three subjects may be important when considering whether or not to perform nasal surgery, as any given individual may have vastly different symptomatic and clinical polysomnographic responses, based on the lack of association between symptoms and nasal cycle. This large degree of variability between individuals may prove to be a valuable clinical consideration in personalized treatment planning, if large-scale studies ultimately reveal a causal relationship between the nasal cycle and sleep disorder phenomena.

Association Between Nasal Cycle and Positional Shift

Changes in the working phase of the nasal cycle have been demonstrated in healthy volunteers, and this response can often be exaggerated in patients with rhinitis, where total unilateral nasal obstruction can occur.15 Although we did not find a significant relationship between body position and working phase, Rohrmeier et al., using long-term flow rhinoflowmetry, described a significant correlation (r = .67; P = .024) between body position and resting phase (the side opposite the working phase) in the recumbent position.19 We found that positional shifts were associated with 62% of all nasal cycles ([11 + 32] / 69). Kimura et al., however, found a markedly smaller percentage of positional shifts (only 18.8%) prior to cyclic phase reversal.23 However, the nasal cycle changes were measured by a portable rhinoflowmeter, not allowing for real-time measurement of the nasal cycle transitions.

In our study, we analyzed the body and head position change with a continuous video recording analyzed in 2-minute epochs, allowing for a more accurate assessment of association between body position and nasal cycle. Our results of a preceding shift in position resulting in 62% of the nasal cycle changes is similar to the 57.6% reported by Rohrmeier et al.19 The clinical and physiologic relevance of this finding is underscored by the fact that the body or head position changed just 1.8 minutes before the nasal shift event. Kimura et al. also reported 68.8% of nasal cycle transitions were associated with REM sleep.23 However, we found only 41% of nasal cycle transitions ([11 + 17] / 69) were associated with REM sleep onset.

Postural change during sleep is an important factor influencing the nasal cycle. A change from supine to lateral decubitus position results in increased nasal resistance in the downside nasal passage, accompanied by decreased nasal resistance in the upside nasal passage, often precipitating a switch of the nasal cycle, thereby affecting the preceding cycle's duration.23,37 Our findings were discordant with the existing literature,38 such that our patients did not spend significantly more time with the working phase in the upside nostril as compared to the downside nostril (3.46 ± 1.33 versus 3.43 ± 4.15 hours, P = .97). Moreover, the PSG findings did not reveal meaningful correlation between body position predominance and working phase predominance (Table S3 and Table S4). Some studies suggest that changes in nasal resistance may be due to reflex changes in sympathetic tone caused by a pressure stimulus to one side of the body.39 As such, positional shifts often result in early adjustment of the nasal cycle; however, this cycling disturbance soon reverts to the spontaneous pattern if a constant position is maintained, particularly if the participant is not in a lateral decubitus position. This was the case for most of our participants: 79% spent the most time supine, generally with 4.45 ± 1.84 hours supine as opposed to only 1.73 ± 1.18 hours on the right side and 1.88 ± 1.36 hours on the left side (analysis of variance F = 29.7, df = 2, P = 2.13*10−10). Additionally, switching the working phase to the up side may also occur without a direct correlation with body position, as was noted in 38% ([9 + 17] / 69) of the documented nasal cycle transitions that had no preceding body position change (with or without a transition to REM sleep). When analyzing the association between nasal cycle or body position and septum deviation, we found that body position is not related to side of septal deviation (Table S2). Additionally, the nasal cycle working phase did not have a higher average duration contralateral to the septal deviation (Table 1) or the patient's symptomatic nostril (data not shown). The lack of association between septal deviation and body position or nasal cycle duration may emphasize the poor association between clinical anatomic factors and the physiology of the nasal cycle noted in the extant literature.24,29 Comparatively, body position working phase correlations may have been limited by the lack of sufficient time spent on a given side, given the predominance of supine sleep limiting statistical power, as noted previously. Nonetheless, the correlations in Table S4 were in the expected direction (specifically, opposite side and working phase), but far from statistical significance. Moreover, the physiologic effect of position may be more manifest by acute changes in position, rather than the maintenance of a position, given that 62% of the nasal cycle transitions were preceded by a body position change. This could be explored in more depth through capturing a sufficient number of body position changes to ascertain whether the ultimate nasal cycle change transitioned to the expected contralateral side.

Association Between Nasal Cycle and Polysomnographic Features of Interest

The bulk of the data in the current literature show very limited improvement in OSA when looking at basic nasal airway procedures such as septoplasty and turbinate reduction.40 In contrast to that data, studies of acutely induced nasal obstruction were found to worsen measures of sleep-disordered breathing (eg, respiratory disturbance index, snoring duration, and ODI) in patients with mild but not moderate to severe OSA.41 Furthermore, nasal patency and total airway resistance significantly affects the collapsibility of the pharyngeal cavity and contributes to the pathogenesis of OSA.42

Most studies of nasal surgery and PSG reports only consider AHI change but do not mention nasal cycle shifts and body position change during the night. Our findings demonstrated that there was no significant relationship between sleep-disordered breathing features of interest (AHI, ODI, or arousal index) and working phase orientation (“up” or “down”) or body position-nasal cycle interactions. That being said, a number of aspects have been learned from these pilot data that may improve such analyses going forward. Variability in duration spent in each phase and position within individuals suggests a need for larger sample sizes to assess the expected effect sizes. Moreover, there is a growing body of data that suggest subphenotypes of sleep apnea may have different physiologic effects.11 Therefore, event subtype (eg, hypopneas versus apneas), stage predominance (non-REM versus REM sleep), and physiologic consequences (eg, event duration/arousal, desaturation, etc.) may aid in interpretation of the contribution of nasal cycle to sleep-disordered breathing, but would require a substantially larger sample to ensure a sufficient number of events are captured in each category.

Patients with PLMS have been found to have an increased vascular tone and a decreased blood flow to the extremities.43 Based on this, when patients activate the corporonasal reflex as a result of positional shifts, it results in turbinate congestion ipsilateral to the dependent body side, thereby reducing airflow on this side.39 In our study, we did not find any correlation between nasal cycle working phase (“up” or “down”) and PLMS. However, few of our patients manifested a substantial number of PLMS, limiting sample size. It is not known whether autonomic activation has a causal effect on PLMS, or if they are just coexisting manifestations. Exploring this potential pathophysiologic link in a larger population that is older (given a higher prevalence of PLMS) would help elucidate the suspected association.

Study Limitations

There were a number of limitations in this study. First, the clinical assessments (physical examination and symptoms) were not based on physiologic measures; use of acoustic rhinomanometry or nasal flowmeter may provide a more accurate clinical assessment that would correlate better with nasal cycle activity. In addition, our physical examination only included the presence or absence of septal deviation. Also, because not all individuals slept in every position/nasal cycle category, some of the data reports were limited, likely not meeting our sufficient a priori power estimates to detect a clinically meaningful (50%) difference in the outcome measure of interest. In addition, combining time spent in supine position with head position to left/right with time spent in left/right lateral decubitus position, respectively, may have affected our results as well. Larger sample sizes in populations enriched for the PSG features of interest will certainly enhance the ability to detect associations. Finally, because of the lack of concomitant use of the traditional nasal flow transducer cannula, we were unable to determine whether the divided nasal cannula resulted in a different OSA severity as measured by AHI. This would be an important next step in assessing the use of the divided nasal cannula during PSG.

CONCLUSIONS

To our knowledge, this is the first study to survey the nasal cycle, replacing the standard undivided nasal cannula with a divided nasal cannula, to analyze the nasal cycle, nasal septum deviation, and body position in relation to a variety of traditional PSG metrics. Replacing an undivided nasal cannula with a divided nasal cannula is easy to implement, adding another physiologic measure to the PSG. Known associations of nasal cycle transitions with body position and sleep stage changes were reaffirmed in our data. Although the divided nasal cannula did not significantly associate with traditional PSG metrics such as the apnea-hypopnea index or periodic limb movement index based on this small pilot study, given the ease with which the divided nasal cannula can be integrated into the PSG, we hope that other sleep researchers will further investigate how the divided nasal cycle may affect PSG metrics and outcomes.

DISCLOSURE STATEMENT

Work for this study was performed at the Sleep Clinic at Stanford University. This was not an industry-supported study. The authors report no conflicts of interest. M.S. is sponsored by the National Counsel of Technological and Scientific Development (CNPq) program from São Paulo, Brazil. L.S. is supported by National Institutes of Health grant T32 HL110952 05. All authors have seen and approved the manuscript.

ABBREVIATIONS

AASM

American Academy of Sleep Medicine

AHI

apnea-hypopnea index

ArI

arousal index

ESS

Epworth Sleepiness Scale

FOSQ

Functional Outcomes of Sleep Questionnaire

LS

left side

LW

left working

LWLS

left working phase, left body/head down

LWRS

left working phase, right body/head down

NOSE

Nasal Obstruction Symptom Evaluation

ODI

oxygen desaturation index

OSA

obstructive sleep apnea

PLMI

periodic limb movement index

PLMS

periodic limb movements of sleep

PSG

polysomnography

REM

rapid eye movement

RWLS

right working phase, left body/head down

RWRS

right working phase, right body/head down

SpO2

oxyhemoglobin saturation

TST

total sleep time

ACKNOWLEDGMENTS

The authors thank Oscar Carrillo for his technical support, helping us integrate the divided nasal cannula into the polysomnogram.

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