Fumihiko Yasuma

Hypothesis: respiratory sinus arrhythmia is an intrinsic resting function of cardiopulmonary system

A hypothesis is presented that explains the physiological reasons why the magnitude of respiratory sinus arrhythmia (RSA) appears to correlate with cardiac vagal tone. The hypothesis is that RSA is an intrinsic resting function of the cardiopulmonary system. Although RSA is mediated by respiratory modulation of cardiac vagal outflow and its magnitude is used as an index of cardiac vagal activity, RSA itself reflects cardiorespiratory interaction. RSA is universally observed among vertebrates throughout the evolution, suggesting that it may bear an intrinsic physiological role. Recent studies have shown that RSA improves pulmonary gas exchange efficiency by matching alveolar ventilation and capillary perfusion throughout respiration cycle. This suggests that in resting animals and humans, RSA could save cardiac and respiratory energy by suppressing unnecessary heartbeats during expiration and ineffective ventilation during waning phases of perfusion. Furthermore, evidence is accumulating for possible dissociation between the magnitude of RSA and vagal control of heart rate, suggesting separated and independent regulations for respiratory modulation of cardiac vagal outflow from those for cardiac vagal tone. By our hypothesis, the apparent associations between RSA and cardiac vagal tone are explained as indirect consequences; i.e., whenever the cardiac vagal tone changes in response to the resting level of the cardiopulmonary system, RSA appears to change parallel to it. Our hypothesis seems more consistent with both physiological and clinical evidence about RSA than that presuming RSA is an index of cardiac vagal activity.

Continuous positive airway pressure improves daytime baroreflex sensitivity and nitric oxide production in patients with moderate to severe obstructive sleep apnea syndrome.

Individuals with obstructive sleep apnea syndrome (OSAS) are at high risk for cardiovascular morbidity and mortality. The effects of OSAS severity and nocturnal continuous positive airway pressure (CPAP) on daytime baroreflex sensitivity (BRS) and nitric oxide (NO) production were investigated in OSAS patients. Fifty-one consecutive males with OSAS and 29 age-matched healthy men underwent the Valsalva test and standard polysomnography. Patients with an apnea-hypopnea index (AHI) of ≥20 episodes per hour were randomized to receive CPAP treatment for 3 months (n=14) or no such treatment (n=19). The BRS index measured from the overshoot phase (phase IV) of the Valsalva maneuver and plasma NO concentration were significantly lower, whereas the AHI, oxygen desaturation time, arousal index, percentage of sleep stage 1, and systolic blood pressure were significantly greater, in patients with an AHI of ≥20/h than in those with an AHI of <20/h or in controls. The 24-h urinary excretion of norepinephrine was significantly reduced and the plasma NO concentration was significantly increased after one night of CPAP. The BRS index for phase IV and the Valsalva ratio were significantly increased in the CPAP group after the 3-month treatment period but remained unchanged in the non-CPAP group of OSAS patients. The daytime BRS index and NO production were thus inversely related to the severity of OSAS, and successful CPAP treatment improved these parameters in patients with moderate to severe OSAS. CPAP may therefore reduce the risk of cardiovascular complications due to endothelial dysfunction or increased sympathetic activity.

Effects of nasal surgery on sleep quality in obstructive sleep apnea syndrome with nasal obstruction.

Background The purpose of this study was to evaluate the effects of nasal surgery on nasal resistance, sleep apnea, and sleep quality in adult male patients with obstructive sleep apnea syndrome (OSAS). A prospective study was performed in OSAS patients who underwent isolated nasal surgery in a tertiary referral center. Methods During the 3-year study period, 49 OSAS patients suffering from symptomatic nasal obstruction/impaired nasal breathing underwent the standard polysomnography before and after surgery. Polysomnography along with measures of nasal resistance and daytime sleepiness (the Epworth sleepiness scale [ESS] scores) were reviewed also. Results Surgery decreased the nasal resistance (0.55 ± 0.37 Pa/cm3 per second versus 0.17 ± 0.19 Pa/cm3 per second; p < 0.001) and ESS scores (11.7 ± 4.1 versus 3.3 ± 1.3; p < 0.001), without changes in the apnea-hypopnea index (AHI; 44.6 ± 22.5 versus 42.5 ± 22.0). Surgery increased nadir oxygen saturation (76.2 ± 10.9% versus 78.8 ± 8.1%; p < 0.01), shortened apnea–hypopnea duration (averaged/maximum; 33.5 ± 7.3/61.1 ± 46.0 versus 28.8 ± 7.4/47.3 ± 36.1 second; p < 0.05/p < 0.01), and improved sleep quality. Conclusion The results suggest that nasal surgery is useful for lowering nasal resistance, ameliorating sleep-disordered breathing, and improving sleep quality and daytime sleepiness in OSAS.

Assessment of pulse rate variability by the method of pulse frequency demodulation

BackgroundDue to its easy applicability, pulse wave has been proposed as a surrogate of electrocardiogram (ECG) for the analysis of heart rate variability (HRV). However, its smoother waveform precludes accurate measurement of pulse-to-pulse interval by fiducial-point algorithms. Here we report a pulse frequency demodulation (PFDM) technique as a method for extracting instantaneous pulse rate function directly from pulse wave signal and its usefulness for assessing pulse rate variability (PRV).MethodsSimulated pulse wave signals with known pulse interval functions and actual pulse wave signals obtained from 30 subjects with a trans-dermal pulse wave device were analyzed by PFDM. The results were compared with heart rate and HRV assessed from simultaneously recorded ECG.ResultsAnalysis of simulated data revealed that the PFDM faithfully demodulates source interval function with preserving the frequency characteristics of the function, even when the intervals fluctuate rapidly over a wide range and when the signals include fluctuations in pulse height and baseline. Analysis of actual data revealed that individual means of low and high frequency components of PRV showed good agreement with those of HRV (intraclass correlation coefficient, 0.997 and 0.981, respectively).ConclusionThe PFDM of pulse wave signal provides a reliable assessment of PRV. Given the popularity of pulse wave equipments, PFDM may open new ways to the studies of long-term assessment of cardiovascular variability and dynamics.

Morphological examination of upper airway in obstructive sleep apnea

OBJECTIVES An aim of this study was to assess the predictive power of an otorhinolaryngological examination of the upper airway to identify risk factors of obstructive sleep apnea syndrome (OSAS) in the patients. METHODS We examined 141 consecutive patients with OSAS. The morphological features were assessed by the designated otorhinolaryngologist while the subjects were sitting relaxedly with tidal breathing. The bilateral nasal resistance was measured using the active anterior rhinomanometry during daytime wakefulness. RESULTS The body mass index (BMI), faucess narrowness, neck circumference, lowest oxygen saturation, tonsil size and modified Mallampati grade (MMP) showed the statistically significant correlations with the apnea-hypopnea index (AHI) of an index of apnoeseverity, however, the age, Epworth sleepiness scale (ESS), nasal resistance and retroglossal space were not significantly associated with the AHI. CONCLUSIONS The upper airway morphology significantly associated with AHI are faucess narrowness, tonsil size, and MMP, but not nasal resistance and retroglossal space.

Influence of movement arousal on circardian rhythm of blood pressure in obstructive sleep apnea syndrome

Objective To investigate the hypothesis that repeated arousals at the termination of apnea/hypopnea in obstructive sleep apnea syndrome (OSAS) are related to abnormal circadian rhythm of blood pressure (BP). Design and methods We performed polysomnography (PSG) with pulse oximetry in 26 middle-aged patients with OSAS aged 42–58 years (mean age 51.8 years). The intensity of arousal on PSG was graded into two levels: grade 1 (EEG arousal, EA), an abrupt shift in EEG frequency, and grade 2 (movement arousal, MA), EEG arousal with an increase in electromyogram activity lasting at least 3 s. The number of apnea/hypopneas per hour (apnea/hypopnea index, AHI), and length of time during which nocturnal oxygen saturation decreased below 90% (oxygen desaturation time, ODT) were also evaluated. Percentage EA and %MA were assessed by the ratio of the number of apneas and hypopneas with EA or MA to the number of apneas and hypopneas in total. The 24 h systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured noninvasively. Multiple regression analysis was performed among AHI, ODT, %EA and %MA or among age, body mass index and %MA. Results The %MA was the most significant factor contributing to the elevated 24 h SBP (r = 0.46, P <0.05); oxygen desaturation (r = 0.44, P <0.05) was the next most important contributing factor. The level and pattern of 24 h BP differed significantly between the patients with %MA 85% and %MA <85% (mean 24 h SBP: 147 ± 16.8 versus 125 ± 19.6 mmHg, P <0.01; mean 24 h DBP: 97.5 ± 14.3 versus 85.6 ± 14.6 mmHg, P <0.01), and also differed between those with severe OSAS, i.e. ODT >130 min, and mild to moderate OSAS, i.e. ODT <130 min, (mean 24 h SBP: 149 ± 15.8 versus 132 ± 20.6 mmHg, P <0.01; mean 24 h DBP: 100 ± 14.1 versus 87.4 ± 14.0 mmHg, P <0.01). Conclusion Our findings suggest that MA and oxygen desaturation in OSAS make an important contribution to abnormal circadian rhythm of BP. We conclude that repeated end-apneic arousal and/or hypoxic asphyxia and the subsequent sleep fragmentation may contibute to nocturnal and diurnal elevation of BP.

Upper airway morphology in patients with obstructive sleep apnea syndrome: Effects of lateral positioning

OBJECTIVES The aim of this study was to clarify the interaction of lateral and supine sleeping positions with upper airway morphology in patients with obstructive sleep apnea syndrome (OSAS). PATIENTS AND METHODS Thirty-one patients with OSAS, whose apnea/hypopnea index (AHI: number of episodes of apnea or hypopnea per hour) was over 15, were enrolled in this study. Subjects were divided in two groups according to positional effects on their AHI. In six patients, a lateral posture decreased the AHI by 50% and more (responders); in the remaining 25, lateral positioning decreased the AHI by less than 50% or even increased the AHI (nonresponders). AHI and body mass index (BMI) of the responders tended to be lower and their mean age was younger than those of nonresponders, but these differences were not statistically significant. We compared the upper airway morphology between the responders and the nonresponders regarding the tonsil size, tongue position (modified Mallanpati grade, reflecting the space between the tongue and soft palate) and the width of the fauces and retroglossal space. In addition, we compared nasal resistance between the groups using active rhinomanometry. RESULTS The width of the fauces was significantly greater (P=0.041) among the responders than among the nonresponders. However, the other parameters were not consistently different between the two, and these differences were not statistically significant either. CONCLUSIONS The distance between the fauces was the sole morphological feature to distinguish the responders and the nonresponders to the positional therapy in patients with OSAS. Lateral positioning during sleep might be a recommended sleep hygiene for OSAS patients with wide fauces.

Relationship between adenoid size and severity of obstructive sleep apnea in preschool children

OBJECTIVE To investigate the contributions of adenoid and tonsil sizes to obstructive sleep apnea syndrome (OSAS) in normal-weight children in two age categories: preschool and schoolchildren. METHODS Fifty-eight normal-weight (body mass index z-score<2) symptomatic children with OSAS (apnea-hypopnea index ≥ 2) were evaluated. The patients were divided into two age categories: preschool (age<6; n=33) and schoolchildren (age ≥ 6; n=25). Polysomnographic findings and adenoid and tonsil sizes were compared. The relative contributions of body mass index and adenoid and tonsil sizes were also investigated with a regression analysis. RESULTS Adenoid grade and apnea index correlated significantly in preschool children (r=0.45, p<0.01). On regression analysis, adenoid grade was a significant predictor of the apnea index in preschool children. The influence of adenoid hypertrophy decreased from preschool to schoolchildren. Tonsil size had little influence on the apnea index in either group. CONCLUSION Adenoid hypertrophy was a major contributor to OSAS in normal-weight preschool children. The upper airway morphology of younger children with OSAS differed from that of older children with OSAS.

Children with severe or moderate obstructive sleep apnoea syndrome show a high incidence of persistence after adenotonsillectomy

Abstract Conclusion: Persistent obstructive sleep apnoea syndrome (OSAS) occurs in approximately 20% of normal-weight children after adenotonsillectomy (T&A) and, in nearly 70% of them, it is caused by adenoid regrowth. Patients with severe or moderate OSAS showed a high incidence of persistent disease even after T&A. Allergic disease, severity and large adenoid size are associated with adenoid regrowth and persistent disease. Objectives: To investigate factors contributing to persistent OSAS and adenoid regrowth after T&A in normal-weight children. Methods: This was a prospective, observational study at a single institute and involved 49 normal-weight children with severe or moderate OSAS (apnoea–hypopnoea index, AHI, ≥ 5) who underwent T&A. Background information, nasal endoscopic data and pre- and postoperative polysomnographic data were collected. A third polysomnography (PSG) was performed 1.5 year postoperatively in children who subsequently developed symptoms of sleep disturbance. Results: Thirteen children (27%, 13/49) were symptomatic 1.5 years after T&A. Allergic rhinitis (38.5% vs 11.1%, p = 0.03) and allergic disease (69.2% vs 30.6%, p = 0.02) were seen more frequently in these children. A third PSG confirmed persistent disease (AHI ≥ 5) in nine children (18.4%, 9/49). Six children (12.2%, 6/49) were diagnosed as having adenoid regrowth and three (6.1%, 3/49) underwent revision adenoidectomy.

Impact of real-world stress on cardiorespiratory resting function during sleep in daily life.

To examine if real-world stress affects the restorative function of sleep in daily life, we studied the impact of college examinations on cardiorespiratory resting function during sleep. In healthy college students, at 1 week before, the day before, and the first day of semester-end examinations pulse wave signal during sleep at their own residences was measured continuously with a wristband-shaped wireless transdermal photoelectric sensor. The cardiorespiratory resting function was assessed quantitatively as the power of a high-frequency component of pulse rate variability, a surrogate measure of respiratory sinus arrhythmia. Changes in anxiety were also evaluated with a state anxiety questionnaire. On the day before the examinations, compared with 1 week before, the score of state anxiety increased and the HF component of pulse rate variability decreased. Among college students, anxiety about college examinations may be accompanied by suppression of the cardiorespiratory resting function during sleep.