Combined effects of a mechanical nasal dilator and a topical decongestant on nasal airflow resistance.

The goal of this study was to compare the isolated and combined effects of two treatments being used to reduce nasal airflow resistance (NR): an internal nasal mechanical dilator (Nozovent; Prevancure; Sté Pouret, Paris, France) and a topical decongestant, fenoxazoline hydrochloride (Aturgyl; Synthelabo; Le Plessis-Robinson, France). The study was performed in 17 healthy subjects. NR was estimated by active posterior rhinometry at a 0.5 L/s flow under four conditions: in the basal state, with the internal nasal mechanical dilator, after treatment with fenoxazoline hydrochloride, and with both fenoxazoline hydrochloride and the mechanical dilator. The mean NR (+/- SD) decreased from 1.65+/-0.54 cm H2O/L/s in the basal state to 1.02+/-0.27 cm H2O/L/s with the mechanical dilator (p < 0.001), 1.03+/-0.47 cm H2O/L/s with fenoxazoline hydrochloride (p < 0.001), and 0.48+/-0.15 cm H2O/L/s with both the mechanical dilator and fenoxazoline hydrochloride (p < 0.001). The decreases in NR observed after using either the mechanical dilator (deltaNR(N)) or fenoxazoline hydrochloride (deltaNR(A)) were not significantly different. The decrease in NR observed with both (deltaNR(N + A)) was not significantly different from the sum deltaNR(N) + deltaNR(A): 1.16+/-0.53 cm H2O/L/s vs 1.25+/-0.63 cm H2O/L/s, respectively (p > 0.05). deltaNR(N + A) strongly correlated with deltaNR(N) + deltaNR(A): deltaNR(N + A) = 0.80 (deltaNR(N) + deltaNR(A)) + 0.15 (r = 0.96; p < 0.0001). However, the slope of the regression line of deltaNR(N + A) vs deltaNR(N) + deltaNR(A) was significantly lower than unity (p < 0.003). These results demonstrate that, although not totally additive, the effects of using the mechanical dilator and fenoxazoline hydrochloride are cumulative. Further studies that include patients with nasal obstruction would allow us to better evaluate the benefit of a therapy combining both treatments.     

Effects of nasal prongs on nasal airflow resistance

STUDY OBJECTIVES: The aim of this study was to investigate whether nasal prongs, which have been proposed to assess nasal flow during sleep, affect nasal airflow resistance (NR). DESIGN: NR was estimated by posterior rhinomanometry at a 0.5 L/s flow, under eight conditions: in the basal state, and with seven different nasal prongs. PARTICIPANTS: The study was performed in 17 healthy supine subjects, 8 of whom had basal NR values within the normal range (< or = 2 cm H(2)O.L(-1).s, group 1), and 9 had increased basal NR values (> 2.5 cm H(2)O.L(-1).s, group 2), because of nare narrowness and/or deviated nasal septum. Measurements and results: NR increased significantly while breathing with nasal prongs (p < 0.0001 in both groups). The changes in NR (DeltaNR) induced by the different nasal prongs were characterized by large intersubject and intrasubject variability, with a maximum DeltaNR of 24.2 cm H(2)O.L(-1).s. Significant differences were found between the DeltaNR induced by the different nasal prongs (p < 0.001 in group 1, and p < 0.0003 in group 2), and for six of them, DeltaNR was significantly higher in group 1 than in group 2 (p < 0.02). CONCLUSIONS: This study demonstrates that nasal prongs can markedly increase NR in subjects presenting with nare narrowness and/or deviated nasal septum. Further investigations that would include nocturnal polysomnography are still required to evaluate the possible influence of nasal prongs on the diagnosis of obstructive sleep apnea syndrome and its severity.     

Static and dynamic upper airway obstruction in sleep apnea: role of the breathing gas properties

Increased upper airway collapsibility in the sleep apnea/hypopnea syndrome (SAHS) is usually interpreted by a collapsible resistor model characterized by a critical pressure (Pcrit) and an upstream resistance (Rup). To investigate the role played by the upstream segment of the upper airway, we tested the hypothesis that breathing different gases would modify Rup but not Pcrit. The study was performed on 10 patients with severe SAHS (apnea-hypopnea index: 59 +/- 14 events/hour) when breathing air and helium-oxygen (He-O2) during non-REM sleep. The continuous positive airway pressure that normalized flow (CPAPopt) was measured. Rup and Pcrit were determined from the linear relationship between maximal inspiratory flow VImax and nasal pressure (PN):VImax = (PN - Pcrit)/Rup. Changing the breathing gas selectively modified the severity of dynamic (CPAPopt, Rup) and static (Pcrit) obstructions. CPAPopt was significantly (p = 0.0013) lower when breathing He-O2 (8.44 +/- 1.66 cm H2O; mean +/- SD) than air (10.18 +/- 2.34 cm H2O). Rup was markedly lower (p = 0.0001) when breathing He-O2 (9.21 +/- 3.93 cm H2O x s/L) than air (15.92 +/- 6.27 cm H2O x s/L). Pcrit was similar (p = 0.039) when breathing He-O2 (4.89 +/- 2.37 cm H2O) and air (4.19 +/- 2.93 cm H2O). The data demonstrate the role played by the upstream segment of the upper airway and suggest that different mechanisms determine static (Pcrit) and dynamic (Rup) upper airway obstructions in SAHS.     

Reducing ventilatory response to carbon dioxide by breathing cold air

To study the effect of cooling of nasal receptors on breathing we had 10 normal male volunteers rebreathe through their noses 8% CO2 in oxygen at "warm" (23 to 30 degrees C) and at "cold" (-4 to 10 degrees C) temperatures. In order to further examine the effect of nasal receptors on the control of breathing, 11 subjects had their nasal response to CO2 measured at the warm temperature before and after topical nasal anesthesia. To exclude an increase in nasal resistance as the cause of the reduced response to CO2, 10 subjects had their nasal resistance measured before and after nasal rebreathing of cold 8% CO2 in oxygen. To also exclude increased bronchial resistance, forced expiratory volume in one second (FEV1) was measured in 12 subjects before and after nasal breathing of cold oxygen for 3 min. The mean ventilatory response to CO2 was reduced from 3.0 +/- 1.6 L/min/mmHg to 2.5 +/- 1.1 L/min/mmHg (p less than 0.05) by the cold air. Topical nasal anesthesia increased the response to CO2 at the warm temperature from 2.4 +/- 0.7 to 2.7 +/- 0.9 L/min/mmHg. The effect of nasal breathing of 8% CO2 in oxygen at the cold temperature was to reduce nasal inspiratory resistance at 1 L/s from 4.3 +/- 3.0 cm H2O L/s to 2.6 +/- 1.0 cm H2O L/s (p less than 0.05). Expiratory resistance at 1 L/s fell from 3.7 +/- 1.5 cm H2O L/s to 2.4 +/- 0.7 cm H2O L/s (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Self-adjusting nasal continuous positive airway pressure therapy based on measurement of impedance: A comparison of two different maximum pressure levels.

STUDY OBJECTIVE: Automatic titration using the forced oscillation technique (FOT) has recently been developed for the treatment of obstructive sleep apnea syndrome (OSAS). So far, it is not known if therapy with automatic nasal continuous positive airway pressure (nCPAP) using a preset upper pressure limitation or a free range (which might lead to higher mean pressure) is preferable with regard to obstructive events, sleep stages, and pressure characteristics. DESIGN: After diagnostic polysomnography, patients were randomly assigned to two settings with the self-adjusting nCPAP (APAP) device based on the FOT. In mode 1, the pressure variation ranged from 4 to 15.5 cm H(2)O, and in mode 2, the pressure variation ranged from 4 cm H(2)O to an individual upper pressure limit. Patients: Eleven men, aged 53.0 +/- 6.8 years with a body mass index of 32.4 +/- 5.1 kg/m(2) and an apnea-hypopnea index (AHI) of 31.6 +/- 26.6/h. MEASUREMENTS AND RESULTS: Manually titrated pressure was at 9.3 +/- 2.1 cm H(2)O, the mean pressure in mode 1 was 5.4 +/- 1.0 cm H(2)O (p < 0.01), and the mean pressure in mode 2 was 5.1 +/- 0.7 cm H(2)O (p < 0.01). A reduction of respiratory events (baseline AHI, 31.6 +/- 26.6/h; AHI in mode 1, 3.4 +/- 4.5; AHI in mode 2, 5.0 +/- 7.2; each with p < 0.001) and an increase in the "rapid eye movement" stage of sleep (baseline, 13.0 +/- 5.5%; mode 1, 22.0 +/- 7.7 [p < 0. 05]; mode 2, 23.0 +/- 7.9 [p < 0.01]) were achieved. In mode 1, the mean pressure was below the manual pressure 91.7 +/- 9.3% of the time, and in mode 2, the mean pressure was below the manual pressure 90.4 +/- 6.3% of the time. The manual pressure was exceeded by 5.5 +/- 7.4% (mode 1) and by 5.2 +/- 3.1% (mode 2). Conclusion: We conclude that nCPAP therapy based on the FOT permits the adequate treatment of OSAS with significantly lower pressure than manually titrated nCPAP therapy does. A presetting of an upper pressure limit has no advantage compared to free range.     

Oscillatory resistance measured during noninvasive proportional assist ventilation.

Setting proportional assist ventilation (PAV) requires the measurement of patient resistance and elastance. To avoid patient sedation/paralysis or the use of an esophageal balloon, noninvasive PAV is indirectly set by the "runaway" method or in accordance with patient comfort. The aim of this study was to ascertain whether the forced oscillation technique (FOT) applied by the ventilator during noninvasive PAV is useful in assessing patient respiratory resistance. Nasal PAV was applied to 14 patients with severe chronic obstructive pulmonary disease. During PAV a modified ventilator applied a 5-Hz pressure oscillation to noninvasively assess FOT resistance (Rrs). Lung resistance (RL) was measured in seven of the patients by using an esophageal balloon. Moreover, measurements were also performed in five of the patients when PAV was applied through the mouth. Rrs was close to RL both during nasal (Rrs = 8.9 +/- 3.1, RL = 9.0 +/- 2.6; cm H(2)O x s/L; n = 7, p > 0.05) and mouth (Rrs = 5.6 +/- 2.1, RL = 5.8 +/- 1.4; cm H(2)O x s/L; n = 5, p > 0.05) breathing. Rrs was slightly greater than the maximum value of flow assistance applied during the setting of PAV (FAmax): 11.1 +/- 5.4 and 9.5 +/- 2.9 cm H(2)O x s/L, respectively (n = 14, p > 0.05), both variables being significantly correlated (r = 0.72, p < 0.05). FOT applied by the PAV ventilator allowed the assessment of patient resistance. These results suggest that FOT could be useful in setting PAV flow assistance and in automatically and continuously updating this setting in accordance with patient resistance.     

Adaptive pressure support servo-ventilation: a novel treatment for Cheyne-Stokes respiration in heart failure

Adaptive servo-ventilation (ASV) is a novel method of ventilatory support designed for Cheyne-Stokes respiration (CSR) in heart failure. The aim of our study was to compare the effect of one night of ASV on sleep and breathing with the effect of other treatments. Fourteen subjects with stable cardiac failure and receiving optimal medical treatment were tested untreated and on four treatment nights in random order: nasal oxygen (2 L/min), continuous positive airway pressure (CPAP) (mean 9.25 cm H(2)O), bilevel (mean 13.5/5.2 cm H(2)O), or ASV largely at the default settings (mean pressure 7 to 9 cm H(2)O) during polysomnography. Thermistor apnea + hypopnea index (AHI) declined from 44.5 +/- 3.4/h (SEM) untreated to 28.2 +/- 3.4/h oxygen and 26.8 +/- 4.6/h CPAP (both p < 0.001 versus control), 14.8 +/- 2.3/h bilevel, and 6.3 +/- 0.9/h ASV (p < 0.001 versus bilevel). Effort band AHI behaved similarly. Arousal index decreased from 65.1 +/- 3.9/h untreated to 29.8 +/- 2.8/h oxygen and 29.9 +/- 3.2/h CPAP, to 16.0 +/- 1.3/h bilevel and 14.7 +/- 1.8/h ASV (p < 0.01 versus all except bilevel). There were large increases in slow-wave and rapid eye movement (REM) sleep with ASV but not with oxygen or CPAP. All subjects preferred ASV to CPAP. One night ASV suppresses central sleep apnea and/or CSR (CSA/CSR) in heart failure and improves sleep quality better than CPAP or 2 L/min oxygen.     

Nasal airflow dynamics: mechanisms and responses associated with an external nasal dilator strip.

The adhesive external nasal dilator strip (ENDS) is widely advocated for prevention of snoring and promotion of nasal breathing during exercise. In the present study, the effects of the ENDS on nasal airflow resistance (Rn) in normal subjects were examined and factors determining individual responses to the ENDS explored. Using posterior rhinomanometry, 20 healthy Caucasian adults (10 males, 10 females; age: 18-56 yrs) were studied during quiet tidal breathing and voluntary hyperpnoea with (ENDS) and without (control) ENDS and with a placebo strip (placebo) before and after application of a topical nasal decongestant (oxymetazoline hydrochloride). During tidal breathing, only nine subjects showed a significantly (p<0.05) decreased inspiratory and/or expiratory Rn with the ENDS ("responders"). During the control, inspiratory Rn (at 0.4 L x s(-1)) was higher in "responders" than "nonresponders" (3.28+/-0.16 versus 2.60+/-0.08 cmH2O x L(-1) x s; p=0.04). The effects of nasal decongestant and the ENDS were additive. During voluntary hyperpnoea, inspiratory Rn (at 1.0 L x s(-1)) and the hysteresis of the inspiratory transnasal pressure/flow curve were decreased with the ENDS in most subjects. It is concluded that the external nasal dilator strip influences nasal airflow dynamics by both dilation of the nasal valve and stabilization of the lateral nasal vestibule walls and may be more effective in subjects with a high resting nasal airflow resistance.     

Influence of respiratory behavior on ventilation,respiratory work and intrinsic PEEP during noninvasive nasal pressure support ventilation in normal subjects

BACKGROUND: In clinical practice, patients have different inspiratory behaviors during noninvasive pressure support ventilation (PSV): some breathe quietly, others actively help PSV by an additional effort, and others even resist the inspiratory pressure of PSV. OBJECTIVE: What is the influence of patient collaboration (inspiratory behavior) on the efficiency of PSV? METHODS: We ventilated 10 normal subjects with nasal PSV (inspiratory/expiratory: 10/0 and 15/5 cm H(2)O) and measured their flow and volume with a pneumotachograph and their esophageal and gastric pressures during three different respiratory voluntary behaviors: relaxed inspiration, active inspiratory work and resisted inspiration. RESULTS: When compared with relaxed inspiration with 10/0 cm H(2)O PSV: (1) an active inspiratory effort increased tidal volume (from 789 +/- 356 to 1,046 +/- 586 ml; p = 0.006), minute ventilation (from 10.40 +/- 4.45 to 15.77 +/- 7.69 liters/min; p < 0.001), transdiaphragmatic work per cycle (from 0.55 +/- 0.33 to 1.72 +/- 1.40 J/cycle; p = 0.002) and inspiratory work per cycle (from 0.14 +/- 0.20 to 1.26 +/- 1.01 J/cycle; p = 0.003); intrinsic positive end-expiratory pressure (PEEP(i)) increased from 1.23 +/- 1.02 to 3.17 +/- 2.30 cm H(2)O; p = 0.002); (2) a resisted inspiration decreased tidal volume (to 457 +/- 230 ml; p = 0.007), minute ventilation (to 6.93 +/- 3.04 liters/min; p = 0.028) along with a decrease in transdiaphragmatic work but no change in PEEP(i). Data obtained during a bilevel PSV of 15/5 cm H(2)O were similar to those obtained with the 10/0 cm H(2)O settings. CONCLUSIONS: Active inspiratory effort increases ventilation during PSV at the expense of an increased breathing work and PEEP(i). Resisted inspiration inversely decreases inspiratory work and ventilation with no air trapping. These differences between inspiratory behaviors could affect the expected beneficial effects of PSV in acutely ill patients.     

A physiologic comparison of nasal and oral positive airway pressure

STUDY OBJECTIVES: The effectiveness of nasal continuous positive airway pressure (CPAP) in treating obstructive sleep apnea (OSA) is based on raising the intramural pressure above a critical collapsing pressure of the oropharyngeal airway. It is currently unclear whether CPAP delivered orally is also capable of raising pressure in the oropharynx above the critical collapse pressure. DESIGN: We tested a novel oral CPAP device to determine whether the pressure-flow relationships are similar to nasal CPAP and whether the device alters these relationships. Patients were selected based on having moderately severe apnea and were randomized to nasal CPAP, nasal CPAP with oral device, or oral CPAP. SETTING: Johns Hopkins University, The Johns Hopkins Asthma and Allergy Center, Baltimore, MD. PATIENTS: Five men and two women with OSA were studied. INTERVENTIONS: Individual pressure-flow curves were constructed during the application of nasal or oral CPAP. RESULTS: We found the following: (1) a similar effective pressure eliminated inspiratory flow limitation for the nasal or oral CPAP; (2) as pressure in the nose or mouth was lowered below the effective pressure, a linear pressure-flow curve was obtained and a critical closing pressure was described; (3) similar mean (+/- SD) critical pressures of -0.3 +/- 5.3, 1.7 +/- 4.0, and 0.5 +/- 2.8 cm H(2)O, respectively, occurred for nasal CPAP, nasal CPAP with the oral device in place, and oral CPAP conditions (p > 0.1); and (4) the comparable mean values for upstream resistance were 27.8 +/- 19, 19.1 +/- 8.3, and 26.5 +/- 26.7 cm H(2)O/L/s, respectively, for the above three conditions (p > 0.1). CONCLUSIONS: We concluded that comparable upper airway pressure-flow relationships were obtained during oral and nasal breathing. Moreover, effective treatment pressure is obtained when constant pressure is applied through either the nasal or oral route.     

Effect of uvulopalatopharyngoplasty on upper airway collapsibility in obstructive sleep apnea.

Previous investigators have demonstrated variable responses to uvulopalatopharyngoplasty (UPP) in patients with obstructive sleep apnea. We hypothesized that this variability is due to either (1) differences in baseline pharyngeal collapsibility preoperatively or (2) differences in magnitude of the decrease in pharyngeal collapsibility resulting from surgery. To determine the relationship between changes in collapsibility and the response to UPP surgery, we measured the upper airway critical pressure (Pcrit) before and after UPP in 13 patients with obstructive sleep apnea. During non-REM sleep, maximal inspiratory airflow (VImax) was quantitated by varying the level of nasal pressure (PN), and Pcrit was determined by the level of PN below which VImax ceased. A positive response to UPP was defined by a greater than or equal to 50% fall in non-REM disordered breathing rate (DBR). In the entire group, UPP resulted in significant decreases in DBR from 71.1 +/- 22.4 to 44.7 +/- 38.4 episodes/h (p = 0.025) and in Pcrit from 0.2 +/- 2.4 to -3.1 +/- 5.4 cm H2O (p = 0.016). Moreover, the percent change in DBR was correlated significantly with the change in Pcrit (p = 0.001). Subgroup analysis of responders and nonresponders demonstrated that significant differences in Pcrit were confined to the responders. Specifically, responders demonstrated a significant fall in Pcrit from -0.8 +/- 3.0 to -7.3 +/- 4.9 cm H2O (p = 0.01), whereas no significant change in Pcrit was detected in the nonresponders (1.1 +/- 1.6 versus 0.6 +/- 2.0 cm H2O. No clinical, polysomnographic, or physiologic predictors of a favorable response were found preoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of nasal continuous positive airway pressure on oxygen body stores in patients with Cheyne-Stokes respiration and congestive heart failure

STUDY OBJECTIVES: The mechanism(s) by which nasal continuous positive airway pressure (CPAP) is effective in the treatment of Cheyne-Stokes respiration (CSR) in patients with congestive heart failure (CHF) remains uncertain, and may involve an increase in total oxygen body stores (dampening), changes in central and peripheral controller gain, and/or improvement in cardiac function. The purpose of this study was to evaluate the effects of nasal CPAP on total oxygen stores, as measured by the rate of fall of arterial oxyhemoglobin saturation (dSaO(2)/dt), to determine if dampening may play a role in the attenuation of CSR in patients with CHF. DESIGN: Prospective controlled trial. SETTING: University hospital. PATIENTS: Nine male patients (mean +/- SD age, 59 +/- 8 years) with CHF and a mean left ventricular ejection fraction (LVEF) of 16 +/- 4%. Interventions and measurements: All patients had known CSR, as identified on a baseline polysomnographic study. Patients then underwent repeat polysomnography while receiving nasal CPAP (9 +/- 0.3 cm H(2)O). The polysomnography consisted of recording of breathing pattern, pulse oximetry, and EEG. dSaO(2)/dt was measured as the slope of a line drawn adjacent to the falling linear portion of the arterial oxygen saturation (SaO(2)) curve associated with a central apnea. All patients underwent echocardiography and right-heart catheterization within 1 month of the study to measure LVEF and cardiac hemodynamics, respectively. RESULTS: There was a significant decrease in the apnea-hypopnea index (AHI) with nasal CPAP, from 44 +/- 27 events per hour at baseline to 15 +/- 24 events per hour with nasal CPAP (p = 0.004). When compared to baseline, dSaO(2)/dt significantly decreased with nasal CPAP from 0.42 +/- 0.15% to 0.20 +/- 0.07%/s (p < 0.001). The postapneic SaO(2), when compared to baseline, significantly increased with nasal CPAP, from 87 +/- 5% to 91 +/- 4% (p < 0.05). The preapneic SaO(2) did not significantly change, from a baseline of 96 +/- 2% to 96 +/- 3% with nasal CPAP (p = 0.8). When compared to baseline, the apnea duration and heart rate did not change with nasal CPAP. While there was a significant correlation noted between baseline postapneic SaO(2) and dSaO(2)/dt (r = 0.8, p = 0.02), no correlation was seen between baseline preapneic SaO(2) and dSaO(2)/dt (r = 0.1, p = 0.7). A significant correlation was noted between baseline dSaO(2)/dt and the AHI (r = 0.7, p = 0.02). With CPAP, there was a significant correlation noted between dSaO(2)/dt and the AHI (R = 0.7, p = 0.04), but no correlation was noted between dSaO(2)/dt and postapneic SaO(2) (R = 0.1, p = 0.8). CONCLUSION: Nasal CPAP significantly decreases dSaO(2)/dt and thus increases total body oxygen stores in patients with CSR and CHF. By increasing oxygen body stores, dampening may be one of the mechanisms responsible for the attenuation of CSR seen with nasal CPAP.     

Clinical outcomes related to interface type in patients with obstructive sleep apnea/hypopnea syndrome who are using continuous positive airway pressure

STUDY OBJECTIVES: To evaluate the effect of interface on objective compliance, patient satisfaction, adverse effects, quality of life, and residual sleep-disordered breathing in patients with obstructive sleep apnea/hypopnea syndrome (OSAHS) using continuous positive airway pressure (CPAP). DESIGN: Randomized, cross-over. SETTING: Two suburban community-based hospital sleep laboratories. PATIENTS: Data were collected on 39 patients with OSAHS (mean age, 48.7 years), in whom CPAP was a novel treatment. INTERVENTIONS: Interventions were nasal pillows (Breeze; Mallinckrodt Corporation; Minneapolis, MN) and nasal mask (Contour; Respironics; Murrysville, PA). MEASUREMENTS AND RESULTS: Outcomes assessed at the completion of each 3-week treatment period were objective compliance, adverse effects, and satisfaction with CPAP (CPAP questionnaire), daytime sleepiness (Epworth sleepiness scale [ESS]), quality of life (Functional Outcomes of Sleep Questionnaire [FOSQ]), sleep diary, and residual sleep-disordered breathing (apnea-hypopnea index [AHI]). Patients were randomly assigned to use the nasal pillows or the nasal mask following laboratory titration and initiated on CPAP (pressure range, 5 to 14 cm H(2)O). The percentage of days utilized favored the nasal pillows (94.1% vs 85.7%; p = 0.02), but minutes of use per night did not differ (nasal pillows, 223 min; nasal mask, 288 min). ESS scores were lower and the FOSQ total scores were higher following CPAP treatment (p < 0.001), but no differential treatment effects were noted. Fewer adverse effects, less trouble getting to sleep and staying asleep, and less air leak were reported with nasal pillows (p < 0.04). The mean +/- SD pretreatment AHI (47.1 +/- 35.1/h) was significantly lower following treatment with CPAP for both types of interface (nasal pillows, 10.2 +/- 9.8/h; nasal mask, 7.0 +/- 7.7/h; p < 0.001). CONCLUSIONS: Nasal pillows are a well-tolerated and effective interface for OSAHS patients receiving CPAP at < or = 14 cm H(2)O. Use of nasal pillows was associated with fewer adverse effects and better sleep quality during the first 3 weeks of CPAP therapy. Further investigation is needed to determine whether interface type affects long-term CPAP use.     

Sigh in acute respiratory distress syndrome

Mechanical ventilation with plateau pressure lower than 35 cm H2O and high positive end-expiratory pressure (PEEP) has been recommended as lung protective strategy. Ten patients with ARDS (five from pulmonary [p] and five from extrapulmonary [exp] origin), underwent 2 h of lung protective strategy, 1 h of lung protective strategy with three consecutive sighs/min at 45 cm H2O plateau pressure, and 1 h of lung protective strategy. Total minute ventilation, PEEP (14.0 +/- 2.2 cm H2O), inspiratory oxygen fraction, and mean airway pressure were kept constant. After 1 h of sigh we found that: (1) PaO2 increased (from 92.8 +/- 18.6 to 137.6 +/- 23.9 mm Hg, p < 0.01), venous admixture and PaCO2 decreased (from 38 +/- 12 to 28 +/- 14%, p < 0.01; and from 52.7 +/- 19.4 to 49.1 +/- 18.4 mm Hg, p < 0.05, respectively); (2) end-expiratory lung volume increased (from 1.49 +/- 0.58 to 1.91 +/- 0.67 L, p < 0.01), and was significantly correlated with the oxygenation (r = 0.82, p < 0.01) and lung elastance (r = 0.76, p < 0.01) improvement. Sigh was more effective in ARDSexp than in ARDSp. After 1 h of sigh interruption, all the physiologic variables returned to baseline. The derecruitment was correlated with PaCO2 (r = 0.86, p < 0.01). We conclude that: (1) lung protective strategy alone at the PEEP level used in this study may not provide full lung recruitment and best oxygenation; (2) application of sigh during lung protective strategy may improve recruitment and oxygenation.     

The role of vascular tone in the control of upper airway collapsibility

Upper airway collapsibility may be influenced by both muscular and nonmuscular factors. Because mucosal blood volume (and therefore vascular tone) is an important determinant of nasal airway patency, vascular tone may be an important nonmuscular determinant of pharyngeal collapsibility. This hypothesis was tested in two experimental models. First, upper airway closing (CP) and opening (OP) pressures and static compliance were measured in nine anesthetized, sinoaortic-denervated, paralyzed cats with isolated upper airways. Vascular tone was decreased with either papaverine or sodium nitroprusside (NTP), and increased with phenylephrine (PE), whereas blood pressure and end-tidal CO2 were maintained constant. Vasodilation increased CP (control = -10.4 +/- 1.3, NTP = -7.3 +/- 1.2 cm H2O; p less than 0.05) and OP (control = -7.9 +/- 1.5, NTP = -3.3 +/- 1.8 cm H2O; p less than 0.05). In contrast, vasoconstriction tended to decrease CP (control = -10.7 +/- 1.5, PE = -11.7 +/- 1.4 cm H2O; p less than 0.09) and OP (control = -8.1 +/- 1.2, PE = -9.9 +/- 1.9 cm H2O; p less than 0.1). Thus, vasodilation increased and vasoconstriction tended to decrease upper airway collapsibility. Upper airway static compliance was unchanged during either drug infusion. In order to assess changes in pharyngeal cross-sectional area (CSA) that occurred during vasodilation, magnetic resonance imaging was utilized in seven cats. During vasodilation with NTP, pharyngeal CSA was reduced from 0.44 +/- 0.10 to 0.30 +/- 0.09 cm2 (p less than 0.05), and pharyngeal volume was reduced from 15.3 +/- 2.4 to 13.9 +/- 2.7 cm3 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Nasal and pharyngeal resistance after topical mucosal vasoconstriction in normal humans

Phenylephrine, an alpha-adrenergic agonist, increases pharyngeal cross-sectional area when applied topically to the nasal and pharyngeal mucosa, as determined by magnetic resonance imaging. In this study, we examined the possibility that the increase in area results from either a decrease in transmural collapsing pressure, as a result of a decrease in upstream (nasal) resistance, or an increase in upper airway muscle activity. In eight normal, awake men we measured inspiratory pharyngeal and nasal resistance and the electrical activity of the genioglossus (EMGGG) and alae nasi (EMG(AN) before and after pharyngeal and nasal + pharyngeal instillation of 1 ml of either 0.25% phenylephrine or normal saline; phenylephrine and saline were tested on separate days. Under control eucapnic conditions, pharyngeal resistance was 0.43 +/- 0.03 cm H2O/L/s, and nasal resistance was 2.43 +/- 0.14 cm H2O/L/s. Pharyngeal resistance was 0.29 +/- 0.03 cm H2O/L/s after nasal + pharyngeal instillation of phenylephrine and 0.98 +/- 0.13 cm H2O/L/s after saline; nasal resistance was 2.18 +/- 0.13 cm H2O/L/s after nasal + pharyngeal instillation of phenylephrine and 3.15 +/- 0.21 cm H2O/L/s after saline. Thus, phenylephrine decreased both nasal and pharyngeal inspiratory resistance. The change in pharyngeal resistance was not dependent on the change in nasal resistance. Eucapnic EMGGG and EMGAN activities did not change after phenylephrine or saline. We conclude that phenylephrine decreased pharyngeal resistance independent of a change in nasal resistance of upper airway muscle activity, and we believe that the changes in resistance we observed reflect a direct effect of phenylephrine on the pharyngeal mucosa and a consequent enlargement of pharyngeal size.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of upper airway obstruction and arousal on peripheral arterial tonometry in obstructive sleep apnea

We evaluated the effects of airflow limitation and arousal on digital vascular tone in 10 patients with obstructive sleep apnea (OSA) using the recently developed, noninvasive technique of peripheral arterial tonometry (PAT). Subjects were maintained at a therapeutic level of continuous positive airway pressure, and nasal pressure was acutely dropped for three to five breaths during nonrapid eye movement sleep over a range of pressures from 9.3 +/- 1.3 to 1.9 +/- 1.3 cm H2O, leading to increasing airway obstruction and decreasing levels of inspiratory airflow. In the absence of a detectable electroencephalographic (EEG) arousal, severe reductions of inspiratory airflow to below 200 ml/second caused significant decreases in PAT amplitude (1.000 +/- 0.007 to 0.869 +/- 0.007 arbitrary units; p < 0.001), whereas mild airflow limitation (> 200 ml/second) had no effect (1.000 +/- 0.009 to 1.011 +/- 0.007 arbitrary units). The presence of an EEG arousal accentuated the response to airflow obstruction, such that the PAT amplitude decreased more (p < 0.001) in the presence of arousal (1.000 +/- 0.007 to 0.767 +/- 0.010 arbitrary units) than in the absence of arousal (1.000 +/- 0.007 to 0.923 +/- 0.007 arbitrary units). We conclude that airflow obstruction in patients with OSA causes an acute digital vasoconstriction that is accentuated in the presence of an EEG arousal.     

Mild isocapnic hypoxia enhances the bronchial response to methacholine in asthmatic subjects

We studied the effect of mild isocapnic hypoxia (FIO2 = 15.5%) on lung mechanics, heart rate, circulating plasma catecholamines, and bronchial responsiveness to methacholine in ten asthmatic adults. Hypoxia did not alter lung mechanics (i.e., dynamic pulmonary compliance [CLdyn], pulmonary resistance [RL]) nor did it increase plasma catecholamines, but it significantly increased bronchial responsiveness to aerosolized methacholine, as assessed by the fall in forced expiratory volume in one second (FEV1: 1.2 +/- 0.18 versus 0.9 +/- 0.14 L/s, p less than 0.05), the rise in RL (RL: 19.1 +/- 1.4 versus 8.4 +/- 1 cm H2O/L/s, p less than 0.05), and the steeper slope of the dose-response curve to methacholine. We concluded that the hypoxic characteristic of asthmatic attacks may aggravate airflow obstruction.     

Upper airway collapsibility in snorers and in patients with obstructive hypopnea and apnea

During sleep, mild reduction in inspiratory airflow is associated with snoring, whereas obstructive hypopneas and apneas are associated with more marked reductions in airflow. We determined whether the degree of inspiratory airflow reduction was associated with differences in the collapsibility of the upper airway during sleep. Upper airway collapsibility was defined by the critical pressure (Pcrit) derived from the relationship between maximal inspiratory airflow and nasal pressure. In 10 asymptomatic snorers, six patients with obstructive hypopneas, and 10 patients with obstructive apneas, during nonrapid eye movement sleep, Pcrit ranged from -6.5 +/- 2.7 cm H2O to -1.6 +/- 1.4 and 2.5 +/- 1.5 cm H2O, respectively (mean +/- SD, p less than 0.001). Moreover, higher levels of Pcrit were associated with lower levels of maximal inspiratory airflow during tidal breathing during sleep (p less than 0.005). We conclude that differences in upper airway collapsibility distinguish among groups of normal subjects who snore and patients with periodic hypopneas and apneas. Moreover, the findings suggest that small differences in collapsibility (Pcrit) along a continuum are associated with reduced airflow and altered changes in pattern of breathing.     

Efficacy of mechanical insufflation-exsufflation in medically stable patients with amyotrophic lateral sclerosis

OBJECTIVE: To determine under what circumstances the use of mechanical insufflation-exsufflation (MI-E) can generate clinically effective expiratory flows for airway clearance (> 2.7 L/s) for clinically stable patients with amyotrophic lateral sclerosis (ALS). MATERIALS AND METHOD: Twenty-six consecutive patients with ALS were studied, 15 with severe bulbar dysfunction. Using a pneumotachograph and with the aid of an oronasal mask, we measured FVC, FEV(1), peak cough flow (PCF), maximum insufflation capacity (MIC), PCF generated from a maximum insufflation MIC (PCFMIC), and PCF generated by MI-E (PCFMI-E). MI-E was delivered at +/- 40 cm H(2)O. Maximum inspiratory pressure (PImax) and maximum expiratory pressure (PEmax) at the mouth were also measured. RESULTS: Although both groups had a similar time from ALS symptom onset to diagnosis, statistical differences (p < 0.05) were found between nonbulbar and bulbar patients in lung function and cough capacity parameters: FVC, 2.58 +/- 1.24 L vs 1.62 +/- 0.74 L; FEV(1), 2.26 +/- 1.18 L vs 1.54 +/- 0.69 L; PImax, - 93.45 +/- 47.47 cm H(2)O vs - 3.64 +/- 25.07 cm H(2)O; PEmax, 140.45 +/- 75.98 cm H(2)O vs 69.93 +/- 32.14 cm H(2)O; MIC, 3.02 +/- 1.22 L vs 1.97 +/- 0.75 L; PCF, 5.91 +/- 2.55 L/s vs 3.42 +/- 1.44 L/s; PCFMIC, 6.68 +/- 2.71 L/s vs 4.00 +/- 1.48 L/s; and PCFMI-E, 4.34 +/- 0.82 L/s vs 3.35 +/- 0.77 L/s. Four patients with bulbar dysfunction and MIC > 1 L had PCFMI-E < 2.7 L/s. The receiver operating characteristic (ROC) curve analysis showed PCFMIC of 4 L/s predicting those patients with PCFMIC greater than PCFMI-E. CONCLUSION: MI-E is able to generate clinically effective PCFMI-E (> 2.7 L/s) for stable patients with ALS, except for those with bulbar dysfunction who also have a MIC > 1 L and PCFMIC <2.7 L/s who probably have severe dynamic collapse of the upper airways during the exsufflation cycle. Clinically stable patients with mild respiratory dysfunction and PCFMIC > 4 L/s might not benefit from MI-E except during an acute respiratory illness.