Glottic aperture and effective minute ventilation during nasal two-level positive pressure ventilation in spontaneous mode

Upper Airway Video Endoscopy: Assessment of the response to positive pressure ventilation and mechanical in-exsufflation

Upper airways (UA) include the nasal cavities, pharynx, and larynx, and its main function is to warm and filter the inspired air. UA dysfunction is in the pathogenesis of various disorders, such as obstructive sleep apnea syndrome (OSAS) and vocal cord dysfunction. In addition, in some neurodegenerative diseases (e.g. Amyotrophic Lateral Sclerosis - ALS), UA dysfunction may also compromise the effective use of ventilatory support (VS). In this context, the endoscopic evaluation of UA may be useful in understanding the OSAS mechanisms, in determining the causes for treatment-induced airway obstruction and even in helping to titrate noninvasive ventilation (NIV) in ALS patients with bulbar or pseudo-bulbar (spastic) dysfunction. Specifically, in OSAS patients, when residual obstructive events persist, although an optimal ventilatory mode has been apparently achieved, along with interface and equipment, the endoscopic evaluation of UA seems to be a valuable tool in understanding its mechanisms, even assisting adjustments to NIV parameters. In addition, it has also been described as being useful in laryngeal response to mechanical in-exsufflation (MI-E) and Exercise-Induced Laryngeal Obstruction (EILO). However, no protocol has yet been published or validated for this. For this reason, a literature review was conducted on UA function and its response to positive pressure and MI-E. Special emphasis has also been given to the current indication for video endoscopy in chronically ventilated patients.

Glottic patency during noninvasive ventilation in patients with chronic obstructive pulmonary disease

BACKGROUND

Non-invasive ventilation (NIV) provides ventilatory support for patients with respiratory failure. However, the glottis can act as a closing valve, limiting effectiveness of NIV. This study investigates the patency of the glottis during NIV in patients with acute exacerbation of Chronic Obstructive Pulmonary Disease (COPD).

METHODS

Electrical activity of the diaphragm, flow, pressure and videolaryngoscopy were acquired. NIV was randomly applied in pressure support (PSV) and neurally adjusted ventilatory assist (NAVA) mode with two levels of support. The angle formed by the vocal cords represented glottis patency.

RESULTS

Eight COPD patients with acute exacerbation requiring NIV were included. No differences were found in median glottis angle during inspiration or peak inspiratory effort between PSV and NAVA at low and high support levels.

CONCLUSIONS

The present study showed that glottis patency during inspiration in patients with an acute exacerbation of COPD is not affected by mode (PSV or NAVA) or level of assist (5 or 15 cm H₂O) during NIV.

Sleep-Disordered Breathing in Neuromuscular Disease: Diagnostic and Therapeutic Challenges

Normal sleep-related rapid eye movement sleep atonia, reduced lung volumes, reduced chemosensitivity, and impaired airway dilator activity become significant vulnerabilities in the setting of neuromuscular disease. In that context, the compounding effects of respiratory muscle weakness and disease-specific features that promote upper airway collapse or cause dilated cardiomyopathy contribute to various sleep-disordered breathing events. The reduction in lung volumes with neuromuscular disease is further compromised by sleep and the supine position, exaggerating the tendency for upper airway collapse and desaturation with sleep-disordered breathing events. The most commonly identified events are diaphragmatic/pseudo-central, due to a decrease in the rib cage contribution to the tidal volume during phasic rapid eye movement sleep. Obstructive and central sleep apneas are also common. Noninvasive ventilation can improve survival and quality of sleep but should be used with caution in the context of dilated cardiomyopathy or significant bulbar symptoms. Noninvasive ventilation can also trigger sleep-disordered breathing events, including ineffective triggering, autotriggering, central sleep apnea, and glottic closure, which compromise the potential benefits of the intervention by increasing arousals, reducing adherence, and impairing sleep architecture. Polysomnography plays an important diagnostic and therapeutic role by correctly categorizing sleep-disordered events, identifying sleep-disordered breathing triggered by noninvasive ventilation, and improving noninvasive ventilation settings. Optimal management may require dedicated hypoventilation protocols and a technical staff well versed in the identification and troubleshooting of respiratory events.

Effects of non-invasive ventilation and posture on chest wall volumes and motion in patients with amyotrophic lateral sclerosis: a case series

Background

The effects of non-invasive ventilation (NIV) on the breathing pattern and thoracoabdominal motion of patients with amyotrophic lateral sclerosis (ALS) are unknown.

Objectives

1) To analyze the influence of NIV on chest wall volumes and motion assessed by optoelectronic plethysmography in ALS patients and 2) to compare these parameters in the supine and sitting positions to those of healthy individuals (without NIV).

Method

Nine ALS patients were evaluated in the supine position using NIV. In addition, the ALS patients and nine healthy individuals were evaluated in both sitting and supine positions. Statistical analysis was performed using the paired Student t-test or Wilcoxon test and the Student t-test for independent samples or Mann-Whitney U test.

Results

Chest wall volume increased significantly with NIV, mean volume=0.43 (SD=0.16)L versus 0.57 (SD=0.19)L (p=0.04). No significant changes were observed for the pulmonary rib cage, abdominal rib cage, or abdominal contribution. The index of the shortening velocity of the diaphragmatic muscle, mean=0.15 (SD=0.05)L/s versus 0.21 (SD=0.05)L/s (p<0.01), and abdominal muscles, mean=0.09 (SD=0.02)L/s versus 0.14 (SD=0.06)L/s (p<0.01), increased during NIV. Comparisons between the supine and sitting positions showed similar changes in chest wall motion in both groups. However, the ALS patients presented a significantly lower contribution of the abdomen in the supine position compared with the controls, mean=56 (SD=13) versus 69 (SD=10) (p=0.02).

Conclusions

NIV improved chest wall volumes without changing the contribution of the chest wall compartment in ALS patients. In the supine position, ALS patients had a lower contribution of the abdomen, which may indicate early diaphragmatic dysfunction.

[Ventilator modes and settings during non-invasive ventilation: effects on respiratory events and implications for their identification. 2011]

Compared with invasive ventilation, non-invasive ventilation (NIV) has two unique characteristics: its non-hermetic nature and the fact that the ventilator-lung assembly cannot be considered as a single-compartment model because of the presence of variable resistance represented by the upper airways. When NIV is initiated, the ventilator settings are determined empirically based on clinical evaluation and blood gas variations. However, NIV is predominantly applied during sleep. Consequently, to assess overnight patient-machine "agreement" and efficacy of ventilation, more specific and sophisticated monitoring is needed. The effectiveness of NIV might therefore be more correctly assessed by sleep studies than by daytime assessment. The simplest monitoring can be done from flow and pressure curves from the mask or the ventilator circuit. Examination of these tracings can give useful information to evaluate if the settings chosen by the operator were the right ones for that patient. However, as NIV allows a large range of ventilatory parameters and settings, it is mandatory to have information about this to better understand patient-ventilator interaction. Ventilatory modality, mode of triggering, pressurization slope, use or not of positive end expiratory pressure and type of exhalation as well as ventilator performances may all have physiological consequences. Leaks and upper airway resistance variations may, in turn, modify these patterns. This article discusses the equipment available for NIV, analyses the effect of different ventilator modes and settings and of exhalation and connecting circuits on ventilatory traces and gives the background necessary to understand their impact on nocturnal monitoring of NIV.

[Nocturnal monitoring of home non-invasive ventilation: Contribution of simple tools such as pulse-oximetry, capnography, built-in ventilator software and autonomic markers of sleep fragmentation]

Complex respiratory events, which may have a detrimental effect on both quality of sleep and control of nocturnal hypoventilation, occur during sleep in patients treated by non-invasive ventilation (NIV). Among these events are patient-ventilator asynchrony, increases in upper airway resistance with or without increased respiratory drive, and leaks. Detection of these events is important in order to select the most appropriate ventilator settings and interface. Simple tools can provide important information when monitoring NIV. Pulse-oximetry is important to ensure that an adequate SpO2 is provided, and to detect either prolonged or short and recurrent desaturations. However, the specificity of pulse-oximetry tracings under NIV is low. Transcutaneous capnography discriminates between hypoxemia related to V/Q mismatch and hypoventilation, documents correction of nocturnal hypoventilation, and may detect ventilator-induced hyperventilation, a possible cause for central apnea/hypopnea and glottic closure. Data provided by ventilator software helps the clinician by estimating ventilation, tidal volume, leaks, rate of inspiratory or expiratory triggering by the patient, although further validation of these signals by independent studies is indicated. Finally, autonomic markers of sympathetic tone using signals such as pulse wave amplitude of the pulse-oximetry signal can provide reliable information of sleep fragmentation.

[The obesity-hypoventilation syndrome]

Obesity, well-known as a cardiovascular risk factor is also a "respiratory" risk factor and can have profound adverse effects on the respiratory system, such as alterations in pulmonary function tests, respiratory mechanics, respiratory muscle strength and endurance, gas exchange, control of breathing and exercise capacity. ABG are frequently altered in obese subjects and abnormalities are directly proportional to BMI. Two main pathophysiological mechanisms may account for gas exchange abnormalities: V/Q inequality, responsible for isolated hypoxemia, and alveolar hypoventilation responsible for the also called "obesity hypoventilation syndrome" (OHS). Hypoventilation in obese patients includes a diversity of mechanisms frequently imbricated, among which the two most frequent are mechanical limitation and blunted ventilatory drive. Two other clinical entities (COPD and OSA) frequently present in the obese patients may potentiate or aggravate this hypoventilation. OHS is frequently underappreciated and diagnosis is rarely made at the steady state. Such diagnosis is frequently made in two situations: either during an exacerbation or when in front of symptoms of respiratory sleep disturbances. The patient is referred to sleep laboratory for screening for OSA. Ventilatory management of these patients will depend on the patient's underlying condition and on sleep study results. It includes CPAP or NIPPV but frequently additional O(2) addition is necessary. OHS represents today one of the most frequent indications of NIV worldwide.

Stability of oxyhemoglobin affinity in patients with obstructive sleep apnea-hypopnea syndrome without daytime hypoxemia

A decrease in hemoglobin affinity for oxygen is considered an adaptive mechanism against tissue hypoxia. Obstructive sleep apnea-hypopnea syndrome (OSAHS) is characterized by recurrent episodes of apnea and hypopnea resulting in arterial oxygen desaturations during sleep. Maillard et al. (10) observed a right shift of the oxyhemoglobin dissociation curve (ODC) and an increase in 2,3-diphosphoglycerate (2,3-DPG) concentration ([2,3-DPG]) in 15 patients with severe OSAHS, but some had slight daytime arterial hypoxemia while breathing room air. The aim of our study was to measure the ODC and 2,3-DPG concentrations in a group of subjects normoxemic during daytime referred to our sleep laboratory for suspicion of snoring or OSAHS. The patients were recruited during a period of 6 mo. All arterial and venous blood samples were taken early in the morning within 1 h of awakening following a full-night polysomnography. ODC and 2,3-DPG were analyzed in 88 patients: 56 OSAHS (oxygen desaturation index: 27.5 +/- 24.5) and 32 non-OSAHS. We found a significant correlation between the P50 and 2,3-DPG levels in the 88 patients: r = 0.502, P < 0.001. We observed no difference between OSAHS and non-OSAHS for the P50 and for [2,3-DPG]. There was no correlation between the severity of OSAHS and either P50 or [2,3-DPG]. Finally, there was no change in these parameters measured at baseline, after 3 days and after 1 mo of treatment by nasal continuous positive airway pressure in 7 patients with OSAHS. We conclude that patients with OSAHS who are normoxemic during daytime have comparable oxyhemoglobin affinity than nonapneic subjects.

Impact of volume targeting on efficacy of bi-level non-invasive ventilation and sleep in obesity-hypoventilation

BACKGROUND

Volume targeting by bi-level positive pressure ventilation (BPPV) has recently been made available by several manufacturers for home care ventilators. Although it may improve nocturnal ventilation, we hypothesized that increased pressure swings related to volume targeting may have a deleterious effect on sleep structure and patient comfort.

METHODS

Patients in stable clinical condition (n=12) treated by BPPV for obesity-hypoventilation (BMI: 44+/-8 kg/m(2)) for a median of 30 months (range: 2-138), underwent nocturnal polysomnography with transcutaneous capnography on 2 consecutive nights with either BPPV and usual ventilator settings or BPPV with volume targeting, in randomized sequence. Subjective quality of sleep (St. Mary's Hospital Questionnaire) and comfort of ventilation (VAS scales) were also assessed.

RESULTS

Mean IPAP, mean tidal volume, and total ventilation increased significantly with volume targeting. Control of nocturnal hypoventilation was slightly improved with volume targeting (nocturnal TcPCO(2): 42+/-9 vs. 45+/-5 mmHg, p=0.04). However, total sleep time and stage 2 sleep were greater without volume targeting, and wake after sleep onset and awakenings >20s increased with volume targeting. Subjectively, patients described a lighter sleep, of lesser quality and more frequent awakenings with volume targeting; ventilation was perceived as less comfortable, with an increased perception of leaks and of "too much air".

CONCLUSION

In stable patients treated by BPPV for obesity-hypoventilation, volume targeting improved control of nocturnal hypoventilation at the expense of a slight decrease in objective and subjective sleep quality, and comfort of ventilation.

Assist-control ventilation vs. low levels of pressure support ventilation on sleep quality in intubated ICU patients

OBJECTIVE

To compare the impact of assist-control ventilation (ACV) and pressure support ventilation with 6 cmH2O inspiratory pressure (low PSV) on sleep quality.

DESIGN

Prospective randomized cross-over study.

PATIENTS

Twenty intubated and mechanically ventilated patients for acute on chronic respiratory failure.

MEASUREMENTS

Patients were monitored by standard polysomnography at the end of their weaning period. Patients were assigned to receive either ACV from 10 p.m. to 2 a.m. and low PSV from 2 a.m. to 6 a.m. (ACV/low PSV group) or low PSV from 10 p.m. to 2 a.m. and ACV from 2 a.m. to 6 a.m. (low PSV/ACV group).

RESULTS

There were significant increases in stages 1 and 2 non-rapid eye movement (NREM) sleep and reduction in wakefulness during the first part of the night and significant increases in stages 3 and 4 NREM sleep during the second part of the night were observed with ACV compared to low PSV. A significant negative correlation was observed between the perceived sleep quality and the amount of wakefulness while the amount of stage 2 NREM sleep was positively correlated with perceived sleep quality.

CONCLUSIONS

ACV was significantly associated with a better sleep quality than those recorded during pressure support. The perception of sleep quality appeared to be better with ACV than with low PSV. On the basis of these results we recommend that intubated and mechanically ventilated patients for acute on chronic respiratory failure should be reventilated at night during their weaning period.

Laryngeal response to nasal ventilation in nonsedated newborn lambs

Although endoscopic studies in adult humans have suggested that laryngeal closure can limit alveolar ventilation during nasal intermittent positive pressure ventilation (nIPPV), there are no available data regarding glottal muscle activity during nIPPV. In addition, laryngeal behavior during nIPPV has not been investigated in neonates. The aim of the present study was to assess laryngeal muscle response to nIPPV in nonsedated newborn lambs. Nine newborn lambs were instrumented for recording states of alertness, electrical activity [electromyograph (EMG)] of glottal constrictor (thyroarytenoid, TA) and dilator (cricothyroid, CT) muscles, EMG of the diaphragm (Dia), and mask and tracheal pressures. nIPPV in pressure support (PS) and volume control (VC) modes was delivered to the lambs via a nasal mask. Results show that increasing nIPPV during wakefulness and quiet sleep led to a progressive disappearance of Dia and CT EMG and to the appearance and subsequent increase in TA EMG during inspiration, together with an increase in trans-upper airway pressure (TUAP). On rare occasions, transmission of nIPPV through the glottis was prevented by complete, active glottal closure, a phenomenon more frequent during active sleep epochs, when irregular bursts of TA EMG were observed. In conclusion, results of the present study suggest that active glottal closure develops with nIPPV in nonsedated lambs, especially in the VC mode. Our observations further suggest that such closure can limit lung ventilation when raising nIPPV in neonates.

Titration of non-invasive positive pressure ventilation in chronic respiratory failure

Non-invasive ventilation (NIV) is widely used for acute and chronic respiratory failure. If arterial blood gas tensions do not improve, the level of support can be increased. However, there may be a limit above which increasing ventilatory support leads only to greater interface leak with no improvement in ventilation. The aim of this study was to establish whether there is such a limit. During a daytime study in 24 ventilated stable patients (10 with chronic obstructive pulmonary disease (COPD), 14 with chest wall deformity, CWD), inspiratory pressures up to 20 cm H(2)O and set tidal volumes up to 10 ml kg(-1) were associated with mask leak of <5 l min(-1). Although leak increased with higher levels of support, there was still an increase in minute ventilation. The mean (2 sd) tolerated pressure was 24 cm H(2)O (8-40) in both groups, and set tidal volume 12.7 ml kg(-1) (5.0-20.4) in CWD and 9.6 ml kg(-1) (3.9-14.8) in COPD. Measures of respiratory effort were significantly reduced at all levels with both forms of ventilatory support. There is debate about whether the therapeutic aim of NIV should be to reduce respiratory muscle effort, or to reverse nocturnal hypoventilation. We conclude that if the primary aim is to improve arterial blood gas tensions and this is not achieved, higher levels of ventilation can be obtained using greater pressure or volume, despite additional interface leak. If the aim is to abolish muscle effort completely, there is little to be gained by increasing the level of inspiratory pressure above 20 (CWD) or 25 (COPD) cm H(2)O.

Comparative study of two different modes of noninvasive home mechanical ventilation in chronic respiratory failure

STUDY OBJECTIVE

Two modes of noninvasive home mechanical ventilation (NIHMV) with volumetric ventilators were compared in patients with chronic respiratory failure.

DESIGN

Retrospective, parallel-group, comparative study.

SETTING

Third-level teaching Hospital in Barcelona (Spain).

PATIENTS AND METHODS

We studied 110 patients with chronic hypercapnic respiratory failure secondary to neuromuscular disease, kyphoscoliosis or post-tuberculosis sequelae, starting NIHMV with volumetric ventilators. The assist/control (A/C) ventilation mode was used in 45 patients and the control (C) mode in 65 patients. Clinical characteristics, pulmonary function results and arterial blood gas findings were assessed in each patient before establishing ventilation and at 6 and 12 months after. The patient's satisfaction with ventilation, the time required for adaptation, and compliance with the prescription were also assessed.

MEASUREMENTS AND RESULTS

Significant improvements in PaO(2) and PaCO(2) (P<0.001) were found at 6 and 12 months with both modes of mechanical ventilation. There were no significant differences between the two modes for pulmonary function or blood gas parameters with the exception of maximum inspiratory pressure (MIP) in patients receiving the C mode, which was significantly different as compared to the baseline value after 12 months of use (mean+/-sd: 36.6+/-14.8 and 44.7+/-24.2 cmH(2)O, respectively; P=0.010). No significant differences were found in adaptation, compliance with ventilation or patient satisfaction between the two modes studied.

CONCLUSIONS

According to several factors analysed, results with the A/C or C mode used with volumetric ventilators appear to be comparable in patients with chronic respiratory disease receiving NIHMV. Choice of mode will depend on the acquired experience of the prescribing physicians in each centre.

[Leak monitoring in noninvasive ventilation]

Nasal mask ventilation has been shown to be effective, but outcomes do not always match expectations because of mouth leaks, patient-ventilator asynchrony, or decreased upper airway patency. These developments are detected when they lead ultimately to circuit leaks that lower the effectiveness of ventilation through pressure loss, poor inspiratory triggering, and prolonged inspiratory time. The quality of sleep is affected, and adverse effects and treatment intolerance may arise. A number of ways to detect leaks and their practical consequences are proposed in this article. We applied 310 leak-detection procedures to 177 patients who had disappointing clinical, gasometric, or polysomnographic outcomes of ventilation. The leak-detection procedures varied according to the type of ventilation and the supposed underlying pathophysiological mechanism. Significant leaks were detected in 132 patients (76%); therapeutic changes were then prescribed to optimize outcomes. We present a practical method to apply in patients with suboptimal ventilation outcomes. If leaks can be detected during treatment, the probable cause of treatment failure can sometimes be established and possible pathophysiological mechanisms better understood. With this knowledge, it may be possible to improve ventilation.

Assistance ventilatoire à domicile : justifications et contraintes physiopathologiques

INTRODUCTION

Domiciliary assisted ventilation (DAV) may be undertaken invasively or non-invasively. Non-invasive DAV is used for patients suffering from alveolar hypoventilation due to restrictive pathology. Invasive DAV is reserved for "indications of necessity" that is when non-invasive ventilation is contraindicated due to the absence of adequate cough and for alveolar hypoventilation leading to hypercapnoea during spontaneous ventilation.

STATE OF THE ART

The main pathophysiological limitation to non-invasive ventilation is the interference of the glottis. In this mode the glottis imposes a variable resistance to the ventilation delivered. Its behaviour is more predictable during Volume controlled than during pressure controlled ventilation. The control parameters of a Volume controlled ventilator are very different from those used in invasive ventilation during which the respiratory system may be regarded as a single compartment (provided a cuffed tube bypasses the upper airway). In non-invasive DAV: mode VCM, tidal volume 13 mls kg(-1), rate 20 cycles min(-1), insp/exp ratio 1/1.2. In invasive DAV: mode VCM, tidal volume 8-10 mls kg(-1), rate 12 cycles min(-1), insp/exp ratio depending on the pathology 1/2.

PERSPECTIVES

As non-invasive DAV is essentially delivered during sleep the parameters for each patient can be optimised during polysomnography because waking, leading to a partial glottic occlusion, interferes with the ventilation delivered.

CONCLUSIONS

Recent understanding of the way the glottis interferes with mechanical ventilation when delivered non-invasively should lead to a revision of earlier practices based on invasive ventilation.

Effects of intermittent negative pressure ventilation on effective ventilation in normal awake subjects

RATIONALE

Previous studies have shown that an increase in inspiratory pressure during nasal intermittent positive pressure ventilation (IPPV) does not result in increased effective minute ventilation (E) due to glottic interference.

STUDY OBJECTIVES

To test the consequences of increases in negative pressure ventilation (NPV) on V(E).

MATERIAL AND METHODS

Eight healthy awake subjects underwent NPV delivered by an iron lung. First, NPV was started at a respirator frequency (f) of 15 cycles per minute with an inspiratory negative pressure (INP) of - 15 cm H(2)O (F15-P15). Then, f was increased to 20 cycles per minute and INP was kept at - 15 cm H(2)O. Next, f was kept at 20 cycles per minute and INP was reduced to - 30 cm H(2)O (F20-P30). Finally, f was decreased to 15 cycles per minute and INP was kept at - 30 cm H(2)O. At each step and for each breath, effective tidal volume (VT), V(E), and end-tidal carbon dioxide pressure were measured. In three subjects, the glottis width was assessed using fiberoptic bronchoscopy.

RESULTS

From spontaneous breathing to the first step of NPV (F15-P15), we observed an inhibition of the phasic inspiratory diaphragmatic electromyogram concomitant to a significant increase in V(E) (p < 0.0005). For the group as a whole, the increase in mechanical ventilation (from F15-P15 to F20-P30) resulted in significant increases in VT and V(E) leading to hypocapnia (p < 0.0005). Moreover, the glottis width did not decrease with the increase in mechanical ventilation.

CONCLUSIONS

We conclude that in normal awake subjects, NPV allowed a significant increase in V(E). These results differ from those previously obtained with nasal IPPV in which the glottic width interferes with the delivered mechanical ventilation.

Sleep fragmentation: comparison of two definitions of short arousals during sleep in OSAS patients

The measurement of arousals during sleep is useful to quantify sleep fragmentation. The criteria for electroencephalography (EEG) arousals defined by the American Sleep Disorders Association (ASDA) have recently been criticized because of lack of interobserver agreement. The authors have adopted a scoring method that associates the increase in chin electromyography (EMG) with the occurrence of an alpha-rhythm in all sleep stages (Université Catholique de Louvain (UCL) definition of arousals). The aim of the present study was to compare the two scoring definitions in terms of agreement and repeatability and the time taken for scoring in patients with obstructive sleep apnoea syndrome (OSAS) of varying severity. Two readers using both ASDA and UCL definitions scored twenty polysomnographies (PSGs) each on two occasions. The PSGs were chosen retrospectively to represent a wide range of arousal index (from 6-82) in OSAS patients. There was no difference in the arousal indices between readers and between scoring methods. The mean+/-SD difference between the two definitions (the bias) was 1.1+/-3.76 (95% confidence interval: -0.66-2.86). There was a strong linear relationship between the arousal index scored with the two definitions (r=0.981, p<0.001). Mean+/-SD scoring duration was significantly shorter for UCL than for ASDA definitions (18.5+/-5.4 versus 25.3+/-6.6 min, p<0.001). In conclusion, it has been found that in obstructive sleep apnoea syndrome patients, the American Sleep Disorders Association and Université Catholique de Louvain definitions were comparable in terms of agreement and repeatability.

Effectiveness of controlled and spontaneous modes in nasal two-level positive pressure ventilation in awake and asleep normal subjects

STUDY OBJECTIVES

The purpose of the present study was to compare in awake and asleep healthy subjects, under nasal intermittent positive pressure ventilation (nIPPV) with a two-level intermittent positive pressure device (two-level nIPPV), the efficacy of the controlled and spontaneous modes, and of different ventilator settings in increasing effective minute ventilation (VE).

PARTICIPANTS

Eight healthy subjects were studied.

SETTING

In the controlled mode, inspiratory positive airway pressure (IPAP) was kept at 15 cm H2O, expiratory positive airway pressure (EPAP) at 4 cm H2O, and the inspiratory/expiratory (I/E) time ratio at 1. The respirator frequencies were 17 and 25/min. In the spontaneous mode experiment, IPAP was started at 10 cm H2O and progressively increased to 15 and 20 cm H2O; EPAP was kept at 4 cm H2O.

MEASUREMENTS AND RESULTS

We measured breath by breath the effective tidal volume (VT with respiratory inductive plethysmography), actual respiratory frequency (f), and effective VE. Using the controlled mode, effective VE was significantly higher on nIPPV than during spontaneous unassisted breathing, except in stage 2 nonrapid eye movement sleep at 17/min of frequency; increases in f from 17 to 25/min led to a significant decrease in VT reaching the lungs, during wakefulness and sleep; effective VE was higher at 25 than at 17/min of frequency only during sleep; periodic breathing was scarce and apneas were never observed. Using the spontaneous mode, with respect to awake spontaneous unassisted breathing, two-level nIPPV at 10 and 15 cm H2O of IPAP did not result in any significant increase in effective VE either in wakefulness or in sleep; only IPAP levels of 20 cm H2O resulted in a significant increase in effective VE; during sleep, effective VE was significantly lower than during wakefulness; respiratory rhythm instability (ie, periodic breathing and central apneas) were exceedingly common, and in some subjects extremely frequent, leading to surprisingly large falls in arterial oxygen saturation.

CONCLUSIONS

It appears that two-level nIPPV should be used in the controlled mode rather than in the spontaneous mode, since it seems easier to increase effective VE with a lower IPAP at a high frequency than at a high pressure using the spontaneous mode. We suggest that the initial respirator settings in the controlled mode should be an f around 20/min, an I/E ratio of 1, 15 cm H2O of IPAP, and EPAP as low as possible.