Two isolated giant gastric duplication cysts in thorax in a newborn

We report a case of a newborn with severe respiratory distress since birth with two giant intrathoracic and separate eneteric duplication cysts in right hemithorax. On day 19, the intrathoracic cysts were removed, and the baby was discharged on his 22nd day of life. Histologic findings confirmed the diagnosis of a gastric duplication cyst. This report is the first case of two isolated, separated and giant right intrathoracic gastric duplication cysts in literature. The diagnostic values of radiological evaluation and surgical and pathological management for precise diagnosis are discussed.

Where should the normal position of the umbilicus be in the neonate?

INTRODUCTION

The aim of this study was to determine the normal position of the umbilicus so as to offer a guide to improve cosmetic results after the repair of congenital abdominal wall defects.

MATERIALS AND METHODS

The position of the umbilical center was determined in 187 neonates with respect to the xiphoid process, the center of the umbilicus and the pubis. The distance between the xiphoid process and the center of the umbilicus (XU), between the pubis and the center of the umbilicus (PU) and from the xiphoid process to the pubis (XP) were measured while the babies lay in a supine position. The PU:XU ratio was calculated based on these measurements.

RESULTS

Mean XP was 11.93±1.40 cm, mean XU was 7.41±1.08 cm and mean PU was 4.52±0.70 (mean±SD). The PU:XU ratio was calculated as 0.61±0.12 (ratio±SD).

CONCLUSION

We suggest that the PU:XU ratio should be 0.61 offering an ideal localization in umbilical reconstruction.

Patient and staff doses in interventional neuroradiology

Radiation doses for interventional examinations are generally high and therefore necessitate dose monitoring for patients and staff. Relating the staff dose to a patient dose index, such as dose-area product (DAP), could be quite useful for dose comparisons. In this study, DAP and skin doses of 57 patients, who underwent neurointerventional examinations, were measured simultaneously with staff doses. Although skin doses were comparable with the literature data, higher DAP values of 215 and 188.6 Gy cm2 were measured for the therapeutical cerebral and carotid examinations, respectively, owing to the use of biplane system and complexity of the procedure. Mean staff doses for eye, finger and thyroid were measured as 80.6, 77.6 and 28.8 microGy per procedure. The mean effective dose per procedure for the radiologists was 32 microSv. In order to allow better comparisons to be made, DAP normalised doses were also presented.

Disseminated Pseudallescheria boydii infection in a nonimmunocompromised host

We present a highly unusual case of pulmonary Pseudallescheria boydii infection in a nonimmunocompromised host with a cavitating mass lesion. The diagnosis was confirmed by open lung biopsy. The patient was treated at another institution with course of amphotericin B, considered an ineffective therapy for this infection, and presented to us with direct extension and invasion of the left atrial appendage and the pulmonary artery, followed by massive pulmonary embolization and hematogenous dissemination to the liver, spleen, kidney, pancreas, and brain.

Chemo- and baroresponses differ in African-Americans and Caucasians in sleep

To determine sleep effects on baro- and ventilatory responses to transient chemo- and barostimulation in African-Americans and Caucasians, 26 nonobese normotensive young subjects (13 African-Americans and 13 Caucasians) were studied awake and in non-rapid-eye movement (NREM) and rapid-eye-movement sleep during induced transient hypoxemia (N2), hypertension (phenylephrine, PE), and concomitant hypoxemia and hypertension (N2 + PE). Arterial blood pressure was recorded by plethysmographic volume clamp, minute ventilation by pneumotachograph, and arterial O2 saturation by pulse oximeter. For all subjects, chronotropic baroresponse (Deltapulse interval/Deltasystolic blood pressure, where Delta is change) increased with NREM sleep (P = 0.007). Baroresponse slope was greater in Caucasians than in African-Americans (ANOVA, P = 0.02). Hypoxemic ventilatory response (Deltaminute ventilation/Deltaarterial O2 saturation) was greater in African-Americans than in Caucasians in NREM sleep (P = 0.01), as was hypoxemic attenuation of baroresponse (N2 + PE, P = 0.03). These data suggest sleep-related differences in arterial chemo- and baroreceptor responses in normal young African-Americans and Caucasians, which may have implications concerning development of systemic hypertension.

Respiratory and arousal responses to acoustic stimulation

STUDY OBJECTIVES

Although sleep-related obstructive apnea is most often associated with transient arousal, the impact of this arousal on respiratory control remains unclear. We tested the hypotheses that acoustic arousing stimulation can generate a significant respiratory response during sleep in healthy subjects and that the magnitude or timing of this response is affected by the presence of electrocortical arousal or inhaled carbon dioxide.

DESIGN

We employed binaural tone bursts (0.5-s duration, 4-KHz center frequency, 99-s interstimulus interval) to elicit repetitive transient arousals from sleep during nocturnal polysomnographic recordings beginning at 10 PM and ending at 6 AM.

PARTICIPANTS

Recordings were conducted in five healthy adult volunteers aged 24 to 37 years.

INTERVENTIONS

Inspired gas was alternated between room air and 3% to 7% CO2 (titrated to yield an approximate 50% increase in minute ventilation) at 1-h intervals.

MEASUREMENTS AND RESULTS

Each 30-s epoch was scored for sleep/wake stage according to standard criteria. Only results obtained during nonrapid eye movement sleep are presented herein. Tone-evoked arousals were detected by computer analysis as increased EEG frequency occurring within 3 s of acoustic stimulation. For each tone, respiratory parameters for each of three prestimulus and four poststimulus breaths were normalized to the overall mean of prestimulus breaths measured during room air breathing for each subject. Tone bursts elicited repetitive transient arousals with a mean duration of approximately 10 s from all stages of sleep. With respect to the three prestimulus breaths, acoustic stimulation was associated with increased tidal volume and decreased inspiratory duration for at least four breaths. These respiratory responses to acoustic stimulation were not significantly influenced by either presence of transient arousal from sleep or inspired gas.

CONCLUSIONS

We conclude that transient EEG arousal may be repeatedly evoked from nonrapid eye movement sleep by transient acoustic stimulation in normal sleepers. This sensory stimulation is associated with augmented ventilation, a response that is not significantly affected by inspired hypercapnia or the presence of generalized EEG arousal.

The association of chronic urticaria and angioedema with autoimmune thyroiditis

BACKGROUND

An increased frequency of autoimmune thyroiditis is seen in patients with chronic urticaria and angioedema (CUA) and it has been hypothesized that autoimmunity may be playing a role in the pathogenesis of CUA. The aim of this study was to learn the extent of autoimmune thyroid disease in a series of patients who presented with CUA.

METHODS

Thyroid function tests and thyroid autoantibodies were measured by radioimmunoassay and immunoradiometric assay respectively in 94 CUA patients and 80 age- and sex-matched healthy volunteers.

RESULTS

Eleven patients (11.7%) were found to have thyroglobulin antibodies (TGA) and nine patients (9.57%) thyroid microsomal (TMA) titers ranging from 150 to 1340.37 and from 165.73 to 8000 IU/mL respectively. Both antibodies were detected in three control cases (3.7%). The association was statistically significant (P < 0.01). Six of 11 patients had thyroid dysfunction and the other five cases were euthyroid.

CONCLUSIONS

Our results justified the use of TMA and TGA for the early diagnosis of autoimmune thyroiditis in combination with CUA. The higher frequency of these antibodies in our patients, along with results from previously published data, suggest that this entity may reflect an autoimmune basis in some CUA patients. Thyroid function tests are not enough to rule out thyroid disease, and thyroid antibody tests should be carried out in all patients with CUA.

Respiratory and electrocortical responses to acoustic stimulation

Although sleep-related obstructive apnea is most often associated with transient arousal, the impact of this arousal on respiratory control remains unclear. We employed binaural tone bursts (.5 second duration) to elicit repetitive transient arousals from sleep during polygraphic recordings in 5 adult volunteers. By this method, we elicited repetitive transient arousals with a mean duration of approximately 10 seconds from all stages of sleep. With respect to the 3 pre-stimulus breaths, acoustic stimulation was associated with increased tidal volume and decreased inspiratory duration for at least 4 breaths. These respiratory responses to acoustic stimulation were not significantly influenced by either presence of transient arousal from sleep or the sleep state from which arousal occurred. We conclude that transient electro-cortical state changes may be repeatedly evoked from all sleep stages by transient acoustic stimulation in normal sleepers. This sensory stimulation represents a significant respiratory stimulus even when generalized arousal from sleep does not occur.

Palatal muscle electromyogram activity in obstructive sleep apnea

Eight subjects (5 men, 3 women, ages 27 to 55) with obstructive sleep apnea syndrome (OSAS) were studied to quantify and compare electromyographic (EMG) activity of levator veli palatini (LVP) and palatoglossus (PG), two velopharyngeal muscles, and genioglossus (GG) during obstructive apnea cycles in non-rapid eye movement (NREM) sleep. EMG activity of three successive preapneic breaths, first and last apneic efforts, and three successive postapneic breaths was quantified for each muscle as peak phasic inspiratory EMG normalized as percent activity of the last preapneic breath. In all subjects, apnea onset coincided with simultaneous inspiratory EMG nadir of all three muscles (LVP = 63 +/- 40%, PG = 74 +/- 53%. GG = 83 +/- 48%. mean +/- SD activity of last preapneic breath). Apnea resolution did not occur until inspiratory EMG of all three muscles simultaneously reached maximal activity, at levels significantly greater than preapneic activity as well as activity of the last preapneic effort (LVP = 215 +/- 205%, PG = 227 +/- 240+, GG = 235 +/- 202%, mean +/- SD activity of last preapneic breath, p < 0.05, Fisher's partial least-squares difference [PLSD] test for each muscle). The presence or absence of electroencephalographic arousal at apnea resolution did not influence these patterns of EMG activity. Inspiratory recruitment of velopharyngeal as well as oropharyngeal muscles appears to be associated with upper airway patency during sleep in patients with OSAS.

Effect of induced transient arousal on obstructive apnea duration

Six untreated male patients (age 19-55 yr) with obstructive sleep apnea underwent nocturnal polysomnography with acoustic stimulation to determine the effect of transient arousal on obstructive apneas during sleep. Binaural tone bursts (25-95 dB) were delivered in late expiration during the second obstructive apnea of a cycle consisting of four consecutive apneas. For the group, stimulated apneas were significantly shorter (P < 0.05, Fisher's protected least significant difference test) than were the unstimulated apneas when transient electrocortical arousal was elicited in both non-rapid-eye-movement (non-REM) sleep [mean 17 +/- 7 (SD) vs. 26 +/- 9, 23 +/- 10, and 26 +/- 12 s for 2nd vs. 1st, 3rd, and 4th apnea, respectively, of each cycle] and REM sleep (mean 19 +/- 10 vs. 35 +/- 15, 45 +/- 18, and 39 +/- 20 s). Without electrocortical arousal, the stimulated apnea was significantly shortened in non-REM (23 +/- 9 vs. 25 +/- 7, 24 +/- 8, and 26 +/- 8 s) but not in REM (32 +/- 16 vs. 37 +/- 12, 32 +/- 15, and 30 +/- 16 s). Tones delivered relatively early and late in the apnea were equally likely to be associated with resolution of the apnea. The nadir of arterial oxygen saturation of hemoglobin was inversely proportional to apnea length, with higher saturation nadirs associated with the stimulated apneas. These data indicate that transient arousal, induced by nonrespiratory stimulation, influences the resolution of obstructive apneas during sleep.

Acoustically induced cortical arousal increases phasic pharyngeal muscle and diaphragmatic EMG in NREM sleep

Six healthy subjects (3 males, 3 females) were studied to assess phasic inspiratory responses of upper airway (UA) and diaphragm muscles to electrocortical arousal independent of other potential respiratory stimulation. Transient electroencephalographic (EEG) arousal (abrupt EEG frequency shift > or = 3 s without awakening) was induced during supine stage 2 non-rapid-eye-movement (NREM) sleep with binaural tone bursts (0.5 s, 4 kHz, 25-95 dB). Electromyograms (EMG) of levator veli palatini (EMGlvp) and genioglossus (EMGgg) were obtained with intramuscular electrodes, and EMG of diaphragm (EMGdi) was obtained with esophageal electrodes. EMG signals were processed as moving time-averaged inspiratory activity over 100-ms windows. For each arousal, each of five consecutive postarousal breaths (R1-R5) was scored for peak inspiratory phasic EMG and normalized as percent averaged EMG of the three prearousal breaths for all muscles. After arousal, EMGlvp was increased for R1-R5 and EMGgg and EMGdi were increased for R1-R4. The increase in EMGlvp was greater than those of EMGgg and EMGdi for all response breaths. There was a significant increase in EMGlvp in all subjects, and EMGgg and EMGdi were significantly increased in three and two subjects, respectively. These data indicate that isolated transient electrocortical arousal is generally associated with phasic inspiratory recruitment of UA and diaphragm muscles in normal humans during NREM sleep; velopharyngeal muscle recruitment appears to be more consistent and of greater magnitude and duration than that of oropharyngeal muscle or diaphragm. We speculate that transient arousal from sleep may contribute to UA patency independent of chemical and mechanical respiratory stimuli.

Nasal CPAP continues to improve sleep-disordered breathing and daytime oxygenation over long-term follow-up of occlusive sleep apnea syndrome

To assess the effects of long-term nasal continuous positive airway pressure (CPAP) in occlusive sleep apnea syndrome (OSA), 17 patients with severe symptomatic OSA had repeated spirometry, arterial blood gases, and nocturnal polysomnograms off nasal CPAP after 3 to 46 months of treatment with nasal CPAP. Without loss of weight or change in respiratory mechanics, the ventilatory disturbance index fell from a mean of 87 events per hour to 57 events per hour (p < 0.0001), correlating with an improvement in mean nocturnal desaturation with sleep-disordered breathing events (r = 0.54, p = 0.03). Moreover, the daytime PaO2 rose significantly from a mean of 69 mm Hg to a mean of 82 mm Hg (P = 0.0001) at follow-up. The rise in daytime PaO2 was not only due to the alleviation of daytime hypercapnea observed in eight of nine hypercapneic subjects since the P(A-a)O2 gradient also decreased significantly. The improvement in PaO2 correlated significantly with the number of months of CPAP therapy, suggesting a continuing effect over time (r = 0.58, p = 0.015). These results indicate that there is a reversible element of the severity of OSA and suggest a result of nasal CPAP therapy may be to reverse the adverse and time-dependent effects of hypoxemia and sleep fragmentation on ventilatory control in severe OSA.

Voluntary hyperventilation in obesity hypoventilation

Arterial blood gas analysis was performed before and after 60 to 90 s of voluntary hyperventilation in 27 consecutive patients with occlusive sleep apnea syndrome (OSA) and daytime hypercapnia. The percentage of fall in PaCO2 from baseline was examined in relationship to age, body mass index, sleep-disordered breathing indices, and pulmonary function variables. In 14 subjects without airflow obstruction, only one individual could not voluntarily hyperventilate into the normal range, whereas 6 of 13 subjects with airflow obstruction could not hyperventilate to eucapnia. The average percentage of fall in PaCO2 was 16 mm Hg (SEM = 1.3 mm Hg). The percentage of fall in PaCO2 correlated significantly with FEV1/FVC ratio (r = 0.47, p = 0.01) and with FEV1 (r = 0.5, p = 0.008). Although the baseline PaCO2 did not correlate with FEV1, the posthyperventilation PaCO2 did (r = 0.54, p = 0.003). Voluntary hyperventilation studies herein suggest a predominant role for impairment of ventilatory control in the maintenance of hypercapnia in OSA since a fall of PaCO2 into the normal range can usually be obtained. The correlation between the percentage of fall in PaCO2 and spirometric measures of respiratory mechanics, as well as the inability of some subjects to normalize the PaCO2 voluntarily suggests an added role for respiratory mechanical impairment in obesity hypoventilation.

Upper airway muscle activity and the thoracic volume dependence of upper airway resistance

Although a thoracic volume dependence of upper airway resistance and caliber is known to exist in seated subjects, the mechanisms mediating this phenomenon are unknown. To test the hypothesis that actively altered end-expiratory lung volume (EELV) affects upper airway resistance in the supine position and to explore the mechanisms of any EELV-induced resistance changes, we studied five normal males during wakefulness. Supraglottic upper airway resistance (Ruaw) was calculated at an inspiratory flow of 0.1 l/s. The genioglossal electromyogram was obtained with indwelling wire electrodes and processed as moving time average. End-tidal CO2 was monitored by infrared analyzer. Observations were made during four 20-breath voluntary maneuvers: two at high and two at low EELV in each subject. Each maneuver was preceded by a control period at functional residual capacity. At high lung volume the EELV was increased by 2.23 +/- 0.54 (SD) liters; Ruaw decreased to 67.8 +/- 35.1% of control, while tonic and phasic genioglossal activities declined to 79.0 +/- 23.1 and 72.4 +/- 29.8%, respectively. At low lung volume the EELV was decreased by 0.86 +/- 0.23 liters. Ruaw increased to 178.2 +/- 186.8%, while tonic and phasic genioglossal activities increased to 243.0 +/- 139.3 and 249.1 +/- 146.3%, respectively (P less than 0.0001 for all). The findings were not explained by CO2 perturbations or respiratory pattern. Multiple linear regression analysis indicated that the genioglossal responses blunted the EELV-induced changes in upper airway patency.(ABSTRACT TRUNCATED AT 250 WORDS)

Successful use of nasal-CPAP for obstructive sleep apnea in Hunter syndrome with diffuse airway involvement

A patient with Hunter syndrome and diffuse airway obstruction had daytime hypersomnolence, snoring, and alveolar hypoventilation. Polysomnography showed severe obstructive sleep apnea. In the past, all reported cases of sleep apnea in patients with mucopolysaccharidoses had been treated with tonsillectomy/adenoidectomy or tracheostomy. This patient, in whom tracheostomy would have been very difficult due to the diffuse nature of his airway involvement, was successfully treated with high pressure nasal CPAP and supplemental oxygen.

Breath-by-breath interactions between inspiratory and expiratory duration in occlusive sleep apnea

We examined interactions between inspiratory duration (TI), expiratory duration (TE), and inspiratory (esophageal) pressure (Pes) generation in seven subjects with confirmed occlusive sleep apnea. Breath-by-breath values of TI, TE, and Pes were identified by digital computer during 21 260-s epochs of repetitive occlusive apnea during non-rapid-eye-movement sleep. The control theory of interacting nonlinear oscillators was used to categorize the interaction between TI and TE for each epoch as either 1) synchronization, the strongest possible interaction between biological oscillators; 2) relative entrainment, a moderate interaction between oscillators; or 3) relative coordination, a weak interaction. The latter two interactions were characterized by systemic oscillations in the moving cross-correlation between TI and TE. The relationship between TI and Pes was analyzed in a similar fashion. Significant oscillations were present in all three parameters (P less than 0.0001 for each). We observed significant negative correlations between TI and TE and between TI and Pes (P less than 0.001 for each) when all breaths for all epochs were pooled. In no epoch was there a significant positive correlation between TI and TE or Pes. All three interactions were observed between TI and TE: five epochs of synchronization, nine of relative entrainment, and seven of relative coordination. In contrast, 19 of 21 epochs exhibited synchronization between TI and Pes, with 2 epochs of relative entrainment. The relative frequency of TI vs. Pes synchronization was significantly greater than TI vs. TE synchronization (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Upper airway and respiratory muscle responses to continuous negative airway pressure

To determine upper airway and respiratory muscle responses to nasal continuous negative airway pressure (CNAP), we quantitated the changes in diaphragmatic and genioglossal electromyographic activity, inspiratory duration, tidal volume, minute ventilation, and end-expiratory lung volume (EEL) during CNAP in six normal subjects during wakefulness and five during sleep. During wakefulness, CNAP resulted in immediate increases in electromyographic diaphragmatic and genioglossal muscle activity, and inspiratory duration, preserved or increased tidal volume and minute ventilation, and decreased EEL. During non-rapid-eye-movement and rapid-eye-movement sleep, CNAP was associated with no immediate muscle or timing responses, incomplete or complete upper airway occlusion, and decreased EEL. Progressive diaphragmatic and genioglossal responses were observed during non-rapid-eye-movement sleep in association with arterial O2 desaturation, but airway patency was not reestablished until further increases occurred with arousal. These results indicate that normal subjects, while awake, can fully compensate for CNAP by increasing respiratory and upper airway muscle activities but are unable to do so during sleep in the absence of arousal. This sleep-induced failure of load compensation predisposes the airways to collapse under conditions which threaten airway patency during sleep. The abrupt electromyogram responses seen during wakefulness and arousal are indicative of the importance of state effects, whereas the gradual increases seen during sleep probably reflect responses to changing blood gas composition.

Effects of loading and unloading the respiratory system on respiratory control and muscle function

To determine the effects of internal respiratory loading and unloading on respiratory neuromuscular function, ventilatory (Vi), occlusion pressure (P0.15), transdiaphragmatic pressure (Pdi) and diaphragmatic electromyogram (EMGdi) responses to CO2 rebreathing were assessed in 6 normal volunteers rebreathing gas mixtures denser (63% SF6, 30% O2, 7% CO2) and less dense (63% He, 30% O2, 7% CO2) than air (63% N2, 30% O2, 7% CO2). Loading with SF6 decreased the Vi response to CO2 rebreathing and increased P0.15 and Pdi for a given EMGdi, while the greater the increase in pressure response the less was the decrease in Vi. Unloading with He had the opposite effect. The pattern of breathing was altered with SF6, with Ti and Te increasing and frequency decreasing, while there was no change in timing with He. Internal loading of inspiration and expiration with SF6 elicits compensatory responses that depend on changes of respiratory timing and enhanced diaphragm efficiency. Adjustments to unloading are generally opposite to that observed with loading.

A comparison of men and women with occlusive sleep apnea syndrome

Among 118 patients with occlusive sleep apnea syndrome (OSA), defined as daytime hypersomnolence and an apnea hypopnea index (AHI) greater than ten events/h, 41 women were compared with 77 men. Body mass index, spirometric study, PaO2, PaCO2, and results from nocturnal polysomnography were examined in a two-way analysis of variance (ANOVA) for the effects of sex, age group, and a sex-age group interaction. The age groups examined were above and below 42 years, the breakpoint for menopause in the women. Younger persons tended to be more obese and to have a higher AHI. Both sexes had similar pulmonary function, AHI, and nocturnal desaturation, but women experienced significantly fewer completely occluded breathing events and had apneas of shorter mean and maximum duration than men of similar ages. No effect of menopausal status per se was observed. In OSA patients, differences in upper airway occlusion and apnea duration suggest differences between the sexes in upper airway physiology or respiratory control.

Determinants of hypercapnia in occlusive sleep apnea syndrome

To assess the relative contributions of age, gender, obesity, pulmonary function, and the severity of sleep-induced respiratory abnormalities to the development of alveolar hypoventilation in patients with occlusive sleep apnea syndrome, prospective data from III patients with occlusive sleep apnea were analyzed by stepwise logistic and multiple regression techniques. The significant variables in a logistic regression model predicting the presence of hypercapnia were daytime arterial oxygen pressure (PaO2; p less than 0.0001) and gender (p less than 0.04), the latter reflecting the higher number of hypercapnic women in our patient population. Multiple regression analysis performed in the hypercapnic group to study the determinants of the severity of elevation of arterial carbon dioxide tension (PaCO2) revealed significant contribution from the PaO2, the apnea-plus-hypopnea index (AHI), and the percent predicted forced vital capacity (r2 = 0.56; p less than 0.0001), whereas in the normocapnic patients, PaCO2 related to PaO2 only. These results suggest that daytime hypoxemia, mechanical impairment of the respiratory system due to obesity or obstructive airway disease (or both), and the severity of sleep-induced respiratory abnormalities as assessed by AHI contribute to the severity of carbon dioxide retention in patients with occlusive sleep apnea in a multifactorial fashion.

Changes in end-expiratory lung volume during sleep in patients with occlusive apnea

Eight patients with occlusive sleep apnea were monitored during non-rapid-eye-movement (NREM) sleep to study the factors that contribute to negative inspiratory pressure generation and thus upper airway occlusion. End-expiratory lung volume assessed by respiratory inductive plethysmography [sum of end-expiratory levels (SUM EEL)] increased early and decreased late during the ventilatory phases (P less than 0.0001, one-way analysis of variance). Inspiratory change in esophageal pressure (Pes) and peak inspiratory diaphragmatic and genioglossal electromyograms (EMGdi and EMGge) decreased while the inspiratory pressure generated for a given diaphragmatic activity (Pes/EMGdi) increased during the preapneic phase (P less than 0.0001, for all). Multiple regression analysis with Pes/EMGdi as the dependent variable (R2 = 0.90) indicated that both the changes in SUM EEL and EMGge significantly contributed to the model (P less than 0.008 and 0.004, respectively). These results indicate that end-expiratory lung volume fluctuates during NREM sleep in patients with occlusive apnea and suggest that these changes along with the changes in upper airway muscle activity contribute to the generation of negative inspiratory pressure, leading to the passive collapse of the upper airways.

Effects of continuous positive airway pressure on upper airway and respiratory muscle activity

To study the effects of continuous positive airway pressure (CPAP) on lung volume, and upper airway and respiratory muscle activity, we quantitated the CPAP-induced changes in diaphragmatic and genioglossal electromyograms, esophageal and transdiaphragmatic pressures (Pes and Pdi), and functional residual capacity (FRC) in six normal awake subjects in the supine position. CPAP resulted in increased FRC, increased peak and rate of rise of diaphragmatic activity (EMGdi and EMGdi/TI), decreased peak genioglossal activity (EMGge), decreased inspiratory time and inspiratory duty cycle (P less than 0.001 for all comparisons). Inspiratory changes in Pes and Pdi, as well as Pes/EMGdi and Pdi/EMGdi also decreased (P less than 0.001 for all comparisons), but mean inspiratory airflow for a given Pes increased (P less than 0.001) on CPAP. The increase in mean inspiratory airflow for a given Pes despite the decrease in upper airway muscle activity suggests that CPAP mechanically splints the upper airway. The changes in EMGge and EMGdi after CPAP application most likely reflect the effects of CPAP and the associated changes in respiratory system mechanics on the afferent input from receptors distributed throughout the intact respiratory system.

Respiratory muscle interaction during NREM sleep in patients with occlusive apnea

To study respiratory muscle interaction in patients with occlusive apnea, diaphragmatic electromyogram (EMGdi) and gastric, pleural, and transdiaphragmatic pressures (Pga, Ppl, and Pdi, respectively) were studied in seven patients during non-rapid-eye-movement (NREM) sleep. Diaphragmatic force output, as assessed by Pdi, followed the periodic changes in EMGdi but during the occlusive phase the increase in Pdi was more than the increase in EMGdi. This increase in Pdi was essentially due to an increase in Ppl, since Pga and EMGdi had a linear relationship (r = 0.98, P less than 0.001) that did not change during the occlusive and ventilatory phases. Abdominal muscle recruitment evident in Pga and abdominal motion tracings during the occlusive phase when paradoxical rib cage motion was observed suggested that this increase in diaphragmatic efficiency was likely due to a change in diaphragmatic length-tension characteristics. These results demonstrate that, in patients with occlusive apneas, the diaphragm is the predominant respiratory muscle during NREM sleep and that its function is supported by abdominal muscle recruitment.

Respiratory timing during NREM sleep in patients with occlusive sleep apnea

To study respiratory timing mechanisms in patients with occlusive apnea, inspiratory and expiratory times (TI and TE) were calculated from the diaphragmatic electromyogram obtained in seven patients during non-rapid-eye-movement (NREM) sleep. Peak diaphragmatic activity (EMGdi) had a curvilinear relationship with TI during the ventilatory and occlusive phases such that TI shortened as EMGdi decreased during the ventilatory phase (r = 0.87, P less than 0.05) and it prolonged as EMGdi increased during the occlusive phase (r = 0.89, P less than 0.02). However, EMGdi vs. TI for the occlusive phase was shifted to the right of that for the ventilatory phase, reflecting the relatively longer TI during upper airway occlusion. TI also had a linear relationship with pleural pressure (r = 0.94, P less than 0.001) that remained unchanged during the ventilatory and occlusive phases such that it prolonged as negative inspiratory pressure increased. These results indicate that respiratory timing is continuously modified in patients with occlusive apnea as inspiratory neural drive fluctuates during NREM sleep and suggest that this modification is due to the net effects of changing inspiratory neural drive and afferent input predominantly from upper airway mechanoreceptors.

Induction of periodic breathing during sleep causes upper airway obstruction in humans

To test the hypothesis that occlusive apneas result from sleep-induced periodic breathing in association with some degree of upper airway compromise, periodic breathing was induced during non-rapid-eye-movement (NREM) sleep by administering hypoxic gas mixtures with and without applied external inspiratory resistance (9 cmH2O X l-1 X s) in five normal male volunteers. In addition to standard polysomnography for sleep staging and respiratory pattern monitoring, esophageal pressure, tidal volume (VT), and airflow were measured via an esophageal catheter and pneumotachograph, respectively, with the latter attached to a tight-fitting face mask, allowing calculation of total pulmonary system resistance (Rp). During stage I/II NREM sleep minimal period breathing was evident in two of the subjects; however, in four subjects during hypoxia and/or relief from hypoxia, with and without added resistance, pronounced periodic breathing developed with waxing and waning of VT, sometimes with apneic phases. Resistive loading without hypoxia did not cause periodicity. At the nadir of periodic changes in VT, Rp was usually at its highest and there was a significant linear relationship between Rp and 1/VT, indicating the development of obstructive hypopneas. In one subject without added resistance and in the same subject and in another during resistive loading, upper airway obstruction at the nadir of the periodic fluctuations in VT was observed. We conclude that periodic breathing resulting in periodic diminution of upper airway muscle activity is associated with increased upper airway resistance that predisposes upper airways to collapse.

Upper airway occlusion during sleep in patients with Cheyne-Stokes respiration

Sleep-induced periodic breathing has been suggested to lead to the development of occlusive apneas in patients with sleep apnea syndrome. If this were true, patients with Cheyne-Stokes respiration should also develop upper airway occlusion during sleep. To study this hypothesis, 6 nonobese patients with Cheyne-Stokes respiration lacking evidence for sleep apnea syndrome and anatomic upper airway abnormalities underwent polysomnography during daytime naps. A total of 463 apneas were analyzed in the 6 patients studied. In 1 patient, no evidence of upper airway occlusion was observed. In the remaining 5 patients, a varying frequency of upper airway occlusion resembling the pattern of mixed apnea was seen in 3 to 97% of the total apneas analyzed. The mean number (+/- 1 SD) of occluded inspiratory efforts per mixed apnea in these 5 patients was 1.69 +/- 0.59. These results show that patients with Cheyne-Stokes respiration may develop upper airway occlusion during sleep and are consistent with the contention that sleep-induced periodic breathing in patients with sleep apnea syndrome is primary to the development of occlusive apneas.

Respiratory load compensation in chronic airway obstruction

To assess respiratory neuromuscular function and load compensating ability in patients with chronic airway obstruction (CAO), we studied eight stable patients with irreversible airway obstruction during hyperoxic CO2 rebreathing with and without a 17 cmH2O X l-1 X s flow-resistive inspiratory load (IRL). Minute ventilation (VE), transdiaphragmatic pressure (Pdi), and diaphragmatic electromyogram (EMGdi) were monitored. Pdi and EMGdi were obtained via a single gastroesophageal catheter with EMGdi being quantitated as the average rate of rise of inspiratory (moving average) activity. Based on the effects of IRL on the Pdi response to CO2 [delta Pdi/delta arterial CO2 tension (PaCO2)] and the change in Pdi for a given change in EMGdi (delta Pdi/delta EMGdi) during rebreathing, two groups could be clearly identified. Four patients (group A) were able to increase delta Pdi/delta PaCO2 and delta Pdi/delta EMGdi, whereas in the other four (group B) the IRL responses decreased. All group B patients were hyperinflated having significantly greater functional residual capacity (FRC) and residual volume than group A. In addition the IRL induced percent change in delta Pdi/delta PaCO2, and delta VE/delta PaCO2 was negatively correlated with lung volume so that in the hyperinflated group B the higher the FRC the greater was the decrease in Pdi response due to IRL. In both groups the greater the FRC the greater was the decrease in the ventilatory response to loading. Patients with CAO, even with severe airways obstruction, can effect load compensation by increasing diaphragmatic force output, but the presence of increased lung volume with the associated shortened diaphragm prevents such load compensation.

Dynamics of respiratory drive and pressure during NREM sleep in patients with occlusive apneas

To study the dynamics of respiratory drive and pressure in patients with occlusive apneas, diaphragmatic electromyogram (EMGdi), esophageal pressure (Pes), and genioglossal electromyogram (EMGge) were monitored during nocturnal sleep in five patients. Both EMGs were analyzed as peak moving time average, and Pes was quantitated as the peak inspiratory change from base line. During the ventilatory phase both EMGs decreased proportionally. The decrease in Pes was less than the decrease observed in EMGdi, and Pes generated for a given EMGdi increased during the preapneic phase in spite of the proportional decrease in EMGdi and EMGge during this period. We conclude that negative inspiratory pressures which lead to the passive collapse of oropharyngeal walls are dependent on both respiratory and upper airway muscle activity and that occlusive apneas of non-rapid-eye-movement (NREM) sleep do occur in spite of proportional changes observed in the activity of both muscle groups. The preapneic increase in negative inspiratory pressures generated for a given respiratory muscle activity is most likely due to the decrease in upper airway muscle activity that is associated with an increase in oropharyngeal resistance.

Relationship between pulmonary function and sleep-induced respiratory abnormalities

The relationships between pulmonary function and sleep-induced respiratory events were studied in 34 consecutive male patients with suspected sleep apnea syndrome. In view of the effects of obstructive airway disease on pulmonary volume and airway resistance (Raw), patients were divided into two groups, those with and those without obstructive airway disease. Percent predicted functional residual capacity (FRC) correlated significantly with the apnea-plus-hypopnea index (AHI) in patients with and without obstructive airway disease (r = -0.62 and p less than 0.01; and r = -0.57 and p less than 0.01, respectively) whereas percent predicted total lung capacity had a significant relationship with AHI only in patients with obstructive airway disease (r = -0.80; p less than 0.001). In patients without such disease, a significant correlation between inspiratory airway conductance (Gaw) and AHI (r = -0.47; p less than 0.05) was also present, while percent predicted FRC and Gaw did not correlate with normalized weight. These findings suggest that decreased pulmonary volume and increased Raw contribute to the severity of sleep-induced respiratory abnormalities in patients with sleep apnea syndrome regardless of the degree of obesity.

Comparison of magnetometer and inductance plethysmography derived Konno-Mead diagrams during CO2 rebreathing

Magnetometers measure changes in antero-posterior diameters of the rib cage and abdomen while respiratory inductance plethysmography (RIP) measures changes in chest wall cross-sectional area. We compared Konno-Mead diagrams derived from isovolume calibrated magnetometers and RIP in the DC-mode during room air and CO2 rebreathing in the sitting and supine positions. Chest wall configurations obtained during quiet tidal breathing were similar in both sitting and supine positions. During CO2 stimulated breathing, however, derived chest wall configurations were at times dissimilar. The RIP per cent rib cage contribution to tidal volume was greater than that of magnetometers during room air and CO2 rebreathing in both sitting and supine positions. Changes in end expiratory levels measured by magnetometers and RIP during CO2 rebreathing are in general proportionate to each other; however, the magnetometers usually depicted quantitatively greater decreases in abdominal end expiratory levels during rebreathing. We conclude that the qualitative and quantitative assessment of chest wall configurations and volume displacement vary depending on the method used. RIP by including lateral wall motion may more accurately reflect compartmental displacements, while magnetometers by solely measuring antero-posterior diameter may better reflect changes in abdominal volume and thus diaphragm configuration.

Effects of position on respiratory muscle function during CO2 rebreathing

The effects of changing from the sitting to supine position on respiratory muscle function was assessed during CO2 rebreathing. Gastric (Pg), pleural (Ppl) and transdiaphragmatic (Pdi) pressures and thoracoabdominal motion were monitored. Diaphragmatic EMG was measured by a bipolar esophageal electrode and quantitated as a moving time average (EMGdi). From sitting to supine, in only 2 of 7 subjects (group A) the diaphragm gained a mechanical advantage as evident by an increased slope of the Pdi versus EMGdi relationship not present in the other 5 subjects (group B). At high levels of ventilation while sitting, only group B increased expiratory abdominal muscle activity leading to a more favorable diaphragm length and a passive descent of the abdomen-diaphragm on inspiration. In the supine position functional residual capacity progressively increased in all subjects and the above abdominal pattern was not seen. We conclude that during upright CO2 rebreathing the recruitment of the expiratory abdominal muscles assists diaphragmatic function by placing the diaphragm in an advantageous pressure generating configuration.

Effects of expiratory positive airway pressure on sleep-induced respiratory abnormalities in patients with hypersomnia-sleep apnea syndrome

In order to explore the efficacy of expiratory positive airway pressure (EPAP) in the prevention of sleep-induced respiratory abnormalities, we studied 9 patients with typical presentation of hypersomnia-sleep apnea syndrome 1 wk apart, without and with 10 cm water of EPAP. We found that EPAP significantly reduced apnea index (p less than 0.01), maximal and mean duration of apneas (p less than 0.01) and desaturation index (p less than 0.001), and significantly improved mean and minimal oxygen saturation (p less than 0.01) and awake supine arterial oxygen saturation (p less than 0.01) in all 9 patients. We also found that EPAP significantly decreased the relative time spent in Stages 1 and 2 NREM sleep (p less than 0.01) and increased the relative time spent in Stages 3 and 4 NREM sleep (p less than 0.01). These results indicate that EPAP reduces frequency and duration of apneas and the degree of nocturnal oxygen desaturation and improves sleep quality in patients with hypersomnia-sleep apnea syndrome.

Respiratory muscle function during CO2 rebreathing with inspiratory flow-resistive loading

We investigated the respiratory muscle contribution to inspiratory load compensation by measuring diaphragmatic and intercostal electromyograms (EMGdi and EMGic), transdiaphragmatic pressure (Pdi), and thoracoabdominal motion during CO2 rebreathing with and without 15 cmH2O X l-1 X s inspiratory flow resistance (IRL) in normal sitting volunteers. During IRL compared with control, Pdi measured during airflow and during airway occlusion increased for a given change in CO2 partial pressure and EMGdi, and there was a greater decrease in abdominal (AB) end expiratory anteroposterior dimensions with increased expiratory gastric pressure (Pga), this leading to an inspiratory decline in Pga with outward AB movement, indicating a passive component to the descent of the abdomen-diaphragm. The response of EMGic to IRL was similar to that of EMGdi, though rib cage (RC)-Pga plots did infer intercostal muscle contribution. We conclude that during CO2 rebreathing with IRL there is improved diaphragmatic neuromuscular coupling, the prolongation of inspiration promoting a force-velocity advantage, and increased AB action serving to optimize diaphragm length and configuration, as well as to provide its own passive inspiratory action. Intercostal action provides increased assistance also. Therefore, compensation for inspiratory resistive loads results from the combined and integrated effort of all respiratory muscle groups.

Periodic breathing and the pathogenesis of occlusive sleep apneas

In order to study the relationship between sleep-induced periodic breathing and the development of occlusive sleep apneas, 6 patients with hypersomnia-sleep apnea syndrome were studied during nocturnal sleep before and approximately 1 month after therapeutic tracheostomy. Post-tracheostomy studies were performed in open and closed tracheostomy states. Sleep-induced periodic breathing resembling the pattern of Cheyne-Stokes breathing was observed in all patients before and after tracheostomy, even when tracheostomy was left open. When tracheostomy was closed all patients developed periodic hypopneas with significant oxygen desaturation, and 4 patients developed occlusive apneas at the nadir of the periodic changes. However, apnea and desaturation indexes during closed tracheostomy were significantly lower than their respective pretracheostomy values. These results indicate that sleep-induced periodic breathing, which represents an instability of respiratory control, is primary to the development of occlusive apneas, and the periodically observed is exaggerated by hypoxemia. Comparison of pre- and post-tracheostomy studies indicate a significant improvement in the underlying disorder most likely caused by the elimination of nocturnal hypoxemia and sleep fragmentation.

Mass loading, sleep apnea, and the pathogenesis of obesity hypoventilation

To define the roles of mechanical loading, respiratory neuromuscular control, and sleep apnea in the pathogenesis of obesity hypoventilation, respiratory muscle drive and output, assessed by diaphragmatic electromyogram (EMGdi) and mouth occlusion pressure (P 0.15), respectively, were determined during CO2 chemostimulation in nonobese volunteers who were subjected to abdominal mass loading, and in three groups of markedly obese patients: eucapnic obese without sleep apnea (O), eucapnic obese with sleep apnea (OSA), and hypercapnic obese with sleep apnea (OH). The P0.15 responses were decreased in OSA and OH, but the EMGdi responses were not significantly different from those in control subjects. In O patients EMGdi responses were significantly greater than those in control subjects as well as those in OSA and OH patients. EMGdi and P0.15 responses increased in all nonobese subjects when they were subjected to mass loading. We conclude that both OSA and OH patients were equally unable to develop the expected increase in respiratory muscle drive and output. The presence of sleep apnea, possibly by causing nocturnal hypoxemia and/or sleep fragmentation, may result in impaired mass load compensation and predispose obese patients to develop hypercapnia.

Pathogenesis of apneas in hypersomnia-sleep apnea syndrome

To define the pathogenesis of apneas, eight patients with hypersomnia-sleep apnea syndrome were studied during nocturnal sleep. Diaphragmatic and genioglossal electromyograms quantitated as moving time average activity showed parallel periodic fluctuations resembling the pattern of Cheyne-Stokes breathing. Hypopneas and occlusive apneas occurred at the nadir of these cyclic changes, and mixed apneas represented an extreme of this periodicity with no inspiratory activity at the nadir of the cycle. Tracings of central apneas were compatible with an extremely prolonged expiratory phase. Electromyogram activity of both muscles showed an inversely linear relationship with oxygen saturation but genioglossal activity at the resolution of upper airway occlusion was increased out of proportion to the increase in diaphragmatic activity and the degree of oxygen desaturation. These results indicated that occlusive and mixed apneas result from an instability of ventilatory control during sleep, which seems to be an exaggeration of periodic breathing observed at sleep onset.

Diaphragmatic EMG and transdiaphragmatic pressure measurements with a single catheter

A single gastroesophageal catheter was used for simultaneous measurements of diaphragmatic electromyogram (EMGdi), esophageal, and gastric pressures in 10 normal volunteers. The catheter consisted of 2 polyethylene tubes, each with an outer diameter of 1.70 mm and an inner diameter of 1.19 mm, 2 platinum wire coils, and esophageal and gastric latex balloons. In all subjects studied, the increase in EMGdi, quantified as the average rate of rise of inspiratory moving average activity, and transdiaphragmatic pressure (Pdi) were linearly related to the increase in end-tidal PCO2 during CO2 rebreathing (range of r, 0.88 to 0.99 and 0.85 to 0.99, respectively). The relation between changes in EMGdi and that of Pdi, mean inspiratory flow, and occlusion pressure were also linear (range of r, 0.83-0.99, 0.73-0.99, and 0.84-0.99, respectively), indicating reliable recordings of EMGdi and Pdi during CO2 rebreathing in upright normal humans.

Diaphragmatic and genioglossal electromyogram responses to isocapnic hypoxia in humans

In order to define the relationship between central control of upper airway and respiratory muscle function, diaphragmatic electromyogram (EMGdi) and genioglossal EMG (EMGge) responses to isocapnic hypoxia were studied in 6 awake supine volunteers. Both EMGs were processed and quantitated as moving time average activity. In all subjects, EMGge showed phasic inspiratory activity synchronous with EMGdi. Increases seen in EMGdi and EMGge were linearly related to the decrease in oxygen saturation (r = 0.89 +/- 0.08 and 0.89 +/- 0.08, respectively). There was also a linear relationship between the relative responses of both EMGs to hypoxia such that a low EMGdi response was associated with a low EMGge response and vice versa (r = 0.92, p less than 0.001). These results indicated that the genioglossus muscle behaves like a respiratory muscle and suggested that central control of upper airway and respiratory muscles in humans are intimately related.

Diaphragmatic and genioglossal electromyogram responses to CO2 rebreathing in humans

To assess the relationship between central control of upper airway and respiratory muscle, simultaneously recorded diaphragmatic electromyogram (EMGdi) and genioglossal EMG (EMG ge) responses to CO2 rebreathing were compared in five supine volunteers. Both EMGs were quantitated in terms of inspiratory peak moving time-average activity. In all subjects both EMGdi and EMGge increased linearly with increasing alveolar CO2 pressure (r = 0.93 +/- 0.04 and 0.87 +/- 0.07, respectively), resulting in a significantly linear EMGge vs. EMGdi relationship (r = 0.91 +/- 0.04). CO2 response slopes of both EMGs were similar and linearly related (r = 0.96, P less than 0.001) such that subjects with low EMGdi response also had a low EMGge response and vice versa. Although the onset of EMGge activity preceded that of EMGdi, and the pattern of both EMGs were different, inspiration duration of both EMGs were similar. These data indicate that in humans both diaphragm and genioglossus muscle share similar control mechanisms and suggest that upper airway function is intimately related to the regulation of breathing.