James S. J. Haight

Site of airway obstruction in patients with obstructive sleep apnea before and after uvulopalatopharyngoplasty

This study describes a simple method, based on a movable catheter technique, for use during routine polysomnography to identify the site of obstruction, and this has been applied to 51 patients with suspected sleep apnea. The obstruction was found to be retropalatal in 30, retrolingual in 7, and could not be determined in 14 patients (12 had no sleep apnea, 1 did not sleep, and 1 had central sleep apnea). Twelve of these patients had uvulopalatopharyngoplasty with preoperative and postoperative polysomnograms to determine the site of obstruction. The preoperative obstruction was retropalatal in nine and retrolingual in three. Postoperatively, four patients (one with retrolingual obstruction and three with retropalatal obstruction) no longer had sleep apnea. In the remaining eight patients, the site of obstruction was unchanged from the preoperative one. Several conclusions result: 1. the movable catheter technique offers a simple way to determine the site of obstruction in patients with significant obstructive sleep apnea, 2. most such patients obstruct in the retropalatal region, and 3. preoperative localization of the site of obstruction to the retropalatal region does not seem to improve the surgical outcome of uvulopalatopharyngoplasty.

Nitric Oxide (NO) and Obstructive Sleep Apnea (OSA)

Nitric oxide (NO) and obstructive sleep apnea are inseparable. Obstructive sleep apnea could be described as the intermittent failure to transport the full complement of nasal NO to the lung with each breath. There NO matches perfusion to ventilation. NO is utilized by the efferent pathways that control the unequal, inspiratory battle between the pharyngeal dilators and the closing negative pressures induced by the thoracic musculature. Recurrent cortical arousals are a major short-term complication, and the return to sleep after each arousal uses NO. The long-term complications, namely hypertension, myocardial infarction, and stroke, might be due to the repeated temporary dearth of NO in the tissues, secondary to a lack of oxygen, one of NO’s two essential substrates.

Changes in Pharyngeal Properties After Uvulopalatopharyngoplasty

Uvulopalatopharyngoplasty is a commonly used modality for surgical treatment of snoring and obstructive sleep apnea. Although this procedure is thought to alter pharyngeal properties, its effect on pharyngeal mechanics has not been studied. The acoustic reflection technique was used to measure pharyngeal area at functional residual capacity and residual volume before and after uvulopalatopharyngoplasty in eight patients referred because of loud snoring. We also calculated the lung volume dependence of pharyngeal area, defined as the percent change in pharyngeal area between functional residual capacity and residual volume, normalized to the area at functional residual capacity. This parameter, which may be related to pharyngeal collapsibility, was obtained before and after uvulopalatopharyngoplasty. Preoperative sleep studies showed that one patient had obstructive sleep apnea (apnea index > 10). Uvulopalatopharyngoplasty resulted in a significant increase (p<0.01) in pharyngeal area (from 3.14 ± 0.71 cm1 to 4.25 ± 1.07 cm2) and residual volume (from 2.49±0.53 cm2 to 3.91±0.83 cm2). Following uvulopalatopharyngoplasty, the pharynx became stiffer, as manifested by a reduction in lung volume dependence of pharyngeal area from 19±12% to 8±13% (p<0.05). Six patients, including the patient with obstructive sleep apnea, reported improvement in snoring. Two patients reported worsening in snoring. One of the two was found to have reduction in pharyngeal area and lung volume dependence of pharyngeal area, and an increase in apnea index from 3 to 33. In selected snorers, uvulopalatopharyngoplasty results in improvement in snoring with a concomitant increase in pharyngeal area and a tendency toward lower pharyngeal collapsibility.

Diagnostic Airway Pressure Recording in Sleep Apnea Syndrome

A comparison was made between polysomnographic recordings and recordings of airflow pressures in the pharynx and respiratory pressures in the esophagus of 10 adult sleeping subjects with differing degrees of apnea. Pressure measurements were obtained by microsensors mounted on a 7F gauge flexible catheter which sited them in the epi-, meso- and hypopharynx and the esophagus. Digitized overnight pressure data were stored on a PC memory card and subsequently displayed for analysis by means of a notebook computer. In 2 patients examination of 200 obstructive, mixed and central apneic events showed no significant differences in recordings of their incidence, duration of classification between polysomnographic and either pharyngeal or esophageal pressure techniques. Onset of apnea was demonstrated with particular clarity by computer integration of the pressure tracings. The multiple pressure sensor method offered a further important advantage in detecting the caudal limits of pharyngeal obstructions by steep elevation of the pressure gradient in the pharyngeal segment between adjacent sensors in which the caudal limit of the obstruction was sited. The multiple pressure sensor technique provided reliable and comprehensive diagnostic information of breathing disorders in sleeping subjects and together with its miniaturized recording equipment the method commends itself as suitable for home monitoring.

Hypoxia depresses nitric oxide output in the human nasal airways.

Objectives The role of oxygen in the nasal air on nasal nitric oxide (NO) output was studied in 13 adult volunteers.

Laryngeal resistance to respiratory airflow in humans

Although vocal cord adduction has been observed during expiration, measurements of absolute values of resistance changes in man have not been reported in the literature. The authors measured resistance to translaryngeal respiratory airflow in inspiratory and expiratory phases of the respiratory cycle of four healthy, awake men during nasal breathing. It was found that, during quiet breathing through a decongested nose, translaryngeal resistance was 1.245 cm H2O/L per second in expiration and 0.354 cm H2O/L per second in inspiration (.005 < P < or = .01), for a percentage of approximately 25% and 50% of extrathoracic expiratory and inspiratory resistances, respectively. Voluntary hyperventilation decreased expiratory resistance, and a partial nasal obstruction abolished the statistical difference between translaryngeal inspiratory and expiratory resistance. These results are in agreement with previous observations of vocal cord movement and are consistent with an expiratory braking effect on airflow.

Sleep and posture

Computer‐assisted open catheter studies of 10 healthy, nose‐breathing men in dorsal and in lateral recumbent sleep demonstrated stable intrasubject transpharyngeal differential pressures and airflow resistances. They averaged 19.6 Pa (± standard deviation [SD] 11.9) and 0.103 Pa/cm3 per second (± SD 0.065) in the dorsal posture and stage II sleep during quiet breathing and were not significantly different in the lateral posture or in stage I sleep. Five subjects were snorers, and their pharyngeal airflow pressures and resistances increased substantially during quiet breathing on assumption of recumbency and much more in sleep. In the 5 subjects who were nonsnorers, postural changes were not significant and sleep increases were moderate. During snoring, transpharyngeal pressures and resistances increased even further, averaging 188 Pa and 1.02 Pa/cm3 per second for the whole group. Transpharyngeal differential pressures and hypopharyngeal transmural pressures frequently exceeded 300 Pa in inspiration and in expiration during periods of snoring. Yet, transpharyngeal differential pressures and resistances did not reveal appreciable differences between phases that would indicate compliant change of pharyngeal cross section. Breathing frequency was unchanged, but ventilation was significantly diminished at elevated upper airway resistances (P<.01). Transpharyngeal resistances and differential pressures varied independently from widely differing nasal resistances. As with our earlier studies, pressure measurements alone clearly demonstrated breathing patterns and events.

Pharyngeal airflow during sleep

This study was conducted to investigate the effects of sleep and nasal resistance on pharyngeal airflow in a group of healthy male adults without complaint of habitual snoring. Twelve subjects aged 21 to 60 years were studied in a sleep laboratory during exclusive nasal breathing. Nasal and pharyngeal airflow variables were measured concomitantly at different stages of sleep. Awake pharyngeal resistance averaged 0.02-0.03 Pa/cm3/s in recumbency. In stage 2 sleep and quiet breathing resistance increased by a factor of 3-4 and by a factor of 7-8 during snoring. Increased nasal loading did not increase pharyngeal resistance further or induce snoring. Mostly, increased pharyngeal resistances were of similar magnitude in both phases of respiration, but in a few instances inspiratory resistance exceeded that in expiration, and in a similar number the reverse was found. Overall, compliance of the pharyngeal airway was not a prominent feature in this group of subjects. The relationship between transpharyngeal pressure and resistance should be studied further in order to simplify future studies of airflow during sleep.

A comparison between two methods of measuring pressure in the pharyngeal airway : transducer probe versus open catheter

A new multi-transducer probe system for measuring pharyngeal pressures was compared with an established open catheter system. Pharyngeal pressure measurements were made at the same time, and site, in subjects awake, at unmodified and with artificially increased nasal airway resistances, and during sleep documented by polysomnography. The two systems yielded almost identical results. It is anticipated that the multi-transducer probe system will prove of clinical value.