Effects of changes in central venous pressure on upper airway size in patients with obstructive sleep apnea.

Intraluminal airway pressure and pharyngeal muscle activity are widely recognized as major determinants of the size and collapsibility of the upper airway. In addition, changes in the volume or pressure of tissue surrounding the pharyngeal airway may significantly influence its size. The present study used fast computed tomography (CT) to determine the effects of changes in central venous pressure (CVP) on upper airway size. Ten awake male patients with obstructive sleep apnea (OSA) were studied. Scans were performed at functional residual capacity (FRC) and at the end of a tidal inspiration (VTei) under three conditions of CVP: (1) at baseline (CVP nl) with patients lying supine; (2) at decreased CVP (CVP-) by inflating blood pressure cuffs to 40 mm Hg on both legs; and (3) at increased CVP (CVP+) by elevating both legs to 33 degrees. At FRC, changes in CVP had no significant effect on either mean or minimum cross-sectional area (CSA) of the upper airway. In contrast, an analysis of variance (ANOVA) indicated that alterations in CVP were associated with changes in mean CSA (p = 0.03) and to a lesser extent in minimum CSA (p = 0.07) at VTei. With the legs elevated (CVP+), neither mean nor minimum CSA showed any significant change with tidal breathing. However, after leg-cuff inflation (CVP-), highly significant increases in both mean (163 +/- 22 to 218 +/- 19 mm2, p = 0.001) and minimum (48 +/- 8 to 85 +/- 12 mm2, p = 0.02) CSA were detected. Changes in mean and minimum CSA with tidal breathing at baseline (CVP nl) were intermediate. These results indicate that changes in CVP significantly alter the response of the upper airway to tidal breathing. They further suggest that increases in upper airway size with tidal breathing may be related to reduction in venous blood volume in pharyngeal and neck tissues as the generation of negative intrathoracic pressure during inspiration increases venous return to the chest.

Effects of body position on the upper airway of patients with obstructive sleep apnea.

Fast-CT scanning was used to study the effects of changes in body position on upper airway (UA) size and shape in 11 awake subjects with obstructive sleep apnea (OSA). Six patients with position (P)-dependent OSA were compared with five patients with nonposition (NP)-dependent OSA. Scans were repeated in the prone (PRN), right side (RS), and supine (SUP) body positions at both functional residual capacity and end-inspiratory tidal volume. Significant group, group by position, and borderline group by respiration effects were detected for minimum but not mean UA dimension data. Significant differences between groups were noted in minimum cross-sectional area and minimum lateral distance but not in minimum anteroposterior distance in the RS and SUP positions. Turning from the PRN to the RS or SUP position tended to decrease UA size in the NP group by decreasing the lateral distance, while the opposite effect was found in the P group. The results indicate that changes in body position during wakefulness affect the lateral but not the anteroposterior dimensions of the UA, and the UA behaves differently in patients with NP and P OSA in response to changes in body position.

Fast-computed tomographic evaluation of the effect of route of breathing on upper airway size and function in normal men.

Nasal obstruction is associated with increased sleep disordered breathing (SDB), even in normal subjects. This increase in SDB may result from narrowing of the orohypopharyngeal (OHP) or retroglossal segment of the upper airway (UA) due to retropositioning of the jaw and tongue base as the mouth is opened and route of breathing changed from nasal to oral. It is postulated that significant narrowing of the OHP occurs with oral breathing even in the awake state. To ascertain the effect of route of breathing on the UA, fast-CT was used to study the UA response to the route of breathing in 30 normal, awake men, with each subject breathing via the nasal and oral routes under the following conditions: end-inspiration during tidal breathing (VTei) and functional residual capacity (FRC). In the velopharyngeal (VP) or retropalatal segment of the UA, minimum (Amin) and mean (Amean) cross-sectional areas (CSA) decreased 49 +/- 11 percent and 16 +/- 6 percent, respectively, with oral compared with nasal breathing at FRC. In the OHP, Amin at FRC increased by 26 +/- 15 percent with oral compared with nasal breathing with no significant change in Amean. Similar changes in CSA of both the VP and OHP were observed at VTei. Genioglossal electromyographic (EMGgg) activity increased from 12 +/- 1 microV breathing nasally to 27 +/- 4 microV breathing orally at FRC. Although the CSA of the VP segment decreased with conversion from nasal to oral breathing, Amin of the OHP segment was unexpectedly observed to increase with oral breathing. The doubling of EMGgg activity with oral breathing suggests that active contraction of the genioglossus may function to increase the patency of the OHP segment during oral breathing in supine, awake, normal subjects.

The effects of transcutaneous electrical stimulation during wakefulness and sleep in patients with obstructive sleep apnea.

Upper airway (UA) collapse in obstructive sleep apnea (OSA) is considered in part to result from the decrease in UA dilator muscle tone that occurs during sleep. We hypothesized that augmentation of UA muscle function by transcutaneous electrical stimulation (TES) might function to enlarge UA size during wakefulness and/or prevent UA collapse during sleep in patients with OSA. Eight male patients with OSA were studied both awake and asleep, with TES administered to the submental region in two patients and to both the submental and subhyoid regions in six patients. Fast-CT scans obtained at FRC and end-inspiration (VTei) demonstrated increased UA size with tidal breathing, p less than or equal to 0.05. The active generation of -10 cm H2O pressure at FRC substantially decreased UA size, p less than or equal to 0.001. However, no changes in UA size were detected at either FRC or VTei with TES applied at 50 and 100% of the maximal tolerated intensity. The collapsibility of the UA in response to the generation of -10 cm H2O pressure was also unchanged by TES. In contrast to the lack of effect of TES on UA size, voluntary protrusion of the tongue increased cross-sectional area (CSA) of the orohypopharyngeal (OHP) segment of the UA, p less than 0.05, and to a lesser extent the CSA of the distal velopharyngeal segment, p = 0.06. When applied during sleep, TES failed to prevent or improve either sleep-disordered breathing or sleep architecture.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast-CT evaluation of the effect of lung volume on upper airway size and function in normal men.

The present study was performed to evaluate the regional changes in pharyngeal cross-sectional area (CSA) that occur with changes in lung volume in normal men. Fast-CT and genioglossal electromyogram (EMGgg) were used to study upper airway (UA) size and dilator muscle activity at TLC, lung volume at end-tidal inspiration (VTei), FRC, and residual volume (RV) in 30 men with a mean age of 46 +/- 3 yr and no significant sleep-disordered breathing, mean AHI = 4 +/- 1 per hour. Compared with values at FRC, minimum CSA (Amin) increased 154 +/- 31% at TLC (p = 0.0001), 19 +/- 10% at VTei (p = 0.03), and there was a trend toward a decrease of 31 +/- 12% at RV (p = 0.07). Similar but smaller changes were observed in mean CSA (Amean), with an increase of 69 +/- 14% at TLC (p = 0.0001), 8 +/- 5% at VTei (p = 0.01), and a decrease of 17 +/- 7% at RV (p = 0.01). Both the velopharyngeal (VP) and orohypopharyngeal (OHP) segments of the UA increased in size with increasing lung volume. Both Amin and Amean of the OHP segment at TLC were larger (55 +/- 19 and 38 +/- 14%, respectively) than the respective measurements in the VP segment. EMGgg activity doubled from 12 +/- 1 microV at FRC to 25 +/- 1 microV at TLC (p = 0.006). There was no change in EMGgg with tidal ventilation or with exhalation to RV. Changes in CSA directly paralleled changes in lung volume in this group of normal awake nonobese men.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast-computed tomography evaluation of age-related changes in upper airway structure and function in normal men.

The reasons for the increase prevalence of snoring and sleep-disordered breathing in elderly adults are not clear. We hypothesized that age-related reductions in upper airway (UA) size, increased UA collapsibility, and/or inadequate compensatory action of the UA dilator muscles were contributory factors. Fast-computed tomography (CT) was used to examine UA size at FRC and atmospheric pressure, as well as its collapsibility and distensibility in response to negative and positive UA pressures actively generated by the subjects at FRC. The electromyographic activity of the genlogiossal muscle group (EMGgg) was recorded to assess UA dilator muscle response. Thirty adult men with normal overnight polysomnography (mean AHI = 4 +/- 1/h) were studied, and three subgroups of 10 subjects each, young (20-39), middle-age (40-59), and old (60-79), were compared. Unexpectedly, minimal UA cross-sectional area (Amin) at FRC and atmospheric pressure was larger in the old group than in the young group (73 +/- 9 versus 49 +/- 7 mm2, p = 0.04). In response to negative UA pressures of -10 and -50 cm H2O, there were no significant age group differences in Amin, indicating that no age-related increase in UA collapsibility was present. Although no significant difference in tonic EMGgg activity at FRC and atmospheric pressure was detected between groups, the old group demonstrated greater EMGgg activity than did the younger age groups in response to negative UA pressure loading (p less than 0.05). This finding indicated increased compensatory UA dilator muscle activity in response to negative pressures in the older subjects.(ABSTRACT TRUNCATED AT 250 WORDS)