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Biomedical subjects

A R Schwartz

Publications and source records attributed to A R Schwartz.

16 recordsLinked to original sources
PubMed1992

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

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

Humans↗
PubMed1991

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

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

Airway Obstruction↗
PubMed1991

Effect of weight loss on upper airway collapsibility in obstructive sleep apnea.

Previous investigators have demonstrated in patients with obstructive sleep apnea that weight reduction results in a decrease in apnea severity. Although the mechanism for this decrease is not clear, we hypothesize that decreases in upper airway collapsibility account for decreases in apnea severity with weight loss. To determine whether weight loss causes decreases in collapsibility, we measured the upper airway critical pressure (Pcrit) before and after a 17.4 +/- 3.4% (mean +/- SD) reduction in body mass index in 13 patients with obstructive sleep apnea. Thirteen weight-stable control subjects matched for age, body mass index, gender (all men), and non-REM disordered breathing rate (DBR) also were studied before and after usual care intervention. During non-REM sleep, maximal inspiratory airflow was measured by varying the level of nasal pressure and Pcrit was determined by the level of nasal pressure below which maximal inspiratory airflow ceased. In the weight loss group, a significant decrease in DBR from 83.3 +/- 31.0 to 32.5 +/- 35.9 episodes/h and in Pcrit from 3.1 +/- 4.2 to -2.4 +/- 4.4 cm H2O (p less than 0.00001) was demonstrated. Moreover, decreases in Pcrit were associated with nearly complete elimination of apnea in each patient whose Pcrit fell below -4 cm H2O. In contrast, no significant change in DBR and a minimal reduction in Pcrit from 5.2 +/- 2.3 to 4.2 +/- 1.8 cm H2O (p = 0.031) was observed in the "usual care" group. We conclude that (1) weight loss is associated with decreases in upper airway collapsibility in obstructive sleep apnea, and that (2) the resolution of sleep apnea depends on the absolute level to which Pcrit falls.

Adult↗
PubMed1989

Effect of positive nasal pressure on upper airway pressure-flow relationships.

To determine the influence of changes in nasal pressure (Pn) on airflow mechanics in the upper airway, we examined the effect of elevations in Pn on upper airway resistance and critical pressure (Pcrit) during stage I/II sleep in six patients with obstructive sleep apnea. When Pn was elevated above a Pcrit, periodic occlusions of the upper airway were eliminated and inspiratory airflow limitation was demonstrated by the finding that inspiratory airflow (VI) became maximal (VImax) and independent of fluctuations in hypopharyngeal pressure (Php) when Php fell below a specific Php (Php'). As Pn was elevated, VI vs. Php demonstrated 1) marked decreases in early and late inspiratory resistances from 75.9 +/- 34.7 and 54.6 +/- 19.0 to 8.0 +/- 1.7 and 7.6 +/- 1.6 cmH2O.l-1.s (P less than 0.05), respectively, and 2) increases in early and late inspiratory Php' to levels that exceeded Pcrit by 3.0 +/- 0.6 and 3.1 +/- 0.7 cmH2O, respectively, at the highest level of Pn applied (P less than 0.01). This latter finding suggests that elevations in Pn result in increases in Pcrit. We suggest that elevations in Pn produce distinct alterations in upper airway resistance and collapsibility, which may influence oppositely the level of airflow through the upper airway during sleep.

Adult↗
PubMed1989

Sleep apnea in the elderly.

Sleep apnea is a common disorder in the elderly and is characterized by recurrent apneas which are associated with periodic oxyhemoglobin desaturations and arousals from sleep. In more severely affected individuals, it may result in marked sleep fragmentation, alterations in daytime function, and increased cardiovascular morbidity and mortality. In milder cases, however, physiologic abnormalities which are recognized may have a questionable impact on morbidity and mortality. Therefore, the decision to treat this disorder rests on accurately assessing the severity of physiologic disturbances in sleep and in breathing, and depends on determining whether daytime function is impaired.

Aged↗
PubMed1988

Induction of upper airway occlusion in sleeping individuals with subatmospheric nasal pressure.

In collapsible biologic conduits, occlusion and cessation of flow occur when upstream pressure falls below a critical pressure (Pcrit). To examine the relationship between Pcrit and the development of upper airway occlusion, we examined the relationship between maximal inspiratory airflow and nasal pressure in seven normal subjects during sleep. At varying levels of subatmospheric pressure applied to a nasal mask during non-rapid-eye-movement (NREM) sleep, maximal inspiratory airflow decreased in proportion to the level of nasal pressure. When nasal pressure fell below a Pcrit, subjects demonstrated upper airway occlusions terminated by arousals. In these normal subjects, the upper airway Pcrit was found to be -13.3 +/- 3.2 (SD) cmH2O. In four subjects who sustained sleep while nasal pressure remained below the Pcrit, recurrent occlusive apneas were demonstrated. The relationship between maximal inspiratory airflow and nasal pressure in each subject was fit by linear regression and demonstrated upper airway Pcrit at the zero-flow intercept that were not significantly different from those observed experimentally. These data demonstrate that the normal human upper airway during sleep is characterized by a negative Pcrit and that occlusion may be induced when nasal pressure is decreased below this Pcrit.

Adult↗
PubMed1988

Upper airway pressure-flow relationships in obstructive sleep apnea.

We examined the pressure-flow relationships in patients with obstructive sleep apnea utilizing the concepts of a Starling resistor. In six patients with obstructive sleep apnea, we applied incremental levels of positive pressure through a nasal mask during non-rapid-eye-movement sleep. A positive critical opening pressure (Pcrit) of 3.3 +/- 3.3 (SD) cmH2O was demonstrated. As nasal pressure was raised above Pcrit, inspiratory airflow increased in proportion to the level of positive pressure applied until apneas were abolished (P less than 0.01). However, at pressures greater than Pcrit, esophageal pressures either did not correlate or correlated inversely with inspiratory airflow provided that esophageal pressure was less than Pcrit. When pressure was applied to a full face mask, inspiratory airflow did not occur and Pcrit could not be obtained at pressures well above Pcrit demonstrated with the nasal mask. These results are consistent with the view that the upper airway functions as a Starling resistor with a collapsible segment in the oropharynx. These findings offer a unifying construct for the association of sleep apnea, periodic hypopnea, and snoring.

Adult↗
PubMed1986

The effect of chronic nocturnal oxygen administration upon sleep apnea.

Administration of nocturnal oxygen for 1 night to patients with obstructive sleep apnea (OSA) causes a moderate reduction in apnea frequency without improving hypersomnolence. Therefore, we administered oxygen chronically to patients with OSA to determine: whether apnea frequency would be further reduced, whether the effect of oxygen upon apnea frequency is correlated with an increased ventilatory response to hypoxia and hypercapnia, and whether hypersomnolence improves with more prolonged oxygen administration. In a single-blinded, nonrandomized trial, we compared the effects of 1 month of oxygen (4 L/min by nasal cannula) with room air (4 L/min by nasal cannula) placebo during sleep in 7 men and 1 woman with obstructive sleep apnea. During non-REM sleep, acute oxygen administration elevated the average low oxy-hemoglobin saturation during apneic events and decreased apnea frequency. These acute effects persisted during chronic oxygen administration but reverted to the preoxygen effects immediately upon discontinuing oxygen. One month of oxygen did not affect the waking ventilatory response to hypoxia or hypercapnia; however, waking PaCO2 increased from 40 +/- 1 mm Hg (mean +/- SE) after placebo to 43 +/- 1 mm Hg after oxygen (p less than 0.01). Neither subjective nor objective hypersomnolence consistently improved after 1 month of oxygen administration. We conclude that: first, oxygen has no effect upon apnea frequency beyond the period of administration, and the reduction of apnea frequency is not correlated with an increased sensitivity to chemical ventilatory stimuli. The reduced apnea frequency may be related to an increased PaCO2 stimulating ventilation during sleep.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1977

The cephalosporins.

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Bacterial Infections↗
PubMed1976

A modified leukocyte nitroblue tetrazolium test in acute bacterial infection.

The increased ability to leukocytes to reduce nitroblue tetrazolium (NBT) has been used to detect the presence of systemic bacterial infection. This test has been utilized to evaluate infections and leukocyte dysfunction in children, but has not been extensively applied to traumatized patients or infected volunteers. Moreover, the technic as originally described presented methodologic difficulties. In this study of 889 such patients, a modified NBT test provided excellent differentiation of 63 systemic bacterial infections (NBT score greater than or equal to 10%) from non-infectious fevers, local enteric diseases, and certain viral and plasmodial infections (NBT score less than or equal to 9%). Splenectomy was associated with a transient false-positive score and clinical typhoid fever with a false-negative response

Acute Disease↗