Accuracy of oximetry with thermistor (OxiFlow) for diagnosis of obstructive sleep apnea and hypopnea.

OBJECTIVES: To evaluate the diagnostic accuracy for obstructive sleep apnea and hypopnea (OSAH) of the OxiFlow (OF) device which combines oximetry with recording of thermistor airflow. DESIGN & SETTING: Patients scheduled for overnight diagnostic polysomnography (PSG) were studied with OF either simultaneously during laboratory PSG (L-OF, n=86), at home on a separate night (H-OF, n=66), or both (n=55). PATIENTS: 97 patients with suspected OSAH, of whom 40 had OSAH defined as an apnea-hypopnea index (AHI) of more than 15 events per hour of sleep on PSG. INTERVENTIONS: NA. MEASUREMENTS & RESULTS: The automated respiratory disturbance index (RDI) generated by the OF software considerably underestimated the AHI by PSG for both L-OF and H-OF. Altering the parameters for hypopnea identification by the software did not improve this. Visual inspection of the computerized OF tracings added considerable diagnostic information, but a manual count of RDI during visual review overestimated AHI. For the identification of cases vs. non-cases of OSAH, receiver operating characteristic area-under-the-curve statistics ranged from 0.77-0.90 for L-OF and from 0.71-0.77 for H-OF. Combining automated analysis with subsequent visual inspection of OF tracings yielded an overall sensitivity of 86% and specificity of 74% for the diagnosis of OSAH during H-OF recordings. Analysis of potential technician time saved indicated a benefit from the use of OF. CONCLUSIONS: OF has diagnostic utility for the identification of OSAH. However, because of hardware and software limitations, it is unclear whether this device is superior to oximetry alone.

Mechanisms of apnea termination in obstructive sleep apnea. Role of chemoreceptor and mechanoreceptor stimuli.

Previous work from our laboratory has indicated that mechanoreceptor feedback from the respiratory muscles may play an important role in arousal and apnea termination in obstructive sleep apnea (OSA). Other studies have pointed to a prominent role for chemoreceptor stimuli. We postulated that mechanoreceptor stimuli from the respiratory system are the primary determinant of apnea termination, and that chemoreceptor stimuli exert their effect indirectly through stimulation of ventilation and thus proprioceptive feedback. To test this, we measured the diaphragmatic tension-time index (TTdi) during obstructive sleep apneas in seven male subjects with severe untreated OSA. We compared the maximal TTdi values at end-apnea during administration of air, O2, and CO2. We reasoned that if mechanoreceptor stimuli mediate apnea termination, changing the degree of chemoreceptor stimulation during apneas should not alter the level of respiratory effort at end-apnea. O2 administration produced a significant increase in end-apneic arterial oxygen saturation (SaO2) and increased apnea duration. CO2 administration led to an increase in pre- and postapneic end-tidal carbon dioxide pressure (PETCO2), and tended to shorten apneas. However, the mean value for maximal end-apneic TTdi was 0.12 +/- 0.01 (SEM) during room air breathing and was unaltered by O2 (0.12 +/- 0.01) or CO2 (0.11 +/- 0.01) administration. The consistency of end-apneic TTdi values despite the varying chemical drive supports the hypothesis that apnea termination in OSA is mediated by mechanoreceptor feedback from the respiratory system, most likely from the respiratory muscles. The influence of chemoreceptor information may be mediated indirectly through an effect on ventilatory effort.

Influence of weight bearing on the adaptations of rat plantaris to ablation of its synergists.

The present study was designed to determine the contribution of weight bearing to the adaptations of the plantaris (PL) to synergist removal. PL from female rats were exposed to 28 days of a simultaneous condition of synergist ablation and hindlimb suspension. At 28 days, contractile responses and morphological measures were obtained and compared with muscles that either had synergists intact or were weight bearing or a combination of both. Synergist ablation prolonged PL maximum isometric twitch tension (Pt), time to peak tension (12%), and one-half relaxation time (12%); increased Pt (26%), maximum isometric tetanic tension (Po, 44%), fatigue resistance (FI, 42%), and fast fiber cross-sectional area (FT CSA, 20%); and decreased Pt/Po (13%) over nonablation counterparts. Suspension decreased PL Pt (26%), Po (26%), rest length (16%), FT CSA (31%), and slow-twitch fiber (ST) number (24%) but increased FI (75%) over weight-bearing counterparts. PL from weight-bearing animals were heavier than from suspended animals, and the extent of this response was greatest after synergist removal. Whole muscle and ST CSA and ST area contribution were greater only in weight-bearing synergist ablation muscles. Daily weight bearing (4 h) in synergist ablation hindlimb suspension groups caused PL weights and ST expressions to be halfway between 24-h suspension and 24-h weight-bearing groups. Our results suggest that weight bearing is not essential to the induction of several adaptations associated with synergist ablation but is required to cause the large muscle mass and ST expression characteristic of this model.

Physiological responses of rat plantaris motor units to overload induced by surgical removal of its synergists.

1. Rat plantaris muscles were subjected to chronic overload by the surgical removal of the soleus and most of the gastrocnemius muscles. Twelve to 16 wk later whole muscle and motor unit (ventral root dissection technique) contractile properties as well as histochemistry were determined. 2. Motor units were categorized as fast, fatigable (FF), fast, intermediate fatigue-resistant (FI), fast, fatigue-resistant (FR), and slow (S) based on contractile characteristics. Muscle fibers were identified as type I and type II according to myofibrillar ATPase staining. 3. Whole muscles demonstrated increases in wet weight, tetanic force, proportion of type I fibers, and mean cross-sectional areas of both type I and II fibers, as a result of chronic overload. 4. Tetanic tension increased by the same relative magnitude in all motor units whereas twitch tension remained unchanged. A significant change in the proportions of the motor unit types occurred in overloaded muscles, such that the latter contained higher proportions of FF and S units, and lower proportions of FI and FR units, than normal muscles. 5. The fatigue profile of a composite constructed from a summation of motor unit responses revealed that the overloaded plantaris displayed fatigue resistance similar to that of the normal plantaris for a given absolute force output. 6. Glycogen-depleted fibers of hypertrophied single motor units demonstrated uniform myofibrillar ATPase and SDH staining characteristics suggesting that metabolic adaptations among fibers of the same unit were similar after 12-16 wk of overload. 7. The finding that overload caused a uniform increase in the tetanic strength of all motor units, whereas alterations in fatigue resistance varied in degree and direction among unit types, demonstrate that these two properties are not controlled in parallel in this model. The smallest units maintain or even increase their fatigue resistance during the hypertrophic process, whereas high threshold units actually decrease in fatigue resistance.

Contractile and electromyographic characteristics of rat plantaris motor unit types during fatigue in situ.

1. The ventral root dissection technique was used to obtain contractile and electromyogram (e.m.g.) characteristics of ninety-five plantaris motor units in situ in pentobarbitone-anaesthetized rats (n = 20). 2. Motor units demonstrated a wide spectrum of sizes, contractile speeds, and fatigue indices, and were categorized in the same manner as cat hind-limb motor units. Fast-fatigable (f.f.) and fast-intermediate fatigue resistant (f.i.) motor units constituted 20.2 and 25.5% of the motor unit population but together generated over 75% of the cumulative tetanic force. Fast-fatigue resistant (f.r.) and slow motor units composed 43.6 and 10.6% of the population while producing less than 25% of the aggregate tetanic force. 3. Only f.f. and a portion of f.i. motor units demonstrated extensive e.m.g. amplitude reductions during a standard fatigue test. Mean percentage e.m.g. decrease (from the first spike of the first burst to the last spike of the last burst) was 74.0 +/- 27.7% for f.f. units and 28.3 +/- 31.0% (mean +/- S.D.) for f.i. motor units. Relationships between percentage e.m.g. decline and motor unit size (tetanic force) showed significant (P less than 0.01) positive correlations in f.f. (r = 0.71) and f.i. (r = 0.69) motor units. 4. Backward extrapolation of the time course of the force-e.m.g. relationship during the fatigue test revealed that declines in e.m.g. may explain 15, 21 and 66% of the force losses in f.r., f.i. and f.f. motor units. Slow motor units were fatigue resistant and demonstrated a mean e.m.g. decline of 4.3 +/- 6.2%. 5. Indirectly stimulated whole muscle was more fatigable than a composite constructed from motor unit data because of more severe e.m.g. amplitude reductions in the former. 6. The motor unit mechanical and electrical responses during the fatigue test do not summate linearly during whole muscle contractile activity. This is most likely due to the presence, during whole muscle activity, of metabolic changes during the fatigue regimen which influence neuromuscular propagation of excitation, which are not as severe during single motor unit activity.

The properties of skeletal muscle.

The authors review the musculoskeletal system and the controversy that surrounds methods for improving and strengthening it. Disorders brought on by over utilization, deficient working habits, lack of appropriate maintenance care and intercurrent stress and fatigue from repetitious daily tasks and poor sleeping habits are recognized and discussed. Also discussed are muscle structure and its relation to the contractive state, muscle energy requirements, motor control, source of muscle strength and factors modulating it, training adaptations in skeletal muscle, methods of strength training, erogenic aids including anabolic steroids and electrical stimulation and the pathologic states in muscles.