Relationships between abdominal and diaphragmatic volume displacements

We investigated the relationship between the volumes displaced by the diaphragm and the abdominal wall during spontaneous breathing in supine anesthetized dogs. Diaphragmatic volume displacement (Vdi) was calculated from measurements taken from anteroposterior fluoroscopic images employing a previously described geometric model. The volume displacement of the abdominal wall (Vabd) was measured with a calibrated Respitrace. Shortening of single diaphragm muscle bundles in costal and crural regions was measured as the distance between radiopaque beads sutured to the peritoneal surface of the muscle. We found that Vdi always exceeded Vabd, but Vabd/Vdi was larger in animals in which the abdominal wall was more compliant. In this preparation, Vdi is better correlated with costal than with crural shortening. Vabd did not correlate with either costal or crural shortening. We infer that the difference between Vdi and Vabd reflects the volume displacement of the lower rib cage caused by diaphragm contraction. This volume difference was tightly correlated with costal shortening. We conclude from these data that coupling between Vdi and Vabd is influenced by the relative compliances of the chest wall and abdomen. Shortening of regions of the diaphragm may have variable relationships to the measured volume displacement, but costal shortening is intimately related to expansion of the lower rib cage.

A model approach to assess diaphragmatic volume displacement

Diaphragmatic volume displacement (Vdi) is calculated from two models using measurements obtained from anteroposterior fluoroscopic images of supine anesthetized dogs. In model 1, diaphragmatic descent was treated as if it were a "piston in a cylinder." In contrast, model 2 incorporated thoracic configuration as well as inspiratory changes in rib cage diameter and diaphragm shape. In one dog, a computerized tomography reconstruction of Vdi was compared with Vdi calculated using the models. Vdi calculated from model 2 lay within 11% of the computerized tomographic value, whereas Vdi based on model 1 was 30% larger. In seven animals, radiopaque markers were sewn to the right costal diaphragm. Digitized fluoroscopic images were used to measure intermarker distance, an index of muscle shortening. For four tidal breaths per dog, in model 2 Vdi averaged 49 +/- 18% of tidal volume and was weakly correlated with costal diaphragm muscle shortening (R = 0.74). It is concluded that Vdi can be estimated from linear dimensions in the coronal plane, provided that inspiratory changes in rib cage diameter and diaphragmatic shape change are taken into account.

Videofluoroscopic assessment of muscle fiber shortening in the in situ canine diaphragm

We tested the hypothesis that dynamic shortening of the costal diaphragm can be accurately estimated from measurements of the radiographic width of the zone of apposition (WZapp) by studying seven supine anesthetized dogs. Both muscle fiber length, represented by the distance between implanted radiopaque markers, and WZapp were measured from digitized recordings of fluoroscopic images utilizing interactive computer software. The WZapp was highly correlated with the length of costal fibers during active respiration in all animals (mean R2 = 0.94). The accuracy in the prediction of fiber length and shortening during breathing is enhanced by inclusion of additional variables describing the displacement of the abdominal wall and the resting geometric orientation of the fibers. We conclude that dynamic fluoroscopic measurement of WZapp is a valuable technique for estimating dynamic diaphragm fiber length and shortening. Depending on the experimental circumstances, WZapp may be a more easily acquired indicator of diaphragm shortening than other variables that have been previously utilized. As such, it may provide a suitable approach to assess active shortening of the diaphragm in humans.

Effect of lower rib cage expansion and diaphragm shortening on the zone of apposition

The relationship among diaphragm length (LD), the width of the zone of apposition (WZapp), and transverse chest diameter (Drc) was developed from model equations and statistical analysis. We present a theoretical model of diaphragm motion that predicts that the decrease in WZapp during inspiration is the result not only of shortening of the diaphragm muscle but also of expansion of the lower rib cage. To test our model, static lengths of costal LD, WZapp, and Drc were measured in 15 normal volunteers using posteroanterior chest X-ray films taken at four or five lung volumes spanning the vital capacity. We found a strong correlation between WZapp and LD: WZapp = 0.95 LD - 15.2 (R2 = 0.81). Expressing WZapp as a combined function of LD and Drc significantly reduced the unexplained variance in WZapp: WZapp = 0.96 LD - 0.47 Drc - 2.18 (R2 = 0.95). The coefficients for LD and Drc derived statistically are close to those predicted from our theoretical model. Repeating the analysis with LD as the dependent variable, we obtained similar results: LD = 0.85 WZapp + 17.1 (R2 = 0.81) and LD = 0.98 WZapp + 0.46 Drc + 3.48 (R2 = 0.94). We conclude that shortening of WZapp is dependent on both diaphragm shortening and rib cage expansion and that roentgenographic measurements of Drc and WZapp can be used to predict diaphragm length and length change.

Driving simulator performance in patients with sleep apnea

Although previous studies have shown that patients with obstructive sleep apnea have a higher automobile crash rate than normal subjects, objective measurements of driving performance in patients with sleep apnea have not been reported. Therefore, we compared the driving performance of subjects with untreated, severe sleep apnea to that of control subjects on two driving simulators. Using a simulator with road films, six subjects with untreated, severe apnea performed worse than did a control group of seven normal subjects on both highway and city/rural driving (p less than 0.05). Using a personal computer program simulating a monotonous highway drive, 12 subjects with untreated sleep apnea performed worse than 12 control subjects. The patients with apnea hit a greater number of road obstacles during their 30-minute simulated drive than did the control subjects (44 +/- 52 in patients with apnea versus 9 +/- 7 in control subjects, p less than 0.05). Six patients with apnea hit fewer road obstacles after treatment with nasal continuous positive airway pressure (CPAP) than before treatment (29 +/- 19 before CPAP versus 13 +/- 8 after CPAP, p less than 0.05). We conclude that: (1) driving simulator performance of untreated subjects with severe obstructive sleep apnea is worse than that of control subjects; (2) driving simulator performance of subjects treated with nasal CPAP improves.

Changes in compartmental ventilation in association with eye movements during REM sleep

The effect of phasic eye movement activity on ventilation during rapid-eye-movement (REM) sleep was studied in seven healthy young adults by use of the respiratory inductive plethysmograph. Mean ventilation (VE) and ventilatory components during REM sleep were not significantly different from that seen in either stages 1-2 or 3-4 sleep. The percent of rib cage contribution to ventilation in REM sleep, 29.3 +/- 5.1%, was reduced compared with 54.4 +/- 5.8% in stage 1-2 and 52.2 +/- 4.3% in stage 3-4 sleep (P less than 0.005). When one separated breaths by the degree of associated phasic eye movement activity, it became apparent that breathing during REM sleep is very heterogeneous. Increasing eye movement activity was associated with inhibition of ventilation with a reduction in VE from 5.1 +/- 0.3 to 3.8 +/- 0.3 l/min. Tidal volume and frequency both fell, whereas inspiratory duration was unchanged. Compartmental ventilation was also affected, with the fall in the rib cage contribution from 37.8 +/- 6.4 to 15.3 +/- 5.6%. Chest wall and abdominal movement became more asynchronous as phasic-eye-movement activity increased and frank paradoxical breathing was seen.

Spectral analysis of ventilation in elderly subjects awake and asleep

We studied the periodicities of ventilation in elderly subjects using digital comb filtering. Two groups of subjects were studied, those with and without sleep apnea. Measurements were made in wakefulness, stage 1-2 sleep, and where possible in stage 3-4 sleep. For each of the digital filters we calculated the average power of the oscillatory output. To compare subject groups we first specifically determined the average power in the filter with the maximum output. The mean of this measurement was greater in elderly subjects with apnea compared with those without apnea, both during wakefulness and stage 1-2 sleep. In both groups of subjects the cycle time of the major ventilatory oscillations was on the order of 40-60 s. There was no difference in this cycle time between the two groups of subjects in wakefulness or stage 1-2 sleep. Thus, whereas similar oscillatory processes occur in subjects with and without apnea, it is the magnitude of the oscillation that differs between the two groups. These conclusions are supported by analysis of the output of individual filters of the digital comb filter. In both groups, stage 1-2 sleep produced significantly increased oscillations in ventilation. Both in wakefulness and stage 1-2 sleep, significantly greater periodicities occurred in the apneic compared with the nonapneic group. In the few subjects who had sufficient data in stage 3-4 sleep for spectral analysis, ventilatory oscillations were virtually absent in this state. Our data suggest that subjects who develop apnea during sleep have an increased propensity for periodic breathing even while awake.

The effects of three methods of orthodontic appliance therapy on some commonly used cephalometric angular variables

This investigation was undertaken to study the effects of the Andresen activator functional appliance therapy, Begg therapy, and cervically directed extraoral forces upon several commonly used cephalometric angular variables, with particular reference to the relationship between the maxillary plane (palatal plane) and anterior cranial base as represented by SN line. The material consisted of 107 cases taken from the files of patients who had attended the Orthodontic Department, Eastman Dental Hospital, London. Ninety of the cases had received orthodontic treatment. For each case pretreatment, posttreatment, and postretention radiographs were traced and angular measurements made by means of a Lysta-Dent digitizer linked to an on-line computer. Descriptive statistics and one-sample and two-sample Student's t tests were performed. None of the treatment methods under investigation had a clinically significant effect upon the maxillary plane. An increase in the inclination of the mandibular plane was a feature of Begg and headgear therapies but not of Andresen therapy. Any increase observed was of a temporary nature. While no change in SNA occurred with Andresen therapy, Begg and headgear therapies produced a permanent reduction in the variable. A small reduction was also produced in SNB by Begg and headgear therapies. The behavior of SNB following Andresen therapy was not significantly different from that in the group of untreated subjects. Each appliance method produced a permanent reduction in ANB; however, a similar reduction was also demonstrated in the control group.

Clinical significance of sleep apnea in the elderly

The generally accepted polysomnographic criteria for diagnosis of sleep apnea is exceeded by elderly subjects with such frequency that the validity of its application to this age group has been questioned. We studied a group of elderly volunteers with nocturnal polysomnography and partitioned them into 2 groups based upon an apnea index of greater than or less than 5 per hour. The results of a protocol evaluating the presence of potential complications of sleep apnea including cardiac arrhythmias, systemic hypertension, cor pulmonale, daytime sleepiness, and cognitive impairment were compared for the 2 groups. No excess incidence of cardiovascular complications was found. Although an increase in daytime sleep tendency was shown for the group with more frequent apneas, no appreciable deficits in cognitive performance were demonstrated. Although apnea during sleep in the elderly may be associated with an increase in daytime sleepiness, it may not necessarily result in other physiologic or neuropsychologic consequences. Therapeutic intervention for these abnormalities should be carefully considered prior to the institution of treatment in light of these observations.

Tooth resorption associated with the eruption of maxillary canines

Six cases of root resorption of lateral incisors, associated with buccally displaced maxillary canines are presented. In each case, the clinical appearance is described followed by a discussion drawing attention to the possible common features and the importance of a detailed radiographic investigation.

Randomized comparative trial of a ward discussion group

A randomized controlled study of 38 catchment unit psychiatric in-patients in a discussion group showed no significant additional benefit compared with 36 in-patients in an activity group. Symptom change scored by three rating groups agreed closely, average r = +0.64. Patients treated with ECT showed 2.6 times as much reduction in morbidity as those not so treated, but there was still no appreciable difference between discussion and activity groups when this was allowed for. Other treatment factors and the Hawthorne effect appeared to obscure any effect due to group therapy.

Evaluation of the IMI portable oxygen analyser

An evaluation of the IMI oxygen analyser is described. The accuracy was found to be adequate for clinical purposes though it was considered that this could be improved if the meter was read with greater discrimination than the existing calibrations and if the zero could be adjusted.

ON SOME LIMITING FACTORS IN THE USE OF SATURATED PETROLEUM OILS AS INSECTICIDES

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