A national Health and Work Strategy: a search for evidence

BACKGROUND

The Health and Safety Executive's new Health and Work Strategy is based on an up-to-date assessment of workplace health priorities. Rather than replicating traditional prioritization approaches, a broader assessment of health and work priorities was carried out using a range of stakeholders.

AIMS

To develop a set of health priorities for further research and intervention activity.

METHODS

Four exercises were carried out, including internal prioritization, two external web-hosted questionnaire studies of younger workers and occupational health professionals, focus groups and tele-depth interviews with workplace health and safety professionals.

RESULTS

The highest rated internal priorities (weighted priority scores) were identified as mesothelioma (70), lung cancer (69.25), chronic obstructive pulmonary disease (COPD; 69), musculoskeletal disorders (MSDs; 66.25), hearing loss (65.75), stress (65.5), asthma (64.5) and hand-arm vibration syndrome (61.5). Using the three highest ranked criteria developed by occupational health professionals ((i) the preventability of the condition, (ii) the impact of the condition and (iii) the number of workers affected), mesothelioma, lung cancer, COPD, MSDs, hearing loss, stress and asthma were identified as the top seven priorities. Generic issues identified included ageing and work, obesity, newer technologies, and ethnicity and cultures of workforces. Apprentices identified stress, depression, anxiety, musculoskeletal and respiratory disorders, fatigue and workload as important workplace health considerations.

CONCLUSIONS

This process identified a number of expected and new areas of health research interest. We believe the findings reflect the real world requirements of work as assessed by occupational health and safety practitioners and workers.

Species-Dependent Inhibition of Platelet Aggregation by Adenosine and Dipyridamole: Paradoxical Potentiation in the Rat

Platelets of cats, rabbits, guinea pigs, rats and human subjects were aggregated with adenosine diphosphate after having been in contact with adenosine or dipyridamole for 5 to 60 min. The species profiles of both agents were the same. Both inhibited aggregation of human and rabbit platelets and the degree of inhibition increased with the time of contact. Neither inhibited aggregation of cat or guinea-pig platelets and both potentiated the rate and extent of aggregation of rat platelets: the degree of potentiation increased with the time of contact. Some reports on the related effects of adenosine and dipyridamole are reviewed and it is suggested that the effects of dipyridamole might be due to an affinity for adenosine receptors.

Correction to: Prediction of unfavorable outcomes in cryptococcal meningitis: results of the multicenter infectious Diseases International Research Initiative (ID-IRI) cryptococcal meningitis study

In the original version of this article, Mustafa Sunbul was not included in the list of authors for this article. The name has been added accordingly.

The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for rapid bacterial identification in patients with smear-positive bacterial meningitis

OBJECTIVES

To assess the potential of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) in rapid identification of bacteria from smear-positive cerebrospinal fluid (CSF) in a cohort of patients with meningitis.

METHODS

Single-centre observational study, including adults and children with community-acquired or postneurosurgical bacterial meningitis. Meningitis was defined using established criteria. Samples of CSF that had a positive CSF Gram stain were directly examined by MALDI-TOF-MS. Identification was considered accurate when identical to the CSF culture or PCR results (species and genus level). Laboratory workers performing the MALDI-TOF-MS and interpreting its results were blinded to the direct smear results, except for the fact that it was positive. MALDI-TOF-MS results were not conveyed to clinicians.

RESULTS

MALDI-TOF-MS was tested on 44 CSF samples; ten samples were obtained from patients with community-acquired meningitis, and 34 samples were from patients with postneurosurgical meningitis. The assay identified bacteria correctly in 17/21 of the samples with Gram-negative rods observed on the direct smear, all obtained from patients who had undergone neurosurgery, (sensitivity 81%, 95% CI 64.2%-97.7%). In the postneurosurgical group, Gram-positive cocci were identified correctly in only 1/11 (9.1%) of the samples, and Candida species were not identified in two samples. Among patients with community-acquired meningitis, the assay did not identify Streptococcus pneumoniae in eight of eight samples, Neisseria meningitidis in one sample (1/1), and Streptococcus agalactiae in one sample (1/1).

CONCLUSIONS

We found MALDI-TOF-MS to be useful in the rapid identification of Gram-negative rods directly from smear-positive CSF samples, but not of Gram-positive bacteria.

Role of parasympathetic (vagal) cardiac control in elevated heart rates of smokers

Smokers may develop chronic increases in cardiac rate and alterations in cardiovascular control. If the increased mean heart rate (HR) in cigarette smokers is due in part to a deficit in vagal cardiac rate control, this should be reflected in a decreased amplitude of respiratory sinus arrhythmia (RSA). To test this hypothesis we studied 36 smokers and 36 non-smokers, matched for age, race, gender and blood pressure. All subjects were studied in the supine and seated positions. Mean heart rate was determined from the ECG during 30 s of quiet breathing; RSA was determined for 10 consecutive deep (>50% vital capacity) slow (5-7/min) breaths. Mean HRs in smokers were significantly higher than in non-smokers, but the increases in mean HRs evoked by a shift from the supine to seated position were lower in smokers than in non-smokers, suggesting that chronic tobacco use may alter the relative contributions of sympathetic and parasympathetic control of cardiac rate. Because neither the RSAs nor the position-dependent increase in RSA were different between smokers and non-smokers, we conclude that the elevated mean HRs in smokers were not the result of decreased respiratory or vasomotor modulation of vagal cardiac control, but instead were the result primarily of sympathetic stimulation.

Swallowing outcomes following laryngectomy and pharyngolaryngectomy

OBJECTIVES

To determine the incidence of dysphagia (defined as the inability to manage a diet of normal consistencies) at hospital discharge and beyond 1 year postsurgery and examine the impact of persistent dysphagia on levels of disability, handicap, and well-being in patients.

DESIGN

Retrospective review and patient contact.

SETTING

Adult acute care tertiary hospital.

PATIENTS

The study group, consecutively sampled from January 1993 to December 1997, comprised 55 patients who underwent total laryngectomy and 37 patients who underwent pharyngolaryngectomy with free jejunal reconstruction. Follow-up with 36 of 55 laryngectomy and 14 of 37 pharyngolaryngectomy patients was conducted 1 to 6 years postsurgery.

MAIN OUTCOME MEASURES

Number of days until the resumption of oral intake; swallowing complications prior to and following discharge; types of diets managed at discharge and follow-up; and ratings of disability, handicap, and distress levels related to swallowing.

RESULTS

Fifty four (98%) of the laryngectomy and 37 (100%) of the pharyngolaryngectomy patients experienced dysphagia at discharge. By approximately 3 years postsurgery, 21 (58%) of the laryngectomy and 7 (50%) of the pharyngolaryngectomy patients managed a normal diet. Pharyngolaryngectomy patients experienced increased duration of nasogastric feeding, time to resume oral intake, and incidence of early complications affecting swallowing. Patients experiencing long-term dysphagia identified significantly increased levels of disability, handicap, and distress. Patients without dysphagia also experienced slight levels of handicap and distress resulting from taste changes and increased durations required to complete meals of normal consistency.

CONCLUSIONS

The true incidence of patients experiencing a compromise in swallowing following surgery has been underestimated. The significant impact of impaired swallowing on a patient's level of perceived disability, handicap, and distress highlights the importance of providing optimal management of this negative consequence of surgery to maximize the patient's quality of life.

Reengineering granulocyte colony-stimulating factor for enhanced stability

Granulocyte colony-stimulating factor is a long-chain cytokine that has both biological and therapeutic applications. It is involved in the production and maturation of neutrophilic progenitor cells and neutrophils and is administered to stimulate the production of white blood cells to reduce the risk of serious infection in immunocompromised patients. We have reengineered granulocyte colony-stimulating factor to improve the thermodynamic stability of the protein, focusing on enhancing the alpha-helical propensity of residues in the antiparallel 4-helix bundle of the protein. These redesigns resulted in proteins with substantially enhanced stability while retaining wild-type levels of biological activity, measured as the ability of the reengineered proteins to stimulate the proliferation of murine myeloid cells transfected with the granulocyte colony-stimulating factor receptor.

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.

Dramatic structural and thermodynamic consequences of repacking a protein's hydrophobic core

BACKGROUND

Rop is an RNA binding, dimeric, four-helix bundle protein with a well-defined, regular hydrophobic core ideally suited for redesign studies. A family of Rop variants in which the hydrophobic core was systematically redesigned has previously been created and characterized.

RESULTS

We present a structural and thermodynamic analysis of Ala2Ile2-6, a variant of Rop with an extensively redesigned hydrophobic core. The structure of Ala2Ile2-6 reveals a completely new fold formed by a conformational "flip" of the two protomers around the dimeric interface. The free-energy profile of Ala2Ile2-6 is also very different from that of wild-type Rop. Ala2Ile2-6 has a higher melting temperature than Rop, but undergoes a slightly smaller free-energy change on unfolding.

CONCLUSIONS

The structure of Ala2Ile2-6, along with molecular modeling results, demonstrate the importance of tight packing of core residues and the adoption of favorable core side chain rotamer values in determining helix-helix interactions in the four-helix bundle fold. Structural disorder at the N and C termini of Ala2Ile2-6 provides a basis for the large differences in the enthalpy and entropy of Ala2Ile2-6 folding compared with wildtype Rop.

Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.

Ventilatory responses to hypercapnia and hypoxia following chronic hypercapnia in the rat

This study investigated the effects of an 18 week exposure to 10% CO(2) in air on minute ventilation (V(E)), breathing pattern and the chemoresponiveness of rats to hypoxic and hyperoxic stimuli. We found that V(E) remained elevated over the 18 weeks. Nonetheless, the breathing pattern changed significantly. Tidal volume increased and the durations of inspiration and the total cycle decreased. After the sustained hypercapnia the mean Pa(CO(2)) was 72.0+/-5.1 (S. D.) mmHg. Every 6 weeks the chemoresponiveness of the CO(2)-exposed rats was tested by an acute exposure sequentially to room air, then a 6% O(2), 10% CO(2) and 84% N(2) gas mixture, and finally a 90% O(2) in 10% CO(2) mixture. On either room air or the hyperoxic-hypercapnic mixture V(E) fell to its pre-hypercapnic level. On the hypoxic-hypercapnic mixture V(E) increased significantly. These results demonstrate that the initial stimulating effect of 10% CO(2) on V(E) persisted for the entire 18 weeks without altering hypoxic or hyperoxic ventilatory responses.

Abdominal motor unit activity during respiratory and nonrespiratory tasks

Abdominal muscles serve multiple roles, but the functional organization of their motoneurons remains unclear. To gain insight, we recorded single motor unit potentials from the internal oblique (IO) and transversus abdominis (TA) muscles of three standing subjects during quiet breathing, a leg lift, and an expiratory threshold load. Inspiratory airflow, recorded from a pneumotachometer, provided tidal volumes and respiratory cycle timing. Fine wires, implanted under ultrasonic imaging, detected single motor unit potentials that were visually distinguished by their spike morphology. From the number of spikes, firing profiles, times of occurrence in the respiratory cycle, and their onset, instantaneous, mean, and peak firing frequencies we deduced that 1) breathing patterns varied across tasks, 2) different motor units were recruited for each task with essentially no overlap, 3) their firing displayed prominent expiratory activity during each task, and 4) the recruitment levels and discharge patterns of IO and TA were different. We conclude that the IO and TA motor pools receive a strong central respiratory drive, yet each pool receives its own distinct, task-dependent synaptic input.

Centralization of low back pain and perceived functional outcome

McKenzie's methods for evaluating and treating low back pain are used often but studied little. When using the McKenzie system, it is important to observe signs of symptom movement to a central location (centralization). This study investigated the relationships between centralization of low back pain and/or radiculopathy and the subjects' rating of functional outcome. Thirty-six subjects with low back pain volunteered to participate and were evaluated and treated by six researchers. Subjects were tested initially and again 14 days after initiation of treatment using the Oswestry Low Back Pain Disability Questionnaire and the Performance Assessment and Capacity Testing Spinal Function Sort (SFS). Symptoms were monitored for the occurrence of "complete centralization." Of the 36 subjects, 25 showed complete centralization within 14 days. The SFS score changes were significantly higher for subjects who completely centralized (p = 0.015). The results supported the hypothesis that subjects who centralize will have improved functional outcome and, thus, quality of life. However, shorter time to occurrence of complete centralization does not necessarily correlate with improved outcome.

Patterns of jaw muscle activity during voluntary chewing

Mastication is controlled by central rhythm and burst generators, but whether this control is similar under automatic and voluntary chewing is not clear. Our first aim was to determine whether increased chewing frequency led to a proportional decrease in both the burst duration (the time of muscle activity) and the interburst interval (time of inactivity) of each muscle or to a minimal decrease in the burst duration and a substantial decrease in the interburst interval. Our second aim was to determine whether these two manifestations of control differed between the opening and closing muscles. Electromyograms from digastric, medial pterygoid, masseter and anterior temporalis muscles were obtained during gum chewing by five subjects at four frequencies. A nearly fourfold decrease in total cycle duration (TCD) with increased chewing frequencies was accompanied by minimal changes in burst duration in the digastric muscle but proportional changes in the jaw closing muscles. The onset latency of the digastric muscle as a percentage of TCD decreased and became negative (i.e. occurred before opening started) as the TCD decreased. The onset latencies of the jaw closing muscles remained roughly 10-20% of the TCD for the three lower chewing frequencies. Control of the opening muscle appears to differ from control of the closing muscles.

Efficacy of school reentry programs

Evaluation of school reentry programs are rarely reported, and statements of the value of reentry programs are usually based on anecdotal information. No known reports of empiric data support claims of positive benefit for burned children. This article reports a multifaceted effort to evaluate the effectiveness of one reentry program involving three approaches: (1) questionnaire answered by the school contact person after reentry program, (2) interviews with a random sample of patients (n = 58) and parents (n = 44) 1 to 5 years after burn, and (3) assessment of patients' behavior problems by teachers on a standardized behavior checklist comparing 10 patients who had a school reentry program involving videos to introduce them to their classmates with 10 patients who were matched for age, sex, and total body surface area burned and had no reentry program beyond phone contact. Results indicate that school reentry programs are popular with teachers and parents. This pilot effort involving empiric data failed to demonstrate a positive effect on the adjustment of the child.

School reentry for the patient with burn injuries: video and/or on-site intervention

The student who has sustained a burn injury, the school's personnel, and the student's peer groups benefit from a school reentry program. Concrete, factual information about the burn injury assists to open lines of communication between the returning student and peers. Also, the concerns and expectations of school personnel are addressed.

Depression of an inhibitory reflex, the masseteric silent period, in recovering alcoholics

Because inhibitory deficits may contribute to motor incoordination of alcoholics, we proposed that the duration of the masseteric silent period (SP), an inhibitory reflex, might be shorter in alcoholics (ALs) than in nonalcoholics (NAs). To test this hypothesis, we measured the SP in a racially mixed group of 12 ALs and 12 NAs matched for age (31-49 years) and sex. All subjects were normotensive, had full dentition, and reported no major medical problems. Sensory and motor conduction velocities of the anterior tibialis, ulnar, and medial nerves were measured for each subject, and were not different in ALs and NAs. Jaw jerk and SP were evoked by tapping the chin manually with a rubber hammer containing a circuit to trigger the oscilloscope display of the masseter EMGs. Averaged mean latencies and durations of the SPs were not significantly different between the right and left masseters. SP latencies were significantly (0.7 msec) shorter in ALs than NAs (p < 0.01). The mean SP duration for ALs (13.9 +/- 1.6 msec) was also significantly shorter than that of the NAs (24.4 +/- 2.4 msec; p < 0.001). Results support the hypothesis that chronic alcoholism may interfere with inhibitory mechanisms in the CNS.

Hyperbaric oxygenation increases arousal and breathing movements in fetal lambs

Oxygenation produced by distending the lungs with 100% O2 increases the occurrence of arousal and fetal breathing movements (FBM), particularly during non-rapid-eye-movement (NREM) sleep, in fetal sheep of > or = 135 days of gestation. We studied the breathing and behavioral responses to a rise in arterial PO2 (PaO2) without lung distension in fetuses between 128 and 132 days of gestation. Twelve fetuses were chronically instrumented to record FBM, behavioral state, blood pressure, arterial blood gas tensions, and pH. Fetal PaO2 was raised by having the ewe breathe 100% O2 at 3 atmosphere absolute pressure spontaneously (group 1, n = 5, 129 +/- 1 days of gestation) or with mechanical ventilation to control fetal arterial PCO2 (group 2, n = 7, 131 +/- 1 days of gestation). Hyperbaric oxygenation raised fetal PaO2 by 20 Torr in both groups. During hyperbaric oxygenation, the occurrence of arousal increased severalfold in both groups. The occurrence of FBM increased during arousal in both groups, during rapid-eye-movement sleep in group 1, and during NREM sleep in group 2. The timing of diaphragmatic activity during arousal and the variability of diaphragmatic activity during NREM sleep were different than those in rapid-eye-movement sleep. We conclude that oxygenation without lung distension increases the occurrence of arousal and of FBM, principally during arousal and NREM sleep, in fetuses of < or = 135 days of gestation.

Control of breathing patterns and abdominal muscles during graded loads and tilt

Tilting from supine to upright purportedly enhances both segmental and pulmonary proprioceptive feedback, whereas an expiratory threshold load (ETL) preferentially enhances pulmonary feedback. To test this we studied 13 adults when supine and 60 degrees and 90 degrees head up. We measured tidal volume, inspiratory duration (TI), and expiratory duration (TE) from flow; estimated end-expiratory lung volume from inspiratory capacity; and determined burst amplitudes and durations from abdominal electromyograms (EMGs). ETLs were incremented from 0 (control) to 25 cmH2O in 5-cmH2O steps. Tidal volume was significantly increased by ETL but was unaffected by body position. Every load prolonged TE, whereas TI remained unchanged. When subjects were supine, abdominal EMGs were silent but became tonically active when subjects were upright. During ETL, abdominal activity became rhythmical and phase locked to expiration. Bursts amplitudes were enhanced with each increment in ETL, but burst durations did not change even though TE was prolonged. The altered breathing pattern and active expiration augmented inspiratory flow and decreased end-tidal PCO2. Responses were greatest when subjects were 90 degrees head up. The load-related increments in abdominal recruitment, with no change in burst durations, fit the concept of two central pattern generators: one controlling pattern and the other controlling rhythm of the central respiratory drive.

Lysine requirement of broiler chicks as affected by protein source and method of statistical evaluation

1. An experiment was designed to test if the lysine requirement, expressed as g lysine/kg CP, was the same for several protein sources. 2. Groundnut meal, groundnut meal adjusted with indispensable amino acids or sesame meal supplied the dietary CP at 180 g/kg diet. Increments of lysine (1.5 g/kg diet) were added to each of these diets. 3. The gain, food intake and food efficiency responses of broiler chicks were analysed using a quadratic equation and a two-slope method. An estimate of lysine requirements was also obtained from a survey of college students. 4. The different methods produced widely different estimates of lysine requirement. 5. The average lysine requirement was estimated at 50.1 g lysine/kg CP for groundnut meal, 61.7 for adjusted groundnut meal and 54.9 for sesame meal. 6. Reasons for the effect of statistical analysis and protein source on lysine requirement are discussed.

Recovery of respiratory sinus arrhythmia in detoxified alcoholic subjects

Although most alcoholic subjects show little autonomic dysfunction, severe alcoholic subjects may have pathological changes in autonomic nerves. We asked if respiratory sinus arrhythmia amplitude (RSA), an index of vagal cardiac control, is decreased in alcoholism and, if so, whether the decrease is reversed with abstinence. RSA was assessed in 17 normotensive alcoholic subjects (A) at 1, 4, 12, and 24 wk of abstinence after detoxification and at similar intervals in 17 controls (C) matched for age, race, and gender. Subjects were studied in both supine and seated positions while breathing in a prescribed deep (> 50% vital capacity) and slow (5-7/min) pattern. Mean heart rate (HR) was determined over 30 s from the electrocardiogram; RSA (the difference between maximum and minimum instantaneous HRs after inspiratory onset) was determined from 10 consecutive breaths. In C, both HR (supine: 61.5 +/- 2.2 beats/min; seated: 71.3 +/- 1.7 beats/min; P < 0.002) and RSA (supine: 22.5 +/- 1.0 beats/min; seated: 28.4 +/- 1.4 beats/min; P < 0.003) were higher when seated than when supine, but neither HR nor RSA varied over 24 wk. At week 1 of abstinence, HRs for A were higher than those for C (supine: 74.2 +/- 2.3 beats/min, P < 0.001; seated: 83.2 +/- 2.7 beats/min, P < 0.003), but by week 24, both seated and supine values returned to control levels. RSA in A at week 1, was only one-half that of C (supine: 11.1 +/- 1.4 beats/min, P < 0.001; seated: 14.7 +/- 1.9 beats/min, P < 0.001) and independent of body position.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinematics of jaw movements during chewing at different frequencies

The three-dimensional jaw movement trajectory and its velocity profile were investigated to provide information regarding the motor control of chewing. This was done on a cycle-by-cycle basis across three voluntarily guided chewing frequencies to test the lack of invariance at the velocity level and the evidence for a cost function. The data revealed that an increase in chewing frequencies resulted in a significant reduction of the three-dimensional path, being significantly higher in opening than closing. The ratio of peak speed/three-dimensional distance, a kinematic index of stiffness, increased with increase in chewing frequency; higher stiffness being associated with faster chewing, the stiffness being significantly higher in opening than in closing. The ratio of peak velocity to mean velocity decreased as a function of increase in chewing frequency only at the highest frequency and this decrease again was different in opening than in closing. The results demonstrated that the velocity profile of chewing movements, like that of speech movements, lacked invariance. Rather than minimizing one cost function, the system used an efficient trade-off between time, space and effort, based on the objective of movements.

Respiratory and abdominal muscle responses to expiratory threshold loading in cystic fibrosis

We hypothesized that the hyperinflation and pulmonary dysfunction of cystic fibrosis (CF) would distort feedback and therefore alter the abdominal muscle response to graded expiratory threshold loads (ETLs). We compared the respiratory and abdominal muscle responses with graded ETLs of seven CF patients with severe lung dysfunction with those of matched healthy control subjects in the supine and 60 degrees head-up positions. Breathing frequency, tidal volume, and ventilatory timing were determined from inspiratory flow recordings. Abdominal electromyograms (EMGs) were detected with surface electrodes placed unilaterally over the external and internal oblique and the rectus abdominis muscles. Thresholds, times of onset, and durations of phasic abdominal activity were determined from raw EMGs; peak amplitudes were determined from integrated EMGs. Graded ETLs were imposed by submerging a tube from the expiratory port of the breathing valve into a column of water at depths of 0-25 cmH2O. We found that breathing frequency, tidal volume, and expired minute ventilation were higher in CF patients than in control subjects during low ETLs; a change in body position did not alter these ventilatory responses in the CF patients but did in the control subjects. All CF patients, but none of the control subjects, had tonic abdominal activity while supine. CF patients recruited abdominal muscles at lower loads, earlier in the respiratory cycle, and to a higher recruitment level in both positions than the control subjects, but burst duration of phasic activity was not different between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chewing frequency and bolus hardness on human incisor trajectory and masseter muscle activity

Nine adults with no orofacial dysfunctions were instructed to chew a standardized piece of soft or hard gum on the right side in time with a metronome set at 46, 100 or 160 beats/min. Jaw movements were recorded with a Myotronics kinesiograph and masseter electromyograms were detected with surface electrodes. The chewing patterns on either gum were not significantly different in any of their spatial or temporal aspects, in mean or peak opening or closing velocities, or in the timing or level of activity in either masseter at any of the three chewing frequencies. These findings suggest that during metronome-paced chewing the change in sensory feedback resulting from a change in gum hardness exerts little or no effect on either the spatial or temporal aspects of masticatory motor output.

Comparison of automatic and voluntary chewing patterns and performance

Chewing, like respiration, is ordinarily performed as an automatic motor act, yet both can be voluntarily controlled. No in-depth analyses of voluntary chewing exist. Therefore, we have analyzed on a cycle-by-cycle basis voluntarily controlled chewing, and compared it with automatic chewing. We assessed the performance during voluntarily controlled chewing by obtaining constant error and variable error scores. Nine healthy adults with full dentition were subjects (Ss). Their three-dimensional jaw movements and movement times were derived from Kinesiograph recordings obtained while chewing a standard piece of gum on the right side of the mouth. Burst durations and onset latencies of masseter activity were obtained from surface-recorded EMGs. Frequency during automatic chewing was obtained from data recorded while the subject viewed a film. Next, the subject chewed in time with a metronome set at this "automatic" rate. Intrasubject variability among 30 consecutive chewing cycles during voluntary was less than during automatic chewing. In every S gape and ipsilateral jaw excursions and the variability of burst durations of masseter activity were less during voluntary than during automatic chewing, showing that both the spatial and temporal aspects of the two types of chewing differ significantly. Ss varied in ability to follow the metronome. A S's constant error might be small, yet his variable error might be large, as if feed-back-based corrections influenced cycle-to-cycle variability. Fast chewers had smaller constant and variable error scores than did slow chewers, suggesting a speed-accuracy relationship. In summary, both temporal and spatial aspects of voluntary chewing were modified compared with those of automatic chewing. During voluntarily controlled chewing, cycle-to-cycle variability was less compared with automatic chewing due to reductions in variability of occlusal phase and the masseter's burst durations, and total jaw excursions were less because gapes and ipsilateral deviations during closing were reduced.

Mandibular movements and jaw muscles' activity while voluntarily chewing at different rates

As a way of learning about the motor control of chewing, we studied how well a subject could voluntarily chew in time with a metronome and defined the changes in the spatial and temporal aspects of the chewing pattern with changes in chewing rate. Timing and extent of mandibular movements were assessed in nine adults from Kinesiograph recordings; timing and level of activity in digastric and both masseter muscles were determined from surface EMGs. Each subject chewed gum in time with a metronome set randomly at 46, 100, 160 beats per minute or at a frequency close to his automatic chewing rate. Cycle-by-cycle analysis showed that subjects varied in their ability to keep pace with the metronome. When chewing at high frequencies, six subjects reduced gape, three did not. Contralateral deflection in opening, when present, was significantly reduced when chewing at high frequencies and this decrease was independent of vertical gape. Durations of opening, closing, and occlusal phases decreased in proportion to the decrease in total cycle duration. Burst duration of diagastric activity decreased about 29% compared with a 77% decrease in cycle duration over all chewing rates. At low frequencies onset of digastric activity occurred after onset of opening. At high frequencies digastric onset preceded opening. Burst durations of both masseter muscles decreased in concert with the decrease in cycle duration. Termination of activity in both masseters was synchronous and always occurred 100 +/- 20 ms prior to the next opening. Therefore, we conclude that (i) individuals vary in ability and strategy for controlling chewing rate voluntarily and (ii) with increases in chewing rates the shortening of burst duration for the digastrics is significantly less than for the masseters.

Electrically evoked responses of the human external oblique abdominal muscle

An electric shock delivered to a mixed intercostal nerve of a standing human subject evokes two responses in the external oblique abdominal EMG, namely an M-wave and an electrically elicited reflex. The reflex latency is very close to that of the mechanically elicited phasic stretch reflex of the external oblique, suggesting that it is a monosynaptic spinal reflex. However, several of its characteristics make it very different from the mechanically evoked reflex and the H-responses of calf or jaw muscles. Unlike the mechanically evoked reflex, the electrically elicited reflex is neither modulated by respiration nor attenuated when the subject assumes a supine posture. Unlike the H-response of calf or jaw muscles, the electrically elicited reflex is extremely reproducible from trial to trial, displays no antidromic occlusion in response to an increase in shock strength, and is neither suppressed nor potentiated by abdominal muscle vibration. A silent period, i.e., an indicator of alpha-motoneuron suppression, follows an electrically elicited reflex only when the subject rotates his trunk away from the recording site. Presumably, inputs from external oblique muscle receptors inhibit their homonymous motoneurons effectively when the muscle is functioning as the chief power generator, but not when it is functioning as an agonist. Using single motor unit analysis, the electrically elicited reflex was shown to be comprised of monosynaptic, oligosynaptic, and multisegmental components with the major component being monosynaptic. These unique characteristics of the EER are presumably a reflection of the external oblique's multisegmental innervation, multilayered anatomy, short neuronal pathways, and diverse functions.

Phasic stretch reflex of the abdominal muscles

This analysis of the abdominal stretch reflex (ASR) evoked by a tap to the abdomen was designed to explore how abdominal motoneurons process signals from respiratory and nonrespiratory sources. We recorded surface EMGs from the external and internal oblique muscles in standing subjects. Amplitudes of the abdominal stretch reflex varied despite constant tap forces, but strong taps evoked a larger reflex than weak taps. Trunk rotation toward the recording side, or voluntary contraction of the external and internal oblique muscles increased the reflex amplitudes, whereas contralateral rotation reduced their occurrence. An abdominal stretch reflex during a voluntary contraction was followed by a silent period of 40 to 80 ms. Often a late wave followed a reflex by 20 to 40 ms. Amplitudes during breathholds at residual lung volume were larger than those evoked during a breathhold at functional residual capacity, suggesting that abdominal stretch reflex amplitudes are inversely proportional to static lung volume. During quiet breathing the reflex amplitude reached a maximum slightly before end-expiration and decreased progressively to a minimum close to end-inspiration. During rebreathing, background abdominal activity was augmented with highest activity in late expiration. Abdominal stretch reflex amplitudes continued to wax and wane in phase with respiration, and the maximal reflex occurred progressively earlier in expiration. In summary, the abdominal stretch reflex reflects strong control from abdominal muscle spindles, lung proprioceptors, and chemoreceptors. The relative contributions of these inputs need to be determined.

Effect of gum hardness on chewing pattern

Chewing rhythms are set by a putative central pattern generator whose output is influenced by sensory feedback. In this study we assessed how an altered feedback imposed by changing the hardness of a gum bolus modifies the timing of chewing, the maximal gape, and the activity in the masseter muscle on the chewing side. Ten adult subjects with no orofacial dysfunction chewed a standard piece of soft or hard gum for at least 3 min in random order. Vertical jaw movements were recorded with a kinesiograph and activity of the masseter muscle was recorded and integrated from surface EMG electrodes. The subjects sat in a dental chair and viewed a video lecture to distract their attention from chewing; they were instructed to chew on the right molars. Cycle-by-cycle analysis showed that 9 of the 10 subjects chewed the hard gum more slowly than the soft with no significant change in gape. The increases in cycle duration were due to changes in the duration of the opening and occlusal phases. The duration of closing was not significantly changed even though the duration and level of masseter activity were both significantly increased. We conclude that gum hardness by altering proprioceptive feedback modifies the output of the masticatory central pattern generator in such a way that the temporal aspects of chewing and the output of the masseteric motor pool are affected.

Effects of whole-body rotation on masseteric motoneuron excitability

Vestibular stimulation is a popular clinical treatment for enhancing the excitability of spinal motoneurons innervating trunk and limb muscles, but whether vestibular stimulation can also influence trigeminal motoneurons is not known. We determined whether or not vestibular stimulation evoked by rotation of a seated subject would modify the excitability of masseteric motoneurons. The amplitude and frequency of occurrence of masseteric compound action potentials evoked by standard chin taps provided measures for assessing masseteric motoneuron excitability. Eleven healthy adults with no orofacial or otologic disorders served as subjects. Each sat in a motorized dental chair with his head stabilized by a halo head-piece so that chair rotation caused labyrinthine excitation. The frequency (3/s) of chin taps and their impact force were maintained constant by microcomputer control. After each tap, a 16-ms sample of EMG recorded from surface electrodes over the right masseter was digitized and stored for subsequent visual inspection. Only compound action potentials meeting rigorous criteria in terms of latency, amplitude, duration, and waveform were accepted as responses. The mean frequencies of occurrence and the mean amplitudes of the responses showed wide variability. Histogram displays of every response for each subject, however, revealed enhanced output from the masseteric motoneuron pool during the decleration and postrotation phases. In subjects not immediately retested this enhancement was persistent but decayed during the next 5 min. In five subjects the experiment was repeated after 1 min. The changes in response variables during phases 3 and 4 were significantly less than on the first trial, suggesting habituation. These results provide quantitative evidence that the dynamic input from vestibular ampullary receptors in response to rotation enhances masseteric motoneuron output.

Identification and assessment of factors contributing to variability of the jaw jerk

Unlike limb monosynaptic reflexes, the jaw jerk reflex ( JJR ) is extremely variable. We studied 35 healthy adults to determine the relative contributions of extrinsic and intrinsic factors underlying this variability. Each subject sat in a dental chair with his head and chin securely stabilized. Chin taps, delivered by a solenoid-driven plunger, were quantified with a piezo -transducer. The reflex response was recorded from surface electrodes over the right masseter muscle. A nasal thermistor signalled phases of respiration. Five of the 35 subjects had no reflex when relaxed, but during 15 degrees neck extension or voluntary contraction of the platysma muscle, a JJR appeared. The amplitude of the reflex varied considerably from trial to trial in all but one subject. A small component of this variability was due to minute changes in tap force despite head and chin stabilization and stimulus uniformity. Mean amplitudes of the reflex tended to increase with increases in tap force, but variability was large indicating intrinsic fluctuations in motoneuron excitability. Voluntary contraction of the platysma muscle and 15 degrees neck extension reliably enhanced the reflex. The JJR showed negligible respiratory modulation during quiet breathing. The reflex's variability in and among subjects precludes the use of the JJR as an index of masseteric motoneuron excitability. Our findings suggest that branchial motoneurons innervating the masticatory muscles receive far more diverse and fluctuating inputs than do somatic motoneurons innervating limb muscles.

Breathing pattern in humans: elevated CO2 or low O2 on positive airway pressure

The purpose of this study was to determine effects on breathing pattern of pressure breathing alone and in combination with chemical stimulation. We analyzed ventilatory responses to elevated airway pressures (positive-pressure breathing, PPB) in subjects breathing air, 12% O2, or elevated CO2. Each subject sat in a body box and breathed via mouth-piece from a bag-in-box. Responses to PPB on air were increased minute ventilation (VI), tidal volume (VT), frequency (f), mean inspiratory (VT/TI) and expiratory (VT/TE) flows, decreased expiratory duration (TE) and end-tidal CO2. If end-tidal CO2 were held constant, VI, VT, and VT/TI increased less. Responses greater than predicted from summing responses to either stimulus alone were observed for VT, f, VT/TI, and VT/TE during 3 and 5% CO2 and for VT, f, and VT/TE during isocapnic hypoxia. Responses to other combined stimuli were sums of responses to the individual stimuli. Thus ventilatory responses to combined PPB and chemical stimuli cannot be predicted simply from summating responses to each independently imposed stimulus, suggesting that sensory information arises from and is integrated at multiple sites.

Multiplicity of functional behavior of human intercostal muscles

Single motor unit activity from the 6th intercostal space in five healthy adults was analyzed during rebreathing, voluntary deep inspiration, Valsalve maneuver and phonation. Action potentials and pneumotach flow were stored on tape and fed to the computer for subsequent analysis. Spike-by-spike analyses revealed three functional types of intercostal motor units. One unit fired almost exclusively during inspiration and its firing was augmented by rebreathing and voluntary deep inspiration (phasic I unit). The second type fired continuously throughout the respiratory cycle with an increase in firing during expiration (tonic E unit); its activity was disrupted during phonation but not during rebreathing, suggesting a postural rather than respiratory function. The third type, silent during quiet breathing, was recruited during rebreathing, voluntary deep inspiration or Valsalve maneuver; its firing started in late inspiration and ceased in early expiration (phase-spanning I-E unit). The relationships between tidal volume and inspiratory time during rebreathing showed that the third type was recruited when tidal volume reached a critical 'volume threshold', suggesting that vagal volume feedback is essential for its activation.

Firing profile of diaphragm single motor unit during hypercapnia and airway occlusion

To define interaction between chemical and vagal-volume feedback we recorded diaphragm single motor unit (SMU) potentials, tracheal pressure, and end-tidal CO2 in spontaneously breathing, anesthetized cats during hypercapnia and during airway occlusion at functional residual capacity (FRC) or end-inspiratory level (EIL) before and after vagotomy. Hypercapnia increased onset, mean, and peak firing frequencies of early-onset SMUs, caused no change in number of spikes per breath (NSPB), and decreased inspiratory burst duration (Tdi). Airway occlusion increased both NSPB and Tdi without changing onset or mean frequencies. NSPB and Tdi increased more during FRC occlusion than during EIL occlusion. Vagotomy caused effects similar to airway occlusion, except that onset frequency decreased. Increases in NSPB or Tdi following vagotomy were greater than those during FRC occlusion. After vagotomy, airway occlusion no longer altered SMU activity, but hypercapnia still increased onset, mean, and peak frequencies, caused no change in NSPB, and decreased Tdi. New findings in this study are 1) the constancy in NSPB of diaphragm SMUs in response to hypercapnia and 2) the decrease in the onset frequency after vagotomy.

Responses of cat's internal intercostal motor units to hypercapnia and lung inflation

Single motor unit potentials from the eighth internal intercostal (IIC) muscle were recorded along with tracheal pressure and end-tidal CO2 (PETCO2) in spontaneously breathing, Dial-urethane anesthetized cats during hypercapnia (3, 5, or 7% CO2) and during lung inflation (LI, 100 ml above functional residual capacity) before and after vagotomy. Hypercapnia depressed IIC activity in 5 of 7 cats; the higher the PETCO2, the lower was the firing rate and the fewer the number of spikes per breath. LI evoked an initial silent phase (ISP) in 6 of 10 cats followed by a prolonged IIC burst. Hypercapnia combined with LI abolished or diminished the ISP and shortened the prolonged burst with an increase in firing rate and a recruitment of new units. Vagotomy silenced IIC activity in 7 of 10 cats, but LI after vagotomy activated IIC activity in 10 of 10 cats, though neither an ISP nor prolonged activity occurred. Our data suggest that major factors in controlling IIC activity are reciprocal inhibition from bulbospinal inspiratory neurons, excitatory and inhibitory inputs mediated by vagal afferents, and a modulation of IIC activity via gamma-loop. Hypercapnia affects the former two factors.

Human breathing patterns on mouthpiece or face mask during air, CO2, or low O2

Steady-state breathing patterns on mouthpiece and noseclip (MP) and face mask (MASK) during air and chemostimulated breathing were obtained from pneumotachometer flow. On air, all 10 subjects decreased frequency (f) and increased tidal volume (VT) on MP relative to that on MASK without changing ventilation (VE), mean inspiratory flow (VT/TI), or mean expiratory flow (VT/TE). On elevated CO2 and low O2, MP exaggerated the increase in VE, f, and VT/TE due to profoundly shortened TE. On elevated CO2, MASK exaggerated VT increase with little change in f. Increased VE and VT/TI were thus due to increased VT. During low O2 on MASK, both VT and f increased. During isocapnia, shortened TE accounted for increased f; during hypocapnia, increased f was related primarily to shortened TI. Thus the choice of a mouthpiece or face mask differentially alters breathing pattern on air and all components of ventilatory responses to chemostimuli. In addition, breathing apparatus effects are not a simple consequence of a shift from oronasal to oral breathing, since a noseclip under the mask did not change breathing pattern from that on mask alone.

Neural plasticity. Part 4. Lesion-induced reorganization of the CNS: recovery phenomena

Most patients treated by physical therapists have suffered some neurological trauma resulting from disease or injury. The traditional teaching used to be that damage of central neurons is irreversible. Within the last decade, however, it has been necessary to cast aside this traditional view because of accumulating evidence that the brain is endowed with remarkable plasticity. This paper reviews experimental evidence revealing morphological and functional changes occurring in the CNS in response to neural lesions. Morphological responses to injury include collateral and terminal sprouting, retrieval of vacated synapses, alterations in the ultrastructure of surviving synapses, and denervation supersensitivity. Functional and adaptive changes induced by injury include the unmasking of ineffective synapses, shifts in receptive fields, and reorganization or altered effectiveness of surviving neural networks. These recovery phenomena attest to the brain's dynamic properties. These new insights contradict our conventional view of the absence of growth and reorganizational capabilities in CNS neurons. These newly identified "recovery phenomena" are destined to have a significant impact on physical therapy in the future.

Neural plasticity: Part 3. Responses to lesions in the peripheral nervous system

This paper describes some of the remarkable recuperative responses that neurons of the peripheral nervous system have to injury of their axons. The initial response is a sealing of the cut ends of the axons, followed by orderly degenerative and phagocytic events in the segments lying distal and proximal to the lesion. The chromatolytic changes occurring in the cell body are adaptive responses involving the morphological, physiological, and biochemical properties of the neuron. The cell loses dendrites and synapses, its electrophysiological properties are altered, and its biochemistry is altered to prepare the neuron for synthesizing proteins needed for formation of growth cones and regeneration of the axon. During this period, the denervated muscle undergoes dramatic atrophic changes that not only modify the electrical nd chemical properties of its membrane but also reduce the diameter and weight of its fibers. This denervation atrophy of muscle is reversible if reinnervation occurs before muscle material has been replaced by connective tissue. Responses to injury of sensory axons depend on the site of the lesion. Cutting a dorsal root causes Wallerian degeneration of the primary afferents' central processes. Collateral sprouts from neighboring uncut root fibers are thought to take over the vacant synapses on the second-order neurons in the dorsal horn. Cutting a sensory axon peripherally eliminates the receptive field of the primary afferent initially, but in time, collaterals from neighboring skin afferents provide the second-order neurons with a new receptive field. Synaptic reclamation and receptive field reorganization are but two dramatic examples of neuronal plasticity that lead to "rewired" neural circuitry.

Enzyme-linked immunosorbent assay for measurement of anti-Moraxella bovis antibodies

Antibodies of the immunoglobulin (Ig) G and IgA classes specific for Moraxella bovis in serum or lacrimal secretions of cattle were detected with an enzyme-linked immunosorbent assay, using soluble extracts of M bovis or whole organisms. The amount of detectable antibodies was influenced by the type of antigenic preparation used in the enzyme-linked immunosorbent assay. The test indicated that 2 subcutaneous inoculations of M bovis cells induce significantly (P less than 0.0001) increased anti-M bovis serum antibodies. The infection of calves with M bovis induced specific IgG antibodies in serum and predominantly IgA antibodies in lacrimal secretions.