Development of approaches and legislation to optimise nurse staffing levels

Nurses and the environment in which they work have an important role in patient safety and quality of care. Evidence demonstrates a link between lower nurse staffing levels and higher nurse workloads on hospital wards with adverse patient outcomes such as increased mortality, infections, falls and hospital stay, as well as adverse effects on staff well-being. Therefore, ensuring adequate numbers of nurses are on duty and available to care for patients safely has become a crucial task for nurses and hospital managers. In March 2016, Wales became the first country in Europe and one of only a small number of countries globally to legislate on nurse staffing levels. In April 2018, the Nurse Staffing Levels (Wales) Act 2016 was fully implemented in acute medical and surgical hospital wards. This article outlines the background to, and development of, nurse staffing approaches in Wales that preceded the introduction of this legislation. It aims to provide nurses with an understanding of the journey towards introducing legislation for nurse staffing levels and workforce planning in Wales, which will be relevant to those affected by the implementation of any legislation in this important area of healthcare. This article also provides information about how the nurse staffing legislation evolved as a result of important work and collaboration that was already undertaken throughout NHS Wales.

What does the future hold for advanced nursing?

This third in a three-part series on advanced nursing explores the future demand for a flexible but regulated nursing career framework. Part 1 explored the historical evolution of advanced nursing, while part 2 discussed the development of a governance framework.

A governance framework for advanced nursing

This second in a three-part series outlines the introduction of a governance framework for advanced nursing practice. Part 1 explored the history of the evolution of advanced practice, while part 3, to be published next week, will discuss the future of advanced practice and how it may shape the career structure of nursing.

Advanced nursing. Part 1: The development of advanced nursing roles

This first in a three-part series on advanced nursing practice reviews its historical evolution. Part 2, to be published next week, reviews the introduction of a governance framework, while part 3 explores the future of advanced practice and how it may shape nursing career structures.

Associations between force and fatigue in fast-twitch motor units of a cat hindlimb muscle

Associations were quantified between the control force and fatigue-induced force decline in 22 single fast-twitch-fatigable motor units of 5 deeply anesthetized adult cats. The units were subjected to intermittent stimulation at 1 train/s for 360 s. Two stimulation patterns were delivered in a pseudo-random manner. The first was a 500-ms train with constant interpulse intervals. The second pattern had the same number of stimuli, mean stimulus rate, and stimulus duration, but the stimulus pulses were rearranged to increase the force produced by the units in the control (prefatigue) state. The associations among the control peak tetanic force of these units, 3 indices of fatigue, and total cumulative force during fatiguing contractions were dependent, in part, on the stimulation pattern used to produce fatigue. The associations were also dependent, albeit to a lesser extent, on the force measure (peak vs. integrated) and the fatigue index used to quantify fatigue. It is proposed that during high-force fatiguing contractions, neural mechanisms are potentially available to delay and reduce the fatigue of fast-twitch-fatigable units for brief, but functionally relevant, periods. In contrast, the fatigue of slow-twitch fatigue-resistant units seems more likely to be controlled largely, if not exclusively, by metabolic processes within their muscle cells.Key words: cat, catch-like property, fatigue, force, motor units, size principle.

A prospective audit of stomas--analysis of risk factors and complications and their management

AIM

To prospectively audit stomas and to determine the nature and rate of complications and their relationship with various risk factors and their management.

MATERIALS AND METHODS

The study was performed prospectively on 97 consecutive patients who had stomas formed between January 2000 to August 2000. Patients were followed up for one year. Risk factors including age, body mass index (BMI), preoperative siting, contour of the abdominal wall, smoking, grade of operating surgeon, emergency or elective procedure, diabetes, type of stoma and suture material used were noted. The type of surgery, and indications for surgery were also recorded. The complications were documented by two qualified stoma nurses and a photographic record taken. Statistical analysis comprising both univariate and multivariate methods, was performed by SPSS 10.

RESULTS

The mean age was 65 years (standard deviation 16.01, range 16-99) and mean body mass index was 24.5 (standard deviation 4.66, range 15-37). Forty-nine of 97 (50.5%) stomas developed one or more complications. Twenty-three patients experienced retraction, 18 had stomas sited in a skin crease, 16 had early and 12 had late skin excoriation, 12 had detachments and a further 12 had parastomal hernia. Eleven further stoma complications were noted including prolapse, necrosis, ischaemia and sloughing. None of the risk factors achieved statistical significance when analysed against the overall complication rate. However, when the risk factors were analysed against individual complications using univariate logistic regression, a high body mass index was associated with more retractions (P = 0.003), early skin excoriation (P = 0.036) and poor siting (stoma in crease) occurred more commonly in emergencies (P = 0.022). Diabetes was associated with late skin excoriation (P = 0.02). Multivariate logistic regressions confirmed an independent association of body mass index, diabetes and emergency surgery with complications. Forty-five of 49 patients who had complications needed some conservative management such as a convexity appliance. Four patients needed refashioning.

CONCLUSION

Body mass index, diabetes and emergency surgery were the significant risk factors identified in our study. Overall complications compare favourably with other series. We found that preoperative siting by stoma nurses and the grade of operating surgeon did not affect the outcome.

Determinants of bone mineral density in older men

Although osteoporosis in men is increasingly recognized as an important health issue and bone mass appears to be a major determinant of fracture, there remain few data concerning the determinants of bone mass in men. To determine the correlates of bone density in men, we studied a large group of older subjects recruited from three rural communities in the northwestern United States. Three hundred and fifty-five men over the age of 60 years (mean 71.5 +/- 7.4 years) without known disorders of mineral metabolism were recruited by community advertising. Bone mineral density was measured at the lumbar spine, proximal femur and radius by dual-energy X-ray absorptiometry, and factors potentially related to skeletal status were assessed by direct measurements or questionnaire. In univariate analyses weight (positively) and age (negatively) were associated with bone density. After adjustment for these two factors, alcohol intake, osteoarthritis and thiazide use were associated with higher bone density, while previous fractures, gastrectomy, peptic ulcer disease, rheumatoid arthritis, glucocorticoid use, hypertension, previous hyperthyroidism, height loss since age 20 years, chronic lung disease and smoking were related to lower density. In multivariate models, only weight and a history of cancer were related to higher bone mass, and age, previous fracture, rheumatoid arthritis, gastrectomy and hypertension were associated with lower density. These data contribute to the emerging field of osteoporosis in men, and may help in the clinical identification of men at higher risk of osteopenia.

The association between water-borne fluoride and bone mineral density in older adults

While the benefit of fluoridation in the prevention of dental caries has been overwhelmingly substantiated, the effect of fluoride on bone mineral density is less clear. This cross-sectional study was designed to compare the bone mineral densities of older adults exposed to various levels of fluoride from community water systems. Participants were recruited from 3 rural communities with naturally occurring fluoride in their water systems at 0.03, 0.7, and 2.5 mg/L. All adults, age 60 and over, were eligible if they were ambulatory and had a long-term history (> or = 20 yrs) of ingesting city water. Bone mineral density (BMD) was measured by means of dual-energy x-ray absorptiometry at 3 anatomical sites: lumbar spine, proximal femur, and forearm. A total of 353 white non-Hispanic women and 317 white non-Hispanic men took part in the study. When the data were stratified by city of residence and gender, men and women living in the community with high levels of fluoride in their community water system had significantly higher lumbar spine BMD than their counterparts from the communities with low and moderate fluoride levels. The women in the high-fluoride community had significantly higher proximal femur BMD, but there were no statistically significant differences among men in either proximal femur or forearm BMD. Long-term exposure (> or = 20 yrs) to higher levels of fluoride appears to have a positive impact on lumbar spine and proximal femur BMD. Based on the results of this study, exposure to fluoride at levels considered "optimal" for the prevention of dental caries (from 0.7 to 1.2 mg/L) appears to have no significant impact on bone mineral density. The relationship between higher levels of fluoride exposure and bone mineral density requires further investigation.

Paracetamol poisoning in the north east of England: presentation, early management and outcome

1. Paracetamol is increasingly involved in self-poisoning in the United Kingdom and remains a common cause of fatal poisoning. 2. To document the epidemiology and early management of paracetamol poisoning data were collected on consecutive patients with suspected paracetamol poisoning presenting to 6 hospitals in the North East of England over 12 weeks in 1994. 3. There were 400 presentations (attendance rate 1.14/10(3) population/yr) involving 343 persons (45% male). Paracetamol concentrations at 4 h correlated weakly with reported paracetamol dose (R = 0.49, P < 0.0001) and were similar comparing those treated and not treated by gastric decontamination. 4. In 38 (9%) cases paracetamol concentrations were above the appropriate nomogram treatment line, including 3% and 20% of patients who reported ingesting less than and more than 12 g respectively. In 21 patients acetylcysteine treatment was deferred until admission to the ward, the mean delay involved was 2.8 h. 5. One patient died, from arrhythmias caused by co-ingested dothiepin. 6. Paracetamol poisoning is common. Most cases do not have potentially toxic plasma paracetamol concentrations, but those who do often present late and antidotal treatment may be delayed inappropriately.

Factors affecting hospital admission and length of stay of poisoned patients in the north east of England

1. Poisoning is a common reason for presentation to hospital and hospital admission but there is no agreed policy for managing these patients. This study examined the management of patients presenting with poisoning and the factors affecting the probability of hospital admission and prolonged stay. 2. Data on all cases of poisoning presenting to six Accident and Emergency departments in the North East of England over 12 weeks in 1994 was collected prospectively from A&E notes. Length of stay and outcome were recorded from hospital computer records. 3. Overall, 73% of patients were admitted to a medical ward. Probability of admission was not independently affected by age or gender but was increased in those with intentional poisoning (Odds Ratio (OR) 3.3 [95% CI 1.8, 6.1]), a history of self harm (OR 1.7, [1.0, 2.9]) or potentially hazardous poisoning (OR 3.7 [2.1, 6.6]). There were significant variations between hospitals (50-80%) which could not be attributed to case mix. 4. Prolonged stay (> 2 nights) was more common in patients over 65 years (OR 6.8 [2.9, 16.1]), those with intentional poisoning (OR 2.7 [1.1, 6.6]) and those with potentially hazardous poisoning (OR 2.6 [1.4, 4.9]). Mean hospital stay was 1.5 days and varied significantly between hospitals from 0.8 to 2.1 days and this was independent of case mix. 5. There are appreciable variations in the management of poisoning between hospitals which are not explained by patient characteristics. Savings would occur if rates of admission and duration of stay were reduced by those hospitals where admission is more frequent or hospital stay is longer. However, the impact of this on long term morbidity is unknown.

Presentation of poisoned patients to accident and emergency departments in the north of England

1. A 12 week prospective survey of all patients of any age with confirmed or suspected poisoning presenting to six accident and emergency departments in the North East of England was performed to establish the local incidence and patterns of presentation of poisoning. 2. 945 episodes of poisoning involving 852 patients were recorded representing approximately 1.2% of all A&E presentations and suggesting an annual attendance rate of 2.7 per 1000 persons per year. 3. Attendance rates varied threefold between hospitals and were similar in males and females overall; between the ages of five and 14 attendances were more common in females (1.9 vs 0.6/10(3)/y) while between 0 and 4 y (3.1 vs 2.4) and 25 and 34 y (3.9 vs 2.9/10(3)/y) they were more common in males. 4. The median interval between poisoning and presentation was 2 h (mean 4.1 h) and only 19% of cases presented within 1 h. Presentation was most common between Friday evening and Tuesday morning and in the late afternoon and evening. 5. 6% of the patients presented more than once with poisoning during the study period and 37% had a past history of deliberate self-harm. The most common poisons involved were paracetamol (43%), opioids (15%) and benzodiazepines (15%). 6. The study illustrates the frequency of presentations of poisoning to A&E departments. The high rate of poisoning in young men and the increasing use of paracetamol are particular causes for concern.

Proprioceptive consequences of tendon vibration during movement

1. Previous studies have used tendon vibration to investigate kinesthetic illusions in the isometric limb and end point control in the moving limb. These previous studies have shown that vibration distorts the perceptions of static joint angle and movement and causes systematic errors in the end point of movement. In this paper we describe the effects of tendon vibration during movement while human subjects performed a proprioceptively coordinated motor task. In an earlier study we showed that the CNS coordinates this motor task-a movement sequence-with proprioceptive information related to the dynamic position and velocity of the limb. 2. When performing this movement sequence, each subject sat at a table and opened the right hand as the right elbow was passively rotated in the extension direction through a prescribed target angle. Vision of the arm was prevented, and the movement velocity was changed randomly from trial to trial, leaving proprioception as the only useful source of kinematic information with which to perform the task. 3. In randomly occurring trials, vibration was applied to the tendon of the biceps brachii, a muscle that lengthens during elbow extension. In some experiments the timing of tendon vibration was varied with respect to the onset of elbow rotation, and in other experiments the frequency of vibration was varied. In each experiment we compared the accuracy of the subject's response (i.e., the elbow angle at which the subject opened the hand) in trials with tendon vibration with the accuracy in trials without tendon vibration. 4. The effect of tendon vibration depended on the frequency of vibration. When the biceps tendon was vibrated at 20 Hz, subjects opened the hand after the elbow passed through the target angle ("overshooting"). Overshooting is consistent with an underestimate of the actual displacement or velocity of the elbow. Vibration at 30 Hz had little or no effect on the elbow angle at hand opening. Vibration at 40 Hz caused subjects to open the hand before the elbow reached the target angle ("undershooting"). Undershooting is consistent with an overestimate of the actual displacement or velocity of the elbow. The size of the error depended on the velocity of the passively imposed elbow rotation. 5. The effect of tendon vibration also depended on the timing of vibration. If 40-Hz vibration began at the onset of movement, the subject undershot the target. If 40-Hz vibration started 5 s before movement onset and continued throughout the movement, the undershoot error increased in magnitude. However, if 40-Hz vibration started 5 s before movement onset and then stopped at movement onset, the subject overshot the target. When vibration was shut off during movement, a transition occurred from an over-shooting error to an undershooting error at a time that depended on the velocity of elbow rotation. 6. In a separate experiment, subjects were instructed to match either the perceived dynamic position or the perceived velocity of rotation imposed on the right elbow by actively rotating the left elbow. In both matching tasks, tendon vibration produced oppositely directed errors depending on the frequency of vibration. Vibration at 20 Hz produced a perception of decreased elbow velocity and a bias in dynamic position in the flexion direction, and vibration at 40 Hz produced the opposite perceptions. 7. We conclude that muscle spindle afferents, which are activated by tendon vibration, are an important source of the dynamic position and velocity information that the CNS uses to coordinate this movement sequence task. The observed effects of vibration timing and frequency suggest that perceptual changes evoked by vibration cannot be explained by the simple summation of sensory input evoked by movement and by vibration. Rather, the bias in perception produced by vibration appears to be related to the difference between vibration- and movement-evoked activity in muscle spindle afferents.

Proprioceptive coordination of discrete movement sequences: mechanism and generality

A "discrete" movement sequence is defined as a movement with a single goal that involves a series of overlapping joint rotations. Reaching-and-grasping and throwing are examples of discrete movement sequences. The central nervous system (CNS) can use reafferent proprioceptive information from one joint rotation in a sequence to coordinate subsequent rotations at other joints. The experiments reported in this paper demonstrate how the human CNS uses proprioceptive information to coordinate discrete movement sequences. We examined the mechanism (at an information processing level) underlying proprioceptive coordination and the generality (i.e., the boundary conditions) of these mechanisms as they apply to everyday movement sequences. Adult human subjects performed a discrete movement sequence that resembles backhand throwing: elbow extension followed by hand opening. The task was to open the hand as the elbow passed through a prescribed "target" angle. We eliminated visual information and made the arrival time at the target angle unpredictable so that the available kinematic information was provided exclusively by proprioception. The subjects were capable of performing this motor task with a high degree of precision, thereby demonstrating that the nervous system can use proprioceptive input to coordinate discrete movement sequences. Our data indicate that precise coordination is achieved by extracting kinematic information related to both the velocity of elbow rotation as well as the elbow position during movement (i.e., "dynamic position"). Dynamic position information appears to be encoded as both absolute joint angle and angular distance, although more precisely as angular distance. Although our experiments were conducted under rather restrictive laboratory conditions, this mechanism of motor coordination might also apply to everyday movement. Our results suggest that this mechanism could be employed for passive as well as active movement sequences, with and without opposing loads; it could exert its influence in discrete movement sequences as brief as 210 ms or as long as 1.5 s; and it does not involve any significant degree of learning (this proprioceptive mechanism appears to be readily available for use on the first attempt of a novel motor task).

Proprioceptive coordination of movement sequences: discrimination of joint angle versus angular distance

1. The purpose of these experiments was to determine the accuracy with which human subjects could discriminate proprioceptive (nonretinotopic) targets during movement. The targets were located at either a specified angle in joint space, or a specified angular distance from an initial joint angle. 2. In these experiments the right elbows of normal human subjects were passively extended from either predictable or unpredictable starting angles. The subjects were instructed to open the right hand to indicate that the elbow was passing through a target joint angle or a target angular distance. The subjects were not given visual information about the location of the elbow, so they had to rely on proprioceptive input to perform this task. The target (criterion joint angle or angular distance) was learned by the use of proprioception during 8-15 practice trials. 3. Four experiments were conducted. In three experiments the target was located at a constant joint angle, and in the fourth experiment the target was located at a constant angular distance from the starting angle. The starting angle in all four experiments was pseudorandomly varied from trial to trial. 4. On the basis of an analysis of constant errors, subjects were more accurate at discriminating angular distance than joint angle. The slope of the relationship between the starting position and the constant errors was dictated by the task requirement. 5. In the distance discrimination experiment, when the starting angle was more flexed than the intermediate (i.e., central) position, the subjects slightly overshot the target distance. Conversely, when the starting angle was more extended than the intermediate position, the subjects slightly undershot the target distance. 6. In the joint angle discrimination experiments, the opposite results were obtained. Subjects overshot the target when the starting position of the elbow was more extended than the intermediate starting position, and they undershot the target when the starting position was more flexed than the intermediate starting position. The amplitude of these systematic errors increased when the subjects were unaware that the initial angle of their elbow was variable. 7. It is concluded that, in kinesthetic tasks of this type, the discrimination of angular distance is more accurate than the discrimination of joint angle. We hypothesize that the nervous system extracts kinematic information related to both joint angle and angular distance from proprioceptors, and that the encoding and or decoding of angular distance is more accurate than that of absolute joint angle.(ABSTRACT TRUNCATED AT 400 WORDS)

Proprioceptive coordination of movement sequences: role of velocity and position information

1. Recent studies have shown that the CNS uses proprioceptive information to coordinate multijoint movement sequences; proprioceptive input related to the kinematics of one joint rotation in a movement sequence can be used to trigger a subsequent joint rotation. In this paper we adopt a broad definition of "proprioception," which includes all somatosensory information related to joint posture and kinematics. This paper addresses how the CNS uses proprioceptive information related to the velocity and position of joints to coordinate multijoint movement sequences. 2. Normal human subjects sat at an experimental apparatus and performed a movement sequence with the right arm without visual feedback. The apparatus passively rotated the right elbow horizontally in the extension direction with either a constant velocity trajectory or an unpredictable velocity trajectory. The subjects' task was to open briskly the right hand when the elbow passed through a prescribed target position, similar to backhand throwing in the horizontal plane. The randomization of elbow velocities and the absence of visual information was used to discourage subjects from using any information other than proprioceptive input to perform the task. 3. Our results indicate that the CNS is able to extract the necessary kinematic information from proprioceptive input to trigger the hand opening at the correct elbow position. We estimated the minimal sensory conduction and processing delay to be 150 ms, and on the basis of this estimate, we predicted the expected performance with different degrees of reduced proprioceptive information. These predictions were compared with the subjects' actual performances, revealing that the CNS was using proprioceptive input related to joint velocity in this motor task. To determine whether position information was also being used, we examined the subjects' performances with unpredictable velocity trajectories. The results from experiments with unpredictable velocity trajectories indicate that the CNS extracts proprioceptive information related to both the velocity and the angular position of the joint to trigger the hand movement in this movement sequence. 4. To determine the generality of proprioceptive triggering in movement sequences, we estimated the minimal movement duration with which proprioceptive information can be used as well as the amount of learning required to use proprioceptive input to perform the task. The temporal limits for proprioceptive processing in this movement task were established by determining the minimal movement time during which the task could be performed.(ABSTRACT TRUNCATED AT 400 WORDS)

Central and peripheral coordination in movement sequences

Motor coordination has been too poorly defined to be a useful construct in studying the control of movement. In general, motor coordination involves controlling both the timing and the kinematics of movement. Yet the motor behaviors typically used for the study of coordination have required controlling only the timing or the spatial aspects of a movement. To understand better the basis of motor behavior, this study examined movement sequences, a class of movement in which both the timing and the kinematics must be controlled. In one experiment we studied a reaching and grasping movement sequence to characterize the central coordination of movement sequences. In another experiment we studied a throwing movement sequence to characterize the peripheral (kinesthetic) coordination of movement sequences. An heuristic model is presented to explain how central and peripheral mechanisms of coordination might interact to produce accurate movement.

Prolonged depression of force developed by single motor units after their intermittent activation in adult cats

The fatigue of fast-twitch, glycolytic mammalian motor units [i.e., type FF; nomenclature of (3)] is dependent, in part, on the stimulation regimen (total number of stimuli, frequency, duty cycle, temporal patterning of stimuli, etc.) used to induce fatigue. To study the effect of the temporal pattern of the stimulus train on the rate and extend of fatigue in single FF units, one theoretically acceptable approach would be to use each motor unit as its own control: i.e., a sequential testing with two fatigue tests that differ only in the temporal organization of their stimuli. The purpose of this communication is to provide evidence that such an approach is not feasible when studying FF units, due to the delayed recovery of force following their repetitive activation. It was shown that 1/s activation of single FF units for only 15 or 45 s with intermittent 40-Hz, 300-ms duration trains significantly reduced their force response to a double-pulse shock for several hours. This finding suggests that in studies designed to test for the effects of different stimulation patterns on the fatigue of single motor units, deeply anaesthetized, reduced animal preparations are not appropriate models for the sequential application of different stimulation regimens to fast-twitch, glycolytic, mammalian motor units.

The effect of the stimulation pattern on the fatigue of single motor units in adult cats

1. The main purpose of this study was to examine the effects of two subtly different stimulus patterns on the force developed by fast-twitch, fatiguable motor units in a cat hindlimb muscle during control (pre-fatigue) and fatiguing contractions. 2. The peak force and the force-time integral responses of nineteen high fatigue (FF) and three intermediate fatigue (FI) motor units of the tibialis posterior muscle in five deeply anaesthetized adult cats were measured at selected times during the course of a 360-s fatigue test. 3. The fatigue test involved a pseudo-random alternation of two patterns of stimulation. One pattern (regular) was composed of a train of stimuli with constant interpulse intervals, set at 1.8 x the twitch contraction time of each unit (interval range, 27-51 ms), and delivered for 500 (or 400) ms. For the total (FF + FI) motor-unit sample, the mean (+/- S.D.) stimulation frequency was 26 +/- 4 Hz (range, 19-37 Hz). The other stimulus pattern (optimized) consisted of three initial stimuli with short (10 ms) interpulse intervals, followed by a constant interpulse-interval train that was adjusted (interval range, 29-62 ms; frequency, 23 +/- 5 Hz; frequency range, 16-36 Hz) such that the total train had the same number of pulses, and the same average frequency and duration as the regular train. 4. The stimulus trains were delivered at 1 s-1 for 360 s, using three-train sequences of each pattern, randomly alternating with one another. The response of the third train in each sequence was selected for the force measurements. The force profile obtained from the fatigue test was subsequently decomposed into two profiles: one attributable to regular and one to optimized stimulation. 5. During the initial responses to the fatigue test, the optimized stimulus pattern produced significantly more force than the regular stimulus pattern. For FF units, the mean increase in peak force (141%) was significantly greater than the increase in the force-time integral (59%). 6. All motor units exhibited an initial potentiation of peak force with the regular stimulation pattern, whereas peak force declined monotonically with the optimized pattern. In contrast, the force-time integral potentiated in the first 30 s for both regular and optimized stimulus patterns. 7. Each motor unit maintained an increased force response to optimized stimulation during the fatigue test, with the greatest relative increase occurring about 120 s into the test, well after the potentiation effect had subsided.(ABSTRACT TRUNCATED AT 400 WORDS)

Fatigue-related changes in motor unit action potentials of adult cats

The purpose of this study was to quantify the changes in motor-unit action potentials (MUAP) and force during a standard motor-unit fatigue test. MUAP waveforms were characterized by the measurement of amplitude, duration, area, and shape (as reflected in a coefficient of proportionality). Fatigue-resistant motor units exhibited small, but statistically significant, changes in MUAP amplitude and area during the fatigue test, whereas fatigable motor units displayed variable changes in MUAP amplitude, duration, and area. For all motor-unit types, the coefficient of proportionality did not change, and hence the change in MUAP area was proportional to the combined changes in amplitude and duration. The between- and within-train changes in MUAP were also distinct for the fatigue-resistant and fatigable motor units. Although several mechanisms could be responsible for the changes in the MUAP as the fatigue test proceeded, the dissociation of the time courses for MUAP and force indicated that these MUAP changes were not the principal reason for the decline in force under these conditions.

Effects of controlled frequency breathing during exercise on blood gases and acid-base balance

The purpose of this study was to determine the effect of a reduced ventilatory frequency (Vf) on blood gases and acid-base changes during three intensities of cycling exercise. VO2max and lactate threshold workload (LaT) of six subjects were assessed on a Monark ergometer. Experimental rides were performed 1) with no restriction on Vf (NB) and 2) with a prescribed Vf of 10/min (CFB). Each exercise period consisted of 8 min at 10% of VO2max below the LaT (WI), followed immediately by 8 min at LaT (WII), followed immediately by 8 min at 10% of VO2max above LaT (WIII). Blood was taken from a heated fingertip at the end of each load and analyzed for lactate concentration, pH, PO2, and PCO2. Respiratory exchange was monitored continuously using open circuit indirect calorimetry. Minute ventilation (VE) was significantly reduced by CFB at all three workloads. The reduced VE resulted in lower (p less than 0.05) blood PO2 at each workload (p less than 0.05), however, neither blood lactate nor VO2 were significantly different between CFB and NB for the three loads. Blood [H+] was significantly higher in CFB than NB at all three loads with the greatest difference between trials at WIII (NB: 37.93 +/- 0.68 nM: CFB: 44.77 +/- 1.02 nM). This was accounted for by a significantly higher PCO2 during CFB in WII and WIII (WII, NB: 33.0 +/- 1.4 mmHg, CFB: 35.7 +/- 2.7 mmHg; WIII, NB: 31.2 +/- 1.7 mmHg, CFB: 38.9 +/- 2.4 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Steroidogenic capacity and ultrastructural morphology of cultured ovine luteal cells

Corpora lutea were surgically collected from superovulated ewes 36 h post-injection of human chorionic gonadotropin (hCG) (Day 2), dissociated (0.2% collagenase), plated, and maintained in culture Days 2-10 in Medium 199 supplemented with 5% calf serum. Accumulation of progesterone in the cultures did not decrease (p greater than 0.05) from Day 3 (17.5 +/- 5.1 nmol/10(6) cells) to Day 10 (4.8 +/- 1.7 nmol/10(6) cells). Calf serum (5%) in the medium supported greater (p less than 0.05) progesterone production than fetal calf serum (5%) or medium without added serum. Steroidogenic cells did not increase (Days 2-10) in numbers, but increased (p less than 0.01) in mean cell diameter (Day 2, 11.7 +/- 0.4 micron; Day 10, 24.5 +/- 1.6 micron). Steroidogenic capacity on Day 10 of cells cultured Days 2-10 (in vitro) was not different (p greater than 0.05) from that of cells collected from the ovary on Day 10 (in vivo); however, steroidogenic cells recovered from plates had greater (p less than 0.01) mean cell diameters (24.5 +/- 1.6 micron, in vitro, compared to 15.2 +/- 1.0 micron, in vivo). Transmission electron microscopy revealed that cultured cells (Days 5, 10) possessed less smooth endoplasmic reticulum but more lipid droplet inclusions, ribosomes, and rough endoplasmic reticulum than cells obtained in situ (Day 10). Electron-dense secretory granules were rarely seen. Although subcellular morphology of ovine luteal cells in culture was altered, these changes did not appear to significantly affect the ability of these cells to produce progesterone.