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Biomedical subjects

V J Robertson

Publications and source records attributed to V J Robertson.

At least 19 recordsLinked to original sources
PubMed2001

Variation in motor threshold with frequency using kHz frequency alternating current.

We investigated the frequency dependence of motor thresholds over the frequency range 1 kHz to 25 kHz. Alternating current (AC), ramped in intensity, was applied transcutaneously, and the induced wrist extensor torque was measured. Plots of log torque versus stimulus voltage were used to accurately determine thresholds. Three kinds of sinusoidal AC stimuli were compared: continuous, 10 ms bursts at 50 Hz, and 50-Hz single-cycle. Differences were attributed to summation of subthreshold depolarizations. The variation in relative thresholds (continuous/single-cycle and burst/single-cycle) indicates that summation occurs more efficiently at higher kHz frequencies. The observed frequency and waveform dependence provides evidence for high-frequency nerve fiber firing rates and fiber dropout when continuous or modulated AC is used, with the effects increasing with AC frequency. The form of the motor response evoked at high frequencies has features that suggest that frequencies above 10-kHz have little or no useful clinical role in rehabilitation procedures.

Adult↗
PubMed2001

Occupational health and safety in physiotherapy: guidelines for practice.

Most physiotherapists (91%) experience work related musculoskeletal disorders (WMSDs) at some time, and one in six makes a career change as a consequence. Many of these disorders are attributed to manual handling of patients. This paper proposes guidelines to reduce the risk of WMSDs based on Australian legislative requirements, the results of a survey of Australian physiotherapists and the literature surrounding injury prevention. These guidelines address the areas of environmental and job design, and the personal physical capabilities of physiotherapists, within the context of law. The paper concludes by calling for further research to explore and develop this area of injury prevention in the physiotherapy profession.

Australia↗
PubMed2001

Hospital stay and discharge outcomes after knee arthroplasty.

The impact of shorter hospital lengths of stay on patient outcomes at discharge from acute care after knee arthroplasty was investigated in a prospective observational outcome study at three Melbourne public hospitals during a 5-month period from October 1999 to March 2000. The participants were 105 consecutive patients (35 at each hospital), with a mean age of 71 years. Outcome measures were length of stay, destination (home or rehabilitation) and functional mobility at discharge from the acute care facility. During the study period mean hospital length of stay across the three hospitals was 6.5 days, more than 30% less than the Victorian average for the preceding year. This was associated with high rates of discharge to rehabilitation facilities (mean 64%), with rates varying between the three hospitals (97%, 57% and 40%). However, in each hospital, one-third of this group had already achieved a level of independent functional mobility adequate for discharge home, highlighting an apparent influence of non-clinical factors on discharge decisions, including pressure to decrease length of stay, hospital policy and availability of a rehabilitation bed. Ways of achieving discharge directly home for a greater number of patients following knee arthroplasty and of determining optimal length of stay are discussed.

Aged↗
PubMed2001

A review of therapeutic ultrasound: effectiveness studies.

BACKGROUND AND PURPOSE: Therapeutic ultrasound is one of the most widely and frequently used electrophysical agents. Despite over 60 years of clinical use, the effectiveness of ultrasound for treating people with pain, musculoskeletal injuries, and soft tissue lesions remains questionable. This article presents a systematic review of randomized controlled trials (RCTs) in which ultrasound was used to treat people with those conditions. Each trial was designed to investigate the contributions of active and placebo ultrasound to the patient outcomes measured. Depending on the condition, ultrasound (active and placebo) was used alone or in conjunction with other interventions in a manner designed to identify its contribution and distinguish it from those of other interventions. METHODS: Thirty-five English-language RCTs were published between 1975 and 1999. Each RCT identified was scrutinized for patient outcomes and methodological adequacy. RESULTS: Ten of the 35 RCTs were judged to have acceptable methods using criteria based on those developed by Sackett et al. Of these RCTs, the results of 2 trials suggest that therapeutic ultrasound is more effective in treating some clinical problems (carpal tunnel syndrome and calcific tendinitis of the shoulder) than placebo ultrasound, and the results of 8 trials suggest that it is not. DISCUSSION AND CONCLUSION: There was little evidence that active therapeutic ultrasound is more effective than placebo ultrasound for treating people with pain or a range of musculoskeletal injuries or for promoting soft tissue healing. The few studies deemed to have adequate methods examined a wide range of patient problems. The dosages used in these studies varied considerably, often for no discernable reason.

Humans↗
PubMed2001

A review of therapeutic ultrasound: biophysical effects.

Almost 2 decades ago, it was pointed out that physical therapists tended to overlook the tenuous nature of the scientific basis for the use of therapeutic ultrasound. The purpose of this review is to examine the literature regarding the biophysical effects of therapeutic ultrasound to determine whether these effects may be considered sufficient to provide a reason (biological rationale) for the use of insonation for the treatment of people with pain and soft tissue injury. This review does not discuss articles that examined the clinical usefulness of ultrasound (see article by Robertson and Baker titled "A Review of Therapeutic Ultrasound: Effectiveness Studies" in this issue). The frequently described biophysical effects of ultrasound either do not occur in vivo under therapeutic conditions or have not been proven to have a clinical effect under these conditions. This review reveals that there is currently insufficient biophysical evidence to provide a scientific foundation for the clinical use of therapeutic ultrasound for the treatment of people with pain and soft tissue injury.

Animals↗
PubMed2000

Impact of HIV infection on meningitis in Harare, Zimbabwe: a prospective study of 406 predominantly adult patients.

OBJECTIVE: To determine the causative organisms and characteristics of patients presenting with features of meningitis. DESIGN: A prospective cross-sectional study. SETTING: Two tertiary university-affiliated hospitals in Harare, Zimbabwe. PATIENTS: Four-hundred and six patients clinically suspected to have meningitis. MAIN OUTCOME MEASURES: Causative organisms of meningitis; clinical and cerebrospinal fluid characteristics. RESULTS: Four-hundred and six predominantly adult (95% were aged > or = 18 years) patients were suspected to have meningitis. Of the 200 patients confirmed to have meningitis, 89 (45%) had cryptococcal meningitis (CM), 54 (27%) had mononuclear meningitis (MM), 31 (16%) had pyogenic meningitis (PM), 24 (12%) had tuberculous meningitis (TBM) and 2 (1%) had undefined meningitis. HIV seropositivity was 100% in CM, 83% in MM, 81% in PM and 88% in TBM patients. In-hospital mortality rate was 38.8% for CM, 34.9% for MM, 68% for PM and 66.7% for TBM. HIV seropositivity was 80% in the 206 patients not found to have meningitis. CONCLUSIONS: All patients suspected to have meningitis had a high HIV sero positivity irrespective of whether they were later confirmed to have meningitis or not. CM was the most common type of meningitis seen. In-hospital mortality was high irrespective of the cause of meningitis.

AIDS-Related Opportunistic Infections↗
PubMed2000

Setting safe and effective suction pressure: the effect of using a manometer in the suction circuit.

OBJECTIVES: To establish the levels of pressure used to perform tracheal suction (TS) and if they are affected by having a manometer visible in the suction circuit. DESIGN: A bench test evaluation of simulated tracheal suction. SETTING: Physiotherapy department of a major teaching hospital in Melbourne, Australia. PARTICIPANTS: Sixty-four nurses and physiotherapists who regularly apply TS to patients in the intensive care units of this hospital. INTERVENTIONS: All subjects used both circuit A (without a visible manometer) and B (with a visible manometer) in a predetermined random order. For both, subjects adjusted the suction control tap to where they said a safe and effective pressure (set pressure) was delivered and then occluded the suction catheter as though suctioning (applied pressure). Subjects then completed a questionnaire on their current TS practise. MEASUREMENTS AND RESULTS: All set pressures (mean = 228.57 mmHg) and all applied pressures (mean = 359. 52 mmHg) were significantly higher (P <.001) when compared to the expected pressures (mean = 135 mmHg). Pressures set without a visible manometer (circuit A) were significantly higher (P <.05) than those using a visible manometer (circuit B) but the applied pressures were not significantly different (P =.166). Neither the investigator (P =.618) or the test order (P =.167) had a significant effect on the outcome. Questionnaire results showed 31 % of subjects considered 100-170 mmHg a safe and effective suction pressure whilst none reported using an objective means of measuring pressure. CONCLUSION: All pressures in both circuits were significantly higher than those recommended as safe in the literature. In addition, pressures were unaffected by the inclusion of a visible manometer in the suction circuit.

Adult↗
PubMed2000

The variation in fatigue rate with frequency using kHz frequency alternating current.

The most commonly used stimulus for functional electrical stimulation is low frequency, short duration pulsed current. A disadvantage is the associated rapid fatigue. The present study investigated the effect of kHz frequency alternating currents on the rate of fatigue with electrically induced skeletal muscle contractions in normal subjects. Alternating current with frequencies between 1 and 15 kHz, interrupted at 50 Hz and applied in 3-s surges with an effective 1:1 duty cycle, was applied transcutaneously for a 10-min period, during which time electrically induced wrist extensor torque was measured. The decline in torque with time was analysed in terms of "fast" and "slow" fatigue components. A systematic frequency dependence was found in each. "Fast" torque decline is interpreted as reflecting fast-fatigue muscle fibre activity and "slow" torque decline, that of fatigue-resistant fibres. With this interpretation, over the frequency range 1-10 kHz, the proportion of fatigue-resistant fibres contributing to the torque increases. It is argued that this is due to selective dropout of fast-fatigue fibres. The findings suggest the potential usefulness of kHz frequency alternating current for functional electrical stimulation.

Adult↗
PubMed2000

Work-related musculoskeletal disorders in physical therapists: prevalence, severity, risks, and responses.

BACKGROUND AND PURPOSE: Physical therapists are at risk for work-related musculoskeletal disorders (WMSDs). Little is known of how therapists respond or of what actions they take to prevent injury. The purpose of this study was to investigate the prevalence and severity of WMSDs in physical therapists, contributing risk factors, and their responses to injury. SUBJECTS: As part of a larger study, a systematic sample of 1 in 4 therapists on a state register (n=824) was surveyed. METHODS: An 8-page questionnaire was mailed to each subject. Questions investigated musculoskeletal symptoms, specialty areas, tasks and job-related risk factors, injury prevention strategies, and responses to injury. RESULTS: Lifetime prevalence of WMSDs was 91%, and 1 in 6 physical therapists moved within or left the profession as a result of WMSDs. Younger therapists reported a higher prevalence of WMSDs in most body areas. Use of mobilization and manipulation techniques was related to increased prevalence of thumb symptoms. Risk factors pertaining to workload were related to a higher prevalence of neck and upper-limb symptoms, and postural risk factors were related to a higher prevalence of spinal symptoms. CONCLUSION AND DISCUSSION: Strategies used to reduce work-related injury in industry may also apply to physical therapists. Increased risk of thumb symptoms associated with mobilization techniques suggests that further research is needed to establish recommendations for practice. The issues for therapists who move within or leave the profession are unknown, and further research is needed to better understand their needs and experiences.

Adult↗
PubMed1998

Sensory, motor, and pain thresholds for stimulation with medium frequency alternating current.

OBJECTIVES: To investigate the effect of frequency of alternating current on the sensory, motor, and pain thresholds in normal subjects, and to establish the optimal frequency for motor stimulation with minimal subject discomfort. DESIGN: A repeated measures design using two groups of 11 subjects. SETTING: A laboratory setting was used. PARTICIPANTS: Participants were volunteers who met the inclusion criteria. INTERVENTIONS: Alternating current with 20 different carrier frequencies between 1 and 35 kHz, all modulated at 50 Hz, was applied to each subject on two separate occasions. For half the subjects, the frequency was increased or decreased sequentially (reversed on second occasion), and for the other half, it was applied in a different random order on each occasion. MAIN OUTCOME MEASURES: The voltage at the sensory threshold was recorded for each applied frequency. This was subsequently repeated for motor and pain thresholds. RESULTS: Sensory, motor, and pain thresholds decreased with increasing frequency between 1 kHz and approximately 10 kHz. Above 10 kHz, the thresholds increased. The ratio pain threshold/sensory threshold increased systematically with increasing frequency over the range examined. By contrast, the ratio pain threshold/motor threshold showed a distinct maximum at a frequency of 10 kHz. Marked accommodation to motor and pain fiber stimulation was observed. CONCLUSIONS: For comfortable sensory stimulation, a high frequency of alternating current is preferable. Discrimination between pain and motor stimulation is maximal at a frequency of approximately 10 kHz. This suggests that the optimal frequency for comfortable motor stimulation, one that is least likely to elicit pain fiber stimulation, is close to 10 kHz.

Adult↗
PubMed1998

Variation in torque production with frequency using medium frequency alternating current.

OBJECTIVES: To investigate the effect of frequency of alternating current on electrically induced torque in healthy subjects, and to establish an optimum frequency for motor stimulation. DESIGN: A repeated-measures design using 12 subjects (part 1) and 3 subjects (part 2). SETTING: A laboratory setting was used. PARTICIPANTS: Participants were volunteers who met the inclusion criteria. INTERVENTIONS: Alternating current with carrier frequencies between 1 and 15kHz, modulated at 50Hz, was applied to each subject on two separate occasions. The frequencies were applied in a different random order on each occasion and different random orders were used between subjects. For part 1 of this study, six frequencies were used: 1, 2, 4, 7, 10, and 15kHz. For part 2, three frequencies were used: 1, 4, and 10kHz. MAIN OUTCOME MEASURES: Part 1: The maximum electrically induced torque, defined as the torque induced at the pain threshold, was recorded for each applied frequency. Part 2: The variation of torque with increasing stimulus intensity was recorded for each applied frequency. RESULTS: Highest electrically induced torque was produced at the lowest frequency examined (1kHz). Torque decreased systematically with increasing frequency over the frequency range examined. The rate of increase in torque with applied stimulus intensity was also found to decrease systematically with increasing frequency in a way that depended strongly on the skinfold thickness of the subject. CONCLUSIONS: Electrical stimulators using an alternating current waveform typically use a carrier frequency in the range of 2kHz to 4kHz for motor stimulation. This study shows that carrier frequencies in this range, modulated at 50Hz, are a compromise between comfort and maximum torque production. For maximum comfort with a low torque, a frequency close to 10kHz is indicated. For maximum torque, a lower frequency of alternating current (1kHz or less) is preferable.

Adult↗
PubMed1998

Cryptococcal meningitis in human immunodeficiency virus-infected patients in Harare, Zimbabwe.

A prospective observational study was conducted over a 10-month period to determine the clinical and laboratory manifestations of cryptococcal meningitis in Zimbabwe, a country where antifungal agents are not widely available. Eighty-nine patients with cryptococcal meningitis (median age, 34 years; range, 11-63 years; 56 males) were identified from 406 patients for whom a clinical diagnosis of meningitis had been made. All patients tested were positive for antibody to human immunodeficiency virus. Cryptococcal meningitis was the first AIDS-defining illness in 88% of patients. Typical presentations were headache, mental impairment, and meningism (median duration, 14 days; range, 1-180 days). The median CD4+ cell count was 70/microL (range, 0-651/microL). The cumulative median survival from the time of diagnosis was 14 days (range, 0-233 days); 22% of patients survived for >30 days. Independent indicators of a good prognosis were not identified. This study provides a unique basis for the development of novel management strategies for patients with cryptococcal meningitis who reside in resource-poor countries.

AIDS-Related Opportunistic Infections↗
PubMed1998

Thoracic spiral CT: influence of subsecond gantry rotation on image quality.

PURPOSE: To determine if the lower milliampere second setting and shorter acquisition time of subsecond spiral computed tomography (CT) affects the image quality of thoracic CT scans. MATERIALS AND METHODS: In 92 consecutive outpatients referred for thoracic CT, spiral CT (120 kV, 292 mA) was performed with 1-second (n = 45) or 0.75-second (n = 47) scanning time. An equal percentage of patients (70%) in each group received intravenous contrast medium. At six mediastinal and six lung zones, degradation due to motion and noise, respectively, were graded independently on a four-point scale by three blinded radiologists. Statistically significant differences were determine with a two-tailed test. RESULTS: Mediastinal image quality was significantly better on 0.75-second scans than on 1-seconds scans (P < .001). Regions with the greatest improvement in image quality were around the aortic root, cardiac ventricles, and aortic arch. Lung image quality was also better on 0.75-second scans than on 1-second scans (P = .04). On 0.75- and 1-second scans, respectively, motion-related artifacts were found to degrade image quality 6.2 and 8.7 times more than noise-related artifacts in the mediastinum and 2.6 and 3.9 times more in the lungs. CONCLUSION: Subsecond spiral CT is associated with improved clarity and diminished motion artifacts on mediastinal and pulmonary images when compared with 1-second spiral CT.

Adolescent↗
PubMed1996

Limited interchangeability of methods of applying 1MHz ultrasound.

OBJECTIVE: To investigate the interchangeability of two different methods used to apply 1 MHz ultrasound for deep tissue heating, namely, the direct contact and the subaqueous methods. DESIGN: An intervention study with a crossover design. SETTING: The setting was a laboratory. PARTICIPANTS: Four specimens, cross-sections of nonliving pig tissue, were used. INTERVENTIONS: Specimens were each exposed to 1 MHz ultrasound under five different conditions: in contact with gel, and subaqueous at 0, 1, 2, and 4 cm from the applicator to the skin. MAIN OUTCOME MEASURES: Tissue temperatures were measured at six thermocouple sites at different depths from the skin surface. RESULTS: Subaqueous ultrasound applied at a distance of 0 cm from the skin produced significantly less tissue heating than direct contact (with gel) ultrasound at the same intensity. Increasing the distance from the applicator to the skin from 0 to 1, 2 and 4 cm resulted in significantly lower mean maximum temperature increases of 69%, 56%, and 44%, respectively, of the 0 cm values. CONCLUSIONS: The methods used clinically to apply ultrasound have only limited interchangeability. Large corrections to the power output are required to compensate when using subaqueous rather than direct (in air) ultrasound, and for applicator to skin distances of beyond 0 cm in subaqueous ultrasound.

Animals↗
PubMed1996

Dosage factors for the subaqueous application of 1MHz ultrasound.

OBJECTIVE: To determine and validate correction factors necessary to ensure consistent dosage of 1MHz ultrasound when applied in water at different applicator-to-skin distances and different levels of intensity. DESIGN: An intervention study with a crossover design. SETTING: A laboratory. PARTICIPANTS: Cross-sections of nonliving pig tissue. INTERVENTIONS: Specimens were each exposed to 1MHz ultrasound under four subaqueous conditions: in contact with the skin and at 1, 2, and 4 centimeters from the applicator to the skin. These conditions were repeated for each of three intensity levels: 0.5W/cm2, 1.0 W/cm2, and 2.0 W/cm2. MAIN OUTCOME MEASURES: Tissue temperatures were measured at six thermocouple locations at different depths from the skin surface. RESULTS: Increasing the distance from the applicator to the skin from 0 to 1, 2, and 4 centimeters resulted in progressive and significantly lower mean maximum temperature increases. The same relation of distance to temperature increase was identified at all intensity levels and was used to calculate dosage factors for distance in water. By multiplying the required intensity by the calculated dosage factors, the temperature increases in tissue were found to equal those produced at 0 centimeters distance. CONCLUSIONS: Large corrections to the intensity output are required to compensate when using ultrasound in water at different applicator-to-skin distances. These dosage (correction) factors are reliable for the range of intensity levels tested under the conditions examined.

Analysis of Variance↗