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Biomedical subjects

D A MacLeod

Publications and source records attributed to D A MacLeod.

33 records · Page 2Linked to original sources
PubMed1990

Cardiac-locomotor coupling while finger tapping.

Coupling between cardiac and locomotor rhythms has been identified while people walk, run, hop and cycle at cadences natural to them. To test the hypothesis that cardiac-locomotor coupling occurs during finger tapping, we studied 20 normal subjects tapping a telegraph key at a comfortable rate for 10 min. 15 subjects (75%) coupled significantly at one or more single-digit integer ratio (heart/tapping rate), the most common of which was 1:2. Such coupling should be considered a potentially confounding variable when studying finger tapping in subjects with disease or medication affecting heart rate. Also, the identification of coupling during the repetitive activity of small upper-extremity muscles suggests that neither increases in cardiac load nor impact-loading, two suggested explanations for why coupling occurs, are necessary for the phenomenon.

Adult↗
PubMed1989

Coupling of cardiac and locomotor rhythms.

The pressure within exercising skeletal muscle rises and falls rhythmically during normal human locomotion, the peak pressure reaching levels that intermittently impede blood flow to the exercising muscle. Speculating that a reciprocal relationship between the timing of peak intramuscular and pulsatile arterial pressures should optimize blood flow through muscle and minimize cardiac load, we tested the hypothesis that heart rate becomes entrained with walking and running cadence at some locomotion speeds, by means of electrocardiography and an accelerometer to provide signals reflecting heart rate and cadence, respectively. In 18 of 25 subjects, 1:1 coupling of heart and step rates was present at one or more speeds on a motorized treadmill, generally at moderate to high exercise intensities. To determine how exercise specific this phenomenon is, and to refute the competing hypothesis that coupling is due to vertical accelerations of the heart during locomotion, we had 12 other subjects cycle on an electronically braked bicycle ergometer. Coupling was found between heart rate and pedaling frequency in 10 of them. Cardiac-locomotor coupling appears to be a normal physiological phenomenon, and its identification provides a fresh perspective from which to study endurance.

Adult↗
PubMed1989

Coupling between cardiac and locomotor rhythms: the phase lag between heart beats and pedal thrusts.

During some rhythmic exercises, the heart and exercise rates may become coupled (be within 1% of each other). If the intraarterial and skeletal intramuscular pressure cycles were reciprocal, blood flow to exercising muscle should be maximized and cardiac load minimized. In this study the authors tested the hypothesis that, while coupling is present, the phase lag between the pedaling and cardiac contraction cycles is consistent and appropriate. Twenty-seven subjects pedaled, at a frequency natural to them, on an electronically braked bicycle ergometer that held the power output constant regardless of pedaling rate. To assess the phase lag between pedal thrust (two per revolution) and heart beat, pedal-gated plots of the electrocardiography signal were generated throughout the most coupled five-minute work load for each of the 9 subjects in whom the rates were within 1% of each other for at least two consecutive four-second samples taken every fifteen seconds. During this interval of thirty-seconds in which the rates were within 1% of each other, the phase lag of most subjects gradually lengthened and shortened and there was considerable variation among subjects, refuting the authors' hypothesis. The results of this study illustrate the importance of beat-by-beat analysis when studying coupling phenomena. The preliminary assumption, that the coupling between cardiac and locomotor rhythms during cycling was on the basis of a single ischemic muscle group, has apparently been disproven.

Adult↗
PubMed1989

"Bedside" test of static rear stability of occupied wheelchairs.

The assessment of static stability can be helpful in wheelchair prescription and adjustment, but ordinarily requires a tipping platform. We developed a simple "bedside" test of rear wheelchair stability, using a goniometer and a plumb line. The angle of the wheelchair handle while the occupied wheelchair was on a level surface was subtracted from the angle measured while the occupied chair was balanced over the rear axle. The intraobserver and interobserver reliability and the validity in comparison with platform testing were assessed by studying 30 patient-occupied wheelchairs. There was a high correlation (r = 0.93, p less than 0.001) between the values obtained from the beside and platform tests and no significant difference between them. Intraobserver and interobserver reliabilities were 0.87 (p less than 0.001) and 0.94 (p less than 0.001). There was no significant difference between the first and second test values done by a single observer; the mean difference (+/- 1SD) between observers, 1.3 degrees (+/- 1.6 degrees), was small but statistically significant. The bedside test is simple, reliable, valid, and suitable for use as a screening test for the platform assessment of rear stability.

Accident Prevention↗
PubMed1988

Effect of limited knee-flexion range on peak hip moments of force while transferring from sitting to standing.

The hypothesis that limiting the knee-flexion range increases the peak hip-extension moment while transferring from sitting to standing was tested by filming (100 fps) ten normal human volunteers. With the knees flexed 105 degrees from full extension (0 degrees) the mean (+/- 1 S.D.) peak hip-extension moment was 142 (+/- 37) Nm. With the knees flexed only 75 degrees subjects threw their arms and trunks forward to a greater extent, with a peak moment of 253 (+/- 65) Nm (p less than 0.0001). If the peak moments rise to a similar degree in patients with arthritis and limited knee-flexion range, they may accelerate hip joint damage or the loosening of hip endoprostheses.

Adult↗
PubMed1988

The effect of locomotion speed on the anterior tibial intramuscular pressure of normal humans.

We examined the hypothesis that anterior tibial intramuscular pressure increases with the speed of locomotion. A solidstate pressure transducer was placed near the tip of an intramuscular fluid-filled catheter and each of ten normal subjects walked, jogged and ran barefoot, at 1.5, 2.5 and 3.5 m s-1 respectively, on a treadmill to which they had been previously familiarized. The pressure signals during ten gait cycles from each subject were sampled at 600 Hz and were averaged at each speed. The peak pressures increased in magnitude as a function of increasing locomotion speed, while the mean pressure remained constant.

Adult↗
PubMed1987

The influence of foot position on standing balance.

To test the hypothesis that variations in foot position would significantly affect standing balance, we studied ten normal subjects on a Kistler force platform which measured the travel and center of pressure displacement. With the feet together there was substantially more mediolateral (ML) travel than with the axes of the feet 15, 30 or 45 cm apart and the mean ML position of the center of pressure was displaced toward the right; there was no consistent effect on anteroposterior (AP) travel or position. As the right foot was placed 10 and 30 cm forward or back, the least amount of ML and AP travel occurred with the feet even or at 10 cm either direction; the mean AP and ML position moved toward the foot which was placed more posteriorly. Of the five foot angles ranging from toes-out 45 degrees to toes-in 45 degrees, the extent of ML and AP travel was lowest in the toes-out 25 degrees position and greatest in the toes-in 45 degrees position; the mean AP and ML position was farthest forward and to the right with toes-in 45 degrees. These findings have implications for the prosthetic replacement of the lower limbs, sports, ergonomics and postural sway studies.

Biomechanical Phenomena↗
PubMed1985

Mortality and morbidity after anterior lesser curve seromyotomy with posterior truncal vagotomy for duodenal ulcer.

A survey has been performed of the mortality and morbidity of anterior lesser curve seromyotomy with posterior truncal vagotomy in the elective treatment of chronic duodenal ulcer. There was one death in a series of 605 patients due to a myocardial infarction, an operative mortality of 0.16 per cent. There was no case of ischaemic necrosis of the lesser curvature or fundus of the stomach. Eleven patients had symptoms of delayed gastric emptying (1.7 per cent) and seven of these underwent a drainage procedure (1.3 per cent). Postoperative dumping did not occur, significant diarrhoea was present in two patients (0.33 per cent). This operation is relatively simple, quick and extremely safe to perform. It is suggested that the more widespread use of this type of elective surgery for duodenal ulcer might reduce the mortality from the condition.

Chronic Disease↗
PubMed1985

Simulated leg-length discrepancy: its effect on mean center-of-pressure position and postural sway.

We hypothesized that leg-length discrepancies of as little as 1cm would induce a significant postural shift and increase the extent of postural sway. We had 14 normal volunteers stand on a force platform with their feet in a standard position. Center-of-pressure data were recorded at 100Hz for 20 seconds while the subjects stood barefoot with no lifts or (in random order) with lifts of 1, 2, 3, and 4cm under their left and right feet. From these data we derived the mean center-of-pressure position and the extent of postural sway. Lifts of as little as 1cm shifted the mean center-of-pressure toward the longer leg to a statistically significant extent (p less than 0.001), the mean difference compared with the barefoot condition being 6.1% of the distance between the feet; increasing the discrepancy did not proportionately increase the effect. The postural sway (total travel of the center-of-pressure) in a mediolateral direction increased significantly with a 1cm discrepancy (p less than 0.01), and continued to increase in proportion to the magnitude of the discrepancy. There were no effects on anteroposterior position or sway and no influence of left-right dominance. These results support our hypothesis that a leg-length discrepancy of as little as 1cm may be biomechanically important.

Adult↗
PubMed1976

Propranolol in the treatment of thyrotoxicosis by subtotal thyroidectomy.

Subtotal thyroidectomy was performed in 40 patients with thyrotoxicosis in whom propranolol alone was used as preparation for surgery. Propranolol was given orally in a dose of 40 mg every 6 h for a mean preoperative period of 17 days (range 4-60 days) and continued for seven days after operation. The mean +/- SE blood loss at operation was only 160 +/- 20 ml. The period of follow-up was from three to nine months. Recurrent thyrotoxicosis has not occurred in any patient. Low levels of total serum triiodothyronine (T3) and total serum thyroxine (T4) were observed in the early postoperative weeks in some patients and were associated with symptoms of mild hypothyroidism, but by six months in the presence of a raised serum thyrotropin (TSH) the thyroid hormone levels returned to normal. Permanent hypothyroidism developed in only two patients. Despite normal or low total serum T3 and T4 levels, the TSH response to thyrotropin-releasing hormone (TRH) was absent in all patients one week after operation. At four weeks and at eight weeks, the response was absent or sub-normal in 70% and 20% of the patients respectively, indicating a delay in the recovery of the hypothalamo-pituitary axis previously exposed to high levels of T3 and T4. It is considered that subtotal thyroidectomy for thyrotoxicosis in patients prepared with propranolol is an acceptable procedure which has some advantages over the conventional preparation with carbimazole and potassium iodide, not the least of which are the potential reduction in preparation time, the more flexible timing of operation, and the reduced operative blood loss.

Female↗
PubMedDate not supplied

Wheelchair-related accidents caused by tips and falls among noninstitutionalized users of manually propelled wheelchairs in Nova Scotia.

The purpose of this study was to document what proportion of noninstitutionalized users of manually propelled wheelchairs are affected by wheelchair-related accidents caused by tips and falls, determine the nature and severity of the resulting injuries, and, by comparison with an unaffected group, identify factors associated with the risk of such accidents. We administered a postal questionnaire to as many as possible of the estimated 2055 members of the target population in the province of Nova Scotia. Among the 577 appropriate respondents, 57.4% reported they had completely tipped over or fallen from their wheelchairs at least once, and 66.0% reported having partially tipped. Of the falls and tips that were reported, 46.3% were forward in direction, 29.5% backward and 24.2% sideways. Many of the accidents occurred outdoors or on ramps. A total of 292 injuries were reported by 272 (47.1%) respondents. Most of the injuries (84.3%) were minor (e.g., abrasions, contusions, lacerations and sprains). Of the 15.8% of injuries that were serious, the most common were fractures (10.6%) and concussions (2.7%). Factors that appear to be associated with an increased risk of accidents and injuries included younger age, male gender, paraplegia or spina bifida as the reason for wheelchair use, having had a wheelchair prescribed, some wheelchair features (lightweight, camber, adjustable rear-axle positions, a knapsack), daily use of a wheelchair, propelling the chair with both hands, use of the wheelchair for recreation, use of a sideways transfer (without a transfer board) and doing repairs themselves or having them done by the dealer. Factors associated with a decreased risk include multiple sclerosis, stroke or arthritis as the reason for wheelchair use, attendant propulsion and the use of a one-person assist for transfers. The results of this study, that wheelchair-related accidents caused by tips and falls are very common, that serious injuries are not unusual and that there is a pattern of risk factors, should be useful to wheelchair users, clinicians, manufacturers and regulatory bodies.

Accidents↗