Biomedical subjects

M Lortie

Publications and source records attributed to M Lortie.

At least 19 recordsLinked to original sources

PubMed2001

Identification of physiological systems: estimation of linear time-varying dynamics with non-white inputs and noisy outputs.

A new technique to identify linear time-varying systems from ensembles of input-output realisations is presented. First, a correlation-based least-squares method is derived. This method consists of solving, for each sampling time, a matrix equation involving estimates of the input autocorrelation and input-output cross-correlation functions computed from data across the ensemble. Then, the matrix inverse needed to solve this matrix equation is replaced with a pseudo-inverse. The model is thus constrained to describe only those components of the dynamics that can be reliably identified. Ignoring 'unidentifiable' components has virtually no adverse effect on the predicted outputs. Simulation results demonstrate that the pseudoinverse technique yields more reliable estimates of the dynamics than a previously proposed least-squares technique when the inputs are coloured and the output signal-to-noise ratio (SNR) is low. With the input spectrum flat up to approximately 10% of the sampling rate and an output SNR of 5dB, the mean variance accounted for (VAF) between the true instantaneous impulse response functions (IRFs) and the instantaneous IRFs estimated with the least-squares technique was 0.2%. In contrast, the mean VAF between the true instantaneous IRFs and the instantaneous IRFs estimated with the pseudoinverse technique was 89.0%.

Ankle Joint↗

PubMed2001

Identification of time-varying Hammerstein systems from ensemble data.

In this paper, we describe a new technique to identify rapidly time-varying Hammerstein systems from ensembles of input-output realizations. The technique involves two steps. A correlation approach is first used to obtain initial estimates of the linear subsystem parameters for every sampling time. An iterative optimization algorithm is then employed to produce final estimates of the system parameters. The input does not need to be white. The technique was tested on simulated data and was found to produce excellent results under realistic conditions.

Algorithms↗

PubMed2000

Observation procedures characterizing occupational physical activities: critical review.

The first objective of this paper is to compare the observation procedures proposed to characterize physical work. The second objective is to examine the following 3 methodological issues: reliability, observer training, and internal validity. Seventy-two papers were reviewed, 38 of which proposed a new or modified observation grid. The observation variables identified were broken down into 7 categories as follows: posture, exertion, load handled, work environment, use of feet, use of hands, and activities or tasks performed. The review revealed the variability of existing procedures. The examination of methodological issues showed that observation data can be reliable and can present an adequate internal validity. However, little information about the conditions necessary to achieve good reliability was available.

Canada↗

PubMed1999

Modulation of stretch reflexes during imposed walking movements of the human ankle.

Our overall objectives were to examine the role of peripheral afferents from the ankle in modulating stretch reflexes during imposed walking movements and to assess the mechanical consequences of this reflex activity. Specifically we sought to define the changes in the electromyographic (EMG) and mechanical responses to a stretch as a function of the phase of the step cycle. We recorded the ankle position of a normal subject walking on a treadmill at 3 km/h and used a hydraulic actuator to impose the same movements on supine subjects generating a constant level of ankle torque. Small pulse displacements, superimposed on the simulated walking movement, evoked stretch reflexes at different phases of the cycle. Three major findings resulted: 1) soleus reflex EMG responses were influenced strongly by imposed walking movements. The response amplitude was substantially smaller than that observed during steady-state conditions and was modulated throughout the step cycle. This modulation was qualitatively similar to that observed during active walking. Because central factors were held constant during the imposed walking experiments, we conclude that peripheral mechanisms were capable of both reducing the amplitude of the reflex EMG and producing its modulation throughout the movement. 2) Pulse disturbances applied from early to midstance of the imposed walking cycle generated large reflex torques, suggesting that the stretch reflex could help to resist unexpected perturbations during this phase of walking. In contrast, pulses applied during late stance and swing phase generated little reflex torque. 3) Reflex EMG and reflex torque were modulated differently throughout the imposed walking cycle. In fact, at the time when the reflex EMG response was largest, the corresponding reflex torque was negligible. Thus movement not only changes the reflex EMG but greatly modifies the mechanical output that results.

Adult↗

PubMed1998

Box Handling in the Loading and Unloading of Vans.

The handling of 2,306 boxes being loaded or unloaded from vans onto or from 4-wheeled trolleys by 31 handlers in a warehouse were characterized. Handling was videotaped and characterized through an analysis grid completed by three trained observers. The following execution parameters were observed: nature of the exertion applied by the upper limbs, plane and direction of the exertion, resulting displacement of the box, grip, use of the lower limbs and the back. Results show that execution parameters used by handlers vary considerably from those usually recommended or studied. For example, symmetric grips were rarely used (4%). The grip was modified during the handling of half the boxes. Significant knee flexion was rarely observed (3% of exertions). Each box was moved by applying an average of 3.5 different exertions. Exertions were mostly applied in a plane parallel to the shoulders; they were rarely executed in a strict sagittal plane (11%). The implication of these observations are discussed.

Journal Article↗

PubMed1997

Relapse and short sickness absence for back pain in the six months after return to work.

OBJECTIVES: To measure the incidence of back pain relapse (causing three consecutive days off work on medical advice) and of short sickness absence (less than three consecutive days), and to determine whether the incidence of such events was affected by overall pain and specific pain related to simple daily movements (functional capacity) assessed at discharge. METHODS: A cohort of workers with a first compensated episode of back pain was prospectively followed up from return to work after rehabilitative treatment. Follow up among 230 workers was carried out monthly by phone for a maximum of six months. Crude and adjusted rate ratios (RRs) along with 95% confidence intervals (95% CIs) were estimated with the Cox's proportional hazards model. RESULTS: Within six months of return to work, 29 workers (12.6%) had relapsed, and another 15 workers (6.5%) had a short sickness absence. 50% of relapses had occurred within 42 days of return to work whereas this figure was 28 days for short sickness absence. In a multivariate model that considered pain and clinical variables at discharge only a scale combining all pain variables (specific daily movements as well as the visual analog overall pain scale) contributed to relapse and short sickness absence as the outcome (RR (95% CI)) (1.53 (0.96-2.43)); the same was true in a model considering pain and workers' views on desired changes to work conditions (1.60; 1.08 to 2.36). CONCLUSIONS: Incidence of relapse or short sickness absence in the first six months after return to work was 19.1%. Of all measured prognostic variables (sociodemographic, clinical, workers' views, and pain), only overall pain and pain associated with carrying out simple daily movements were helpful in predicting relapse or short sickness absence.

Absenteeism↗

PubMed1997

Agmatine affects glomerular filtration via a nitric oxide synthase-dependent mechanism.

Arginine decarboxylase is present in the kidney and metabolizes the amino acid, arginine, to agmatine. Agmatine increases filtration rate in single nephrons (J. J. Lortie, W. F. Novotny, O. W. Peterson, V. Vallon, K. Malvey, M. Mendonca, J. Satriano, P. Insel, S. C. Thomson, and R. C. Blantz. J. Clin. Invest. 97:413-420, 1996). Experiments were conducted to determine whether exogenously administered agmatine exerts these effects via interaction with nitric oxide synthase (NOS) and whether this interaction depends upon alpha 2-adrenergic receptors. Agmatine microperfused (1 microM) into the urinary space of surface glomeruli of the rat increased nephron filtration rate from 33 +/- 4 to 40 +/- 5 nl/min with complete recovery within 10 min. When NG-monomethyl-L-arginine (L-NMMA), a nonselective NOS inhibitor, was systemically infused, agmatine no longer increased single-nephron glomerular filtration rate (SNGFR). BHT-933, an alpha 2-adrenergic agonist, did not increase SNGFR and was unaffected by concurrent L-NMMA. In vitro incubation of freshly harvested glomeruli with agmatine resulted in significant increases in the generation of cGMP, effects similar to carbachol, and blocked by nitro-L-arginine methyl ester (L-NAME) but not yohimbine, an alpha 2-adrenergic antagonist. Agmatine exerts effects on glomerular ultrafiltration via a constitutive NOS-dependent mechanism, and this does not require the participation of alpha 2-adrenoreceptors.

Agmatine↗

PubMed1996

Knee movement strategies differentiate expert from novice workers in asymmetrical manual materials handling.

One way to generate hypotheses on appropriate handling principles is to compare the strategies of highly skilled workers (experts) with those of novice workers (novices). This study was conducted to determine whether experts differ from novices in their handling strategies and to determine the effects of these differences in joint motions and net reaction moments at the trunk (L5/S1) and knees. Six experts and five novices were compared transferring two loads (12 and 22 kg) from four different initial low positions to a standardized low position on a trolley. The external forces were obtained from two AMTI force platforms, and two 16 mm Locam cameras coupled with two mirrors were used to obtain the three-dimensional kinematic data. An inverse dynamic analysis was performed on each segment and the net reaction moments were evaluated at L5/S1 and the knees; trunk posture, knee flexion angles and feet spacings were also calculated. Results showed that both groups minimized trunk asymmetries of posture and efforts; however, the experts were characterized by reduced knee flexion (31 degrees vs 53 degrees) and total knee excursion (20 degrees vs 38 degrees), increased flexion moments (72 vs 58 Nm) but reduced extension moments (4 vs 26 Nm) and valgus moments (30 vs 54 Nm). The experts' strategies appear safer overall because they reduce trunk asymmetry, asymmetrical efforts on the knee and stress on the femoropatellar joint. Moreover, these strategies present a potential for reduced mechanical energy expenditure due to lower knee excursions and increased knee stability due to reduced knee flexion.

Adult↗

PubMed1996

Prognostic factors for return to work after a first compensated episode of back pain.

OBJECTIVES: To determine which factors measured at baseline and during the course of treatment influence time to return to work after a first compensated episode of back pain. METHODS: The design is a treatment inception cohort including 305 compensated workers out of 402 eligible ones presenting at two rehabilitation centres for conventional treatment. Crude and adjusted rate ratios (RRs) along with 95% confidence intervals (95% CIs) were estimated with the Cox's proportional hazards regression. RESULTS: 50% of workers had not returned to work after 112 days of follow up, and 11.3% still had not after 270 days. At the end of the study period (maximum follow up time was 1228 days), 230 workers (75.4%) had returned to work, 6.5% had not, and a similar percentage had retired, gone into vocational training, or returned to school. In the final model stratified for radiating pain during treatment, which was an important prognostic variable, workers between 21 to 30 years of age had a greater chance of returning to work (RR (95% CI) 1.43 (1.04 to 1.98) than those > or = 30. The other factors associated with a greater chance of returning to work were: a diagnosis of sprain or pain upsilon a diagnosis of intervertebral disc disorder (2.20 (1.23-3.91)), < 30 days of waiting between the accident and the beginning of treatment (1.30 (0.96 to 1.77)), a good flexion at baseline (1.52 (1.04 to 2.23)), absence of neurological symptoms during treatment (1.40 (0.98-2.00)), > 24 months of employment in the industry (1.49 (1.10 to 2.03)), working for a public industry upsilon a private one (1.63 (1.21 to 2.19)), and the ability to take unscheduled breaks (1.45 (1.06 to 1.97)). CONCLUSIONS: Even with a first episode of back pain, time to return to work is long and the proportion not returning is high. Return to work as expected is influenced by disease and host characteristics but also by social and work factors. Reinstatement programmes should account for all these factors.

Adult↗

PubMed1996

Activities of nitric oxide in normal physiology and uremia.

Nitric oxide (NO) generated from arginine exerts a variety of renal and extrarenal physiological and pathophysiological effects. NO is generated by two types of nitric oxide synthases: acutely responsive, constitutive NOS and slower, more persistent inducible NOS (iNOS). The latter is transcriptionally dependent, often stimulated by cytokines. NO regulates glomerular ultrafiltration, tubular reabsorption, and intrarenal renin secretion; many of these renal effects are mediated by interactions with angiotensin II and adrenergic (alpha 2) activity. Decreased NO activity also enhances tubuloglomerular feedback activity, which could contribute to renal vasoconstriction, NaCl retention, and elevated blood pressure. Loss of renal function could influence NO activity via: (1) endothelial dysfunction; (2) decreased arginine synthesis by kidney; (3) responses to arginine analogs that act as NOS inhibitors; (4) increased cytokine activity; and (5) altered oxidation:reduction status of cells, etc. For example, platelet dysfunction in uremia may be caused by cytokine-induced iNOS activation. Moreover, acutely responsive, constitutive NOS activity may be depressed in progressive loss of renal function. Decreased NO activity might contribute to baroreceptor dysfunction observed in hypertension and progressive renal disease. Studies of the impact of uremia suggest that iNOS may be chronically stimulated by cytokines, whereas acutely responsive, constitutive NOS activity may be concurrently depressed.

Animals↗

PubMed1995

Reuse of disposable laparoscopic instruments: a study of related surgical complications.

OBJECTIVE: To determine the rate of surgical complications related to reuse of disposable laparoscopic instruments. DESIGN: A review of all laparoscopic and thoracoscopic procedures done between August 1990 and January 1994 in which disposable laparoscopic instruments were reused. SETTING: Department of general surgery in a 461-bed teaching hospital. PATIENTS: Patients who underwent 874 laparoscopic and thoracoscopic procedures in which disposable laparoscopic instruments were reused according to validated reprocessing protocols. MAIN OUTCOME MEASURES: The incidence of superficial and deep wound infections and complications related to instrument malfunction. RESULTS: The combined rate for deep and superficial infections was 1.8%. No complications related to a disposable instrument malfunction were found. CONCLUSION: Disposable laparoscopic instruments may be safely reused under carefully monitored conditions and with strict guidelines.

Disposable Equipment↗

PubMed1995

Disorders of body fluid balance: a new look into the mechanisms of disease.

OBJECTIVE: To review the mechanisms of disease on the basis of dysfunction in body fluid distribution secondary to abnormalities in capillary permeability and plasma membrane transport disorders, leading to quantitative and qualitative alterations of the interstitial space, a mainly strategic compartment positioned between the microcirculation and cell mass. DATA SOURCES: The recent literature on the mechanisms involved in the control of body fluid balance, with special reference to microcirculation and interstitial compartment physiology, as well as published and unpublished original data from the authors laboratory. DATA EXTRACTION AND SYNTHESIS: To illustrate the importance of capillary permeability dysfunction in the development of disease, animal (rat and dog) models of chronic renal failure, acute diuretic-induced fluid depletion, diabetes mellitus, arterial hypertension and ischemia-reperfusion of the kidney were used in an attempt to show that in all these experimental models, basic capillary permeability dysfunction (measured by the extravasation of Evans blue, a marker of albumin leakage) develops in specific microcirculation beds. As a consequence, tissue edema (interstitial and/or cellular) develops and likely impairs the traffic of nutrients and waste products to and from the cellular mass, and/or challenges the microcirculation, leading to organ damage. Kidney dysfunction is measured by conventional clearance methods (renal hemodynamics and tubular function). In some models, the eventual mediators of vascular abnormality are examined by use of pharmacological tools. CONCLUSIONS: The critical role of microcirculation dysfunctions, in particular capillary permeability, resulting in interstitial compositional changes is presented as the basis of disease. The apparent specificity of target organ damage may represent the nonspecific result of physicochemical alteration in the strategic interstitial fluid compartment.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1994

Regional changes in the extravasation of albumin in the canine kidney: comparison of bradykinin and water diuresis.

This report describes the adaptation of the albumin bound Evans blue dye (EB) extraction technique and its use in identifying regional changes in albumin extravasation rates. We present data to justify our technical approach and highlight the use of this method by describing differences resulting from two different models of induced diuresis and natriuresis. Results observed under control conditions (Group 1) are compared to those obtained following the infusion of bradykinin (BK) into the left kidney (Group 2) or hypotonic saline-induced water diuresis (Group 3). EB and water content of tissue samples of cortex (CTX), outer medulla (OM), inner medulla (IM), and papilla (PAP) regions are reported. Under control conditions a significant heterogeneous distribution of EB and water content (wet/dry tissue weight) between zones was observed. Left kidney EB values for the CTX, OM, IM, and PAP in Group 1 were 125 +/- 11, 398 +/- 56, 763 +/- 51, and 741 +/- 52 micrograms EB/g dry tissue and respective wet/dry tissue ratios were 4.48 +/- 0.05, 5.10 +/- 0.19, 7.13 +/- 0.37, and 6.35 +/- 0.32. In Group 2, BK caused a selective increase in cortex EB content to 201 +/- 7 (P < 0.01) micrograms EB/g dry tissue, without altering water content values. Results of EB extraction in Group 3 revealed no change in the CTX but significant increases in the OM, IM, and PAP regions: 576 +/- 40 (P < 0.01), 910 +/- 60 (P < 0.01), and 850 +/- 69 (P < 0.05) micrograms EB/g dry tissue, respectively. Likewise, tissue water content values were unchanged in the CTX but significantly greater in the OM, IM, and PAP: 6.02 +/- 0.22, 8.90 +/- 0.25, and 8.40 +/- 0.17, respectively (P < 0.01, all three values). This technique clearly shows the regional heterogeneity of the renal microvascular network and allows the localization of intrarenal changes in albumin extravasation. This method provides evidence that BK increases albumin extravasation in the cortex only and that changes in the renal medulla are obtained in hypotonic saline-induced water diuresis.

Albumins↗

PubMed1994

Renal reperfusion injury: sequential changes in function and regional albumin extravasation.

We report on the renal function and regional extravasation of albumin-bound Evans blue dye (EB) in the kidneys of anesthetized dogs following 30 min occlusion of the left renal artery. Left kidney (LK) function was halted and no change in right kidney (RK) function was observed during ischemia. Clearances of para-amino-hippurate and inulin from the LK were significantly (P < 0.01) less than control after 10 min of reperfusion, 22.6 +/- 6.8 vs 90.1 +/- 7.8 and 9.0 +/- 2.9 vs 34.2 +/- 2.1 ml/min, respectively. Renal hemodynamic parameters never did fully recover in subsequent periods but filtration fraction was unchanged from control throughout the reperfusion period. Urine flow and sodium excretion from the LK was significantly (P < 0.01) less than control values after 10 min of reperfusion, 0.41 +/- 0.14 vs 0.80 +/- 0.08 ml/min and 60 +/- 21 vs 161 +/- 8 mu eq/min, respectively, but fully recovered in subsequent periods. Significant (P < 0.01) decrease from control values in the LK content of EB was observed in the inner medulla and papilla regions after 30 min of reperfusion, 586 +/- 60 vs 763 +/- 51 and 549 +/- 54 vs 741 +/- 52 micrograms/EB/g dry tissue, respectively. After 60 min of reperfusion in the LK, significant (P < 0.05) changes from control in EB content were evident exclusively in the outer medulla, increasing from 398 +/- 56 to 491 +/- 17 micrograms/EB/g dry tissue, respectively. A general edema in the LK, measured as an increase in the ratio of wet/dry tissue weight, became evident only after 60 min of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗

PubMed1994

Manual handling in warehouses: the illusion of correct working postures.

Results from a study on load handling in two warehouses are presented. The loads were mainly handled with the back bent and in twisted postures. The so-called 'correct lifting' method was rare. The dimensional constraints of storing systems and the influence of the environment and load characteristics on handling strategies are described. As a conclusion, it is proposed that training in lifting skills should be replaced by training in manual handling in general, and by ergonomic improvements.

Accidents, Occupational↗

PubMed1993

Comparison of spinal health indicators in predicting spinal status in a 1-year longitudinal study.

A 1-year longitudinal study was performed to assess and compare the predictive qualities of spinal health indicators (excluding the cervical spine) among aircraft assembly workers having at least 1 year seniority in a large assembly plant. Ten health indicators were compared to determine their sensitivity and predictive power with regard to back compensation and absenteeism in 12 months follow-up, and the presence of any limitation at work due to the back, or symptoms to the back at the end of the interval. The initial response to a self-administered questionnaire was obtained from 269 male workers, of whom 205 (76.2%) completed the follow-up questionnaire. Initial prevalence of symptoms to the back was 42.3%, limitation in performing at work was 28.1%, consultation of a health professional was 7.3%, and a history of compensation for the back (ever) was reported by 30.4%. During the year of follow-up, 16 (6%) of the 269 workers initially enrolled were granted 17 compensated episodes. Of the 205 workers who responded to the follow-up, 33 (16.1%) have been absent from work (with or without compensation) because of their back. The presence, at the beginning of the study, of a limitation in performing at work or in activities of daily living and a history of compensation (ever) were the three indicators independently associated with the occurrence of compensation or absenteeism (total work disability) related to a back problem during the following year.(ABSTRACT TRUNCATED AT 250 WORDS)

Absenteeism↗

PubMed1992

The role of B1- and B2-kinin receptors in the renal tubular and hemodynamic response to bradykinin.

Bradykinin (BK) is known to induce diuresis (UV), natriuresis (UNaV), and increased renal blood flow (RPF) with little or no change in glomerular filtration rate (GFR). In this study, BK is infused alone and concurrently with B1- or B2-kinin receptor antagonists into the left kidney of pentobarbital-anesthetized dogs. The intrarenal infusion of BK (bolus: 0.5 microgram/kg, followed by a sustaining dose: 0.05 micrograms.kg-1.min-1) affected left kidney function only. In the left kidney, UV increased from 0.42 +/- 0.21 to a maximum of 1.88 +/- 0.55 ml/min (P less than 0.01) and UNaV rose from 55 +/- 13 to 160 +/- 17 mueq/min (P less than 0.01), while RPF was enhanced from 86 +/- 11 to 125 +/- 24 ml/min (P less than 0.05), and GFR remained unchanged. When a B1-receptor antagonist ([Leu8]-des-Arg9-BK; 2.0 micrograms.kg-1.min-1) was infused concurrently with BK, the increase in urine flow was not different from BK alone. UNaV was transiently attenuated by 50% in this group (P less than 0.05). A B2-receptor antagonist (D-Arg0,[Hyp3,D-Phe7]-BK; 2.0 micrograms.kg-1.min-1) infused with BK significantly (P less than 0.05) and selectively inhibited by 50% the maximal diuresis provoked by BK alone. UNaV in this group was not different from that induced by BK alone. Finally, the concurrent infusion of either B1- or B2-antagonist completely inhibited the rise in RPF observed when BK was infused alone. We conclude that BK infused into the renal artery of dogs in vivo can alter UV and UNaV independently of global renal hemodynamic (RPF and GFR) changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Training in handling: an evaluative study.

Training programmes in handling have been one of the most used means of preventing work-related backache. The effectiveness of these programmes has not yet been demonstrated however, since they have rarely been evaluated. The purpose of this study was precisely to assess one of these programmes in the hospital sector which specifically dealt with the handling of patients. A field study was conducted and handling methods used by 32 trained orderlies were characterized using an observational grid developed and validated specifically to describe patient handling operations. The extent to which these orderlies used the handling methods taught was determined, and the observed deviations from these methods were characterized and interpreted. The results show that the handling principles taught (working with a straight back using the legs) were not frequently used in the workplace. Furthermore, the use of training was closely related to the type of handling carried out. In handling operations in which the effort includes a horizontal component (mainly those carried out in bed) the training was hardly used, while in vertical handling operations the taught principles were more frequently used. These results suggest that actual training is not well adapted to the handling of patients, particularly to horizontal handling carried out in the bed. Two main deficiencies in the actual programmes are pointed out. First, it is shown that, for reasons of physical constraints, training could not always be applied; second, the rationale of the taught principles could also be questioned, particularly the emphasis given to the use of the legs.

Allied Health Personnel↗