Twist Rate Research Articles

Multi-phase-shifted helical long period fiber grating based temperature-insensitive optical twist sensor.

A compact temperature-insensitive optical fiber twist sensor based on multi-phase-shifted helical long period fiber grating has been proposed and experimentally demonstrated in this paper. A multi-phase-shifted helical long period fiber grating is fabricated with a multi-period rotation technology. A π/2 and a 3π/2 phase shift is introduced in the helical long period fiber grating by changing the period. The helical pitch can be effectively changed with a different twist rate, which is measured by calculating the wavelength difference between two phase shift peaks. Although the wavelength of the phase shift peak also shifts with a change of the temperature, the wavelength difference between two phase shift peaks is constant due to two fixed phase shifts in the helical long period fiber grating, which is extremely insensitive to temperature change for the multi-phase-shifted helical long period fiber grating. The experimental results show that a sensitivity of up to 1.959 nm/(rad/m) is achieved.

Some basic solutions for nonlinear creep

The aim of the paper is to derive the exact analytical expressions for torsion and bending creep of rods that obey the Norton–Bailey, Prandtl–Garofalo and Naumenko–Altenbach–Gorash constitutive models. The common secondary creep constitutive model is the Norton–Bailey law which gives a power law relationship between creep rate and stress. The closed form solutions for fractional Norton–Bailey creep law are derived. The analytical formulas express the torque and bending moment as functions of the time for the period of relaxation. Other formulas express the twist rate and curvature as functions of the time for the duration of engineering creep experiment. The derived formulas are suitable for the practically important problems of machinery. Namely, the formulas are relevant for calculation of hereditary effects for helical, leaf and disk springs and twisted shafts.

Nonreciprocal phase shift caused by magnetic-thermal coupling of a polarization maintaining fiber optic gyroscope

A theory for nonreciprocal phase shift caused by cross coupling generated in a polarization maintaining (PM) fiber optic gyroscope (FOG) under the combined action of magnetic and temperature fields is proposed. The magnetic-thermal coupling in the FOG originates from the interaction of the magnetic field, fiber twist, birefringence caused by thermal stress, and the intrinsic and bending birefringence of the fiber. The cross coupling changes with temperature. When the PM fiber has a diameter of 250 μm, beat length of 3 mm, length of 500 m, twist rate of 1 rad/m, and optical source wavelength of 1310 nm, the maximum degree of magnetic-thermal coupling generated by a 1 mT radial magnetic field within the temperature range of -20°C to 60°C is -5.47%.

O053 Enhanced diastolic untwisting and attenuated systolic twisting rate at rest in a large homogenous cohort of elite athletes: features of the athletes heart independent of left ventricular morphology

O053 Enhanced diastolic untwisting and attenuated systolic twisting rate at rest in a large homogenous cohort of elite athletes: features of the athletes heart independent of left ventricular morphology

The control of twisting somersaults

In the takeoff and early flight phase of a twisting somersault, joint coordination is based on feed-forward control whereas in the late stages of the flight phase configuration adjustments are made using feedback control to ensure accurate completion of the movement and appropriate landing orientation. The aim of this study was to use a computer simulation model of aerial movement to investigate the extent to which arm and hip movements can control twist and somersault rotation in the flight phase of a twisting somersault. Two mechanisms were considered for the control of twist in simulated target trampoline movements with flight times of 1.4s. In the first case a single symmetrical arm adduction correction was made using delayed feedback control based on the difference between the twist rate in a perturbed simulation and the twist rate in a target movement comprising a forward somersault with 1½ twists. Final corrections were made using symmetrical arm abduction and hip flexion to adjust the twist and somersault angles. In the second case continual asymmetrical arm adduction/abduction adjustments were used to remove the tilt from a perturbed full twisting backward somersault using delayed feedback control based on twist angle and angular velocity. The first method was able to cope with perturbations to a forward somersault with 1½ twists providing the feedback time delay was less than 200ms. The second method was able to correct a perturbed full twisting backward somersault providing the feedback time delay was less than 125ms.

Three dimensional dynamics of pretwisted beams: A spectral-Tchebychev solution

Abstract This paper presents the application of the spectral-Tchebychev (ST) technique for solution of three-dimensional dynamics of unconstrained pretwisted beams with general cross-section (including both straight and curved cross-sections). In general, the dynamic response of pretwisted beams presents three-dimensional (3D) motions, including coupled bending–bending–torsional–axial motions. As such, accurately solving pretwisted beam dynamics requires a 3D solution approach. In this work, the integral boundary value problem based on the 3D linear elasticity equations is solved numerically using the 3D-ST approach. To simplify evaluation of the volume integrals, the boundaries are simplified by applying two coordinate transformations to render the pretwisted beam with curved cross-section into an equivalent straight beam with rectangular cross-section. Three sample pretwisted beam problems with rectangular, curved, and airfoil cross-sections at different twist rates are solved using the presented approach. In each case, the convergence of the solution is analyzed, and non-dimensional natural frequencies and mode shapes are compared to those from a finite-element (FE) solution. Furthermore, cross-sectional stress and displacements are obtained from the 3D-ST solution. Lastly, the non-dimensional natural frequencies from the 3D-ST and a 1D/2D solutions are compared. It is concluded that the 3D-ST solution can capture the three-dimensional dynamic behavior of pretwisted beams as accurately as an FE solution, but for a fraction of the computational cost. Furthermore, it is shown that 1D/2D solution can lead to significant errors at high twist rates, and thus, the 3D-ST solution should be preferred.

Expression and significance of E-cadherin, N-cadherin, transforming growth factor-β1 and Twist in prostate cancer

ObjectiveTo study the expression of E-cadherin, N-cadherin, TGF-β1 and Twist protein and investigate its significance in the occurrence and development of prostate cancer. MethodsThe expression of E-cadherin, N-cadherin, TGF-β1 and Twist protein in 59 prostate cancer tissues and 21 adjacent tissues were detected by immunohistochemical SABC staining, and the correlation with clinicopathological features was analyzed. ResultsPositive rates of E-cadherin, N-cadherin, TGF-β1 and Twist were 32.2%, 54.2%, 71.2% and 74.6%, respectively, in prostate cancer tissues and 85.7%, 9.52%, 19.0% and 9.52%, respectively, in cancer-adjacent tissues, with significant differences between the two groups (P<0.05). The reduced expression of E-cadherin was related to the differentiation of prostate cancer tissues and PSA level, but was not associated with clinical stage, lymph node metastasis, bony metastasis and age. The increased expression of N-cadherin, TGF-β1 and Twist was related to the differentiation of prostate cancer tissues, clinical stage, lymph node metastasis, bony metastasis, but not to age. The difference in positive expression of N-cadherin and TGF-β1 was significant between PSA≤20 μg/L group and PSA>20μg/L group, but the positive expression of Twist was not significant between groups. The expression of E-cadherin was highly negatively correlated with that of N-cadherin and also highly negatively correlated with that of Twist. The expression of TGF-β1 was correlated with those of E-cadherin, N-cadherin and Twist. ConclusionsThe reduced expression of E-cadherin, abnormal expression of N-cadherin, transformation form E-cadherin to N-cadherin and the increased expression of TGF-β1 and Twist play an important role in the occurrence and development of prostate cancer.

Two- and Three-Dimensional Speckle Tracking Analysis of the Relation Between Myocardial Deformation and Functional Capacity in Patients With Systemic Hypertension

The purpose of this study was to investigate left ventricular (LV) mechanics in hypertensive patients by 2- and 3-dimensional (3D) speckle tracking imaging, and determine the relation between the LV mechanics and functional capacity in this population. This cross-sectional study included 51 recently diagnosed, untreated, hypertensive patients, 49 treated subjects with well-controlled arterial hypertension, 52 treated participants with uncontrolled hypertension, and 50 controls adjusted by gender and age. All the subjects underwent 24-hour blood pressure monitoring, complete 2-dimensional and 3D examination, and cardiopulmonary exercise testing. 3D global longitudinal, circumferential, radial, and area strains were similar between the control group and well-controlled hypertensive patients but significantly decreased in comparison with patients with untreated or inadequately controlled hypertension. Similar findings were obtained for LV torsion and twist rate, whereas LV untwisting rate significantly deteriorated from the controls, across the well-controlled group, to the patients with untreated or uncontrolled hypertension. Peak oxygen uptake was significantly lower in the patients with untreated and uncontrolled hypertension than in the controls and the well-treated hypertensive patients. Peak oxygen uptake was independently associated with LV untwisting rate (β = 0.28, p = 0.03), 3D LV ejection fraction (β = 0.31, p = 0.024), and 3D global longitudinal strain (β = 0.26, p = 0.037) in the whole hypertensive population in our study. In conclusion, LV mechanics and functional capacity are significantly impaired in the patients with uncontrolled and untreated hypertension in comparison with the controls and the well-controlled hypertensive patients. Functional capacity is independently associated with 3D global longitudinal strain, LV untwisting rate, and 3D LV ejection fraction.

Measuring mechanical strain and twist using helical photonic crystal fiber

Solid-core photonic crystal fiber (PCF) with a permanent helical twist exhibits dips in its transmission spectrum at certain wavelengths. These are associated with the formation of orbital angular momentum states in the cladding. Here we investigate the tuning of these states with mechanical torque and axial tension. The dip wavelengths are found to scale linearly with both axial strain and mechanical twist rate. Analysis shows that the tension-induced shift in resonance wavelength is determined both by the photoelastic effect and by the change in twist rate, while the torsion-induced wavelength shift depends only on the change in twist rate. Twisted PCF can act as an effective optically monitored torque-tension transducer, twist sensor, or strain gauge.

Left ventricular strain distribution in healthy dogs and in dogs with tachycardia-induced dilated cardiomyopathy

BackgroundRecently, left ventricular (LV) strain distribution pattern has been assessed in several cardiac disease states. Tachycardia-induced cardiomyopathy (TIC) is an animal model of non-ischemic cardiomyopathy well characterized in terms of global LV dysfunction but with poor understanding of regional variability in LV function. We hypothesized that TIC induces specific changes in LV strain distribution pattern.MethodsTwenty five adult mongrel conscious dogs were trained to lie down calmly for echocardiography. In seven selected dogs, we implanted pacing system for TIC induction under general anesthesia. We measured LV geometry and function, strains, and torsion before and after the development of TIC in awake non-sedated state.ResultsIn 25 healthy dogs, all three types of normal strain significantly increased from base to apex (p <0.05), while a definite and recognizable twist could be measured due to presence of shear strain. In 7 dogs with TIC, marked changes in LV mechanics occurred throughout the cardiac cycle, resulting in decrease of strain (p <0.001), twist (p <0.05), and negative peak twist rate (p <0.05). Interestingly, the relative decrease of strain due to TIC was more pronounced in the apex (p < 0.001), with the radial strain decreasing the most (p < 0.05).ConclusionTIC is accompanied by decreased systolic LV strain and twist deformation, as well as loss of early diastolic recoil. In addition, the decrease of strain was more profound in the apex. This “reverse” distribution of LV strain may help us understand LV dysfunction in the presence of nonischemic etiology.

Quantification of Popliteal Artery Deformation During Leg Flexion in Subjects With Peripheral Artery Disease: A Pilot Study

To quantify the in vivo deformations of the popliteal artery during leg flexion in subjects with clinically relevant peripheral artery disease (PAD). Five patients (4 men; mean age 69 years, range 56-79) with varying calcification levels of the popliteal artery undergoing endovascular revascularization underwent 3-dimensional (3D) rotational angiography. Image acquisition was performed with the leg straight and with a flexion of 70°/20° in the knee/hip joints. The arterial centerline and the corresponding branches in both positions were segmented to create 3D reconstructions of the arterial trees. Axial deformation, twisting, and curvatures were quantified. Furthermore, the relationships between the calcification levels and the deformations were investigated. An average shortening of 5.9%±2.5% and twist rate of 3.8±2.2°/cm in the popliteal artery were observed. Maximal curvatures in the straight and flexed positions were 0.12±0.04 cm(-1) and 0.24±0.09 cm(-1), respectively. As the severity of calcification increased, the maximal curvature in the straight position increased from 0.08 to 0.17 cm(-1), while an increase from 0.17 to 0.39 cm(-1) was observed for the flexed position. Axial elongations and arterial twisting were not affected by the calcification levels. The popliteal artery of patients with symptomatic PAD is exposed to significant deformations during flexion of the knee joint. The severity of calcification directly affects curvature, but not arterial length or twisting angles. This pilot study also showed the ability of rotational angiography to quantify the 3D deformations of the popliteal artery in patients with various levels of calcification.

Effects of varying twist and twist rate sensitivities on the interpretation of torsion testing data

The Nadai and Fields and Backofen expressions are widely used to convert the torque/twist data obtained during torsion testing into shear stress/shear strain curves as well as von Mises equivalent stress/equivalent strain curves. However, when employed in the conventional manner using average values of the twist hardening exponent N, they overestimate the critical strains for the initiation of twinning, dynamic transformation and dynamic recrystallization by comparison with the values determined using compression testing. By contrast, when the local or instantaneous values of the exponent are employed, the torsion and compression results are in good agreement. Another feature of the corrected curves is that they indicate that considerably more dynamic softening takes place during the high temperature deformation of austenite than suggested by the average N flow curves. It is shown that, despite the lack of work conjugacy between the torque-twist and stress–strain curves, the above expressions always lead to the correct constitutive behavior at the external radius.

Effects of non-dipper blood pressure pattern on left ventricular rotational mechanics in hypertensive patients with type 2 diabetes mellitus: a speckle tracking study

We aimed to evaluate the effects of non-dipper BP pattern on left ventricular (LV) rotational mechanics in hypertensive patients with type 2 diabetes mellitus (T2DM) with the utility of two-dimensional speckle tracking echocardiography (2D-STE). Eighty-six hypertensive patients with T2DM were enrolled. All patients underwent 2D-echocardiography and 24-h-ambulatory blood pressure monitoring. Fifty-nine (59.3%) patients had non-dipper BP pattern and all subjects had normal LV function. Patients with non-dipper BP pattern had decreased systolic tissue velocity (p: 0.006), increased peak systolic apical rotation and rotation rate (p: 0.008 and p: 0.014, respectively), and peak LV twist and twist rate (p: 0.005 and p: 0.012, respectively). Analysis of LV diastolic parameters showed that, early diastolic tissue velocity (Em) was decreased and E/Em ratio and LV mass (LVM) index were increased in non-dipper group while the time to LV untwisting rate was delayed. In multivariate analysis, peak LV twist (β = 0.459, p: < 0.001) and twist rate (β = 0.388, p: 0.001) were independently associated with the difference between mean arterial pressure (MAP)-asleep and MAP-awake. In correlation analysis adjusted for age, sex and LVM index, the time to LV untwisting rate was positively correlated with the difference between MAP-asleep and MAP-awake (r: 0.290 vs. p: 0.008) and E/Em ratio (r: 0.280 vs. p: 0.010). LV rotational mechanics are impaired in T2DM non-dipper hypertensive patients, indicating LV systolic and diastolic dysfunction. 2D-STE may permit better understanding of the underlying pathophysiology and development of preventive strategies.

Left ventricular twist and untwist rate provide reliable measures of ventricular function in myocardial ischemia and a wide range of hemodynamic states

Although rotational parameters by speckle tracking echocardiography (STE) have been previously compared to sonomicrometry and cardiac magnetic resonance imaging, few have examined the relationship between left ventricular (LV) rotational mechanics and intraventricular measures of load-independent contractility, LV stiffness, or ventriculoarterial coupling. The aim of this study was to compare the changes in LV rotational indices to intraventricular pressure–volume (PV) relationships under a range of inotropic states induced by pharmacological interventions, acute ischemia, and changes in preload. In nine pigs, simultaneous echocardiographic imaging and LVPV measurements were performed during pharmacologically induced high or low inotropy and during acute ischemia by ligation of the left anterior descending coronary artery (LAD). Maximal ventricular elastance (Emax), arterial elastance (Ea), ventricular–arterial coupling (Emax/Ea), dP/dt, tau, and other hemodynamic parameters were determined. Dobutamine and esmolol infusions led to inversely correlated changes in hemodynamic measurements of LV function. Apical but not basal rotation and diastolic rotation rate were decreased by esmolol and increased by dobutamine. The LV twist correlates well with Emax (r = 0.83) and Emax/Ea (r = 0.80). Apical diastolic rotation rate also correlates with dP/dtmin (r = −0.63), τ (r = −0.81), and LV stiffness (r = −0.52). LAD ligation decreased systolic and diastolic LV rotation in apical (P < 0.05), but not basal myocardium. Occlusion of the inferior vena cava, to reduce preload, increased apical rotation in systole and diastole. LV rotational parameters measured by STE provide quantitative and reproducible indices of global LV systolic and diastolic function during acute changes in hemodynamics.

Factors Influencing the Twisting and Untwisting Properties of the Left Ventricle during Normal Pregnancy

During pregnancy, important hemodynamic changes occur, consistent with an increase in preload and decrease in afterload and systemic vascular resistance. The aim of the present study was to investigate the changes in left ventricular (LV) strain and rotational properties during the 3 trimesters of normal pregnancy and to examine the factors that drive these changes. Twenty-seven pregnant women (29.7 ± 6.9 years) and 11 age-matched nonpregnant controls (29.9 ± 5.4 years) were evaluated. Conventional echocardiography and two-dimensional speckle tracking imaging were performed at 8-12 (1st trimester), 21-28 (2nd trimester), and 33-36 (3rd trimester) weeks of pregnancy. LV rotation, twist, untwisting rate, and circumferential strain were measured using the parasternal short-axis views at basal and apical levels. Global longitudinal strain was calculated from the LV apical views. Peak LV twist and peak untwisting rate increased significantly in the 3rd trimester of normal pregnancy (13.48 ± 2.90°, 13.12 ± 3.30°, 16.83 ± 3.61°, P < 0.001; and -111.52 ± 23.54°/sec, -107.40 ± 26.58°/sec, -144.30 ± 45.14°/sec, P < 0.001; in the 1st, 2nd, and 3rd trimester, respectively). Global longitudinal and circumferential strain of the apex decreased significantly from the 2nd trimester. An independent association was found between the change in LV twist and the change in LV end-systolic volume between the 1st and 3rd trimester. Peak untwisting rate at the 3rd trimester correlated significantly with peak twist and LV end-diastolic volume. During normal pregnancy, LV twist and peak untwisting rate increase in the 3rd trimester and correlate with end-systolic and end-diastolic volume, respectively. Circumferential strain of the apex and global longitudinal strain decrease from the 2nd trimester.

High-temperature mechanical response of A359–SiCp–30%: torsional loading (II)

Aluminum metal–matrix composites are lightweight materials that have the potential to supplant steel in many applications. The current work helps to identify the parameters that confer maximal strength and ductility. Torsion tests were performed on the as-cast aluminum metal–matrix composite A359–SiCp–30% at a variety of temperatures and twist rates. Dependence of material properties on temperature and strain rate were identified from equivalent stress–strain curves constructed from the reduced data. Examination of the microstructure was performed on the as-cast material and on fracture surfaces. A temperature- and strain rate-dependent constitutive model was applied to simulation of the mechanical response of the torsion specimen. Trends in material properties corroborate and extend trends identified previously under tensile loading with regard to temperature and strain rate dependence. Shear properties of simulated specimens agree with properties obtained through experimentation.

Adults with growth hormone deficiency have subclinical left ventricular dysfunction without vascular dysfunction, suggesting intrinsic myocardial disease

Background: Growth hormone deficiency (GHD) is associated with increased cardiovascular events. Our preliminary data, on 20 patients, suggested the presence of subclinical longitudinal left ventricle (LV) dysfunction. Therefore, we performed detailed assessment of cardiac and arterial function in 50 patients with GHD, in order to assess the mechanisms of subclinical cardiac involvement. Methods: 50 patients with GHD (47±15 yrs, 34 males), free of any cardiovascular disease or diabetes, were compared with 50 normals (N) (age- and sex- matched). Global LV systolic function was assessed from fractional shortening (LVFS), ejection fraction (LVEF), MAPSE, and cardiac index (CI); regional LV systolic function, by speckle tracking echocardiography (STE), from global longitudinal strain (GLS), global radial strain (GRS), and global circumferential strain (GCS); torsion from basal and apical rotation (RotB, RotA), LV torsion (LVtor), twist and untwist rate (TR, UTR). Arterial function was assessed from intima-media thickening, local wave speed, elastic modul, and stiffness index (β); endothelial function from flow mediated dilation. ProBNP and stimulated seric growth hormone (GHs) were measured. Results: GHD patients had decreased parameters of global, longitudinal, and circumferential LV systolic functions (table), with similar GRS (51.6±18.2 vs 56±16.7); meanwhile, they had lower torsion and increased proBNP (61±50 vs 24±21, p=0.006). On contrary, they had normal arterial and endothelial functions. Levels of GHs correlated positively to LVtor and TR, and inversely to UTR (r=0.61, r=0.72, r=-0.63, all p<0.001). View this table: Table 1. Comparison between GHD patients and N Conclusion: Patients with GHD had subclinical LV systolic dysfunction. Since arterial and endothelial functions are not significantly affected, our findings suggest that GHD patients have intrinsic myocardial disease, probably due to insufficient development or contractile function of myocardial fibres.

Early detection and prediction of taxanes-induced cardiac dysfunction by assessment of myocardial deformation

Taxanes are extremely potent drugs, used in therapeutic regimes for breast cancer. However, the applicability is limited by the risk of cardiotoxicity. Guidelines define chemotherapy-induced cardiac dysfunction based on conventional parameters, such as left ventricular (LV) ejection fraction (EF) or fractional shortening (FS). Since normal EF or FS can mask LV impairment, our aim was to define other parameters, such as 4D LV deformation or biomarkers, able to diagnose early cardiac dysfunction, and to predict cardiotoxicity. Methods: 20 women with breast cancer (51±9 yrs), without cardiac disease, EF>50%, scheduled to be treated with taxanes, were assessed at baseline, after 1st cycle, and at the completion of treatment (cumulative dose of 417±154 g/m2). Conventional and 4D auto LV quantification echo were used to assess LV geometry, EF, FS, and systolic deformation: radial, longitudinal, circumferential strain (RS, LS, CS), and area strain (AS). STE was used to measure LV rotation: peak apical and basal rotation (RotA and RotB), LV twist (LVT), and twist and un-twist rate (TR and UTR). Cardiac troponin I and C-reactive protein were also measured. Results: After the 1st cycle of taxanes, there were reductions in longitudinal and radial deformation, and area strain, persistent after the completion of treatment, whereas LV dimensions, EF, FS, circumferential deformation, and rotation remained unchanged. On contrary, at the final of chemotherapy there was a significant decrease of EF (57±4% vs 63±3%, p=0.001), with no further changes of circumferential deformation and rotation or biomarkers level. A decrease of AS of 18% after the 1st cycle of taxanes was the best independent (r2=0.81, p=0.001) and accurate (100% sensitivity and 73% specificity, AUC 0.63) predictor of EF reduction at the completion of treatment. View this table: LV deformation and rotation Conclusion: Assessment of myocardial deformation by 4D echo detects early LV dysfunction and can predict further changes in EF, and therefore, can be used to monitor taxanes-induced cardiac dysfunction.

Left Ventricular Twist and Circumferential Strain in Dogs with Myxomatous Mitral Valve Disease

During the cardiac cycle, the ventricle undergoes a twisting motion because of the oblique orientation of the left ventricular (LV) myofibers. This can be quantified by speckle-tracking echocardiography (STE). In mitral regurgitation (MR) in humans, the short axis deformation has been suggested as being pivotal to LV function. Decreased and delayed LV twist has been described in experimental MR, but has not been studied in myxomatous mitral valve disease (MMVD). (1) Magnitude (CSt) and rate (CSRs) of systolic circumferential deformation decrease before the onset of congestive heart failure (CHF); (2) magnitude and rate of LV twist decrease, and onset of untwist is delayed, with increasing MMVD severity. A total of 97 privately owned small- to medium-sized dogs. Severity of MMVD was assessed by echocardiography and presence of clinical signs of CHF. Magnitude and rate of LV twist and circumferential deformation were evaluated by STE. Dogs with CHF receiving treatment had increased CSt, CSRs, early diastolic untwisting rate, and delayed onset of untwist compared to dogs with minimal MMVD and increased systolic twist compared to dogs with mild MMVD (all P < .01). CSt and time to onset of untwist increased with echocardiographic variables of MR severity (all P < .002). CSRs and several LV twist variables decreased with increasing systolic LV internal diameter (all P < .01). No STE-derived variable was decreased before onset of CHF. In dogs with CHF receiving treatment, the delayed onset of relaxation might indicate LV dysfunction and the hyperdynamic CSt and LV twist reflect compensatory mechanisms.

Temperature‐ and strain‐independent torsion sensor utilising polarisation‐dependent loss of Hi‐Bi FBGs

A temperature- and strain-independent torsion sensor based on analysis of polarisation-dependent loss (PDL) characteristics of high-birefringent (Hi-Bi) fibre Bragg gratings (FBGs), is proposed and demonstrated. Unlike the amplitude spectra, the PDL response has higher sensitivity to torsion. Experimetal results demonstrate that the difference between the two peaks in the PDL spectra has a linear relationship with the twist rate, but remains invariant with changes in temperature and strain. In addition, it was observed that the PDL responses to the clockwise twist are just opposite of the responses to the couterclockwise twist.