The effect of a combined rehabilitation program on the temporomandibular joint in systemic sclerosis evaluated by ultrasound exam.

PURPOSE: Temporomandibular joint (TMJ) involvement is frequent in Systemic Sclerosis (SSc). Dysfunction and X-ray changes of TMJ were described only in few observational studies. Treatment as well has been seldom considered. Aim of the present study was to evaluate the effects on TMJ of two specifically designed physiotherapy protocols. METHODS: The study group included 26 SSc outpatients (22 females and 4 males with mean age ± SD 59.08 ± 10.31 years). Thirteen patients were randomly assigned to a treatment (protocol 1) including home exercises for TMJ and thirteen to a treatment (protocol 2) including home exercises and a combined procedure. The rehabilitation effects on the TMJ were evaluated by ultrasound examination (UE) in static and dynamic phases. UE was performed in all patients before and at the end of the treatment and after a follow up (8 weeks). RESULTS: Both rehabilitation protocols induced a significant improvement (protocol 1: p < 0.01 and protocol 2: p < 0.005) of mouth opening with a long-lasting effect. Protocol 2 was more effective than protocol 1. A significant increase of bilateral condyle-head temporal bone distance was detected by UE at the end of both treatments. It was maintained at follow-up in patients treated with Protocol 2. CONCLUSIONS: The present investigation shows that a rehabilitation program characterized by home exercises with a combined procedure is useful to recover the function of TMJ. The data also show that UE is helpful in the evaluation of TMJ in SSc and in the assessment of the efficacy of the rehabilitation programs.

Effects of the number of actin-bound S1 and axial force on X-ray patterns of intact skeletal muscle.

Effects of the number of actin-bound S1 and of axial tension on x-ray patterns from tetanized, intact skeletal muscle fibers were investigated. The muscle relaxant, BDM, reduced tetanic M3 meridional x-ray reflection intensity (I(M3)), M3 spacing (d(M3)), and the equatorial I(11)/I(10) ratio in a manner consistent with a reduction in the fraction of S1 bound to actin rather than by generation of low-force S1-actin isomers. At complete force suppression, I(M3) was 78% of its relaxed value. BDM distorted dynamic I(M3) responses to sinusoidal length oscillations in a manner consistent with an increased cross-bridge contribution to total sarcomere compliance, rather than a changed S1 lever orientation in BDM. When the number of actin-bound S1 was varied by altering myofilament overlap, tetanic I(M3) at low overlap was similar to that in high [BDM] (79% of relaxed I(M3)). Tetanic d(M3) dependence on active tension in overlap experiments differed from that observed with BDM. At high BDM, tetanic d(M3) approached its relaxed value (14.34 nm), whereas tetanic d(M3) at low overlap was 14.50 nm, close to its value at full overlap (14.56 nm). This difference in tetanic d(M3) behavior was explicable by a nonlinear thick filament compliance which is extended by both active and passive tension.

Myosin lever disposition during length oscillations when power stroke tilting is reduced.

M3 reflection intensity (I(M3)) from tetanized, intact skeletal muscle fiber bundles was measured during sinusoidal length oscillations at 2.8 kHz, a frequency at which the myosin motor's power stroke is greatly reduced. I(M3) signals were approximately sinusoidal, but showed a "double peak" distortion previously observed only at lower oscillation frequencies. A tilting lever arm model simulated this distortion, where I(M3) was calculated from the molecular structure of myosin subfragment 1 (S1). Simulations showed an isometric lever arm disposition close to normal to the filament axis at isometric tension, similar to that found using lower oscillation frequencies, where the power stroke contributes more toward total S1 movement. Inclusion of a second detached S1 in each actin-bound myosin dimer increased simulated I(M3) signal amplitude and improved agreement with the experimental data. The best agreement was obtained when detached heads have a fixed orientation, insensitive to length changes, and similar to that of attached heads at tetanus plateau. This configuration also accounts for the variations in relative intensity of the two main peaks of the M3 reflection substructure after a length change. This evidence of an I(M3) signal distortion when power stroke tilting is suppressed, provided that a large enough amplitude of length oscillation is used, is consistent with the tilting lever arm model of the power stroke.

Non-cross-bridge calcium-dependent stiffness in frog muscle fibers.

At the end of the force transient elicited by a fast stretch applied to an activated frog muscle fiber, the force settles to a steady level exceeding the isometric level preceding the stretch. We showed previously that this excess of tension, referred to as "static tension," is due to the elongation of some elastic sarcomere structure, outside the cross bridges. The stiffness of this structure, "static stiffness," increased upon stimulation following a time course well distinct from tension and roughly similar to intracellular Ca(2+) concentration. In the experiments reported here, we investigated the possible role of Ca(2+) in static stiffness by comparing static stiffness measurements in the presence of Ca(2+) release inhibitors (D600, Dantrolene, (2)H(2)O) and cross-bridge formation inhibitors [2,3-butanedione monoxime (BDM), hypertonicity]. Both series of agents inhibited tension; however, only D600, Dantrolene, and (2)H(2)O decreased at the same time static stiffness, whereas BDM and hypertonicity left static stiffness unaltered. These results indicate that Ca(2+), in addition to promoting cross-bridge formation, increases the stiffness of an (unidentified) elastic structure of the sarcomere. This stiffness increase may help in maintaining the sarcomere length uniformity under conditions of instability.

Frequency-dependent distortion of meridional intensity changes during sinusoidal length oscillations of activated skeletal muscle.

Bundles of intact, tetanized skeletal muscle fibers from Rana temporaria were subjected to sinusoidal length oscillations in the frequency domain 100 Hz to 3 kHz while measuring force and sarcomere length. Simultaneously, intensity of the third-order x-ray reflection of the axial myosin unit cell (I(M3)) was measured using synchrotron radiation. At oscillation frequencies <1 kHz, I(M3) was distorted during the shortening phase of the sinusoid (i.e., where bundle length was less than rest length). Otherwise, during the stretch phase of oscillations at all frequencies, during the shortening phase of oscillations above 1 kHz, and for bundles in the rigor state, I(M3) was approximately sinusoidal in form. Mean I(M3) during oscillations was reduced by 20% compared to the isometric value, suggesting a possible change in S1 disposition during oscillations. However, the amplitude of length change required to produce distortion (estimated from the phase angle at which distortion was first evident) corresponded to that of a step release sufficient to reach the maximum I(M3), indicating a mean S1 disposition during oscillations close to that during an isometric tetanus. The mechanical properties of the bundle during oscillations were also consistent with an unaltered S1 disposition during oscillations.

Crossbridge kinetics in single frog muscle fibres in presence of ethylene glycol.

Single fibres isolated from frog muscle were tetanically stimulated at 14 degrees C to produce isometric tetani at a sarcomere length of about 2.16 microm, using a striation follower device to measure the sarcomere length of a selected segment of fibre. Force-velocity data were obtained by applying ramp releases at pre-set velocity at the tetanus plateau. Sarcomere stiffness was measured at isometric plateau and during isotonic shortening by using sinusoidal length changes at 2 kHz frequency and about 1 nm per half sarcomere (hs) peak to peak amplitude. A correction method was used to compensate for the force truncation due to the quick recovery. After data collection, the bathing solution was substituted with Ringer plus ethylene glycol (EG) at 2 M (11.2% v/v). When the fibre was fully equilibrated with the new solution, the measurements were repeated. Ethylene glycol reduced the speed of the tetanus rise and tetanus relaxation without altering the isometric tension, and reduced the maximum shortening velocity by about 20%. During isotonic contraction tension and stiffness at each given shortening velocity were reduced by about the same amount, so that the stiffness/tension ratio remained almost unaltered. Force-velocity and stiffness data in both standard and EG Ringer were analysed in terms of a two state model (Huxley, 1957). The analysis showed that our results can be accounted for by assuming that EG at 2 M concentration reduces all the rate constants for crossbridges interaction by about the same amount.

Sarcomere tension-stiffness relation during the tetanus rise in single frog muscle fibres.

The sarcomere stiffness was measured in single muscle fibres during the development of tetanic tension using a method insensitive to fibre inertia and viscosity. The stiffness was calculated by measuring the ratio between tension and sarcomere length during a period of fast sarcomere elongation at constant velocity. Tension changes were corrected for force truncation by the quick recovery mechanism. The results show that the relation between force and stiffness deviates from the direct proportionality less than previously reported. If the deviation is due to the presence of a linear myofilament compliance in series with the cross-bridges, our data suggest that myofilament compliance accounts for about 30% of the sarcomere compliance. This value is significantly smaller than 50-70% determined by X-ray diffraction measurements. These two different findings, however, may be reconciled by assuming that the myofilament compliance is non-linear increasing appropriately at low tension.

Mechanical properties of frog muscle fibres at rest and during twitch contraction.

Data reported in the literature suggest that crossbridges in rapid equilibrium between attached and detached states (weakly binding bridges), demonstrated in relaxed skinned fibres at low ionic strength, could be present also in intact fibres under physiological conditions. In addition, it was suggested that the well known leading of stiffness over force during the tension development in stimulated muscle fibres could be due to an increased number of weakly binding bridges induced by the stimulation. The experiments reviewed in this paper were made to investigate these possibilities. Fast ramp length changes were applied to single frog muscle fibres at rest and during the early phases of activation. The corresponding force changes were analysed, searching for the components expected from the presence of weakly binding bridges. The results showed no mechanical indication for the presence of weakly binding bridges in both skinned and intact fibres, either at rest or during activation. It was also found that a portion of the fibre stiffness increase induced by stimulation leads the formation of crossbridges.

Submillisecond changes in myosin lattice spacing resulting from rapid length changes.

The speed of the myofilament lattice spacing response to rapid changes in load or length of single, intact muscle fibres of the frog, was investigated during isometric tetani. During ramp releases at close to Vmax and during step length changes (completed within 250 microseconds), lattice spacing was calculated from the equatorial X-ray diffraction pattern (sampled at 250 microseconds time resolution using synchrotron radiation). Ramp releases (total shortening=1.39 %) caused a spacing increase, described with an exponential function (alpha=271 s-1, amplitude=1.15 nm) plus an elastic component having the time course of discharge of axial tension (amplitude 0.28 nm). For a step release (amplitude=0.87%), lattice expansion could be described with an exponential (alpha =1005 s-1, amplitude=0.56 nm) plus an elastic component of 0.25 nm amplitude. Lattice compression was associated with a step stretch (amplitude=0.62 %), and was also quasi-exponential (alpha=367 s-1, amplitude=0.74 nm), with an elastic component of 0.28 nm. The spacing change time course for length steps resembled that of the accompanying quick recovery of axial tension and the associated change in the meridional 14.5 nm reflection intensity, which are both believed to be determined by the kinetics of the molecular power stroke. Therefore, this shows that lattice spacing changes, arising from radial forces exerted by attached crossbridges, are fast enough to occur during the power stroke event.

Volume changes of the myosin lattice resulting from repetitive stimulation of single muscle fibers.

Single muscle fibers at 1 degreesC were subjected to brief tetani (20 Hz) at intervals of between 20 s and 300 s over a period of up to 2 h. A band lattice spacing increased during this period at a rate inversely dependent on the rest interval between tetani. Spacing increased rapidly during the first 10 tetani at a rate equivalent to the production of 0.04 mOsmol.liter-1 of osmolyte per contraction, then continued to expand at a much slower rate. For short rest intervals, where lattice expansion was largest, spacing increased to a limiting value between 46 and 47 nm (sarcomere length 2.2 micrometer), corresponding to accumulation of 30 mOsmol.liter-1 of osmolytes, where it remained constant until repetitive stimulation was terminated. At this limiting spacing, force was reduced by up to 30%. The effect of lattice swelling on the lattice compression that accompanies isometric force recovery from unloaded shortening was to increase the compression, similar to that observed in hypotonic media at a similar spacing. During recovery from repetitive stimulation, spacing recompressed to its original value with a half-time of 15-30 min. These findings suggest that mechanical activity produces an increase in osmotic pressure within the cell as a result of product accumulation from cross-bridge and sarcoplasmic reticulum ATPases and glycolysis.

Force responses to fast ramp stretches in stimulated frog skeletal muscle fibres.

Force responses to fast ramp stretches at various velocities were recorded from single muscle fibres isolated from either lumbricalis digiti IV or tibialis anterior muscle of the frog (Rana esculenta) at sarcomere length between 2.15 and 3.25 microns at 15 degrees C. Stretches were applied at rest, at tetanus plateau and during the tetanus rise. Stretches with the same velocity but different accelerations were imposed to the fibre to evaluate the effect of fibre inertia on the force responses. Length changes were measured at sarcomere level with either a laser diffractometer or a striation follower apparatus. The force response to a fast ramp stretch could be divided into two phases. The initial fast one (phase 1) lasts for the acceleration period during which the stretching velocity rises up to the steady state. The second slower phase (phase 2) lasts for the remainder of the stretch and corresponds to the well-known elastic response of the fibre. Most of this paper is concerned with phase 1. The amplitude of the initial fast phase was proportional to the stretching velocity as expected from a viscous response. This viscosity was associated with a very short (about 10 microseconds) relaxation time. The amplitude of the fast phase increased progressively with tension during the tetanus rise and scaled down with sarcomere length approximately in the same way as tetanic tension and fibre stiffness. These data suggest that activated fibres have a significant internal viscosity which may arise from crossbridge interaction.

Myofilament compliance and sarcomere tension-stiffness relation during the tetanus rise in frog muscle fibres.

The sarcomere stiffness was measured in single muscle fibres during the development of tetanic tension using a method insensitive to fibre inertia and viscosity. The stiffness was calculated as the ratio between tension changes and sarcomere length changes during a period of fast sarcomere elongation at constant velocity. The results show that, unlike previous measurements with step or sinusoidal length changes, the relation between relative force and relative stiffness on the tetanus rise is linear. Consequently, the development of stiffness upon stimulation is synchronous with the development of force. Since a substantial fraction of sarcomere compliance is localized in the myofilaments, this result can be accounted for by assuming that either myofilament compliance is highly non-linear or that crossbridges stiffness during the tetanus rise is not proportional to crossbridge tension.

Studies on the 14.5 nm meridional X-ray diffraction reflection during length changes of intact frog muscle fibres.

The intensity of the 14.5 nm meridional reflection (M3) from activated skeletal muscle fibres was studied in both single fibres and fibre bundles during the imposition of length changes. During shortening at small load, the intensity of the reflection decreased within 2 ms to less than 20% of isometric intensity, then recovered partially during the remainder of the shortening. When shortening was terminated, recovery of intensity was delayed. Small shortening steps (0.5% fibre length) produced a fall in M3 intensity (IM3) delayed by ca. 250 microseconds compared to the fall in tension. For larger step releases (1% fibre length), the fall in IM3 was not delayed. The fall in IM3 could be almost completely reversed by a subsequent restretch applied within 1.5 ms. Beyond 10 ms after the initial release, the restretch caused a further fall in intensity. A rapid step stretch (0.5% fibre length) also caused a fall in IM3 without delay, which was partially reversed by a release applied within 10 ms. A second small release applied 3 ms (or less) after the first caused a second fall in M3 intensity, but without delay and with faster time course. Small amplitude sinusoidal length oscillations (0.15-0.2% sarcomere; 1 kHz) caused a sinusoidal change in M3 intensity, which was 180 degrees out of phase with the force oscillations, and lacked distortion during its release phase.

Crossbridge viscosity in activated frog muscle fibres.

Force responses to fast ramp stretches at various velocities were recorded in single muscle fibres isolated from tibialis anterior muscle of the frog (Rana esculenta) at a sarcomere length between 2.15 and 3.25 microns at 15 degrees C. Stretches were applied at the tetanus plateau and during tetanus rise. Length changes were recorded at the sarcomere level using either a laser diffractometer or a striation follower apparatus. The immediate force response to the stretch is not simply elastic, as is usually assumed, but is composed of the sum of at least two components: (i) elastic (force proportional to the amount of stretch); and (ii) viscous (force proportional to the rate of stretch). The viscous response is associated with a short (about 10 microseconds) relaxation time. The amplitude of the viscous component increases progressively with tension during the tetanus rise and scales down with sarcomere length approximately in the same way as the tetanic tension. These results suggest that the viscosity of activated fibres may arise from crossbridge kinetics.

Absence of mechanical evidence for attached weakly binding cross-bridges in frog relaxed muscle fibres.

1. Passive force responses to ramp stretches at various velocities were measured in intact and skinned single muscle fibres isolated from the lumbricalis muscle of the frog. Force was measured using a fast capacitance transducer and sarcomere length was measured using a laser light diffraction technique at a point very close to the fixed end so as to avoid effects of fibre inertia. Experiments were performed at 15 degrees C with sarcomere length between 2.13 and 3.27 microns under high (170 mM) and low (20 mM) ionic strength. 2. The analysis shows that the force response is the sum of at least three components: (i) elastic (force proportional to the amount of stretch), (ii) viscous (force proportional to rate of stretch), and (iii) viscoelastic (resembling the response of a pure viscous element in series with an elastic element). 3. The amplitude of all these components increased progressively with sarcomere length in the whole range measured. 4. A further component, attributable to the short-range elasticity (SREC), was present in the force response of the intact fibres. 5. The amplitude of the force response decreased substantially upon skinning at high ionic strength but increased again at low ionic strength. The SREC was completely abolished by skinning. 6. None of the components of the force response was found to have the properties expected from the previously postulated 'weakly binding bridges'.

Development of stiffness precedes cross-bridge attachment during the early tension rise in single frog muscle fibres.

1. Force responses to ramp stretches were recorded in single muscle fibres isolated from the lumbricalis muscle of the frog. Stretches were applied at rest and at progressively increasing times after a single stimulus. 2. The increase of fibre stiffness that precedes tension development has a 'static' component that accounts for the whole fibre stiffness increase during the latent period and at very low tension at the beginning of the twitch. 3. Static stiffness increase was not affected by 2,3-butanedione-2-monoxime, a drug that almost completely inhibited twitch tension. 4. Static stiffness increased approximately 5-fold as the sarcomere length was increased from 2.1 to 2.84 microns. 5. These results suggest that static fibre stiffness increase is not attributable to the formation of non-force-generating cross-bridges.

Lattice spacing changes accompanying isometric tension development in intact single muscle fibers.

The myosin lattice spacing of single intact muscle fibers of the frog, Rana temporaria, was studied in Ringer's solution (standard osmolarity 230 mOsm) and hyper- and hypotonic salines (1.4 and 0.8 times standard osmolarity respectively) in the relaxed state, during "fixed end" tetani, and during shortening, using synchrotron radiation. At standard tonicity, a tetanus was associated with an initial brief lattice expansion (and a small amount of sarcomere shortening), followed by a slow compression (unaccompanied by sarcomere length changes). In hypertonic saline (myosin lattice compressed by 8.1%), these spacing changes were suppressed, in hypotonic saline (lattice spacing increased by 7.5%), they were enhanced. During unloaded shortening of activated fibers, a rapid lattice expansion occurred at all tonicities, but became larger as tonicity was reduced. This expansion was caused in part by the change in length of the preparation, but also by a recoil of a stressed radial compliance associated with axial force. The lattice spacing during unloaded shortening was equal to or occasionally greater than predicted for a relaxed fiber at that sarcomere length, indicating that the lattice compression associated with activation is rapidly reversed upon loss of axial force. Lattice recompression occurred upon termination of shortening under standard and hypotonic conditions, but was almost absent under hypertonic conditions. These observations indicate that axial cross-bridge tension is associated with a compressive radial force in intact muscle fibers at full overlap; however, this radial force exhibits a much greater sensitivity to lattice spacing than does the axial force.

Cross-bridge attachment and stiffness during isotonic shortening of intact single muscle fibers.

Equatorial x-ray diffraction pattern intensities (I10 and I11), fiber stiffness and sarcomere length were measured in single, intact muscle fibers under isometric conditions and during constant velocity (ramp) shortening. At the velocity of unloaded shortening (Vmax) the I10 change accompanying activation was reduced to 50.8% of its isometric value, I11 reduced to 60.7%. If the roughly linear relation between numbers of attached bridges and equatorial signals in the isometric state also applies during shortening, this would predict 51-61% attachment. Stiffness (measured using 4 kHz sinusoidal length oscillations), another putative measure of bridge attachment, was 30% of its isometric value at Vmax. When small step length changes were applied to the preparation (such as used for construction of T1 curves), no equatorial intensity changes could be detected with our present time resolution (5 ms). Therefore, unlike the isometric situation, stiffness and equatorial signals obtained during ramp shortening are not in agreement. This may be a result of a changed crossbridge spatial orientation during shortening, a different average stiffness per attached crossbridge, or a higher proportion of single headed crossbridges during shortening.

Time-resolved equatorial X-ray diffraction measurements in single intact muscle fibres.

Equatorial X-ray diffraction techniques have been successfully applied to the intact single muscle fibre preparation under length clamp and "fixed end" conditions. 10 and 11 intensity changes and stiffness have been measured in the same preparation. Under isometric conditions, equatorial signals and stiffness led force by 14-20ms during the rise of tetanic tension. During relaxation, stiffness and equatorial signals lagged force. The time course of the intensity changes suggests a low force crossbridge state is present to a greater extent during the rise of tetanic tension and during relaxation than at the tetanus plateau. During isotonic shortening at Vmax, stiffness fell to 30% of its isometric level, while equatorial signals fell to 60%. Since stiffness and equatorial signals are thought to detect attached crossbridges, either the average stiffness per attached bridge measured at 4kHz during shortening is less than at the plateau, or the relation between equatorial intensities and the proportion of attached crossbridges during isotonic shortening differs from that measured under isometric conditions. Active tension also affects the lattice spacing. The myosin lattice was compressed during the development of longitudinal force. This implies a radial component of crossbridge tension. The lattice compression was smaller in a compressed lattice and larger in an expanded lattice.

Force response of unstimulated intact frog muscle fibres to ramp stretches.

The possibility that weakly binding bridges are attached to actin in the absence of Ca2+ under physiological conditions was investigated by studying the force response of unstimulated intact muscle fibres of the frog to fast ramp stretches. The force response during the stretching period is divided into two phases: phase 1, coincident with the acceleration period of the sarcomere length change and phase 2, synchronous with sarcomere elongation at constant speed. The phase 1 amplitude increases linearly with the stretching speed in all the range tested, while phase 2 increases with the speed but reaches a plateau level at about 50 x 10(3) nm/half sarcomere per second. The analysis of data shows that phase 1, which corresponds to the initial 5-10 nm/half sarcomere of elongation, is very likely a pure viscous response; its amplitude increases with sarcomere length and it is not affected by the electrical stimulation of the fibre. Phase 2 is a viscoelastic response with a relaxation time of the order of 1 ms; its amplitude increases with sarcomere lengths and with the stimulation. These data suggest that weakly binding bridges are not present in a significant amount in unstimulated intact fibres.