intramuscular pressure measurements during exercise

INTRAMUSCULAR PRESSURE MEASUREMENTS DURING EXERCISE

JORMA R. STYF, MD

This article reviews advantages and problems with different techniques of intramuscular pressure recordings during exercise. The importance of dynamic properties of a pressure recording system is shown. Reference values for different intramuscular pressure parameters for normal and abnormal conditions are presented. Pressure findings are related to pathophysiology of chronic compartment syndrome and other reasons for leg pain. KEY WORDS: chronic compartment syndrome, dynamic properties, force generation, intramuscular pressure, muscular hypertension syndrome, muscle contraction pressure, muscle relaxation pressure

History and clinical signs are insufficient to establish the diagnosis of chronic compar tment syndrome. 1-3 However, they are valuable in selecting patients with chronic leg pain for intramuscular pressure measurements. 3'4 Therefore, measurement of intramuscular pressure has an important role in diagnosis of the syndrome. Measurements during exercise are also useful in physiological research to study muscle biomechanics 5-s and limb function. 9-14

DYNAMIC PROPERTIES OF A PRESSURE RECORDING SYSTEM

The static and dynamic properties of a pressure recording system must fulfill certain criteria to allow proper recordings of intramuscular pressures during exercise. The dynamic accuracy of a recording system is the fidelity with which the system reproduces a dynamic event. Errors of the dynamic accuracy can have serious diagnos- tic consequences when intramuscular pressures are recorded during exercise in clinical practice and in research. For instance, if the system is overdamped, physiological pressure changes during muscle contraction and muscle relaxation cannot be studied. 3"as

Several of the methods used for intramuscular pressure measurements at rest have been applied for measurements of pressures during exercise in clinical diagnosis 9'12'16"17 and to estimate muscle load in physiological studies. 6-8 However , the dynamic propert ies of the pressure recording system is evaluated in only a few re- portso 8A5 The dynamic properties must be known to

From the Department of Orthopaedics, Ostra Hospital, GSteborg, Sweden.

Address reprint requests to Jorma R. Styf, MD, Department of Or- thopaedics, 0stra Hospital, S-41685 GStenberg, Sweden.

Copyright © 1995 by W. B. Saunders Company 1060-1872/95/0304-0004505.00/0

permit proper interpretation of intramuscular pressure recordings during exercise. The dynamic properties of a fluid-filled catheter manometer system depend on catheter materials, lengths, inner diameters, number of con- nectors, and the compliance of the whole catheter manometer system. Therefore, all dynamic measurements of intramuscular pressure should be preceded by dynamic calibration.

The resonance frequency and the rise time (Fig 1) of the pressure recording system may be used to judge the dynamic properties of the system. These parameters can be determined with the sinusoidaI wave generator or by the pressure step function technique. ~5 This is most important because many factors, including different catheter materials and catheter dimensions and the experimental set up may affect the f requency response. 3"15'1s Generally a frequency response exceeding the event to be measured by up to 20 Hz is required to record the amplitude of the event accurately.19

The compliance (C) of a transducer is the relation between the volume change (V) and the pressure change (P), given by the equation C = V/P. The compliance of the diaphragm is much larger than that of the saline-filled catheter or transducer cavity, provided that the saline solution is bubble-free and the catheter material is rela- tively noncompliant. Thus, its effect on the system is the same as that caused by connecting an additional ca- pacitor in parallel.

A crucial part of the preparation for pressure recordings is filling the transducer and the transducer line with saline that is free of entrapped air bubbles. Even fine bubbles in the recording system increase the total compliance considerably and decrease the resonant frequency. Again, because air bubbles may be invisible it is important to have some means for testing the dynamic performance after filling. If cold saline from the refrig- erator is used, air bubble formation will increase in room temperature. The same is true when saline of room temperature in the catheter is exposed to the warm (35 ° to 38°C) skin and muscle tissue during exercise.

Operative Techniques in Sports Medicine, Vol 3, No 4 (October), 1995: pp 243-249 243

Pressure

100%

0

90%

.~o°# ..........

Td Time

Fig 1. The rise time can be calculated by the pressure step function technique. Rise time (Tr) for a pressure recording system is defined as the time period for the output signal to pass through the range of 10% to 90% of its final value. Time delay (Td) is the time period required for the signal to reach its final value,

PRACTICAL RECOMMENDATIONS

The Pressure Record ing System

The following steps are helpful in maintaining high dynamic properties of the pressure recording system: (1) use high-quality stop cocks and a minimum number of luer locks; (2) apply a known pressure and close the stop cocks. If the pressure falls within a few seconds, then there is a significant leakage. (3) Transducers, amplifi- ers, and recorders should be tested for noise, linearity, stability, and hysteresis; (4) the transient dynamic test should regularly be performed at the end of the proce- dure. Many publications on measurements of dynamic intramuscular pressure recordings lack documentation of transient testing. (5) Damping of an underdamped catheter manometer system is applied by constricting the transducer line with a binding screw close to the transducer.

Incorrect Correct

0-5 0 \ \

~ ~ - - Muscle

Tendon

DISTAL. PROX I MAL.

Fig 2. A schematic drawing showing the importance of in- troducing the catheter parallel with muscle fibers. It is helpful to know the pennation angle o~, that is the angle between the muscle fiber and the tendon.

Intramuscular pressure is a function of the depth of the catheter in the muscle. Depth is defined by how many layers of muscle fibers cover the catheter tip. In many cases, depth of the catheter is defined as the distance from the centrally located tendon within the muscle to the tip of the catheter, not the distance from the skin or fascia, at Therefore, catheters should be placed in a stan- dardized way to a depth that will allow the muscle fibers to shorten 20% of their resting length without hitting the tendon. If the tendon hits the catheter tip during concentric contractions, two problems may occur: it hurts or the tip of the catheter may become bent, which may cre- ate partial occlusion and decreased dynamic properties of the pressure recording system.

Check of Catheter Position

Catheter position can be checked by sonography 22 or by a function test. 23 By asking the subject to move different joints, different muscles in the compartment will be acti- vated. Catheter location can be confirmed by the pressure response to these movements.

Catheter Insert ion Techn ique

Catheters for intramuscular pressure recordings during exercise must be inserted as atraumatically as possible. The introducer and the catheter should be inserted as parallel to the fibers as possible, with the cutting tip of the needle retracted within the plastic sheath of the introducer (Fig 2). Once the introducer has penetrated the skin and the fascia, the tip of the needle should be with- drawn into the plastic sheath of the introducer. In this way damage to the muscle fiber will be minimized. Surrounding muscle fibers will help to guide the plastic sheath at insertion into the direction of least resistance, which is parallel to the fibers. Once the catheter is in place, this allows the muscle fibers to slide over the catheter tip in a parallel fashion during concentric and eccentric muscular activity. In this way the physiological re- actance to the measurement will be minimized. 2° That means that the patient experiences less discomfort during muscular activity and will be able to exercise the muscles in a normal way without pain inhibition.

Position of the Leg

Position of the patient, position of the joint over which the tendon acts, and external compression from the underlying surface must be controlled because they will in- fluence intramuscular pressure.

TYPICAL DISTORTIONS OF INTRAMUSCULAR PRESSURE RECORDINGS

In the underdamped system the amplitude of the higher frequency components of the pressure wave are ampli- fied (Fig 3). In such a system it may be difficult to measure the exact pressure level. For the overdamped system these higher frequency components are attenuated. Overdamped systems like the noninfusion system with a wick catheter show a time delay of up to several seconds (Fig 4). The risk for partial occlusion of pressure

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Fig 3. By changing the standard for pressure recording from 100 mm Hg (A) to 20 mm Hg at (B), the pressure between contractions, that is the muscle relaxation pressure, can be read more accurately. In this recording the system for pressure recording is underdamped, which makes it difficult to read the correct muscle relaxation pressure, labeled as mrp in the figure.

catheters is increased when noninfusion systems are used (Fig 5).

DIFFERENT TECHNIQUES FOR PRESSURE MEASUREMENTS

Every technique for intramuscular pressure measurements has its own advantages and disadvantages. Be- fore the technique for pressure recording is selected, it is important to decide on the exercise protocol. Will the pressure be measured at rest and/or during exercise? Will the patient exercise on an ergometer in the labora- tory or run in the field? The answers to these questions are helpful in selecting an optimal pressure recording technique.

The different techniques for different pressure record-

Fig 4. Intramuscular pressure recordings with a microcapillary infusion technique (MCI) (upper trace) and a noninfusion technique (wick) (lower trace) during, a: a single muscle contraction. The time delay is several seconds for the noninfusion technique, b: Dynamic exercise. The correct pressures during muscle contraction and muscle relaxation cannot be recorded with the noninfusion technique, c: At rest after exercise. Intramuscular pressure oscillations can be measured by the infusion technique. Both catheters are within the same muscle at the same depth. (Reprinted with permission.)

r- i - T 7 ! - 7 7 " . A s

Fig 5. (A) Pressure recordings with a catheter that is subto- tally occluded by a clot. The rise time becomes more than 10 seconds after a few contractions. (B) Suddenly decreasing dynamic properties in a pressure recording system. During the first few contraction cycles the pressure during muscle contraction and muscle relaxation was possible to measure.

ings may be classified as the following: (1) injection techniques, (2) infusion techniques, (3) noninfusion techniques, and (4) transducer tipped techniques. Most of the methods have been thoroughly evaluated and are generally accepted for pressure recordings at rest. How- ever, the needle injection technique can only be used to record pressures at rest . 24-27 This technique has been shown to be less accurate than the other techniques for pressure recordings, 26'28"29 especially if pressure recordings are made during injection as recommended by Whitesides. 29 The injection technique measures tissue resistance and gives an artificially high reading if pressure is measured during injection. However, a needle or catheter with one or multiple side holes at its tip re- duces the risk of recording artificially high pressures, especially when pressures are recorded by the meniscus method after an injection. 29

Infusion Techniques The constant pump infusion technique 3° and the noncon- stant microcapillary infusion technique ls are both suitable for recording of intramuscular pressures at rest and during exercise. 12,15,31,32 The magnitude of the infusion rate is important. Both methods can be combined with different types of catheters. 15,30,32 The compliance of muscle tissue decreases during muscle contraction. There- fore, the risk of reading artifactually high muscle contraction pressure reading with the microcapillary infusion technique is less than with the constant pump infusion technique. The reason for this is that the infusion rate with the microcapillary infusion technique is minimal or even zero during muscle contraction. The compliance of muscle tissue at rest is high. 33'34 Intramuscular pressure is fairly constant when 0.1 to 3.0 mL/h of saline is in- fused, ls'35 However, if a Teflon (Atos Medical Inc., M66rby, Sweden) catheter with an open tip and multiple side holes at its tip is used, infusion rates exceeding 0.2 mL/h are often unnecessary for pressure recordings during intermittent exercise.

Noninfusion Techniques Different noninfusion techniques 26"28 have been used to record pressures at rest and during exercise. 2'9'36"37 It has been shown that the wick catheter method is unsuit-

IMP MEASUREMENTS DURING EXERCISE 2 4 5

able for recording intramuscular pressure during exercise because of its low dynamic properties, s'~s Values of pressure recordings during muscle contraction and muscle relaxation depend on the contraction frequency as shown in Fig 6, and on the relative time duration of muscle contraction and muscle relaxation. Pressures during exercise were not accurately recorded with a slit catheter because the catheter tip occluded. 38 For this reason, slit catheters must be flushed repeatedly when pressures are recorded with a noninfusion technique. I's'31'3s In this situation, the device is no longer to be considered a noninfusion technique but rather an intermittent injection technique. Furthermore, the tip design of the slit catheter has been reported to be more traumatic to the local tissue during muscular activity. 38

Transducer-Tipped Catheters Transducer-tipped catheters are suitable for recordings of muscle contraction pressure during complex movements of the extremity because they eliminate any problem of the changing hydrostatic column. The catheters are also suitable for recordings of pressures at rest after exercise. However, the catheters do not have recommendations for recordings of muscle relaxation pressure during exercise because of the piston effect. 39 This effect gives negative pressure values during muscle relaxation possibly by the vacuum from sliding fibers over the tip of the catheter. Catheters with a large diameter are more prone to this effect. However, the effect diminishes after some 5 to 10 minutes of exercise.

NORMAL INTRAMUSCULAR PRESSURE RECORDINGS

The following reference values of intramuscular pressures refer to the supine position and with the tip of the catheter at the heart level.

Fig 6. Muscle contraction pressure and muscle relaxation pressure, that is pressure between contractions in a relaxed muscle, during constant muscle load at a: 75, b: 37, and c: 18 contractions/rain. The readings in the upper trace that are obtained with a microcapillary infusion technique show the same magnitude of pressure values. In the lower trace the readings depend on the contraction frequency because of the prolonged rise time of the noninfusion system. (Re- printed with permission.)

Intramuscular Pressure at Rest

Normal pressures in most muscles are about 5 mm Hg 3'12'15'26'31'40°43 but pressures up to 10 and 15 mm Hg have been reported. 2'44'45 The recorded pressure depends on the method used, the position of the leg, 22 and the depth of the catheter in the muscle. 21'46

Muscle Contraction Pressure During Exercise

The upper traces in Figs 4 and 6 show measurement of muscle contraction pressure during exercise. The magnitude of muscle contraction pressure during exercise depends on the force output from the muscle. 7'8 Pressures ranging from 100 up to 250 mm Hg have been recorded in the anterior tibial muscle. 3'5'6'8"15'44

Muscle Relaxation Pressure

The magnitude of muscle relaxation pressure during exercise, that is the pressure be tween contractions, depends on the volume load of the muscle (Figs 4 and 6). This pressure increases to values between 10 and 25 mm Hg in different muscles at the time of muscle fatigue. 15'32

Intramuscular Pressure at Rest After Exercise

Intramuscular pressure immediately at rest after exercise to muscle fatigue is normally between 10 and 25 mm Hg, which is fairly equal to the muscle relaxation pressure at the end of exercise in a supine subject. This pressure parameter depends on the volume load of the muscle. In an upright subject, the muscle relaxation pressure during exercise is lower than the pressure at rest after exercise.13 The reason for this is the effect of the calf muscle pump that is shown in Fig 7. Intramuscular pressure

40 mmHg m

O

J

5sec. P I

Fig 7. This pressure recording shows the effectiveness of the calf muscles to pump to lower intramuscular pressure after each muscle contraction. Arrow up indicates start of contraction. The pressure decreases after a few muscle contractions. The oscillations of the intramuscular pressure recording are caused by the arterial pulse in the volume loaded muscle in an upright person.

246 JORMA R. STYF

re turns to preexerc ise levels wi th in 5 to 10 minutes. 3,26,32,43,45,47-49

MEASUREMENT OF ABNORMAL INTRAMUSCULAR PRESSURES

Intramuscular Pressure at Rest Before Exercise

Intramuscular pressure at rest before exercise is increased in pat ients with chronic compar tment syndrome. 2"3'12A5'43"45'47 However, the wide range of pressures at rest and their dependence on the position of the ankle joint and the depth of the catheter in the muscle, as well as the position of the subject makes the use of this parameter unreliable in the diagnosis of chronic compartment syndrome. 21"22"46 Also, pressure at rest before exercise may increase by active muscle tension from pain and by external compression by the underlying surface. For these reasons the use of this pressure parameter alone is not recommended. 3"4"~8

Muscle Contraction Pressure During Exercise

Recordings of muscle contraction pressure and muscle re laxat ion p r e s s u r e du r ing exercise requi re good dynamic proper t ies of the pressure recording system. 3"6'8'12'15'32"35's°'s1 Muscle contraction pressure during exercise depends on the force output from the muscle. Therefore, this pressure parameter is unrelated to the pathophysiology of chronic compartment syndrome and should not be used to diagnose the syndrome. Muscle contraction pressure is often low at the end of exercise because the force generation decreases because of muscle fatigue.

Muscle Relaxation Pressure

Muscle relaxation pressure during exercise is the pressure between contractions and depends on the volume load of the muscle. It is shown in the upper traces of Figs 5 and 7. Muscle relaxation pressure exceeding 35 to 55 mm Hg correlates well with the development of pain, swelling, and impaired muscle function in patients with chronic compartment syndromes 3"4"18 and to decreased muscle blood flow. s° This pressure depends on the volume load of the muscle tissue. It is related to the pathophysiology of the syndrome and is the best parameter to study during exercise in patients with the syndrome. How- ever, at the end of exercise, some patients are not able to relax their muscles completely between contractions because of muscle pain and fatigue. Muscle relaxation pressure should always be related to intramuscular pressure at rest after exercise. If these two pressures are fairly similar levels, many pitfalls can be avoided. Ex- amples of such pitfalls are increased muscle relaxation pressure caused by inability to relax muscles or a high muscle contraction frequency.

Mean Muscle Pressure The mean muscle pressure is calculated from the contraction and relaxation pressure. Mean muscle pressure exceeding values between 50 to 85 mm Hg have been used as criteria in diagnosing chronic compar tment syndrome. 32'37 However, by definition mean muscle pressure values depend on both the contraction and relaxation pressures. Therefore, the mean pressure is sec- ondary to changes of both these pressures . Mean muscle pressure is an unreliable and physiologically unrelated parameter to use in the diagnosis of chronic compartment syndrome. 3'1s'5°'52 The level of the mean muscle pressure also depends on the relative duration of the contraction and relaxation. The longer the duration of the muscle contraction, the higher the mean muscle pressure. Contraction cycles of short duration followed by a long muscle relaxation time give low mean muscle pressure values. Such recordings are artifacts that are caused by the frequency and relative duration of the muscle contraction and relaxation time. Overdamped pressure recording systems with an increased rise time, like the wick catheter system, are prone to give this artefact. This is also true for any catheter system that becomes partially occluded.

Intramuscular Pressures at Rest After Exercise Pressures exceeding 30 to 35 mm Hg at rest after exercise and a time period exceeding 6 to 10 minutes to normalize the increased pressure have been used as criteria for diagnosis of the syndrome. 2'3'~2As'47 This parameter is useful if pressure during exercise is not recorded. In- creased pressure by active muscle tension because of pain must be excluded and external compression by the underlying bed must be avoided. There is a risk of making a false diagnosis of chroniccompartment syndrome if the pressure at rest after exercise is used as the only diagnos- tic criterium. 3 Patients with muscular hypertension syndrome have increased intramuscular pressure at rest after exercise but normal muscle relaxation pressures during exercise. 3 The reason for this is their inability to relax their muscles at rest after exercise because of pain. The history and clinical findings in these patients are different from those with chronic compartment syndrome and they showed similarity with patients with tension myalgia as described by others, s3 After the results of pressure monitoring this condition has been labeled "muscular hyper tension syndrome. ''3 Simultaneous electro- myograph recordings would be helpful to differ between the two conditions. In patients with chronic compartment syndrome the pressure increase depends only on the volume load of the compartment and that the elec- tromyograph signal is silent. In patients with muscular hypertension syndrome the increased pressure depends on an inability to relax their muscles.

Intramuscular Pressure Oscillations at Rest After Exercise Increased amplitude of pulse-synchronous oscillations of intramuscular pressure at rest after exercise can normally be recorded when the muscle is swollen. 3"15"1s'54 The

IMP MEASUREMENTS DURING EXERCISE 247

S @ C O n G S

i i i i ~ I '

! , i~ I i ' " , , r . . . . . .

A ~ B C D

Fig 8. (A) By choosing a low pressure standard of 40 mm Hg, the muscle relaxation pressure during exercise can be studied. ($ ) indicates end of exercise. (B) The increased pressure at rest after exercise in this case is caused by postex- ercise hyperaemia. (C) The dynamic properties of the upper trace are improved after flushing of the catheter with 0.1 mL of saline. (D) Intramuscular pressure 3 minutes at rest after exercise. The amplitude of the oscillations have decreased because the volume load of the leg is smaller and the compliance is now higher.

pressure amplitude at rest after exercise is significantly higher in patients with the syndrome. This is caused by the decreased compliance of the compartment. The pressure amplitude varies with the volume of each arterial pulse and the compliance of the compartment (Fig 8).

SUMMARY

The dynamic properties of a pressure recording system are important for accurate measurements of intramuscular pressures during exercise. A photo of an original dynamic pressure recording should always be published with the article. In this way the reader can evaluate the dynamic properties. Muscle relaxation pressure during exercise and/or intramuscular pressure at rest after exercise are the most reliable parameters to study in diagnosis of chronic compartment syndrome. Muscle contraction pressure is a measure on the force generation from the muscle. Pressure recordings during injection with the needle-manometer technique are not recommended. Catheters for pressure recordings should be inserted parallel with muscle fibers to minimize the physiological re- actance. Bent catheters, partial occlusion, external compression, patient and joint position, and catheter depth in the muscle can result in erroneous pressure recordings. Measurements of intramuscular pressure during exercise also include a significant learning curve and is an art of electromanometri.

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the human leg: The effect of plaster casting and ankle position. J Bone Joint Surg [Am] 76:1476-1481, 1994

IMP MEASUREMENTS DURING EXERCISE 249

intramuscular pressure measurements during exercise

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