- Email: [email protected]
Diaphragmatic Alterations in Sedentary and Exercised Emphysematous Hamsters
=hragmatic Alterations In entary and Exercised Emphysematous Hamsters* G. A Farw, M.D.; and Ch. Hou8ao&, M.D., FCCP
he alterations contractile, structural, fatigue, histoT chemical and biochemical properties of the diaphragm in
(DIA) were evaluated in a group of sedentary emphysematous (SE)and exercised emphysematous (EE) hamsters. Emphysema was produced with elastase. Daily, one hour of exercise was performed on a treadmill. The experimental period lasted 24 weeks. Functional residual capacity (FRC), measured by means of a pressure box, was found to be significantly increased in SE and EE as compared to a sedentary control (SC) group. Training or emphysema produced no changes in the time-to-peak tension, half-relaxation time, force-frequency curve and maximal tetanic tension (Po) of the DIA. The DIA length-tension (L-T) curve, however, of SE and EE showed a significant parallel shift to the left of the L-T curve from SC animals, ie Po was generated at shorter absolute DIA lengths. The decrease in lengths was found to occur in proportion to the increase in FRC. The responsible mechanism was due mainly to a loss of sarcomeres in the chronically shortened DIA. The DIA of SE and EE showed a signi6cantly greater resistance to fatigue compared to DIA from SC animals. The responsible mechanism was a signi6cant increase in the DIA oxidative capacity {citrate synthase} with a concomitant decrease in the glycolytic capacity {PFJ{capacity}of both SE and EE groups as compared to SC. The difference in fatiguability ofDIA between SE and EE was not significant. Histochemically, the DIA from groups SE showed a selective fast fiber atrophy as compared to SC animals. 'Iraining prevented the fast fiber atrophy and caused a slow fiber hypertrophy of DIA fibers as compared to SC. We conclude that the DIA undergoes a series of alterations in emphysema. Some of the contractile properties, as well as the structure of the DIA adapt in emphysema to maintain an operational length close to its optimal. The biochemical and histochemical properties are also altered in the emphysematous DIA, such that fatiguability is markedly reduced. 1hlining of these animals tended to prevent a fast fiber atrophy and also resulted in a slow fiber hypertrophy. *From Meakins-Christie Laboratories, McGill University, Montreal, Canada.
Diaphragm Structure and Function In Elastase-Induced Emphysema* Steven G. Kelaen, M.D., F.C.C.l; GeraldS. Supinski, M.D., F:C.C.l; andArle Oliven, M.D. *From the Pulmonary Division, Department of Medicine, Case Western Reserve University, School of Medicine, Cleveland. Supported in ~ by a Program Project Grant (HL-25830) and an Academic Award to Dr. ICelSen (HL-00450). Reprint requem: Dr. KelBen, &om 2211 Weam Bldg, UnWerBity HOspital, 2065 Adelbert Rotul, Cleveland 44106
.l1terations in lung function in emphysema increase the
.t1 load on the diaphragm and decrease its length.r" In
limb skeletal muscle, which demonstrates a high degree of plasticity, however; chronic alterations in muscle load or length elicit adaptive changes in muscle structure which augment force production. l5.J8 The effect of emphysema on the structure and function of the human diaphragm, the major respiratory muscle, remains unclean 1-&.11-. Uncertainty exists in part because muscle force and length can be measured only indirectly and imperfectly in man from measurements of pressure and volume, respectively, and in part because of the presence of confounding variables difficult to control in man, such as nutritional status, body habitus, and superimposed disease. I Therefore, we examined the structure and function of the diaphragm in an animal model of emphysema induced by elastase administration in which the changes in lung structure and function have been shown to resemble closely the human condition. 1-8 METIIODS
Studies were performed in 67 Syrian Golden hamsters in whom emphysema was induced by a single intratracheal injection of pancreatic elastase (25 units/lOO WOOdy wt) and 73 saline-injected controls. Diaphragmatic muscle function was examined in a subgroup of30 elastase and 34 control animals and assessed in vitro from the length-tension and force-velocity characteristics of muscle strips obtained from the costal region. 1O Studies of muscle structure (weight, thickness, &ber composition and size, and sarcomere number) were performed in the remainder and will not be reported
here."
MtI8cle Force Approximately 4-mm wide strips of diaphragmatic muscle, immobilized at the rib and central tendon by fine steel hooks, were mounted vertically in an organ bath containing Krebs-Henselheit solution at room temperature and aerated with a 95% 0.-5% CO. mixture. The hooks securing the central tendon were embedded in a Plexiglas rod attached to a force transducer. Muscle length was altered using a rack-and-pinion gear that raisecL and lowered the force transducer. Fiber length was measured with a graduated Plexiglas grid. Supermaximal electrical stimuli were delivered in O.2-ms pulses by field stimulation. The isometric force generated was measured by the force transducer. Because skeletal muscle force depends on sarcomere rather than muscle length, a laser dift"ractiontechnique was used to characterize the relationship of contractile fOrce to sarcomere as well as muscle fiber length.IO·1I-14 This technique has previously been shown to measure accurately sarcomere length both statically and dynamically in single fibers, muscle bundles, and whole muscles. BrieRy, difteJ\ences in light absorption by the alternating dark (A) and light (I) bands cause striated muscle to behave like a multilayerd, onedimensional dift"ractiongrating in whicheach I band acts as a point source of light. When exposed to coherent, monochromatic light, the muscle generates a visible dift"ractionpattern. Sarcomere length, the distance between the midpoint of adjacent I bands, is the grating interval which can be calculated using the dift"raction equation: average sarcomere length
=
~
sin (arctan ~ D where ~ = the wavelength oflaser light; d = the distance between zero and first-order dift"ractionbands; and D = distance between the muscle and the point at which the dift"ractionpattern is measured. CHEST I 85 I 8 I June. 1984 I Supplement
55S
he alterations contractile, structural, fatigue, histoT chemical and biochemical properties of the diaphragm in
(DIA) were evaluated in a group of sedentary emphysematous (SE)and exercised emphysematous (EE) hamsters. Emphysema was produced with elastase. Daily, one hour of exercise was performed on a treadmill. The experimental period lasted 24 weeks. Functional residual capacity (FRC), measured by means of a pressure box, was found to be significantly increased in SE and EE as compared to a sedentary control (SC) group. Training or emphysema produced no changes in the time-to-peak tension, half-relaxation time, force-frequency curve and maximal tetanic tension (Po) of the DIA. The DIA length-tension (L-T) curve, however, of SE and EE showed a significant parallel shift to the left of the L-T curve from SC animals, ie Po was generated at shorter absolute DIA lengths. The decrease in lengths was found to occur in proportion to the increase in FRC. The responsible mechanism was due mainly to a loss of sarcomeres in the chronically shortened DIA. The DIA of SE and EE showed a signi6cantly greater resistance to fatigue compared to DIA from SC animals. The responsible mechanism was a signi6cant increase in the DIA oxidative capacity {citrate synthase} with a concomitant decrease in the glycolytic capacity {PFJ{capacity}of both SE and EE groups as compared to SC. The difference in fatiguability ofDIA between SE and EE was not significant. Histochemically, the DIA from groups SE showed a selective fast fiber atrophy as compared to SC animals. 'Iraining prevented the fast fiber atrophy and caused a slow fiber hypertrophy of DIA fibers as compared to SC. We conclude that the DIA undergoes a series of alterations in emphysema. Some of the contractile properties, as well as the structure of the DIA adapt in emphysema to maintain an operational length close to its optimal. The biochemical and histochemical properties are also altered in the emphysematous DIA, such that fatiguability is markedly reduced. 1hlining of these animals tended to prevent a fast fiber atrophy and also resulted in a slow fiber hypertrophy. *From Meakins-Christie Laboratories, McGill University, Montreal, Canada.
Diaphragm Structure and Function In Elastase-Induced Emphysema* Steven G. Kelaen, M.D., F.C.C.l; GeraldS. Supinski, M.D., F:C.C.l; andArle Oliven, M.D. *From the Pulmonary Division, Department of Medicine, Case Western Reserve University, School of Medicine, Cleveland. Supported in ~ by a Program Project Grant (HL-25830) and an Academic Award to Dr. ICelSen (HL-00450). Reprint requem: Dr. KelBen, &om 2211 Weam Bldg, UnWerBity HOspital, 2065 Adelbert Rotul, Cleveland 44106
.l1terations in lung function in emphysema increase the
.t1 load on the diaphragm and decrease its length.r" In
limb skeletal muscle, which demonstrates a high degree of plasticity, however; chronic alterations in muscle load or length elicit adaptive changes in muscle structure which augment force production. l5.J8 The effect of emphysema on the structure and function of the human diaphragm, the major respiratory muscle, remains unclean 1-&.11-. Uncertainty exists in part because muscle force and length can be measured only indirectly and imperfectly in man from measurements of pressure and volume, respectively, and in part because of the presence of confounding variables difficult to control in man, such as nutritional status, body habitus, and superimposed disease. I Therefore, we examined the structure and function of the diaphragm in an animal model of emphysema induced by elastase administration in which the changes in lung structure and function have been shown to resemble closely the human condition. 1-8 METIIODS
Studies were performed in 67 Syrian Golden hamsters in whom emphysema was induced by a single intratracheal injection of pancreatic elastase (25 units/lOO WOOdy wt) and 73 saline-injected controls. Diaphragmatic muscle function was examined in a subgroup of30 elastase and 34 control animals and assessed in vitro from the length-tension and force-velocity characteristics of muscle strips obtained from the costal region. 1O Studies of muscle structure (weight, thickness, &ber composition and size, and sarcomere number) were performed in the remainder and will not be reported
here."
MtI8cle Force Approximately 4-mm wide strips of diaphragmatic muscle, immobilized at the rib and central tendon by fine steel hooks, were mounted vertically in an organ bath containing Krebs-Henselheit solution at room temperature and aerated with a 95% 0.-5% CO. mixture. The hooks securing the central tendon were embedded in a Plexiglas rod attached to a force transducer. Muscle length was altered using a rack-and-pinion gear that raisecL and lowered the force transducer. Fiber length was measured with a graduated Plexiglas grid. Supermaximal electrical stimuli were delivered in O.2-ms pulses by field stimulation. The isometric force generated was measured by the force transducer. Because skeletal muscle force depends on sarcomere rather than muscle length, a laser dift"ractiontechnique was used to characterize the relationship of contractile fOrce to sarcomere as well as muscle fiber length.IO·1I-14 This technique has previously been shown to measure accurately sarcomere length both statically and dynamically in single fibers, muscle bundles, and whole muscles. BrieRy, difteJ\ences in light absorption by the alternating dark (A) and light (I) bands cause striated muscle to behave like a multilayerd, onedimensional dift"ractiongrating in whicheach I band acts as a point source of light. When exposed to coherent, monochromatic light, the muscle generates a visible dift"ractionpattern. Sarcomere length, the distance between the midpoint of adjacent I bands, is the grating interval which can be calculated using the dift"raction equation: average sarcomere length
=
~
sin (arctan ~ D where ~ = the wavelength oflaser light; d = the distance between zero and first-order dift"ractionbands; and D = distance between the muscle and the point at which the dift"ractionpattern is measured. CHEST I 85 I 8 I June. 1984 I Supplement
55S