Mechanical properties of the isolated canine pericardium.

SUMMARY We have assessed viscoelastic properties of pericardium within the physiological range of stresses and related mechanical behavior to fiber direction as defined by scanning electron microscopy. Stiffness, stress relaxation, and creep were measured in samples taken from the anterior surface of 14 canine pericardia. Stress-strain relations generally were not exponential; stiffness at a stress of 1 g/nun* ranged from 12.9 to 239 g/mm l during stretch and varied both from pericardium to pericardium and with the orientation of the strip within the sample (anisotropy). The strips exhibited hyst«retic behavior which was not proportional to rate of strain. Following a rapid increase in stress, creep averaged less than 1% and stress relaxation, 34%, in a 30-minute test period. The orientation of the strip with the greatest stiffness was consistent from pericardium to pericardium, and correlated with a layer of collagen fibers oriented along the major axis of the strip. Circ Res 49: 807-814, 1981 SOME previous studies of the properties of pericardial strips (Rabkin et al., 1974(Rabkin et al., , 1975 have applied large, non-physiological loads to the tissue in order to define such material properties as tensile strength (stress of failure). Others (Vito, 1979) have not taken into account orientation of the strips because of claimed isotropy of the pericardium (Hildebrandt et al., 1969). Finally, no studies have combined detailed analysis of mechanical properties with microscopic examination of the structures responsible for those properties. In the present study, we investigated the elastic and viscoelastic properties of the pericardium, particularly at low stresses, while avoiding high, non-physiological stresses. To relate pericardia! structure to physiology, mechanical properties were related to the orientation of the collagen fibers within the strips, visualized by scanning electron microscopy. Methods A circular sample of parietal pericardium approximately 3 cm in diameter was removed from the Received August 14, 1980; accepted for publication April 7, 1981 anterior surface of the heart of 14 dogs and maintained in oxygenated (95% 0 2 , 5% CO 2 ) Krebs-Henseleit solution at 37°C. Fatty tissue overlying the pericardium was dissected away if necessary. From one to four strips, approximately 2 x 13 mm, were cut from each section, for a total of 42 strips. Adjacent parallel strips were used to test the reproducibility of analysis of mechanical properties, and strips oriented to each other at 45° or 90°C were tested for isotropy of the pericardium. Spring clips were attached to the ends of the pericardial strips which then were studied in an apparatus usually used for isolated papillary muscle studies (Sulman et al., 1974; Wiegner and Bing, 1977) with a force range of 0-10 g. Quantization error was less than 20 mg for force and 5 /xm for length measurements. Length and width of the strips were measured with a Gaertner cathetometer and telescope. Length and force servosystems facilitated computer control of ...

Section: Discussioncontrasting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Mechanical and structural correlates of canine pericardium.

Wiegner¹,

Bing²,

Borg³

et al. 1981

“…Second, it is likely that, even after 1 week of volume overload, small and possibly variable amounts of hypertrophy had already occurred (Wikman-Coffelt et al, 1979) which could have influenced the relationship between the pericardium and the level of left ventricular filling. Third, pericardial strips exhibit creep when appropriately loaded (Rabkin et al, 1974). To the extent that early pericardial creep may have occurred, it is possible that the pericardium may have been variably prestretched as a result and, hence, variably stiffer in this group of animals.…”

Section: Discussionmentioning

confidence: 98%

Influence of the pericardium on left ventricular end-diastolic pressure-segment relations during early and later stages of experimental chronic volume overload in dogs.

LeWinter¹,

Pavelec²

1982

SUMMARY. Although the pericardium can exert a restraining effect on filling of the normal left ventricle, it is uncertain to what extent the pericardium influences left ventricular filling during chronic volume overload. We measured left and right ventricular pressure and left ventricular segment dimension before and after pericardiectomy over a range of left ventricular end-diastolic pressure from <5 to >20 mm Hg in open-chest dogs with volume overload due to a prior systemic arteriovenous fistula. In six dogs studied "early" (7-9 days) during volume overload, left ventricular end-diastolic dimension was significantly larger and right ventricular end-diastolic pressure lower following pericardiectomy at matched levels of left ventricular end-diastolic pressure greater than 10-12 mm Hg. In six dogs studied "late" (34-50 days) during chronic volume overload, there were no significant changes in left ventricular end-diastolic dimension after pericardiectomy at comparable levels of end-diastolic pressure. To account for the influence of changes in right ventricular enddiastolic pressure after pericardiectomy, we also compared left ventricular end-diastolic dimensions before and after pericardiectomy at matched "corrected" left ventricular end-diastolic pressure [(left ventricular end-diastolic pressure) -(right ventricular end-diastolic pressure X interventricular septal surface area/total left ventricular surface area)]. This "correction" of the left ventricular enddiastolic pressure did not significantly alter the results in either the "early" or "late" group. These results indicate that restraint to filling by the pericardium in this model of volume overload is present early but becomes markedly diminished during later phases. (Circ Res 50: 501-509, 1982)A NUMBER of prior studies have demonstrated that the pericardium may normally restrain left ventricular filling (Hefner et al., 1961;Bartle et al., 1968; Spotnitz and Kaiser, 1971;Glantz et al., 1978;Shirato et al., 1978;Mirsky and Rankin, 1979;Stokland et al., 1980). Although the absolute magnitude of this effect and the level of diastolic pressure and volume at which it begins are uncertain, it appears to be present consistently at left ventricular diastolic pressures above the normal operating range. Therefore, early during the course of volume overload lesions, before there has been a chance for either major left ventricular dilatation and hypertrophy, it is possible that the pericardium might have a physiologically significant restraining effect, providing the left ventricular diastolic pressure is abnormally elevated. Indeed, there is inferential evidence in patients (Bartle and Hermann, 1967) that this occurs. However, there is no information available as to whether the effect persists during later phases of chronic volume overload or whether, instead, the pericardium enlarges in parallel with an increase in cardiac mass, thus diminishing any restraining effect. In the present study, we sought to determine directly whether the pericardium limits left ven...

“…Data from the dogs studied sequentially suggested that substantial limitation of ventricular filling was present immediately after instrumentation but reversed with time. This early restraining effect may have been related to pericardial retraction occurring during instrumentation, and reversal of this effect may be analogous to pericardial creep (Rabkin et al, 1974;LeWinter et al, 1982). As illustrated by data from one of these dogs (Fig.…”

Section: Discussionmentioning

confidence: 90%

Pericardial influences on ventricular filling in the conscious dog. An analysis based on pericardial pressure.

Tyson¹,

Maier²,

Olsen³

et al. 1984

SUMMARY. Twenty-five dogs were chronically instrumented to investigate the effects of the normal pericardium on cardiac function. Pulse-transit ultrasonic transducers were implanted to measure multiple ventricular dimensions. The pericardium was incised transversely at the base of the heart and precisely reapproximated, so as to disturb its characteristics minimally. One week later, the dogs were studied in the conscious state, and left ventricular, right ventricular, pericardial, and pleural pressures were measured with matched micromanometers. Data were recorded before and after blood volume expansion. Absolute end-diastolic pericardial pressure varied directly with pleural pressure during the respiratory cycle. Transpericardial pressure (pericardial-pleural pressure) varied little with respiration and was related directly to ventricular diameter during the cardiac cycle with peak transpericardial pressure uniformly occurring at end-diastole. With volume infusion, normalized end-diastolic minor axis diameter and left ventricular transmural pressure (left ventricular-pleural pressure) increased significantly from 0.14 ± 0.01 and 9.5 mm Hg ± 1.0 mm Hg, respectively, in the control state to 0.20 ± 0.01 and 19.3 mm Hg ± 1.2 mm Hg after volume loading. End-diastolic transpericardial pressure also increased significantly from 2.3 ± 0.5 mm Hg to 4.1 ± 0.3 mm Hg, and represented approximately 21% of transmural left ventricular pressure. When measurements were obtained sequentially after implantation, transpericardial pressure was initially high but decreased with time, presumably due to pericardial creep. After volume loading, right ventricular end-diastolic transmural pressure averaged 9.6 mm Hg, and pericardial pressure constituted 42% of right ventricular pressure. Thus, pericardial restraining effects may predominantly influence right ventricular filling and affect the left ventricle through series interaction. In the normal conscious dog, transpericardial pressure remains low over the entire physiological range, and the direct influence of the normal pericardium on diastolic filling of the left ventricle appears to be minimal. (Circ Res 54:173-184, 1984)