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Pericardial Pressure during Transverse Acceleration in Dogs without Thoracotomy By Natalio Banchero, M.D., Wilhelm J. Rutishauser, M.D., Anastasios G. Tsakiris, M.D., and Earl H. Wood, M.D., Ph.D. Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 ABSTRACT Intrapericardial pressures were recorded via a saline-filled Teflon catheter (o. d., 1.3 mm) in 11 anesthetized dogs studied without thoracotomy. Seven animals were studied before, during, and after 1-min exposures to transverse accelerations that ranged from 1G (normal gravitational environment) to 7G when in the supine (+Gj), prone (—Gx), left decubitus (+G V ), and right decubitus (—Gy) positions. Four additional animals were studied at 1G only, while in these same body positions. Pressures also were recorded from both atria, right ventricle, aorta, esophagus, and the potential pleural space. Mean end-expiratory intrapericardial pressure varied directly with the vertical height of the recording site in the thorax during all conditions studied, as would be expected in a hydrostatic system. Transpericardial pressures were not significantly different from zero at all levels of acceleration studied. Transmural left and right atrial pressures were independent of the height of the recording site in the thorax and were unchanged during exposures to transverse accelerations that ranged from plus to minus 7GX. ADDITIONAL KEY WORDS pulmonary artery to vein shunts arterial hypoxemia acceleration pulmonary mechanics hemoconcentration manned space flight hydrostatic effects of acceleration • In spite of widespread interest in the influence of the pericardium on cardiac hemodynamics, few measurements of intrapericardial pressure under normal conditions have been made (1-4). In nearly all studies of pericardial pressure, the sensing tip of the transducer assembly used has been introduced into the pericardial sac through thoracotomy and pericardiotomy (1-3). Recently a technique From the Mayo Clinic and the Mayo Foundation, Rochester, Minnesota. This investigation was supported in part by research Grants NsG-327 from the National Aeronautics and Space Administration; AF 33 (567)8899 from the United States Air Force; H-3532 and FR-00007 from the National Institutes of Health, U. S. Public Health Service; and CI 10 from the American Heart Association. Dr. Banchero and Dr. Tsakiris are Career Investigator Fellows of the American Heart Association. Dr. Wood is a Career Investigator of the American Heart Association. Dr. Rutishauser is a Research Fellow of the Swiss Academy of Medical Sciences. Accepted for publication November 9, 1968. Circulation Rtit.rcb, Vol. XX, J,*M*r, 1967 has been described for measuring intrapericardial pressure in dogs without thoracotomy (5, 6). This technique was used to study the intrathoracic pressure relationships that occur during exposures to transverse acceleration in different body positions. Method Intrapericardial pressures were recorded from 11 mongrel dogs. Anesthesia was effected with morphine sulfate (3 mg/kg) and sodium pentobarbital (20 mg/kg) and maintained throughout the experiment by additional doses of pentobarbital administered intravenously when deemed necessary. Seven dogs (weight 15.5 to 19.9 kg) were studied before, during, and after 1-min exposures to average levels of 2.1, 4.4, and 6.7G forward ( + G J , backward ( - G J , right lateral (+G T ) and left lateral (—GT) acceleration on a centrifuge with a radius of 4.42 m. Four dogs (weight 13.5 to 15.5 kg) were studied at 1G (normal gravitational environment) only when in the supine, prone, left lateral, and right lateral body positions. Animals were supported in the four different body positions by plastic half-body 67 66 Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 casts* described previously (7, 8). Dogs breathed spontaneously through an endotracheal tube secured by an inflatable cuff. Pericardial pressures were measured via a no. 4 French, radiopaque, Teflon, bird's-eye opentip catheter introduced percutaneously into the pericardial space by means of a suprasternal approach developed in this laboratory (6). The assembly used for the percutaneous introduction of this pericardial catheter (length, 40 cm; o. d., 1.3 mm; i. d., 0.7 mm) has been described previously (4, 6). In this study the pericardial catheter tip was positioned at the ventral aspect of the heart near the inner surface of the sternum; however, in 2 animals (dogs 1 and 5) the tip slipped backward soon after insertion so that pressures were recorded in them from more dorsal aspects of the pericardial sac. Pressures were also recorded in other parts of the cardiovascular system, the pleural space, and the esophagus. Two no. 6 French Lehman catheters (80 cm long; o.d., 2.0 mm; i.d., 1.2 mm) and a no. 5 French Lehman catheter (80 cm long; o.d., 1.7 mm; i.d., 0.9 mm) were introduced percutaneously via the left jugular vein and positioned so that their tips were in the main pulmonary artery, the outflow tract of the right ventricle, and the right atrium, respectively. A no. 6 French, Teflon, open-tip catheter (80 cm long; o.d., 1.9 mm; i.d., 1.3 mm) was introduced into the left atrium from the right external jugular vein by a transseptal technique (9). A no. 5 French, Teflon, bird's-eye, open-tip catheter (100 cm long; o.d., 1.7 mm; i.d., 1.0 mm) was advanced to the aortic arch via a 16-gauge needle introduced into the right femoral artery. A nylon catheter (20 cm long; o.d., 1.2 mm; i.d., 0.7 mm) for the recording of arterial oxygen saturation and dilution curves was introduced percutaneously into the left femoral artery. Four Teflon, bird's-eye, open-tip catheters (60 cm long; o.d., 1.3 mm; i.d., 0.7 mm) were introduced percutaneously into the potential pleural space by means of a technique previously described from this laboratory (6-8). An esophageal catheter (40 cm long; o.d., 3 mm; i.d., 1.5 mm) was placed in the esophagus at the level of the heart. All catheters were fluid-filled and connected to Model P23D-Statham strain gauges. In the group of animals exposed to transverse acceleration, the oxygen saturation of blood from femoral and pulmonary arteries was continuously recorded by cuvette oximeters (10). The results of measurements of pleural pressure and the oxygen saturation of blood are reported elsewhere (7, 10). Atrial, pulmonary artery, and systemic ar'Fabricated and supplied through the courtesy of David Clark and Company, Worcester, Mass. BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD terial pressures, blood oxygen saturation, die contours of arterial dilution curves, and the calculated cardiac output were normal in all animals at 1G, thus excluding the presence of practically significant intracardiac or great vessel shunts or other gross cardiac abnormalities (11, 12). Lateral and anteroposterior roentgenograms of the chest were taken at end-expiration (Fig. 1). In the animals exposed to acceleration, the roentgenograms were taken at 1G and at 55 sec after the plateau level of acceleration was reached (7). DP ^ ^ 1 *- Ao Mid-Ll/t -LP^PA] FIGURE 1 Lateral wentgenogram of 1 animal (dog 6) supported in a half-body cast in the prone position at 1G, showing the topographic relation of heart, lungs, and catheters used for simultaneous recording of intrathoracic pressures in a dog without thoracotomy. The mid-lung coronal plane, indicated by a horizontal steel wire, was used as a zero reference level. Saline menisci in the thistle tubes Mt and M3 are also set at this level. "PerC indicates the catheter in the pericardial space inserted via a suprasternal approach. In this instance its tip is located in the most ventral part of the pericardial sac just dorsal to the sternum. In addition, pressures were recorded from catheters whose tips were in the right atrium (RA), right ventricle (RV), pulmonary artery (PA), aorta (Ao), and esophagus (Eso). The catheter marked PV was inserted into the left atrium by transseptal puncture (via the right external jugular vein) and in this instance advanced so that its tip was just upstream to the atrial orifice of a pulmonary vein. DP, LP, RP, and VP are catheters in the pleural space. Note in this dog the close proximity of the tips of the pericardial and ventral pleural (VP) catheters. CirCKUlwn Resurcb, Vol XX, Jsmmtry 1967 67 PERICARDIAL PRESSURES IN DOGS Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 The position in the centrifuge cockpit of the supporting half-body cast was adjusted so that the longitudinal marker (steel wire) of the x-ray cassette matched the mid-lung coronal and the mid-lung sagittal planes of the dog, respectively (7). The level of intersection of these planes with the cephalocaudad position of the tricuspid valve was used as the zero reference point. In the 4 animals studied at IG, the mid-thoracic coronal and the mid-thoracic sagittal planes were used as zero levels when in the supine and prone and right and left lateral body positions, respectively. Tntrapericardial pressures were referred to the level of the catheter tip on the basis of its position (height from zero reference level) measured from the biplane roentgenograms (7, 8). Correction for the influence of acceleration on the catheter-manometer systems was made by the "thistle tube" technique described elsewhere (7). The level of acceleration was calculated from the rate of rotation of the centrifuge (rpm) measured by a tachometer, and the angle of tilt of the centrifuge cockpit was recorded from a potentiometer coupled to the axis of the cockpit. Acceleration was also measured by an accelerometer (Statham Model A3-10-350) (7). Recordings were made simultaneously on two photokymographic cameras (paper widths, 44.5 and 30.5 cm, and speeds, 5.0 and 25.0 mm/sec, respectively) and in parallel on magnetic tape (13). Intrapericardial pressures reported in this paper were those obtained during runs in which the angle of tilt of the cockpit was within 1 degree and the resultant acceleration level within 5% of the values during the respective thistletube run used for zero base-line correction. Within these limits the maximal error at the highest level of acceleration would be less than 3 cm H,O. Transient high-pressure flushes were used to check the validity of recorded pressures (7). No pressure recording with evidence of damping was measured. The amount of Ringer's fluid introduced by one flush is about 0.02 ml. Periodical aspirations of pericardial fluid were attempted, and volumes from a fraction to several milliliters of clear or blood-tinged fluid could frequently be obtained both as soon as the catheter was introduced and at intervals during the procedure. Similar flushes were performed for the intravascular pressures, and only those tracings without evidence of damping were analyzed. At the end of the experiment, autopsy was performed on all dogs to verify the position of the catheter tips and the absence of air within the thorax. No air was detected in any of the animals in this study. The maximal dorsal-ventral and lateral dimensions of the heart and the lungs of these dogs, measured from the biplane roentgenograms, have been reported previously along with the changes in their dimensions and topographic relationships produced by acceleration in the four body positions studied (7). Results PERICARDIAL PRESSURES AT IG Relationships between mean intrapericardial pressures and vertical positions of the respective catheter tips in the thorax when in the supine (+G X ), prone (—G*), left lateral (+G y ) and right lateral (—Gr) body positions were similar to those observed in a hydrostatic system, that is, changes in pressure of 1 cm H^.O/cm of vertical distance (Fig. 2, Table 1). This relationship was also observed in dog 8 in which pressures were recorded simultaneously from two sites in the pericardial space near the ventral and dorsal margins of the heart, respectively. In this animal the stepwise withdrawal of one catheter showed a linear tntrapericardial pressure gradient of about 1 cm H 2 0/cm of vertical distance (Fig. 2). The same relationship was maintained when changes in pericardial pressure were produced by injection or withdrawal of different amounts of Ringer's solution into the pericardial sac while pericardial pressures TABLE 1 Mean Intrapericardial Pressure Recorded at IG When Dogs Were in Different Body Positions Body position Supine ( + 1GX) Prone ( - 1 C J Left lateral decubitus (+1GV) Right lateral decubihis ( - l G y ) # Mean values from 7 dogs ± 1 SD. CircuUiion Rtsurcb, Vol. XX, ],nu*rj 1967 Verticil distance* from mid-lunf plane (cm) Pressure* (cm HiO) 3.8 ±1.6 —4.1 ± 1.4 -5.9 ± 3.7 0.6 ±2.1 -1.3 ±2.3 -5.3 ±3.1 —0.7 ± 2.8 -3.0 ±2.1 BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD 68 were recorded simultaneously from these two sites (Fig. 3). PERICARDIAL PRESSURES DURING TRANSVERSE ACCELERATION Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 Intrapericardial pressures during exposures to transverse acceleration in the four body positions were related to the position of the recording catheter tips (Figs. 4, 5, and 6). During exposures to backward acceleration (— G x ), when the position of the pericardial catheter tip was uniformly below the mid-lung coronal plane (Figs. 1 and 4), progressively higher intrapericardial pressures were recorded with increasing levels of acceleration; and the values attained were as high as 45 cm HL.O during exposures to —6.5d. During exposures to forward (+Gj) acceleration, a variable degree of dor- sal (backward) displacement of the catheter tips occurred at the higher levels of acceleration as a consequence of the dorsal displacement of the heart during the exposures (Figs. 4 and 7). The changes in intrapericardial pressures recorded during these exposures were dependent on the position of the recording catheter tips. In the 2 dogs in which the catheter tip moved to sites below the mid-lung coronal plane, positive pericardial pressures were recorded, while increasingly negative pressures were recorded in the 5 dogs in which the catheter tip remained above the mid-lung level (Fig. 4). Similarly, progressively more positive intrapericardial pressures were recorded at increasing levels of right Dog 8 PERICARDIAL A - _I • A • • 8r Do« /0 • 5 \ BOOY POSITION Suplnt HG, -IGK Pront L. LoiTol+I tIC, R.Laltnl-I -IG, Do« /0 • \ X e I_I o • N \ \ \ • \ A i 1 i 1 \ \ i -/5 -/0 -/5 MEAN END-EXPIRATORY PERICARDIAL PRESSURE at CATHETER TIP (cm H,O) FIGURE 2 Relation of mean end-expiratory pericardial pressure to vertical position in the thorax in the 4 dogs studied at IG only. Pressures recorded in the four body positions are indicated by the symbols. A negative value on each ordinate indicates that the catheter tip was positioned below the mid-thoracic plane. The dashed lines indicate a gradient of 1 cm H,O/cm of vertical distance. Note that the gradients for intrapericardial pressure were about 1 cm Hfilcm of vertical distance from the mid-thoracic plane. In dog 8, changes in intrapericardial pressure were also studied during stepwise withdrawal of a second catheter (II) inserted in the pericardial sac (open symbols) while the dog was in the supine position. CircmUticm Rtsturcb, Vol. XX, JMUMOTJ 1967 PERICARDIAL PRESSURES IN DOGS 69 Pericardial I Ptrlcordlal II Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 /O -5 Supint Front + IG, -/G x A • A O 0 END-EXPIRATORY AT CATHETER PERICARDIAL TIP (cm HgO) 5 PRESSURE FIGURE 3 Relation of mean end-expiratory intrapericardial pressure to vertical position in the thorax with changes in the volume of pericardial fluid in 1 animal (dog 8). Pericardial I (closed symbols) was located at the ventral aspect of the heart, and pericardial II (open symbols) was at the dorsal asiiect of the heart. The solid lines connect pressure values recorded simultaneously from the two pericardial catheters. The dashed line indicates a gradient of 1 cm HgO/cm of vertical distance. Lines 1 and 4 indicate the control values of intrapericardial pressure gradients when in the supine (circles) and prone (triangles) body positions, respectively. When the dog was in the supine position, the infusion of 10 ml of Ringer's solution produced similar increases in pericardial pressures recorded at the two sites (line 2). After withdrawal of 10 ml, pericardial pressures returned to levels similar to those measured at the control state (line 3). In the prone body position, withdrawal of 4 ml produced a decrease in intrapericardial pressures (line 5). The infusion of 10 ml produced an increase in pressures (line 6). After withdrawal of 11 ml (line 7), values close to those observed during the previous set of observations laheUed 5 were recorded. Note that in all instances the differences in pressures recorded simultaneously from the ventral and dorsal sites in the pericardial sac amounted to an average gradient of about 1 cm H.JD/cm of vertical distance separating the respective catheter tips. lateral (+GV) and left lateral (-G y ) acceleration when the catheters were below the midlung sagittal plane, and less positive pressures were recorded when the tip was above this level (Fig. 5). The interpolated values for intrapericardial pressure at zero G (that is, the intercepts of the dashed lines with the zero G axis) of about —3 cm H2O were similar when dogs were in the supine and prone positions and when in the left lateral and right lateral positions (Figs. 4 and 5). This is presumably the value that would be obtained for pericardial OrcuUiton Rtsetrcb, Vol. XX, Jmmrj 1967 pressure at zero G, that is, in a weightless environment. The relationship of mean end-expiratory intrapericardial pressure to the hydrostatic distance from mid-lung level, that is, the G level times the vertical distance in centimeters from mid-lung level in the four directions of acceleration is shown in Figure 6. The fact that individual values of intrapericardial pressure fall along the dashed line indicates that changes in pressure of about 1 cm H2O/cm of vertical distance occurred, as would be expected to occur in a hydrostatic system. At the higher levels of backward (—Gx) acceleration, 70 BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD RELATIONSHIP BETWEEN INTRAPERICARDIAL PRESSURE AND INTRAPLEURAL PRESSURE intrapericardial pressures were higher than those expected in a hydrostatic system, possibly because the specific gravity of the heart and its contained blood is greater than one. Values for intrapericardial pressures at 1G obtained after exposures to different levels of acceleration in the four body positions were not systematically different from the values obtained before the exposures. Pressure Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 '-60 MEAN at -30 Changes in pressure recorded simultaneously on the pericardial and pleural sides of the pericardium have been studied by comparison of the pressure values obtained when the tips of the pericardial and pleural catheters were located within 1 cm of each other as measured by biplane roentgenograms. This was Values 0 30 Height 60 END-EXPIRATORY PRESSURE CATHETER TIP (cm H20) '8 of Recording 4 0 - 4 DISTANCE above MID-LUNG (cm) Site -8 FIGURE 4 Variations of pericardial pressure with the level of acceleration and the vertical height of the recording site in the thorax of 7 dogs without thoracotomy studied while in the supine (+GJ and prone (-GJ positions. Acceleration values on the ordinate are plotted as positive values, that is, above the zero C line for fonoard (+GJ exposures, and as negative values, that is, below the zero G line for backward (-GJ exposures. A negative sign on the abscissa of the left panel indicates the catheter tip was below the mid4ung plane. Note that when the dog was supine (+GX acceleration) the pericardial catheter tip was always above mid-lung level at 1G (right upper panel,) and the pericardial pressure at this site was uniformly negative (average —6 cm H,O). Wlien the dogs were rotated to the prone position (-GJ, the catheter tip was always below mid-lung (right lower panel) and pericardial pressures at 1G were uniformly less negative (average 0 cm HtO) than the values obtained at these same anatomic sites at 1G when the dogs were in the supine position. During increased levels of +GX acceleration, the catheter tip was displaced progressively lower in the thorax with the downward movement of the heart at higher levels of +GX. In the 2 animals in which the pericardial catheter moved to sites actually below the mid-lung plane during exposures of + 7GT, the pericardial pressure was increased concomitantly to positive values. In contrast, in the animals in which the pericardial datheter tip remained above the mid-lung plane, the pericardial pressures recorded at +7CX were more negative than the values obtained at + 1GW (left upper panel). When the dogs were prone (—Gx acceleration), the heart was resting on the sternum and ventral rib cage at 1G and there was practically no additional downward (ventral) displacement of the dependent catheter tip during increased levels of —Gw. In this situation a progressive increase in pericardial pressure uniformly occurred to attain values as high as 45 cm H,O at —6.5Gm (left lower panelj. The average level of pericardial pressure interpolated to zero G (intersection of dashed lines with the zero G line) was about —3 cm Hfi in this presumed weightless condition. Symbols identify values from same dogs as in Figures 4, 5, and 8. Simultaneous pleural pressure and blood oxygen saturation values reported elsewhere (7, 8) are identified by same symbols. CircnUiion Rtsrtrcb, Vol. XX, Jcnturj 1967 PERICARDIAL PRESSURES IN DOGS 71 the case in 3 animals (dogs 4, 6, and 7) (Fig. 1). No systematic differences were observed in the pressures recorded at these respective pleural and pericardial sites, the pericardial pressure being slightly higher in 12 of 21 measurements performed at various levels of acceleration in all four body positions (Fig. 7). An estimation of the transpericardial pressure was possible by correction of the pleural pressure to the level of the pericardial catheter tip. The average transpericardial pressure of 0.8 cm H2O estimated in this manner was not significantly different from zero. Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 RELATIONSHIP BETWEEN INTRAPERICARDIAL PRESSURE AND ATRIAL PRESSURES This relationship was studied in the 7 dogs exposed to acceleration (Fig. 8). Mean left atrial pressures, referred to mid-lung coronal plane, were 3.3 and 1.3 cm HoO when dogs were in the supine (+1GJ and prone (— l G ^ body positions, respectively. The mean right atrial pressures of 0.7 and 0.4 cm H2O, re- spectively, were slightly less than the simultaneous left atrial pressures (Fig. 8). During exposures to different levels of forward (+GX) and backward (— Gx) acceleration, slight increases in atrial pressures were observed at the higher levels of plus and minus Gx acceleration. It should be remembered, however, that, due to the sevenfold increase in the effective weight of the blood at 7G and the dorsal-ventral dimension of the lungs of these dogs of about 12 cm, the pulmonary venous pressure at the most dependent (dorsal) regions of the lungs averaged about 50 cm H2O during exposures to +7G I; whereas the pulmonary venous pressure at the most dependent (ventral) regions of the lungs averaged about 70 cm H2O during exposures to —7GX. Concomitantly in superior regions of the lungs, if collapse of pulmonary veins does not occur, highly negative pulmonary venous pressures are present at these same levels of acceleration. Pressure -Values Height of Recording Site 8r flr -4 - -60 -30 0 30 6O MEAN END - EXPIRATORY PRESSURE at CATHETER TIP (cm HZO) -8 4 0 DISTANCE MID-LUNG above (cm) FIGURE 5 Variations of pericardial pressure with the level of acceleration and the vertical height of the recording site in the thorax while in the left (+Ct) and right (—CJ decubtius positions. Note that, as was the case for the Gx acceleration, progressively more positive pericardial pressures were recorded with increasing acceleration when the catheter tip was below the mid-lung sagittal level and less positive pressures were recorded when the tip was above this level. The average of the interpolated value for pericardial pressure at zero C when the dogs were rotated from the left to the right decubitus position of about —3 cm H2O was not significantly different from the value obtained at zero C for the supine and prone positions. CircmUlion Rtiurcb, Vol. XX, ]tntun 1967 72 BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 The average of the interpolated values for left atrial pressure at zero G (intersection of dashed line with zero G axis) of about 2 cm H2O was slightly greater than the interpolated value of 0.5 cm H«O obtained for right atrial pressure in this presumed weightless condition. Referring the mean atrial pressure and mean end-expiratory intrapericardial pressure to the same vertical height made an estimation of transmural atrial pressures possible. The differences between mean atrial pressures referred to the level of the pericardial catheter tip and the intrapericardial pressures are shown in the right panels of Figure 8. Transmural left atrial and right atrial pressures of about 4 and 2 cm H2O, respectively, were observed at 1G in these two body positions. No significant systematic changes in transmural atrial pressures occurred during exposures to increased levels of acceleration of up to plus and minus 7Gx. Similarly, the values inter- polated to zero G were also 4 and 2 cm H^O for left and right atrial transmural pressures, respectively, in this presumed weightless condition. Discussion Investigations of the effects of the pericardium and pericardial pressures on cardiac hemodynamics have been directed mainly to abnormal conditions (1-4, 14-22). Data available on normal intrapericardial pressure are meager (1-4). Because nearly all studies have been carried out after thoracotomy and pericardiotomy, the relationship of the pressures recorded to those present in the intact animal is open to question. The pericardial sac has been reported to contain from 0.3 to 1 ml of a clear liquid called "liquor pericardii" or pericardial fluid, which makes the pericardial space a real space, at least in certain parts (23). Aspiration was carried out immediately after ACCELERATION • Forward (*GM) A Backward (-G,) • Right Lattrol (+Gy) » tll Lattral (-Gr) c I 13 h- o S E -10 - O • — ID la o -a a -30 -20 MEAN END-EXPIRATORY PERICARDIAL PRESSURE at CATHETER TIP (cm HZO) FIGURE 6 Relation of mean end-expiratory intrapericardial pressure to the hydrostatic distance of the recording site above mid-lung (that is, G times centimeters from mid-lung), during transverse acceleration of 1 to 7G in the four body positions. The diagonal dashed line indicates a gradient of 1 cm H,O/G X cm. Note that the values are scattered along this line; this indicates that changes in pressure within the pericardial sac behave like a hydrostatic system, this effect being independent of the body position. Circuluion Ruttrcb, Vol. XX, Jtmmsn 1967 73 PERICARDIAL PRESSURES IN DOGS Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 each insertion of the pericardial catheter as a means of verifying a successful pericardial puncture. One to five milliliters of fluid could be obtained in each instance when the puncture was successful. If the catheter was inadvertently introduced into the pleural space, fluid could not be aspirated after the attempted mediastinal pericardial puncture. Aspiration was attempted at intervals throughout the experiment to verify that the small volume of fluid normally present within the pericardial sac was maintained as normal as possible. Ringer's fluid (5 to 10 ml) introduced into the pericardial space via the recording catheter could be completely recovered by subsequent aspiration. Values reported herein are mean end-expiratory intrapericardial pressures referred to the catheter tip. The changes in pericardial pressure associated with the cardiac and respiratory cycles have not been analyzed in detail. In the normal gravitational environment (1G) as well as under the influence of transverse acceleration in four body positions, mean end-expiratory intrapericardial pressure was related to the height of the recording site. Changes in intrapericardial pressure with vertical distance in the thorax are similar to those that would be expected in a hydrostatic system, that is, changes in pressure of 1 cm H20/cm of vertical distance. This type of relationship has been observed in all conditions studied. When dogs are exposed to forward (+G*) acceleration (supine position), the heart is « A • C O 6 D O Forward i*Gt) Socl-or, (-G,) Rlfkt Llltrel l*Gr) LtU Lattrat l-Gy) 21 oa o -Q O -20 -10 MEAN at 0 10 20 30 40 END- EXPIRATORY PRESSURE CATHETER TIP (cm H20) FIGURE 7 Comparison of simultaneous values of mean end-expiratory pericardial and pleural pressures recorded at contiguous sites in the thorax at different hydrostatic distances from mid-lung during transverse accelerations of 1 to 7C in four body positions. Only values obtained when the tips of the pericardial and pleural catheters were located within 1 cm of each other are shown. The solid lines connect simultaneously recorded pleural and pericardial pressure values. Numerals indicate individual dogs. The dashed line indicates a 1 to 1 gradient, as would be obtained in a hydrostatic system. Note that no systematic difference was observed between these pleural and pericardial pressures, thus indicating that transpericardial pressure was not systematically different from zero and therefore that the pericardial membrane was not restricting cardiac dilatation under these circumstances. Circulation Rtiurcb, Vol. XX, ]inmry 1967 74 BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 suspended in the thorax by a band of elastic fascicles, the stemopericardiac ligament (23). A variable degree of dorsal (backward) displacement always occurred at high levels of forward acceleration (7). The pericardial catheter tip was displaced downward along with the heart, and changes in intrapericardial pressure were related to these displacements (Fig. 4). Smaller displacements of the heart and catheter tip were observed during exposures to right lateral (+G y ) acceleration (dogs in left decubitus position) and to the left lateral (—GT) acceleration (dogs in right decubitus position). However, displacements of the heart and pericardial catheter tip, when dogs were exposed to backward (— Gx) acceleration (dogs prone), were negligible (7). In this body position, the heart rests on and is Atrial LEFT supported by the inner surface of the sternum and ventral rib cage. Therefore, the distance from the pericardial catheter tip to the midlung reference plane was practically unchanged in the range of acceleration from - l t o ^ G , (Fig. 4). Since atrial pressures were only slightly changed during exposures to forward and backward acceleration, the hydrostatic indifference point of atrial pressures in dogs is about mid-lung level (24, 25). The fact that transpericardial pressure was not significantly different from zero and unchanged at different levels of transverse acceleration, irrespective of body positions, indicates that this membrane plays only a passive role under these circumstances and is not subjected to the pressure imbalances that occur in the Pressures 8r Transmural Pressures (Atrial - Pericardial) LEFT RIGHT RIGHT / Uj -4 - -20 O 20 -8 -20 PRESSURE REFERRED Io (cm H20) IF 0 20 M-ID- LUNG -20 0 20 -20 0 20 PRESSURE at PERICARDIAL CATHETER TIP (cm H20) FIGURE 8 Relation of atrial pressures to the level of transverse acceleration when in the supine (-\-GJ and the prone (-GJ body positions. Note (left panels) that at mid-lung level there was only a slight increase in atrial presures over the range from + 7GX to —7GX acceleration. The average of the interpolated values for zero G (intersections of dashed lines with zero G line) of 2 cm H,O for left atrial pressure was slightly greater than the interpolated average value of 1 cm HtO obtained for right atrial pressure in this presumed weightless condition. Note fright panels) transmural atrial pressures (that is, the difference between mean atrial and mean pericardial pressures corrected to the same vertical height in the thorax) were not systematically affected by the level of acceleration in the range from + 7GX to —7Gr. The average interpolated values for transmural left atrial pressure at zero C of about 5 cm HtO were slightly in excess of the analogous value for right atrial pressure of about 3 cm HtO. OrcnUliom Rtstmrcb, Vol. XX, Jtmutry 1967 PERICARDIAL PRESSURES IN DOGS Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 lungs. However, because the average values of pulmonary venous pressure in dependent regions of the lungs of about 50 and 70 cm HL.O at levels of +7G r and —7GX, respectively, were considerably in excess of the colloido-osmotic pressure of plasma, rapid formation of pulmonary edema in these regions of the lungs would be expected to occur at these levels of acceleration (26). In these same animals a progressive decrease in transmission of the infrared light of arterial blood, indicating hemoconcentration, was observed during exposures to acceleration of 4G or above in all body positions (10); this suggests that excessive loss of fluid from the bloodstream was occurring presumably via dependent capillary beds in the pulmonary and the systemic circulation over which effective counter pressures were not being applied. The gradient in pressure with vertical position observed within the pericardial sac probably is due to the weight of the heart and other thoracic contents. The slightly higher pericardial pressures obtained at the higher levels of backward acceleration (Fig. 6) may be related to the fact that the specific gravity of the heart and its contained blood, which overlay the catheter tip in the prone body position, is slightly greater than one. The fact that pericardial pressures were equal and independent of body positions in the interpolated zero G condition confirms the hypothesis that the differences in pericardial pressures at different sites in the thorax obtained at 1G and during exposures to acceleration are caused by the weight of the thoracic contents, since, if this were the case, these differences would be expected to disappear under conditions of weightlessness, as our results suggest. In the case of the potential pleural space, a distinction has been made between "fluid" and "surface" pleural pressures, the fluid pressure being more negative than the surface pressure (27). Under the conditions of our experiments (dogs in the horizontal position, pleural and pericardial catheters of 1.3 mm, o. d.), no evidence was elicited that the fluid pressures at the lung or heart surfaces were CircuUlioa Risurcb, Vot XX, Jtnuary 1967 75 different from the surface pressures at the same surfaces. End-expiratory pressures recorded at the catheter tip were stable over long periods, indicating that, if fluid were being absorbed from the tip of the catheter, it was being continually replaced from the normally present pools of pleural and pericardial fluids via the aqueous film separating the pleural or periepicardial surfaces. When small amounts of fluid were introduced via the catheter tips by transient high pressure flushes, the pressures immediately returned to the preflush values. If a localized, more negative fluid pressure was being recorded by these fluid-filled catheter systems, it would be expected that introduction of fluid via the catheter tip would cause the recorded pressures to become more positive and approach the surface pressures until the injected fluid was absorbed and the more negative fluid pressure was again recorded. No evidence of this phenomenon was obtained in these experiments. It appears that a thin film of pericardial fluid is present in all portions of the periepicardial space because small (I to 5 ml) volumes of pericardial fluid could always be withdrawn immediately after puncture of the pericardium in these dogs, and volumes of Ringer's fluid injected via the pericardial catheter could be almost completely recovered by application of negative pressure to the extrathoracic end of the catheter. These findings indicate that pericardial fluid is transmitted relatively freely throughout the periepicardial space and, hence, it would be anticipated that hydrostatic pressures would likewise be transmitted throughout this space. The finding of a pressure gradient of 1 cm of water/cm of vertical distance in this space supports this concept. During life on earth, blood in the cardiac chambers is continually subjected to gravitational hydrostatic forces as well as to inertia! hydrostatic forces whenever the motion (velocity) of the body is changed in magnitude or direction. Since the heart is relatively flaccid and fluid filled, the maintenance of proper function of this pump would be much 76 BANCHERO, RUTISHAUSER, TSAKIRIS, WOOD Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 more certain if it were suspended in a hydrostatic system which automatically applied perfectly compensated hydrostatic pressures to all of its external surfaces whenever the gravitational or inertial forces acting on this organ were altered. The pericardial pressure values obtained in this study in different body positions and at levels of acceleration varying from the normal (1G) gravitational attraction of the earth up to an inertial force of 7G suggest that, within this range of environmental force, this is the case. The finding that pleural and pericardia] pressures recorded at contiguous sites in the thorax were not significantly different (Fig. 6) indicates that in these regions the pericardium is not subjected to transverse tensions and suggests that the pleural pressure in regions juxtaposed to the heart must also have a gradient of approximately 1 cm of water/cm of vertical distance in the thorax. Recent studies in this laboratory of both pleura] and esophageal pressures in dogs and esophageal pressures in man in the erect position support this interpretation (28, 29). cardial, esophageal, and atrial pressures in dogs without thoracotomy. Physiologist 5: 1.35, 1962. 6. Technics for measuremerf of intrapleural and pericardial pressures in dogs studied without thoracotomy and methods for their application to study of intrathoracic pressure relationships during exposure to forward acceleration (+Gx). Tech. Doc. Rep. AMRL-TDR-63-107. U. S. Air Force 6570 Aerospace Med. Res. Lab. 1-24, December, 1963. 7. References 1. HOLT, J. P., RHODE, E. A., AND KINES, H.: Peri- cardial and ventricular pressure. Circulation Res. 8: 1171, 1960. 2. KATZ, L.' N., AND GAUCHAT, H. W.: Observa- tions on pulsus paradoxus (with special reference to pericardial effusions). II. Experimenta. Arch. Internal Med. 33: 371, 1924. 3. 8. 9. 5. NEWCOMBE, C. P., SINCLAIR, J. D., DONALD, D. E., AND WOOD, E. H.: Detection and as- sessment of mitral regurgitation by left atrial indicator-dilution curves. Circulation Res. 9: 1196, 1961. 10. BANCHERO, N., CRONIN, L., RUTISHAUSER, W. J., TSAKIRIS, A. C., AND WOOD, E. H.: Effects of transverse acceleration on blood oxygen saturation. J. Appl. Physiol. (In press.) 11. WOOD, E. H., AND SWAN, H. J. C : Right heart catheterization. In Cardiology: An Encyclopedia of the Cardiovascular System, vol. 2, part 4. New York, McGraw-Hill Book Company, Inc., 1959, pp. 292-322. 12. WOOD, E. H.: Diagnostic applications of indicator-dilution technics in congenital heart disease. Circulation Res. 10: 531, 1962. 13. WOOD, E. H.: Use of human centrifuge to study circulatory, respiratory and neural physiology in normal human beings. Proc. 3rd IBM Med. Symposium, Endicott, New York, 1961, pp. 323-380. 14. ADCOCK, J. D., LYONS, R. H., AND BARNWELL, J. B.: Circulatory effects produced in a patient with pneumopericardium by artificially varying the intrapericardial pressure. Am. Heart J. 19: 283, 1940. 15. BARNARD, H. L.: The functions of the pericar- dium. J. Physiol. (London) 22: Facing page xliii, 1897-98. 4. RENNER, H. M., AND WOOD, E. H.: Intraperi- cardial, intrapleural, and intracardiac pressures during acute heart failure in dogs studied without thoracotomy. Circulation Res. 19: 1071, 1966. RUTISHAUSER, W. J., BANCHERO, N., TSAKIRIS, A. G., EDMUNDOWICZ, A. C, AND WOOD, E. H.: Pleural pressures at dorsal and ventral sites in supine and prone body positions. J. Appl. Physiol. 21: 1500, 1966. MORGAN, B. C, GUNTHEHOTH, W. G., AND DILLARD, D. H.: Relationship of pericardial to pleural pressure during quiet respiration and cardiac tamponade. Circulation Res. 16: 493, 1965. RUTISHAUSER, W. J., BANCHERO, N., TSAKIRIS, A. G., AND WOOD, E. H.: Pleural and esopha- geal pressures during forward, backward, and lateral acceleration. (Submitted for publication.) Acknowledgments These studies were made possible by the assistance of many of our colleagues, among whom the help of Ralph Sturm, Robert Hansen, Patrick Caskey, Don Hegland, Julius Zarins, Ray Swanson, Volney Streifert, Miss Lucille Cronin, and Mrs. Jean Frank was of particular importance. WOOD, E. H., NOLAN, A. C, DONALD, D. E., EDMUNDOWICZ, A. C, AND MARSHALL, H. W.: 16. BERGLUND, E., SARNOFF, S. J., AND ISAACS, J. P.: Ventricular function: Role of the pericardium in regulation of cardiovascular hemodynamics. Circulation Res. 3: 133, 1955. EDMUNDOWICZ, A. C, DONALD, D. E., AND WOOD, E. H.: Relationship of intrapleural 17. BRECHER, G. A., AND GALLETTI, P. M.: Func- pressures at multiple thoracic sites to peri- tional anatomy of cardiac pumping. In HandCircmUtion Rutsrcb, Vol XX, Jtniuirj 1967 77 PERICARDIAL PRESSURES IN DOGS book of Physiology, Sec. 2, vol. 2, Circulation. Washington, D. C, American Physiological Society, 1963, pp. 759-798. 18. Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 23. 26. 24. GUYTON, A. C, AND GRECANTI, F. P.: A physi- ologic reference point for measuring circula- Circulation Rtfearch, Vol. XX, Janusrj 1967 The hydrostatic pressures. In WOOD, E. H., NOLAN, A. C, DONALD, D. E., AND CRONIN, L.: Influence of acceleration on 27. ACOSTONI, E., AND MEAD, J.: Statics of the respiratory system. In Handbook of Physiology, Sec. 3, vol. 1, Respiration. Washington, D. C., American Physiological Society, 1964, pp. .387^09. 28. BANCHERO, N., TSAKIHIS, A. G., AND WOOD, E. H.: Regional differences in pleural and esophageal pressures in dogs in the upright body position studied without thoracotomy. Physiologist 8: 106, 1965. MILLER, M. E., CHRISTENSEN, G. C, AND EVANS, H. E.: Anatomy of the Dog. Philadelphia, W. B. Saunders Company, 1964, p. 267. H.: pulmonary physiology7. Federation Proc. 22: 1024, 1963. NELEMANS, F. A.: Die Funktion des Perikards. Arch. need, de physiol. 24: 337, 1940. 22. WICCERS, C. J.: Circulatory Dynamics: Physiologic Studies. New York, Grune & Stratton, Inc., 1952, p. 63. GAUER, O. Gravitational Stress in Aerospace Medicine, edited by O. H. Gauer and C. D. Zuidema. Boston, Little, Brown & Company, 1961, p. 16. KUNO, V.: The significance of the pericardium. J. Physiol. (London) 50: 1, 1915. 20. LUCIANI, L.: Human Physiology, vol. 1, Circulation and Respiration. (Translated by Frances A. Welby.) London, Macmillan & Co., Ltd., 1911, 592 pp. 21. 25. ISAACS, J. P., BERCLU.VD, E., AND SARNOFF, S. J.: Ventricular function III. The pathologic physiology of acute cardiac tamponade studied by means of ventricular function curves. Am. Heart J. 49: 66, 1954. 19. tory pressures in the dog—particularly venous pressure. Am. J. Physiol. 185: 137, 1956. 29. BANCHEHO, N., SCHWARTZ, P., AND WOOD, E. H.: Intraesophageal pressure gradient in man. (Submitted for publication.) Pericardial Pressure during Transverse Acceleration in Dogs without Thoracotomy NATALIO BANCHERO, WILHELM J. RUTISHAUSER, ANASTASIOS G. TSAKIRIS and EARL H. WOOD Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017 Circ Res. 1967;20:65-77 doi: 10.1161/01.RES.20.1.65 Circulation Research is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 1967 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7330. 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