Effect of adenosine-induced controlled hypotension on canine myocardial performance, blood flow and metabolism

The effect of adenosine-induced controlled hypotension (CH) on myocardial performance, blood flow, and metabolism was studied in nine pentobarbital-anaesthetized, open-chest dogs. Adenosine was continuously infused i.v. (0.69 +/- 0.06 and 1.36 +/- 0.11 mg/kg/min) at two stepwise increased rates (12-14 min-periods) in order to induce approximately 20 and 40% reduction of the mean arterial pressure (MAP 62 +/- 4 and 43 +/- 1 mmHg, respectively). The reduction of MAP was associated with decreases in heart rate (6 +/- 2%, P less than 0.05 and 21 +/- 4%, P less than 0.01), left intraventricular systolic pressure (14 +/- 3%, P less than 0.01 and 32 +/- 3%, P less than 0.01), left ventricular end-diastolic pressure (23 +/- 9%, P less than 0.05 and 42 +/- 9%, P less than 0.01) and ventricular intramyocardial systolic pressure (15 +/- 6% n.s. and 27 +/- 6%, P less than 0.01). The rate pressure product was markedly reduced by 49 +/- 3% (P less than 0.01) at the highest infusion rate. The mean coronary vein pressure (20.3 +/- 2.8 mmHg) was unaffected by the adenosine infusion. The systolic pressure time index (SPTI) was decreased by 33 +/- 3% (P less than 0.01) during the highest infusion rate of adenosine, while the diastolic perfusion time index (DPTI) was 15.4 +/- 2.2 mmHg X s and remained unchanged. The DPTI:SPTI ratio increased by 40 +/- 13% (P less than 0.05), suggesting a sufficient endocardial oxygen supply.(ABSTRACT TRUNCATED AT 250 WORDS)     

The acute effect of intra-aortic balloon counterpulsation during extracorporeal life support: an experimental study

Hemodynamically unstable patients supported by an extracorporeal life support (ECLS) circuit often receive additional support by intra-aortic balloon pump (IABP). However, it is not established whether support of the failing heart is improved by adjunctive IABP in both peripheral cannulation (PC) and central cannulation (CC) settings. Seven sheep were supported by an IABP and an ECLS system which were cannulated centrally as well as peripherally. In each cannulation configuration, hemodynamic and cardiac function indices were measured at baseline, ECLS, and ECLS plus IABP. The primary variables were mean coronary artery flow (Qcor), diastolic pressure time index (DPTI), left ventricular (LV) pressure-volume area (PVA), and tension time index (TTI). Additional IABP with ECLS support (CC/PC) decreased LV afterload (LV systolic peak pressure -4%, P<0.05/-8%, P<0.02), as well as TTI -2%/-10% and PVA -10%/-12% (P<0.03). Coronary perfusion was increased by additional IABP: CC, Qcor, +9%, and DPTI, +18% (P<0.02); PC, Qcor,+6%, and DPTI, +11% (P<0.05). IABP augmented the myocardial oxygen supply/demand ratios (CC/PC): Qcor/(PVA.heart rate) (+21%/+22%, P<0.02) and DPTI/TTI (+27%/+24%, P<0.03). In case of low arterial pressure (<50 mm Hg) and reduced ECLS flow, the overall hemodynamic profile improved only with central cannulation. We conclude that in both central and peripheral ECLS cannulation settings, adjunctive IABP improves the myocardial oxygen supply demand balance. In case of low cardiac output and insufficient extracorporeal flow with PC, adjunctive IABP may be contraindicated.     

Systemic hypertension following myocardial revascularization. A method of treatment using epidural anesthesia.

Seven of 12 patients (58%) undergoing myocardial revascularization surgery became hypertensive in the immediate postoperative period. The hypertensive patients had significant elevations in peripheral vascular resistance (22.0 +/- 2.0 S.E. resistance units) compared to measurements in normotensive patients (15.6 +/- 1.3 S.E. resistance units) (p less than 0.05), whereas the heart rates and cardiac indices were similar. Administration of thoracic epidural anesthesia to postoperatively hypertensive patients lowered systemic arterial pressure by decreasing peripheral vascular resistance (p less than 0.005) but not affecting the pulse rate and cardiac index. The ratio diastolic pressure-time index/systemic pressure-time index (DPTI/SPTI), an indirect measurement of subendocardial oxygenation, increased from preanesthetic values of 0.80 +/- 0.08 S.E. to 1.09 +/- 0.09 S.E. (p less than 0.025) after the systemic arterial pressure was lowered in postoperatively hypertensive patients. Hypertensive episodes following myocardial revascularization procedures appear related to increased alpha-adrenergic activity, which products elevation in peripheral vascular resistance. Decreasing peripheral vascular resistance by chemical sympathectomy with thoracic epidural anesthesia lowers the systemic arterial pressure and improves the DPTI/SPTI ratio.     

Regional myocardial blood flow in left ventricular hypertrophy. An experimental investigation in Newfoundland dogs with congenital subaortic stenosis

To test the hypothesis that left ventricular hypertrophy (LVH) may predispose the subendocardium to ischemia, we studied regional myocardial blood flow in dogs with the fibrous ring form of subvalvular aortic stenosis and concentric LVH. Radioactive microspheres, 9 +/- 1 mu in diameter, were used. Eleven dogs with LVH (left ventricular body weight ratio of 6.35 +/- 0.46 gm/kg [mean +/- SEM] and peak left ventricular outflow gradient of 51 +/- 7 mm Hg) were compared to 12 normal dogs (left ventricular/body weight ratio of 3.41 +/- 0.12 gm/kg and peak left ventricular outflow gradient of 6 +/- 3 mm Hg). The two groups of dogs were subjected to comparable experimental interventions including (1) tachycardia produced by atrial pacing (221 +/- 4 beats/min), (2) ascending aortic constriction producing systolic hypertension (212 +/- 5 mm Hg), and (3) creation of an aortic-right atrial fistula lowering diastolic blood pressure (38 +/- 3 mm Hg). Basal regional myocardial blood flow was distributed similarly for LVH and normal dogs (endocardial/epicardial ratio = 0.90 +/- 0.05 and 0.94 +/- 0.03, respectively). During experimental interventions, regional blood flow remained equal to all myocardial layers in normal dogs; however, the endocardial/epicardial ratio diminished in LVH dogs during atrial tachycardia to 0.61 +/- 0.08, during systolic hypertension to 0.68 +/- 0.06, and during diastolic hypotension to 0.50 +/- 0.09. When the diastolic/systolic pressure time index ratio (DPTI/SPTI) was less than 0.8, subendocardial ischemia occurred in dogs with LVH (endocardial/epicardial ratio = 0.66 +/- 0.04) but not in normal dogs (endocardial/epicardial ratio = 0.92 +/- 0.03) (p less than 0.0001). Animals with infracoronary obstruction and LVH demonstrate greater susceptibility to development of subendocardial ischemia for identical hemodynamic interventions than do normal animals.     

Cardiac Function During Induction and Early Anesthesia with Methoxyflurane. An Evaluation Using Systolic Time Intervals and Pressure Time Indices

In addition to the standard monitoring of heart rate and blood pressure, the Systolic Time Intervals were used to evaluate cardiac performance, and the Pressure Time Indices (tension time index = TTI; diastolic pressure time index = DPTI) were used to estimate myocardial oxygen balance. Twelve patients with known heart disease were studied during induction with thiopental, intubation, and early anesthesia with methoxyflurane.
Cardiac performance diminished after thiopental; and during methoxyflurane it was reflected in increases in pre-ejection period (PEP) and the ratio PEP/LVET. Intubation resulted in a hyperactive state of the heart, as shown by maximal decreases in PEP and PEP/LVET.
Myocardial oxygen balance - estimated from the supply/demand ratio (DPTI/ TTI) - was impaired after thiopental. After intubation, DPTI/TTI decreased to its lowest value due to an excess of myocardial oxygen demand (TTI) over myocardial oxygen supply (DPTI), signifying a transitory underperfusion of the subendocardium. During methoxyflurane the oxygen balance was gradually restored towards control value.
The Systolic Time Intervals and the Pressure Time Indices provided valuable information on cardiac function not available from standard monitoring alone.     

A physiologic comparison of external cardiac massage techniques

On the basis of recent investigation, controversy has arisen regarding which of several cardiopulmonary resuscitation methods optimizes hemodynamics. The present study was designed to compare five recently described chest compression techniques: high-impulse manual chest compression at 150/min, mechanical compression at 60/min with simultaneous ventilation, mechanical compression at 60/min with simultaneous ventilation and either systolic or diastolic abdominal compression, and pneumatic vest compression at 60/min. Eight dogs were chronically instrumented with electromagnetic flow probes in the ascending and descending aorta while matched micromanometers measured aortic, left ventricular, and pleural pressures. At study, each dog was anesthetized with morphine, intubated, and the heart was fibrillated by rapid ventricular pacing. The five cardiopulmonary resuscitation methods were performed randomly in each preparation within 7 to 10 minutes of arrest. In four dogs, brachiocephalic blood flow was computed as total cardiac output minus descending aortic blood flow, and in all dogs coronary perfusion pressure was calculated as mean diastolic aortic pressure minus mean diastolic left ventricular pressure. Average cardiac output for seven studies was 662 +/- 61 ml/min with high-impulse manual compression, 340 +/- 46 ml/min with mechanical compression and simultaneous ventilation, 336 +/- 45 ml/min with mechanical compression and simultaneous ventilation with systolic abdominal compression, 366 +/- 52 ml/min with mechanical compression and simultaneous ventilation with diastolic abdominal compression, and 196 +/- 29 ml/min with vest resuscitation (high-impulse manual compression significantly greater than other techniques by multivariate analysis, p less than 0.05). Brachiocephalic blood flow generally followed cardiac output and was statistically the greatest with high-impulse manual compression at 273 +/- 47 ml/min (p less than 0.05). Finally, high-impulse manual compression provided the highest coronary perfusion pressure of 31 +/- 4 mm Hg (p less than 0.05) compared to 23 +/- 2 mm Hg for mechanical compression and simultaneous ventilation, 23 +/- 2 mm Hg for mechanical compression and simultaneous ventilation with systolic abdominal compression, 23 +/- 3 mm Hg for mechanical compression and simultaneous ventilation with diastolic abdominal compression, and 11 +/- 2 mm Hg for vest resuscitation. These data demonstrate that high-impulse manual compression generated physiologically and statistically superior hemodynamics when compared with other methods in this model of cardiopulmonary resuscitation.     

The effects of positive end-expiratory pressure during active compression decompression cardiopulmonary resuscitation with the inspiratory threshold valve

The use of an inspiratory impedance threshold valve (ITV) during active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) improves perfusion pressures, and vital organ blood flow. We evaluated the effects of positive end-expiratory pressure (PEEP) on gas exchange, and coronary perfusion pressure gradients during ACD + ITV CPR in a porcine cardiac arrest model. All animals received pure oxygen intermittent positive pressure ventilation (IPPV) at a 5:1 compression-ventilation ratio during ACD + ITV CPR. After 8 min, pigs were randomized to further IPPV alone (n = 8), or IPPV with increasing levels of PEEP (n = 8) of 2.5, 5.0, 7.5, and 10 cm H(2)O for 4 consecutive min each, respectively. Mean +/- SEM arterial oxygen partial pressure decreased in the IPPV group from 150 +/- 30 at baseline after 8 min of CPR to 110 +/- 25 torr at 24 min, but increased in the PEEP group from 115 +/- 15 to 170 +/- 25 torr with increasing levels of PEEP (P <0.02 for comparisons within groups). Mean +/- SEM diastolic aortic minus diastolic left ventricular pressure gradient was significantly (P < 0.001) higher after the administration of PEEP (24 +/- 0 vs 17 +/- 1 mm Hg with 5 cm H(2)O of PEEP, and 26 +/- 0 vs 17 +/- 1 mm Hg with 10 cm H(2)O of PEEP), whereas the diastolic aortic minus right atrial pressure gradient (coronary perfusion pressure) was comparable between groups. Furthermore, systolic aortic pressures were significantly (P < 0.05) higher with 10 cm H(2)O of PEEP when compared with IPPV alone (68 +/- 0 vs 59 +/- 2 mm Hg). In conclusion, when CPR was performed with devices designed to improve venous return to the chest, increasing PEEP levels improved oxygenation. Moreover, PEEP significantly increased the diastolic aortic minus left ventricular gradient and did not affect the decompression phase aortic minus right atrial pressure gradient. These data suggest that PEEP reduces alveolar collapse during ACD + ITV CPR, thus leading to an increase in indirect myocardial compression. IMPLICATIONS: Inspiratory impedance during active compression-decompression cardiopulmonary resuscitation improves perfusion pressures, and vital organ blood flow during cardiac arrest. Increasing levels of positive end-expiratory pressure during performance of active compression-decompression cardiopulmonary resuscitation with an inspiratory impedance valve improves oxygenation, and increases the diastolic aortic-left ventricular pressure gradient and systolic arterial blood pressure.     

A skeletal muscle ventricle made from rectus abdominis muscle in the dog

This study examined the ability of a skeletal muscle-powered assist ventricle to augment cardiac output in 10 dogs with experimentally induced heart failure. Heart failure was induced with the use of the beta-blocking agents atenolol and propranolol. A "skeletal muscle ventricle" was then surgically constructed by wrapping the rectus abdominis muscle, with an intact neurovascular supply, around a double open-ended compressible pouch. The skeletal muscle ventricle was then interposed in a left ventricular apicoaortic conduit. The motor nerves to the skeletal muscle ventricle were stimulated by a custom designed pulse generator and caused tetanic contraction of the ventricle during diastole of every fourth natural heart beat. Stimulation was continued for 60 min. Cardiac output, systolic and diastolic blood pressures, mean blood pressure, left ventricular end diastolic pressure, and central venous pressure were then monitored prior to, during, and several times after skeletal muscle ventricle stimulation to evaluate assist ventricle function. There was an increased cardiac output in all 10 dogs at all recording times during skeletal muscle ventricle assistance compared to the cardiac output prior to stimulation of the assist ventricle. The mean increase in cardiac output after 30 min of assist ventricle stimulation was 31.0 +/- 14% (P less than 0.01), and at 60 min was 8.0 +/- 1% (P less than 0.05). The mean diastolic blood pressure after 1 and 30 min of skeletal muscle ventricle assistance (50.0 +/- 2.9 and 48.6 +/- 2.2 mm Hg, respectively) was increased (P less than 0.05) vs the preassistance value (44.9 +/- 2.8 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cardiac functional and morphologic changes of renal allograft recipients in the early posttransplant period

After renal transplantation there is a substantial alteration in cardiac morphology and functions. This prospective study was undertaken to observe changes in different cardiac parameters in early months after transplantation. PATIENTS AND METHODS: Twenty-two allograft recipients (primary disease glomerulonephritis) were evaluated in the immediate pretransplant period (0 month) and 1 and 3 months after transplantation by clinical and echocardiographic (M mode, 2D) evaluations. RESULTS: Pretransplant echocardiogram showed left ventricular hypertrophy (LVH) in 100% subjects, LV dilation in 52%, and systolic dysfunction in 18%. By the third month, significant differences in systolic blood pressure (SBP-161 +/- 16 to 133 +/- 26 mm Hg, P < .002); diastolic BP (DBP-101 +/- 9 to 86 +/- 11 mm Hg, P < .006), and hemoglobin level (Hgb-7.3 +/- 1.6 to 11.2 +/- 3.9 g/dL, P < .006) were evident. Echocardiography showed decreased left atrial diameter (LADd-41 +/- 5 to 35 +/- 3 mm, P < .001); left ventricular internal diameter (LVIDd-54 +/- 6 to 47 +/- 6 mm, P < .02); left ventricular muscle mass index (LVMI-379 +/- 114 to 248 +/- 58 g/m(2), P < .001); and left ventricular end diastolic volume index (LVEDVI-96 +/- 28 to 64 +/- 17 ml/m2, P < .002). Bivariate correlations showed positive associations of mean blood pressure (MBP) and serum creatinine with LVMI, LVEDVI, and negative association of hemoglobin with MBP, serum creatinine, LVMI, and LVEDVI. CONCLUSION: From these observations, we concluded that cardiac morphological parameters start improving in the early posttransplant period. Improvements in renal function, anemia status, and lower blood pressure showed strong associations with these changes.     

Determinants of systolic and diastolic flow in coronary bypass grafts with inotropic stimulation

Using implanted pulsed Doppler microprobes sutured on saphenous bypass grafts in ten patients we studied, 6 h after cardiac surgery, the effects of 5 and 10 micrograms.kg-1.min-1 of dobutamine on mean (Qm), systolic (Qs), and diastolic (Qd) coronary bypass graft flows, as well as on coronary systolic (integral of Qs) and diastolic (integral of Qd) blood volumes entering the myocardium per cardiac beat. Qm increased during the inotropic stimulation from 61.8 +/- 19.2 to 81.1 +/- 21.8 ml.min-1 (P less than 0.001) and resulted from an unchanged Qs and from a large increase in Qd (P less than 0.01). Qd increased more than did diastolic arterial pressure and was related to rate pressure product taken as an index of myocardial oxygen consumption (r = 0.76, P less than 0.001). Despite the dobutamine-induced increase in heart rate (P less than 0.01), integral of Qs, and integral of Qd, the systolic and diastolic inflow volumes per cardiac beat were unchanged. We conclude that increased myocardial blood supply through the saphenous vein bypass graft during inotropic stimulation by dobutamine resulted from different systolic and diastolic events. The oxygenated blood volume entering the coronary vascular bed per beat was unchanged despite tachycardia.     

Comparative analysis of the hemodynamic and respiratory parameters during laparoscopic versus open living donor nephrectomy: an experimental model

Increased intrabdominal pressure induced by pneumoperitoneum induces modifications in cardiovascular and respiratory systems. The aim of the study was to analyze the hemodynamic and respiratory modifications produced by pneumoperitoneum during living donor nephrectomy in a porcine experimental model. Twenty pigs underwent left nephrectomy, 10 by laparoscopy and 10 by an open approach. The following parameters were measured: mean arterial pressure (MAP), central venous pressure, cardiac output (CO), systemic vascular resistance (SVR), end tidal CO2 (ETCO2), minute volume (MV), respiratory airway pressure (RAP), and "compliance." Both groups were monitored for cardiac and respiratory systems at basal, 5, 30, and 60 minutes as well as postsurgery. The comparative analysis demonstrated increased CO with a higher difference at 30 minutes (4.33 +/- 0.73 vs 8.54 +/- 1.26 L/min, P < .001); decreased SVR (1118.81 +/- 302.52 vs 663.37 +/- 81.45 dinas x s x cm(-5), P < .001), and elevated MAP among the laparoscopic group (66.5 +/- 11.52 vs 80.25 +/- 2.49 mm Hg, P = .004). Analysis of respiratory modifications showed an initial increase in ETCO2 (44.3 +/- 2.6 vs 54.1 +/- 12.56 mm Hg, P < .035) and a higher MV administered (5.6 +/- 0.1 vs 7.01 +/- 0.96 L/min, P = .03) to the laparoscopy group. An increased RAP was observed at 5 minutes (22.11 +/- 2.76 vs 28.8 +/- 3.68 mm Hg, P < .001), in the laparoscopic group and lower levels of "compliance" at the same moment in that group (16 +/- 1.66 vs 14.9 +/- 4.07 cm H2O). Laparoscopic nephrectomy caused an increase in CO and MAP and decreased SVR. Likewise there were elevations of RAP, ETCO2, and MV and a slight decrease in the "compliance."     

Intraoperative Application of Intraaortic Balloon Counterpulsation Determined by Clinical Monitoring of the Endocardial Viability Ratio

Persistent unrecognized subendocardial ischemia with development of subendocardial necrosis is a major cause of patient death following cardiopulmonary bypass. The lesion is caused by a discrepancy between the oxygen needs of subendocardial muscle and the available blood supply. If sole reliance is placed upon monitoring conventional vital signs, the more subtle factors contributing to decreased blood flow may go unrecognized.Reported studies have confirmed that the adequacy of subendocardial perfusion can be predicted by calculating the supply/demand ratio, defined as the ratio of the diastolic pressure-time index (DPTI) divided by the systolic pressure-time index (TTI). An analog computer was designed and built that measures the area under the systolic and diastolic component, calculates the DPTI/TTI ratio, and digitally displays the result as the endocardial viability ratio (EVR).The EVR was used to determine the adequacy of left ventricular subendocardial blood flow in 64 consecutive patients undergoing cardiac operations. Unidirectional intraaortic balloon counterpulsation (IABC) was utilized in 14 patients with 9 long-term survivors. The difference in mean EVR between survivors and nonsurvivors at the initiation of balloon support was statistically significant. Early application of unidirectional IABC when subendocardial ischemia persists following open cardiac procedures may prevent deterioration to subendocardial necrosis with subsequent morbidity or mortality.     

Hemodynamic responses to epinephrine-containing local anesthetic injection and to emergence from general anesthesia in transsphenoidal hypophysectomy patients

Patients undergoing transsphenoidal pituitary surgery may experience hypertensive episodes during the intranasal injection of vasoconstrictor-supplemented local anesthetics or emergence from general anesthesia. The present research characterized the blood pressure responses during transsphenoidal surgery and tested the hypothesis that the underlying pituitary disease influences the incidence and magnitude of the blood pressure responses. The records of 100 patients were retrospectively reviewed. All had direct blood pressure measurements recorded using a computer-based anesthesia recording system. Mean age was 49 +/- 17 years (+/- SD) and 52% were male. Blood pressure increased by 60 +/- 37 mm Hg systolic and 23 +/- 22 mm Hg diastolic with intranasal injection and 42 +/- 24 mm Hg systolic and 23 +/- 16 mm Hg diastolic during emergence from general anesthesia. Systolic blood pressure increased by greater than 50% in 58% of patients following intranasal injection and in 33% of patients upon emergence from anesthesia. Blood pressure responses did not differ with respect to endocrinopathy type (Cushing's disease, acromegaly, or other pathology), gender, age, surgeon, history of prior transsphenoidal surgery, history of either hypertension or diabetes, or preoperative use of either beta-adrenergic or calcium channel-blocking drugs. There was poor correlation between the epinephrine dose injected (range 30-220 microg) and systolic blood pressure response (r = 0.24; r2 = 0.06; P = 0.031). Blood pressure increases were not associated with cardiac arrhythmias, persistent myocardial ischemia, or myocardial infarction. The authors conclude that in transsphenoidal hypophysectomy patients, large blood pressure increases are common with intranasal injection and upon awakening from general anesthesia. However, the authors were not able to find a variable that might enable the prediction of which patients are most likely to experience the most intense blood pressure elevations.     

A comparison of the Vasotrac with invasive arterial blood pressure monitoring in children after pediatric cardiac surgery

The Vasotrac is a device that provides near-continuous and noninvasive arterial blood pressure monitoring and may be an alternative to direct intraarterial measurement. It has been evaluated in adult patients, but minimal information is available for pediatric patients. We evaluated agreement between measurements of arterial blood pressure and heart rate obtained from the Vasotrac versus an arterial catheter in a pediatric population. Children undergoing corrective cardiac surgery were enrolled. Simultaneous arterial blood pressure measurements were obtained postoperatively from the Vasotrac unit and an arterial catheter. Bland-Altman plots were constructed to assess agreement. Paired correlation analysis, bias, and precision calculations were performed. Sixteen patients, mean age 10.1 +/- 2.3 yr and weight 34.6 +/- 11.9 kg, were enrolled. Four-thousand-one- hundred- two paired measurements were obtained. Arterial blood pressures measured noninvasively correlated with catheter measurements with Pearson r values of 0.90, 0.80, and 0.91 for systolic, diastolic, and mean arterial blood pressures, respectively (all P < 0.001). There was excellent agreement between arterial blood pressure measurement methods. Absolute mean differences based on mixed-model regression with 95% confidence intervals were 4.0 mm Hg (3.0-5.0 mm Hg), 4.3 mm Hg (3.1-5.5 mm Hg), and 3.5 mm Hg (2.5-4.0 mm Hg) for systolic blood pressure, diastolic blood pressure, and mean blood pressure, respectively. Arterial blood pressure measurements obtained from the Vasotrac agreed well with invasive arterial monitoring in pediatric patients.     

Perioperative assessment of left ventricular function by pressure-volume loops using the conductance catheter method

Interpretation of perioperative measurements of cardiac function during cardiac surgery is complicated by changes in loading conditions induced by anesthesia, cardiopulmonary bypass (CPB), and the surgical procedure itself. Quantification of left ventricular (LV) function by pressure-volume relations as obtained by the conductance catheter would be advantageous because load-independent indices can be determined. Accordingly, we evaluated methodological aspects of the conductance-catheter technique and documented LV function before and after CPB in eight patients undergoing coronary artery bypass grafting. LV pressure-volume loops by transesophageal echocardiography-guided transaortic application of the conductance catheter were obtained at steady-state and during preload reduction by temporary occlusion of the inferior cava. All patients remained hemodynamically stable, and no complications occurred. Complete data were acquired within 15 min before and after CPB. Cardiac output (5.2 +/- 1.3 L/min to 6.0 +/- 1.4 L/min) and LV ejection fraction (46% +/- 17% to 48% +/- 19%) did not change, but end-diastolic pressure increased significantly after CPB (8 +/- 2 mm Hg to 16 +/- 7 mm Hg; P < 0.05). Load-independent systolic indices remained constant (end-systolic elastance: 1.31 +/- 1.20 mm Hg/mL to 1.13 +/- 0.59 mm Hg/mL). Diastolic function changed significantly after CPB, as the relaxation time constant decreased from 64 +/- 6 ms to 52 +/- 5 ms (P < 0.05) and the chamber stiffness constant increased from 0.016 +/- 0.014/mL to 0.038 +/- 0.016/mL (P < 0.05). We conclude that the conductance catheter method provides detailed data on perioperative myocardial function and may be useful for evaluating the effects of new surgical and anesthetic procedures. IMPLICATIONS: Pressure-volume loops provide on-line quantification of intrinsic systolic and diastolic myocardial function in a load-independent fashion. This study shows the feasibility of perioperative pressure-volume analysis by use of the conductance-catheter method. This method provides detailed data about the immediate effects of surgery and may be used to evaluate complex cardiac procedures.     

Fractal or biologically variable delivery of cardioplegic solution prevents diastolic dysfunction after cardiopulmonary bypass.

OBJECTIVE: To determine whether myocardial protection is improved by restoring physiologic variability to the cardioplegia pressure signal during cardiopulmonary bypass, we compared cardiac function in pigs in the first hour after either conventional cold-blood cardioplegia (group CC) or computer-controlled biologically variable pulsatile cardioplegia (group BVC). METHODS: Invasive monitors and sonomicrometry crystals were placed, and cardiopulmonary bypass was initiated. The aorta was crossclamped, and cold blood cardioplegic solution was infused intermittently through the aortic root with either conventional cardioplegia (n = 8) or biologically variable pulsatile cardioplegia (n = 8; mean pressure, 75 mm Hg for 85 minutes). The crossclamp was released, cardiac function was restored, and separation from cardiopulmonary bypass was completed. With stable temperature and arterial blood gases, hemodynamics and systolic and diastolic indices were compared at 15, 30, and 60 minutes after cardiopulmonary bypass. RESULTS: Diastolic stiffness doubled from 0.027 +/- 0.016 mm Hg/mm (mean +/- SD) at baseline to 0.055 +/- 0.036 mm Hg/mm (P =.003) at 1 hour after bypass in group CC, associated with increased left ventricular end-diastolic pressure from 9 +/- 2 to 11 +/- 2 mm Hg (P =.001), mean pulmonary artery pressure from 14 +/- 2 to 20 +/- 3 mm Hg (P =.003), and serum lactate levels from 2.0 +/- 0.5 to 5.6 +/- 2.3 mmol/L (P =.008). Systolic function was not affected. In group BVC diastolic stiffness, left ventricular end-diastolic pressure, and pulmonary artery pressure values were not different from control values at any time after bypass, and serum lactate levels were significantly less than with conventional cold blood cardioplegia. Peak pressure variability with biologically variable pulsatile cardioplegia fit a power-law equation (exponent = -3.0; R(2) = 0.97), indicating fractal behavior. CONCLUSION: Diastolic cardiac function is better preserved after cardiopulmonary bypass with biologically variable pulsatile cardioplegia and fractal perfusion. This may be attributed to enhanced microcirculatory perfusion with improved myocardial protection. A model supporting these results is presented.     

Inhibition of sympathetic neural outflow during thiopental anesthesia in humans

The effects of sodium thiopental on postganglionic muscle sympathetic nerve activity (MSNA) and the reflex augmentation in MSNA produced by hypotension were examined in seven ASA physical status I and II patients, 34-65 yr old. Direct recordings of MSNA were obtained from a 5-micron-tipped, epoxy-coated needle percutaneously placed into the common peroneal nerve. Induction of anesthesia with sodium thiopental (4 mg/kg) significantly decreased R-R interval duration an average of 157 +/- 44 ms (mean +/- SEM) decreased systolic pressure (radial artery) an average of 11 +/- 4 mm Hg, and reduced tonic MSNA from 38 +/- 11 to 18 +/- 5 bursts/100 cardiac cycles (P less than 0.01). Baroreceptor reflex regulation of cardiac intervals and MSNA were determined by sequential boluses of nipride (100 micrograms) and phenylephrine (150 micrograms). Awake baroreceptor slopes relating R-R interval to systolic pressure were 9.5 +/- 2.9 ms/mm Hg and decreased 61% to 2.4 +/- 0.5 ms/mm Hg (P less than 0.01) during sodium thiopental infusions (0.25 mg.kg-1.min-1). Moreover baroreceptor slopes relating MSNA to diastolic pressure in awake patients were -4.0 +/- 0.9 bursts/mm Hg and were reduced by 95% to -0.3 +/- 0.18 bursts/mm Hg (P less than 0.01). Despite the fact that hypotension did not elicit increases in MSNA in anesthetized patients, laryngoscopy and tracheal intubation produced profound augmentations in MSNA. Thus, sodium thiopental reduces tonic levels of MSNA and markedly attenuates baroreceptor reflex control mechanisms. However, profound augmentations in sympathetic activity occurred in response to laryngoscopy and tracheal intubation during thiopental anesthesia.     

Pericardiovascular approach to cardiac assist: acute feasibility study

We tested the hypothesis that external synchronized compression of the cardiovascular system can achieve effective hemodynamic assistance while circumventing problems associated with the blood-polymer interface in traditional cardiac assist devices. Ten dogs were studied to develop and test prototype devices and evaluate their hemodynamic effectiveness. Copulsation assistance was studied in animals with fibrillating hearts using Anstadt pericardiac cups. Mean systolic arterial pressure of 81.2 mm Hg and cardiac output of 2.9 L/min were achieved. Counterpulsation assistance was studied by inflating during diastole a balloon placed between the thoracic aorta and periaortic sheath and deflating the balloon during systole. In 4 dogs, 25 +/- 8.6% (SEM) of diastolic augmentation and 8.3 +/- 1.2% of systolic unloading were achieved. These preliminary results indicate the feasibility of a pericardiovascular approach to cardiac assistance. Further device development and the integration of copulsation and counterpulsation may improve cardiac output, reduce cardiac afterload, augment coronary perfusion, and ultimately benefit patients with severe heart failure.     

Maximizing hemodynamic effectiveness of biventricular assistance by direct cardiac compression studied in ex vivo and in vivo canine models of acute heart failure

OBJECTIVE: Direct cardiac compression improves effective ventricular contractility. However, associated reductions in filling volumes and increases in arterial pressure occurring at the onset of direct cardiac compression limit the degree to which cardiac output is augmented. We tested the hypothesis that active preload and afterload control maximizes the hemodynamic effectiveness of direct cardiac compression.Methods and results: Studies in isolated canine hearts loaded with a computer-controlled volume servo system that mimicked heart failure were used to clearly define the hemodynamic effects of direct cardiac compression. Immediately on initiation of direct cardiac compression, ventricular end-diastolic pressure and volume decreased substantially, arterial pressure increased, but stroke volume did not change significantly. When end-diastolic pressure was restored to about 20 mm Hg, stroke volume doubled; decreasing afterload resistance further increased stroke volume by about 30%. Such load adjustments were then tested in vivo in a canine model of acute heart failure induced by coronary artery microembolizations titrated to decrease cardiac output to 33% +/- 9% of control as end-diastolic pressure rose to 20.6 +/- 2.2 mm Hg. Direct cardiac compression decreased end-diastolic pressure to 11.4 +/- 2.6 mm Hg while increasing cardiac output from 0.8 +/- 0.2 to 1. 4 +/- 0.5 L/min (to only approximately 55% of normal). Restoring end-diastolic pressure to 19.6 +/- 2.2 mm Hg by infusions of saline solution increased cardiac output to 1.9 +/- 0.5 L/min. Afterload reduction (nitroprusside), while maintaining end-diastolic pressure at 19.8 +/- 1.3 mm Hg, increased cardiac output to its baseline, 2.8 +/- 1.1 L/min. CONCLUSIONS: Direct cardiac compression significantly improves ventricular pumping capacity and can restore cardiac output to about 60% of normal in the setting of acute heart failure. When combined with active preload and afterload manipulations, direct cardiac compression can restore cardiac output to normal.     

Reversibility of pulmonary artery hypertension in aortic stenosis after aortic valve replacement

Fifty-two surgical patients with isolated aortic valve stenosis were studied preoperatively and postoperatively to determine the incidence of pulmonary hypertension and its response to surgical intervention. Pulmonary artery systolic hypertension was classified as absent (group 1, less than 30 mm Hg), mild (group 2, 30 to 39 mm Hg), moderate (group 3, 40 to 59 mm Hg), and severe (group 4, greater than 60 mm Hg). Thirty-seven of our patients (71%) had preoperative pulmonary hypertension. There was a positive correlation between left ventricular end-diastolic pressure and both systolic and diastolic pulmonary artery pressures preoperatively (p less than 0.001). After operation we found a decrease in mean systolic pulmonary pressure in group 4, from 85.8 +/- 23 mm Hg to 41.2 +/- 10.4 mm Hg (a 52% decrease, p less than 0.001), and in group 3, from 48.9 +/- 5.9 mm Hg to 32.1 +/- 7.1 mm Hg (a 34% decrease, p less than 0.001). A significant decrease in the mean diastolic pressure was found only in group 4, in which the pressure decreased from 33.7 +/- 8.7 mm Hg to 26.0 +/- 7.6 mm Hg (p less than 0.05). The operative mortality was 1.9%. Our data indicate that pulmonary artery hypertension in aortic stenosis is common, is related to end-diastolic pressure, and can be expected to improve in the early postoperative period.