Changes in intracranial pulse pressure amplitudes after shunt implantation and adjustment of shunt valve opening pressure in normal pressure hydrocephalus

Summary Background  We have previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (NPH) patients responding to shunt surgery. Whether or not shunt implantation or adjustment of the shunt valve opening pressure modifies the intracranial pulse pressure amplitudes in NPH patients remains to be established. This report summarises our observations. Patients and methods  Thirteen patients with NPH (idiopathic in nine and secondary in four) are presented in whom continuous intracranial pressure (ICP) monitoring was done before and after shunt implantation. In two, ICP monitoring was also done during adjustment of shunt valve opening pressure. The mean ICP and mean ICP wave amplitude (i.e. pulse pressure amplitudes) were determined in 6-s time windows. Results  After shunt implantation there was a fall in both mean ICP and mean ICP wave amplitude; the reduction in the two ICP parameters correlated significantly. However, mean ICP in the supine position was normal (i.e. <15 mmHg) in 12 of 13 patients before shunt placement, and remained normal after shunting. According to our criteria, the mean ICP wave amplitudes were elevated before shunting in 12 of 13 patients and became “normalised” the day after shunting in nine patients. The reduction in mean ICP wave amplitude after shunt was highly significant at the group level. Moreover, adjustment of shunt valve opening pressure modified the levels of mean ICP wave amplitudes. Conclusions  The present observations in 13 NPH patients indicate that shunt implantation reduces mean ICP wave amplitudes. Moreover, the level of reduction can be tailored by adjustment of the shunt valve opening pressure.     

Long-term studies of hemoglobin-oxygen affinity in hypoxemic dogs with a right-to-left cardiac shunt

Long-standing hypoxemia was surgically created in dogs by inserting an aortic homograft between the inferior vena cava and right atrium. Ligation of the caval—atrial junction resulted in a right-to-left cardiac shunt. Arterial p O₂ fell immediately and P₅₀ increased within 20 min. The 2,3-diphosphoglycerate concentration rose in 4 hr following surgery, while hemoglobin concentration increased within 7 days. Alterations in hemoglobin—oxygen affinity can occur rapidly and may be beneficial compensatory responses to acute and chronic hypoxemia caused by a right-to-left cardiac shunt.     

Alterations in cardiac lymph dynamics in acute myocardial ischemia in dogs

Lymph-flow rate and lymph composition were measured in the first 4 hr of acute myocardial ischemia in anesthetized dogs. Ligation of the left anterior descending branch of the left coronary artery resulted in significant reductions in arterial blood pressure and heart rate as well as in an increase in S-T segment voltage of the electrocardiogram within 1 hr of coronary artery ligation. Two hours after the induction of myocardial ischemia, significant increases occurred in creatine phosphokinase activity present in cardiac lymph. Three hours after the onset of ischemia, lymph-flow rate increased. Both increases continued for the remainder of the 4-hr observation period. At the end of the 4-hr period, there were significant decreases in the bound activity of the lysosomal protease, cathepsin D, indicative of lysosomal disruption. Moreover, there was a significantly elevated lymph/plasma ratio of the globulins, indicative of increased coronary capillary permeability. None of these changes occurred in sham-operated dogs. These results suggest that lysosomal disruption occurs early in myocardial ischemia. These and other factors may lead to an increased capillary permeability which promotes the uptake of protein in the cardiac extracellular fluid. These proteins including intramyocardial cell enzymes are carried back to the systemic blood, in large part, by cardiac lymphatic vessels. Measurements of cardiac lymph thus provide considerable useful information about the pathophysiologic processes occurring in myocardial ischemia.     

Changes in ventricular hemodynamics caused by a systemic-pulmonary shunt

Systemic pulmonary shunts are both surgically created (Blalock-Taussig anastomosis) and obliterated (patent ductus arteriosus), but the effects of such a vascular communication on left ventricular hemodynamics have not been examined quantitatively. To study these effects, innominate arterial allografts were sutured between the descending thoracic aorta and the left main pulmonary artery in nine mongrel dogs. Left ventricular output (LVO) and shunt flow (SF) were monitored with electromagnetic flow probes while simultaneous phasic and mean pressures were recorded from the right atrium, aorta (AOP), and pulmonary artery. Data points (192) were analyzed while SF was varied between 0.02 and 5.5 liters/min using a variable-sized constricting band. Regression analysis showed increases (P less than 0.01) in LVO, stroke work (SW), and stroke volume (SV) in all dogs which were linearly related to SF (r = 0.64-0.99). Increasing SF was also associated with decreases (P less than 0.01, r = 0.61-0.99) in resistance (RES) facing the left ventricle and in diastolic (D) AOP. To compensate for differences in allograft size and to quantify the effects of a patent shunt, the regression equations were used to compare the percentage change in all parameters at SF = 0 and SF = 1.5 liters/min. Increases occurred in SV (46 +/- 21%), SW (32 +/- 14%), and LVO (48 +/- 21%), and decreases were present in DAOP (15 +/- 12%) and RES (32 +/- 13%). These data show that despite the decreases in pressure or the decreases in resistance facing the left ventricle in the presence of a systemic pulmonary shunt, a substantial increase in stroke work occurs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vascular dynamics of an experimental cerebral arteriovenous shunt in the primate.

An arteriovenous fistula which shunted arterial blood from the circle of Willis to the internal jugular vein was created in ten monkeys. Continued patency of the shunt was confirmed angiographically. Cerebral blood flow measurements were then obtained with the shunt both open and occluded. Flow was also determined in response to elevations of systemic arterial pressure and raised arterial carbon dioxide tensions (PaCO2), again with the shunt both patent and occluded. In addition, flow through the shunt alone was measured in response to elevations of systemic arterial pressure and PaCO2. The results suggest that flow through our arteriovenous shunt is minimally autoregulated to changes in systemic arterial pressure and is only slightly responsive to changes in PaCO2.     

Does the shunt opening pressure influence the effect of shunt surgery in normal pressure hydrocephalus?

Summary Thirteen patients with normal pressure hydrocephalus were operated upon with an externally manoeuvrable shunt system (Sophy SU8) in order to investigate its influence on clinical outcome, intracranial pressure and cranial CT parameters. The opening pressure was set at high at surgery and lowered stepwise at intervals of three months to medium and low. The clinical condition, intracranial pressure and cranial CT parameters were examined at the end of the 3 months interval on each pressure level.The patients improved within the first 3 months inspite of an unchanged mean intracranial pressure and remained in a stable clinical condition during the rest of the study period. The intracranial pressure was significantly reduced at 9 months. The ventricular index, Evans index, temporal horn and third ventricle width were reduced 3 months post-operatively and did not change significantly during the rest of the study. The pre-operative third ventricle width was correlated to high psychometric test results after shunt surgery. Reduction in ventricular index, Evans index and third ventricle width after surgery correlated to improvement in psychometric scoring.The clinical improvement after shunt surgery for normal pressure hydrocephalus is seen within 3 months and is independent of the adjusted valve pressure.     

Effects of sevoflurane and isoflurane on cardiac and coronary dynamics in chronically instrumented dogs

To assess the hemodynamic properties of the new inhalational anesthetic sevoflurane, 22 dogs were chronically instrumented for measurement of heart rate, aortic, left ventricular and left atrial pressures, cardiac output, and coronary blood flow. Dogs were randomly assigned to two groups, receiving either 1.2 and 2 MAC of sevoflurane (n = 11) or isoflurane (n = 11). At 1.2 and 2 MAC, sevoflurane produced an increase in heart rate (+60 +/- 12% and +54 +/- 9%, respectively), dose-dependent aortic hypotension (-22 +/- 4% and -38 +/- 4%, respectively), systemic vasodilation (-22 +/- 5% and -19 +/- 5%, respectively), dose-dependent decrease in stroke volume (-31 +/- 6% and -48 +/- 4%, respectively), and left ventricular dP/dt (-40 +/- 4% and -61 +/- 10%, respectively). Cardiac output decreased only at 2 MAC (-17 +/- 6%). Finally, coronary blood flow increased at 1.2 MAC of sevoflurane (+29 +/- 8%). Except for heart rate, sevoflurane and isoflurane produced similar effects. At 1.2 MAC, sevoflurane produced a greater increase in heart rate than isoflurane (+60 +/- 12% vs. +33 +/- 9%). The authors conclude that, except for heart rate, the effects of sevoflurane on cardiac function and coronary blood flow are almost identical to those induced by isoflurane in the chronically instrumented dog.     

Changes of oxygen transport variables and serum lactate during open-chest cardiac massage in dogs

The aim of this study was to investigate the influence of critically low cardiac output (CO) upon oxygen transport. We especially focused on the changes of mixed venous oxygen saturation (S−vO₂) in the presence of oxygen consumption ( ) debts. Additionally, we examined the correlation between the cumulative oxygen deficit (Def ) and serum lactate. Def was calculated as the integrated area under the tissue ) deficit (baseline -acutal ) and time curve. To produce severe low CO, we performed openchest cardiopulmonary resuscitation (CPR) in 11 anesthetized dogs for 1 h. We made the measurements before (baseline values) and during the CPR at 10-min intervals. Supplydependent was observed when CO decreased below 40 ml·min⁻¹·kg⁻¹. The mean value of S−vO₂ in the range of supply-dependent was 13±2% and did not change significantly during 1 h of CPR. The changes of lactate from baseline values were linearly correlated with Def (r=0.62,P<0.01), but absolute values of serum lactate were not.