Excessive increase in circulating catecholamines during cross-clamping of the descending thoracic aorta in pigs

The purpose of this study was to determine the plasma catecholamine response to cross-clamping of the descending thoracic aorta in pigs and to relate the plasma catecholamine response to cardiac output during cross-clamping. This prospective, controlled animal study was done at the University Hospital of Trondheim, Norway. Eight pigs (19–25 kg) underwent cross-clamping of the descending thoracic aorta for 30 minutes. The time course of plasma adrenaline, plasma noradrenaline, and ascending aortic blood flow were measured. It was found that the increase of plasma catecholamines during cross-clamping of the descending thoracic aorta in pigs was parallel to the increase of aortic blood flow during cross-clamping. Plasma adrenaline increased from 0.22 nmol/L to a maximum of 11.75 nmol/L and plasma noradrenaline increased from 0.17 nmol/L to a maximum of 46.92 nmol/L after 10 minutes of cross-clamping (p=0.01). Ascending aortic blood flow increased from 2.6 L/minute to a maximum of 4.7 L/minute after 10 minutes of cross-clamping (p=0.01). Our findings support the theory that increased plasma catecholamines might be a mechanism of increased cardiac output during cross-clamping of the descending thoracic aorta. The increase of plasma catecholamines during cross-clamping is most likely due to distal hypotension with increased sympathetic activity.The work was performed at the Department of Surgery, University Hospital of Trondheim, Norway.     

Clinical application of intrathecal lidocaine administration in surgery of the descending thoracic aorta

We studied the protective effects of intrathecally administered lidocaine against ischemic spinal cord injury during surgery. Seven patients (mean age 63.7 years, malefemale=61) with descending thoracic aortic aneurysms underwent reconstructive surgery. Following intrathecal lidocaine administration (10 ml), the operation was performed under femorofemoral bypass with an oxygenator. The aorta was cross-clamped at the distal end of the descending thoracic aorta and the proximal end of the lesions. The cross-clamping time was 47.1±23.3 minutes (mean ± SD). The operative procedure was total replacement of the descending thoracic aorta in five cases and patch closure in two. There were no operative deaths but paraparesis developed in two cases of total replacement. Neurological deficit was transient and disappeared in one case. In the other case, with 88 minutes of normothermic aortic cross-clamping, paraparesis gradually improved but was persistent after 7 months of follow-up. Graft anastomosis at the distal aortic arch was time consuming in this case and presumably caused prolonged spinal cord ischemia. Intrathecal administration of lidocaine was likely to reduce ischemic spinal cord injury and increase tolerance of the spinal cord to ischemia caused by prolonged aortic cross-clamping. This method was considered to provide a useful assistance to expand the safety limit of spinal cord ischemia in surgical reconstruction of the descending thoracic aorta requiring aortic occlusion. Tissue protective effects of intrathecal lidocaine administration may be further augmented by combining with deep hypothermia.     

Segmental volume distensibility of the canine thoracic aorta in vivo

Segments of the canine ascending aorta, upper descending thoracic aorta, and middle descending thoracic aorta were instrumented with ultrasonic dimension gauges and a cathetertip manometer simultaneously to measure changes in segment diameter, length, and intravascular pressure. Volume distensibility (EV) was calculated as the sum of circumferential extensibility (EC), longitudinal extensibility (EL), and high order extensibilities (EK) for each segment. The EC and EL were linear expressions that represented percentage volume changes per mmHg pulse pressure due to circumferential and longitudinal dimensional changes. The high order extensibilities (second and third order) accounted for the percentage volume changes per mmHg pulse pressure due to the interactions between circumferential and longitudinal dimensional changes. Mean(SEM) EV values from six dogs were 1.62(0.31), 0.84(0.08), and 0.62(0.08)% delta V/mmHg delta P for the ascending aorta, upper descending thoracic aorta, and middle descending thoracic aorta segments respectively. The EV, EL, and EK of the ascending aorta segment were significantly greater than those of the upper descending thoracic aorta and middle descending thoracic aorta segments, whereas EC was significantly less in the ascending aorta than in both the upper descending thoracic aorta and middle descending thoracic aorta segments. It is concluded that there are regional differences in aortic distensibility and its components in vivo. Longitudinal wall motion is an important determinant of these aortic mechanical properties.     

Pressure-volume recordings of human subcutaneous tissue: A study in patients with edema following arterial reconstruction for lower limb atherosclerosis

The interstitial fluid pressure-volume relationship was studied in patients who developed leg edema following arterial reconstruction for femoropopliteal atherosclerosis. The increase in subcutaneous tissue volume of the operated limbs was estimated by surface measurements and computed tomography. The subcutaneous interstitial fluid pressure (P_if) of the legs was recorded by the wick-in-needle technique and averaged ?0.7 mm Hg in healthy controls. Postoperatively, P_if was ?0.8 mm Hg in patients who did not develop local edema compared to +2.2 mm Hg in patients with postoperative edema. _if increased with increasing subcutaneous tissue volume in patients with moderate edema (0–100% subcutaneous tissue volume increase), but insignificant further increase in P_if was observed with additional edema (100 to 600%). A maximal P_if of +5 mm Hg was observed in edematous legs indicating a high compliance of the subcutaneous tissue in patients with postreconstructive leg edema.     

Endarterectomy and external prosthetic grafting of the ascending and transverse aorta under hypothermic circulatory arrest

A 78-year-old woman presented with acute pulmonary edema, a blood pressure of 250/160 mmHg, and a 4/6 diastolic murmur of probable aortic origin. Aortography revealed 4+ aortic regurgitation, left ventricular dysfunction, a right coronary artery with good distal run-off but complete proximal occlusion, a fusiform aneurysm of the ascending and transverse aorta (with a transverse dissection in the left anterolateral wall of the upper ascending aorta, but no evidence of intramural lumen), and milder, isolated dilatation of the descending thoracic aorta. Upon operation, on 8 September 1987, I discovered an incompetent aortic valve, advanced atherosclerosis in the ascending and transverse aorta, and a loose intimal flap--but no false lumen--in the upper ascending aorta. After valve replacement and construction of a vein graft to the distal right coronary artery, I decided against replacement of the diseased segment of the ascending and transverse aorta and chose, instead, aortic endarterectomy reinforced by external grafting, as a simpler, quicker, and safer procedure for this patient. Safety was further enhanced by use of profound hypothermia (16 degrees C) to induce total circulatory arrest during the brief period (15 minutes) required for endarterectomy of the arch and approximation of the flap. The patient was discharged 19 days after surgery and continues well and asymptomatic to the present, 21 months after surgery; her milder dilatation of the descending thoracic aorta, which was not treated, is stable and is being monitored.     

Comparison of isollurane with sodium nitroprusside for controlling hypertension during thoracic aortic cross-clamping

The aims of this randomized study were (1) to determine if isoflurane is effective in controlling blood pressure during thoracic aortic cross-clamping, and (2) to compare its effects on hemodynamics and oxygen transport to those of sodium nitroprusside. Sodium nitroprusside (SNP group, n = 10) or isoflurane (ISO group, n = 10) was started 2 minutes before cross-clamping and was adjusted to maintain systolic arterial pressure as near as possible to preinduction values. The duration of thoracic aortic cross-clamping was 26 ± 4 minutes in the SNP group and 30 ± 4 minutes in the ISO group. Administration of isoflurane and sodium nitroprusside was stopped 2 minutes before unclamping. The same anesthetic technique using fentanyl, 6 μg/kg, flunitrazepsm, 0.02 mg/kg, pancuronium, 0.1 mg/kg, and 50% N₂O was used for all patients. At the time of clamping, either isoflurane (maximal expired concentration, 2.6% ± 0.3%) or sodium nitroprusside (cumulative dose, 11.1 ± 1.0 mg) was effective in maintaining the systolic blood pressure below 160 mm Hg, whereas the pulmonary capillary wedge pressure did not change. However, only SNP was able to bring the arterial pressure above the cross-clamp back to postinduction levels. During clamping, stroke index values were similar in both groups, but cardiac index increased only in patients receiving SNP. In both groups, at clamping and unclamping, PvO₂ was higher than postinduction values, indicating that throughout the study the oxygen needs of the perfused area were adequately met. There was no evidence of acute left ventricular decompensation because pulmonary capillary wedge pressures did not abruptly increase, nor did pulmonary edema occur. It is concluded that isoflurane added to fentanyl anesthesia is acceptable for thoracic aortic aneurysm surgery because it allows safe and effective control of hypertension during clamping without compromising hemodynamics and oxygen transport.     

Diagnosis and early surgical management of traumatic thoracic aortic disruption

OBJECTIVE: Traumatic rupture of the thoracic aorta is a major cause of death. Survival greatly depends on early diagnosis, degree of injuries to other districts and timing of repair. To address the controversial aspects of this condition, we retrospectively reviewed our experience. METHODS: Between April 1984 and December 1998, 39 patients (31 males, 79%), with a mean age of 33 +/- 7 (range, 17 to 59 years), underwent surgical repair at our institution. Final diagnosis of aortic disruption was achieved in 33 patients (85%) by aortogram, and in 6 (15%) by transesophageal echocardiography (TEE) alone. Four patients (8%) had a false negative chest X-ray on admission. Twenty-four patients (61.5%) had additional major injuries to other districts (n = 4, cranial trauma; n = 13, cranial trauma + pelvic fracture; n = 5, lesions to abdominal viscera; n = 2, lesions to abdominal viscera + pelvic fracture). Surgical techniques included simple aortic cross-clamping in 7 patients (18%), partial femoral-femoral bypass in 17 (44%), and partial left heart bypass in 15 (38%). Two patients underwent direct aortic suture (5%), whereas 37 (95%) had interposition of a vascular graft. RESULTS: Three patients (8%) died after major hemorrhaging during the early phases of our experience. Paraplegia occurred in 1 patient (2.5%) in the single aortic cross-clamping group. There was no morbidity directly attributable to the administration of heparin for cardiopulmonary bypass. CONCLUSION: Although aortography is still the gold standard to achieve diagnosis, the use of TEE as a method of detecting traumatic injury to the thoracic aorta appears feasible in critical patients, advantageously saving time. With a meticulous surgical approach and the use of an effective method for distal aortic perfusion during repair, it is possible to achieve good outcomes.     

Creation of aortic dissection model in swine

The use of mongrel dogs for experimental purposes was recently restricted and this report presents the experience of creating an aortic dissection model in swine. All the swine in group 1 were anesthetized without pentobarbital and the descending aorta was side-clamped during the creation of the aortic dissection. The false lumen of the completed dissection was patent in the long term despite not having the anchoring suture that the previous canine model required to stabilize the opening of the entry tear. All the swine anesthetized with pentobarbital (ie, group 2) died of heart failure either during cross-clamping of the descending aorta or postoperative aortography. In conclusion, creation of a thoracic aortic dissection is possible in swine, but cross-clamping of the thoracic descending aorta and pentobarbital anesthesia should be avoided.     

Regional wave travel and reflections along the human aorta: a study with six simultaneous micromanometric pressures

The human aorta and its terminal branches were investigated in normal subjects during elective cardiac catheterization to evaluate regional wave travel and arterial wave reflections. A specially designed catheter with six micromanometers equally spaced at 10 cm intervals was positioned with the tip sensor in the distal external iliac artery and the proximal sensor in the aortic arch. Simultaneous pressures were obtained and analyzed for foot-to-foot wave velocity, and Fourier analysis was used to derive apparent phase velocity. These quantities were assessed during control (n = 9), during Valsalva (n = 8) and Müller (n = 4) maneuvers, and during femoral artery occlusion by bilateral manual compression (n = 8). During control, regional cross-sectional areas, determined from aortography, and regional foot-to-foot pulse wave velocities were used to calculate the local reflection coefficient in the proximal descending aorta (gamma = 0.05), at the junction of the renal arteries (gamma = 0.43), and at the terminal aortic bifurcation (gamma = 0.13). To test the hypothesis that significant reflections originate in the aorta, at the level of the renal arteries, aortograms were used to design a latex tube model with geometric properties similar to the descending aorta. Velocities and reflection characteristics in the model and in vivo were compared. Inspection of thoracic aortic pressures under control conditions revealed a reflected wave originating from the region of the aorta at the level of the renal arterial branches while abdominal pressures exhibited reflection from a site peripheral to the terminal aortic bifurcation. In the low frequency range, apparent phase velocity was found to be higher proximal to the renal arteries as compared with at the distal sites. In addition, the minimum value occurred at a higher frequency in the lower thoracic aorta than at more distal sites. The effects of reflection on apparent wave velocity in the tube model were consistent with data obtained in vivo. The Valsalva maneuver diminished the reflection from the aortic region of the renal arteries, thus allowing the distal reflected wave to become more evident on the thoracic pressure waveforms. Bilateral femoral artery occlusion usually enhanced the distal reflection and the Müller maneuver usually resulted in small increases in reflections. In conclusion, the geometric and elastic nonuniformity of the aorta results in two major sites of arterial wave reflection that influence the aortic pressure waveforms in man.(ABSTRACT TRUNCATED AT 400 WORDS)     

The influence of aging and aortic stiffness on permanent dilation and breaking stress of the thoracic descending aorta.

OBJECTIVE: To assess the influence of aging and aortic stiffness on the extent of irreversible deformation and breaking stress of the human thoracic aorta. METHODS: From 14 human heart valve donors without aortic disease (mean age 35 years, range 8-59 years), 14 intact segments of the thoracic descending aorta were studied within 48 h after cardiac arrest. In an experimental setup, the segments were submitted to increasing hydrostatic pressure loads, both statically and dynamically, while radius and wall thickness were monitored echocardiographically. Pressure-radius curves were constructed. Radius and wall thickness were determined at a pressure of 100 mmHg. Radius at elastin resting length and collagen recruitment pressure (Pcol, mmHg) were derived from the pressure-radius relationship and stress-strain curves were constructed to yield Young's moduli of elastin and collagen. Distensibility (D, mmHg-1) was determined while loading the segment with a sinusoidal pressure wave of 120/50 mmHg at both 0.5 and 1 Hz. Subsequently increasing static pressure loads of 400, 800, 1200 and 1600 mmHg were applied. After each pressure load, the increase in aortic radius at a pressure of 100 mmHg (Rinc) was determined. The experiment continued until rupture occurred and breaking stress (sigma break, N m-2) was calculated, donor age and aortic stiffness were correlated with Rinc and sigma break of the aortic segments. RESULTS: Mean breaking stress of the 14 segments was 2.7 x 10(6) N m-2. Breaking stress was negatively correlated with age (r2 = 0.66) and positively with D (r2 = 0.44) and with Pcol (r2 = 0.18). Seven segments survived a pressure load of 800 mmHg, in these vessels, the extent of irreversible dilation was positively correlated with age (r2 = 0.42) and negatively with D (r2 = 0.40) and Pcol (r2 = 0.40). CONCLUSION: Permanent deformation and rupture of the human thoracic aorta following pressure overload are influenced by age, distensibility and collagen recruitment pressure.     

Measurement of upper esophageal sphincter pressure. Effect of acute emotional stress

Recent studies suggest that resting upper esophageal sphincter pressure is more labile than previously thought, being augmented during rapid manometric pull-through and markedly decreased during sleep and anesthesia. The effect of acute emotional stress on resting upper esophageal sphincter pressure was evaluated in 13 normal subjects with a manometric sleeve assembly. Manometric sideholes were positioned in the pharynx and cervical and thoracic esophagus while the sleeve sensor straddled the upper esophageal sphincter. Subjects were stressed intermittently by 14-min periods of a dichotic listening task. As incentive, a financial reward was offered and made commensurate with performance. Alterations of heart rate, blood pressure, and skin conductance confirmed the effectiveness of the stressor. The overall mean upper esophageal sphincter pressure during control periods was 46.5 mmHg (SEM = 4.7). During stress there was a significant mean increase (11.8 +/- 2.9 mmHg; p = 0.002) in upper esophageal sphincter pressure from control levels, and the pressure increase during the first 2-min epoch of stress was 20.8 +/- 3.9 mmHg (p = 0.0003). Emotional stress causes significant elevation of upper esophageal pressure in normal subjects. This effect is likely to influence resting sphincter pressure measurements, particularly if measurement conditions are stressful to the subject.     

Myocardial depression following declamping of the infrarenal aortic cross-clamp

Reduced cardiac output during cross-clamping of the aorta has been attributed to the increased afterload. A second mechanism involves reperfusion of the ischemic lower torso. The author studied cardiac contractility during and following one hour of infrarenal aortic cross-clamping. Methods: Ultrasonic crystals were implanted on the anterior and posterior aspects of the left ventricle in 11 anesthetized dogs to measure the external minor diameter. A pressure transducer was placed in the left ventricular, and aortic and Swan-Ganz catheters were introduced. The animals were divided into two groups: A Clamp group (n=6) sustaining one hour of infrarenal aortic cross-clamping, and a Control group (n=5) who underwent a sham operator. Hemodynamic data were collected during the one hour of cross-clamping and for the next two hours. Results: Cardiac function did not change significantly at one and two hours following removal of the clamp. Cardiac output decreased from 1.70±0.22 L/min at baseline to 1.30±0.14 and 1.19±0.10 at one and two hours, respectively, following removal of the clamp. The end-systolic pressure-volume relationship (Emax) decreased from 29.7±6.3 mm Hg/mm at baseline to 18.1±3.6, 16.5±4.6, and 17.2±3.5 at thirty minutes, one hour, and two hours, respectively, after declamping. The Control group showed no significant changes in cardiovascular parameters at any time during the experiment. Conclusion: Infrarenal aortic cross-clamping causes myocardial depression following declamping but not during clamping.     

Comparison of superoxide dismutase,thiopental, and nimodipine for maintenance of somatosensory evoked responses during aortic cross-clamping and declamping in dogs

Paraplegia is a potential complication of aortic cross-clamping. The occurrence of this devastating sequels has caused increased interest in the use of somatosensory evoked responses ISER) to monitor spinal cord ischemia during aortic cross-clamping. This study was designed to examine changes in SERs during clamping and declamping of the canine aorta after injection of superoxide dismutase (SOD), thiopental (T), and nimodipine (N). In the control group, cross-clamping the aorta produced an increase in latency and a decrease in amplitude of the SER starting at two minutes. Isoelectric SERs were obtained after 16 minutes of aortic cross-clamping, but recovered with cross-clamp removal. When the aorta was clamped for more than 16 minutes in the control group, the isoelectric SERs obtained were irreversible. After the injection of SOD and T, SER latencies and amplitudes changed to a smaller degree with aortic cross-clamping and did not become isoelectric even after 20 minutes of clamping. During aortic cross-clamp removal in the control group, SERs initially improved and then showed signs of reperfusion ischemia, which disappeared after eight minutes. There were no significant SER changes due to reperfusion when SOD or T or the combination was given prior to aortic cross-clamping. There was no difference in SER changes from the control group during aortic cross-clamping and after release of cross-clamping when N was given. Nimodipine did not alter SER changes from aortic cross-clamping alone. In summary, SOD and T, alone or in combination, protect the spinal cord against ischemia during aortic cross-clamping and declamping.     

Myocardial ischemia due to infrarenal aortic cross-clamping during aortic surgery in patients with severe coronary artery disease.

Hemodynamic measurements were performed and ECG recorded before and shortly after infrarenal aortic cross-clamping during operation for abdominal aortic aneurysm in five patients without evidence of heart disease (group I) and in ten patients with severe coronary artery disease (group II). All patients sustained an increase in systemic arterial pressure. Group I demonstrated a decrease in pulmonary artery, pulmonary capillary wedge (PCW), and central venous pressures when the aorta was clamped, whereas group II demonstrated an increase. The difference in response of the groups is significant (P less than 0.05). All three patients who responded to cross-clamping with increases of 7 mm Hg or greater in PCW demonstrated myocardial ischemia during cross-clamping. None of the values measured prior to cross-clamping predicted with certainty the response to cross-clamping. Sodium nitroprusside reversed the elevation of left ventricular filling pressure in all three patients, and in two patients, relieved evidence of myocardial ischemia concurrently. In the third patient, ventricular irritability was abolished by lidocaine and did not recur. We conclude that infrarenal aortic cross-clamping may cause myocardial ischemia in patients with severe coronary artery disease. This ischemia may be predicted by a rise in PCW at the time of cross-clamping, and vasodilator therapy is indicated in such patients.     

Evaluation of aortic coarctation after surgical repair: role of magnetic resonance imaging and Doppler ultrasound.

OBJECTIVE--To compare the usefulness of magnetic resonance imaging (MRI) and Doppler ultrasound with that of cross sectional echocardiography and oscillometric blood pressure measurement for the evaluation of aortic coarctation after surgical repair. DESIGN--Prospective study. Aortic diameters measured by cross sectional echocardiography, MRI, and angiography (selected cases) and functional data determined by physical examination, oscillometric blood pressure measurement, and continuous wave Doppler. SETTING--Tertiary referral centre. PATIENTS--40 patients aged 2-28 years (mean 10.6 years) who had had surgical correction of aortic coarctation (mean follow up 5.7 years). RESULTS--In all patients MRI gave diameter measurements of the aortic arch and the thoracic aorta whereas in half of them cross sectional echocardiographic measurement of the isthmic region failed. The correlation coefficient for aortic diameters measured by MRI and angiography was 0.97 and that between MRI and echocardiography was 0.89. Peak velocities in the descending aorta correlated better with residual narrowing of the aortic isthmus or distal aortic arch or both than systolic blood pressure gradients between the upper and lower limbs. A peak velocity of < 2 m/s in the descending aorta during systole excluded important restenosis. Prolongation of anterograde blood flow during diastole always indicated a morphological abnormality--either important restenosis or aneurysmal dilatation. CONCLUSIONS--MRI was better than cross sectional echocardiography for imaging the aortic arch after coarctation repair and measuring its diameter. Peak velocity in the descending aorta correlated better with residual stenosis than did the systolic blood pressure gradient between the upper and lower limbs and this index could be used to indicate a need for MRI.     

Failure of selective shunting to intercostal arteries to prevent spinal cord ischemia during experimental thoracoabdominal aortic occlusion.

Paraplegia from spinal cord ischemia during thoracoabdominal aneurysm repair remains an unpredictable and unpreventable complication. In an effort to prevent spinal cord ischemia during aortic cross-clamping, preoperative angiographic localization of the blood supply to the spinal cord was performed in dogs. Sixteen animals underwent 60 minutes of thoracoabdominal aortic cross-clamping either without (control, n = 8) or with (shunted, n = 8) a selective shunt. Shunting was performed from the aortic arch to that isolated aortic segment angiographically shown to supply the thoracolumbar anterior spinal artery. Spinal cord blood flow was measured with microspheres just prior to cross-clamping, at 5 and 60 minutes after cross-clamping and at 5 minutes after restoration of aortic blood flow. Functional neurologic outcome was evaluated in animals at 24 hours postoperatively. Shunting did not decrease spinal cord injury. Seven of the 8 animals in the control group and 7 of the 8 in the shunted group developed paraplegia or paraparesis. Thoracic, but not lumbar spinal cord blood flow, was significantly increased in shunted animals. Spinal cord blood supply in dogs may be more segmental than previously believed. Technical problems in angiographic localization, spinal artery spasm, loss of spinal cord autoregulation or poor collateral circulation from the distal thoracic to the lumbar cord may also account for these results. Although shunting to aortic segments supplying the anterior spinal artery during thoracoabdominal aortic clamping may be attractive in humans, no benefit could be shown in this experimental model.     

Measuring interstitial fluid pressure with fiberoptic pressure transducers

In this report we describe a practical procedure for measuring interstitial fluid pressure (IFP) using fiberoptic pressure transducers based on optical interferometry. Eight mice were used for subcutaneous IFP measurements and four mice for intramuscular IFP measurements with a FOBPS-18 fiberoptic pressure transducer. We used four mice for subcutaneous IFP measurements with a SAMBA-420 MR fiberoptic pressure transducer. One measurement was made for each mouse simultaneously by using a fiberoptic system and an established approach, either transducer-tipped catheter or wick-in-needle technique. The mean IFP values obtained in subcutaneous tissues were -3.00 mm Hg (SEM-/+0.462, n=8), -3.25 mm Hg (SEM-/+0.478, n=4), -3.34 mm Hg (SEM-/+0.312, n=6), and -2.85 (SEM-/+0.57, n=6) for the FOBPS fiberoptic transducer, the SAMBA fiberoptic transducer, the transducer-tipped catheter, and the wick-in-needle technique, respectively. There was no difference between these techniques to measure IFP (Friedman test, p=0.7997). The subcutaneous IFP measurements showed strong linear correlation between fiberoptic transducer and transducer-tipped catheter (R(2)=0.9950) and fiberoptic transducer and wick-in-needle technique (R(2)=0.9966). Fiberoptic pressure transducers measure the interstitial fluid pressure accurately, comparable to conventional techniques. The simplified IFP measurement procedures described in this report will allow investigators to easily measure IFP, and elucidate the unit pressure change per unit volume change (dP/dV) in normal or cancer tissues in the presence of strong electromagnetic fields encountered in MRI.     

Spinal fluid dynamics during thoracic- and thoracoabdominal aortic surgery.

AIM: The intention was to investigate cerebrospinal fluid pressure (CSFP) and volume of cerebrospinal fluid (CSF) drained during and after thoracic- and thoracoabdominal aneurysm repair. The findings were related to the occurrence of postoperative neurologic deficits. METHODS: Twenty-nine patients (12 with thoracic and 17 with thoracoabdominal aortic aneurysm) were operated without shunting or extracorporeal circulation. For monitoring of CSFP an intrathecal catheter was placed in all patients. The volume of CSF withdrawn intraoperatively, on the day of operation as well as on the 1st and 2nd postoperative day was recorded. RESULTS: Twenty-six patients had no postoperative neurologic sequelae. One patient had postoperative paraplegia while 2 had paraparesis. The three patients with neurologic sequelae had higher CSFP intraoperatively than those without neurologic symptoms (P=0.04). Median CSFP during aortic cross-clamping was 19 mmHg and 10 mmHg and the median volumes of CSF drained on the day of operation 210 and 85 mL in the two groups, respectively. There was a significant positive correlation between CSFP and central venous pressure. CONCLUSIONS: A higher intraoperative CSFP was observed in patients with neurologic sequelae following thoracic- and thoracoabdominal aneurysm repair. Further, there was a tendency of higher volumes of CSF drained in this group of patients. Although, the series is too small to allow firm conclusions, it supports the view that CSFP monitoring and drainage is beneficial during thoracic- and thoracoabdominal aneurysm repair.     

Benefits from angiotensin-converting enzyme inhibitor 'beyond blood pressure lowering': beyond blood pressure or beyond the brachial artery?

OBJECTIVE: The substantial benefits of ramipril over conventional therapy in high-risk patients are not always associated with clinically significant differences in brachial arterial pressure, and largely remain unexplained. We undertook this acute study to establish the magnitude of and reason for different acute effects of ramipril and atenolol on arterial pressure. METHODS: We enrolled 30 patients, who took 10 mg ramipril, 100 mg atenolol, and placebo at intervals of > or = 7 days, in a randomized, double-blind, placebo-controlled trial. After baseline, measurements were taken at 30-60 min intervals for 5 h, and comprised cuff brachial pressure, radial artery tonometry with generation of central aortic pressure, and pulse wave velocity for aorta, upper limb and lower limb arteries. RESULTS: Both ramipril and atenolol reduced arterial pressure, and the diastolic pressure fall was similar in the aorta and brachial artery, but the systolic pressure fall for ramipril was greater than for atenolol (by 5.2 mmHg, P < 0.0001) in the aorta compared with the brachial artery. The aortic systolic pressure difference with ramipril in comparison with atenolol was accompanied by an absolute difference of 10.7% (P < 0.0001) in the augmentation index, denoting a reduction in peripheral wave reflection by ramipril. The aortic pulse wave velocity fell to a similar degree with ramipril in comparison with atenolol, but fell to a greater degree (1.35 and 0.44 m/s, respectively, P < 0.0001 for both) in muscular arteries of the lower and upper limbs. CONCLUSION: A greater (average, 5.2 mmHg) decrease in aortic systolic pressure caused by ramipril may explain the greater benefit of ramipril over atenolol. The difference is attributable to decreased stiffness of peripheral arteries and a reduction in wave reflection.     

Effects of chronic hypertension on vasa vasorum in the thoracic aorta

The outer layers of the thoracic aorta receive substantial blood flow through vasa vasorum within the aortic wall. Flow delivered via these channels is functionally important because medial necrosis occurs when vasa vasorum are ligated. If flow through vasa vasorum is limited in chronic hypertension, this could contribute to medial necrosis and, perhaps, aortic dissection. In these experiments, flow and conductance in vasa vasorum were assessed in twelve awake dogs with renal hypertension (arterial pressure = 127 +/- 4 mmHg [mean +/- SE]) and nine normotensive controls (arterial pressure = 100 +/- 3 mmHg [P less than 0.001]). At rest, blood flow delivered via vasa vasorum to the thoracic aorta was similar in hypertensive and normotensive dogs (5.2 +/- 0.9 and 4.8 +/- 0.4 ml . min-1 X 100 g-1 respectively). Thus, in hypertensive dogs, conductance of the vasa vasorum decreased to maintain flow constant. During maximal dilatation induced by iv adenosine (4.7 mumol . kg-1 per min) flow delivered via vasa vasorum increased by 100% in both hypertensive and normotensive dogs. Calculations of maximum conductance indicate that vasodilator capacity was decreased by 67% in vasa vasorum of hypertensive dogs. These data suggest that vasodilator capacity of vasa vasorum in the thoracic aorta is limited in chronic hypertension. This abnormality could contribute to the pathogenesis of medial necrosis and aortic dissection in hypertensive patients.