Noncoronary collateral myocardial blood flow.

This study shows that noncoronary collateral flow occurs in normal hearts after chronic coronary occlusion and with left ventricular hypertrophy in variable amounts (0.2 to 16 ml/100 gm/min). Luminal--left ventricular flow is greatest when the heart is arrested by aortic cross-clamping, falls significantly when perfusion pressure is lowered to 50 mm Hg, and increases slightly when blood viscosity is reduced (hemodilution). Our findings indicate that the heart which is arrested by aortic cross-clamping may not be anoxic.     

Hyperosmotic mannitol and collateral blood flow to ischemic myocardium

Elevation of extracellular osmolality reduces the extent of myocardial and endothelial cell swelling that accompanies acute ischemia, and the reduction of cell swelling is associated with an increase in collateral blood flow to the ischemic area. However, little is known about the effects of hyperosmolality on the vascular resistance of the collateral coronary vasculature. We compared the effects of hyperosmolar mannitol with those of nitroglycerin and dipyridamole on the vascular resistance of large collateral coronary vessels and of the small arterial vasculature in an isolated heart model of regional ischemia. Elevation of osmolality by mannitol increased collateral blood flow to the ischemic region through at least two mechanisms. First, increasing osmolality resulted in dilation of large arterial conductance vessels, similar to that produced by nitroglycerin. In addition, mannitol produced an effect on the coronary circulation at a microvascular level which, per se or in combination with its effect on larger collateral conductance vessels, increased collateral blood flow to ischemic regions.     

Multistep approach to electrical stimulation after cardiomyoplasty

Still a controversial procedure, cardiomyoplasty (CMP) improves the failing heart's ability to contract by using a latissimus dorsi muscle (LDM), but to date, hemodynamic results correlate poorly with clinical improvement. The following two causes for apprehension bar attempting to change the conventional electrical stimulation (ES) protocol to improve CMP results: (1) fear of beginning ES for LDM-assisted contraction immediately postmobilization and CMP and (2) fear of stopping or slowing ES during sleep periods. METHODS: In ten different experimental series, I used animal models of CMP to determine how to apply ES to newly mobilized LDM, how to begin partial cardiac assist immediately post-CMP, and how to suspend ES for 12 hours daily. RESULTS: From my experimental series I noted the following three results. (1) Different ES regimens applied 1 hour postmobilization changed the contractile force (CF). After a 30-minute fatigue test, CF decreased by 34% +/- 3% with continuous ES at 30 contractions per minute (cpm), by 23% +/- 2% with continuous ES at 15 cpm, by 25% +/- 5% with ES in a work-rest regimen at 30 cpm, and by 8% +/- 3% with ES in a work-rest regimen at 15 cpm. (2) Imitation of partial cardiac assist immediately postmobilization slightly decreased CF. Sixteen days postmobilization, during a 30-minute fatigue test in animals in which ES had been started immediately after mobilization, CF decreased by only 6% +/- 3% and did not change when ES was combined with imitation of cardiac assist for 30 minutes twice daily (work-rest regimen). (3) ES cessation for 24 hours daily or 12 hours daily in CMP model created no difference in ejection fraction (EF) with ES (54% +/- 4% vs 53% +/- 5%, respectively (or in left ventricular end-diastolic volume (LVEDV, 234.3 ml +/- 1.0 ml vs 24.8 mL +/- 0.6 mL, respectively) or in LV end-systolic volume (LVESV; 12.1 mL +/- 0.7 mL vs 12.8 mL +/- 0.7 mL, respectively). CONCLUSION: For improving angiographic potential in the LDM, ES can be started safely immediately post-CMP at 15 cpm (a 1:4 or 1:5 regimen) and single impulses per burst. For partial cardiac assist and for improving LDM performance, cardiac assist can be used for 30 minutes twice daily immediately post-CMP. To rest the muscle and save it from overuse, muscle contraction can be either stopped or slowed down during hours of sleep.     

Identification and control of noncoronary collateral blood flow

To identify the source of noncoronary collateral myocardial blood flow and to establish methods to control it during induced ischemia, 29 dogs were placed on cardiopulmonary bypass. The right and left ventricles were vented, vent flows were measured volumetrically, and intracavitary left ventricular (LV) pressures were monitored. After induction of ischemia by aortic cross-clamping and infusion of cardioplegic solution, six different microspheres 7 to 10 microns in diameter were injected into the aorta at six different times to measure myocardial blood flow during the following interventions:vent drainage of the right or left ventricle or both, proximal ligation of both coronary arteries, severance of the proximal pulmonary artery or the ascending aorta or both, and ligation of the bronchial arteries. Without effective LV venting, LV intracavitary pressure rose to 7.0 +/- 0.1 mm Hg (mean +/- standard error of the mean) and myocardial blood flow in the anterior left ventricle was 2.3 +/- 1.3 ml/100 gm/min. When the LV vent was opened, vent flow was 35.9 +/- 3.5 ml/min and myocardial blood flow fell to 0.3 +/- 0.2 ml/100 gm/min. Right ventricular (RV) vent flow was absent except when the LV vent was occluded, and this RV vent flow was abolished by ligating the coronary arteries. With bronchial artery ligation, LV vent flow ceased and myocardial blood flow was virtually absent. These studies demonstrate that myocardial blood flow does occur during induced ischemia, but that the source of this blood flow is primarily through systemic-pulmonary channels. True noncoronary collateral myocardial blood flow was virtually nonexistent.     

Experience in heart transplantation after dynamic cardiomyoplasty.

We report a case undergoing heart transplantation due to gradual progression of heart failure four years and one month after dynamic cardiomyoplasty. This case reports a 61-year-old man who received drug therapy after being diagnosed as having idiopathic dilated cardiomyopathy, but his heart failure progressed to New York Heart Association (NYHA) class III-IV, and heart transplantation was thought to be indicated. However, dynamic cardiomyoplasty was performed because this patient rejected heart transplantation. An implantable cardioverter/defibrillator (ICD) was implanted for postoperative ventricular arrhythmia. After that, his symptoms rapidly improved, but his heart failure gradually worsened two years after surgery and heart transplantation was performed four years and one month after dynamic cardiomyoplasty. Since transplantation he has had an uneventful postoperative course without rejection or complications.     

Techniques to enhance the ileal conduit

There is a need for operations by which the complications of ileal conduits can be prevented or corrected. The author details techniques to ensure the formation of a short conduit, to shorten a conduit through a peristomal incision, and to correct ileocutaneous stomal stenosis.     

Atrial cardiomyoplasty in a Fontan circulation.

INTRODUCTION: The Fontan circulation is a direct connection between the systemic veins and the pulmonary artery (PA). Consequently, the pulmonary flow is passive due to the gradient between the right and left atrial pressure. In patients with increased pulmonary vascular resistance, the surgical procedure of atrio-pulmonary connection is therefore prone to failure. The goal of this experiment was to increase the pulmonary flow in an experimental model of a Fontan circulation by performing a right atrial cardiomyoplasty (ACMP). METHODS: In 19 Foxhounds the left m. latissimus dorsi (LD) was mobilised and transferred as a pedicle into the chest. After sternotomy a 'Fontan circulation' was created under cardiopulmonary bypass (CPB) by connecting the right atrium (RA) with the PA by a valveless conduit. The tricuspid valve was closed with a patch. In 11 dogs (group 1) a valve was implanted in the inferior vena cava (IVC) and pulmonary inflow impedance was increased by partial occlusion of the conduit to a gradient of 10 mmHg between RA and PA. In the other eight dogs (group 2) no valve was implanted, but flowmeters were placed in the IVC and the superior vena cava (SVC). In all dogs the RA was enlarged by a fascia lata patch before the LD was wrapped over the RA and stimulated synchronously to the R-wave with burst impulses. RESULTS: After coming off CPB, relatively high central venous pressures (22.5+/-5.8 mmHg) were necessary to maintain haemodynamic stability. With LD-stimulation in a 1:3 mode in group 1, RA pressure (P) increased from 23.1+/-7.7 to 45+/-10.5 mmHg (P<0.001), pulmonary atrial pressure (PAP) from 15.5+/-4.3 to 25.5+/-7.6 mmHg (P<0.001) and central venous pressure increased to 33.1+/-11.3 mmHg (P<0.05). Stroke volume increase from 11.4+/-4.7 to 17.2+/-4.3 ml and peak conduit-flow from 1286.3+/-880.3 to 2329+/-1173 ml/min (all P<0.001). In a 1:1 stimulation mode a pulsatile pressure/flow profile was obtained in the PA-conduit. Furthermore, at higher frequencies of about 120 beats/min muscle relaxation was still fast enough as not to interfere with the RA filling. In group 2 caval flow without stimulation occurred mainly during diastole. However, with LD-stimulation, a strong backflow into IVC and SVC was observed resulting in a less pronounced pressure/flow increase in the PA. CONCLUSIONS: Our experimental model demonstrates the possibility of a 'ventricularisation' of the RA by using the force of the LD. However, the haemodynamic benefit of ACMP was achieved only, when a valve was implanted in the ICV.     

Development of a pump flow estimator for rotary blood pumps to enhance monitoring of ventricular function

Estimation of instantaneous flow in rotary blood pumps (RBPs) is important for monitoring the interaction between heart and pump and eventually the ventricular function. Our group has reported an algorithm to derive ventricular contractility based on the maximum time derivative (dQ/dt_max as a substitute for ventricular dP/dt_max) and pulsatility of measured flow signals. However, in RBPs used clinically, flow is estimated with a bandwidth too low to determine dQ/dt_max in the case of improving heart function. The aim of this study was to develop a flow estimator for a centrifugal pump with bandwidth sufficient to provide noninvasive cardiac diagnostics. The new estimator is based on both static and dynamic properties of the brushless DC motor. An in vitro setup was employed to identify the performance of pump and motor up to 20 Hz. The algorithm was validated using physiological ventricular and arterial pressure waveforms in a mock loop which simulated different contractilities (dP/dt_max 600 to 2300 mm Hg/s), pump speeds (2 to 4 krpm), and fluid viscosities (2 to 4 mPa·s). The mathematically estimated pump flow data were then compared to the datasets measured in the mock loop for different variable combinations (flow ranging from 2.5 to 7 L/min, pulsatility from 3.5 to 6 L/min, dQ/dt_max from 15 to 60 L/min/s). Transfer function analysis showed that the developed algorithm could estimate the flow waveform with a bandwidth up to 15 Hz (±2 dB). The mean difference between the estimated and measured average flows was +0.06 ± 0.31 L/min and for the flow pulsatilities ?0.27 ± 0.2 L/min. Detection of dQ/dt_max was possible up to a dP/dt_max level of 2300 mm Hg/s. In conclusion, a flow estimator with sufficient frequency bandwidth and accuracy to allow determination of changes in ventricular contractility even in the case of improving heart function was developed.     

Techniques of postoperative blood flow monitoring after free tissue transfer: An overview

Ever since free tissue transfer has been established in microsurgery, success rates have greatly improved over the years, partly due to improved technical performance of microvascular anastomoses with better optical and instrumental aids. However, flap failure still occurs in 5–10%, mainly due to blood vessel thrombosis within the first 24 postoperative hours. Salvation rates of failing free tissue transfers can be optimized by in-time diagnosis of irreversibly compromised tissue blood flow and immediate operative reexploration. Therefore, there is a special demand for adequate and reliable postoperative monitoring techniques. This article gives an overview of all monitoring techniques, which have been performed both in the experimental and clinical setting thus far. © 1994 Wiley-Liss, Inc.     

Muscle blood flow after amputation. Increased flow with medullary plugging

At below-knee amputation for arterial insufficiency in 31 patients, the muscle blood flow of quadriceps and triceps surae was measured by clearance of 99mTc pertechnetate pre- and postoperatively. In 15 patients, myoplastic amputation was performed and in 16 patients the medullary cavity of the tibial stump was plugged with cortex of the removed bone as well. Plugging caused a two-third increase in muscle blood flow.     

Failure of naloxone to affect focal incomplete cerebral ischemia and collateral blood flow in cats

Focal incomplete cerebral ischemia was created in 20 adult cats by retro-orbital middle cerebral artery (MCA) occlusion under halothane anesthesia. Arterial blood flow (CBF), bilateral electroencephalographic (EEG) recordings, and systemic arterial blood pressure (SABP) were monitored for the 1st hour of occlusion. Ten animals were treated with 10 mg/kg of naloxone within 10 minutes of MCA clipping, followed by a continuous infusion of naloxone at 2 mg/kg/hr for the duration of the occlusion (8 hours). Ten animals were treated in a similar fashion with physiological saline (control). Blood flow was restored after 8 hours. The brains were examined at the time of death or 7 days after the occlusion period. There was no difference between the two groups regarding cerebral infarction size or distribution, neurological outcome, SABP, PaCO2, or CBF. Minor changes in EEG amplitude observed in the naloxone-treated group appear to represent interaction of the drug with halothane after prolonged administration. The authors conclude that naloxone did not modify the outcome of focal cerebral ischemia in the cat.     

Pulse oximetry compared with Doppler ultrasound for assessment of collateral blood flow to the hand

Ischaemic injury to the hand after arterial cannulation is a rare but well documented complication and routine testing of the adequacy of collateral circulation is widely advocated. The widespread availability of the pulse oximeter in the operating theatre. its applicability in circumstances where the patient is unable to cooperate, and its dependence on pulsatile blood flow suggest that this device could potentially be usefully applied to the assessment of collateral blood flow. The reliability of the pulse oximeter to detect the presence or absence of collateral circulation was prospectively compared to Doppler ultrasound in 109 hands from 64 adult patients. Nine hands demonstrated inadequate ulnar collateral flow, one hand demonstrated inadequate radial collateral flow and a persistent median artery was found in one hand. In all patients the results of pulse oximeter testing (probe placed on the thumb correlated precisely with the results obtained with the Doppler device (probe located over the lateral aspect of the superficial palmar arch). These results demonstrate pulse oximetry to be a reliable method of assessing collateral blood flow to the hand before arterial cannulation.     

Quantitative measurements of collateral arterial blood flow in nonarterialized rat liver grafts

The early development of arterial blood flow in the grafted liver after orthotopic liver transplantation in the rat without reconstruction of the hepatic artery was studied. Arterial liver blood flow was measured on day 21 after transplantation with NEN-TRAC microspheres (size 15.5±0.1 m) and labelled with ¹⁰³Ru. The arterial liver blood flow in the grafted liver was 0.778±0.247 ml/min per gram for transplanted rats after 21 days. One day after transplantation, the blood flow was only 0.006±0.002 ml/min per gram. The results of this study demonstrate that there was no arterial blood flow on day 1 after transplantation, as expected, but that there was a high arterial blood flow in the transplanted liver by day 21. This was also supported by the angiographic findings. The early development of arterial blood flow via collaterals may account for the excellent results that we and others have attained in orthotopic liver transplantation without rearterialization in the rat.     

Renal blood flow and intrarenal distribution of blood flow after decapsulation in the postischemic kidney.

Previous reports suggest the value of renal decapsulation in the prevention of renal failure after acute ischemia. It has been suggested that this response is due to a release of "compartmental" pressure resulting in increased blood flow to the decapsulated kidney. Ten dogs were evaluated following 90 minutes of renal ischemia created by occlusion of the suprarenal aorta. Each animal underwent random unilateral decapsulation, with the contralateral kidney acting as control. Labeled 15 micron microspheres (Se85 and Ce141) were injected into the left ventricle at 15 minutes and one hour following decapsulation in six dogs. In the remaining animals the injection was carried out at 15 minutes and 48 hours. No difference in renal blood flow was found between decapsulated and control kidneys in either group. Similarly, using sectioned kidneys no difference in intrarenal distribution of blood flow was found. These data suggest that the effects caused by decapsulation are not due to hemodynamic alterations.     

Characteristics of extrahepatic collateral blood flow in patients with cirrhosis of the liver

Percutaneous transhepatic portography was performed in 120 patients with cirrhosis of the liver with the intrahepatic form of pleural hypertension. It was shown that the degree of portal hypertension was associated with the presence of collateral circulation rather than with its distribution. The preferable way of collateral shunt is thought to be the gastroesophageal anastomosis which is not however hemodynamically effective. The results obtained show that natural collateral circulation is not able to provide decompression of the portal system.     

Effect of radial artery harvest on collateral forearm blood flow and digital perfusion

BACKGROUND: Changes describing digital and forearm circulation after radial artery harvest have been reported infrequently. METHODS: This prospective study examined digital perfusion and forearm collateral circulation preoperatively and postoperatively in patients who underwent coronary artery bypass grafting with radial artery free grafts. Noninvasive evaluation was conducted with digital photoelectric plethysmography and color flow and pulsed Doppler studies. RESULTS: Thumb perfusion index decreased from 1.25 to 0.84 (30%, P <.001) in the unoperated extremities and from 1.23 to 0.80 (36%) in the operated extremities (P <.001). Doppler studies in extremities after radial artery harvest demonstrated an increase in ulnar artery diameter from 3.87 to 4.66 mm (15.7%, P <.001) and a rise in ulnar blood flow velocity from 38.96 to 48.46 cm/s (17.4%) preoperatively to 8 weeks postoperatively (P <.001). No hand ischemia was noted. CONCLUSIONS: Our study identified a mild reduction in digital perfusion and an increase in ulnar artery flow velocity and diameter with no clinical sequelae or compromise in hand function after radial artery harvest in properly selected patients.