Babs R. Soller

Decreasing myocardial pH reflects ischemia during continuous warm retrograde cardioplegic arrest

Warm continuous retrograde cardioplegia is thought to prevent myocardial ischemia. We tested this hypothesis by subjecting canine hearts to 2 hours of either antegrade or retrograde perfusion with normothermic blood cardioplegia. Ischemic alterations were evaluated through the measurement of myocardial pH, tissue levels of adenosine triphosphate and lactate, and the preservation of left ventricular contractility. Antegrade perfusion resulted in uniformly positive changes in the myocardial pH in both ventricles, preserved levels of adenosine triphosphate, and small increases in the myocardial lactate levels. In contrast, retrograde perfusion caused the myocardial pH to decrease, especially in the right ventricle. Tissue lactate levels rose to a significantly greater extent during retrograde perfusion and adenosine triphosphate levels declined, although not to a statistically significant degree. Finally, myocardial function, as assessed by the preload recruitable work area, was preserved (103% +/- 20% of baseline) in the antegrade group but was markedly diminished (33% +/- 6%) in retrogradely perfused left ventricles 35 minutes after the aortic cross-clamp was removed. These data suggest that ischemic metabolism and the subsequent alteration of myocardial function take place despite continuous retrograde perfusion with normothermic blood cardioplegia.

Retrograde abdominal visceral perfusion: Is it beneficial?

BACKGROUND It is proposed that retrograde abdominal perfusion be used in combination with retrograde cerebral perfusion to provide total body visceral protection during aortic reconstruction; however, its physiologic effects remain unknown. METHODS We compared the effect of superior vena caval perfusion alone with that of combined superior and inferior vena caval perfusion on the liver and kidney in 6 mongrel dogs. Organ blood flow was measured using ultrasonic flow probes on the hepatic artery, the portal vein, and the renal artery. Regional tissue blood flow to the liver and the kidney was assessed using colored microspheres and pH probes. Anesthetized dogs were placed on total cardiopulmonary bypass. After cooling to 20 degrees C, retrograde perfusion was begun with 30 minutes of superior vena caval perfusion followed by another 30 minutes of bicaval perfusion, or vice versa. RESULTS Very little renal blood flow was measured with either method of retrograde perfusion. Although the liver received more blood flow in comparison to the kidney, there was no significant difference between superior vena caval perfusion alone and bicaval perfusion. The addition of inferior vena caval perfusion results in portal hypertension, hepatic congestion, ascites, and bowel edema. CONCLUSIONS In the canine model, bicaval perfusion does not provide superior protection to the liver and kidneys when compared with superior vena caval perfusion alone.

Thoracoscopic Lobectomy With Endoarterial Vascular Control: An Experimental Study in Swine

BACKGROUND Video-assisted lobectomy lacks vascular control and presents the potential for serious hemorrhage in a closed cavity. The use of a lighted, flow-directed balloon catheter in the pulmonary artery as an endovascular control device was evaluated. METHODS A modified light-bearing Swan-Ganz catheter was placed in the left or right pulmonary artery using fluoroscopy. The lit catheter was identified easily through the arterial wall at thoracoscopy. Its inflation allowed the control of proximal blood flow as required. Fully thoracoscopic lobectomy was carried out by isolating and dividing the lobar branches of the pulmonary artery, the pulmonary vein, and the bronchus in anesthetized swine. RESULTS Forty-two video-assisted anatomic lobectomies were completed in 30 pigs with balloon catheter control of the pulmonary artery. The balloon effectively controlled experimental hemorrhage caused by puncturing arterial branches (n = 4). It allowed the transection of unlooped lobar arteries (n = 42) and the main interlobar pulmonary artery (n = 3). Catheter displacement back to the heart occurred in 5 animals and balloon catheter technical failures occurred in 3. CONCLUSIONS The lighted, flow-directed balloon catheter was an effective means of avoiding acute hemorrhage and achieving vascular control in a swine lobectomy model.

Diminished Myocardial Function Precedes Tissue Acidosis during Coronary Hypoperf usion

The current study sought to elucidate the relationship between myocardial pH and function during a significant but not absolute reduction in coronary flow. In a canine model, a partial coronary arterial stenosis was created, with the left anterior descending coronary artery (LAD) flow reduced by 50% compared to prestenosis levels, and maintained at that level for the duration of the study. During the experiment, interstitial myocardial pH and regional myocardial function, as assessed by the regional preload recruitable work area (PRWA), were measured. PRWA was depressed to 60% of baseline values, on average, for the entire period of reduced LAD flow. In contrast to the pattern observed with myocardial blood flow and systolic function, metabolic evidence of myocardial ischemia, that is, reduced myocardial pH did not become significantly different from baseline levels until after LAD flow had been reduced for 15 min. Thus, measurable changes in myocardial pH appeared slowly over time despite the fact that regional myocardial blood flow was decreased immediately. Therefore, myocardial pH cannot be used to anticipate alterations in myocardial contractile function.

Optical measurement of tissue pH for surgical and critical care monitoring

Tissue pH is an important physiological parameter which indicates both blood flow and cell metabolic state. Continuous monitoring of tissue pH can provide an assessment of the level of anaerobic metabolism and a measure of whether organs or muscles are revivable or have died. A noninvasive, optical technique for deep tissue pH determination has been demonstrated in-vivo using near infrared (NIR) spectroscopy and partial least-squares (PLS) multivariate calibration. NIR reflectance spectra (700 - 1100 nm) were collected from skin covered muscle in a rabbit, canine myocardium, and swine bowel along with reference pH values measured in the same tissue using microelectrodes. Muscle and myocardial pH were varied by controlling the blood supply through vessel occlusion; bowel pH was altered through hemorrhagic shock. PLS cross- validation techniques and data preprocessing methods were used to relate the tissue pH to spectra. The standard error of prediction for each of the multivariate calibrations was less than 13% of the average pH change in each of the animal models. Optically measured tissue pH promises to provide a noninvasive monitor for ischemia during heart and plastic surgery and an early indicator of shock in the ICU patient.

In-vivo determination of myocardial pH during regional ischemia using near-infrared spectroscopy

pH electrodes have been used during open heart surgery to ensure adequate delivery of blood and oxygen to the myocardium during the surgical procedure. The electrodes are cumbersome and suffer from motion artifacts. Near infrared spectroscopy was evaluated as a noninvasive method of measuring myocardial pH during regional ischemia in seven beating dog hearts. Two pH microelectrodes were implanted in the distribution area of the left anterior descending (LAD) coronary artery. The LAD was occluded to stop the myocardial blood flow and to initialize regional ischemia. Ischemia was maintained for 20 minutes before the LAD was released to resume blood flow. A fiber-optic probe was used to collect the reflected NIR light over the spectral region of 575 nm to 1100 nm from the heart muscle. Partial least-squares multivariate calibration technique was applied to relate the myocardial pH changes to the NIR spectral changes in the region of 700 to 1100 nm. Calibration models based on data collected on each individual dog heart had an average of 7 factors with an R2 of 0.84. The standard error of prediction (SEP) averaged 0.09 pH units for a mean pH change of 0.73 pH units, adequate for monitoring pH changes during cardiac surgery.

Hypothermic cardioplegic arrest is associated with increased myocardial adenosine.

The current study examined the effects of temperature on myocardial pH, contractile function and adenosine triphosphate metabolism, particularly the production of adenosine. We matched intermittent delivery of blood cardioplegia in two groups (hypothermia 15 degrees C; normothermia 37 degrees C), for 2 h of cardioplegic arrest. Hypothermic perfusion resulted in a markedly alkalotic pH, and nearly a threefold increase in adenosine and adenosine monophosphate levels compared to normothermic hearts. Tissue levels of adenosine triphosphate were preserved to the same extent in each group, despite the increased energy requirements of normothermia. Myocardial contractile function was not statistically different between the two groups at 30 min and 2 h after the cross clamp was removed. These data suggest that both methods, hypothermia via its reduced energy demands, and normothermia through continued glycolytic metabolic activity, allow the myocardium to maintain energy stores and resume adequate function. However, hypothermic perfusion results in an accumulation of adenosine, demonstrating that temperature should be considered when attempting to manipulate the generation and accumulation of the compound.

Noninvasive sensors in critical care medicine: near-infrared spectroscopy for the detection of altered microvascular blood flow in severe sepsis and septic shock

It is estimated that 750,000 cases of severe sepsis occur in the United States annually, at least 225,000 of which are fatal, resulting in significant utilization of healthcare resources and expenses. Significant progress in the understanding of pathophysiology and treatment of this condition has been made lately. Among the newer treatment strategies for critically ill patients are the administration of early goal directed therapy, and Recombinant Human Activated Protein C (Drotrecogrin alfa (activated) [DTAA]) for severe sepsis. However, mortality remains unacceptably high.

Development of an in-vivo PLS calibration model for the noninvasive measurement of blood, hematocrit using NIR spectroscopy

Near infrared spectra and hematocrit reference measurements were collected from 37 cardiac and vascular surgery patients and calibration models developed using partial least squares analysis. Factors which influence the development of accurate models are discussed.

Design and development of a sensor for the direct and continuous measurement of inhaled nitric oxide: factors affecting sensitivity

Nitric oxide (NO), in concentrations between 0 and 20 ppm, is currently being used as an inhaled agent to treat patients with post surgical complications and respiratory disorders. Because excessive levels of NO can be detrimental to the patient, NO must be monitored accurately and continuously. Currently available instruments have problems that limit their usefulness for this application. This paper discusses the development of an inexpensive, direct and continuous sensor for the measurement of inhaled nitric oxide. The sensor incorporates a 0.05 inch, gas permeable, flow-through liquid cell into a probe, which can be incorporated into a ventilator circuit. Sensor operation is based on the complexation reaction of NO with cytochrome-c, a biologically derived heme. The complex is monitored spectrophotometrically by measuring the absorbance in the visible region of the spectrum at 563 nm. The sensor is specific to NO in the presence of oxygen. This paper will address experiments to optimize sensitivity of the sensor. Increasing the flow rate and pressure of NO into the sensing chamber increased the optical absorbance at a high concentration of NO. Increasing the concentration of cytochrome-c increased the sensitivity of the sensor. The sensor is currently sensitive to a minimum concentration of 5 ppm and linear in the range of 5 to 175 ppm.