Search

Objective: To compare tissue pH in the stomach, bowel, and abdominal wall muscle during hemorrhagic shock and recovery using tissue electrodes; also, to compare tissue electrode pH measurements to gastric intramucosal pH (pH 1 ), gastric luminal PCO 2 , and PCO 2 gap (gastric luminal CO 2 - arterial CO 2 ) measured with an air-equilibrated tonometer. Design: Prospective animal study. Setting: University animal research laboratory. Subjects: Eight anesthetized, mechanically ventilated Yorkshire swine. Interventions: Hemorrhagic shock was initiated by withdrawing blood over a 15-min period to lower systolic blood pressure to 45 mm Hg. Shock was maintained for 45 mins and was followed by a 5-min resuscitation to normal blood pressure with a blood/ lactated Ringer's (1:2) mixture. Recovery was monitored for 60 mins. Measurements and Main Results: pH was measured with electrodes in the submucosa of the stomach, the submucosa of the small bowel, and the abdominal wall muscle. Gastric luminal PCO 2 was measured with an air-equilibrated tonometer and pH 1 and PCO 2 gap were calculated. Each organ showed a different sensitivity to shock and resuscitation. The bowel pH responded most rapidly to the onset of hemorrhagic shock and had the largest change in tissue pH. The bowel also showed the most rapid recovery during resuscitation. The submucosal pH of the stomach responded more slowly than the bowel, but faster than the abdominal wall muscle pH, gastric PCO 2 gap, or pH i . The smallest changes in organ pH as a result of hemorrhagic shock were seen in the abdominal wall muscle and the stomach as assessed by gastric tonometry. Conclusions: Direct measurement of tissue pH indicates that intra-abdominal organ pH varies during hemorrhagic shock. The small bowel pH changes the most in magnitude and rapidity compared with stomach pH or abdominal wall muscle pH. Tonometrically derived parameters were not as sensitive in the detection of tissue acidosis during shock and resuscitation as pH measured directly in the submucosa of the stomach or small bowel.

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.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Nitric Oxide is a simple gaseous compound which serves as a regulatory molecule in a number of physiological processes. Due to its biological role as a potent local vasodilator,there has been widespread interest in the therapeutic use of gaseous nitric oxide a selective pulmonary vasodilator. Our goal is the development of a sensor for the direct and continuous measurement of inhaled nitric oxide concentrations. This study evaluated the reversibility of potential sensing compounds upon reaction with nitric oxide. Previously, absorption spectroscopy was used to study the sensitivity of the Fe II, Fe III and oxygenated forms of three biologically active hemes known to rapidly react with NO: hemoglobin, myoglobin, and cytochrome-c. This study focused on the photo-reversibility of the hem's reaction with nitric oxide. Hemoglobin, myoglobin and cytochrome-c in the Fe III state reversibly reacted with nitric oxide. Hemoglobin and myoglobin in the Fe II state non-reversibly reacted with nitric oxide to form an unstable product. Cytochrome-c (FeII) does not react with nitric oxide. The oxy forms of hemoglobin and myoglobin react with nitric oxide to form their respective met forms, unreversible via photolysis. For all reversible reactions, photolysis was gradual and complete within five minutes.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

Objective. Tissue pH measurement has a number of clinical applications, including the monitoring of both muscle pH and organ pH as an indicator of compromised blood flow and anaerobic metabolism. The objective of this work was to demonstrate the feasibility of a noninvasive measurement of deep tissue pH using near-infrared reflectance spectroscopy and multivariate calibration techniques.Methods. Six studies were done on five New Zealand white rabbits. Two pH electrodes were implanted in the teres major muscle and a vascular clamp placed across the single artery feeding the muscle. Reflected light was collected through the skin from a site between the two electrodes as the pH was lowered by closing the clamp and raised by opening the clamp. Partial least squares analysis with cross-validation techniques was used to relate pH to light absorption at 201 evenly spaced wavelengths between 700 and 1100 nm.Results. On average, the tissue, pH started at 7.13 ± 0.09 and decreased to 6.74 ± 0.09, returning to 7.13 ± 0.09 after reperfusion. Calibration models fit for each rabbit had an average of nine factors with an R2 of 0.98 and a prediction error of 0.016 ± 0.002 pH units.Conclusions. We believe this to be the firstin vivo demonstration of a noninvasive method for measuring tissue pH in skin-covered muscle using near-infrared reflectance spectroscopy and multivariate calibration techniques.

Nitric oxide (NO) is an important regulatory molecule in physiological processes including neurotransmission and the control of blood pressure. It is produced in excess during septic shock, the profound hypotensive state which accompanies severe infections. In-vivo measurement of NO would enhance the understanding of its varied biological roles. Our goal is the development of an intravascular fiber-optic sensor for the continuous measurement of NO. This study evaluated nitric oxide sensitive compounds as potential sensing materials in the presence and absence of oxygen. Using absorption spectroscopy we studied both the Fe II and Fe III forms of three biologically active hemes known to rapidly react with NO: hemoglobin, myoglobin, and cytochrome-c. The Fe II forms of hemoglobin and myoglobin and the Fe III form of cytochrome-c were found to have the highest sensitivity to NO. Cytochrome c (Fe III) is selective for NO even at high oxygen levels, while myoglobin is selective only under normal oxygen levels. NO concentrations as low as 1 (mu) M can be detected with our fiber-optic spectrometer using cytochrome c, and as low as 300 nM using myoglobin. Either of these materials would be adequate to monitor the increase in nitric oxide production during the onset of septic shock.