Catálogo de publicaciones - libros

Dysoxia, a state in which O supply is inadequate to meet tissue metabolic needs, is often first detected in regional organs such as the gut. An increase in P is believed to reflect the development of gut dysoxia. The stomach is a well-documented clinical site for detecting gut P; however, measurement issues make this a less than ideal monitoring site. Other sites along the GI tract may be equally sensitive to detect changes in P. Rectal CO measurement may have the advantage of being less invasive, low risk, and continuous without the limitations associated with gastric monitoring. In this study, we compared P at two sites (gastric, rectum) at baseline and during a dysoxic challenge, cardiac arrest. We obtained similar values of P at both sites.

Ten male Wistar rats were anesthetized with l%–2% Isoflurane/50% nitrous oxide/balanced O and the tail artery and right atrium were cannulated. Severinghaustype active tip P electrodes (Microelectrode Inc, Bedford, NH) were calibrated and one electrode was surgically inserted into the stomach (G-P) and a second electrode was placed in the rectum (R-P). Animals were stabilized following surgery. Cardiac arrest was induced by administering a rapid injection of norcuron (0.1–0.2 mg/kg) and potassium chloride solution (0.5 M/L; 0.12 mL/100 gm of body weight). Animals were monitored for 15 minutes post-arrest. Data were collected at one minute intervals using the software Data Collect. All data are reported as mean ± SD.

Baseline G-P was 64 ± 17 torr, not significantly different from R-P, 58 ± 7 torr. After 15 minutes of cardiac arrest, G-P rose to 114 ± 42 torr, again not significantly different from R-P, which reached 112 ± 35 torr. Monitoring P in the rectum is less invasive and might provide similar information when compared with gastric monitoring at baseline and during a dysoxic challenge.

The phosphorescence lifetime imaging system previously used to image oxygen in the retina of the cat eye was modified to allow imaging of phosphorescence lifetimes in the much smaller mouse eye. Following the lead of Shonat and coworkers, a frequency domain approach was used in which the excitation light source was modulated in a 50% on:50% off square wave while the gate of the intensified CCD camera was similarly modulated but delayed with respect to the excitation. These were analyzed by fitting the intensity at each pixel to a sinusoid. The phase of the phosphorescence relative to the excitation was determined and from the phase shift and frequency, the phosphorescence lifetime was calculated. The Stern-Volmer relationship was then used to calculate the oxygen pressure at each pixel of the image array. High resolution maps of phosphorescence lifetime and oxygen pressure in the retina of the mouse eye have been attained. The retinal veins draining into the optic head appear as large, highly phosphorescent vessels against a lower phosphorescence background with a network of smaller vessels. The oxygen pressure in the retinal veins is typically from 20 to 30 mm Hg while the background has somewhat higher oxygen pressures. Experiments are underway to resolve the oxygen in the choroid from that in the retina. The arteries on the retinal surface can be observed, but their small diameter, relatively high oxygen pressures (> 90 mm Hg), and surrounding tissue with much lower oxygen pressures, makes accurate determination of the oxygen pressure a challenge.

Tumors usually become localized absorbers at near infrared (NIR) wavelengths due to the increase in hemoglobin amount around the tumor, which is caused by angiogenesis. When a tumor is small and/or deeply seated, the contrast by the hemoglobin only, however, may not be strong. For such situation, contrast agents may be helpful, because they are preferentially accumulated in the tumor due to the unorganized tumor vascularure.

In this study, indocyanine green (ICG) was used as a contrast enhancer. ICG is safe, absorbs NIR, and also generates fluorescence. A breast tissue-like model, embedded with a tumor model (1.2 × 0.7 × 0.5 cm) with/without ICG at a 1 cm depth, was constructed and the surface was scanned by a NIR time-resolved spectroscopy instrument. Enhanced contrast by ICG was confirmed in both absorption and fluorescence. For absorption, transmittance contrast was approximately two times higher than reflectance. In reflectance, the contrast by fluorescence was approximately four times higher than absorption. This study result shows that the information on both the absorption and fluorescence by ICG can be effectively used in detecting a tumor. A study of the ICG effect on deeper absorber detection is in progress.

Insufficient oxygen delivery and retinal hypoxia have been implicated as causal in the development of many devastating diseases of the eye. While the two-dimensional imaging of retinal oxygen tension (PO) has now been applied in a variety of different animal models, it is fundamentally a luminescence-based system lacking depth discrimination. However, mammalian retinal tissue is nourished by two distinct vascular beds, the retinal and the choroidal vasculatures, and they are exceedingly difficult to separate using traditional two-dimensional imaging strategies. Numerous studies have demonstrated that retinal and choroidal PO differ substantially. Therefore, the single PO value currently returned through data analysis cannot accurately represent the separate contributions of the choroidal and retinal vasculatures to the state of retinal oxygenation. Such a separation would significantly advance our understanding of oxygen delivery dynamics in these two very distinct vasculatures. In this study, we investigate new strategies for generating separate retinal and choroidal PO maps in the rodent retina using our existing phosphorescence-based lifetime imaging system.

We describe our results on the effect in rats of two commonly used, volatile anesthetics on cerebral tissue PO (PtO) and other physiological parameters at FiO levels ranging from 0.35 to 0.1. The study was performed in 12 rats that had lithium phthalocyanine (LiPc) crystals implanted in the left cerebral cortex. FiO was maintained at 0.35 during surgical manipulation and baseline EPR measurements, after which time, each animal was exposed to varying levels of FiO (0.26, 0.21, 0.15, and 0.10) for 30 minutes at each level. No significant difference in PtO was observed between the isoflurane and halothane groups at any FiO level, and the cerebral arterial PO (PaO) also was similar for both groups. However, the cerebral PtO under both isoflurane and halothane anesthesia was lower during hypoxia (FiO ≤ 0.15) than under normoxia (FiO=0.21) and there was a significant difference in mean arterial blood pressure (MABP) between isoflurane and halothane groups under both mild and severe hypoxia. The pH and cerebral arterial PCO (PaCO) were similar for the halothane and isoflurane groups during normoxia (FiO=0.21) and mild hypoxia (FiO=0,15), but following severe hypoxia (FiO=0.10), both parameters were lower in the halothane anesthetized animals. These results confirm that cerebral PO cannot be inferred directly from measurements of other parameters, indicating that methodology incorporating continuous direct measurement of brain oxygen will lead to a better understanding of cerebral oxygenation under anesthesia and hypoxia.

The cardiovascular and cerebrovascular responses to head-up postural change are compromised in pure autonomic failure (PAF) patients because of sympathetic denervation. The aim of this study was to characterize the rate of change of systemic mean blood pressure (MBP) and cerebral haemodynamics in response to passive posture changes. Nine PAF patients and 9 age-matched controls took part in this study. MBP and oxy- (OHb), deoxy-haemoglobin (HHb), and tissue oxygenation index (TOI) on the forehead were continuously monitored non-invasively using the Portapres® and near-infrared spectroscopy (NIRS), respectively. From visual inspection of the haemoglobin difference signal (Hb=OHb-HHb), seven distinct phases were marked (1: supine, 2: start passive tilt, 3: head up to 60° degrees, 4: end of tilt, 5: tilt reversal, 6: return to supine, 7: rest); the same time points were used for all of the other signals. For each phase, the slope was calculated using a linear regression algorithm. Significant differences were found between PAF patients and controls in the Hb slope magnitudes for phases 3 (<.05) and 5 (=.01), and the duration of phase 2 (<.05). MBP slope magnitudes showed significant differences for phases 2 (<.01) and 5 (<.01). These differences in the rate of change suggest differences in blood vessel resistance related to sympathetic activation.

The CAS neonatal NIRS system determines absolute regional brain tissue oxygen saturation (SnO) and brain true venous oxygen saturation (SnvO) non-invasively. Since NIRS-interrogated tissue contains both arterial and venous blood from arterioles, venules, and capillaries, SnO is a mixed oxygen saturation parameter, having values between arterial oxygen saturation (SaO) and cerebral venous oxygen saturation (SVO). To determine a reference for SnO, the relative contribution of SvO to SaO drawn from a brain venous site vs. systemic SaO is approximately 70:30 (SvO:SaO). If the relationship of the relative average contribution of SvO and SaO is known and does not change to a large degree, then NIRS true venous oxygen saturation, SnvO, can be determined non-invasively using SnO along with SaO from a pulse oximeter.

When cells experience hypoxia, they either die by apoptosis or adapt to the hypoxic conditions by a series of compensatory mechanisms. Hypoxia inducible factor-1 (HIF-1) is a transcription factor involved in both processes, but the exact mechanisms regulating whether the cells survive (adapt) or perish by apoptosis are largely unknown.

We hypothesize that the balancing between apoptosis and adaptation is governed by a triangular feedback system involving the α-subunit of HIF-1, p53, and jun activating binding protein 1 (Jab1). Jab1 and p53 bind competitively to the same domain on HIF-1α resulting in either stabilization or degradation of HIF-1α, respectively. Moreover, p53 is stabilized by binding to HIF-1α, whereas its interaction with Jab1 targets p53 for degradation. Thus as a consequence we propose that the ratio between p53 and Jab1 determine whether a hypoxic induction of HIF-1 results in apoptosis or adaptation, with Jab1 as the factor promoting adaptation. On this background we consider Jab1 an interesting molecular target for anticancer therapy.

The first pathologists, oncologists, and medical physicists were aware that tumors were populated by an aberrant vasculature. The classic observations of Thomlinson and Gray in the 1950’s established that O diffusion distances caused tumor to grow in cords. Tumor necrosis was observed surrounding a Krogh cylinder of viable tumor. That work helped explain earlier work by Warburg, who demonstrated a predisposition for tumors to favor anaerobic respiration, and it became the basis for 5 decades of subsequent research aimed at improving tumor oxygenation at the time of radiation. The role of O in modifying radiation response was attributed exclusively to the reactive free radicals that can be formed when O is present. These radicals produce approximately three-fold more irreparable double strand breaks in DNA.

Subsequently it became clear that tumor had nutritional insufficiencies in addition to hypoxia. Ischemic regions are hypoglycemic, acidotic, have poor penetration of drugs, increased interstitial pressure, and altered immunological states. Ischemic regions can have intermittent reflow and associated redox stress. The relative impact of O compared to these associated phenomenon, and the degree to which hypoxia causes or follows these associated physiologic stresses, have been studied in detail. ISOTT scientists are responsible for much of the elucidation of the specific effects of O, ADP/ATP ratios, hypoglycemia, and acidosis on tumor responses to radiation and hyperthermia. Many questions still remain.

Hyperoxia may facilitate the formation of reactive oxygen species. Recent experiments indicated signs of oxidative stress after 3.5 h hyperoxic diving. We analyzed in the urine of healthy, 100% O-breathing male volunteers before and after 45 min sea-water diving (170 kPa) or 30 min resting at 280 kPa in a pressure chamber (HBO) for sub-fractions of hydroxybenzoate (HB), monohydroxybenzoate (MHB), and of dihydroxybenzoate (DHB). Measurements were performed by HPLC and electrochemical or UV-detection. Additionally, urinary concentrations of thiobarbituric acid-reactive sub-stances (TBARS) and of creatinine (CREA) were analyzed by standard colorimetric assays. During HBO treatment, TBARS, DHB, 2,4-DHB, and 3,4-DHB increased significantly. MHB and CREA did not change. 2,4- and 3,4-DHB-alterations correlated with changes in TBARS. Diving induced urine dilution and stimulated oxygen consumption. Urinary TBARS and HB rose significantly higher during diving at 170 kPa than during HBO at 280 kPa. A different pattern in urinary sub-fractions of DHB could be observed in divers: 2,6 > 2,3 > 2,5 > 3,4. Changes in 2,6- and 2,5-DHB correlated significantly with alterations in TBARS. 2,6-DHB probably indicated renal oxidant stress similar to previously described animal experiments. It is concluded that analyzing urinary HB may provide a sensitive measure to quantify and qualify oxidant stress in divers.