Intracoronary delivery of adenovirus encoding adenylyl cyclase VI increases left ventricular function and cAMP-generating capacity.

BACKGROUND: We tested the hypothesis that intracoronary injection of a recombinant adenovirus encoding adenylyl cyclase type VI (AC(VI)) would increase cardiac function in pigs. METHODS AND RESULTS: Left ventricular (LV) dP/dt and cardiac output in response to isoproterenol and NKH477 stimulation were assessed in normal pigs before and 12 days after intracoronary delivery of histamine followed by intracoronary delivery of an adenovirus encoding lacZ (control) or AC(VI) (1.4x10(12) vp). Animals that had received AC(VI) gene transfer showed increases in peak LV dP/dt (average increase of 1267+/-807 mm Hg/s; P=0.0002) and cardiac output (average increase of 39+/-20 mL. kg(-1). min(-1); P<0.0001); control animals showed no changes. Increased LV dP/dt was evident 6 days after gene transfer and persisted for at least 57 days. Basal heart rate, blood pressure, and LV dP/dt were unchanged, despite changes in cardiac responsiveness to catecholamine stimulation. Twenty-three hour ECG recordings showed no change in mean heart rate or ectopic beats and no arrhythmias. LV homogenates from animals receiving AC(VI) gene transfer showed increased AC(VI) protein content (P=0.0007) and stimulated cAMP production (P=0.0006), confirming transgene expression and function; basal LV AC activity was unchanged. Increased cAMP-generating capacity persisted for at least 18 weeks (P<0.0002). CONCLUSIONS: Intracoronary injection of a recombinant adenovirus encoding AC provides enduring increases in cardiac function.

Cardiac-directed adenylyl cyclase expression improves heart function in murine cardiomyopathy.

BACKGROUND: We tested the hypothesis that increased cardiac myocyte adenylyl cyclase (AC) content increases cardiac function and response to catecholamines in cardiomyopathy. METHODS AND RESULTS: Transgenic mice with cardiac-directed expression of AC type VI (ACVI) were crossbred with mice with cardiomyopathy induced by cardiac-directed Gq expression. Gq mice had dilated left ventricles, reduced heart function, decreased cardiac responsiveness to catecholamine stimulation, and impaired beta-adrenergic receptor (betaAR)-dependent and AC-dependent cAMP production. Gq/AC mice showed improved basal cardiac function in vivo (P=0.01) and ex vivo (P<0.0005). When stimulated through the betaAR, cardiac responsiveness was increased (P=0.02), and cardiac myocytes showed increased cAMP production in response to isoproterenol (P=0.03) and forskolin (P<0.0001). CONCLUSIONS: Increasing myocardial ACVI content in cardiomyopathy restores cAMP-generating capacity and improves cardiac function and responsiveness to betaAR stimulation.

Adenylylcyclase increases responsiveness to catecholamine stimulation in transgenic mice.

BACKGROUND: The cellular content of cAMP generated by activation of adenylylcyclase (AC) through the beta-adrenergic receptor (betaAR) is a key determinant of a cell's response to catecholamine stimulation. We tested the hypothesis that increased AC content, independently of betaAR number, increases responsiveness to catecholamine stimulation in vivo. METHODS AND RESULTS: Transgenic mice with cardiac-directed expression of ACVI showed increased transgene AC expression but no change in myocardial betaAR number or G-protein content. When stimulated through the betaAR, cardiac function was increased, and cardiac myocytes showed increased cAMP production. In contrast, basal cAMP and cardiac function were normal, and long-term transgene expression was not associated with abnormal histological findings or deleterious changes in cardiac function. CONCLUSIONS: The amount of AC sets a limit on cardiac beta-adrenergic signaling in vivo, and increased AC, independent of betaAR number and G-protein content, provides a means to regulate cardiac responsiveness to betaAR stimulation. Overexpressing an effector (AC) does not alter transmembrane signaling except when receptors are activated, in contrast to receptor/G-protein overexpression, which yields continuous activation and has detrimental consequences. Our findings establish the importance of AC content in modulating beta-adrenergic signaling in the heart, suggesting a new target for safely increasing cardiac responsiveness to betaAR stimulation.

Dissociation between regional dysfunction and beta-adrenergic receptor signaling in heart failure.

We have previously shown that left ventricular (LV) pacing-induced heart failure is associated with preserved wall thickening in the interventricular septum (IVS) compared with the posterolateral wall (PLW). The current study focuses on the relationship between regional myocardial function and altered beta-adrenergic receptor (beta-AR) signaling. We studied 15 pigs: 6 controls and 9 paced from the left ventricle (225 beats/min, 26 +/- 3 days). Heart failure was documented by decreased LV fractional shortening (P < 0.0001) and increased left atrial pressure (P < 0.0001). In heart failure, despite marked differences in basal regional function (percent wall thickening: IVS, 33 +/- 10% vs. PLW, 13 +/- 7%; P = 0.0003), there were no differences between the two regions in beta-AR responsiveness, measured by regional wall thickening in response to dobutamine infusion and any measurement of adrenergic signaling. Adenylyl cyclase activity, beta-AR number, and beta-AR/Gs coupling were markedly reduced in failing LV without regional differences. In animals with heart failure, LV G protein receptor kinase (GRK) isoform 2 content was unchanged and GRK5, the other major GRK isoform, was increased more than threefold (IVS, 0.51 +/- 0.20 vs. 0. 12 +/- 0.12 arbitrary densitometric units, P = 0.01; PLW, 0.47 +/- 0. 15 vs. 0.13 +/- 0.09 arbitrary densitometric units, P = 0.03), but again, there were no regional differences. These data indicate that systemic rather than regional factors govern LV adrenergic signaling and that regional adrenergic signaling abnormalities poorly predict wall thickening in the same regions.

RHD gene polymorphisms among RhD-negative Chinese in Taiwan.

BACKGROUND AND OBJECTIVE: The rare occurrence of anti-D-associated hemolytic disease of the newborn among Chinese is attributable in part to the existence of the weak D phenotype Del among apparently RhD-negative individuals. While existing advances in the molecular genetics of the Rh blood group have been noted in recent years, the genomic structure of the Del phenotype has seldom been studied in the literature. We try to explore the genomic structure of the RhD gene among apparently Rh-negative Chinese in Taiwan in this study. METHODS: Genomic DNA from 230 samples of apparently RhD-negative Chinese was studied using four polymerase chain reaction (PCR)-based RhD typing methods. These PCR methods amplified RHD and RHCE genes at exons 4, 5, 7 and 10. All nucleotides responsible for exofacial amino acid differences between RhD and RhCeEe peptides, including amino acids 169, 170, 172, 223, 226, 233, 238, 350, 353, and 354, were contained in these amplified DNA segments. Southern blot analysis using RHD cDNA fragments as probes was performed. RESULTS: According to the serological study, 155 samples (67.4%) were genuinely RhD-negative and 75 samples (32.6%) were of the Del phenotype. Successful amplifications for RHD sequences were possible in all 75 Del samples using four PCR methods. Apparently, all Del individuals carried an intact RHD gene. While 145 individuals of 155 genuinely Rh-negative (63.0% of apparently RhD-negative individuals) had total deletion of their RHD genes, 10 individuals (4.3% of apparently RhD-negative individuals) were shown to have a preserved 3' noncoding region of the RHD exon 10 and a gross deletion of RHD exons 4-10. CONCLUSIONS: Three classes of RhD-negative polymorphisms among Chinese in Taiwan were observed. These included Del with grossly intact RHD and weak RhD expression, genuinely RhD-negative with partial preservation of the RHD gene, and genuinely RhD-negative with total deletion of the RHD gene. A molecular study is warranted to clarify the mechanism responsible for the weak RHD gene expression in Del individuals.

Echocardiographic and hemodynamic determinations of the ventricular filling pattern in some teleost fishes.

The current concept of ventricular filling in elasmobranch and teleost fishes is that atrial contraction is the primary, if not the exclusive, determinant of ventricular filling. Recent echocardiographic and on-line hemodynamic data for elasmobranchs, however, have demonstrated a biphasic ventricular filling pattern, characterized by an early phase that occurs during ventricular relaxation and a late phase that follows atrial systole. This study reports echocardiographic and hemodynamic analyses of ventricular filling in three teleost genera (Paralabrax, Channa, Monopterus) having markedly different heart morphologies. Both the profiles of the atrioventricular pressure gradient in Paralabrax and the ventricular inflow velocity in all three genera indicate a biphasic ventricular filling pattern. Although the relative contribution of the early and late filling phases differed among the species studied, interspecific differences in heart structure did not obscure the biphasic pattern. Also, pericardiectomy did not affect the biphasic ventricular filling pattern in Paralabrax. The presence of biphasic filling in teleosts establishes a functional similarity with the elasmobranchs and, because the biphasic ventricular filling pattern predominates in higher vertebrates, suggests that this ventricular filling mechanism may be present in the entire subphylum Vertebrata.

Oxygen transport and cardiovascular responses to exercise in the yellowfin tuna Thunnus albacares.

Yellowfin tuna Thunnus albacares (1400-2175 g) instrumented with electrocardiogram electrodes and pre- and post-branchial catheters were subjected to incremental swimming velocity tests. Increasing velocity, from a minimal speed of 1.0 FLs-1, where FL is fork length, resulted in a 1.4-fold increase in heart rate (from 61.4 to 84.6 beats min-1), an elevated ventral-aortic blood pressure (from 10.8 to 12.2 kPa) and a decreased systemic vascular resistance. Relative branchial vascular resistance at minimal speed ranged from 24.4 to 40.0% of total vascular resistance and tended to increase with velocity. Yellowfin blood has a high oxygen-carrying capacity (16-18 ml O2 dl-1), and a low in vivo oxygen affinity (P50 = 5.3 kPa). Exercise caused a rise in arterial saturation (from 74 to 88%) and a decline in venous saturation (from 48 to 44%), resulting in a 1.3-fold increase in tissue oxygen extraction from the blood (arterial-venous oxygen content difference). Whereas arterial oxygen partial pressure (PO2) tended to increase with exercise, venous PO2 remained unchanged (approximately 5.3 kPa). The observed decrease in venous oxygen content was brought about by a lowered blood pH (from 7.80 to 7.76) and a large Bohr shift. Cardiac output and the increased blood oxygen extraction are estimated to have contributed nearly equally to the increased oxygen consumption during exercise. The large venous oxygen reserve still available to yellowfin tuna at maximal prolonged velocities suggests that the maximal oxygen delivery potential of the cardiovascular system in this species is not fully utilized during aerobic swimming. This reserve may serve other aerobic metabolic processes in addition to continuous swimming.

Heart rate and stroke volume contribution to cardiac output in swimming yellowfin tuna: response to exercise and temperature.

Cardiac performance in the yellowfin tuna (Thunnus albacares, 673-2470 g, 33-53 cm fork length, FL) was examined in unanesthetized fish swimming in a large water tunnel. Yellowfin tuna were fitted with either electrocardiogram electrodes or a transcutaneous Doppler blood-flow probe over the ventral aorta and exposed to changes in swimming velocity (range 0.8-2.9 FLs-1) or to an acute change in temperature (18-28 degrees C). Heart rates (fH) at +/-1 degree C (30-130 beats min-1) were lower on average than previous measurements with non-swimming (restrained) tunas and comparable with those for other active teleosts at similar relative swimming velocities. Although highly variable among individuals, fH increased with velocity (U, in FLs-1) in all fish (fH = 17.93U + 49.93, r2 = 0.14, P < 0.0001). Heart rate was rapidly and strongly affected by temperature (Q10 = 2.37). Blood flow measurements revealed a mean increase in relative cardiac output of 13.6 +/- 3.0% with exercise (mean velocities 1.23-2.10 FLs-1) caused by an 18.8 +/- 5.4% increase in fH and a 3.9 +/- 2.3% decrease in stroke volume. These results indicate that, unlike most other fishes, cardiac output in yellowfin tuna is regulated primarily through increases in fH. Acute reductions in ambient temperature at slow swimming velocities resulted in decreases in cardiac output (Q10 = 1.52) and fH (Q10 = 2.16), but increases in stroke volume (Q10 = 0.78). This observation suggests that the lack of an increase in stroke volume during exercise is not due to the tuna heart operating at maximal anatomical limits.

Mechanisms of venous return and ventricular filling in elasmobranch fish.

The current concept of ventricular filling in the elasmobranch fish (sharks and rays) is that a subambient pericardial pressure establishes a negative diastolic pressure gradient for the atrium and that ventricular end-diastolic volume is exclusively determined by atrial systole. In contrast, recent findings using echo-Doppler and digital imaging techniques have demonstrated two filling phases in the elasmobranch ventricle. In this study, simultaneous atrial and ventricular pressure measurements made on sharks with an open or intact pericardium establish that atrial pressure is above ventricular diastolic pressure until the onset of ventricular systole. A positive biphasic atrioventricular pressure gradient thus ensures ventricular filling during early diastole, as a result of ventricular relaxation, as well as during atrial systole. Although a reduction in pericardial pressure resulted in a decline in the atrial and ventricular pressure, a positive atrioventricular pressure gradient is conserved. The finding that atrial diastolic pressure is not lower than ventricular diastolic pressure, when combined with previous results showing that pericardial pressure is generally at or above ambient and that ventricular filling is biphasic, constitutes a strong body of evidence favoring the operation of a direct venous inflow as the mechanism by which the elasmobranch heart fills.

Nonmitochondrial oxygen utilization by rabbit blastocysts and surface production of superoxide radicals.

A minimum value for nonmitochondrial oxygen utilization in rabbit blastocysts at day 6 post coitum was determined by measuring oxygen consumption in the presence of cyanide. A microcathode oxygen electrode was used to monitor oxygen concentration continuously during blastocyst incubation in a newly devised culture medium, and the uninhibited blastocyst was found to consume 2.79 +/- 0.09 microliters O2 h-1 cm-2. This rate was reduced by 51% in the presence of 1 mmol KCN l-1. The addition of nitroblue tetrazolium to the cyanide-containing medium reduced net oxygen consumption by an additional 23% as the nitroblue tetrazolium was reduced to formazan. The ability of rabbit blastocysts to reduce nitroblue tetrazolium in the presence of cyanide was investigated using a spectrophotometric assay. Fractionation of blastocyst cells revealed that the enzymatic activity chiefly responsible for formazan production partitioned with the membrane/particulate fraction and could be solubilized by the detergent NP40. The enzyme was NAD(P)H-dependent, did not require divalent cations for activity, and appeared to contain no haeme moiety. The rate of formazan production in the spectrophotometric assay was markedly reduced by the presence of superoxide dismutase. The oxygen electrode and spectrophotometer data indicate that there is a superoxide-generating NAD(P)H oxidase on the blastocyst surface. Calculations based on the average surface area of rabbit blastocysts at day 6 show that these embryos can produce at least 8 nmoles of superoxide per embryo h-1. Potential deciduogenic effects of blastocyst-derived superoxide and its dismutated product, hydrogen peroxide, are discussed.

Digital image analysis of shark gills: modeling of oxygen transfer in the domain of time.

Digital radiographic imaging of blood circulation through leopard shark gills establishes a secondary lamellar transit time of 6.5 s. This duration, combined with estimates of cardiac output and hemoglobin-oxygen affinity, permits novel modeling of gill oxygen transfer in the time domain. The temporal model allows assessment of factors contributing to previously noted discrepancies between physiological and morphometric branchial oxygen conductance estimates. Lamellar transit time for shark blood is 20 times greater than human alveolar transit time, and thus correlates with a slower rate of hemoglobin-oxygen binding and a greater diffusion distance.

The phenotype and gene frequencies of human platelet specific antigens among Chinese in Taiwan.

Human platelet specific antigens (HPA) were serologically typed among 48 to 567 samples of blood from Chinese in Taiwan by using the mixed passive hemag-glutination method (MPHA). The prevalence found was: HPA-la (P1A1), > 99.9% (48/48); HPA-2b (Koa or Siba), 9.0% (51/567); HPA-3a (Baka), 84.8% (481/567); HPA-4a (Yukb), > 99.9% (567/567); HPA-4b (Yuka), 0.5% (3/567); HPA-5b (Br(a)), 32.6% (185/567); and Nak(a), 98.4% (558/567). The gene frequencies for these antigens were: HPA-la (P1A1), > 0.999; HPA-2b (Koa or Siba), 0.046; HPA-3a (Bak(a)), 0.611; HPA-4a (Yukb), 0.997; HPA-4b (Yuka), 0.003; HPA-5b (Br(a)), 0.179; and Nak(a), 0.874. The distribution of HPA's for Chinese differ from those for Caucasians and for Japanese. When compared to Caucasians, Chinese show a higher prevalence of HPA-la (P1A1), higher prevalence of HPA-5b (Br(a)), lower prevalence of HPA-2b (Koa or Siba) and lower prevalence of HPA-3a (Baka). Both Chinese and Japanese have a very high prevalence rate of HPA-la (P1A1), ie. close to 100%. However, the prevalence of HPA 2-2b (Koa or Siba) and HPA-4b (Yuka) is slightly lower in Chinese than in Japanese; and, the prevalence rate for HPA-3a (Baka) is slightly higher in Chinese than in Japanese.

Respiratory, Blood, and Heart Enzymatic Adaptations of Sebastolobus alascanus (Scorpaenidae; Teleostei) to the Oxygen Minimum Zone: A Comparative Study.

The scorpaenid fishes Sebastolobus alascanus and Scorpaena guttata have similar life styles but differ in their depth distributions: S. guttata lives in shallow water (< 180 m); adult S. alascanus occur predominantly on the upper continental slope (400-1200 m) where the oxygen minimum zone (OMZ) prevails and ambient temperature is much colder. Respiratory properties and the activities of heart-tissue enzymes of these species were compared to determine the effect of different thermal and ambient O2 regimens on metabolism. Measured over the appropriate habitat temperature ranges, the oxygen consumption (VO2) of S. alascanus is two to four times less than that of S. guttata. Correction for differences in habitat temperature accounted for over 50% of this reduction. The depth-related decrease in VO2 for these two benthic fishes is less than that observed for pelagic fishes. The VO2 of S. guttata decreases at O2 concentrations below 1 ml/l, whereas the VO2 of S. alascanus is regulated down to 0.3 ml/l. The ventilation frequency (Vf) of both species increases in progressive hypoxia; but at < 0.5 ml/l, the Vf of S. guttata declines, while that of S. alascanus does not. When measured at the same temperature, pH and CO2, the blood-O2 affinity of S. guttata is significantly lower than that of S. alascanus. The anaerobic/aerobic enzyme activity ratio of pyruvate kinase to citrate synthase, which correlates with the ability of heart tissue to tolerate hypoxia, is significantly higher for S. alascanus than S. guttata. Lactate dehydrogenase (LDH) activity in freshly collected S. alascanus is also significantly above that of specimens acclimated to normoxic water in the laboratory. Only the skeletal muscle isozyme of LDH (LDH-A) is present in the heart of S. alascanus, whereas S. guttata has both LDH-A and heart (LDH-B) isozymes. Data for metabolic rate, critical O2 tension, blood oxygen affinity, and heart metabolic enzyme profiles all show essential adaptations of S. alascanus for life in the OMZ.

Metabolic rate, heart rate, and tailbeat frequency during sustained swimming in the leopard shark Triakis semifasciata.

Heart rate, metabolic rate, and tailbeat frequency were simultaneously recorded from seven leopard sharks (Triakis semifasciata) during steady swimming at controlled speeds to evaluate the usefulness of heart rate as a measure of field metabolic rate. Heart rate was monitored by acoustic telemetry using a frequency modulated ECG transmitter. Metabolic rate was measured as oxygen consumption in a swimming tunnel respirometer. For instrumented sharks, mean resting oxygen consumption rate and heart rate were 105.3 +/- 35.6 (SE) mg O2.kg-1.h-1 and 36.6 +/- 1.8 (SE) beats.min-1, respectively. While swimming at the maximum sustained speed (0.84 +/- 0.03 lengths.s-1) for 30-60 min, these rates were 229.3 +/- 13.2 mg O2.kg-1.h-1 and 46.9 +/- 0.9 beats.min-1. Although a significant linear regression was obtained between metabolic rate and heart rate, a low overall correlation coefficient may result from the existence of separate individual regressions and confounding changes in stroke volume and/or arteriovenous oxygen difference. Heart rate was approximately as closely correlated with oxygen consumption rate as swimming speed was. A significant linear relationship was obtained between tailbeat frequency and swimming speed to speeds of 0.75 lengths.s-1.

Branchial blood flow distribution in the blue shark (Prionace glauca) and the leopard shark (Triakis semifasciata).

Electromagnetic flow (EMF) quantification of total cardiac stroke flow is not feasible for most elasmobranchs because the vascular anatomy precludes probe placement adjacent to the heart and proximal to all afferent branchial arteries (aba). Most previous studies report a fractional cardiac flow, made with the EMF probe placed on the ventral aorta between the innominate arteries and aba 3. Estimation of total cardiac stroke flow from such data requires a flow correction factor obtained by sacrificing the fish, and carrying out a two step in situ/in vitro flow calibration procedure which is based on tenuous assumptions. Ventral aortic blood flow measurements using the EMF techniques were carried out on large blue sharks, and radiographic imaging studies of ventral aortic and branchial blood flow were done on leopard sharks to verify previously estimated fractional cardiac stroke flow correction factors. The innominate flow fraction determined for both species in these studies are similar and agree with previous estimates for elasmobranchs. EMF data for Prionace show 38% of cardiac stroke flow goes to the innominate arteries, 23% into aba 3, 12% into aba 4, and 27% into aba 5. Radiographic analyses with Triakis reveal that 32% of its cardiac stroke volume flows into the innominate arteries which is in agreement with the in situ/in vitro fractional flow estimate (33%).

O2 tension, swimming-velocity, and thermal effects on the metabolic rate of the Pacific albacore Thunnus alalunga.

The oxygen consumption rates (VO2) of 9 albacore tuna, Thunnus alalunga (8.5-12 kg) were measured at sea in a swimming respirometer to determine the effects of relative swimming velocity, ambient O2 tension, and water temperature. Significant positive relationships were obtained between tail-beat frequency and relative speed and between relative speed and VO2. The albacore metabolic rate was not appreciably affected by exposure to water temperatures ranging from 13.5 degrees to 16.9 degrees C. Brief exposure to hyperoxia (200-400 mmHg), which was done to reduce the initial stress upon fish in the respirometer, did not affect VO2. Hypoxia (50-99 mmHg), however, did tend to reduce VO2 and affect swimming velocity.

Pericardial and vascular pressures and blood flow in the albacore tuna, Thunnus alalunga.

Pericardial, ventricular, and dorsal aortic pressures, and blood flow were measured in tabled, anesthetized albacore tuna, Thunnus alalunga (7.8-10.7 kg) captured at sea off Monterey, California (USA) during August 1985. Mean pericardial pressure was -10.0/-2.6 cm H2O (Systolic/Diastolic, [S/D]) and mean pericardial pulse pressure was 7.5. Heart rate averaged 87 beats per minute. Mean ventricular pressure was 97.0/12.9 cm H2O [S/D] and mean dorsal aortic pressure was 64. High ventricular and dorsal aortic pressures of albacore reflect the perfusion requirement of its metabolically active tissues and compensate for the energy losses resulting from blood flow through the gills to arterial heat exchanger to capillaries and again back to the venous heat exchanger. As in elasmobranchs, the remarkably high pericardial pulse pressure, large pericardial volume, and negative pericardial pressure in the albacore suggest that its pericardium is more rigid than that of most teleosts and thus facilitates cardiac filling. Published cardiac output values for most non-tunas, when corrected for body size differences, are less than the mean weight specific cardiac output of albacore (29.4 ml/kg per min, range 12.9-51.9).

The significance of the late fall in myocardial PCO2 and its relationship to myocardial pH after regional coronary occlusion in the dog.

After acute regional coronary occlusion, myocardial tissue PCO2, as measured by mass spectrometry, rises, reaches a peak, and then gradually falls. This late fall in myocardial tissue PCO2 could be due to (1) a gradual increase in tissue blood flow (and hence improved carbon dioxide washout), (2) a gradual consumption of tissue bicarbonate, (3) a gradual reduction in the production of carbon dioxide due to progressive cellular damage, or (4) an artifact caused by the continued presence of the mass spectrometer probe in the ischemic tissue. To determine which of these four mechanisms is responsible for the late fall in myocardial tissue PCO2, we subjected 27 anesthetized open-chest dogs to 3-hour occlusion of the left anterior descending coronary artery. Both myocardial tissue PCO2 and intramyocardial hydrogen ion concentration were measured in the myocardial segment supplied by the left anterior descending coronary artery. Ten dogs (group 1) were killed after the occlusion (occlusion I), and 11 dogs (group 2) underwent reocclusion (occlusion II) at the same site after a 45-minute period of reflow. Regional myocardial blood flow was measured periodically by the intramural injection of 127Xe. Changes in myocardial tissue PCO2 and hydrogen ion concentration were related to ultrastructural changes in the tissues adjacent to the myocardial tissue PCO2 probe. Regional myocardial blood flow remained unchanged throughout the 3-hour occlusion, ruling out increased carbon dioxide washout as a cause for its late fall. Tissue hydrogen ion concentration, as measured by a new lead glass electrode, correlated well with myocardial tissue PCO2, with the reduction in regional myocardial blood flow, and with ischemic damage assessed histologically. Myocardial hydrogen ion concentration also exhibited a late fall after the occlusion, from a peak of 199.8 +/- 27.8 nmol/liter to 91.9 +/- 12.1 nmol/liter (mean +/- SEM). This ruled out consumption of tissue bicarbonate as the cause for the late fall in myocardial tissue PCO2. Peak rise in myocardial tissue PCO2 after occlusion II (71.2 +/- 7.9 mm Hg) was significantly lower than peak myocardial tissue PCO2 after occlusion I (116.7 +/- 13.9 mm Hg, P less than 0.001). The difference between these latter two values, as well as the magnitude of fall in myocardial tissue PCO2 during occlusion I, related directly to the degree of histological damage observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of a dual-function pH and PCO2 in vivo sensor.

A newly developed, dual-function pH and PCO2 sensor was evaluated in this study. The sensors were placed in the femoral arteries of dogs anesthetized with sodium pentobarbital. Comparisons were made between systemic arterial pH and PCO2 measured using the sensor and those measured from blood samples drawn at 15-min intervals over a 7-h period using a bench instrument. The mean pH of the bench instrument measurements was 7.43. The mean difference of the sensor measurements from the bench instrument measurements for 207 comparisons was 0.0003 pH +/- 0.061 SD. The mean PCO2 of the bench instrument measurements was 40 mmHg. The mean difference of the sensor measurements from those of the bench instrument for 212 comparisons was -1.43 mmHg +/- 5.17 SD. The sensors performed equally well in the presence of metabolic or respiratory acidosis and alkalosis. The dual-function sensors evaluated in this study are useful for trend monitoring of pH and PCO2 over at least a 7-h period without recalibration. With improvement in the consistency of sensor construction, these sensors will be reliable in vivo sensing devices for blood pH and PCO2 and thus valuable research and clinical instruments.