Efficient myocyte gene delivery with complete cardiac surgical isolation in situ

BACKGROUND

Previously, we used cardiopulmonary bypass with incomplete cardiac isolation and antegrade administration of vector for global cardiac gene delivery. Here we present a translatable cardiac surgical procedure that allows for complete surgical isolation of the heart in situ with retrograde (through the coronary venous circulation) administration of both vector and endothelial permeabilizing agents to increase myocyte transduction efficiency.

METHODS

In 6 adult dogs the heart was completely isolated with tourniquets placed around both vena cavae and cannulas and all pulmonary veins. On cardiopulmonary bypass, the aorta and pulmonary artery were crossclamped, and the heart was isolated. Crystalloid cardioplegia at 4 degrees C containing 10(13) particles of adenovirus encoding LacZ and 15 microg of vascular endothelial growth factor was infused retrograde into the coronary sinus and recirculated for a total of 30 minutes. The dogs were then weaned from cardiopulmonary bypass and allowed to recover. With a catheter, 3 control dogs underwent retrograde infusion of the same cocktail without cardiac isolation or cardiopulmonary bypass.

RESULTS

Beta-galactosidase activities in the cardiopulmonary bypass group were several orders of magnitude higher in both the right and left ventricles when compared with those in the control group (P < .05). X-gal staining from the cardiopulmonary bypass group showed unequivocal evidence of myocyte gene expression globally in a significant proportion of cardiac myocytes. No myocyte gene expression was observed in the control group.

CONCLUSION

A novel cardiac surgical technique has been developed. This approach with cardiac isolation and retrograde delivery of vector through the coronary sinus results in efficient myocyte transduction in an adult large animal in vivo.

Relationship between race and mortality and morbidity after valve replacement surgery

BACKGROUND

Previous studies have shown that black race is an independent predictor of increased operative mortality after coronary artery bypass surgery. Given the higher incidence of hypertension and hypertension-associated left ventricular hypertrophy in blacks, we hypothesized that black race might be associated with increased risk of mortality and morbidity after aortic valve replacement (AVR) or mitral valve replacement (MVR). We could not identify a previous study that used a multivariable model to evaluate the association between race and operative mortality after AVR or MVR.

METHODS AND RESULTS

The Society of Thoracic Surgeons National Cardiac Database was used for a retrospective review of 3137 black and 46,249 white patients who underwent MVR alone or AVR alone from 1999 through 2002. Multivariate logistic regression was used to assess the association between race and mortality and 6 other adverse outcomes (stroke, renal failure, prolonged ventilation, prolonged postoperative stay, sternal infection, and bleeding) after adjustment for covariates. Unadjusted operative mortality for MVR only was 5.60% for blacks versus 6.18% for whites (OR 0.90 [95% CI 0.71 to 1.14]) and 4.60% for blacks versus 3.62% for whites for AVR only (OR 1.28 [95% CI 1.02 to 1.62]). After adjustment for other risk factors, black race was not a significant predictor of operative mortality after AVR or MVR; however, black race was associated with an increased risk of several complications: prolonged ventilation after AVR or MVR, postoperative stay >14 days after AVR or MVR, reoperation for bleeding after AVR, and postoperative renal failure after MVR. There was no significant association between race and the risk of stroke or deep sternal wound infection for either AVR or MVR.

CONCLUSIONS

In contrast to previously published results that defined race as an independent risk factor for operative mortality after coronary artery bypass surgery, race does not appear to be a significant predictor of operative mortality after isolated AVR or MVR; however, there is evidence of an association between race and certain complications.

Uniform scale-independent gene transfer to striated muscle after transvenular extravasation of vector

BACKGROUND

The muscular dystrophies exemplify a class of systemic disorders for which widespread protein replacement in situ is essential for treatment of the underlying genetic disorder. Somatic gene therapy will require efficient, scale-independent transport of DNA-containing macromolecular complexes too large to cross the continuous endothelia under physiological conditions. Previous studies in large-animal models have revealed a trade-off between the efficiency of gene transfer and the inherent safety of the required surgical and pharmacological interventions to achieve this.

METHODS AND RESULTS

Rats and dogs underwent limb or hemibody isolation via atraumatic tourniquet placement or myocardial isolation via heterotopic transplantation. Recombinant adenovirus (10(13) particles per kilogram) or recombinant adeno-associated virus (10(14) genome copies/kg) encoding the lacZ transgene was delivered through pressurized venous infusion without pharmacological mediators. Muscle exhibited almost 100% myofiber transduction in rats and dogs by X-galactosidase staining and significantly higher beta-galactosidase levels compared with nonpressurized delivery. No significant difference was seen in beta-galactosidase levels between 100- or 400-mm Hg groups. The <50-mm Hg group yielded inhomogeneous and significantly lower transgene expression.

CONCLUSIONS

Uniform scale- and vector-independent skeletal and cardiac myofiber transduction is facilitated by pressurized venous infusion in anatomic domains isolated from the central circulation without pharmacological interference with cardiovascular homeostasis. We provide the first demonstration of uniform gene transfer to muscle fibers of an entire extremity in the dog, providing a firm foundation for further translational studies of efficacy in canine models for human diseases.

The Canine Right Caudal and Accessory Lobe Pulmonary Veins: Revised Anatomical Description, Clinical Relevance, and Embryological Implications

Necropsy dissections were performed on nine dogs to provide an anatomical description of the right caudal and accessory lobe pulmonary veins. In all dogs, the pulmonary vein from the right caudal lung lobe initially paralleled the right caudal lung lobe bronchus, running cranially, medially, and ventrally. It diverged from the bronchus at the level of the pulmonary artery and bronchus of the accessory lung lobe. At this point, the pulmonary vein from the right caudal lung lobe coursed dorsal to the pulmonary artery and bronchus of the accessory lung lobe. Medial to the bronchus of the accessory lung lobe, it received the pulmonary vein from the accessory lung lobe on its ventral surface. Within the pericardium, this common venous trunk merged with the caudal aspect of the left atrium either with or immediately adjacent to the left caudal lobe pulmonary vein. These findings were corroborated during surgical dissection to achieve isolation of the heart in five dogs as part of an experimental study on intravascular gene delivery to the heart. These anatomical findings are relevant to clinical and experimental surgery and raise interesting questions about the embryological development of pulmonary veins in the dog.

Immunohistochemical localization of CYP1A, vitellogenin and Zona radiata proteins in the liver of swordfish (Xiphias gladius L.) taken from the Mediterranean Sea, South Atlantic, South Western Indian and Central North Pacific Oceans

Cytochrome P4501A (CYP1A) monoxygenase, vitellogenin (Vtg) and Zona radiata proteins (Zrp) are frequently used as biomarkers of fish exposure to organic contaminants. In this work, swordfish liver sections obtained from the Mediterranean Sea, the South African coasts (South Atlantic and South Western Indian Oceans) and the Central North Pacific Ocean were immunostained with antisera against CYP1A, Zrp, and Vtg. CYP1A induction was found in hepatocytes, epithelium of the biliary ductus and the endothelium of large blood vessels of fish from the Mediterranean Sea and South African waters, but not from the Pacific Ocean. Zrp and Vtg were immunolocalized in hepatocytes of male swordfish from the Mediterranean Sea and from South African waters. Plasma Dot-Blot analysis, performed in Mediterranean and Pacific specimens, revealed the presence of Zrp and Vtg in males from Mediterranean but not from Pacific. These results confirm previous findings about the potential exposure of Mediterranean swordfish to endocrine, disrupting chemicals and raise questions concerning the possible presence of xenobiotic contaminants off the Southern coasts of South Africa in both the South Atlantic and South Western Indian Oceans.

The Society of Thoracic Surgeons practice guideline series: transmyocardial laser revascularization

BACKGROUND

Patients with chronic severe angina refractory to medical therapy who cannot be completely revascularized with either percutaneous catheter intervention or coronary artery bypass graft surgery present clinical challenges. Transmyocardial laser revascularization, either as sole therapy or as an adjunct to coronary artery bypass graft surgery, may be appropriate for some of these patients. Although transmyocardial revascularization has consistently been demonstrated as an efficacious means of relieving angina, the mechanism of its effects are still debated, and criteria for the selection of patients for this novel therapy have not been adequately defined.

METHODS

We reviewed the available evidence to allow us to make recommendations for the appropriate therapeutic applications of transmyocardial revascularization following the format of the American Heart Association and the American College of Cardiology guidelines for diagnostic and therapeutic procedures. Our recommendations were classified as class I, IIA, IIB, or III. For each recommendation we defined the level of supporting evidence as A, B, or C.

RESULTS

We identified class I indications for transmyocardial revascularization as sole therapy and class IIA indications for transmyocardial revascularization as an adjunct to coronary artery bypass graft surgery with levels of evidence A and B, respectively.

CONCLUSIONS

Transmyocardial laser revascularization may be an acceptable form of therapy for selected patients: as sole therapy for a subset of patients with refractory angina and as an adjunct to coronary artery bypass graft surgery for a subset of patients with angina who cannot be completely revascularized surgically.

Myosin gene mutation correlates with anatomical changes in the human lineage

Powerful masticatory muscles are found in most primates, including chimpanzees and gorillas, and were part of a prominent adaptation of Australopithecus and Paranthropus, extinct genera of the family Hominidae. In contrast, masticatory muscles are considerably smaller in both modern and fossil members of Homo. The evolving hominid masticatory apparatus--traceable to a Late Miocene, chimpanzee-like morphology--shifted towards a pattern of gracilization nearly simultaneously with accelerated encephalization in early Homo. Here, we show that the gene encoding the predominant myosin heavy chain (MYH) expressed in these muscles was inactivated by a frameshifting mutation after the lineages leading to humans and chimpanzees diverged. Loss of this protein isoform is associated with marked size reductions in individual muscle fibres and entire masticatory muscles. Using the coding sequence for the myosin rod domains as a molecular clock, we estimate that this mutation appeared approximately 2.4 million years ago, predating the appearance of modern human body size and emigration of Homo from Africa. This represents the first proteomic distinction between humans and chimpanzees that can be correlated with a traceable anatomic imprint in the fossil record.

From controlled trials to clinical practice

OBJECTIVES

We sought to examine trends in the use and outcomes of transmyocardial revascularization (TMR) in community practice. We also identified important risk factors for TMR and compared outcomes of TMR combined with coronary artery bypass graft surgery (TMR + CABG) versus bypass alone in patients receiving incomplete revascularization.

BACKGROUND

Although it is approved for use as a stand-alone procedure, there are limited data on the outcomes of (TMR + CABG).

METHODS

We identified 3,717 patients receiving TMR at 173 U.S. hospitals participating in the Society of Thoracic Surgeons (STS) National Cardiac Database. Baseline characteristics and outcomes in these patients were compared with those from six published randomized TMR trials. Multivariable logistic regression was used to identify clinical risk factors for mortality with TMR. Risk-adjusted mortality was also compared for TMR + CABG relative to CABG only in patients not amenable to complete traditional revascularization.

RESULTS

Between January 1998 and December 2001, the number of STS hospitals performing TMR and total procedural counts increased markedly, driven predominately by more TMR + CABG cases. Overall mortality rates for TMR-alone and TMR + CABG were 6.4% and 4.2%, respectively. Operative risks were significantly higher in those patients with recent myocardial infarction, unstable angina, and depressed ventricular function. Among patients receiving incomplete revascularization, TMR + CABG was not associated with decreased mortality risk compared with CABG alone, adjusted odds ratio 1.11 (95% confidence interval 0.74 to 1.67).

CONCLUSIONS

The use of TMR, and in particular, TMR + CABG, is expanding in community practice. Although procedural risks are high, there is room for optimization through improved patient selection and timing of the procedure. Further studies of TMR + CABG are needed given its growing use and unclear benefits.

Cardiac surgery in African Americans

Retrospective and prospective randomized studies that provide information on the influence of race on the morbidity and mortality of cardiac surgical procedures are reviewed. We intentionally focus our attention on the specific outcomes of these procedures in African Americans because African Americans have a high incidence of all-cause cardiovascular mortality and a high prevalence of a number of risk factors associated with cardiovascular mortality. Furthermore, numerous studies have confirmed that blacks, as a function of race, lack equal access to diagnostic and therapeutic invasive cardiac procedures. Here we use the terms "black" and "African American" interchangeably. In this context we interpret both terms to refer to Americans of African descent. Similarly, we use the term "white" or "Caucasian" interchangeably to refer to Americans of European descent.

Cardiac surgery in nonagenarians and centenarians

BACKGROUND

Nonagenarians and centenarians are a rapidly growing segment of the population. No previous study has used a national database to compare outcomes in these patients to those of other groups undergoing cardiac surgical procedures.

STUDY DESIGN

The Society of Thoracic Surgeons National Database was used to review retrospectively 662,033 patients (5 patients more than 100 years of age; 1,092 patients 90 to 99 years; 59,576 patients 80 to 89 years; and 621,360 patients 50 to 79 years of age) who underwent cardiac surgical procedures from 1997 through 2000. These included 575,389 patients who had undergone coronary artery bypass grafting (CABG) only; 56,915 patients with CABG and concomitant mitral or aortic valve replacement or repair (CABG+VALVE); and 49,729 patients with mitral or aortic valve repair or replacement only (VALVE-only). A multivariate logistic regression model was developed to examine predictors of operative mortality in patients more than 90 years of age.

RESULTS

For CABG-only patients, operative mortality was 11.8% for patients more than 90 years of age, 7.1% for those 80 to 89 years, and 2.8% for those 50 to 79 years. The incidence of renal failure and prolonged ventilation was highest among patients more than 90 years of age (9.2% and 12.2%), compared with those 80 to 89 years (7.7% and 10.5%) or 50 to 79 years (3.5% and 6.0%). For VALVE-only patients and CABG+VALVE patients operative mortality for those more than 90 years of age was 11.4% and 12.0%, respectively, compared with 8.3% and 11.5% for those 80 to 89 years and 4.3% and 7.6% for those 50 to 79 years. The major preoperative risk factors for operative mortality among patients more than 90 years of age undergoing isolated CABG were as follows (C-index, 0.68): emergent/salvage: odds ratio, 2.26; 95% confidence interval, 1.38-3.69; preoperative intraaortic balloon pump: odds ratio, 2.79; 95% confidence interval, 1.47-5.32; renal failure: odds ratio, 2.08; 95% confidence interval, 1.12-3.86; peripheral vascular disease or cerebrovascular vascular disease: odds ratio, 1.39, 95% confidence interval, 0.96-2.02; mitral insufficiency: odds ratio, 1.50; 95% confidence interval, 0.93-2.41. Approximately 57% of the nonagenarians and centenarians lacked any of the first four risk factors and had an operative mortality of 7.2%.

CONCLUSIONS

Operative mortality and complication rates associated with cardiac surgical procedures are highest for nonagenarians and centenarians. But with careful patient selection, a majority of these patients have a lower risk of CABG-related mortality approaching that of younger patients.

Evidence of a high percentage of intersex in the Mediterranean swordfish (Xiphias gladius L.)

The first evidence of the presence of intersexuality in a wild population of Mediterranean swordfish (Xiphias gladius L.) is reported. Forty of 162 specimens (25%) macroscopically classified as males, showed the presence of female germ cells within the testes. In two specimens grouped previtellogenic oocytes were present; all the other specimens possessed single scattered previtellogenic oocytes. The presence of vitellogenin was demonstrated immunohistochemically in the liver of both intersex and normal males. These findings could be due to the exposure to oestrogen-mimicking substances.

Homograft aortic root replacement during pregnancy

Operative cardiac interventions have been performed on pregnant women with varying degrees of success since the late 1950s. Currently, reported maternal mortality for cardiac operations is similar to the mortality rate for nonpregnant female patients. However, fetal mortality remains high, at approximately 20%. Aortic root replacement with an aortic homograft in a 34-year-old pregnant woman with bacterial endocarditis at 18 weeks gestation is presented. Fetal echocardiography during and after bypass was employed.

Global cardiac-specific transgene expression using cardiopulmonary bypass with cardiac isolation

BACKGROUND

The available techniques for intravascular gene delivery to the heart are inefficient and not organ-specific. Yet, effective treatment of heart failure will likely require transgene expression by the majority of cardiac myocytes. To address this problem, we developed a novel cannulation technique that achieves efficient isolation of the heart in situ using separate cardiopulmonary bypass (CPB) circuits for the heart and body in dogs.

METHODS

The arterial inflow and venous effluent from the two circuits were physically isolated. The efficiency of separation was 98% to 99% in three preliminary experiments using Evans Blue dye-labeled albumin. In 6 dogs, the cardiac circuit was perfused with oxygenated crystalloid cardioplegia at 37 degrees C containing approximately 4 x 10(11) particles of an adenovirus encoding LacZ (AdCMVLacZ) with a perfusion pressure of 170 to 200 mm Hg for 15 minutes allowing virus to recirculate through the heart approximately 15 times. Cross-clamp time was 26 +/- 2 minutes and CPB time was 90 +/- 3 minutes.

RESULTS

Five animals survived and were euthanized at 7 days. Beta-galactosidase activities measured using a chemiluminescent assay were three orders of magnitude higher in all areas of the heart than in the liver. Histological analyses revealed heterogeneous X-Gal staining of myocytes in all areas of the myocardium.

CONCLUSIONS

Despite using a constitutive promoter, this technique yields relatively cardiac-specific transgene expression and is potentially translatable to clinical applications. Future studies will allow for further optimization of the conditions necessary for vector-mediated gene delivery to the heart.

Structural and functional properties of hemocyanin from Cyanagraea praedator, a deep-sea hydrothermal vent crab

Cyanagraea praedator (Crustacea: Decapoda: Brachyura) is an endemic species of the East Pacific Rise hydrothermal vents, living in the upper part of black smoker chimneys. Because we were seeking species that have made respiratory adaptations to the hydrothermal environment, we looked at Cyanograea hemocyanin (Hc) and determined its quaternary structure and the oxygen-binding properties in relation to temperature, pH, and lactate. C. praedator Hc is composed of dodecamers and hexamers, with dodecamers formed by the perpendicular association of two hexamers. The composition of these polymers was determined by electrophoresis and, for the first time, by electrospray mass spectrometry. Dodecamers and hexamers are composed of six subunits common to the two forms, with molecular mass ranging from 75,008 Da to 75,534 Da. In addition, we found two dodecamer-specific subunits, at 75,419 Da and 75,629 Da. The native hemocyanin possesses a high oxygen affinity (P(50) varies between 4 and 10 Torr at pH 7.5, 15 degrees C) and a large Bohr coefficient (Delta log P(50)/DeltapH approximately -1.8). Oxygen affinity is not affected by lactate or, surprisingly, temperature between 5 degrees C and 35 degrees C (DeltaH = 1.16 kJ/mol(1) 5-35 degrees C). Dialysis of native hemolymph elicited a significant increase in Hc-O(2) affinity (DeltaP(50) = 2.5 Torr at pH 7.5), an effect opposite the usual trend observed for crustacean hemocyanins. In this article these functional properties are interpreted in relation to characteristics of the environment.

The Batista procedure. Theoretical analysis and clinical implications

BACKGROUND

The Batista procedure leads to dramatic early improvement in left ventricular function in some patients and a worsening in function in others. The theoretical and actual clinical effects of the procedure on early postoperative left ventricular function remain controversial. The purpose of this study is to utilize an appropriate mathematical model to determine the effects of the Batista procedure on stroke volume and myocardial wall stress. Our hypothesis is that the preoperative end-systolic stress (ses) is an important predictor of early postoperative myocardial function after this procedure. A corollary is that an index related to ses may be useful in selecting patients for this procedure.

METHODS

An analysis of the Batista procedure is developed, based upon a spherical membrane model of the ventricle. This model shows how ventricular dilatation distorts the systolic and diastolic pressure-volume relations.

RESULTS

Dilatation initially improves ventricular performance; but further dilatation, beyond a critical value, produces an unstable state with sharply falling performance. For a ventricle operating significantly beyond the point of critical dilatation, our theoretical results suggest that the Batista procedure not only reduces myocardial stress but may improve stroke volume. The end-systolic stress, ses is an indicator of how close a ventricle is to the critical dilatation point.

CONCLUSIONS

There is a theoretical basis for the Batista procedure. Resection of myocardium not only decreases wall stress but may improve stroke volume for sufficiently dilated and depressed ventricles. Patients with markedly elevated end-systolic stress may benefit most from the Batista procedure.

Modulation of haemocyanin oxygen affinity: properties and physiological implications in a changing world

Crustacean haemocyanin oxygen affinity may be modified through changes in concentration of various inorganic and organic allosteric modulators. These may act in both positive and negative directions, increasing or decreasing haemocyanin oxygen affinity, and assist both in oxygen loading at the gills and oxygen release in the tissues. Inorganic ions, except for Mg(2+), do not normally influence cooperativity or the Bohr effect, whereas most of the organic modulators decrease cooperativity without affecting the Bohr coefficient. Several new findings on the influence of sulphide and thiosulphate are reviewed together with evidence for unidentified factors that decrease haemocyanin oxygen affinity. The physiological implications of all these findings are discussed in the context of maintaining a flexible response to a changing environment.

The effect of race on coronary bypass operative mortality

OBJECTIVES

The study was done to determine whether race is an independent predictor of operative mortality after coronary artery bypass graft (CABG) surgery.

BACKGROUND

Blacks are less frequently referred for cardiac catheterization and CABG than are whites. Few reports have investigated the relative fate of patients who undergo CABG as a function of race.

METHODS

The Society of Thoracic Surgeons National Database was used to retrospectively review 25,850 black and 555,939 white patients who underwent CABG-alone from 1994 through 1997. A multivariate logistic regression model was developed to determine whether race affected risk-adjusted operative mortality.

RESULTS

Operative mortality was 3.83% for blacks versus 3.14% for whites (unadjusted black/white odds ratio [OR] 1.23 [1.15-1.31]). Blacks were younger, more likely female, hypertensive, diabetic and in heart failure. Nonetheless, the influence of these and other preoperative risk factors on procedural mortality was quite similar in black and white patients. After controlling for all risk factors, race remained a significant independent predictor of mortality in the multivariate logistic model (adjusted black/white OR 1.29 [1.21, 1.38]). Proportionately, these differences were greatest among lower-risk patients. The race-by-gender interaction was significant (p<0.05). The unadjusted mortality for black men, 3.30% and white men, 2.64% differed significantly (p<0.05), whereas for women there was no difference (black, 4.49%; white 4.41%).

CONCLUSIONS

Black race is an independent predictor of operative mortality after CABG except for very high-risk patients. The difference in mortality is greatest for male patients and, though statistically significant, is small in absolute terms. Therefore, patients should be referred for CABG based on clinical characteristics irrespective of race.

Management of postoperative arrhythmias

Arrhythmias occur commonly in patients after cardiac surgery. Atrial fibrillation is the most common arrhythmia in the postoperative period; it accounts for significant morbidity to the patient and prolonged hospital stays, and it contributes significantly to the cost of hospitalization. It occurs more commonly in elderly men and in patients undergoing valvular procedures. Beta blockers are effective agents that keep patients from developing postoperative atrial fibrillation and help maintain ventricular rate control. Prophylaxis with antiarrhythmic agents such as amiodarone and sotalol and recently with atrial pacing have shown promise in recent randomized trials. Patients with atrial fibrillation that persists for longer than 48 hours appear to be at a greater risk for cerebroembolic events and should receive anticoagulation unless a contraindication exists. Although frequent premature ventricular contractions and nonsustained ventricular tachycardia (NSVT) occur frequently in patients after cardiac surgery, sustained ventricular tachycardia and ventricular fibrillation are rare and are associated with a poor prognosis. Polymorphic ventricular tachycardia may occur in the setting of myocardial ischemia, metabolic disturbances, and drug toxicities (including antiarrhythmic agents used to treat atrial fibrillation). Poor left ventricular function is a potent risk factor for sudden death in patients with NSVT. Patients with persistent NSVT and ischemic cardiomyopathy with left ventricular ejection fractions of less than 40% should undergo electrophysiologic testing. Conduction abnormalities that may be encountered in patients after cardiac surgery are rarely life threatening. Patients who have undergone valve replacement or repair are at higher risk of developing significant bradyarrhythmias that may require temporary pacing.

Angiogenesis in myocardial laser "revascularization"

The clinical and experimental data relevant to the theoretical mechanisms and clinical results of laser myocardial "revascularization" are reviewed. Both transmyocardial (TMR) and percutaneous (PMR) approaches are considered. Special attention is paid to the issue of TMR-induced angiogenesis. Both TMR and PMR result in a reduction in angina symptoms in patients refractory to conventional therapy and are likely to act through common pathways. TMR-induced angiogenesis appears to result from the up-regulation of vascular growth factors. However, the available data suggest that the angiogenic response is not a unique consequence of laser revascularization. Rather, the angiogenesis associated with TMR is likely to be a non-specific response of the myocardium to injury.

Acute type A aortic dissection: retrograde perfusion with left superior vena cava

Retrograde cerebral perfusion with hypothermic circulatory arrest confers additional cerebral protection during repair of type A aortic dissection. We present a 42-year-old man with acute type A aortic dissection and a persistent, left superior vena cava. Cannulation of the right and left superior vena cava is used for retrograde perfusion of both hemispheres with bilateral monitoring of electroencephalogram and somatosensory-evoked potentials during and after the hypothermic circulatory arrest interval.

Myocardial laser revascularization: the controversy and the data

The clinical and experimental data relevant to the theoretical mechanisms and clinical results of laser myocardial revascularization are reviewed. Both transmyocardial and percutaneous approaches are considered. Both types result in a reduction in anginal symptoms in patients refractory to conventional therapy and are likely to act through common pathways. The proximate mechanisms for the transmyocardial revascularization effect most likely relate to myocardial inflammation, secondary stimulation of growth factors, and denervation of the myocardium.

Angiogenesis in transmyocardial laser revascularization. A nonspecific response to injury

BACKGROUND

The mechanism of action of transmyocardial laser revascularization (TMR) is poorly understood. TMR has been shown to stimulate angiogenesis in porcine and canine myocardium.

METHODS AND RESULTS

We examined the possibility that angiogenesis also occurs in ovine myocardium and that it is a nonspecific tissue injury response. Five Dorset sheep underwent creation of transmyocardial channels of equal diameter in both the apical and basal regions of the left ventricle through the use of both CO2 laser in 1 region and a power drill in the alternate region of the same heart. All channels were closed at 4 weeks. Histology showed channel remnants composed of granulation tissue, fibrosis, and new vessels (NV). These changes were not distinguishable on the basis of the method of channel creation. The average diameter of the channels was similar (laser, 630 +/- 180 microns; drill, 750 +/- 280 microns) (P = NS). NV with smooth muscle media were seen within the channel remnant and immediately surrounding this region using Verhoeff-Van Gieson (elastic) stain. The densities of the NV within the channel remnants were similar (laser, 1.87 +/- 1.05 NV/high-power field [hpf]; drill, 1.92 +/- 1.09 NV/hpf; P = NS), and both were significantly greater than the density of vessels in remote regions, > 5 mm from the channel center (remote laser area, 0.09 +/- 0.28 NV/hpf; remote drill area, 0.04 +/- 0.21 NV/hpf; P = NS for remote areas, P < 0.001 for laser versus remote laser, P < 0.001 for drill versus remote drill area).

CONCLUSIONS

These findings demonstrate that the CO2 laser stimulates angiogenesis in normal ovine myocardium and suggest that this response represents a nonspecific reaction to tissue injury.

Transmyocardial laser revascularization fails to prevent left ventricular functional deterioration and aneurysm formation after acute myocardial infarction in sheep

OBJECTIVE

Transmyocardial laser revascularization is an investigational technique for revascularizing ischemic myocardium in patients with inoperable coronary arterial disease. This study tests the hypothesis that laser revascularization prevents left ventricular functional deterioration and aneurysm formation after acute anteroapical myocardial infarction.

METHODS

An ultrasonic ascending aortic flow probe and snares around the distal left anterior descending and second diagonal coronary arteries were placed in 26 Dorsett hybrid sheep. Ten to 14 days later, snared arteries were occluded to produce an anteroapical infarction of 23% of left ventricular mass. Before infarction 14 animals had 34 +/- 4 transmyocardial perforations in the area of the anticipated infarction made with a carbon dioxide laser. Twelve animals served as controls. Hemodynamic measurements and transdiaphragmatic quantitative echocardiograms were obtained before, immediately after, and 2, 5, and 8 weeks after infarction. Eighteen sheep completed the protocol.

RESULTS

All animals had large anteroapical left ventricular aneurysms with massive ventricular enlargement. Immediately after infarction the anterior wall became thinner and dyskinetic in all sheep. At 8 weeks aneurysmal size and shape were indistinguishable between groups. Two days after infarction, laser holes were filled with fibrin. At 5 and 8 weeks the infarct consisted of dense collagen, fibroblasts, scattered calcifications, myocyte fragments, neutrophils, macrophages, and no laser holes. There were no significant differences at any time between groups for cardiac pressures or output, ventricular volumes, ejection fraction, stroke work, and the stroke work-left ventricular end-diastolic pressure index.

CONCLUSION

Transmyocardial laser perforations do not revascularize acute myocardial infarction in sheep.

Physiology and biochemistry of the pseudobranch: an unanswered question?

The structure and function of the pseudobranch has long interested scientists, but its overall role has remained a mystery. Previous studies have attributed respiratory, endocrine, osmoregulatory and sensory roles to the pseudobranch, and the present review concentrates on new findings. Perfusion experiments on the pseudobranch of the rainbow trout (Oncorhynchus mykiss) using both erythrocyte suspensions and Ringer solution have shown that this organ is able to generate values for the respiratory quotient (RQ) greater than 1.0. The release of carbon dioxide into the perfusate was found to be largely independent of flow between perfusion rates of 120-190 microl/min and could be inhibited by acetazolamide (10(-5) M), indicating a role for carbonic anhydrase. Noradrenaline (10(-5) M) had no effect on oxygen consumption or carbon dioxide release of the pseudobranch. The rate of carbon dioxide release was also dependent on the pH of the pre-pseudobranch perfusate, carbon dioxide release being reduced at lower perfusate pH values. Based on the glucose balance of the isolated saline-perfused rainbow trout pseudobranch and on the enzyme profiles for the rainbow trout, cod, swordfish and deep-water grenadier pseudobranch, it is suggested that the pentose phosphate shunt might be a source of carbon dioxide, yielding the high RQ values found for this organ. Most evidence now available indicates that the pseudobranch is integrally linked with the choroid rete and the supply of oxygen to the retina of the fish eye.

Ecophysiological adaptations to dry thermal environments measured in two unrestrained Namibian scorpions, Parabuthus villosus (Buthidae) and Opisthophthalmus flavescens (Scorpionidae)

The daily changes in body temperature experienced by Parabuthus villosus (Buthidae), a scorpion found on the gravel plains around Gobabeb, Namibia, and by Opisthophthalmus flavescens (Scorpionidae), a dune-dwelling species from the same area, were measured under similar field conditions. Thermocouples implanted under the segments of the mesosoma measured maximum temperatures as high as 43 degrees C in the shade. Air temperatures reached a maximum of 33 degrees C during the daytime and a minimum of 12 degrees C at night. Very low metabolic rates compared with those of other nonsedentary invertebrates were recorded in both species; oxygen consumption ranged from 8 microL g-1 h-1 at 16 degrees C to 115 microL g-1 h-1 at 40 degrees C. A pulsed Doppler system was used to measure heart rate in situ in free-moving scorpions. At night, heart rate declined to about 4 beats min-1 in resting undisturbed scorpions. During daylight excursions and while scorpions hunted for food, heart rates as high as 180 beats min-1 were observed. Heart rate was linearly correlated with temperature in P. villosus, with a slope of 2.37 (Q10 = 2.18), but in O. flavescens only a limited correlation was observed, with a slope of 1.18 (Q10 = 1.69). In O. flavescens, heart rate showed hysteresis as body temperature rose during daylight and then decreased during the late afternoon and evening; the reverse was observed in P. villosus. In both species, haemocyanin-oxygen affinity was independent of temperature, with a higher oxygen affinity and a larger pH sensitivity in O. flavescens. The Q10's of oxygen consumption and heart rate are quite different in O. flavescens but not as different in P. villosus. Although changes in the cardiovascular system, such as stroke volume, may also play a role in meeting increased oxygen demand, the features of the haemocyanin oxygen transport system, such as the absence of temperature sensitivity and a marked pH sensitivity, can also influence the maintenance of VO2 under temperature stress. The differences in the normal thermal habitats of the two species may be used to explain the distinctions between the evolved physiological responses to temperature increase shown by the two species.

Autogenously lined skeletal muscle ventricles in circulation. Up to nine months' experience

Skeletal muscle ventricles were constructed in fifteen dogs. After a delay period of 4 weeks the skeletal muscle ventricles were connected to the descending thoracic aorta with a polytetrafluoroethylene bifurcation graft (Gore-Tex bifurcation graft, W.L. Gore & Associates, Inc., Elkton, Md.). The aorta was ligated between the two limbs of the graft so that there was obligatory blood flow through the skeletal muscle ventricle. Nine skeletal muscle ventricles were lined with autogenously derived tissue, either pleura or pericardium, whereas six had no specific lining other than an induced fibrous reaction. The skeletal muscle ventricles were activated to contract during cardiac diastole. Aortic diastolic counterpulsation was achieved in all dogs, with ten surviving from 1 week to beyond 9 months. Thrombus eventually developed in all but three of the skeletal muscle ventricles, but no dog had clinical evidence of thromboemboli. The three thrombus-free skeletal muscle ventricles were lined with pleura, including the animal surviving beyond 9 months. These results indicate that canine skeletal muscle can provide aortic diastolic counterpulsation for 9 months without clinically apparent thromboembolic complications.

Skeletal muscle bioenergetics during frequency-dependent fatigue

The bioenergetic correlates of skeletal muscle fatigue were assessed in vivo with phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy. After surgical construction of latissimus dorsi muscle ventricles, seven beagles underwent 31P-NMR spectroscopy during 12-min exercise protocols at 25- and 85-Hz stimulation frequencies and during both isovolumetric and dynamic contractions. Exercise at 85 Hz was associated with significantly greater fatigue than exercise at 25 Hz. At both frequencies, the onset of exercise was associated with a marked increase in inorganic phosphate (Pi) and a decrease in phosphocreatine (PCr). As the muscle fatigued at 85 Hz but not at 25 Hz, the phosphorus spectra returned to near baseline with a decrease in Pi and increase in PCr. For a given amount of force generated, the Pi-to-PCr ratio was higher for dynamic contractions than for isovolumetric contractions. This study indicates that high-frequency fatigue is unlikely to result from the direct effects of high-energy phosphate metabolism and that contractions producing external work consume more metabolic energy than equally forceful isometric contractions.

Reversible hexadimethrine-induced alterations in glomerular structure and permeability

Female Munich-Wistar rats received hexadimethrine (HDM) i.v. until the onset of proteinuria (PEAK)--a period of not more than 30 min. There were four experimental groups: C (control), H (HDM only), HH (HDM and heparin), and HHD (identical to HH but with dextran clearances measured). Rats in groups HH and HHD received a heparin bolus after the PEAK period, whereas rats in group H did not. HDM led to dramatic increases in both albumin and IgG excretion. Glomerular filtration rate and renal plasma flow rate were reduced by 30 to 50% after HDM infusion. Neutral dextran clearances for radii greater than 30 A were elevated during the PEAK period, and, concurrently, there was extensive intraglomerular microthrombosis, obliteration of foot processes, and disruption of filtration slit diaphragms. One hour later, glomerular filtration rate, renal plasma flow rate, dextran clearances, and proteinuria returned to baseline in groups HH and HHD but not in group H. Recovery in heparin-treated rats was associated with reversal of HDM-associated morphological alterations. Membrane pore-size parameters calculated from the dextran clearances indicate that HDM leads to a detect in glomerular size-selectivity. The facts that maximal albuminuria tended to precede maximal excretion of IgG and that increases in albumin excretion were proportionately greater than those of dextran or IgG suggest that HDM also leads to a time-dependent defect in glomerular charge-selectivity.

Performance of skeletal muscle ventricles: effects of ventricular chamber size

Skeletal muscle ventricles were constructed in 12 dogs. In one group of dogs (n = 7) the skeletal muscle ventricles were constructed around a 17 ml Teflon mandrel, and in the other group (n = 5) a 45 ml mandrel was used. Use of the larger mandrel resulted in an increase in compliance and greater stroke work over the physiologic range of preloads and afterloads. With the larger mandrel, stroke work consistently exceeded normal canine stroke work at physiologic filling pressures.

Functional right-heart replacement with skeletal muscle ventricles

Skeletal muscle ventricles were constructed from the latissimus dorsi in seven dogs. All skeletal muscle ventricles underwent a vascular delay period followed by 4-7 weeks of electrical preconditioning. In group 1 (n = 5), the skeletal muscle ventricle was used to replace native right-heart function. Venous return from the superior and inferior venae cavae was directed to the skeletal muscle ventricle with outflow directed to the pulmonary artery. In group 2 (n = 2), the skeletal muscle ventricle was used for partial bypass of the right heart. In both groups, right-heart bypass was continued for as long as 8 hours. In group 1 after 4 hours of continuous complete right-heart bypass, stroke work was 163 +/- 63% of canine right ventricular stroke work. Skeletal muscle ventricle output was 1.14 +/- 0.02 l/min, central venous pressure was 13 +/- 1.5 mm Hg, and systemic systolic blood pressure was 95 +/- 9 mm Hg. Skeletal muscle ventricles are capable of performing the work of the right heart with near-physiological filling pressures.

Skeletal muscle ventricles: improved performance at physiologic preloads

We attempted to construct skeletal muscle ventricles (SMVs) so that they would develop optimal stroke work at physiologic preloads of 5 to 15 mm Hg. Thirty-one SMVs were constructed in mongrel dogs. The effects of electrical preconditioning with 2 Hz continuous and 25 Hz burst patterns were evaluated, as well as the application of passive stretch to the muscle fibers during preconditioning. We evaluated the stroke work developed by these SMVs at afterloads of 30 mm Hg and 80 mm Hg in vivo, using a mock circulation device. During mock circulation studies, the SMVs were stimulated via the thoracodorsal nerve with either a 25 Hz or 85 Hz burst pattern. SMVs with 2 Hz preconditioning developed significantly higher stroke work than SMVs with 25 Hz preconditioning under all conditions of afterload, preload, and stimulation frequency (p less than or equal to 0.001). Under these conditions, for the 2 Hz preconditioned SMVs, passive stretch during preconditioning resulted in a further significant increase in developed stroke work (p less than 0.05). For these SMVs, with an 85 Hz stimulation frequency, stroke work averaged 410% of canine RV stroke work, and 59% of canine LV stroke work at physiologic preloads and afterloads.

Antirheumatic agents: CNS toxicity and its avoidance

Altered drug metabolism, polypharmacy, multiple diseases, and errors in self-medication are all factors seen in the elderly which increase the risk for side effects from antirheumatic drug therapy. The geriatric presentation of central nervous system (CNS) toxicity, which is common yet frequently overlooked, is reviewed as it pertains to various drugs commonly used to treat rheumatic disease. Practical advice on avoiding common pitfalls in antirheumatic prescribing is offered.

Long-term neurostimulation of skeletal muscle: its potential for a tether-free biologic cardiac assist device

Skeletal muscle has a tremendous capacity to adapt. This adaptive phenomenon is seen perhaps to the greatest extent when skeletal muscle is subjected to chronic low frequency stimulation via the motor nerve. There is a decrease in glycolytic enzymes and an increase in oxidative enzymes, as well as a change in the contractile proteins and an increase in the mitochondrial volume fraction of the muscle fiber. These adaptive changes result in a muscle that is considerably more fatigue-resistant. Specifically herein, we report on a pneumatic aortic counterpulsator device powered by skeletal muscle. These muscle pumps functioned continuously and pumped blood effectively in tether-free animals for several weeks.

Acute, fatal illness in cattle exposed to boron fertilizer

Twenty-six cows died after accidental exposure to boron fertilizer. Cows developed diarrhea, weakness, ataxia, signs of depression, and died, usually within a few hours. Seizure-like behavior was noticed in 2 cows, and 2 were suspected of aborting. High boron concentrations in tissues from affected cows confirmed ingestion of an appreciable amount of boron fertilizer. In an attempt to confirm the diagnosis of boron poisoning, boron fertilizer was administered to goats. A kid goat given 3.6 g of fertilizer/kg of body weight developed clinical signs similar to those seen in the cattle. Boron compounds such as sodium borate and boric acid have been considered generally nontoxic, and reports of livestock toxicosis are uncommon. This case report suggests that these compounds may be palatable under certain circumstances leading to ingestion of toxic quantities.

Skeletal muscle ventricles as a potential right heart assist or substitute

Skeletal muscle ventricles (SMV) were constructed from canine latissimus dorsi muscle and chronically stimulated to pump fluid within a totally implantable mock circulation device. They were stimulated to contract at either 95/min (N = 7) or 54/min (N = 4). The preload was chronically maintained at 20 mmHg. After 1 month of continuous pumping the SMV were capable of generating a stroke work of 0.134 X 10(6) ergs and power output of 0.021 watts, representing 61% and 42% of the stroke work and power output of the native canine right ventricle, respectively.

Physiological adaptations of the intertidal rockpool teleost Blennius pholis L., to aerial exposure

Gas exchange, metabolism, ventilation, circulation and acid-base balance in water and air were investigated in Blennius pholis. The rates of gas exchange in water and air were similar with the RQ remaining around 0.8. Aerial gas exchange was equally divided between the head/gills and the tail region. Ventilatory adaptations involved a reduction in rate in air and the mode of ventilation changed from flow-through to tidal, with closed opercula. A transient bradycardia developed on transition to air before heart frequency (fH) returned to aquatic levels. During aerial exposure PvCO2 rose only by 1 Torr with a concomitant decrease in pH of 0.19 pH-units. At the same time a metabolic acidosis was observed which could not be fully accounted for by the formation of lactic acid in the blood, although tissue lactate levels did not change significantly. No histological evidence was found for the presence of carbonic anhydrase in the epithelial cells of the skin or the oesophagus to aid aerial CO2 excretion. Inhibition of CA activity by addition of methazolamide to blood, however, caused PvCO2 to rise by 3 Torr and pHv to decrease by 0.4 pH unit. It is concluded that B. pholis is physiologically well adapted to aerial exposure through adjustments in ventilation and circulation and that erythrocytic carbonic anhydrase plays a major role in CO2 transfer.

Heteroporous model of glomerular size selectivity: application to normal and nephrotic humans

A heteroporous model of the glomerular filtration barrier was developed and used to interpret dextransieving data in healthy volunteers (normal controls), in patients with nephrotic range proteinuria (grouped as grades I-III, according to severity), and in a group of previously nephrotic patients whose proteinuria was in remission ("resolved controls"). Several hypothetical pore-size distributions were compared in terms of their ability to describe the selective increases in the fractional clearance of large dextrans observed with increasing severity of proteinuria. The most successful model examined was based on the assumption that the major portion of the capillary wall functions as an isoporous membrane, but that a small fraction of the filtrate passes through pores that are unable to discriminate among dextrans of different sizes. The value of the membrane parameter that reflects the relative importance of the nonselective pores was found to increase in parallel with the fractional clearance of immunoglobulin G; it increased progressively in going from normal controls to resolved controls to grades I-III nephrotics. The observed patterns of protein excretion could not, however, be explained entirely by a loss of glomerular size selectivity. Variations in membrane selectivity on the basis of molecular charge and/or molecular configuration are also likely to have been important.

Oxygen binding in blood of Xenopus laevis (Amphibia) and evidence against Root effect

Blood oxygen binding was examined in the amphibian, Xenopus laevis, with the particular aim of determining whether the O2 capacity is diminished when blood pH is lowered, which is known as the Root effect in blood of some fishes. Hemoglobin-bound O2 concentration, [O2Hb], was determined by the Lex-O2-Con technique, and both total hemoglobin, [Hb]tot, and Met-hemoglobin, [MetHb], contents were measured spectrophotometrically. From these measurements were calculated the oxygen capacity, O2cap, and the content of active hemoglobin, [Hb]act, i.e. the difference between [Hb]tot and [MetHb]. The main finding was the independence of the ratio of O2cap/[Hb]act on pH, when differences between samples in [Hb]tot and the presence of MetHb, which was particularly pronounced at low pH, where properly accounted for. It is concluded that the Root effect does not exist in blood of the amphibian Xenopus laevis.

Modulation of haemocyanin oxygen affinity in the intertidal prawn Palaemon elegans (Rathke)

The modulation of haemocyanin oxygen affinity was studied at 10 degrees C in the blood of the intertidal prawn Palaemon elegans. On increasing the L-lactate concentration in dialysed blood from 0 to 9.1 mM, P50 decreased from 27 to 11 torr at pH 7.8. Undialysed blood exhibited a higher oxygen affinity than dialysed blood with the same lactate concentration indicating the presence of an unidentified factor which increased oxygen affinity. After dialysis both winter and summer blood exhibited the same intrinsic oxygen affinity and response to lactate. The response of oxygen affinity to lactate was exponential, low concentrations of lactate (0-5 mM) markedly increasing oxygen affinity. The lactate effect in dialysed blood expressed as delta logP50/delta log[L-lactate] was -0.56 at pH 7.8 and -0.63 at pH 7.4. The effect of lactate on oxygen affinity, delta P50, was similar in dialysed and whole blood. The effect of the unidentified factor (delta P50, between dialysed and undialysed blood) at the same lactate concentration was 13.1 and 15.1 torr at pH 7.8 in winter and summer blood, respectively. At pH 7.4 the delta P50 was 38 torr for both summer and winter blood. Differences in oxygen affinity between blood collected in summer and winter could be explained by differences in blood lactate concentrations.

Root effect induced by CO2 and by fixed acid in the blood of the eel, Anguilla anguilla

The decrease in O2 capacity with decreasing pH (Root effect) was studied in eel blood in which pH was varied in the range 5 to 9 both by addition of acid or base (fixed-acid Root effect) and by varying PCO2 (CO2 Root effect). Hemoglobin-bound oxygen was independent of PO2 above 150 Torr and was thus referred to as O2 capacity (O2cap). At pH below 8.5, O2cap decreased sigmoidally with pH to attain, below a pH of 6.0, a value which, at 15 degrees C, averaged about 48% of the maximum O2cap, measured above pH 8.5. At 25 degrees C, this reduction was even more pronounced. For pH above about 6.5 the decline in O2cap was independent of whether the pH was diminished by CO2 or by fixed acid. Below pH 6.5, however, the CO2 Root effect exceeded the fixed-acid Root effect. Below pH of 7.5, the buffer value of true plasma increased with declining pH and attained a negative value in the range where CO2 exerted a specific action on the Root effect.

Biophysical basis of glomerular permselectivity

The mammalian glomerular capillary wall normally restricts the transmural passage of plasma proteins while offering little resistance to the filtration of water and small solutes. The basis for this selectivity has been explored extensively in recent years, through clearance measurements of endogenous (mainly albumin, transferrin, and immunoglobulins) and exogenous (horseradish peroxidase) proteins, and a variety of nonprotein polymers such as dextrans and polyvinylpyrrolidone. In conjunction with efforts to localize particulate and soluble tracers by high resolution ultrastructural techniques, such measurements have now made it possible to define the determinants of the glomerular filtration of macromolecules in terms of discrete structural barriers as well as such biophysical influences as hemodynamics and the molecular size- and charge-selective characteristics of the capillary wall. These experimental approaches have been aided greatly by the development of theoretical models that enable investigators to describe macromolecular filtration in terms of hydrodynamic principles applied to isoporous membranes. Although the initial models failed to consider the important role of membrane fixed negative-charge characteristics in influencing protein filtration, this shortcoming has led to the recent introduction of a theoretical model that also takes this factor into consideration. The aim of this brief review is to summarize these various theoretical approaches to the understanding of glomerular permselectivity and, wherever possible, to cite specific tests of these theories based on experimental studies in humans and animals.

Glomerular charge alterations in human minimal change nephropathy

A theoretical model of charge and size selectivity for the glomerulus has been applied to human data. Using previously published values for GFR, renal plasma flow, systemic oncotic pressure, and fractional clearances of neutral dextrans, albumin, salivary amylase, and transferrin, membrane parameters describing the glomerular barrier were determined for normal individuals under control conditions and during lysine infusion (which retards tubule protein reabsorption), and for patients with minimal change nephropathy (MCN). To permit the estimation of membrane charge from fractional clearances, molecular charge values for human transferrin (-9.4 Eq/mole) and human salivary amylase (-4.1) were determined by measuring electrophoretic mobilities of these proteins in polyacrylamide gels. Assuming no large changes in the transmural hydraulic pressure difference (delta P), the glomerular ultrafiltration coefficient (Kf, the product of hydraulic permeability and capillary surface area) was calculated to be reduced by greater than 50% in MCN. The effective pore radius (approximately 55 A) is virtually unaltered in MCN, suggesting that the decline in Kf is due to a reduced number of pores. The degree of albuminuria observed in MCN is attributable to an approximately 50% reduction in the concentration of fixed negative charges in the glomerular capillary wall. The concentrations of fixed charges calculated from albumin data in normal individuals (140 to 160 mEq/liter) and in patients with MCN (60 to 90 mEq/liter) are insensitive to the assumed values of delta P.

Buffering and CO2 dissociation of body fluids in the pupa of the silkworm moth, Hyalophora cecropia

To assess the extent of CO2 storage and the changes in the acid-base status that occur during intermittent CO2 excretion in insects, total CO2 content and pH were measured in whole body homogenates (= tissue homogenates) of Hyalophora cecropia pupae at various levels of Pco2 at 20 degrees C. The CO2 dissociation curve, i.e. plot of total CO2 content in tissue homogenates against Pco2 was nearly linear in the Pco2 range from 15 to 50 Torr, the mean slope being 0.138 mM . Torr-1. This value, which constitutes the effective CO2 solubility, was nearly three times the physical solubility in the tissue homogenate which averaged 0.053 mM . Torr-1. Plots of bicarbonate concentration in whole body tissue water against pH yielded an average buffer value of 75 mmol . pH-1 per kg tissue water. The high buffer value results in a small pH change, about 0.04 units, when Pco2 varies between 20 and 45 Torr in the respiratory cycle. The absolute value of mean tissue pH at Pco2 = 30 Torr predicted from the buffer line, 6.57, agrees well with direct measurement in hemolymph samples.