Invasive or More Direct Measurements Can Provide an Objective Early-Stopping Ceiling for Training Deep Neural Networks on Non-invasive or Less-Direct Biomedical Data.

Early stopping is an extremely common tool to minimize overfitting, which would otherwise be a cause of poor generalization of the model to novel data. However, early stopping is a heuristic that, while effective, primarily relies on ad hoc parameters and metrics. Optimizing when to stop remains a challenge. In this paper, we suggest that for some biomedical applications, a natural dichotomy of invasive/non-invasive measurements, or more generally proximal vs distal measurements of a biological system can be exploited to provide objective advice on early stopping. We discuss the conditions where invasive measurements of a biological process should provide better predictions than non-invasive measurements, or at best offer parity. Hence, if data from an invasive measurement are available locally, or from the literature, that information can be leveraged to know with high certainty whether a model of non-invasive data is overfitted. We present paired invasive/non-invasive cardiac and coronary artery measurements from two mouse strains, one of which spontaneously develops type 2 diabetes, posed as a classification problem. Examination of the various stopping rules shows that generalization is reduced with more training epochs and commonly applied stopping rules give widely different generalization error estimates. The use of an empirically derived training ceiling is demonstrated to be helpful as added information to leverage early stopping in order to reduce overfitting.

Improvement of automated analysis of coronary Doppler echocardiograms.

Coronary artery disease is the leading cause of heart disease, and while it can be assessed through transthoracic Doppler echocardiography (TTDE) by observing changes in coronary flow, manual analysis of TTDE is time consuming and subject to bias. In a previous study, a program was created to automatically analyze coronary flow patterns by parsing Doppler videos into a single continuous image, binarizing and separating the image into cardiac cycles, and extracting data values from each of these cycles. The program significantly reduced variability and time to complete TTDE analysis, but some obstacles such as interfering noise and varying video sizes left room to increase the program's accuracy. The goal of this current study was to refine the existing automation algorithm and heuristics by (1) moving the program to a Python environment, (2) increasing the program's ability to handle challenging cases and video variations, and (3) removing unrepresentative cardiac cycles from the final data set. With this improved analysis, examiners can use the automatic program to easily and accurately identify the early signs of serious heart diseases.

Single-cell RNA-sequencing analysis of aortic valve interstitial cells demonstrates the regulation of integrin signaling by nitric oxide.

Calcific aortic valve disease (CAVD) is an increasingly prevalent condition among the elderly population that is associated with significant morbidity and mortality. Insufficient understanding of the underlying disease mechanisms has hindered the development of pharmacologic therapies for CAVD. Recently, we described nitric oxide (NO) mediated S-nitrosylation as a novel mechanism for preventing the calcific process. We demonstrated that NO donor or an S-nitrosylating agent, S-nitrosoglutathione (GSNO), inhibits spontaneous calcification in porcine aortic valve interstitial cells (pAVICs) and this was supported by single-cell RNA sequencing (scRNAseq) that demonstrated NO donor and GSNO inhibited myofibroblast activation of pAVICs. Here, we investigated novel signaling pathways that are critical for the calcification of pAVICs that are altered by NO and GSNO by performing an in-depth analysis of the scRNA-seq dataset. Transcriptomic analysis revealed 1,247 differentially expressed genes in pAVICs after NO donor or GSNO treatment compared to untreated cells. Pathway-based analysis of the differentially expressed genes revealed an overrepresentation of the integrin signaling pathway, along with the Rho GTPase, Wnt, TGF-ß, and p53 signaling pathways. We demonstrate that ITGA8 and VCL, two of the identified genes from the integrin signaling pathway, which are known to regulate cell-extracellular matrix (ECM) communication and focal adhesion, were upregulated in both in vitro and in vivo calcific conditions. Reduced expression of these genes after treatment with NO donor suggests that NO inhibits calcification by targeting myofibroblast adhesion and ECM remodeling. In addition, withdrawal of NO donor after 3 days of exposure revealed that NO-mediated transcriptional and translational regulation is a transient event and requires continuous NO exposure to inhibit calcification. Overall, our data suggest that NO and S-nitrosylation regulate the integrin signaling pathway to maintain healthy cell-ECM interaction and prevent CAVD.

Loss of Jagged1 in mature endothelial cells causes vascular dysfunction with alterations in smooth muscle phenotypes.

BACKGROUND: Notch signaling is an evolutionarily conserved pathway that functions via direct cell-cell contact. The Notch ligand Jagged1 (Jag1) has been extensively studied in vascular development, particularly for its role in smooth muscle cell maturation. Endothelial cell-expressed Jag1 is essential for blood vessel formation by signaling to nascent vascular smooth muscle cells and promoting their differentiation. Given the established importance of Jag1 in endothelial cell/smooth muscle crosstalk during development, we sought to determine the extent of this communication in the adult vasculature for blood vessel function and homeostasis. METHODS: We conditionally deleted Jag1 in endothelial cells of adult mice and examined the phenotypic consequences on smooth muscle cells of the vasculature. RESULTS: Our results show that genetic loss of Jag1 in endothelial cells has a significant impact on Notch signaling and vascular smooth muscle function in mature blood vessels. Endothelial cell-specific deletion of Jag1 causes a concomitant loss of JAG1 and NOTCH3 expression in vascular smooth muscle cells, resulting in a transition to a less differentiated state. Aortic vascular smooth muscle cells isolated from the endothelial cell-specific Jag1 deficient mice retain an altered phenotype in culture with fixed changes in gene expression and reduced Notch signaling. Utilizing comparative RNA-sequence analysis, we found that Jag1 deficiency preferentially affects extracellular matrix and adhesion protein gene expression. Vasoreactivity studies revealed a reduced contractile response and impaired agonist-induced relaxation in endothelial cell Jag1-deficient aortas compared to controls. CONCLUSIONS: These data are the first to demonstrate that Jag1 in adult endothelial cells is required for the regulation and homeostasis of smooth muscle cell function in arterial vessels partially through the autoregulation of Notch signaling and cell matrix/adhesion components in smooth muscle cells.

Direct Interstitial Decongestion in an Animal Model of Acute-on-Chronic Ischemic Heart Failure.

Removal of excess fluid in acute decompensated heart failure (ADHF) targets the intravascular space, whereas most fluid resides in the interstitial space. The authors evaluated an approach to interstitial decongestion using a device to enhance lymph flow. The device was deployed in sheep with induced heart failure (HF) and acute volume overload to create a low-pressure zone at the thoracic duct outlet. Treatment decreased extravascular lung water (EVLW) volume (mL/kg) (-32% ± 9%, P = 0.029) compared to controls (+46% ± 9%, P = 0.003). Device-mediated thoracic duct decompression effectively reduced EVLW. Human studies may establish device-based interstitial decongestion as a new ADHF treatment.

Nitric oxide prevents aortic valve calcification by S-nitrosylation of USP9X to activate NOTCH signaling.

Calcific aortic valve disease (CAVD) is an increasingly prevalent condition, and endothelial dysfunction is implicated in its etiology. We previously identified nitric oxide (NO) as a calcification inhibitor by its activation of NOTCH1, which is genetically linked to human CAVD. Here, we show NO rescues calcification by an S-nitrosylation-mediated mechanism in porcine aortic valve interstitial cells and single-cell RNA-seq demonstrated NO regulates the NOTCH pathway. An unbiased proteomic approach to identify S-nitrosylated proteins in valve cells found enrichment of the ubiquitin-proteasome pathway and implicated S-nitrosylation of USP9X (ubiquitin specific peptidase 9, X-linked) in NOTCH regulation during calcification. Furthermore, S-nitrosylated USP9X was shown to deubiquitinate and stabilize MIB1 for NOTCH1 activation. Consistent with this, genetic deletion of Usp9x in mice demonstrated CAVD and human calcified aortic valves displayed reduced S-nitrosylation of USP9X. These results demonstrate a previously unidentified mechanism by which S-nitrosylation-dependent regulation of a ubiquitin-associated pathway prevents CAVD.

Effects of intravenous administration of perzinfotel, fentanyl, and a combination of both drugs on the minimum alveolar concentration of isoflurane in dogs.

OBJECTIVE-To determine the effects of IV administration of perzinfotel and a perzinfotel-fentanyl combination on the minimum alveolar concentration (MAC) of isoflurane in dogs. ANIMALS-6 healthy sexually intact Beagles (3 males and 3 females). PROCEDURES-All dogs were instrumented with a telemetry device for continuous monitoring of heart rate, arterial blood pressure, and core body temperature (at a femoral artery). Dogs were anesthetized with propofol (6 mg/kg, IV) and isoflurane. Isoflurane MAC values were determined in 3 experiments in each dog, separated by at least 7 days, before (baseline) and after the following treatments: no treatment (anesthetic only), perzinfotel (20 mg/kg, IV), fentanyl (5 microg/kg bolus, IV, followed by a continuous IV infusion at 0.15 microg/kg/min), and a fentanyl-perzinfotel combination (20 mg of perzinfotel/kg, IV, plus the fentanyl infusion). Bispectral index and oxygen saturation as measured by pulse oximetry were also monitored throughout anesthesia. RESULTS-Without treatment, the mean +/- SD isoflurane MAC for all 6 dogs was 1.41 +/- 0.10%. Baseline MAC was 1.42 +/- 0.08%. Intravenous administration of perzinfotel, fentanyl, and the perzinfotel-fentanyl combination significantly decreased the MAC by 39%, 35%, and 66%, respectively. Perzinfotel and perzinfotel-fentanyl administration yielded significant increases in the bispectral index. Mean, systolic, and diastolic arterial blood pressures significantly increased from baseline values when perzinfotel was administered. Systolic arterial blood pressure significantly increased from the baseline value when perzinfotel-fentanyl was administered. No adverse effects were detected. CONCLUSIONS AND CLINICAL RELEVANCE-IV administration of perzinfotel, fentanyl, or a perzinfotel-fentanyl combination reduced isoflurane MAC in dogs and increased arterial blood pressure.

Anesthetic and cardiopulmonary effects of intramuscular morphine, medetomidine, ketamine injection in dogs.

OBJECTIVE: To determine the quality and duration of anesthesia and the cardiopulmonary effects of a morphine, medetomidine, ketamine (MMK) combination administered intramuscularly (IM) to dogs. STUDY DESIGN: Descriptive injectable anesthetic protocol evaluation. ANIMALS: Eight intact adult Beagle dogs: five males, three females. METHODS: The electrocardiogram, heart rate, direct arterial blood pressure, and core body temperature were monitored in eight chronically instrumented dogs. Each dog received 0.2 mg kg(-1) morphine sulfate, 20 microg kg(-1) medetomidine hydrochloride, and 5 mg kg(-1) ketamine hydrochloride IM. Anesthetic and analgesic effects (clamping the tail and metatarsus) were categorized, and the times to lateral recumbency, orotracheal intubation, extubation, and sternal recumbency were recorded. Respiratory, cardiovascular, temperature, and acid-base variables were recorded 5 minutes before, and 3, 10, 20, 30, 45, 50, and 60 minutes after MMK. Atipamezole, 100 microg kg(-1) IM, was administered 60 minutes after MMK administration and data recorded 10 minutes later. RESULTS: The onset of anesthesia was uneventful and rapid. Time to lateral recumbency was 7.1 +/- 4.1 minutes. The tracheas of four dogs were orally intubated in 5.1 +/- 0.8 minutes. After MMK administration most dogs were unresponsive to noxious stimulation from 20 to 60 minutes and heart rate, cardiac index and venous blood pH were significantly decreased from baseline values. Arterial blood pressure increased initially and then returned to baseline values. Times to extubation (four dogs) and return to sternal recumbency after atipamezole administration were 2.8 +/- 1.8 and 4.3 +/- 4.4 minutes, respectively. CONCLUSION: The IM administration of MMK produced anesthesia and analgesia in Beagle dogs. Hemodynamic data were within accepted normal values. Atipamezole administration produced rapid return to consciousness in all dogs. CLINICAL RELEVANCE: Morphine/medetomidine/ketamine may be used for minor medical and surgical procedures requiring short-term anesthesia and analgesia but it is not recommended for medical procedures that are painful.

Effects of propofol on intraocular pressure in premedicated and nonpremedicated dogs with and without glaucoma.

OBJECTIVE To establish a study cutoff for evidence of glaucoma on the basis of IOP measurements from a large population of healthy dogs and to assess the effects of IV propofol administration on IOPs in premedicated and nonpremedicated dogs with and without glaucoma defined by this method. DESIGN Prospective, descriptive study. ANIMALS 234 client-owned dogs. PROCEDURES IOPs measured in 113 healthy dogs (226 eyes) were used to calculate an IOP value indicative of glaucoma. The IOPs were measured in an additional 121 dogs (237 eyes) undergoing ophthalmic surgery. Midazolam-butorphanol was administered IV as preanesthetic medication to 15 and 87 dogs with and without glaucoma, respectively. A placebo (lactated Ringer solution) was administered IV to 8 and 11 dogs with and without glaucoma, respectively. Anesthesia of surgical patients was induced with propofol IV to effect. The IOPs and physiologic variables of interest were recorded before (baseline) and after preanesthetic medication or placebo administration and after propofol administration. RESULTS An IOP > 25 mm Hg was deemed indicative of glaucoma. Compared with baseline measurements, mean IOP was increased after propofol administration in nonpremedicated dogs without glaucoma and unchanged in nonpremedicated dogs with glaucoma. Propofol-associated increases in IOP were blunted in premedicated dogs without glaucoma; IOP in affected eyes of premedicated dogs with glaucoma was decreased after preanesthetic medication and after propofol administration. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that preexisting IOP influences the response to anesthetic drugs, and administration of preanesthetic medication with muscle-relaxing properties may blunt or reduce propofol-induced increases in IOP. Further research with a larger number of dogs is needed to confirm our results in dogs with glaucoma.

A pilot study evaluating adaptive closed-loop fluid resuscitation during states of absolute and relative hypovolemia in dogs.

OBJECTIVE: To evaluate and determine the performance of a partially automated as well as a fully automated closed-loop fluid resuscitation system during states of absolute and relative hypovolemia. DESIGN: Prospective experimental trial. SETTING: Research laboratory. ANIMALS: Five adult Beagle dogs. METHODS: Isoflurane anesthetized mechanically ventilated dogs were subjected to absolute hypovolemia (controlled: 2 trials; uncontrolled: 3 trials), relative hypovolemia (2 trials), and the combination of relative and absolute controlled hypovolemia (2 trials). Controlled and uncontrolled hypovolemia were produced by withdrawing blood from the carotid or femoral artery. Relative hypovolemia was produced by increasing the isoflurane concentration (1 trial) or by infusion of intravenous sodium nitroprusside (1 trial). Relative hypovolemia combined with controlled absolute hypovolemia was produced by increasing the isoflurane concentration (1 trial) and infusion of IV sodium nitroprusside (1 trial). Hemodynamic parameters including stroke volume variation (SVV) were continuously monitored and recorded in all dogs. A proprietary closed-loop fluid administration system based on fluid distribution and compartmental dynamical systems administered a continuous infusion of lactated Ringers solution in order to restore and maintain SVV to a predetermined target value. MEASUREMENTS AND MAIN RESULTS: A total of 9 experiments were performed on 5 dogs. Hemodynamic parameters deteriorated and SVV increased during controlled or uncontrolled hypovolemia, relative hypovolemia, and during relative hypovolemia combined with controlled hypovolemia. Stroke volume variation was restored to baseline values during closed-loop fluid infusion. CONCLUSIONS: Closed-loop fluid administration based on IV fluid distribution and compartmental dynamical systems can be used to provide goal directed fluid therapy during absolute or relative hypovolemia in mechanically ventilated isoflurane anesthetized dogs.

Minimally invasive determination of cardiac output by transthoracic bioimpedance, partial carbon dioxide rebreathing, and transesophageal Doppler echocardiography in beagle dogs.

Minimally invasive cardiac output was determined using transthoracic bioimpedance (BICO), partial carbon dioxide rebreathing (NICO) and transesophageal Doppler echocardiography (TEECO) and compared to thermodilution (TDCO) in 6 beagle dogs. The dogs were 2 years old, weigh between 9.1-13.0 kg and were anesthetized with nitrous oxide-oxygen-sevoflurane. All dogs were administered a neuromuscular blocking drug and artificially ventilated during anesthesia. Thirty paired measurements of TDCO and each non-invasive method were collected during low, intermediate, and high values of cardiac output achieved by varying the depth of anesthesia and the administration of dobutamine. Cardiac output values ranged from 1.10-2.50 L/min for BICO compared to 0.81-4.88 L/min for TDCO; 0.70-2.60 L/min for NICO compared to 0.89-4.45 L/min for TDCO; and 0.59-4.37 L/min for TEECO compared to 0.57-4.15 L/min for TDCO. The limits of agreement and percentage error were -0.58 +/- 1.56 L/min and +/- 75.4% for BICO, -1.04 +/- 1.08 L/min and +/- 56.0% for NICO, and 0.03 +/- 0.26 L/min and +/- 12.3% for TEECO compared to TDCO. In conclusion, TEECO provided the best agreement to TDCO in sevoflurane anesthetized beagle dogs.

A Systematic Review of the Quality of IV Fluid Therapy in Veterinary Medicine.

OBJECTIVE: To evaluate the quality of the veterinary literature investigating IV fluid therapy in dogs, cats, horses, and cattle. DESIGN: Systematic review. PROCEDURES: The preferred reporting of items for systematic review and meta-analysis protocols (PRISMA-P) was employed for systematic review of all relevant IV fluid therapy manuscripts published from January 1969 through December 2016 in the Commonwealth Agricultural Bureaux International (CABI) database. Independent grading systems used to evaluate manuscripts included the updated CONsolidated Standards of Reporting Trials 2012 checklist, risk of bias for animal intervention studies, criteria for levels of evidence, and methodological quality (Jadad scale). The quality of articles published before and after 2010 was compared. RESULTS: One hundred and thirty-nine articles (63 dogs, 7 cats, 39 horses, 30 cattle) from 7,258 met the inclusion criteria. More than 50% of the manuscripts did not comply with minimal requirements for reporting randomized controlled trials. The most non-compliant items included identification of specific predefined objectives or a hypothesis, identification of trial design, how sample size was determined, randomization, and blinding procedures. Most studies were underpowered and at risk for selection, performance, and detection bias. The overall quality of the articles improved for articles published after 2010. CONCLUSION AND CLINICAL RELEVANCE: Most of the veterinary literature investigating the administration of IV fluid therapy in dogs, cats, horses, and cattle is descriptive, does not comply with standards for evidence, or provide adequate translation to clinical practice. Authors should employ and journal editors should enforce international consensus recommendations and guidelines for publication of data from animal experiments investigating IV fluid therapy.

CXL-1020, a Novel Nitroxyl (HNO) Prodrug, Is More Effective than Milrinone in Models of Diastolic Dysfunction-A Cardiovascular Therapeutic: An Efficacy and Safety Study in the Rat.

The nitroxyl (HNO) prodrug, CXL-1020, induces vasorelaxation and improves cardiac function in canine models and patients with systolic heart failure (HF). HNO's unique mechanism of action may be applicable to a broader subset of cardiac patients. This study investigated the load-independent safety and efficacy of CXL-1020 in two rodent (rat) models of diastolic heart failure and explored potential drug interactions with common HF background therapies. In vivo left-ventricular hemodynamics/pressure-volume relationships assessed before/during a 30 min IV infusion of CXL-1020 demonstrated acute load-independent positive inotropic, lusitropic, and vasodilatory effects in normal rats. In rats with only diastolic dysfunction due to bilateral renal wrapping (RW) or pronounced diastolic and mild systolic dysfunction due to 4 weeks of chronic isoproterenol exposure (ISO), CXL-1020 attenuated the elevated LV filling pressures, improved the end diastolic pressure volume relationship, and accelerated relaxation. CXL-1020 facilitated Ca2+ re-uptake and enhanced myocyte relaxation in isolated cardiomyocytes from ISO rats. Compared to milrinone, CXL-1020 more effectively improved Ca2+ reuptake in ISO rats without concomitant chronotropy, and did not enhance Ca2+ entry via L-type Ca2+ channels nor increase myocardial arrhythmias/ectopic activity. Acute-therapy with CXL-1020 improved ventricular relaxation and Ca2+ cycling, in the setting of chronic induced diastolic dysfunction. CXL-1020's lusitropic effects were greater than those seen with the cAMP-dependent agent milrinone, and unlike milrinone it did not produce chronotropy or increased ectopy. HNO is a promising new potential therapy for both systolic and diastolic heart failure.

Bilateral Arteriovenous Shunts as a Method for Evaluating Tissue-Engineered Vascular Grafts in Large Animal Models.

There remains a need for large animal models to evaluate tissue-engineered vascular grafts (TEVGs) under arterial pressure to provide preclinical data for future potential human clinical trials. We present a comprehensive method for the interrogation of TEVGs, using an ovine bilateral arteriovenous (AV) shunt implantation model. Our results demonstrate that this method can be performed safely without complications, specifically acute heart failure, steal syndrome, and hypoxic brain injury, and it is a viable experimental paradigm. Our method allows for a non-invasive evaluation of TEVGs in terms of graft flow, graft diameter, and graft patency, while also allowing for graft needle puncture under ultrasound guidance. In addition, traditional pathological analysis, histology, and immunohistochemistry may be performed with the contralateral side providing paired control data to eliminate inter-subject variability while reducing the total number of animals. Further, we present a review of existing literature of preclinical evaluation of TEVGs in large animal models as AV conduits.

Test of the usefulness of a paradigm to identify potential cardiovascular liabilities of four test articles with varying pharmacological properties in anesthetized guinea pigs.

The evaluation of proarrhythmic and hemodynamic liabilities for new compounds remains a major concern of preclinical safety assessment paradigms. Contrastingly, albeit functional liabilities can also translate to clinical morbidity and mortality, lesser preclinical efforts are focused on the evaluation of drug-induced changes in inotrope and lusitrope, particularly in the setting of concomitant hemodynamic/arrhythmic liabilities. This study aimed to establish the feasibility of an anesthetized guinea pig preparation to assess functional liabilities in the setting of simultaneous drug-induced electrocardiographic/hemodynamic changes, by evaluating the effects of various compounds with known cardiovascular properties on direct and indirect indices of left ventricular function. In short, twenty nine male guinea pigs were instrumented to measure electrocardiograms, systemic arterial pressure, and left ventricular pressure-volume relationships. After baseline measurement, all animals were given intravenous infusions of vehicle and two escalating concentrations of either chromanol 293B (n = 8), milrinone (n = 6), metoprolol (n = 7), or nicorandil (n = 8) for 10 minutes each. In all cases, these compounds produced the expected changes. The slope of preload-recruitable stroke work (PRSW), a pressure-volume derived load independent index, was the most sensitive marker of drug-induced changes in inotropy. Among the indirect functional indices studied, only the "contractility index" (dP/dtmax normalized by the pressure at its occurrence) and the static myocardial compliance (ratio of end diastolic volume and pressure) appeared to be adequate predictors of drug-induced changes in inotropy/lusitropy. Overall, the data confirms that both electrophysiological and mechanical liabilities can be accurately assessed in an anesthetized guinea pig preparation.

Dose-Dependent Hemodynamic, Biochemical, and Tissue Oxygen Effects of OC99 following Severe Oxygen Debt Produced by Hemorrhagic Shock in Dogs.

We determined the dose-dependent effects of OC99, a novel, stabilized hemoglobin-based oxygen-carrier, on hemodynamics, systemic and pulmonary artery pressures, surrogates of tissue oxygen debt (arterial lactate 7.2 ± 0.1 mM/L and arterial base excess -17.9 ± 0.5 mM/L), and tissue oxygen tension (tPO2) in a dog model of controlled severe oxygen-debt from hemorrhagic shock. The dose/rate for OC99 was established from a pilot study conducted in six bled dogs. Subsequently twenty-four dogs were randomly assigned to one of four groups (n = 6 per group) and administered: 0.0, 0.065, 0.325, or 0.65 g/kg of OC99 combined with 10 mL/kg lactated Ringers solution administered in conjunction with 20 mL/kg Hextend IV over 60 minutes. The administration of 0.325 g/kg and 0.65 g/kg OC99 produced plasma hemoglobin concentrations of 0.63 ± 0.01 and 1.11 ± 0.02 g/dL, respectively, improved systemic hemodynamics, enhanced tPO2, and restored lactate and base excess values compared to 0.0 and 0.065 g/kg OC99. The administration of 0.65 g/kg OC99 significantly elevated pulmonary artery pressure. Plasma hemoglobin concentrations of OC99 ranging from 0.3 to 1.1 g/dL, in conjunction with colloid based fluid resuscitation, normalized clinical surrogates of tissue oxygen debt, improved tPO2, and avoided clinically relevant increases in pulmonary artery pressure.

Arterial blood pressure as a predictor of the response to fluid administration in euvolemic nonhypotensive or hypotensive isoflurane-anesthetized dogs.

OBJECTIVE: To determine the effects of rapid small-volume fluid administration on arterial blood pressure measurements and associated hemodynamic variables in isoflurane-anesthetized euvolemic dogs with or without experimentally induced hypotension. DESIGN: Prospective, randomized, controlled study. ANIMALS: 13 healthy dogs. PROCEDURES: Isoflurane-anesthetized dogs were randomly assigned to conditions of nonhypotension or hypotension (mean arterial blood pressure, 45 to 50 mm Hg) and treatment with lactated Ringer's solution (LRS) or hetastarch (3 or 10 mL/kg [1.4 or 4.5 mL/lb] dose in a 5-minute period or 3 mL/kg dose in a 1-minute period [4 or 5 dogs/treatment; ≥ 10-day interval between treatments]). Hemodynamic variables were recorded before and for up to 45 minutes after fluid administration. RESULTS: IV administration of 10 mL/kg doses of LRS or hetastarch in a 5-minute period increased right atrial and pulmonary arterial pressures and cardiac output (CO) when dogs were nonhypotensive or hypotensive, compared with findings before fluid administration; durations of these effects were greater after hetastarch administration. Intravenous administration of 3 mL of hetastarch/kg in a 5-minute period resulted in an increase in CO when dogs were nonhypotensive. Intravenous administration of 3 mL/kg doses of LRS or hetastarch in a 1-minute period increased right atrial pressure and CO when dogs were nonhypotensive or hypotensive. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of LRS or hetastarch (3 or 10 mL/kg dose in a 5-minute period or 3 mL/kg dose in a 1-minute period) improved CO in isoflurane-anesthetized euvolemic dogs with or without hypotension. Overall, arterial blood pressure measurements were a poor predictor of the hemodynamic response to fluid administration.

Cardiac function after acute support with direct mechanical ventricular actuation in chronic heart failure.

Direct mechanical ventricular actuation (DMVA) exerts direct cardiac compression/decompression and does not require blood contact. The safety and effects of DMVA support in chronically dysfunctional beating hearts in vivo have not been established. This study evaluated hemodynamics and load-independent systolic/diastolic cardiac function before/after acute support (2 hours) using DMVA in small hearts with induced chronic failure. Chronic heart failure was created in seven small dogs (15 ± 2 kg) via either serial coronary microembolizations or right-ventricular overdrive pacing. Dogs were instrumented to measure cardiac output, hemodynamic pressures, left ventricular volumes for pressure-volume analysis via preload reduction. Temporary cardiac support using a DMVA device was instituted for 2 hours. Hemodynamic and mechanical assessments, including dobutamine dose-responses, were compared both before and after support. Hemodynamic indices were preserved with support. Both left-ventricular systolic and diastolic function were improved postsupport, as the slopes of the preload-recruitable stroke work (+29 ± 7%, p < 0.05) and the end-diastolic pressure-volume relationship (EDPVR: -28 ± 9%, p < 0.05) improved post-DMVA support. Diastolic/systolic myocardial reserve, as assessed by responsiveness to dobutamine challenges, was preserved after DMVA support. Short-term DMVA support can safely and effectively sustain hemodynamics, whereas triggering favorable effects on cardiac function in the setting of chronic heart failure. In particular, DMVA support preserved load-independent diastolic function and reserve.

Effects of intravenous administration of lactated Ringer's solution on hematologic, serum biochemical, rheological, hemodynamic, and renal measurements in healthy isoflurane-anesthetized dogs.

OBJECTIVE: To determine the hematologic, serum biochemical, rheological, hemodynamic, and renal effects of IV administration of lactated Ringer's solution (LRS) to healthy anesthetized dogs. DESIGN: 4-period, 4-treatment cross-over study. ANIMALS: 8 healthy mixed-breed dogs. PROCEDURES: Each dog was anesthetized, mechanically ventilated, instrumented, and randomly assigned to receive LRS (0, 10, 20, or 30 mL/kg/h [0, 4.5, 9.1, or 13.6 mL/lb/h]), IV, on 4 occasions separated by at least 7 days. Blood hemoglobin concentration and serum total protein, albumin, lactate, and electrolyte concentrations; PCV; colloid osmotic pressure; arterial and venous pH and blood gases (Po2; Pco2); whole blood and plasma viscosity; arterial and venous blood pressures; cardiac output; results of urinalysis; urine production; glomerular filtration rate; and anesthetic recovery times were monitored. Oxygen delivery, vascular resistance, stroke volume, pulse pressure, and blood and plasma volume were calculated. RESULTS: Increasing rates of LRS administration resulted in dose-dependent decreases in PCV; blood hemoglobin concentration and serum total protein and albumin concentrations; colloid osmotic pressure; and whole blood viscosity. Plasma viscosity; serum electrolyte concentrations; data from arterial and venous blood gas analysis; glomerular filtration rate; urine production; heart rate; pulse, central venous, and arterial blood pressures; pulmonary vascular resistance; and oxygen delivery did not change. Pulmonary artery pressure, stroke volume, and cardiac output increased, and systemic vascular resistance decreased. CONCLUSIONS AND CLINICAL RELEVANCE: Conventional IV infusion rates of LRS to isoflurane-anesthetized dogs decreased colligative blood components; increased plasma volume, pulmonary artery pressure, and cardiac output; and did not change urine production or oxygen delivery to tissues.

Evaluation of oscillometric and vascular access port arterial blood pressure measurement techniques versus implanted telemetry in anesthetized cats.

OBJECTIVE: To compare the use of a semi-invasive vascular access port (VAP) device or noninvasive oscillometry versus invasive telemetry for blood pressure measurements in cats. ANIMALS: 6 healthy cats. PROCEDURES: 30 days before the study, all cats received an implanted telemeter and a VAP device. During normotension and experimentally induced hypertension, blood pressure was measured with the implanted devices and with noninvasive oscillometry at 4 time points. RESULTS: Compared with invasive telemetry, VAP had a correlation coefficient from 0.8487 to 0.9972, and noninvasive oscillometry had a correlation coefficient from 0.7478 to 0.9689. CONCLUSIONS AND CLINICAL RELEVANCE: Use of the VAP device and noninvasive oscillometry had a high degree of correlation with invasive telemetry as the gold standard for blood pressure measurement. Use of a VAP device resulted in a slightly higher degree of correlation, compared with noninvasive oscillometry.