Hierarchical Task Analysis Reimagined as a Planning Tool for Surgery During Exploration Space Flight.

Background: Preparation for exploration class space flight requires planning to support human life in many circumstances including healthcare emergencies such as the need for acute surgical care, a notable example of which is appendicitis. Although performing a laparoscopic appendectomy on Earth is routine for a trained general surgeon, it is far from routine for a non-surgeon working in microgravity where IVs do not drip, drains do not drain, and gaseous anesthetic is out of the question. Because the procedure for laparoscopic appendectomy is so well documented, it was the ideal procedure on which to base a study on how to deconstruct a surgical procedure to examine all actions, skills, equipment, and supplies needed for success by non-surgeons working in an extreme environment. Study Design: Our challenge was to develop a task analysis model robust enough to include 3 performers (in the roles of surgeon, assistant, and anesthesiologist) including each action and instrument or supply item needed in chronological order, while indicating which actions were completed independently and which were done in tandem. We also had to indicate where variations in the actions would be determined by the negative response of the patient (failure mode), and which actions and supply items needed further research to accommodate working in microgravity. We opted to begin with a hierarchical task analysis model (HTA) because the steps in the task are sequential; but we expanded the typical linear presentation of data to a multi-column spread sheet with active links to instructional video clips where needed. Content development was an iterative process beginning with a scoping review of literature to select a baseline task analysis of the procedure. The SAGES 2010 approach was selected as most comprehensive, but logically focused on the surgeon's performance with few references to the assistant or anesthesiologist. Those gaps were filled using content from training materials developed for surgical technicians and nurse anesthetists. The second step was an expert review of the spread sheet to identify gaps and inadequacies. The third step was a minute comparison of spread sheet content to actions and equipment as documented on 2 videotapes of the procedure performed by our team surgeon on otherwise healthy patients. The final review was accomplished by replicating the procedure on 360° video (with narration) using the spread sheet as a guide, then cross checking and correcting the spread sheet to correspond with the 360° video. This test procedure was performed on a lightly preserved, fresh cadaver since working at that very slow, deliberate pace would not be in the best interest of an actual patient. Results: In this study, simulation was actually used to test the expanded HTA rather than to evaluate a learner. The final spread sheet included 178 lines, 13 columns, 13 illustrations, and 4 active links to instructional video clips. Thirteen items or issues were identified as needing further research, 8 action sequences were identified as generalizable skills, and 27 supply or equipment items were identified as multipurpose. Excluding the pharmaceuticals necessary for IV general anesthesia (that research is on-going), we were able to replicate a laparoscopic appendectomy on a fresh cadaver using no more than 30 items. The procedure was done using 3 trocars with very few instrument exchanges through the trocars since the surgical assistant assumed the role of laparoscopic camera operator during the procedure. Conclusion: An expanded HTA of a surgical procedure can produce many useful outcomes including integrated training for all team members, review of instrumentation and supplies and, in our case, identifying areas for adapting to an extreme environment. Using an interdisciplinary team including instructional designers, subject matter experts from medicine and biomedical engineering, and media production enriched the process.

Use of Gloves to Examine Intermittent Palm Cooling's Impact on Rowing Ergometry.

ABSTRACT: O'Brien, IT, Kozerski, AE, Gray, WD, Chen, L, Vargas, LJ, McEnroe, CB, Vanhoover, AC, King, KM, Pantalos, GM, and Caruso, JF. Use of gloves to examine intermittent palm cooling's impact on rowing ergometry. J Strength Cond Res 35(4): 931-940, 2021-The aim of this study was to examine the use of gloves on intermittent palm cooling's impact on rowing ergometry workouts. Our methods had subjects (n = 34) complete 3 rowing ergometer workouts of up to 8 2-minute stages separated by 45- or 60-second rests. They were randomized to one of the following treatments per workout: no palm cooling (NoPC), intermittent palm cooling as they rowed (PCex), or intermittent palm cooling as they rowed and post-exercise (PCex&post). Palm cooling entailed intermittent cold (initial temperature: 8.1° C) application and totaled 10 (PCex) and 20 (PCex&post) minutes, respectively. Workouts began with 8 minutes of rest after which pre-exercise data were obtained, followed by a ten-minute warm-up and the workout, and 20 minutes of post-exercise recovery. Numerous physiological and performance variables were collected before, during, and after workouts, and each was analyzed with either a two- or three-way analysis of variance. Our results include, with a 0.05 alpha and a simple effects post hoc, the distance rowed analysis produced a significant workout effect with PCex, PCex&post > NoPC. There were also significant interworkout differences for heart rate (HR) (NoPC > PCex) and blood lactate concentration (NoPC > PCex, PCex&post). We conclude that lower HRs and blood lactate concentrations from intermittent cooling caused subjects to experience less fatigue during those workouts and enabled more work to be performed. Continued research should identify optimal cooling characteristics to expedite body heat removal. Practical applications suggest that intermittent palm cooling administered with gloves enhance performance by abating physiological markers of fatigue.

Ergogenic and Physiological Outcomes Derived From a Novel Skin Cooling Device.

ABSTRACT: Gray, WD, Jett, DM, Cocco, AR, Vanhoover, AC, Colborn, CE, Pantalos, GM, Stumbo, J, Quesada, PM, and Caruso, JF. Ergogenic and physiological outcomes derived from a novel skin cooling device. J Strength Cond Res 35(2): 391-403, 2021-Our study's purpose assessed a cooling headband's ergogenic and physiological impacts. Subjects (15 women and 13 men) completed six visits; the final 3 entailed rowing workouts with the following treatment conditions: no head cooling (NoHC), intermittent head cooling during exercise (HCex), and intermittent head cooling during exercise and post-exercise recovery (HCex&post). Data collection occurred at the following times (a) pre-exercise and post-warm-up, (b) between stages of up to eight 2-minute bouts, and (c) at 5, 10, 15, and 20 minutes post-exercise. In addition to distance rowed, thermal, cardiovascular, perceptual, and metabolic measurements were obtained. Results included a small yet significant intertreatment difference (HCex, HCex&post > NoHC) for distance rowed. Our cardiovascular and metabolic indices exhibited sex and time differences but likely did not contribute to the ergogenic effect. Yet, left hand temperatures (LHT) exhibited significant 2-way and 3-way interactions that were the likely source of the ergogenic effect. Auditory canal temperature (AUDT) results suggest the head is sensitive to heat increases, yet LHT data show headband use evoked significantly greater temperature increases at the hand's palmar surface, indicative of heat transfer. We conclude, and our practical applications suggest, the headband's ergogenic effect was manifested by cold-induced vasodilation at the hand's palmar surface, rather than heat losses through the head.

Safety assessment of open appendectomies for complicated acute appendicitis in children: a comparison of trainees and specialists.

PURPOSE: The aim of this study was to compare the outcome of children with complicated acute appendicitis (CAA) who underwent open appendectomy (OA) performed either by trainees under the direct supervision of an SPS, or an SPS. METHODS: Two hundred thirty eight patients with CAA were reviewed operated on either by a junior trainee (JT) or a senior trainee (ST) under the direct supervision of an SPS or by an SPS. The outcome measures were the overall rate of complications, operative time (OT), length of hospital stay (LHS) and 30-day readmission rate. RESULTS: No statistical differences were observed between the three groups regarding the overall complication rates and 30-day readmission rate. Although, no statistical differences were observed in the mean OT between the three groups, the mean OT for perforated appendicitis (PA) performed by JTs was significantly longer than when performed by SPSs (p 0.012). Furthermore, there was a statistically significant difference between JTs and SPSs in terms of LHS for patients with PA (p 0.028). CONCLUSION: This study suggests that no statistical differences were observed between the supervised trainees and SPSs regarding the overall complication rate and 30-readmission rate when they performed OA for GA or PA except of a longer OT and LHS for PA performed by JTs.

Load-Power Relationships for High-Speed Knee Extension Exercise.

Chen, L, Davison, SW, Selimovic, EA, Mueller, RE, Beatty, SR, Carter, KA, Parmar, PJ, Symons, TB, Pantalos, GM, and Caruso, JF. Load-power relationships for high-speed knee extension exercise. J Strength Cond Res 33(6): 1480-1487, 2019-Seventy subjects did 4 knee extensor workouts with their left legs to assess load-power relationships produced on a high-speed trainer (HST; Newnan, GA, USA). Each workout is composed of 4 sets done on the HST at a different load (1, 4.4, 6.7, 9 kg). A Latin Squares Design determined load sequence per workout. Average power (AP) and peak power (PP) and those same values normalized to body mass (BM) and fat-free mass (AP/BM, PP/BM, AP/FFM, PP/FFM) were each analyzed with 2 (gender) × 4 (load) analysis of variances, with repeated measures for load. We assessed relationships between normalized loads and AP and PP values with correlation coefficients. Average power results revealed a significant interaction, with men > women at 9 kg. Peak power/body mass also yielded an interaction, with women > men at 6.7 and 9 kg. Average power/fat-free mass and PP/FFM each produced interactions, with women > men at 4.4, 6.7, and 9 kg. Correlation coefficients showed significant (r = 0.80-0.82) relationships between normalized loads and AP and PP values. In conclusion, the very low inertial resistance to initiate each repetition on this novel device may in part explain our PP/BM, AP/FFM, PP/FFM results, in which higher values were achieved by women. Our practical applications imply that the low inertial resistance for HST repetitions negates male size and strength advantages typically seen when power is measured.

Extracorporeal membrane oxygenation versus counterpulsatile, pulsatile, and continuous left ventricular unloading for pediatric mechanical circulatory support.

OBJECTIVES: Despite progress with adult ventricular assist devices, limited options exist to support pediatric patients with life-threatening heart disease. Extracorporeal membrane oxygenation remains the clinical standard. To characterize (patho)physiologic responses to different modes of mechanical unloading of the failing pediatric heart, extracorporeal membrane oxygenation was compared to intra-aortic balloon pump, pulsatile-flow ventricular assist device, or continuous-flow ventricular assist device support in a pediatric heart failure model. DESIGN: Experimental. SETTING: Large animal laboratory operating room. SUBJECTS: Yorkshire piglets (n = 47; 11.7 ± 2.6 kg). INTERVENTIONS: In piglets with coronary ligation-induced cardiac dysfunction, mechanical circulatory support devices were implanted and studied during maximum support. MEASUREMENTS AND MAIN RESULTS: Left ventricular, right ventricular, coronary, carotid, systemic arterial, and pulmonary arterial hemodynamics were measured with pressure and flow transducers. Myocardial oxygen consumption and total-body oxygen consumption were calculated from arterial, venous, and coronary sinus blood sampling. Blood flow was measured in 17 organs with microspheres. Paired Student t tests compared baseline and heart failure conditions. One-way repeated-measures analysis of variance compared heart failure, device support mode(s), and extracorporeal membrane oxygenation. Statistically significant (p < 0.05) findings included 1) an improved left ventricular blood supply/demand ratio during pulsatile-flow ventricular assist device, continuous-flow ventricular assist device, and extracorporeal membrane oxygenation but not intra-aortic balloon pump support, 2) an improved global myocardial blood supply/demand ratio during pulsatile-flow ventricular assist device and continuous-flow ventricular assist device but not intra-aortic balloon pump or extracorporeal membrane oxygenation support, and 3) diminished pulsatility during extracorporeal membrane oxygenation and continuous-flow ventricular assist device but not intra-aortic balloon pump and pulsatile-flow ventricular assist device support. A profile of systems-based responses was established for each type of support. CONCLUSIONS: Each type of pediatric ventricular assist device provided hemodynamic support by unloading the heart with a different mechanism that created a unique profile of physiological changes. These data contribute novel, clinically relevant insight into pediatric mechanical circulatory support and establish an important resource for pediatric device development and patient selection.

A hermetically sealed, fluid-filled surgical enclosure for microgravity.

INTRODUCTION: Expeditionary spaceflight is fraught with significant risks to human health, including trauma and other emergency medical events. To address several of the basic challenges of surgical care in reduced gravity, we are developing the Aqueous Immersion Surgical System (AISS), an optically clear enclosure pressurized by a fluid medium. The AISS is designed to prevent contamination of the spacecraft with blood and tissue debris, reduce intraoperative blood loss, and maintain visualization of the operative field. METHODS: An early prototype of the AISS was tested in reduced gravity during parabolic flight. A clear, aqueous field was created in a watertight chamber containing a mock vascular network. Hemorrhage was simulated by severing several of the analogue vessels. Experiments were performed to evaluate the benefits of surrounding a surgical cavity with fluid medium, as compared to an air environment, with respect to maintaining a clear view and achieving hemostasis. RESULTS: Qualitative evaluation of audio and video recorded during parabolic flight confirm AISS capacity to maintain visualization of the surgical field during a hemorrhage situation and staunch bleeding by raising interchamber pressure. DISCUSSION: Evaluation of the AISS in reduced gravity corroborates observations in the literature regarding the difficulty in maintaining visualization of the surgical field when performing procedures in an air environment. By immersing the surgical field in fluid we were able to apply suction directly to the hemorrhage and also achieve hemostasis.

Reasons for Delayed Diagnosis of Pediatric Acute Appendicitis during the COVID-19 Era: A Narrative Review.

Global pandemics cause health system disruptions. The inadvertent disruption in surgical emergency care during the Coronavirus Disease 2019 (COVID-19) pandemic has been the topic of several published studies. Our aim was to summarize the reasons that led to the delayed diagnosis of pediatric appendicitis during the COVID-19 era. This systematic literature search evaluated studies containing pediatric appendicitis patient data regarding outcomes, times to hospital admission or times from symptom onset to emergency department visit. Studies elucidating reasons for delays in the management of pediatric appendicitis were also reviewed. Ultimately, 42 studies were included. Several reasons for delayed diagnosis are analyzed such as changes to public health measures, fear of exposure to COVID-19, increased use of telemedicine, COVID-19 infection with concurrent acute appendicitis, recurrence of appendicitis after non-operative management and increased time to intraoperative diagnosis. Time to hospital admission in conjunction with patient outcomes was extracted and analyzed as an indicative measure of delayed management. Delayed diagnosis of acute appendicitis has been documented in many studies with various effects on outcomes. Suspicion of pediatric acute appendicitis must always lead to prompt medical examination, regardless of pandemic status. Telemedicine can be valuable if properly applied. Data from this era can guide future health system policies.

Intravenous Fluid Resuscitation Capabilities in Simulated Reduced Gravity.

BACKGROUND: Critical care for exploration space missions may require intravenous (IV) fluid resuscitation therapy. Resource constraints may limit availability of standard, Earth-based infusion technologies. The effect of variable acceleration on infusion flow rates using simple fluid resuscitation supplies was investigated.METHODS: Infusions of water or blood analog (40% glycerol) from a 1 L IV bag were performed using pressure bag augmentation at 0, 150, or 300 mmHg. The solution bag rested on an adjustable mount, configured to different heights to simulate relevant gravitational accelerations (1 G, Martian G, lunar G, and 0 G). The bag emptied through an IV line with a 14- or 20-gauge angiocath into a 3-mmHg venous pressure reservoir. Flow rates were measured using an in-line flow probe. Three determinations were made for each test condition.RESULTS: Temporal flow rate data for all test conditions displayed one-phase exponential decay. At 300 mmHg pressurization, maximum infusion rates ranged from 92-222 mL ⋅ min-1 for water and from 21-49 mL ⋅ min-1 for blood analog. All reduced gravity conditions had significantly longer infusion times in comparison to 1 G for both test solutions.DISCUSSION: Reduced acceleration significantly altered flow rates and infusion times for fluid resuscitation. Fluid resuscitation protocols specify a desired volume to infuse for a target time (e.g., 20-30 mL ⋅ min-1 for a 75-kg adult). This data demonstrates that this protocol parameter can be achieved with infusion pressure bag augmentation alone and provides information for the refinement of fluid resuscitation protocols for exploration space missions.Pantalos GM, Heidel JS, Jain IM, Warner SE, Barefoot TL, Baker RO, Hailey M. Intravenous fluid resuscitation capabilities in simulated reduced gravity. Aerosp Med Hum Perform. 2023; 94(8):596-603.

Identification of a marker of infection in the breath using a porcine pneumonia model.

Objective: Pneumonia, both in the community and the hospital setting, represents a significant cause of morbidity and mortality in the cardiothoracic patient population. Diagnosis of pneumonia can be masked by other disease processes and is often diagnosed after the patient is already experiencing the disease. A noninvasive, sensitive test for pneumonia could decrease hospitalizations and length of stay for patients. We have developed a porcine model of pneumonia and evaluated the exhaled breath of infected pigs for biomarkers of infection. Methods: Anesthetized 60-kg adult pigs were intubated, and a bronchoscope was used to instill a solution containing 12 × 108 cfu of methicillin-sensitive Staphylococcus aureus or a control solution without bacteria (Sham) into the distal airways. The pigs were then reintubated on postoperative days 3, 6, and 9, with bronchoscopic bronchial lavages taken at each time point. At each time point, a 500-mL breath was captured from each pig. The breath was evacuated over a silicon microchip, with the volatile carbonyl compounds from the breath captured via oximation reaction, and the results of this capture were analyzed by ultra-high performance liquid chromatography mass spectrometry. Results: A total of 64% of the pigs inoculated with methicillin-sensitive S. aureus demonstrated consolidation on chest radiography and increasing counts of methicillin-sensitive S. aureus in the bronchial lavages over the span of the experiment, consistent with development of pneumonia. Analysis of the exhaled breath demonstrated 1 carbonyl compound (2-pentenal) that increased 10-fold over the span of the experiment, from an average of 0.0294 nmol/L before infection to an average of 0.3836 nmol/L on postoperative day 9. The amount of 2-pentenal present was greater in the breath of infected pigs than in the noninfected pigs or the sham inoculated pigs at postoperative days 6 and 9. Using an elevated concentration of 2-pentenal as a marker of infection yielded a sensitivity of 88% and specificity of 92% at postoperative day 6, and a sensitivity and specificity of 100% at postoperative day 9. Conclusions: We were able to successfully develop a clinical pneumonia in adult 60-kg pigs. The concentration of 2-pentenal correlated with the presence of pneumonia, demonstrating the potential for this compound to function as a biomarker for methicillin-sensitive S. aureus infection in pigs.

Intraaortic balloon pump timing discrepancies in adult patients.

The objective of this clinical study was to quantify the incidence and magnitude of intraaortic balloon pump (IABP) inflation and deflation landmark discrepancies associated with the IABP catheter arterial pressure waveform. Cardiac surgery patients with an IABP inserted prior to surgery were recruited. Following cardiac exposure, a high-fidelity pressure catheter was inserted into the aortic root for digital recording. The radial artery pressure signal was simultaneously recorded from the patient monitor along with the arterial pressure and electrocardiogram waveforms from the IABP console while operating at 1:1 and 1:2 synchronization. In selected patients, recordings were obtained with the IABP timed to the high-fidelity aortic root waveform. In all 11 patients, inflation and deflation landmark delays were observed when comparing the aortic root waveforms to the IABP arterial pressure waveforms (inflation delay = 74 ± 29 [23-117] ms; deflation delay = 71 ± 37 [24-141] ms, mean ± standard deviation [min-max]). Delays were greater when compared to the radial artery waveform (inflation delay = 175 ± 50 [100-233] ms; deflation delay = 168 ± 52 [100-274] ms). In all cases, the landmark delays were statistically different from zero (P < 0.001). Diastolic augmentation and afterload reduction varied with waveform source. Conflicting indications of afterload reduction occurred in four patients. Timing to the aortic root waveform resulted in greater diastolic pressure augmentation and afterload reduction but mixed changes in stroke volume. Delay and distortion of the arterial waveform was consistently found when measured through the IABP catheter lumen. These delays can alter IABP efficacy and may be eliminated by using high-fidelity sensing of aortic pressure.

Three-dimensional Versus Two-dimensional Laparoscopic Surgery for Colorectal Cancer: Systematic Review and Meta-analysis.

BACKGROUND/AIM: Three-dimensional (3D) laparoscopy is being steadily adopted instead of two-dimensional (2D) for various procedures. Our aim was to compare the outcomes between 2D and 3D laparoscopic procedures for colorectal cancer in order to ascertain the safety, efficacy and potential advantages of 3D imaging systems. MATERIALS AND METHODS: A systematic database search was conducted in March 2019. Comparative studies reporting clinical outcomes between patients undergoing elective colorectal procedures using either 2D or 3D laparoscopic equipment were eligible. RESULTS: Six studies were selected, including 614 patients in total. Minor reduction in operative time, similar blood loss and increased number of harvested lymph nodes was noted for the 3D group. There was no difference for conversion to open surgery, time to flatus, postoperative hospital stay or postoperative complications. CONCLUSION: 3D Laparoscopic surgery for colorectal cancer may result in reduction of operative time and higher lymph node yields, leading to improved survival.

Comparison of Blood Viscoelasticity in Pediatric and Adult Cardiac Patients.

Evidence is accumulating that blood flow patterns in the cardiovascular system and in cardiovascular devices do, in some instances, depend on blood viscoelasticity. Thus, to better understand the challenges to providing circulatory support and surgical therapies for pediatric and adult patients, viscous and elastic components of complex blood viscoelasticity of 31 pediatric patients were compared to those of 29 adult patients with a Vilastic-3 rheometer. A random effects model with categorical age covariates found statistically significant differences between pediatric and adult patients for log viscosity (p = 0.005). Log strain (p < 0.0001) and hematocrit (p < 0.0001) effects were also significant, as were the hematocrit-by-log-strain (p = 0.0006) and age-by-log strain (p = 0.001) interactions. The hematocrit-by-age interaction was not significant. For log elasticity, age differences were insignificant (p = 0.39). The model for log elasticity had significant log strain (p < 0.0001), log strain squared (p < 0.0001) and hematocrit (p < 0.0001) effects, as well as hematocrit-by-log-strain and hematocrit-by-log-strain-squared interactions (p = 0.014). A model for log viscosity with continuous age was also fit to the data, which can be used to refine cardiovascular device design and operation to the age of the patient. We conclude that there are distinct differences between pediatric and adult blood viscosity, as well as substantial variation within the pediatric population, that may impact the performance of devices and procedures.

Development and early testing of a simple subcutaneous counterpulsation device.

The intra-aortic balloon pump has been widely and successfully used as a treatment for cardiac dysfunction, but it only has short-term applications. To overcome this limitation, a superficial counterpulsation device (CPD) is being developed to provide extended counterpulsation support to promote myocardial recovery. The CPD is a valveless, monoport, pneumatically driven, 40-ml sac that is intended to be implanted in a pacemaker-type pocket in the subclavian fossa. The sac is designed to fill in systole and empty during diastole through an outflow graft anastomosed to the subclavian artery. A feasibility study was conducted to investigate acute hemodynamic responses to the CPD in eight calves with diminished cardiac function. The CPD augmented aortic diastolic pressure, reduced left ventricular peak systolic and aortic ejection pressures by up to 18%, and increased diastolic coronary flow by up to 21% and stroke volume by up to 12%. A cadaver fit study demonstrated that the human subclavian artery is a reasonable anastomosis site to consider and that the 40-ml CPD needs to be reduced in size to provide a better anatomical fit. The clinical attractiveness of this approach is that it may provide extended support through a subcutaneous surgical procedure.

Predicted hemodynamic benefits of counterpulsation therapy using a superficial surgical approach.

A volume-displacement counterpulsation device (CPD) intended for chronic implantation via a superficial surgical approach is proposed. The CPD is a pneumatically driven sac that fills during native heart systole and empties during diastole through a single, valveless cannula anastomosed to the subclavian artery. Computer simulation was performed to predict and compare the physiological responses of the CPD to the intraaortic balloon pump (IABP) in a clinically relevant model of early stage heart failure. The effect of device stroke volume (0-50 ml) and control modes (timing, duration, morphology) on landmark hemodynamic parameters and the LV pressure-volume relationship were investigated. Simulation results predicted that the CPD would provide hemodynamic benefits comparable to an IABP as evidenced by up to 25% augmentation of peak diastolic aortic pressure, which increases diastolic coronary perfusion by up to 34%. The CPD may also provide up to 34% reduction in LV end-diastolic pressure and 12% reduction in peak systolic aortic pressure, lowering LV workload by up to 26% and increasing cardiac output by up to 10%. This study demonstrated that the superficial CPD technique may be used acutely to achieve similar improvements in hemodynamic function as the IABP in early stage heart failure patients.

The effect of gravitational acceleration on cardiac diastolic function: a biofluid mechanical perspective with initial results.

Echocardiographic measurements of astronaut cardiac function have documented an initial increase, followed by a progressive reduction in both left ventricular end-diastolic volume index and stroke volume with entry into microgravity (micro-G). The investigators hypothesize that the observed reduction in cardiac filling may, in part, be due to the absence of a gravitational acceleration dependent, intraventricular hydrostatic pressure difference in micro-G that exists in the ventricle in normal gravity (1-G) due to its size and anatomic orientation. This acceleration-dependent pressure difference, DeltaP(LV), between the base and the apex of the heart for the upright posture can be estimated to be 6660 dynes/cm(2) ( approximately 5 mm Hg) on Earth. DeltaP(LV) promotes cardiac diastolic filling on Earth, but is absent in micro-G. If the proposed hypothesis is correct, cardiac pumping performance would be diminished in micro-G. To test this hypothesis, ventricular function experiments were conducted in the 1-G environment using an artificial ventricle pumping on a mock circulation system with the longitudinal axis anatomically oriented for the upright posture at 45 degrees to the horizon. Additional measurements were made with the ventricle horizontally oriented to null DeltaP(LV)along the apex-base axis of the heart as would be the case for the supine posture, but resulting in a lesser hydrostatic pressure difference along the minor (anterior-posterior) axis. Comparative experiments were also conducted in the micro-G environment of orbital space flight on board the Space Shuttle. This paper reviews the use of an automated cardiovascular simulator flown on STS-85 and STS-95 as a Get Away Special payload to test this hypothesis. The simulator consisted of a pneumatically actuated, artificial ventricle connected to a closed-loop, fluid circuit with adjustable compliance and resistance elements to create physiologic pressure and flow conditions. Ventricular instrumentation included pressure transducers in the apex and base as well as immediately upstream of the inflow valve and downstream of the outflow valve, and a flow probe downstream of the outflow valve. By varying the circulating fluid volume, ventricular function could be determined for varying preload pressures at a regulated, mean afterload pressure of 95 mm Hg. This variation in preload condition permitted the construction of a ventricular function curve for the micro-G environment for comparison to the same curve for the 1-G environment. Data were collected from both missions at the upper end of the ventricular function curve. Experiment operation in the 1-G, supine orientation or in the micro-G environment eliminated the DeltaP(LV) observed in the 1-G, upright orientation. Consistent with the hypothesis, additional atrial pressure was required in micro-G to obtain stroke volumes and flow rates similar to those measured in 1-G for the upright posture. The necessary increase in atrial pressure was approximately 5 mm Hg in these experiments. In the same range of flow rates and stroke volumes, similar flows were observed in the 1-G supine posture for atrial pressures intermediate to the 1-G upright and micro-G values, also consistent with the hypothesis. Additional experiments on board the Space Shuttle are in preparation to gather data across the rest of the normal physiologic range of the ventricular function curve.

Does conventional intra-aortic balloon pump trigger timing produce optimal hemodynamic effects in vivo?

PURPOSE: The intra-aortic balloon pump (IABP) provides circulatory support through counterpulsation. The hemodynamic effects of the IABP may vary with assisting frequency and depend on IAB inflation/deflation timing. We aimed to assess in vivo the IABP benefits on coronary, aortic, and left ventricular hemodynamics at different assistance frequencies and trigger timings. METHODS: Six healthy, anesthetized, open-chest sheep received IABP support at 5 timing modes (EC, LC, CC, CE, CL, corresponding to early/late/conventional/conventional/conventional inflation and conventional/conventional/conventional/early/late deflation, respectively) with frequency 1:3 and 1:1. Aortic (Q(ao)) and coronary (Q(cor)) flow, and aortic (P(ao)) and left ventricular (PLV) pressure were recorded simultaneously, with and without IABP support. Integrating systolic Q(ao) yielded stroke volume (SV). RESULTS: EC at 1:1 produced the lowest end-diastolic P(ao) (59.5 ± 7.8 mmHg [EC], 63.4 ± 11.1 mmHg [CC]), CC at 1:1 the lowest systolic PLV (69.1 ± 6.5 mmHg [CC], 76.4 ± 6.5 mmHg [control]), CC at 1:1 the highest SV (88.5 ± 34.4 ml [CC], 76.6 ± 31.9 ml [control]) and CC at 1:3 the highest diastolic Qcor (187.2 ± 25.0 ml/min [CC], 149.9 ± 16.6 ml/min [control]). Diastolic P(ao) augmentation was enhanced by both assistance frequencies alike, and optimal timings were EC for 1:3 (10.4 ± 2.8 mmHg [EC], 6.7 ± 3.8 mmHg [CC]) and CC for 1:1 (10.8 ± 6.7 mmHg [CC], -3.0 ± 3.8 mmHg [control]). CONCLUSIONS: In our experiments, neither a single frequency nor a single inflation/deflation timing, including conventional IAB timing, has shown superiority by uniformly benefiting all studied hemodynamic parameters. A choice of optimal frequency and IAB timing might need to be made based on individual patient hemodynamic needs rather than as a generalized protocol.

Modeling and control of a brushless DC axial flow ventricular assist device.

This article presents an integrated model of the human circulatory system that incorporates circulatory support by a brushless DC axial flow ventricular assist device (VAD), and a feedback VAD controller designed to maintain physiologically sufficient perfusion. The developed integrated model combines a network type model of the circulatory system with a nonlinear dynamic model of the brushless DC pump We show that maintaining a reference differential pressure between the left ventricle and aorta leads to adequate perfusion for different pathologic cases, ranging from normal heart to left heart asystole, and widely varying physical activity scenarios from rest to exercise.

Characterization of an adult mock circulation for testing cardiac support devices.

A need exists for a mock circulation that behaves in a physiologic manner for testing cardiac devices in normal and pathologic states. To address this need, an integrated mock cardiovascular system consisting of an atrium, ventricle, and systemic and coronary vasculature was developed specifically for testing ventricular assist devices (VADs). This test configuration enables atrial or ventricular apex inflow and aortic outflow cannulation connections. The objective of this study was to assess the ability of the mock ventricle to mimic the Frank-Starling response of normal, heart failure, and cardiac recovery conditions. The pressure-volume relationship of the mock ventricle was evaluated by varying ventricular volume over a wide range via atrial (preload) and aortic (afterload) occlusions. The input impedance of the mock vasculature was calculated using aortic pressure and flow measurements and also was used to estimate resistance, compliance, and inertial mechanical properties of the circulatory system. Results demonstrated that the mock ventricle pressure-volume loops and the end diastolic and end systolic pressure-volume relationships are representative of the Starling characteristics of the natural heart for each of the test conditions. The mock vasculature can be configured to mimic the input impedance and mechanical properties of native vasculature in the normal state. Although mock circulation testing systems cannot replace in vivo models, this configuration should be well suited for developing experimental protocols, testing device feedback control algorithms, investigating flow profiles, and training surgical staff on the operational procedures of cardiovascular devices.

Physiologic control of rotary blood pumps: an in vitro study.

Rotary blood pumps (RBPs) are currently being used as a bridge to transplantation as well as for myocardial recovery and destination therapy for patients with heart failure. Physiologic control systems for RBPs that can automatically and autonomously adjust the pump flow to match the physiologic requirement of the patient are needed to reduce human intervention and error, while improving the quality of life. Physiologic control systems for RBPs should ensure adequate perfusion while avoiding inflow occlusion via left ventricular (LV) suction for varying clinical and physical activity conditions. For RBPs used as left ventricular assist devices (LVADs), we hypothesize that maintaining a constant average pressure difference between the pulmonary vein and the aorta (deltaPa) would give rise to a physiologically adequate perfusion while avoiding LV suction. Using a mock circulatory system, we tested the performance of the control strategy of maintaining a constant average deltaPa and compared it with the results obtained when a constant average pump pressure head (deltaP) and constant rpm are maintained. The comparison was made for normal, failing, and asystolic left heart during rest and at light exercise. The deltaPa was maintained at 95 +/- 1 mm Hg for all the scenarios. The results indicate that the deltaPa control strategy maintained or restored the total flow rate to that of the physiologically normal heart during rest (3.8 L/m) and light exercise (5.4 L/m) conditions. The deltaPa approach adapted to changing exercise and clinical conditions better than the constant rpm and constant deltaP control strategies. The deltaPa control strategy requires the implantation of two pressure sensors, which may not be clinically feasible. Sensorless RBP control using the deltaPa algorithm, which can eliminate the failure prone pressure sensors, is being currently investigated.