Noninvasive motion ventilation (NIMV): a novel approach to ventilatory support

The Endothelium as a Therapeutic Target in Diabetes: A Narrative Review and Perspective

Diabetes has reached worldwide epidemic proportions, and threatens to be a significant economic burden to both patients and healthcare systems, and an important driver of cardiovascular mortality and morbidity. Improvement in lifestyle interventions (which includes increase in physical activity via exercise) can reduce diabetes and cardiovascular disease mortality and morbidity. Encouraging a population to increase physical activity and exercise is not a simple feat particularly in individuals with co-morbidities (obesity, heart disease, stroke, peripheral vascular disease, and those with cognitive and physical limitations). Translation of the physiological benefits of exercise within that vulnerable population would be an important step for improving physical activity goals and a stopgap measure to exercise. In large part many of the beneficial effects of exercise are due to the introduction of pulsatile shear stress (PSS) to the vascular endothelium. PSS is a well-known stimulus for endothelial homeostasis, and induction of a myriad of pathways which include vasoreactivity, paracrine/endocrine function, fibrinolysis, inflammation, barrier function, and vessel growth and formation. The endothelial cell mediates the balance between vasoconstriction and relaxation via the major vasodilator endothelial derived nitric oxide (eNO). eNO is critical for vasorelaxation, increasing blood flow, and an important signaling molecule that downregulates the inflammatory cascade. A salient feature of diabetes, is endothelial dysfunction which is characterized by a reduction of the bioavailability of vasodilators, particularly nitric oxide (NO). Cellular derangements in diabetes are also related to dysregulation in Ca²⁺ handling with increased intracellular Ca²⁺overload, and oxidative stress. PSS increases eNO bioavailability, reduces inflammatory phenotype, decreases intracellular Ca²⁺ overload, and increases antioxidant capacity. This narrative review and perspective will outline four methods to non-invasively increase PSS; Exercise (the prototype for increasing PSS), Enhanced External Counterpulsation (EECP), Whole Body Vibration (WBV), Passive Simulated Jogging and its predicate device Whole Body Periodic Acceleration, and will discuss current knowledge on their use in diabetes.

Whole Body Periodic Acceleration (pGz) as a non-invasive preconditioning strategy for pediatric cardiac surgery

We hypothesized that pGz has cardio and neuroprotective effects due to upregulation of pathways which include eNOS, anti-apoptotic, and anti-inflammatory pathways. We analyze protein expression of these pathways in the brain of neonatal piglets, as well as report on the myocardial function after Deep Hypothermic Circulatory Arrest (DHCA) and pGz preconditioning. Animal data affirms both a cardio and neuroprotective role for pGz. These findings suggest that pGz can be a simple, non-invasive cardio and neuroprotective strategy preconditioning strategy in children requiring surgical intervention.

Whole body periodic acceleration (pGz) preserves heart rate variability after cardiac arrest

AIMS

Heart rate variability (HRV) is a measure of the balance between the sympathetic and parasympathetic autonomic nervous system and lack thereof an ominous sign in many cardiac and neurological conditions including post-cardiac arrest syndrome. Whole body periodic acceleration (pGz) has been shown to be cardio protective when applied prior to during and after cardiac arrest (CA). Here, we investigate whether or not pGz pre or post treatment after CA preserves HRV.

METHODS

Eight min of unsupported ventricular fibrillation followed by CPR and defibrillation was carried out in 32 anesthetized and paralyzed male swine who were randomized to pretreatment (1h pGz prior to CA, pre-pGz [n=8]) or post-treatment (pGz beginning at 30min after return of spontaneous circulation ([ROSC], post-pGz [n=8]) or none (CONT [n=8]). pGz was applied together with conventional mechanical ventilation. In a separate group (n=8), infusion of TRIM (nNOS inhibitor) was used to determine the effects of nNOS inhibition on HRV.

RESULTS

Time and frequency domain measures of HRV were determined along with measurements of blood gases and hemodynamics, obtained at baseline and at 30, 60, 120 and 180min after ROSC. All animals had ROSC and there were no significant differences for arterial blood gases, mean blood pressure and coronary perfusion pressure after ROSC among the groups. HRV was significantly depressed after cardiac arrest and remained depressed in CONT group. In contrast, both pre and post pGz treated groups had significantly higher and preserved time domain measures of HRV (RMSSD and SDNN) from 60 to 180min after ROSC, and nNOS inhibition markedly reduced HRV. The frequency domain of HRV did not show changes.

CONCLUSIONS

In a pig model of CA, pre or post treatment with pGz preserves HRV. Inhibition of nNOS markedly reduced HRV. Post-treatment with pGz is a novel therapeutic strategy that might serve as an adjunct to current pharmacological or hypothermia modalities to potentially improve outcomes from post-cardiac arrest syndrome.

Arterial pressure and cerebral blood flow variability: friend or foe? A review

Variability in arterial pressure and cerebral blood flow has traditionally been interpreted as a marker of cardiovascular decompensation, and has been associated with negative clinical outcomes across varying time scales, from impending orthostatic syncope to an increased risk of stroke. Emerging evidence, however, suggests that increased hemodynamic variability may, in fact, be protective in the face of acute challenges to perfusion, including significant central hypovolemia and hypotension (including hemorrhage), and during cardiac bypass surgery. This review presents the dichotomous views on the role of hemodynamic variability on clinical outcome, including the physiological mechanisms underlying these patterns, and the potential impact of increased and decreased variability on cerebral perfusion and oxygenation. We suggest that reconciliation of these two apparently discrepant views may lie in the time scale of hemodynamic variability; short time scale variability appears to be cerebroprotective, while mid to longer term fluctuations are associated with primary and secondary end-organ dysfunction.

Biological basis of neuroprotection and neurotherapeutic effects of Whole Body Periodic Acceleration (pGz)

Exercise is a well known neuroprotective and neurotherapeutic strategy in animal models and humans with brain injury and cognitive dysfunction. In part, exercise induced beneficial effects relate to endothelial derived nitric oxide (eNO) production and induction of the neurotrophins; Brain Derived Neurotrophic Factor (BDNF) and Glial Derived Neurotrophic Factor (GDNF). Whole Body Periodic Acceleration (WBPA (pGz), is the motion of the supine body headward to footward in a sinusoidal fashion, at frequencies of 100-160 cycles/min, inducing pulsatile shear stress to the vascular endothelium. WBPA (pGz) increases eNO in the cardiovascular system in animal models and humans. We hypothesized that WBPA (pGz) has neuroprotective and neurotherapeutic effects due to enhancement of biological pathways that include eNOS, BDNF and GDNF. We discuss protein expression analysis of these in brain of rodents. Animal and observational human data affirm a neuroprotective and neurotherapeutic role for WBPA (pGz). These findings suggest that WBPA (pGz) in addition to its well known beneficial cardiovascular effects can be a simple non-invasive neuroprotective and neurotherapeutic strategy with far reaching health benefits.

Microcirculatory and therapeutic effects of whole body periodic acceleration (pGz) applied after cardiac arrest in pigs

AIMS

Cardiac arrest (CA) and resuscitation are models of whole body ischemia reperfusion injury. Interventions performed prior to (pre-treatment) or after (post-treatment) can result in cardioprotection. Myocardial stunning, characterized by microcirculatory and contractile dysfunction after CA, is an important component of the post-cardiac arrest syndrome. Periodic acceleration (pGz), produced by the cyclical motion of the supine body headward to footward, increases microcirculatory blood flow to vital organs and elicits production of endothelial derived cytoprotective factors in normal animals. We tested the hypothesis that application of pGz 30 min after return of circulation from CA, as a delayed post-treatment strategy, would improve regional microcirculatory blood flow to vital organs and functional indices of myocardial stunning in pigs.

METHODS

8 min of unsupported VF followed by cardiopulmonary resuscitation and defibrillation was carried out in twenty anesthetized and paralyzed male swine who were randomized to delayed post-treatment with pGz (dPost) or none (CONT). pGz was begun 30 min after return of circulation along with conventional mechanical ventilation. Hemodynamics, echocardiogram, and regional blood flows were measured as well as biochemical index of cardiac tissue injury.

RESULTS

All animals had spontaneous return of circulation after cardiopulmonary resuscitation (CPR) and defibrillation. dPost animals had less myocardial stunning and greater regional blood flows to the heart, brain, kidneys, ileum and stomach than CONT. Post-treatment with pGz blunted the increase in Troponin I produced by CA and resuscitation, and, induced a greater rise in endothelial derived nitric oxide synthase (eNOS) and its phosphorylation (p-eNOS).

CONCLUSIONS

Delayed post-treatment with pGz as a therapeutic strategy, protects against early myocardial stunning in VF cardiac arrest by improving microcirculatory blood flow to the heart and also protects other vital organs by this mechanism.

Simulated transport alters surfactant homeostasis and causes dose-dependent changes in respiratory function in neonatal Sprague-Dawley rats

OBJECTIVE

Forces transmitted to the neonate as a consequence of accelerations during transport have been associated with adverse neonatal outcomes including broncho-pulmonary dysplasia. In this study, we sought to determine the relationship between the duration of transport and respiratory performance in the rat model.

METHODS

Four groups of Sprague-Dawley rat pups (10-12 pups/groups) were exposed to simulated medical transport on postnatal day of life 11 or 12. Each group was exposed to an average impulse of 27.4 m/s(2)/min for 0, 30, 60 or 90 min. During the exposure periods, impulse was monitored by computerized sampling using a digital accelerometer. Post-exposure, animals were immediately prepared, placed on mechanical ventilation and analyzed for elastance, tissue damping, airway resistance, ratio of damping to elastance (eta), hysteresivity, and inertance at positive end expiratory pressures (PEEPs) of 0, 3 and 6 cm(3) of H(2)O. Total phospholipid content and surfactant proteins A, B, and C mRNA levels in broncho-alveolar lavage fluid and lung tissue were obtained.

RESULTS

Increased transport time resulted in a significant step-wise increase in airway resistance at all levels of PEEP (P<0.01). Static compliance decreased significantly after 60 min at PEEPs of 3 and 6 cm H(2)O (P<0.01). Eta significantly decreased with greater transport time at a PEEP of 6 cm H(2)O (P<0.05). Tissue damping increased with duration of transport time across all PEEP levels, but only exhibited statistical significance at a PEEP of 0 cm H(2)O (P<0.05). No differences were seen in hysteresivity or inertance. Compared with controls, transport was associated with significant reductions in total phospholipid content and mRNA levels of surfactant proteins B and C.

CONCLUSION

Rat pups experienced significant deterioration of respiratory function with increasing duration of simulated transport.

Whole body periodic acceleration (pGz) improves survival and allows for resuscitation in a model of severe hemorrhagic shock in pigs

BACKGROUND

Whole body periodic acceleration (pGz), the repetitive, head-foot sinusoidal motion of the body, increases pulsatile shear stress on the vascular endothelium producing increased release of endothelial derived nitric oxide (eNO) into circulation. Based upon prior CPR investigations, we hypothesized that pGz instituted prior to and during hemorrhagic shock (HS) should improve survival.

MATERIALS AND METHODS

Sixteen anesthetized male pigs, 23 ± 5 kg, were randomized to receive 1 h pGz or no pGz (CONT) prior to and during severe controlled graded HS up to 2-1/2 h. HS was induced by removing blood at 10 mL/kg increments from the circulation at 30-min intervals up to a maximum blood loss of 50 mL/kg. Thirty minutes after maximum blood loss, shed blood and lactated Ringers solution was infused intravenously.

RESULTS

All animals survived up to 30 mL/kg blood loss. Survival and return to normal blood pressure to 120 min was achieved in 50% of animals receiving pGz compared with none in CONT. Cardiac output, blood pressure, and oxygen delivery decreased equally in both groups but oxygen consumption was significantly lower with pGz than CONT during all hemorrhage time points. Regional blood flow (RBF) was preserved in brain, heart, kidneys, ileum, and stomach in both groups up to 40 mL/kg of blood loss. After 40 mL/kg blood loss, RBF was much better preserved in pGz than CONT.

CONCLUSIONS

pGz applied 1 h prior to and during severe graded hemorrhagic shock delays onset of irreversible shock, enabling potential restoration of blood loss and survival.

Periodic acceleration (pGz) prior to whole body ischemia reperfusion injury provides early cardioprotective preconditioning

AIMS

Periodic acceleration (pGz) is a method that applies repetitive sinusoidal head-to-foot motion to the horizontally positioned body. pGz adds pulses to the circulation as a function of frequency, thereby increasing shear stress to the endothelium. Pulsatile shear stress increases release of cardioprotective endothelial-derived nitric oxide prostaglandin E-2 and prostacyclin into the circulation. We investigated whether pGz may be effective as an early preconditioning strategy when applied one hour prior to whole body ischemia reperfusion injury induced by ventricular fibrillation (VF).

MAIN METHODS

Twenty anesthetized and paralyzed male swine were randomized to one hour of pGz and conventional mechanical ventilation [PC] or solely conventional mechanical ventilation [Control] prior to VF and resuscitation. After eight minutes of unsupported VF, cardiopulmonary resuscitation was carried out followed by defibrillation. Hemodynamics, electrocardiogram, echocardiogram, regional blood flows, and markers of global myocardial injury were measured. Protein expression of endothelial-derived nitric oxide synthase (eNOS), phosphorylated eNOS (p-eNOS), serine/threonine kinase Akt total (t-Akt), and phosphorylated (p-Akt) were determined by immunoblotting.

KEY FINDINGS

All animals had spontaneous return of circulation after cardiopulmonary resuscitation (CPR) and defibrillation. Preconditioned animals had less hemodynamically significant arrhythmias, less myocardial stunning, and greater regional blood flows to the brain, heart, kidneys, and ileum than Controls. Troponin I and creatine phosphokinase values in PC were 65% of the values present in Controls. In addition, preconditioned animals had higher protein expression of cardiac eNOS, p-eNOS, t-Akt, and p-Akt than Controls.

SIGNIFICANCE

pGz preconditioning confers early cardioprotection in a model of whole body ischemia reperfusion injury.

In vivo upregulation of nitric oxide synthases in healthy rats

Periodic acceleration (pGz), sinusoidal motion of the whole body in a head-foot direction in the spinal axis, is a novel noninvasive means for cardiopulmonary support and induction of pulsatile shear stress. pGz increases plasma nitrite levels, in vivo and in vitro. Additionally, pGz confers cardioprotection in models of ischemia reperfusion injury. We hypothesize that pGz may also confer a cardiac phenotypic change by upregulation of the expression of the various NO synthase (NOS) isoforms in vivo. pGz was applied for 1h to awake restrained male rats at 2 frequencies (360 and 600 cpm) and acceleration (Gz) of +/-3.4 m/s(2). pGz did not affect arterial blood gases or electrolytes. pGz significantly increased total nitrosylated protein levels, indicating increased NO production. pGz also increased mRNA and protein levels of eNOS and nNOS, and phosphorylated eNOS in heart. pGz increased Akt phosphorylation (p-AKT), but not total Akt, or phosphorylated ERK1/2. Inducible (i) NOS levels were undetectable with or without pGz. Immunoblotting revealed the localization of nNOS, exclusively in cardiomyocyte, and pGz increased its expression. We have demonstrated that pGz changes myocardial NOS phenotypes. Such upregulation of eNOS and nNOS was still evident 24h after pGz. Further studies are needed to understand the biochemical and biomechanical signal transduction pathway for the observed NOS phenotype changed induced by pGz.

Low-amplitude pulses to the circulation through periodic acceleration induces endothelial-dependent vasodilatation

Low-amplitude pulses to the vasculature increase pulsatile shear stress to the endothelium. This activates endothelial nitric oxide (NO) synthase (eNOS) to promote NO release and endothelial-dependent vasodilatation. Descent of the dicrotic notch on the arterial pulse waveform and a-to-b ratio (a/b; where a is the height of the pulse amplitude and b is the height of the dicrotic notch above the end-diastolic level) reflects vasodilator (increased a/b) and vasoconstrictor effects (decreased a/b) due to NO level change. Periodic acceleration (pG(z)) (motion of the supine body head to foot on a platform) provides systemic additional pulsatile shear stress. The purpose of this study was to determine whether or not pG(z) applied to rats produced endothelial-dependent vasodilatation and increased NO production, and whether the latter was regulated by the Akt/phosphatidylinositol 3-kinase (PI3K) pathway. Male rats were anesthetized and instrumented, and pG(z) was applied. Sodium nitroprusside, N(G)-nitro-l-arginine methyl ester (l-NAME), and wortmannin (WM; to block Akt/PI3K pathway) were administered to compare changes in a/b and mean aortic pressure. Descent of the dicrotic notch occurred within 2 s of initiating pG(z). Dose-dependent increase of a/b and decrease of mean aortic pressure took place with SNP. l-NAME produced a dose-dependent rise in mean aortic pressure and decrease of a/b, which was blunted with pG(z). In the presence of WM, pG(z) did not decrease aortic pressure or increase a/b. WM also abolished the pG(z) blunting effect on blood pressure and a/b of l-NAME-treated animals. eNOS expression was increased in aortic tissue after pG(z). This study indicates that addition of low-amplitude pulses to circulation through pG(z) produces endothelial-dependent vasodilatation due to increased NO in rats, which is mediated via activation of eNOS, in part, by the Akt/PI3K pathway.

Periodic acceleration (pGz) acutely increases endothelial and neuronal nitric oxide synthase expression in endomyocardium of normal swine

INTRODUCTION

Periodic acceleration (pGz) is a non-invasive method of increasing pulsatile shear stress to the endothelium. pGz is achieved by the sinusoidal head to foot motion to the supine body. pGz increases endogenous production of nitric oxide in whole animal models and isolated perfused vessel preparations, and is cardioprotective when applied prior to, during and after ischemia reperfusion. In part, the protective effects of pGz are attributable to nitric oxide (NO). The purpose of this investigation was to determine whether pGz up-regulates NOS isoforms in the endomyocardium.

METHODS AND RESULTS

Fifteen swine weight 15-20 kg, were anesthetized, instrumented to measure hemodynamics and randomized. Ten animals received 1h of pGz at 180 cycles/min and Gz+/-3.9 m/s(2) [pGz] in addition to conventional ventilatory support and five served as time controls.

RESULTS

pGz produced a 2.3+/-0.4 and a 6.6+/-0.1 fold significant increase in eNOS and phosphorylated eNOS, 3.6+/-1.1 fold increase in nNOS, and no significant change in iNOS. pGz also produced a 2.4+/-0.3 and 3.9+/-0.2 folds significant increase in both total(t-Akt) and phosphorylated (p-Akt) Akt.

CONCLUSIONS

pGz is associated with an increase in both total and phosphorylated eNOS and nNOS protein expression in endomyocardium, and induced significant increase in total and phosphorylated-Akt. The data indicates that pGz is a novel method to induce eNOS and nNOS production in the endomyocardium. Therefore, pGz may serve as a powerful non-invasive intervention to activate the beneficial cardiac effects of endothelial and neuronal NOS.

Acute effects of "delayed postconditioning" with periodic acceleration after asphyxia induced shock in pigs

Asphyxia cardiac arrest and shock are models for whole body ischemia reperfusion injury. Periodic acceleration (pGz) achieved by moving the body on a platform is a novel method for inducing pulsatile vascular shear stress and endogenous production of endothelial nitric oxide, prostaglandin E2, tissue plasminogen activator, and adrenomedullin. The aforementioned are cardioprotective during and after ischemia reperfusion injury. We investigated whether pGz, applied 15 min after return of spontaneous circulation (ROSC) would serve as an effective "delayed" post conditioning tactic to lessen acute reperfusion injury markers in a pediatric swine model of asphyxia induced shock. Asphyxia shock was induced in 20 swine weight 3.9 +/- 0.6 kg. Fifteen minutes after ROSC, the animals were randomized to receive conventional mechanical ventilation (CMV, [Control]) or CMV with pGz. All animals had ROSC and no significant differences in blood gases or hemodynamics after ROSC. pGz treated had significantly less myocardial dysfunction post resuscitation, (i.e. better % ejection fraction (EF), % fractional shortening (FS), and wall motion score index) and lower biochemical indices of reperfusion injury (lower TNF-alpha, IL-6, and Troponin I, and myeloperoxidase activity). Delayed postconditioning with pGz ameliorates acute post resuscitation reperfusion injury and improves myocardial dysfunction after asphyxia-induced shock.

Non-selective cyclooxygenase inhibition before periodic acceleration (pGz) cardiopulmonary resuscitation (CPR) in a porcine model of ventricular fibrillation

Whole body periodic acceleration (pGz) along the spinal axis is a novel method of cardiopulmonary resuscitation (CPR). Oscillatory motion of the supine body in a horizontal fashion provides ventilation and blood flow to vital organs during cardiac arrest and pulsatile shear stress to the vascular endothelium. We previously showed in pigs that pGz-CPR affords better overall survival, post resuscitation myocardial function, and neurological outcomes compared to conventional chest compression CPR. pGz through pulsatile shear stress on the vascular endothelium elicits acute production of prostaglandins and endothelial-derived nitric oxide (eNO) in whole animal models and in vitro preparations. The salutary effects associated with pGz-CPR compared to chest compression CPR are in part related to endothelial-derived nitric oxide. Both eNO and prostaglandins are cardioprotective in ischemia reperfusion models. To differentiate between the roles of these mediators, indomethacin a non-selective cyclooxygenase inhibitor (COX) was used as a tool to investigate prostaglandin effects during pGz-CPR by acute outcomes of survival, cardioprotection and regional blood flows (RBF). Two groups of anesthetized, intubated pigs weighing 25-36kg were studied. Prior to electrical induction of ventricular fibrillation (VF) animals received equal volumes of either saline placebo Control (CONT) (n=9) or indomethacin (INDO), (n=8), (2mg/kg). After 3min of unsupported VF, both groups received 15min of pGz-CPR followed by pharmacologic and electrical attempts for resuscitation. Return of circulation (ROSC) to 3h occurred in (78%) in CONT and (63%) in INDO pretreated animals. There was no statistically significant difference in hemodynamics between groups at baseline or during the protocol. At baseline, INDO caused a decrease in brain RBF. Two hours after ROSC, INDO blunted the hyperemia response to brain and heart. Echocardiographic evidence of myocardial dysfunction was most notable for the INDO group in the wall motion score index (WMSI). After 3h of ROSC there was a 4-fold difference in both creatine phosphokinase (CPK) and Troponin I concentration between INDO and CONT. Therefore, non-specific acute inhibition of COX in part blunts the salutary effects of pGz-CPR. These data suggest that prostaglandins in part are involved in the cardio protection induced by pGz during CPR.

Adrenomedullin is increased by pulsatile shear stress on the vascular endothelium via periodic acceleration (pGz)

Periodic acceleration (pGz) is produced by a platform which moves the supine body repetitively in a headward to footward direction. The imparted motion produces pulsatile shear stress on the vascular endothelium. Pulsatile shear stress on the vascular endothelium has been shown to elicit production of a host of cardioprotective, cytoprotective mediators. The purpose of this study was to ascertain if pGz also enhances production of adrenomedullin (AM) in normal healthy swine. Twelve pigs (weight range 20-30 kg) were anesthetized, intubated and placed on conventional mechanical ventilation. All animals were secured to the motion platform. In one group (pGz) (n=7) was activated for 1h, and monitored for an additional 3h. A control group (CONT) (n=5) served as time control. Arterial blood gases, hemodynamic measurements, and serum for AM, interleukin 4, 6 and thromboxane B(2) (TBXB2) were measured at baseline, immediately after pGz, and 3h after pGz had been discontinued. There was no significant change from baseline value in IL-4, IL-6 or TBXB2. Mean arterial blood pressure decreased in pGz-treated animals from 115+/-10 at baseline to 90+/-8 after 60 min of pGz (p<0.01). AM levels increase from 776+/-176 pg/ml baseline to 1160+/-68 pg/ml immediately after pGz, and remained elevated to 1584+/-160 pg/ml, 3h after pGz (p<0.01 vs. BL). This is the first report of AM-enhanced production using a non-invasive method of increasing pulsatile shear stress on the vascular endothelium. pGz increases production of AM in normal healthy swine. These changes are independent of IL-4, IL-6 or TBXB2 production.

Periodic acceleration (pGz) CPR in a swine model of asphyxia induced cardiac arrest. Short-term hemodynamic comparisons

BACKGROUND

Asphyxia is one of the most common causes of pediatric cardiac arrest, and becoming a more frequently recognized cause in adults. Periodic acceleration (pGz) is a novel method of cardiopulmonary resuscitation (CPR). pGz is achieved by rapid motion of the supine body headward-footward that generates adequate perfusion and ventilation during cardiac arrest. In a swine ventricular fibrillation cardiac arrest model, pGz produced a higher return of spontaneous circulation (ROSC), superior neurological outcome, less echocardiography evidence of post resuscitation myocardial stunning, and decreased indices of tissue injury. In contrast to standard chest compression CPR, pGz does not produce rib fractures. We investigated the feasibility of pGz in severe asphyxia cardiac arrest and assessed whether beneficial effects seen in the VF model of cardiac arrest could be realized.

METHODS AND RESULTS

Sixteen swine weight 4+/-1 kg were anesthetized, tracheally intubated, and instrumented to measure, hemodynamics and echocardiography. Asphyxia was induced by occlusion of the tracheal tube. After loss of aortic pulsations (median time 10 min) animals were observed for three additional minutes following which all were in cardiac arrest. The animals were then randomized to receive 10 min of pGz or standard chest compression ventilation performed with a commercial device (Thumper). A single dose of epinephrine (adrenaline) and sodium bicarbonate were given and defibrillation attempted if appropriate for a maximum of 10 min. Both groups received fractional inspired O2 concentration of 100% during CPR and after resuscitation. Four animals in each group (50%) had an initial ROSC, however only two of the four initial survivors remained alive 3h after ROSC. There were no significant differences in blood pressure, coronary perfusion pressure during CPR and after early ROSC between groups. pGz treated animals had significantly lower pulmonary artery pressure; 20+/-4 mmHg compared to Thumper 46+/-5 mmHg, 30 min after ROSC (p<0.01). Surviving animals in both groups had severe myocardial dysfunction at 30 min after ROSC. At necropsy, 25% of the Thumper treated animals had rib fractures, while none occurred in the pGz group.

CONCLUSIONS

In a lethal model of asphyxia cardiac arrest, pGz is equivalent to standard CPR, with respect to acute outcomes and resuscitation survival rates but is associated with significantly lower pulmonary artery pressures and does not produce traumatic rib fractures.

Endothelium and cardiopulmonary resuscitation

The endothelium is a viable target for injury, repair and cellular modulation. Because of its vast extension and active metabolic status of producing mediators for vasomotor tone, coagulation, and inflammation, it is a key target for therapy during ischemia/reperfusion injury. Cardiopulmonary resuscitation is a model of whole-body ischemia/reperfusion injury. It has become apparent that the endothelium participates in a host of responses elicited by ischemia/reperfusion. This review examines the role of the endothelium during and after ischemia/reperfusion and the participation by its mediators and evidence for endothelial involvement during and after cardiopulmonary resuscitation. The strategic location of the endothelium makes it an excellent signal transduction mechanism for a host of disease processes. In addition to biochemical stimuli, mechanical stimulation of the endothelium elicits production of several mediators, including endothelium-derived nitric oxide, prostaglandins, and antithrombotics and anticoagulants. Whole-body, periodic acceleration is a novel method of stimulating the endothelium via pulsatile shear stress. Periodic acceleration has been shown to be an effective experimental method of cardiopulmonary resuscitation, with evidence of postresuscitation cardioprotective effects. This review indicates that understanding endothelial modulation during and after ischemia/reperfusion will significantly improve therapeutic choices.

Post-resuscitation reperfusion injury: Comparison of periodic Gz acceleration versus Thumper CPR

The effects of whole body, periodic acceleration (pGz) on cardiopulmonary resuscitation outcome, organ blood flow and tissue inflammatory injury were examined in an experimental pig model, and compared with Thumper (TH)-CPR. VF was induced in 16 pigs, and remained untreated for 3 min, followed by either pGz-CPR or TH-CPR for 15 min. Defibrillation attempts were made at 18 min of VF. Six of eight animals had ROSC in both groups. Post-arrest myocardial dysfunction was present in both groups and progressed over hours. pGz-CPR animals had less wall motion abnormality and higher left ventricular ejection fraction than TH-CPR. The post-resuscitation haemodynamic variables returned to baseline after 3h of ROSC in pGz-CPR group, and remained low in TH-CPR group. The brain blood flow during CPR was similar between TH-CPR and pGz-CPR, 17% and 20% of pre-fibrillation values, respectively. The cardiac blood flow during CPR was significantly lower in pGz-CPR than TH-CPR (TH: 10.2% and pGz: 1.9% of pre-fibrillation value), as well as in other organs. The brain and heart blood flow was significantly higher than pre-fibrillation values after 30 min of ROSC in both groups. The pGz group had significantly higher blood flow in brain, heart and kidney than TH-CPR after 30 min of ROSC. Blood flow in all organs decreased below pre-fibrillation values at 2h of ROSC. Tissue inflammatory injury progressed over hours in the post-resuscitation phase. pGz-CPR group had significantly lower myeloperoxidase (MPO) activity and plasma creatine phosphokinase (CPK) and cardiac troponin I, TNF-alpha, and IL-6 than TH-CPR. Results from the present study demonstrate again that pGz-CPR is an effective method of cardiopulmonary resuscitation, with less post-reperfusion injury compared to TH-CPR.

Whole-body periodic acceleration modifies experimental asthma in sheep

RATIONALE

Nitric oxide is released from vascular endothelium in response to increased pulsatile shear stress. Nitric oxide inhibits mast cell activation and is antiinflammatory and therefore might be protective in asthma.

OBJECTIVES

We determined if a noninvasive motion platform that imparts periodic sinusoidal inertial forces to the whole body along the spinal axis (pGz) causing release of endothelial nitric oxide modulates experimental asthma in sheep.

METHODS

Allergic sheep were untreated (control) or were treated with pGz alone or after receiving intravenously the nitric oxide synthase inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME) before aerosol challenge with Ascaris suum, and the effect on antigen-induced airway responses was determined. Bronchoalveolar lavage cells obtained 6 h after antigen challenge were analyzed for nuclear factor-kappaB (NF-kappaB) activity in the respective groups.

RESULTS

pGz treatment for 1 h before antigen challenge reduced the early airway response and blocked the late airway response but did not prevent the antigen-induced airway hyperresponsiveness 24 h after challenge. Administration of L-NAME before pGz completely reversed this protection, whereas L-NAME alone did not affect the antigen-induced responses. NF-kappaB activity was 1.9- and 1.8-fold higher in the control and L-NAME + pGz groups, respectively, compared with pGz-treated animals. Extending the pGz treatment to twice daily for 3 d and then 1 h before antigen challenge blocked the early and late airway responses, the 24-h airway hyperresponsiveness, and the airway inflammatory cell response.

CONCLUSION

Whole-body pGz modulates allergen-induced airway responses in allergic sheep.

Biophysics of cardiopulmonary resuscitation with periodic z-axis acceleration or abdominal compression at aortic resonant frequencies

Periodic z-axis acceleration (pGz)-CPR involves an oscillating motion of a whole patient in the head-to-foot dimension on a mechanized table. The method is able to sustain blood flow and long-term survival during and after prolonged cardiac arrest in anesthetized pigs. However, the exact mechanism by which circulation of blood is created has remained unknown.

OBJECTIVES

To explain the hemodynamic mechanism of pGz-CPR and to suggest some theoretically useful improvements.

METHOD

Computer modeling using a hybrid analytical-numerical approach, based upon Newton's second law of motion for fluid columns in the aorta and vena cavae, Ohm's law for resistive flow through vascular beds, and a 10-compartment representation of the adult human circulation. This idealized 70-kg human model is exercised to explore the effects upon systemic perfusion pressure of whole body z-axis acceleration at frequencies ranging from 0.5 to 5 Hz. The results, in turn, suggested studies of abdominal compression at these frequencies.

RESULTS AND CONCLUSIONS

Blood motion induced in great vessels by periodic z-axis acceleration causes systemic perfusion when cardiac valves are competent. Blood flow is a function of the frequency of oscillation. At 3.5 Hz, periodic acceleration using +/-0.6G and +/-1.2 cm oscillations induces forward blood flow of 2.1L/min and systemic perfusion pressure of 47 mmHg. A form of resonance occurs at the frequency for peak-flow, in which the period of oscillation matches the round-trip transit time for reflected pulse waves in the aorta. For +/-1.0 G acceleration at 3.5 Hz, systemic perfusion pressure is 80 mmHg and forward flow is 3.8L/min in the adult human model with longitudinal z-axis motion of only +/-2 cm. Similar results can be obtained using abdominal compression to excite resonant pressure-volume waves in the aorta. For 20 mmHg abdominal pressure pulses at 3.8 Hz, systemic perfusion pressure is 7 mmHg and forward flow is 2.8L/min. pGz-CPR and high-frequency abdominal CPR are the physically realistic means of generating artificial circulation during cardiac arrest. These techniques have fundamental mechanisms and practical features quite different from those of conventional CPR and the potential to generate superior systemic perfusion.

Echocardiographic comparison of cardiopulmonary resuscitation (CPR) using periodic acceleration (pGz) versus chest compression

OBJECTIVE

This investigation compared the effects of conventional cardiopulmonary resuscitation (CPR) using an automated Thumper chest compression device to periodic acceleration CPR (pGz-CPR) on early post-resuscitation ventricular function assessed by echocardiography, in an adult pig model of CPR.

BACKGROUND

Whole body periodic acceleration along the spinal axis (pGz) is a new method of cardiopulmonary resuscitation (CPR). Biomechanical forces and biochemical release produced by pGz impart ventilation and increase blood flow. Our laboratory has reported normal neurological and cardiovascular function 48 h after return of spontaneous circulation in animals that have undergone 22 min of pGz-CPR.

METHODS

Ventricular fibrillation (VF) was induced in 16 animals (25-35 kg). After 3 min of non-interventional period, the animals were randomized to receive either pGz-CPR or Thumper-CPR for 15 min. After 18 min of VF, a single dose of vasopressin and bicarbonate were administered and defibrillation attempted. An echocardiogram was performed at baseline and serially for 6h. Ejection fraction (EF), fractional shortening (FS) and wall motion were assessed by 2D and M-mode echocardiography.

RESULTS

Return of spontaneous circulation to 360 min occurred in 5/8 (62%) of the animals receiving Thumper-CPR and in 7/8 (88%) receiving pGz-CPR. FS and EF were impaired after CPR, but pGz-CPR animals had less impairment than Thumper-CPR animals. Further, wall motion score index (WMSI) was more impaired after Thumper-CPR and remained as such even 6h post-CPR.

CONCLUSION

pGz holds promise as a new method for CPR with better left ventricular (LV) function post-CPR than the more traditional chest compression method.

Periodic acceleration: effects on vasoactive, fibrinolytic, and coagulation factors

Cellular and isolated vessel experiments have shown that pulsatile and laminar shear stress to the endothelium produces significant release of mediators into the circulation. Periodic acceleration (pGz) applied to the whole body in the direction of the spinal axis adds pulses to the circulation, thereby increasing pulsatile and shear stress to the endothelium that should also cause release of mediators into the circulation. The purpose of this study was to determine whether addition of pulses to the circulation through pGzwould be sufficient to increase shear stress in whole animals and to acutely release mediators and how such a physical maneuver might affect coagulation factors. Randomized control experiments were performed on anesthetized, supine piglets. The treatment group (pGz) ( n = 12) received pGzwith a motion platform that moved them repetitively head to foot at ±0.4 g at 180 cpm for 60 min. The control group ( n = 6) was secured to the platform but remained on conventional ventilation throughout the 4-h protocol. Compared with control animals and baseline, pulsatile stress produced significant increases of serum nitrite, prostacyclin, PGE2, and tissue plasminogen activator antigen and activity, as well as D-dimer. There were no significant changes in epinephrine, norepinephrine, cortisol, and coagulation factors between groups or from baseline values. Pulsatile and laminar shear stress to the endothelium induced by pGzsafely produces increases of vasoactive and fibrinolytic activity. pGzhas potential to achieve mediator-related benefits from the actions of nitric oxide and prostaglandins.

Airflow synchronous with oscillatory acceleration reflects involuntary respiratory muscle activity

To explore mechanisms causing involuntary airflow synchronous with oscillatory axial whole body acceleration (oscillatory axial acceleration, OAA) such as that during locomotion, we monitored airflow, acceleration, and electromyograms (EMGs) of the rib cage and abdominal muscles in standing subjects undergoing OAA at 3, 6, and 9 Hz at accelerations of 0.1-0.95 g. Subjects relaxed or performed static respiratory maneuvers at constant lung volume with glottis open. Oscillatory airflows (0.01-3.01 s(-1)) synchronous with OAA were not consistent with expectations for a passive respiratory system, and were larger during active respiratory efforts than during relaxation. Peak inspiratory airflow usually preceded peak upward acceleration by 90-180 degrees. In 80% of runs with respiratory muscles voluntarily activated or relaxed, EMGs showed activity synchronous with OAA. Changes in periodic muscle activity coincided with changes in oscillatory airflow. We conclude that periodic muscle activity, probably a reflex response to body wall deformation during OAA, strongly influences the involuntary airflow synchronous with OAA.

Cardiopulmonary resuscitation (CPR) using periodic acceleration (pGz) in an older porcine model of ventricular fibrillation

Cardiopulmonary resuscitation (CPR) can be achieved by repetitive motion of the body headwards to footwards in the spinal axis, at 2 Hz and +/- 0.6 G in a juvenile pig model of ventricular fibrillation. Return of spontaneous circulation and normal neurological outcome occurred after a total of 22 min of ventricular fibrillation that included a 3-min noninterventional period [Resuscitation 56 (2003) 215; Resuscitation 51 (2001) 55]. Since older pigs have stiffer rib cages than juvenile pigs and their hemodynamic response to various stimuli might differ, this study was carried out to determine whether this method of CPR, termed pGz-CPR, was just as effective in older pigs. pGz-CPR was also compared to chest compression CPR using an automated mechanical device (CONV-CPR). Ventricular fibrillation was instituted in older pigs weighing 23-34 kg and a 3-min noninterventional period was observed, followed by 15 min pGz-CPR in eight pigs or 15 min CONV-CPR in eight pigs. Return of spontaneous circulation (ROSC) occurred after defibrillation in all eight pigs with pGz-CPR and in six of eight pigs with CONV-CPR. Two of eight pigs with CONV-CPR and none of the eight pigs with pGz-CPR had rib fractures. Hemodynamic instability 15 min after ROSC occurred in all animals with CONV-CPR whereas only three of eight pigs with pGz-CPR demonstrated hemodynamic instability (P < 0.05). We conclude that pGz-CPR in older pigs produces similar ROSC reported by other investigators in pigs without the risk of rib fractures. Further, pGz-CPR is associated with a lower incidence of periods of hemodynamic instability following ROSC than CONV-CPR.

Survival and normal neurological outcome after CPR with periodic Gz acceleration and vasopressin

BACKGROUND

We showed previously that whole body periodic acceleration along the spinal axis (pGz) is a novel method of cardiopulmonary resuscitation (CPR). The ultimate assessment of the value of any CPR technique is the neurological outcome after using such a technique. In this study, we determined the neurological outcome in pigs after prolonged pGz-CPR, with administration of vasopressin immediately prior to defibrillation. Neurological outcome after pGz-CPR was compared to a control group where no intervention occurred for the same time period (C-NoInterv).

METHODS AND RESULTS

Ventricular Fibrillation (VFIB) was induced in 12 animals. After a 3 min non-interventional interval, the animals received either pGz-CPR (n=7), or C-NoInterv (n=5) for 15 min. After 18 min of VFIB, a single dose of vasopressin (0.8 U/kg) was administered along with sodium bicarbonate and bretylium, and defibrillation was attempted. All animals in the pGz-CPR group had return of spontaneous circulation (ROSC) and normal neurological assessment at 24 h. Neurologic outcome remained normal at 48 h. In contrast, none of the animals in the C-NoInterv had ROSC.

CONCLUSION

Prolonged pGz-CPR, with administration of vasopressin immediately prior to defibrillation results in normal neurological outcomes at 24 h.

Regional blood flow during periodic acceleration

OBJECTIVE

To determine whether a motion platform that imparts noninvasive periodic acceleration (pGz) forces to the body causes systemic vasodilation and changes local organ blood flow.

DESIGN

Prospective paired blocked design.

SETTING

Medical center research laboratory.

SUBJECTS

Juvenile Yorkshire pigs.

INTERVENTIONS

Juvenile pigs (12 kg) were anesthetized, paralyzed, and placed on a motion platform that oscillated at a frequency of 4 Hz and a force of approximately 0.4 G.

MEASUREMENTS AND MAIN RESULTS

Regional blood flows, as assessed by colored microspheres, increased during pGz relative to values obtained before pGz. Blood flow (mL.min-1.100 g-1) significantly increased to the epicardium (71%), endocardium (93%), cerebrum (183%), brain stem (177%), renal cortex (53%), ileal mucosa (69%), gastric antral mucosa (72%), and liver (86%). Spleen and skeletal muscle blood flow increased without statistical significance, 38% and 158% with pGz, relative to paired control values. Regional blood flows returned to baseline 10 mins after discontinuation of pGz, except in the myocardial layers, where blood flow remained significantly elevated. There was no difference compared with baseline in heart rate, arterial blood gases, and blood pressure, but serum nitrite concentration was significantly higher (58%) during pGz. In another series of animals, pGz increased pulmonary artery blood flow directly proportional to the magnitude of the applied acceleration force with frequency held constant.

CONCLUSIONS

Periodic sinusoidal inertial forces in the spinal axis increase blood flow to tissues. The increased blood flow is reversible and may be caused by vasodilation secondary to local mediator release. These effects may be desirable in clinical conditions of low tissue oxygen delivery and perfusion.

Novel CPR with periodic Gz acceleration

The effects of periodic Gz acceleration (pGz) on cardiovascular function and hemodynamics were determined in a pig model of acute cardiopulmonary resuscitation (CPR). The application of pGz (horizontal head-to-foot oscillations) at 2 Hz increased cardiac output in fibrillated animals proportional to the amplitude of the applied acceleration force that plateaued at 0.7 G. Cardiac output in fibrillating animals was restored to 20% of the values obtained before fibrillation with pGz-CPR and arterial blood gas values were normal during this period. The central vascular pressure gradient driving blood flow was only about 6 mmHg, suggesting low vascular resistance during pGz-CPR. In another study, capillary blood flow was determined before and after pGz-CPR using colored microspheres. Capillary perfusion was detected in all tissue beds studied during pGz-CPR. Significant capillary blood flow was detected in the endocardium and brain stem during pGz-CPR that represented 39 and 197% of control values before fibrillation, respectively. Thus, the cardiac output during pGz-CPR was preferentially distributed to the myocardial and brain tissues. In a final group, animals were successfully resuscitated with return of spontaneous circulation (ROSC) after pGz-CPR for 15 min following cardiac fibrillation with a 3-min non-intervention period. Following ROSC, blood pressure was maintained at pre-arrest values for 2 h without any pharmacological or mechanical support. Arterial blood gases during the pGz-CPR and the ROSC periods were normal and not different from values obtained before fibrillation. None of the control animals (18 min of fibrillation without pGz-CPR) survived the experimental protocol and only two of these six animals briefly returned to spontaneous circulation (<20 min). In conclusion, experimental pGz-CPR produces cardiac output, capillary blood flow, and ventilation sufficient to maintain fibrillating animals for 18 min with ROSC for 2 h without support.

Hemodynamic effects of periodic G(z) acceleration in meconium aspiration in pigs

The hemodynamic effects of periodic acceleration (pG(z)), induced in the spinal axis with noninvasive motion ventilation (NIMV), were studied in a piglet model of pulmonary hypertension associated with meconium aspiration. Animals (n = 12) were anesthetized, paralyzed, intubated, and supported by conventional mechanical ventilation (CMV). Thirty minutes after tracheal instillation of meconium solution (6 ml/kg), either CMV (n = 6) was continued or NIMV (n = 6) was initiated. Changes in systemic and pulmonary hemodynamics and arterial blood gases were tracked for 2 h after aspiration. Thermodilution, cardiac output, and heart rate were not significantly different after meconium aspiration in the pG(z) group relative to the CMV controls. Aortic pressure and systemic vascular resistance were significantly lower (approximately 30%) after meconium aspiration in NIMV animals relative to CMV animals. Pulmonary arterial pressure and pulmonary vascular resistance were also significantly lower, by 100%, after aspiration of meconium in the NIMV animals compared with the CMV controls. Meconium aspiration significantly decreased total respiratory compliance by approximately 50% and increased total respiratory resistance by approximately 100% in both CMV and NIMV animals, but such alterations did not differ between the two groups. Both CMV and NIMV satisfactorily supported ventilation in these paralyzed animals. In conclusion, NIMV through pG(z) in the spinal axis decreased systemic and pulmonary vascular resistance in piglets after meconium aspiration.