PRecision Event Monitoring for PatienTs with Heart Failure using HeartLogic (PREEMPT-HF) study design and enrolment.

AIMS: The HeartLogic multisensor index has been found to be a sensitive predictor of worsening heart failure (HF). However, there is limited data on this index's association and its constituent sensors with HF readmissions. METHODS AND RESULTS: The PREEMPT-HF study is a global, multicentre, prospective, observational, single-arm, post-market study. HF patients with an implantable defibrillator device or cardiac resynchronization therapy with defibrillator with HeartLogic capabilities were eligible if sensor data collection was turned on and the HeartLogic feature was not enabled. Thus, the HeartLogic Index/alert and heart sounds sensor trends were unavailable via the LATITUDE remote monitoring system to clinicians (blinded). Evaluation of subject medical records at 6 months and a final in-clinic visit at 12 months was required for collection of all-cause hospitalizations and HF outpatient visits. The purpose of this study is exploratory, no formal hypothesis tests are planned, and no adjustment for multiple testing will be performed. A total of 2183 patients were enrolled at 103 sites between June 2018 and June 2020. A significant proportion of the patients were implanted with implantable defibrillator devices (39%) versus cardiac resynchronization therapy with defibrillator (61%); were female (27%); over 65 (61%); New York Heart Association class I (13%), II (53%), and III (33%); ejection fraction < 25% (21%); ischaemic (50%); and with a history of renal dysfunction (23%). CONCLUSIONS: The PREEMPT study will provide clinical data and blinded sensor trends for the characterization of sensor changes with HF readmission, tachyarrhythmias, and event subgroups. These data may help to refine the clinical use of HeartLogic and to improve patient outcomes.

Multiple cArdiac seNsors for mAnaGEment of Heart Failure (MANAGE-HF) - Phase I Evaluation of the Integration and Safety of the HeartLogic Multisensor Algorithm in Patients With Heart Failure.

BACKGROUND: Patients with heart failure (HF) and reduced ejection fraction suffer from a relapsing and remitting disease course, where early treatment changes may improve outcomes. We assessed the clinical integration and safety of the HeartLogic multisensor index and alerts in HF care. METHODS: The Multiple cArdiac seNsors for mAnaGEment of Heart Failure (MANAGE-HF) study enrolled 200 patients with HF and reduced ejection fraction (<35%), New York Heart Association functional class II-III symptoms, implanted with a cardiac resynchronization therapy-defibrillator or and implantable cardioverter defibrillator, who had either a hospitalization for HF within 12 months or unscheduled visit for HF exacerbation within 90 days or an elevated natriuretic peptide concentration (brain natriuretic peptide [BNP] of ≥150 pg/mL or N-terminal pro-BNP [NT-proBNP] of ≥600 pg/mL). This phase included the development of an alert management guide and evaluated changes in medical treatment, natriuretic peptide levels, and safety. RESULTS: The mean age of participants was 67 years, 68% were men, 81% were White, and 61% had a HF hospitalization in prior 12 months. During follow-up, there were 585 alert cases with an average of 1.76 alert cases per patient-year. HF medications were augmented during 74% of the alert cases. HF treatment augmentation within 2 weeks from an initial alert was associated with more rapid recovery of the HeartLogic Index. Five serious adverse events (0.015 per patient-year) occurred in relation to alert-prompted medication change. NTproBNP levels decreased from median of 1316 pg/mL at baseline to 743 pg/mL at 12 months (P < .001). CONCLUSIONS: HeartLogic alert management was safely implemented in HF care and may optimize HF management. This phase supports further evaluation in larger studies. TRIAL REGISTRATION: ClinicalTrials.gov (NCT03237858).

Evaluation of Medicare Claims for the Development of Heart Failure Diagnostics.

BACKGROUND: Although claims data provide a large and efficient source of clinical events, validation is needed prior to use in heart failure (HF) diagnostic development. METHODS AND RESULTS: Data from the Multisensor Chronic Evaluations in Ambulatory Heart Failure Patients (MultiSENSE) study, used to create the HeartLogic HF diagnostic, were linked with fee-for-service (FFS) Medicare claims. Events were matched by patient ID and date, and agreement was calculated between claims primary HF diagnosis codes and study event adjudication. HF events (HFEs) were defined as inpatient visits, or outpatient visits with intravenous decongestive therapy. Diagnostic performance was measured as HFE-detection sensitivity and false-positive rate (FPR). Linkage of 791 MultiSENSE subjects returned 320 FFS patients with an average follow-up duration of 0.94 years. Although study and claims deaths matched exactly (n = 14), matching was imperfect between study hospitalizations and acute inpatient claims events. Of 239 total events, 165 study hospitalizations (69%) matched inpatient claims events, 28 hospitalizations matched outpatient claims events (12%), 14 hospitalizations were study-unique (6%), and 32 inpatient events were claims-unique (13%). Inpatient HF classification had substantial agreement with study adjudication (κ = 0.823). Diagnostic performance was not different between claims and study events (sensitivity = 75.6% vs 77.6% and FPR = 1.539 vs 1.528 alerts/patient-year). HeartLogic-detected events contributed to > 90% of the HFE costs used for evaluation. CONCLUSIONS: Acceptable event matching, good agreement of claims diagnostic codes with adjudication, and equivalent diagnostic performance support the validity of using claims for HF diagnostic development.

Institution of localized high-frequency electrical stimulation targeting early myocardial infarction: Effects on left ventricle function and geometry.

BACKGROUND: Although strategies have focused on myocardial salvage/regeneration in the context of an acute coronary syndrome and a myocardial infarction (MI), interventions targeting the formed MI region and altering the course of the post-MI remodeling process have not been as well studied. This study tested the hypothesis that localized high-frequency stimulation instituted within a formed MI region using low-amplitude electrical pulses would favorably change the trajectory of changes in left ventricle geometry and function. METHODS: At 7 days following MI induction, pigs were randomized for localized high-frequency stimulation (n = 5, 240 bpm, 0.8 V, and 0.05 ms pulses) or unstimulated (n = 6). Left ventricle geometry and function were measured at baseline (pre-MI) and at 7, 14, 21, and 28 days post-MI using echocardiography. MI size at 28 days post-MI was determined by histochemical staining and planimetry. RESULTS: At 7 days post-MI and before randomization to localized high-frequency stimulation, left ventricular ejection fraction and end-diastolic volume was equivalent. However, when compared with 7-day post-MI values, left ventricle end-diastolic volume increased in a time-dependent manner in the MI unstimulated group, but the relative increase in left ventricle end-diastolic volume was reduced in the MI localized high-frequency stimulation group. For example, by 28 days post-MI, left ventricle end-diastolic volume increased by 32% in the MI unstimulated group but only by 12% in the MI localized high-frequency stimulation group (P < .05). Whereas left ventricular ejection fraction appeared unchanged between MI groups, estimates of pulmonary capillary wedge pressure, a marker of adverse left ventricle performance and progression to failure, increased by 62% in the MI unstimulated group and actually decreased by 17% in the MI localized high-frequency stimulation group when compared with 7-day post-MI values (P < .05). MI size was equivalent between the MI groups, indicative of no difference in the extent of absolute myocardial injury. CONCLUSIONS: The unique findings from this study are 2-fold. First, targeting the MI region following the resolution of the acute event using a localized stimulation approach is feasible. Second, localized stimulation modified a key parameter of adverse post-MI remodeling (dilation) and progression to heart failure. These findings demonstrate that the MI region itself is a modifiable tissue and responsive to localized electrical stimulation.

Long-term vagal stimulation for heart failure: Eighteen month results from the NEural Cardiac TherApy foR Heart Failure (NECTAR-HF) trial.

BACKGROUND: The NECTAR-HF study evaluated safety and feasibility of vagal nerve stimulation (VNS) for the treatment of heart failure patients. The first six-month randomized phase of the study did not show improvement in left ventricular remodelling in response to VNS. This study reports the 18-month results and provides novel findings aiming to understand the lack of efficacy of VNS, including a new technique assessing the effects of VNS. METHODS: Ninety-six patients were randomized 2:1 to active or inactive VNS for 6months, thereafter VNS was activated for all patients. The primary safety endpoint was 18-month all-cause mortality. RESULTS: Ninety-one patients continued in the long-term evaluation with active VNS. The on-therapy survival estimate at 18months was 95% with a 95% one-sided lower confidence limit of 91%, (better than the predefined criterion). Left ventricular systolic volume decreased in the crossover group (VNS OFF→ON; 144±37 to 139±40, p<0.05) after VNS activation; LVESD (5.02±0.77 to 4.96±0.82, p>0.05) and LVEF (33.2±4.9 to 33.3±6.5, p>0.05) did not change. A new technique to detect subtle heart rate changes during Holter recordings, i.e. "heat maps", revealed that VNS evoked heart rate response in only 13/106 studies (12%) at 6 and 12months with active VNS. CONCLUSIONS: Although a favourable long-term safety profile was found, improvements in the efficacy endpoints were not seen with VNS. A new technique for detecting acute heart rate responses to VNS suggests that the recruitment of nerve fibres responsible for heart rate changes were substantially lower in NECTAR-HF than in pre-clinical models.

Modulation of heart rate by temporally patterned vagus nerve stimulation in the anesthetized dog.

Despite current knowledge of the myriad physiological effects of vagus nerve stimulation (VNS) in various mammalian species (including humans), the impact of varying stimulation parameters on nerve recruitment and physiological responses is not well understood. We investigated nerve recruitment, cardiovascular responses, and skeletal muscle responses to different temporal patterns of VNS across 39 combinations of stimulation amplitude, frequency, and number of pulses per burst. Anesthetized dogs were implanted with stimulating and recording cuff electrodes around the cervical vagus nerve, whereas laryngeal electromyogram (EMG) and heart rate were recorded. In seven of eight dogs, VNS-evoked bradycardia (defined as ≥10% decrease in heart rate) was achieved by applying stimuli at amplitudes equal to or greater than the threshold for activating slow B-fibers. Temporally patterned VNS (minimum 5 pulses per burst) was sufficient to elicit bradycardia while reducing the concomitant activation of laryngeal muscles by more than 50%. Temporal patterns of VNS can be used to modulate heart rate while minimizing laryngeal motor fiber activation, and this is a novel approach to reduce the side effects produced by VNS.

Vagal Nerve Stimulation Evoked Heart Rate Changes and Protection from Cardiac Remodeling.

This study investigated whether vagal nerve stimulation (VNS) leads to improvements in ischemic heart failure via heart rate modulation. At 7 ± 1 days post left anterior descending artery (LAD) ligation, 63 rats with myocardial infarctions (MI) were implanted with ECG transmitters and VNS devices (MI + VNS, N = 44) or just ECG transmitters (MI, N = 17). VNS stimulation was active from 14 ± 1 days to 8 ± 1 weeks post MI. The average left ventricular (LV) end diastolic volumes at 8 ± 1 weeks were MI = 672.40 µl and MI + VNS = 519.35 µl, p = 0.03. The average heart weights, normalized to body weight (± std) at 14 ± 1 weeks were MI = 3.2 ± 0.6 g*kg(-1) and MI + VNS = 2.9 ± 0.3 g*kg(-1), p = 0.03. The degree of cardiac remodeling was correlated with the magnitude of acute VNS-evoked heart rate (HR) changes. Further research is required to determine if the acute heart rate response to VNS activation is useful as a heart failure biomarker or as a tool for VNS therapy characterization.

Chronic vagal stimulation for the treatment of low ejection fraction heart failure: results of the NEural Cardiac TherApy foR Heart Failure (NECTAR-HF) randomized controlled trial.

AIM: The neural cardiac therapy for heart failure (NECTAR-HF) was a randomized sham-controlled trial designed to evaluate whether a single dose of vagal nerve stimulation (VNS) would attenuate cardiac remodelling, improve cardiac function and increase exercise capacity in symptomatic heart failure patients with severe left ventricular (LV) systolic dysfunction despite guideline recommended medical therapy. METHODS: Patients were randomized in a 2 : 1 ratio to receive therapy (VNS ON) or control (VNS OFF) for a 6-month period. The primary endpoint was the change in LV end systolic diameter (LVESD) at 6 months for control vs. therapy, with secondary endpoints of other echocardiography measurements, exercise capacity, quality-of-life assessments, 24-h Holter, and circulating biomarkers. RESULTS: Of the 96 implanted patients, 87 had paired datasets for the primary endpoint. Change in LVESD from baseline to 6 months was -0.04 ± 0.25 cm in the therapy group compared with -0.08 ± 0.32 cm in the control group (P = 0.60). Additional echocardiographic parameters of LV end diastolic dimension, LV end systolic volume, left ventricular end diastolic volume, LV ejection fraction, peak V02, and N-terminal pro-hormone brain natriuretic peptide failed to show superiority compared to the control group. However, there were statistically significant improvements in quality of life for the Minnesota Living with Heart Failure Questionnaire (P = 0.049), New York Heart Association class (P = 0.032), and the SF-36 Physical Component (P = 0.016) in the therapy group. CONCLUSION: Vagal nerve stimulation as delivered in the NECTAR-HF trial failed to demonstrate a significant effect on primary and secondary endpoint measures of cardiac remodelling and functional capacity in symptomatic heart failure patients, but quality-of-life measures showed significant improvement.

Rationale and study design of the NEuroCardiac TherApy foR Heart Failure Study: NECTAR-HF.

AIMS: Increased sympathetic activation and reduced parasympathetic tone are important pathophysiological contributors to the progression of heart failure, and are associated with poor outcome in patients. The aim of this study is to determine if vagal nerve stimulation (VNS) is a promising approach to modulate autonomic function and slow cardiac remodelling and the progression of heart failure. METHODS: The NECTAR-HF (NEural Cardiac TherApy foR Heart Failure) trial is designed to evaluate whether the Boston Scientific VNS device is safe and may attenuate cardiac remodelling, improve cardiac function and increase exercise capacity, in symptomatic heart failure patients (New York Heart Association Class II-III) with left ventricular systolic dysfunction (ejection fraction ≤35%) and receiving optimal medical therapy. Patients will be randomized in a 2:1 ratio to receive standard optimal medical treatment plus VNS system in an active mode vs. optimal medical treatment plus VNS system in an inactive mode, for a 6 month period. After the 6 month control period, inactive VNS systems will be activated and all patients will receive VNS. The study is powered to detect differences in the primary efficacy endpoint of change in left ventricular end systolic diameter. Secondary endpoints include ejection fraction, left ventricular volumes, quality of life scores, functional capacity, and changes in biomarkers. CONCLUSION: This Phase II, randomized clinical trial conducted with vagal stimulation for heart failure will provide important new information on the potential of this novel and promising technique.

Vagus nerve stimulation improves left ventricular function in a canine model of chronic heart failure.

AIMS: Autonomic dysfunction is a feature of chronic heart failure (HF). This study tested the hypothesis that chronic open-loop electrical vagus nerve stimulation (VNS) improves LV structure and function in canines with chronic HF. METHODS AND RESULTS: Twenty-six canines with HF (EF ∼35%) produced by intracoronary microembolizations were implanted with a bipolar cuff electrode around the right cervical vagus nerve and connected to an implantable pulse generator. The canines were enrolled in Control (n = 7) vs. VNS therapy (n = 7) or a crossover study, with crossovers occurring at 3 months (C × VNS, n = 6; VNS × C, n = 6). After 6 months of VNS, LVEF and LV end-systolic volume (ESV) were significantly improved compared with Control (ΔEF Control -4.6 ± 0.9% vs. VNS 6.0 ± 1.6%, P < 0.001) and (ΔESV Control 8.3 ± 1.8 mL vs. VNS -3.0 ± 2.3 mL, P = 0.002. Plasma and tissue biomarkers were also improved. In the crossover study, VNS also resulted in a significant improvement in EF and ESV compared with Control (ΔEF Control -2.3 ± 0.65% vs. VNS 6.7 ± 1.1 mL, P < 0.001 and ΔESV Control 3.2 ± 1.2 mL vs. VNS -4.0 ± 0.9 mL, P < 0.001). Initiation of therapy in the Control group at 3 months resulted in a significant improvement in EF (Control -4.7 ± 1.4% vs. VNS 3.7 ± 0.74%, P < 0.001) and ESV (Control 1.5 ± 1.2 mL vs. NS -5.5 ± 1.6 mL, P = 0.003) by 6 months. CONCLUSIONS: In canines with HF, long-term, open-looped low levels of VNS therapy improves LV systolic function, prevents progressive LV enlargement, and improves biomarkers of HF when compared with control animals that did not receive therapy.

High-resolution measurement of electrically-evoked vagus nerve activity in the anesthetized dog.

OBJECTIVE: Not fully understanding the type of axons activated during vagus nerve stimulation (VNS) is one of several factors that limit the clinical efficacy of VNS therapies. The main goal of this study was to characterize the electrical recruitment of both myelinated and unmyelinated fibers within the cervical vagus nerve. APPROACH: In anesthetized dogs, recording nerve cuff electrodes were implanted on the vagus nerve following surgical excision of the epineurium. Both the vagal electroneurogram (ENG) and laryngeal muscle activity were recorded in response to stimulation of the right vagus nerve. MAIN RESULTS: Desheathing the nerve significantly increased the signal-to-noise ratio of the ENG by 1.2 to 9.9 dB, depending on the nerve fiber type. Repeated VNS following nerve transection or neuromuscular block (1) enabled the characterization of A-fibers, two sub-types of B-fibers, and unmyelinated C-fibers, (2) confirmed the absence of stimulation-evoked reflex compound nerve action potentials in both the ipsilateral and contralateral vagus nerves, and (3) provided evidence of stimulus spillover into muscle tissue surrounding the stimulating electrode. SIGNIFICANCE: Given the anatomical similarities between the canine and human vagus nerves, the results of this study provide a template for better understanding the nerve fiber recruitment patterns associated with VNS therapies.

Excitation properties of the right cervical vagus nerve in adult dogs.

Vagus nerve stimulation (VNS) is an approved treatment for epilepsy and depression, and it is currently under investigation for applications in Alzheimer's disease, anxiety, heart failure, and obesity. However, the mechanism(s) by which VNS has its effects are not clear, and the stimulation parameters for obtaining therapeutic outcomes appear highly variable. The purpose of this study was to quantify the excitation properties of the right cervical vagus nerve in adult dogs anesthetized with propofol and fentanyl. Input-output curves of the right cervical vagus nerve compound action potential and laryngeal muscle electromyogram were measured in response to VNS across a range of stimulation parameters: amplitudes of 0.02-50mA, pulsewidths of 10, 50, 100, 200, 300, 500, and 1,000µs, frequencies of 1-2Hz, and train lengths of 20 pulses with 3 different electrode configurations: monopolar cathode, proximal anode/distal cathode, and proximal cathode/distal anode. Electrode configuration and stimulation waveform (monophasic vs. asymmetric charge-balanced biphasic) did not affect the threshold or recruitment of the vagal nerve fibers that were activated. The rheobase currents of A- and B-fibers were 0.4mA and 0.7mA, respectively, and the chronaxie of both components was 180µs. Pulsewidth had little effect on the normalized threshold difference between activation of A- and B-fibers. The results provide insight into the complement of nerve fibers activated by VNS and guidance to clinicians for the selection of optimal stimulation parameters.

Selective control of physiological responses by temporally-patterned electrical stimulation of the canine vagus nerve.

Vagus nerve stimulation (VNS) is effective for treating epilepsy and depression, and has emerging indications for anxiety and heart failure. However, stimulation-evoked side effects remain a challenge for long-term compliance. We investigated the feasibility of reducing VNS side effects by using a temporally-modified stimulation pattern. In 4 anesthetized canines, we measured changes in both the heart rate and evoked laryngeal muscle activity. Compared to baseline, we found that a 5% duty cycle (measured by the number of pulses per second of stimulation) could still evoke a 21% reduction in heart rate; whereas compared to continuous stimulation (3 mA, 300 µs pulsewidth, 20 Hz) the same 5% duty cycle reduced the evoked laryngeal muscle activity by 90%. The results of this study indicate that temporally-patterned stimulation may provide an effective tool for optimizing VNS therapy.

Disability type influences heart rate response during power wheelchair sport.

PURPOSE: The purpose of this study was to determine the influence of disability type on exercise response during power wheelchair competition. The secondary purpose was to determine the extent to which heart rate responses during competition meet cardiorespiratory fitness training intensities for the general population. METHODS: Forty-eight athletes who had cerebral palsy (CP, N = 31), spinal cord injury (SCI, N = 10), or muscular dystrophy (MD, N = 7), and were competing in the 2003 Power Soccer National Tournament, volunteered to participate. Heart rate was recorded every 5 s throughout pre-game and game conditions by Polar S610 monitors. Average heart rate (HR) values were determined for GAME and RESPONSE (change score between GAME HR and pre-game HR). The Kruskal-Wallis nonparametric test was used to determine whether a significant difference among group medians existed on the dependent measure, RESPONSE (P < 0.05). RESULTS: A significant difference on RESPONSE (P < 0.05) existed among athletes with CP (29 bpm), SCI (17 bpm), and MD (26 bpm). The median RESPONSE for athletes with CP was 12 bpm higher than athletes with SCI, and this difference was significant (P < 0.01). Further, 22 athletes with CP (71%), 5 athletes with MD (71%), and 1 athlete with SCI (10%) exceeded 55% of estimated HR(max) for at least 30 min during competition. CONCLUSION: Disability type influences the heart rate response to power wheelchair sport, and may affect the ability to sustain training intensities associated with fitness improvement.

Thermal pain perception after aerobic exercise.

OBJECTIVE: To examine thermal pain perception before, 5 minutes after, and 30 minutes after 30 minutes of treadmill exercise at 75% of maximal oxygen uptake (V o 2 max). DESIGN: Repeated-measures. SETTING: Sports science laboratory. PARTICIPANTS: Convenience sample of 14 healthy male and female volunteers (mean age +/- standard deviation, 32+/-3y). INTERVENTIONS: Sensory thresholds, pain thresholds, and pain ratings to hot and cold stimuli were measured before and after 30 minutes of treadmill exercise at 75% of V o 2 max. The hot and cold stimuli were delivered by using a thermode placed on the thenar eminence of the nondominant hand. Thermal sensory and pain thresholds were determined during continuous ramps in temperature of the thermode. MAIN OUTCOME MEASURES: Pain ratings were measured on a visual analog scale at 10-second intervals over 2 minutes of thermal pain stimulation. RESULTS: There were no significant changes in thermal sensitivity, pain thresholds, or pain ratings for either heat or cold after 30 minutes of exercise at 75% of V o 2 max. CONCLUSIONS: Pain perception to thermal stimuli was unaltered after 30 minutes of exercise at 75% of V o 2 max, an intensity and duration of exercise previously shown to alter pain perception to electric and mechanical stimuli.

Intensity and duration threshold for aerobic exercise-induced analgesia to pressure pain.

OBJECTIVE: To examine how exercise-induced analgesia is affected by the duration and intensity of aerobic exercise. DESIGN: Repeated-measures design. SETTING: Exercise science laboratory. PARTICIPANTS: Convenience sample of 12 healthy male and female volunteers (mean age +/- standard deviation, 32+/-9 y). INTERVENTIONS: Pain ratings were assessed before and at 5 and 30 minutes after treadmill exercise of 10 minutes at 75% maximal oxygen uptake (Vo(2)max), 30 minutes at 50% Vo(2)max, and 30 minutes at 75% Vo(2)max (randomized order and no less than 48 h between each bout). MAIN OUTCOME MEASURES: Pain ratings were measured on a visual analog scale at 10-second intervals during a 2-minute pressure-pain stimulus to the nondominant index finger. RESULTS: Pain ratings were significantly decreased (P<.05) from pre-exercise values 5 minutes after 30 minutes of exercise at 75% Vo(2)max but returned toward baseline by 30 minutes after exercise. There were no significant changes in pain ratings after 10 minutes of exercise or after exercise at 50% Vo(2)max. CONCLUSIONS: There are thresholds for both the intensity (>50% Vo(2)max) and duration (>10 min) of exercise required to elicit exercise analgesia.

Laser revascularization of ischemic skeletal muscle.

BACKGROUND: Clinical trials have shown that transmyocardial laser revascularization is an effective secondary treatment for ischemic heart disease patients. Laser revascularization may also provide an alternative method for treating peripheral vascular disease. METHODS: The purpose of this study was to investigate the potential for laser revascularization in ischemic skeletal muscle. Eighteen rabbits (3-4 kg) were instrumented chronically with transit time ultrasound flowprobes on both common iliac arteries. All rabbits performed graded exercise tests on a treadmill where maximal blood flow was recorded. Unilateral hindlimb ischemia was produced by ligation of one femoral artery. At week 3 postligation, 10 rabbits received laser therapy and 8 underwent a sham surgery. In each of four muscles (gracilius, medialis, sartorius, and biceps femoris) 5 to 22 laser channels were created (average = 52 channels per leg). RESULTS: At week 3 postligation the maximal blood flow of the ischemic limb for the treated group was 64 +/- 3 ml/min (mean +/- SEM) and at 6 weeks postlaser therapy maximal blood flow increased to 75 +/- 5 ml/min. The sham surgery group had a maximal blood flow of 58 +/- 4 ml/min at week 3 postligation and 66 +/- 3 ml/min at week 6 postsham surgery. CONCLUSION: These results indicate that laser therapy does not induce angiogenesis and vascular remodeling in the ischemic hindlimb of a rabbit which exceeds that seen with a sham surgery.

Endogenous vascular remodeling in ischemic skeletal muscle: a role for nitric oxide.

To test the hypothesis that nitric oxide (NO) production is essential for endogenous vascular remodeling in ischemic skeletal muscle, 22 New Zealand White rabbits were chronically instrumented with transit-time flow probes on the common iliac arteries and underwent femoral ligation to produce unilateral hindlimb ischemia. Iliac blood flow and arterial pressure were recorded at rest and during a graded exercise test. An osmotic pump connected to a femoral arterial catheter continuously delivered N-nitro-l-arginine methyl ester (a NO synthase inhibitor) or a control solution (N-nitro-d-arginine methyl ester or phenylephrine) to the ischemic limb over a 2-wk period. At 1, 3, and 6 wk after femoral ligation, maximal treadmill exercise blood flow in the ischemic limb was reduced compared with baseline in each group. However, maximal exercise blood flow was significantly (P < 0.05) lower in the l-NAME-treated group than in controls for the duration of the study: 48 +/- 4 vs. 60 +/- 5 ml/min at 6 wk. Consistent with the reduction in maximal blood flow response, the duration of voluntary exercise was also substantially (P < 0.05) shorter in the l-NAME-treated group: 539 +/- 67 vs. 889 +/- 87 s. Resting blood flow was unaffected by femoral ligation in either group. The results of this study show that endogenous vascular remodeling, which partially alleviated the initial deficit in blood flow, was interrupted by NO synthase inhibition. Therefore, we conclude that NO is essential for endogenous collateral development and angiogenesis in ischemic skeletal muscle in the rabbit.

Attenuated vascular responsiveness to noradrenaline release during dynamic exercise in dogs.

During dynamic exercise, there is reduced responsiveness to alpha(1)- and alpha(2)-adrenergic receptor agonists in skeletal muscle vasculature. However, it is desirable to examine the sympathetic responsiveness to endogenous release of neurotransmitter, since exogenous sympathomimetic agents are dependent upon their ability to reach the abluminal receptor. Therefore, to further our understanding of sympathetic control of vasomotor tone during exercise, we employed a technique that would elicit the release of endogenous noradrenaline (norepinephrine) during dynamic exercise. Mongrel dogs (n = 8, 19-24 kg) were instrumented chronically with transit time ultrasound flow probes on both external iliac arteries. A catheter was placed in a side branch of the femoral artery for intra-arterial administration of tyramine, an agent which displaces noradrenaline from the nerve terminal. Doses of 0.5, 1.0 and 3.0 microg ml(-1) min(-1) of iliac blood flow were infused for 1 min at rest and during graded intensities of exercise. Dose-related decreases in iliac vascular conductance were achieved with these concentrations of tyramine. The reductions in iliac vascular conductance (means +/- S.E.M.) were 45 +/- 6 %, 30 +/- 4 %, 26 +/- 3 % and 17 +/- 2 %, for the 1.0 microg ml(-1) min(-1) dose at rest, 3.0 miles h(-1), 6.0 miles h(-1) and 6.0 miles h(-1), 10 % gradient, respectively. At all doses, the magnitude of vasoconstriction caused by administration of tyramine was inversely related to workload. We conclude that there is a reduced vascular responsiveness to sympathoactivation in dynamically exercising skeletal muscle.