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Regional differences in cholinergic activity in the cardiac conduction system have been difficult to study. We tested the utility of (+)-m-[125I]iodobenzyl)trozamicol(+)-[125I]MIBT), a novel radioligand that binds to the vesamicol receptor located on the synaptic vesicle in presynaptic cholinergic neurons, as a functional marker of cholinergic activity in the conduction system. The (+)-[125I]MIBT was injected intravenously into four rats. Three hours later, the rats were killed and their hearts were frozen. Quantitative autoradiography was performed on 20-micron-thick sections that were subsequently stained for acetylcholinesterase to identify specific conduction-system elements. Marked similarities existed between (+)-[125I]MIBT uptake and acetylcholinesterase-positive regions. Optical densitometric analysis of regional (+)-[125I]MIBT uptake revealed significantly greater (+)-[125I]MIBT binding (nCi/mg) in the atrioventricular node (AVN) and His bundle regions compared with other conduction and contractile elements (AVN: 3.43 +/- 0.37; His bundle: 2.16 +/- 0.30; right bundle branch: 0.95 +/- 0.13; right atrium: 0.68 +/- 0.05; right ventricle: 0.57 +/- 0.03; and left ventricle: 0.57 +/- 0.03; p < 0.05 comparing conduction elements with ventricular muscle). This study demonstrates that (+)-[125I]MIBT binds avidly to cholinergic nerve tissue innervating specific conduction-system elements. Thus, (+)-[125I]MIBT may be a useful functional marker in studies on cholinergic innervation in the cardiac conduction system.

Although previous studies have suggested that aging results in an increase in vascular stiffness, diseases that increase in prevalence with advanced age may have confounded the results of some of this past research. The purpose of this investigation was to determine whether aging per se results in reduced arterial compliance by using animals that are resistant to atherosclerosis and do not develop hypertension or hyperlipidemias with advanced age. We evaluated systemic and regional (femoral) arterial compliance in older (110 ± 8 months old) and in younger (27 ± 2 months old) female beagle dogs by using a computer-based assessment of the diastolic decay of arterial pressure waveforms and a modified Windkessel model of the circulation. Although systemic arterial pressure was very similar in both age groups, cardiac output was 29% lower ( p = 0.03) and systemic vascular resistance was 24% higher ( p = 0.02) in the older dogs. Moreover, there was an age-related reduction in systemic arterial compliance, derived both from the exponential decay in the arterial pulse (C 1 ) ( p = 0.05) and that derived from the oscillatory component of the diastolic pulse wave (C 2 ) ( p = 0.04). By contrast, although femoral vascular resistance was 25% higher in the older dogs ( p = 0.04), regional (femoral) vascular compliance measured after femoral arterial occlusion was also 25% reduced but was not significantly changed with age ( p = 0.14). These results demonstrate that systemic arterial compliance is reduced with age in dogs, extending this finding to animals without age-related diseases that frequently occur in older human beings. Regional compliance, evaluated in the isolated femoral vascular bed, also tends to be reduced with age, but variability in this parameter in dogs reduces the significance of this finding.

Objective: Active compression-decompression (ACD) cardiopulmonary resuscitation (CPR) utilizes a hand-held suction device with a pressure gauge that enables the operator to compress as well as actively decompress the chest. This new CPR method improves hemodynamic and ventilatory parameters when compared with standard CPR. ACD-CPR is easy to perform but may be more labor intensive. The purpose of this study was to quantify and compare the work required to perform ACD and standard CPR. Methods: Cardiopulmonary testing was performed on six basic cardiac life support- and ACD-trained St. Paul, MN fire-fighter personnel during performance of 10 min each of ACD and standard CPR on a mannequin equipped with a compression gauge. The order of CPR techniques was determined randomly with >1 h between each study. Each CPR method was performed at 80 compressions/min (timed with a metronome), to a depth of 1.5–2 inches, and with a 50% duty cycle. Results: Baseline cardiopulmonary measurements were similar at rest prior to performance of both CPR methods. During standard and ACD-CPR, respectively, rate-pressure product was 18.2 ± 3.0 vs. 23.8 ± 1.7 (×1000, P < 0.01); mean oxygen consumption 15.98 ± 2.29 vs. 20.07 ± 2.10 ml/kg/min or 4.6 ± 0.7 vs. 5.7 ± 0.6 METS (P < 0.01); carbon dioxide production 1115.7 ± 110 vs. 1459.1 ± 176 ml/min; respiratory exchange ratio 0.88 ± 0.04 vs. 0.92 ± 0.04 (P = NS); and minute ventilation 35.5 ± 5.1 vs. 45.6 ± 9.2 l/min (P < 0.01). Conclusions: Approximately 25% more work is required to perform ACD-CPR compared with standard CPR. Both methods require subanaerobic energy expenditure and can therefore be sustained for a sufficient length of time by most individuals to optimize resuscitation efforts. Due to the slightly higher work requirement, ACD-CPR may be more difficult to perform compared with standard CPR for long periods of time, particularly by individuals unaccustomed to the workload requirement of CPR, in general.