Marcelo R. Risk

Quantitative sensory testing cannot differentiate simulated sensory loss from sensory neuropathy

Objective: To differentiate the quantitative sensory testing (QST) results of subjects simulating small and large fiber sensory loss from those of normal subjects and subjects with sensory peripheral neuropathy. Background: QST is used to measure sensory thresholds in clinical, epidemiologic, and research studies. It is not known whether there are objective test results that characterize the subject seeking to deceive the examiner. Methods: The Computer Aided Sensory Examination IV 4, 2, and 1 stepping algorithm was used to determine vibration and cold perception in nine naïve subjects. Subjects were asked to simulate sensory loss (on two occasions) and to respond normally on one occasion. Test results were compared to those of subjects with diabetic sensory neuropathy. Each QST trial was performed three times. Results: Reproducibility, measured by the intraclass correlation coefficient, was similar in all groups for the vibration perception test (simulation 1: 0.68 [95% CI 0.31, 0.91], simulation 2: 0.82 [95% CI 0.54, 0.95], normal response: 0.77 [95% CI 0.47, 0.94], and subjects with peripheral neuropathy: 0.76 [95% CI 0.18, 0.95]) and the cold perception test (simulation 1: 0.53 [95% CI 0.12, 0.85], simulation 2: 0.82 [95% CI 0.55, 0.95], normal subjects: 0.67 [95% CI 0.30, 0.90] and subjects with peripheral neuropathy: 0.88 [95% CI 0.57, 0.97]), all just noticeable difference units. There were no differences between performance characteristics in the two simulation trials. Responses to null stimuli did not differentiate between groups. Conclusion: Test performance characteristics do not permit discrimination among subjects simulating sensory loss, subjects with normal responses, and subjects with peripheral neuropathy.

Benefits of aortic and pulmonary counterpulsation using dynamic latissimus dorsi myoplasty

BACKGROUND Intraaortic and pulmonary artery counterpulsation are useful techniques to support circulation during either left or right ventricular dysfunction. Electrically stimulated skeletal muscles wrapped around the aorta, used as means of cardiac failure treatment, have proved to be an effective method of handling experimental left ventricular failure. In this article we report an induced cardiac failure model in acute open chest dogs and describe the hemodynamic improvement of simultaneous aortic and pulmonary artery counterpulsation. METHODS This was achieved with a bilateral latissimus dorsi muscle flap, stimulated with a software written in C++ for Windows. Dynamic aortomyoplasty was performed using the left latissimus dorsi muscle flap around the descending aorta, and dynamic pulmonaromyoplasty was achieved wrapping the pulmonary trunk with the right latissimus dorsi muscle flap. In all animals blood pressures and cardiac output were measured after cardiac failure induced by a high-dose of propranolol hydrochloride (3 mg/kg intravenously) before and after latissimus dorsi muscle flap stimulation. RESULTS Aortopulmonary counterpulsation resulted in a significant increase in mean aortic pressure, mean pulmonary pressure, and cardiac output. In addition, a significant decrease was observed in end-diastolic left ventricular pressure, systemic vascular resistance, and pulmonary vascular resistance. Subendocardial viability index (diastolic pressure-time index/systolic tension-time index) in aortomyoplasty and tension time index in pulmonaromyoplasty showed significant improvement when cardiac assistance was performed by electrical stimulation of both muscles (p = 0.037 and p = 0.001, respectively). CONCLUSIONS Treatment of experimentally induced cardiac failure using aortopulmonary counterpulsation allows effective hemodynamic improvement in open-chest dogs.

Juxtaaortic counterpulsation: comparison with intraaortic counterpulsation in an animal model of acute heart failure.

This study was designed to compare the effects of juxtaaortic balloon counterpulsation (JABC), performed in ascending aorta and the aortic arch, with those yielded by intraaortic balloon counterpulsation (IABC) in descending aorta, in experimental animals during induced cardiac failure.JABC was achieved with a manufactured Dacron prosthesis and a balloon pump placed between the prosthesis and the wrapped aorta.JABC resulted in a significant increase of cardiac output (from 2.33 ± 0.82 to 2.61 ± 1.12 L/min, p < 0.05), cardiac index (from 0.071 ± 0.025 to 0.080 ± 0.033 L/min/kg, p < 0.05) and diastolic pressure augmentation evaluated through diastolic and systolic areas beneath the aortic pressure curve (DABAC/SABAC) index (from 0.94 ± 0.21 to 1.10 ± 0.33, p < 0.01). End diastolic aortic pressure showed a significant decrease with JABC (from 31.90 ± 7.09 to 27.83 ± 9.72 mm Hg, p < 0.05). A close association between percentage of DABAC/SABAC increases obtained with IABC and JABC was observed (r2 = 0.67; p < 0.001).Counterpulsation obtained by a juxtaaortic catheter placed in the arch and the ascending wrapped aorta results in an effective hemodynamic improvement comparable with that achieved by an intraaortic catheter in open chest sheep.

High-Pass Filter Characteristics of the Baroreflex – A Comparison of Frequency Domain and Pharmacological Methods

Pharmacological methods to assess baroreflex sensitivity evoke supra-physiological blood pressure changes whereas computational methods use spontaneous fluctuations of blood pressure. The relationships among the different baroreflex assessment methods are still not fully understood. Although strong advocates for each technique exist, the differences between these methods need further clarification. Understanding the differences between pharmacological and spontaneous baroreflex methods could provide important insight into the baroreflex physiology. We compared the modified Oxford baroreflex gain and the transfer function modulus between spontaneous RR interval and blood pressure fluctuations in 18 healthy subjects (age: 39±10 yrs., BMI: 26±4.9). The transfer function was calculated over the low-frequency range of the RR interval and systolic blood pressure oscillations during random-frequency paced breathing. The average modified Oxford baroreflex gain was lower than the average transfer function modulus (15.7±9.2 ms/mmHg vs. 19.4±10.5 ms/mmHg, P<0.05). The difference between the two baroreflex measures within the individual subjects comprised a systematic difference (relative mean difference: 20.7%) and a random variance (typical error: 3.9 ms/mmHg). The transfer function modulus gradually increased with the frequency within the low-frequency range (LF), on average from 10.4±7.3 ms/mmHg to 21.2±9.8 ms/mmHg across subjects. Narrowing the zone of interest within the LF band produced a decrease in both the systematic difference (relative mean difference: 0.5%) and the random variance (typical error: 2.1 ms/mmHg) between the modified Oxford gain and the transfer function modulus. Our data suggest that the frequency dependent increase in low-frequency transfer function modulus between RR interval and blood pressure fluctuations contributes to both the systematic difference (bias) and the random variance (error) between the pharmacological and transfer function baroreflex measures. This finding suggests that both methodological and physiological factors underlie the observed disagreement between the pharmacological and the transfer function method. Thus both baroreflex measures contribute complementary information and can be considered valid methods for baroreflex sensitivity assessment.

Spectral Analysis of Cardiorespiratory Signals

The study of the rhythmic and nonrhythmic oscillations of the arterial blood pressure (ABP) was first described by Hales [19] two centuries ago. Twenty seven years later, Albrecht von Haller described fluctuations of the cardiac rhythm. In 1847, Carl Ludwig [31], by mean of continuous recordings of physiological events in horses and dogs, was able to graph the rhythmic fluctuations of the ABP. The motivation behind these experiments was to clarify the spontaneous behavior and to overcome the lack of interpretation for these oscillations. It is interesting to remind the first description relating an evident correlation with respiratory fluctuations, mainly because the ease of its visualization, both in laboratory animals and humans beings.