Surgery – Truss – Pad
Patent
1996-01-16
1997-11-04
Getzow, Scott M.
Surgery
Truss
Pad
128708, A61B 50456
Patent
active
056829019
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of measuring autonomic activity of a patient and a method of determining a level or degree of heart failure in a patient.
2. Related Art
The rate at which a human heart beats is controlled by a feedback loop provided by a neurohumoral mechanism, the basic component of which is the autonomic nervous system, i.e. the sympathetic and parasympathetic nervous system. The autonomic nervous system is believed to modulate the natural activity of the sinus node of the heart. The sinus node effectively provides a contraction signal for the chambers of the heart, which is further modulated by the atrioventricular (A/V) node which controls movement of the ventricles. The frequency of the sinus node increases when sympathetic activity increases and decreases with increased parasympathetic activity. The resulting instantaneous heart rate provides quantitative information on the activity of the system.
Increased sympathetic and depressed parasympathetic nervous activity is common in heart failure. Acute myocardial ischaemia can be accompanied by signs of either sympathetic or parasympathetic hyperactivity. A number of experimental and clinical studies have shown that sympathetic system activity and reactivity is increased in an important subgroup of hypertensive patients. Increased sympathetic activity is suspected of predisposing the heart to ventricular fibrillation.
Heart rate variability can be decreased with severe ischaemic heart disease, congestive heart failure, ageing and diabetic neuropathy. The sympathetic nervous system, the renin-angiotensin system, and arginine vasopressin may represent potential and real targets for pharmacologic manipulation. The early identification of patients with severe ischaemic heart disease and severe heart failure at high risk of sudden death is a prerequisite for early aggressive intervention.
Furthermore, with the improvement in recent years of surgical and medical management, the accurate determination and classification of patients into high and low risk groups is becoming increasingly important. Therefore a method and apparatus for measuring autonomic activity and accurately detecting and determining the level or degree of heart failure in a patient is particularly desirable.
A number of heart rate variability studies have been conducted in the past and relied on the conventional understanding that the heart constitutes a linear system. For example, the standard deviation of the period between consecutive heart beats of a patient has been used in the past to determine whether the patient is susceptible to hem rate variability and increased sympathetic activity. However, this measure has been found to be in valid in particular cases and is extremely sensitive to artefact and ectopic activity. A group of American doctors has recently applied non-linear analysis techniques to analyse heart rate variability. The doctors attached Holter monitors to a number of healthy and heart failure risk patients over 24 hour periods and the recorded signals were analysed to extract R-R interval data of each patient. Electronic signals representative of the human heart beat have a characteristic PQRS shape waveform for each beat, and the R-R interval is the period of time between successive R peaks of adjacent waveforms. Poincare plots, as discussed hereinafter, were produced from the obtained R-R interval data but could not be used to accurately determine heart failure or the degree of heart failure, as the variability was open to influence by a number of external factors during the 24 hour period, and consequently was dependent on activities conducted by the subjects.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a method of measuring activity of the autonomic nervous system of a patient comprising:
Advantageously, the method includes determining a level of parasympathetic activity for said patient from the width of said plot about a line perpendicula
REFERENCES:
patent: 5201321 (1993-04-01), Fulton
patent: 5447520 (1995-09-01), Spano et al.
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