Clinical engineering in Romania. The coming of age.

Biomedical engineering (BME) includes clinical engineering and bioengineering. Bioengineering is academically oriented towards theory and research in biology using the methods of exact sciences such as maths and physics, while clinical engineering (CE) has a rather practical orientation focusing on the general management of clinic/hospital equipment and providing aid to the medical staff in the use of advanced technologies for diagnosis and therapy purposes. The Romanian physiological community has been closely involved in the growth of BME that has now come of age in this country. Radu Vrâncianu's great intuition in opening the door to this science and its practical application in an institution created by Daniel Danielopolu definitely represented a good chance for Romanian public health. Recently, both clinical engineering and medical bioengineering have been introduced into the Romanian Classification of Occupations.

Idioventricular low frequency oscillation in QT interval responds univocally to RR confusing kinds of mental stress.

Seventeen male subjects, aged nineteen to twenty, went through a protocol including, while supine, relaxation at rest (10 min) and mental stress (MS) by a Kraepelin (arithmetic) test (5 min), as part of a larger study. With a polygraphic analog recording set-up we also collected a 1 ms - digital facsimile of a lead II-like thoracic ECG with maximum T-wave (Codas, Dataq Instr). Twenty-three stress responses were assigned to three classes according to known cardiotacho-, plethysmo-, and pneumo-graphic marks of "concentrated attention mainly," "emotion," or still "high emotion." During each setting the most stationary 3 min RR epoch in cardiotachogram was selected for joint RR & QT beat-by-beat variability study. RR and QT intervals were detected using a published algorithm. Conventional RR and QT Fourier autospectra were computed, while using RR*QT mean square coherence spectrum we detached the RR-independent, idioventricular (IV) fraction of QT low frequency (LF: 0.04-0.15 Hz) power of variability (IV QT-LF). IV QT-LF responded consistently to varieties of mental stress that confuse RR-LF or let QT-LF unchanged, best witnessing the cortically-issued ventricular adrenergic strain. Indeed, while emotion propels the same way all spectral variables above, concentrated attention increased (Wilcoxon) significantly IV QT-LF only (0.54-0.80 ms2) and decreased RR-LF (715-463 ms2). Findings hold promise of a non-invasive, high resolution Holter based monitoring of sympathetic status of myocardium, robust vis-à-vis of confusion caused by the autonomic interplay at sino-atrial node.

Mental stress enhances the sympathetic fraction of QT variability in an RR-independent way.

In 10 healthy male volunteers aged 19-20, spectral power of the beat-by-beat QT interval was measured at the Traube-Herring-Mayer (THM) band (0.05 to 0.15 Hz) when the subject was at rest and during atrial pacing. After resting in dorsal decubitus for 10 minutes, right atrial pacing was performed at a slight elevation above sinus rhythm as well as at 100 or at 110 beats per minute for 7 minutes each. In addition, during pacing at 100 or 110 bpm, the subject was required to perform a Kraepelin Arithmetic test. There was a statistically significant increase in QT spectral power at the THM band, while heart rate was maintained unchanged during the periods of mental stress versus rest. This experiment confirms the potential independence of the QT interval from heart rate and suggests that THM fraction of QT spectral power has a double subordination: during relaxed rest it follows mostly RR-fluctuation; during stress an RR-independent contribution is added, which presumably reflects the supra-normal sympathetic drive on the ventricles.

Polysensory response characteristics of dorsal root ganglion neurones that may serve sensory functions during myocardial ischaemia.

OBJECTIVE: To determine the response characteristics of dorsal root ganglion neurones that may serve sensory functions during myocardial ischaemia. METHODS: Extracellular recordings were made from 54 spontaneously active and 5 normally quiescent dorsal root ganglion neurones (T2-T5) in 22 anaesthetized open-chest dogs under control conditions and during epicardial mechanical or chemical stimulation and myocardial ischaemia. RESULTS: The activity of 78% of spontaneously active and all quiescent neurones with left ventricular sensory fields was modified by left ventricular ischaemia. Forty-six spontaneously active neurones (85%) were polysensory with respect to mechanical and chemical stimuli. The 5 quiescent neurones responded only to chemical stimuli. Spontaneously active neurones associated with left ventricular mechanosensory endings (37 neurones) generated four different activity patterns in response to similar mechanical stimuli (high or low pressure active, high-low pressure active, high-low pressure inactive). A fifth group generated activity which was not related to chamber dynamics. Adenosine, adenosine 5'-triphosphate, substance P and bradykinin modified 72, 61, 65 and 63% of the spontaneously active neurones, respectively. Maximum local mechanical or chemical stimuli enhanced activity to similar degrees, as did ischaemia. Each ischaemia-sensitive neurone displayed unique activity patterns in response to similar mechanical or chemical stimuli. CONCLUSIONS: Most myocardial ischemia-sensitive dorsal root ganglion neurones associated with epicardial neurites sense mechanical and multiple chemical stimuli, a small population sensing only mechanical or chemical stimuli. Activity patterns generated by these neurones depend on their primary sensory characteristics or those of other neurones that may converge on them, as well as the type and magnitude of the stimuli that impinge upon their sensory fields, both normally and during ischaemia.

Hypobaric hypoxia: dual sympathetic control in the light of RR and QT spectra.

ECGs of 21 candidate-pilots and 19 pilots were recorded during: 1) exposure to 5500 m hypobaric hypoxia (HH) while sitting, in the sequence: 1a) initial 7 min of adaptation (A); 1b) later 7 min of recovery (R) after short but intense tread-mill effort; and 2) final 7 min baseline (B), while sitting and requested to relax, at "0 m altitude" in the hypobaric room. RR and QT short-term variability were studied using spectral powers within Traube-Hering-Mayer (THM: 0.05-0.15 Hz) and respiratory (RESP: 0.2-0.4 Hz) bands. Mean RR proved highest capability to aggregate individual response-profiles: 15 pilots and 9 candidates entered the main (normal) cluster, featured by a comparison "triangle" set as expected: A > R < B > A. QT-THM power closely followed: 10 subjects (ss) in very normal cluster, defined as: A < R > B < A, while secondary clusters in candidates and pilots were interpreted by not-successful relaxation and exaggerated start-effects, respectively. Subjects with QT-THM normal clusters (A < R > B < A has group averages, p < = 0.05), also showed a quasi-normal "triangle" for mean RR, (A = R < B > A). During adaptation to hypoxia, pilots' QT-THM was higher than candidates' one (p < 0.02, Wilcoxon test). Study supports the emerging capability of QT-THM spectral power to index ventricular sympathetic control. Exposure to hypobaric hypoxia proved to be in these subjects a psycho-physiologic rather than a purely physiologic test.

Cortical control of sinus arrhythmia in man studied by spectral analysis.

Eighteen healthy male volunteers, 21-26 years old, participated in a study intended to detect cortical control of beat-to-beat heart rate variability independent of the effects on breathing and mean heart rate. They were tested while seated and standing relaxed (baseline), and while performing tasks requiring concentrated attention while sitting. The mental concentration elicited a typical cardiorespiratory response manifested by moderate acceleration and shallowing of respiration with a small increase of mean heart rate (HR), a pattern already widely acknowledged as typically associated with concentration. With the aid of a variable tone delivered to the ear as a guide, the subjects were trained to breathe at the same rate without concentrating in order to test the influence of respiration on the concentration pattern. ECG, thermistor pneumogram and ear-lobe photo-plethysmogram were recorded and data reduction was performed on 3 minute or 1 minute data sequences selected for the best steady-state. Statistical treatment was limited to a subgroup of 10 subjects in whom there was no overlapping of the spectra of respiratory and Traube-Hering-Mayer sinus arrhythmia (RSA and THM-SA, respectively). Mental concentration elicited significant depression of both RSA and THM-SA even if the respiratory parameters were kept constant.

Migration of the true pacemaker within the sinoatrial cell aggregate in man.

The functional anatomy of the sinoatrial node (SAN) in man is first reviewed, together with its possible anatomical substructure. The true group pacemaker (PM) shift under autonomic drive is then related to a continuous competition between the intrinsic auto-firing period hierarchy and the autonomic topological susceptibility hierarchy. Accordingly, the PM 'skip' to both lower and higher periods following an abrupt and consistent acetylcholine (ACh) release at the SAN periphery, and the PM 'slip' towards a relocation of the next period, as a possible response to a slower and smaller ACh release, are considered. The PM 'skip' and 'slip' as boundaries of the true PM excursion within the SAN during the respiratory cycle, and their statistical properties, are then examined. Under current heart rate control menus in normals, the PM skip appears to follow central influence, whereas the conservative or slipping PMs suggest peripheral control. Finally, interpretation of the PM skip as a salutary sign of functional reserve is proposed, and a method of alleviating the PM skip which confounds electrophysiological testing of the SAN function in patients is devised.

The weight of the cortical inflow against medullary reflexes as enlightened by spectral analysis of HR and SP waves.

Components of the autonomic drive to the heart were studied in 5 young normals subjected to: 1. sustained lung inflation (SLI) in various postures; 2. mental loading by concentration of attention; 3. face immersion (FI) in cold water under SLI or snorkel breathing, when sitting; 4. superpositions of 1-3 experimental interventions. Recorded were: cardiotachogram (CTG as RR interval) and T-wave amplitude from ECG, ear-lobe photo-plethysmogram, digital impedance rheogram, thermistor pneumogram (PNG). Heart rate (HR) and systolic pressure (SP) data were treated using the Fourier analysis on a M118B microcomputer. Preliminary data-exploration, reported in a previous paper, has verified the capability of the Fourier spectrum to spot in short quasistationary data-series known marks of single interventions and has pointed to the amphotrop nature of SLI and FI maneuvers. Present work approaches the same data from the point of view of the competition between various regulatory menus under combined interventions. The "cortico-cardiac reflex"--HR stabilizing under mental loading versus rest based upon balanced reduction in both respiratory and vasomotor sinus arrhythmia (RSA and VSA, respectively)--appeared now as a middle size actor upon medullary areas; it is overridden, yet not put to silence by the powerful orthostatic reflex; it is comparable (SLI) or major (FI) vis-a-vis of synergic vagal reflexes whose more easily approachable mechanisms could offer it meaningful models. Capacitating this "reflex" in the containment of intricated arrhythmias with extrinsic involvement or in "educating" the benefic vagal prevalence upon the heart should observe these precisions.

Model of respiratory sinus arrhythmia in man.

The first section of the model delineates the parasympathetic signal as a function of the interaction between the respiratory and the vagal neurones of the common brainstem network. The second section is a version of Chess and Calaresu's description of the vagus/heart period system in the sympathetically blocked cat. The sympathetic influence is introduced in the third section, taking into account the autonomic effects on the transmembrane potential of the sinoatrial pacemaker as found in the rabbit. The model was implemented on a dedicated analogue computer with an accuracy of 1 per cent. The concordance between the analogue and the breathing/respiratory sinus arrhythmia (RSA) system in humans was studied using simulated respiratory signals. The results confirm the central origin of the RSA as a meaningful modelling premise and indicate the dependence of the RSA amplitude on the operating point of the vagus.

Autonomic control of the heart in some vagal maneuvers and normal sleep.

Components of the autonomic control of the heart were studied in 5 young normals subjected to: 1) sustained lung inflation (SLI) in various postures; (2) mental loading by concentration of attention, 3) face immersion in cold water under SLI or snorkel breathing, when sitting; 4) superposition of above experimental interventions. We recorded cardiotachogram (RR interval) and T-amplitude from ECG, ear lobe photoplethysmogram, digital impedance rheogram, thermistor respiration. Cardiac data were explored by means of Fourier spectral analysis on a M 118 B microcomputer. Results caution that allegedly unilateral stimulation by some "vagal" maneuvers triggers in fact amphotropic heart rate control menus involving sympathetic nonreciprocal response. Subsequent bradycardia should be interpreted as an absolute indicator of the parasympathetic function only when a separate measure of the sympathetic counterpart is available. In vigil young adult at physical rest the medullary cardiovascular centers appear as subjected to "sliding capture" by their prominent input signal--as determined by various receptor stimulation or cortical status, the latter preserving a higher priority at competing task demands. In a coupled study 9 normals were polygraphically monitored (EEG, EOG, ear duct temperature and the above variables as well) during 2 nonconsecutive nights and cardiac data were spectrally examined along various sleep stages. Results suggest an increased dual autonomic tone during REM that could be related to reported stage-specific arrhythmias. Reciprocal dynamics of the respiratory versus lower frequency variability of RR interval from NREM to REM sleep points to a useful discriminant for computer sleep stage scoring.

Electrophysiological testing of sinus node function in man.

The paper reviews basic concepts, measurement principles, abnormality criteria, errors and limitations as well as technical aspects involved in the intracavitary exploration of sinus node dysfunction in man, from a standpoint connecting the cardiologist's and the clinical engineer's views.

Vagal involvement in sinus arrhythmia attenuation under mental load.

Experimental data document the slight increase of heart rate found during mildly stressing mental load as not being sufficient to explain concomitant sinus arrhythmia attenuation by pure sympathetic reaction. A general outlook on autonomic regulation and more specific direct and indirect arguments show heart rate response to mental load as underlain by a higher level balance of sympathetic and vagal drives. Their competition results mostly in slight increase yet sometimes in preservation or decrease of mean HR, while the consistency of sinus arrhythmia attenuation remains to reflect vagal increase specifically connected to cortex activation.

Conduction velocity in slower motor fibres.

Measuring conduction velocity in slower fibres (CVSF), through a partial antidromic block (Hopf-Seppäläinen method), allows estimating the dispersal of conduction velocity in motor fibres by the difference between the maximal motor conduction velocity (MCV) and CVSF. Investigations performed in workers exposed to medium concentrations of carbon disulphide show difference between MCV and CVSF as providing a more sensitive indicator for early diagnosis of peripheral neuropathies than MCV.