PubMed Health⌕ Search

Biomedical subjects

A Concu

Publications and source records attributed to A Concu.

15 recordsLinked to original sources
PubMed1990

Unchanging cardiac activity while increasing respiratory activity at the start of exercise in man: a beat-by-beat analysis by means of the impedance cardiography method.

Both respiratory and cardiodynamic parameters were analyzed (the latter non invasively by means of a computerized impedance cardiograph) in 6 subjects at the start of voluntary dorsal ankle flexions. Increased mean inspiratory flow with a slow reduction in end tidal PCO2 was shown in the breath following the start of movements, and these findings indicate the nervous origin of this hyperventilation. Within the same breath, left cardiac output, stroke volume and ventricular ejection time remained unchanged, and the same is true of heart rate and ventricular performance indexes depending on both the first derivative of the base thoracic electrical bioimpedance and on the mean left ventricle ejection flow, as well as in the systemic venous return index depending on the basal value of the thoracic impedance. These results, indicating that no cardiodynamic intervention in the neurogenic hyperventilation was seen, show that nervous stimuli elicited at the start of voluntary exercise may exert a direct action on respiratory control structures.

Adult↗
PubMed1989

Contribution of central and reflex nervous activity to the rapid increase in pulmonary ventilation at the start of muscular exercise in man.

To investigate the relative contributions of the central and peripheral neural drive to hyperventilation at the onset of muscular exercise, five volunteers were tested during the first ten breaths while performing both voluntary (VM) and passive (PM) ankle rotations with a frequency of 1 Hz and through an angle of 10 degrees. Resulting breathing patterns for the two movements were compared. Hypocapnic hyperventilation, found in both PM and VM, indicated its neural origin. Respiratory changes were higher in VM than in PM. In both experimental conditions, increases in ventilation (VE) depended more on respiratory frequency (f) than on tidal volume (VT). Moreover, increases in VT adapted, breath-by-breath, to values lower than the initial ones, while increases in f rose progressively. Expiratory time was reduced more than inspiratory time (TI); increases in inspiratory flow (VT/TI) depended to the same extent on changes in both TI and VT. Increases in expiratory tidal volume were initially higher than in inspiratory tidal volume, thereby producing a reduction in functional residual capacity. Because PM respiratory changes could be considered to be of nervous reflex origin only, the identical breathing patterns in PM and VM indicated that the hyperventilation found also in VM was mainly of reflex origin. The increase in VE was considered to be dependent on a greater stimulus from muscle proprioreceptors.

Adult↗
PubMed1988

Respiratory and cardiac effects of passive limb movements in man.

The purpose of these experiments is to see if reflex nervous hyperventilation obtained by passive limb movements in man is a consequence of the activation of a direct ascending nervous pathway from mechanoreceptors of moving limbs to respiratory centres, or if it is the consequence of a primary enhanced cardiodynamic activity. Contemporaneous measurements of pulmonary ventilation and cardiac output (the latter with the trasthoracic bioimpedance method) were carried out in subjects whose ankles were passively moved at an angle of 10 degrees and a frequency of 1 Hz, each test lasting three breaths. Results showed a fast increase in pulmonary ventilation in all test breaths (+27% from control) mainly depending on respiratory frequency increases and accompanied by a tendency to reduce end tidal PCO2. Cardiac output did not change during tests because of a lack of changes in heart rate and stroke volume. The lack of cardiac output increases during this reflex hyperventilation supports the existence of a direct neural pathway from limb proprioreceptor afferents to respiratory structures.

Adult↗
PubMed1979

Respiratory ventilation during muscular contraction in man.

Brief contraction of arm muscles affects respiratory ventilation either by increasing respiratory frequency or by increasing the instantaneous flow. Both these changes occur at a time subsequent to muscle contraction and can be attributed to a reflex mechanism originating from the muscles.

Adult↗
PubMed1978

Intranigral kainic acid: evidence for nigral non-dopaminergic neurons controlling posture and behavior in a manner opposite to the dopaminergic ones.

The unilateral, intranigral administration of kainic acid (k.a.) produced a syndrome characterized by early sequelae of contra- and ipsilateral circling and by a chronic contralateral turning associated with moderate loss of neurons in the pars reticulata. The acute contralateral circling seems to be related to dopaminergic nigro-neostriatal neuron stimulation, since it was prevented by previous intranigral injections of 6-OHDA. The acute ipsilateral circling and the chronic contralateral turning, on the other hand, seem to be independent of the integrity of the dopaminergic system and may be due to an initial stimulation, followed by destruction, of a nigral neuronal system which mediates turning behavior in a manner opposite to that of nigro-striatal dopamine. Treatment with D-amphetamine or apomorphine changed the contralateral into ipsilateral turning, while haloperidol potentiated the contralateral turning. Bilateral injection of k.a. into the nigra resulted in chronic stereotyped sniffing and gnawing, which were not inhibited by haloperidol. Moreover, haloperidol did not produce catalepsy in these animals. It is suggested that the intranigral k.a. injection destroyed a neuronal system antagonistic to dopamine and resulted in a reduction of the response to DA-receptor stimulation of the c. striatum.

3,4-Dihydroxyphenylacetic Acid↗