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Biomedical subjects

A Concu

Publications and source records attributed to A Concu.

At least 19 recordsLinked to original sources
PubMed2006

Poor reliability of heart rate monitoring to assess oxygen uptake during field training.

The aim of this study was to quantify the error associated with the assessment of oxygen uptake (VO2) by heart rate (HR) monitoring in 15 athletes freely performing their training session. A laboratory-derived equation was used on the running track to calculate VO2 (VO2est) from HR. Oxygen uptake was also assessed by means of a portable gas analyzer (VO2real). Bland and Altman statistics were carried out in order to evaluate agreement between VO2real and VO2est. The excess in carbon dioxide production (CO2excess) was measured to test the hypothesis that the subject with the highest CO2excess had the highest VO2est - VO2real difference. VO 2real was on average 0.14 l x min (-1) below VO2est. The limits of agreement of this difference were between + 0.77 and - 0.48 l x min (-1). Thus, on average VO2real was overestimated by VO2est. Spearman non-parametric statistics found a significant correlation between CO2excess and VO2est - VO2real difference (R = 0.55, p = 0.031). This study demonstrates that the use of HR monitoring to assess VO2 during field training overestimates VO2real, especially when a substantial increase in CO2excess occurs. Therefore, this method should be used with care when an excessive amount of CO2 is produced as occurs in activities that involve the lactic acid anaerobic source of energy production.

Adult↗
PubMed2003

Does reduction of blood prolactin levels reveal the activation of central dopaminergic pathways conveying reward in top athletes?

Prolactin blood levels are modulated directly by CNS via the known tubero-infundibular dopaminergic neurons which exert an inhibitory action on lactotrope cells in the hypophysis. Prolactin is devoid of peripheral negative feedback and via lesser known central pathways (e.g., mesolimbic and mesocortical) might be further tuned by means of appropriate stimuli (e.g., addictive drugs, gambling, exercise and so forth). Therefore, a prolactin test can be utilised to obtain an objective index to assess the compliance to exercise in men. This index may be used to identify the most suitable athlete for a given sport and mainly to survey exercise as rewarding behaviour in trained people. Prolactin was assessed in male top world windsurfers (WS) and in a control group of non-windsurfer trained subjects (CS) during an exercise simulating marine windsurfing. The result was that prolactin levels decreased significantly in WS with respect to CS when compared with pre-test levels (WS: -22.7%; P<0.05).

Dopamine↗
PubMed2002

Haemodynamics during a complete exercise induced atrioventricular block.

The case is reported of an athlete who, during an exercise test, had a complete atrioventricular block without symptoms of cardiac output failure. Heart rate, stroke index, cardiac index, and myocardial contractility were monitored during the episode by an impedance cardiograph. The most important findings of this report are the continuous increase in stroke index, which compensated for the lack of heart rate response, and the normal cardiac index values achieved during the exercise. This stroke index response was mainly due to an increase in myocardial contractility.

Adult↗
PubMed2002

External mechanical work versus oxidative energy consumption ratio during a basketball field test.

BACKGROUND: A field test consisting of 5 continuous runs at the maximum speed possible, playing the ball, starting from the centre line to the basket with a final shot, was studied in order to obtain an index of mechanical work efficiency in basketball players (micro-index=Jmec/Joxy) and evaluate the correlation between micro-index and velocity, acceleration, mechanical power and lactacid anaerobic capacity, respectively. METHODS: Eight male basketball players were studied; Jmec was the external mechanical work output obtained by means of a video image analysis software which gave the potential and the kinetic translational energies of athletes running and jumping and their velocity, acceleration and mechanical power. By means of a telemetric device (Kosmed K4), for measuring O2 consumption ( VO2), we obtained oxidative work (Joxy). By using this device we also assessed the excess of CO2, which was considered an index of lactacid anaerobic capacity. RESULTS: Non-parametric Spearman statistics revealed a significant correlation between mu index and mean velocity (p<0.01, r=0.90), acceleration (p<0.05, r=0.78), mechanical power (p<0.05 r=0.76) and CO2 excess (p<0.01, r=0.95). Consequently athletes who had the best index of mechanical efficiency also had the best biomechanical quality and the greatest lactacid anaerobic capacity. CONCLUSIONS: This study strongly supports the hypothesis that in basketball anaerobic capacity is important in achieving high values of speed, acceleration, mechanical power and endurance velocity.

Acceleration↗
PubMed2000

Hemodynamic during a postexertional asystolia in a healthy athlete: a case study.

Hemodynamic events leading to spontaneous postexertional vasovagal syncope are not completely understood because of the lack of beat-to-beat data. We report a case study of a young athlete who undergoes a syncopal episode during the recovery period following a maximal cycle-ergometer test. The episode was monitored by an impedance cardiograph which can gather noninvasively beat-to-beat the flow of heart rate (HR), stroke volume (SV), cardiac output (CO), diastolic filling rate (SV/DT), and myocardial contractility index (PEP/LVET). The most important findings of this report are the dramatic reduction of SV/DT preceding the syncope, the increment of SV together with the reduction of HR preceding and following the syncope, the prompt recovery of CO values after the syncopal episode despite the bradycardia, and the reduction of PEP/LVET after the syncope. This report confirms the importance of active recovery immediately after strenuous exercise and supports the hypothesis that the reduction of SV/DT in the presence of an inotropic stimulation can trigger the vasovagal reaction.

Adolescent↗
PubMed2000

Oscillations in stroke volume and cardiac output arising from oscillatory ventilation in humans.

Oscillations in the cardiovascular system have been observed in patients with periodic breathing. It is not clear whether these are driven by primary oscillations in the respiratory system or whether an intrinsic cardiovascular instability is required, as previous studies with subjects performing voluntary periodic breathing have failed to produce the cardiovascular oscillations. We investigated whether cardiovascular oscillations occurred in healthy controls performing voluntary periodic breathing. Six healthy subjects performed voluntary periodic breathing with guidance from a real-time computer display. We measured ventilation, end-tidal partial pressures of O2 (PO2) and CO2 (PCO2), heart rate, blood pressure (BP), arterial oxygen saturation and stroke volume and cardiac output by transthoracic impedance cardiography. Fourier analysis was used to quantify the size and phase of the periodic breathing-induced oscillations in these parameters. Periodic breathing (amplitude 30% of mean ventilation) induced oscillations in end-tidal PO2 (amplitude 0.8 kPa), end-tidal PCO2 (amplitude 0.3 kPa), R-R interval (amplitude 32.6 ms), systolic BP (amplitude 3 mmHg), diastolic BP (amplitude 3 mmHg), stroke volume (amplitude 8.0 ml, mean 79.5 ml) and cardiac output (amplitude 0.6 1, mean 5.9 l x min(-1)). The oscillations in stroke volume and cardiac output were nearly in phase with ventilation, with their peaks occurring 5.6 and 6.1 s, respectively, after the peak in ventilation. An oscillatory ventilatory pattern entrains the cardiovascular system in healthy controls into fluctuations, not only in heart rate and BP, but also in stroke volume and cardiac output.

Adult↗
PubMed1998

Field test for mechanical efficiency evaluation in matching volleyball players.

Field tests were performed in 10 volleyball (VB) players (4 females and 6 males) in order to obtain an index of mechanical work efficiency (mu' = Wmec/Woxy) while athletes played a game. Wmec was the mechanical work output, obtained by means of home made video image analysis software, by summing potential, kinetic translational and kinetic rotational energies of running and jumping athletes. Woxy was the oxidative energy consumption obtained from O2 consumption (VO2) by a telemetry device (Cosmed K2) that also gave values of pulmonary ventilation (VE) and heart rate (HR). VB were studied at rest before a game (R), during attacking phases (A) and during defensive phases (D). At R were found: VE = 11 +/- 1 l x min(-1), HR = 78 +/- 7b x min(-1), VO2 = 3.71 +/- 1.1 ml x kg(-1) x min(-1), Woxy = 75.1 +/- 22.3 J x kg(-1) x min(-1). During A all variables increased: VE = 49 +/- 6l x min(-1), HR = 149 +/- 15 b x min(-1), VO2 = 23.1 +/- 3.3ml x kg(-1) x min(-1), Woxy = 482.8 +/- 69.0 J x kg(-1) x min(-1), and Wmec 275.5 +/- 57.0 J x kg(-1) x min(-1) with mu'=0.57 +/- 0.09. In D HR (-9%), VE, VO2 and Woxy (-18%) were reduced when compared to A, decreasing mu' to 0.21 +/- 0.05. On the other hand mu' was found higher than 0.25 during A indicating an anaerobic contribution to energy expenditure; in D the mu' lower than 0.25 indicated a restoration of anaerobic energy sources. It might be proposed that a greater difference in mu' values between A and D also means a higher anaerobic energy contribution to the volleyball game.

Adult↗
PubMed1993

Stroke volume response to progressive exercise in athletes engaged in different types of training.

Using the impedance cardiography method, heart rate (fc) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min.week-1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake (VO2max) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min.week-1) doing aerobic conditioning exercises and who had a VO2max 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W.min-1) up to fc of 150 beats.min-1. In group C, SI had increased significantly (P < 0.05) at fc of 90 beats.min-1 (+32%) and maintained this difference up to 110 beats.min-1, only to return to resting values on reaching 130 beats.min-1 with no further changes. In group VB, SI peaked (+54%) at fc of 110 beats.min-1, reaching a value significantly higher than that of group C, but decreased progressively to 22% of the resting value on reaching 150 beats.min-1. In group D, SI peaked at fc of 130 beats.min-1 (+54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats.min-1. As a consequence, the mean CI increase per fc unit was progressively higher in VB than in C (+46%) and in D than in VB (+105%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
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↗
PubMed1984

Effects of long-lasting stimulation of extensor muscle nerves on pulmonary ventilation in cats.

Increments in pulmonary ventilation were shown to occur in anaesthetized cats during long-lasting stimulation of a peripherally cut extensor muscle nerve at maximal intensity for group I afferent fibers. However, these increments tended to gradually adapt to a lower value when stimuli were delivered at high frequency and constant rate whereas a tendency to potentiation, up to a steady state, occurred when stimulation was intermittent. End-tidal PCO2 initially decreased with a tendency to adaptation in the case of continuous stimulation, and decreased progressively in the case of intermittent stimulation. It is concluded that the nervous mechanisms producing hyperpnoea exhibit fatigue during their constant excitation while their effects sum up during intermittent stimulation.

Adaptation, Physiological↗
PubMed1983

Respiratory responses to stimulation of large fibers afferent from muscle receptors in cats.

Experiments were carried out on cats to re-examine the respiratory effects of the stimulation of the large afferent fibers originating in the receptors of the hindlimb muscles. During the contraction of the triceps surae induced by stimulating the ventral roots, pulmonary ventilation increased due to an increase in tidal volume and, usually, in respiratory frequency. An increase in ventilation occurred also during stimulation at group I strength of the central end of the previously cut nerves to the triceps surae (LGS + MG) and to the posterior biceps plus the semitendinosus (PBST) muscles. Appreciable increase in ventilation was seen for stimuli near threshold for group I (Ia + Ib) afferent fibers of the LGS + MG nerves, while stimuli at group Ib strength were needed to produce the same effects when using the PBST nerves. It is concluded that group Ib fibers afferent from muscle receptors play a role in the reflex control of respiration.

Afferent Pathways↗
PubMed1980

[Auditory evoked potential in normal rats and after para-chlorophenylalanine (PCPA) treatment].

We have studied the latency behaviour of an early component of the cortical acoustic evoked potentials (EAEP) in albino rats after administration of p-chlorophenylalanine (PCPA), a rather selective tryptophan-hydroxylase inhibitor, at a dose of 100 mg/kg daily for 3 days. The rats were implanted with 3 chronic electrodes: one in the bregma, one in the nasion and 3rd inserted in the periauricular skin. Series of clicks originating from a square pulse of 0.12 msec duration were administrated. Brain responses were amplified by an EEG and averaged by a computer with different post-stimuli analysis times. A first group of 4 rats was tested with clicks of 100 dB (HTL) intensity and brain responses were analysed at 5,10,25,50,100 msec post-stimuli times. Results demonstrate that after PCPA administration there is a latency reduction of EAEP components that have a latency higher than 20 msec. In a second group of 4 rats we have analysed those EAEP components with an intensity of clicks ranging from 60 to 110 dB and results demonstrate that, when PCPA was administered, Latencies of those components were significatively lower than the controls at each stimuli intensity tested. We concluded that 5-HT may influence the acoustic pathways activity and this is according to remarks of other A.A. that found a correlation between acoustic stress and brain 5-HT levels.

Animals↗
PubMed1980

[Behavior of the discharge of the Golgi tendon organs during subtetanic muscular contraction].

In a series of isotonic muscle contractions induced by repetitive stimulation at frequencies higher than 0.1 Hz the pause in the afferent discharge of the muscle spindles tends to decrease as a function of time and as a function of frequency, while the afferent discharge of the Golgi tendon organs, as measured in the same experimental conditions, remains constant. The results support the hypothesis that the changes in the spindle are due to changes in the visco-elastic properties of the intrafusal muscle fibers (1). Since no muscolar tissue is present within the Golgi tendon organs (4) their afferent discharge and the pause, which occurs during the relaxation phase (3) do not change as seen in the spindles.

Achilles Tendon↗