Search PubMed⌕ Search

Biomedical subjects

C Roussos

Publications and source records attributed to C Roussos.

At least 109 records · Page 6Linked to original sources
PubMed1996

Control of breathing in mechanically ventilated patients.

During mechanical ventilation, the respiratory system is under the influence of two pumps, the ventilator pump and the patient's own respiratory muscles. Depending on the mode of mechanical ventilatory support, ventilation may be totally controlled by the ventilator or may be determined by the interaction between patient respiratory effort and ventilator function. In either case, compared to spontaneous breathing, the breathing pattern is altered and this may influence: 1) force-length and force-velocity relationships of respiratory muscles (mechanical feedback); 2) chemical stimuli (chemical feedback); 3) the activity of various receptors located in the respiratory tract, lung and chest wall (reflex feedback); and 4) behavioural response (behavioural feedback). Changes in these feedback systems may modify the function of the ventilator, in a way that is dependent on the mode of mechanical ventilatory support, ventilator settings, mechanics of the respiratory system and the sleep/awake stage. Thus, the response of ventilator to patient effort, and that of patient effort to ventilator-delivered breath are inevitably the two components of control of breathing during mechanical ventilation; the ventilatory output is the final expression of the interaction between these two components. As a result of this interaction, the various aspects of control of breathing of the respiratory system may be masked or modulated by mechanical ventilation, depending on several factors related both to patient and ventilator. This should be taken into consideration in the management of mechanically ventilated patients.

Behavior↗
PubMed1995

The load of inspiratory muscles in patients needing mechanical ventilation.

We studied 31 consecutive mechanically ventilated patients with acute respiratory failure in two stages: (1) During spontaneous breathing through the respirator, switching from full mechanical assistance to continuous positive airway pressure mode with 0 cm H2O pressure. We measured maximum inspiratory pressure and continuously monitored the pattern of breathing. After 8 to 25 min, none of the patients were able to sustain spontaneous breathing and mechanical ventilation was required to resume. (2) Subsequently, during mechanical ventilation, by manipulating the variables of the ventilator we simulated the pattern of spontaneous breathing the patients had just before the re-institution of mechanical ventilation. We assessed the respiratory mechanics by the constant flow end-inspiratory and end-expiratory occlusion method. Intrinsic positive end-expiratory pressure was present in 29 patients. The ratio of the mean inspiratory pressure per breath over the maximum inspiratory pressure (Pi/pimax), as well as Ppeak/pimax, had excessively high mean values, equal to 0.42 +/- 0.11 and 0.56 +/- 0.10, respectively. Pressure-time index was 0.14 +/- 0.04. When we plotted the Pi/Pimax and Ppeak/Pimax against the dynamic increase in FRC, we found that the Pi/Pimax of 13 patients (42%) and the Ppeak/Pimax of 25 of 31 patients (81%) were placed above a hypothetical critical line, representing the critical inspiratory pressures above which fatigue may occur. In addition, almost all patients were gathered around the critical line. We conclude that during discontinuation from mechanical ventilation (MV) almost all patients breathe against a high inspiratory load and their inspiratory muscles perform work that may lead to fatigue.

Adult↗
PubMed1995

Atypical forms of paroxysmal positional nystagmus.

Benign paroxysmal positional vertigo (BPPV) is a common cause of vertigo, and has a typical constellation of physical findings. Atypical forms of paroxysmal positional nystagmus (APPN) also exist, and are thought to represent conditions which are in fact not "benign". We studied 100 consecutive patients with positional vertigo in order to learn whether APPN differed from classic BPPV in etiology or clinical fate, and to learn the incidence of central nervous system (CNS) disorders in these patients. APPN was present in 38% of these patients with diverse causes. One-fourth had CNS disorders or vascular insufficiency, the remainder, otogenic or idiopathic. APPN was more likely than BPPV to have a prolonged (persistent or recurring) clinical course. Although most cases eventually resolved, duration of symptoms tended to be longer, regardless of etiology. We conclude that APPN has a less favorable prognosis than typical BPPV, and that a CNS etiology should be suspected in prolonged cases.

Adult↗
PubMed1994

Tracheal gas insufflation reduces the tidal volume while PaCO2 is maintained constant.

OBJECTIVE: The aims of the present study were two-fold: first, to confirm the effect of tracheal gas insufflation (TGI) throughout the respiratory cycle on alveolar ventilation at various catheter flows and constant total inspired VT as an adjunct to conventional volume cycled mechanical ventilation in patients with acute lung injury; second, to test the efficacy of TGI in the reduction of toal VT, peak and mean airway pressure while maintaining PaCO2 in its baseline value. The hemodynamic effect and the consequences on oxygenation as result of the reduction of VT, were also estimated. DESIGN: Prospective study of patients with acute lung injury requiring mechanical ventilation. SETTING: 12 bedded, adult polyvalent intensive care unit in a teaching hospital. PATIENTS: 7 paralyzed and sedated patients with acute respiratory failure were studied. All patients were clinically and hemodynamically stable without fluctuation of the body temperature. All patients were orally intubated with cuffed endotracheal tubes, and mechanically ventilated with a standard circuit of known compliance. INTERVENTIONS: Continuous flows (4 and 6 l/min) were delivered through a catheter positioned 1 cm above carina while tidal volume or PaCO2 were maintained constant at their baseline value. RESULTS: In this study a modest level of TGI significantly enhanced CO2 elimination in patients with acute respiratory failure. Improved ventilatory efficiency resulted from the functional reduction of dead space during TGI allowing the same PaCO2 to be maintained at the same frequency with lower tidal volume and lower airway pressure requirement. Tidal volume, peak and mean airway pressure decreased linearly with catheter flow, without significant changes in oxygenation, while PaCO2 remained stable. CONCLUSION: The results of this study suggest that TGI may be an useful adjunct mode of mechanical ventilation that limits alveolar pressure and minute ventilation requirements.

Acute Disease↗
PubMed1994

Effect of two tidal volumes on oxygenation and respiratory system mechanics during the early stage of adult respiratory distress syndrome.

PURPOSE: To study the effect of two tidal volumes on gas exchange, lung mechanics, and hemodynamics in 12 patients with acute respiratory distress syndrome (ARDS) within the first 72 hours of mechanical ventilation. METHODS: Tidal volume (VT) was increased by 40% from the initial value at fixed positive end-expiratory pressure (PEEP) and matched minute ventilation by adjusting the respiratory rate (RR) of the ventilator. Initial VT and RR were 592 +/- 42 mL and 19 +/- 1 min-1, respectively. High VT amounted to 825 +/- 54 mL with a RR of 12 +/- 1 min-1. RESULTS: We found that at high VT (1) the index of oxygenation increased from 0.22 +/- 0.03 to 0.32 +/- 0.04 (P < .001) with a parallel decrease in the right to left venous admixture from 0.26 +/- 0.02 to 0.23 +/- 0.02 (P < .001), and in the ratio of physiological dead space to tidal volume (VDS/VT) from 0.53 +/- 0.05 to 0.46 +/- 0.04 (P < .01), without impairment to hemodynamics and (2) respiratory system compliance improved significantly from 34.8 +/- 2.8 mL/cm H2O to 37.2 +/- 2.9 mL/cm H2O (P < .05). In 4 patients, we performed pressure-volume curves on PEEP with the ventilator finding an upward concavity reflecting progressive alveolar recruitment with increasing inflation volume in 3. CONCLUSIONS: High-tidal ventilation in the early stage of ARDS improved gas exchange, suggesting recruitment during the inspiratory phase. However, the benefit of better oxygenation should be weighed against the potential risk of barotrauma induced at high VT.

Adolescent↗
PubMed1992

Round table conference on ventilatory failure, Brussels, Belgium, March 16-18, 1991.

It was possible to reach agreement on several important issues relating to VF. First, the phenomenon of CO2 retention may have both pathophysiologic and compensatory components. There is increased awareness of the nature, intensity, and significance of the cross-talk between the ventilatory control center and the pump itself, as expressed in breathing pattern and indices of ventilatory drive. We are learning to interpret that information more effectively to assess functional reserve. Second, knowledge concerning the relative importance of various muscle groups is still incomplete, and the impact of disease on muscle function, lung mechanics, and ventilatory control is not fully understood. Dynamic hyperinflation and sleep disturbances provide two clear examples of conditions whose wide-ranging influence on drive, workload, and muscle function was, until quite recently, under appreciated. Finally, there was a general consensus that our therapeutic approaches to VF should be modified to reflect improved understanding of the pathogenesis of CO2 retention and iatrogenic lung injury. In the acute setting, measures to limit alveolar distention, such as controlling airway pressure, revising blood gas targets, and/or using adjunctive methods for blood gas exchange may avoid barotraumatic edema and rupture. The potential for non-invasive ventilation to avert intubation, facilitate ventilator withdrawal, and help patients with chronic VF to achieve compensation without machine dependence is now being actively investigated. This two day conference proved a stimulating forum for interchange of ideas regarding the state of the field, and allowed many opportunities for scientific interaction, both during outside the formal program.(ABSTRACT TRUNCATED AT 250 WORDS)

Europe↗
PubMed1992

Effects of diaphragmatic ischemia on the inspiratory motor drive.

To assess the effect of diaphragmatic ischemia on the inspiratory motor drive, we studied the in situ isolated and innervated left diaphragm in anesthetized, vagotomized, and mechanically ventilated dogs. The arterial and venous vessels of the left diaphragm were catheterized and isolated from the systemic circulation. Inspiratory muscle activation was assessed by recording the integrated electromyographic (EMG) activity of the left and right costal diaphragms and parasternal intercostal and alae nasi muscles. Tension generated by the left diaphragm during spontaneous breathing attempts was also measured. In eight animals, left diaphragmatic ischemia was induced by occluding the phrenic artery for 20 min, followed by 10 min of reperfusion. This elicited a progressive increase in EMG activity of the left and right diaphragms and parasternal and alae nasi muscles to 170, 157, 152, and 128% of baseline values, respectively, an increase in the frequency of breathing efforts, and no change in left diaphragmatic spontaneous tension. Thus the ratio of left diaphragmatic EMG to tension rose progressively during ischemia. During reperfusion, only the frequency of breathing efforts and alae nasi EMG recovered completely. In four additional animals, left diaphragmatic ischemia was induced after the left phrenic nerve was sectioned. Neither EMG activity of inspiratory muscles nor respiratory timing changed significantly during ischemia. In conclusion, diaphragmatic ischemia increases inspiratory motor drive through activation of phrenic afferents. The changes in alae nasi activity and respiratory timing indicate that this influence is achieved through supraspinal pathways.

Afferent Pathways↗
PubMed1992

Effect of tidal volume and PEEP in ethchlorvynol-induced asymmetric lung injury.

We examined the effects of positive end-expiratory pressure (PEEP) and tidal volume on the distribution of ventilation and perfusion in a canine model of asymmetric lung injury. Unilateral right lung edema was established in 10 animals by use of a selective infusion of ethchlorvynol. Five animals were tested in the supine position (horizontal asymmetry) and five in the right decubitus position (vertical asymmetry). Raising PEEP from 5 to 12 cmH2O improved oxygenation despite a redistribution of blood flow toward the damage lung and a consistent decrease in total respiratory system compliance. This improvement paralleled a redistribution of tidal ventilation to the injured lung. This was effected primarily by a fall in the compliance of the noninjured lung due to hyperinflation. The effects of higher tidal volume were additive to those of PEEP. We propose that the major effect of PEEP in inhomogeneous lung injury is to restore tidal ventilation to a population of alveoli recruitable only at high airway pressures.

Animals↗
PubMed1992

Effect of phrenic afferent stimulation on pattern of respiratory muscle activation.

Ventilation and electromyogram (EMG) activities of the right hemidiaphragm, parasternal intercostal, triangularis sterni, transversus abdominis, genioglossus, and alae nasi muscles were measured before and during central stimulation of the left thoracic phrenic nerve in 10 alpha-chloralose anesthetized vagotomized dogs. Pressure in the carotid sinuses was fixed to maintain baroreflex activity constant. The nerve was stimulated for 1 min with a frequency of 40 Hz and stimulus duration of 1 ms at voltages of 5, 10, 20, and 30 times twitch threshold (TT). At five times TT, no change in ventilation or EMG activity occurred. At 10 times TT, neither tidal volume nor breathing frequency increased sufficiently to reach statistical significance, although the change in their product (minute ventilation) was significant (P less than 0.05). At 20 and 30 times TT, increases in both breathing frequency and tidal volume were significant. At these stimulus intensities, the increases in ventilation were accompanied by approximately equal increases in the activity of the diaphragm, parasternal, and alae nasi muscles. The increase in genioglossus activity was much greater than that of the other inspiratory muscles. Phrenic nerve stimulation also elicited inhomogeneous activation of the expiratory muscles. The transversus abdominis activity increased significantly at intensities from 10 to 30 times TT, whereas the activity of the triangularis sterni remained unchanged. The high stimulation intensities required suggest that the activation of afferent fiber groups III and IV is involved in the response. We conclude that thin-fiber phrenic afferent activation exerts a nonuniform effect on the upper airway, rib cage, and abdominal muscles and may play a role in the control of respiratory muscle recruitment.

Animals↗
PubMed1991

Diaphragmatic fatigue produced by constant or modulated electric currents.

In anesthetized rabbits the efficiency of phrenic nerve stimulation with trains of electric current was studied either when ventilation was effected entirely by bilateral nerve stimulation (electrophrenic ventilation) or during unilateral nerve stimulation when animals were ventilated with a pump and open chest. Trains of rectangular electric pulses (RPT) with constant amplitude and frequency or sine waves, both the amplitude and frequency of which were modulated and controlled by a computer (MSWT), were used with each animal. MSWT closely reproduced the physiological shape of transdiaphragmatic pressure waves. Diaphragm fatigue, as determined from the decrease in the maximal relaxation rate of twitches, occurred after 20 minutes of bilateral or unilateral nerve stimulation with RPT, but only after 60 min (unilateral stimulation) or 98 min (bilateral stimulation) with MSWT. These data show the importance of the motor signal pattern in long-lasting nerve stimulation.

Animals↗
PubMed1991

Respiratory muscle activation by limb muscle afferent stimulation in anesthetized dogs.

In 10 chloralose anaesthetized and spontaneously breathing dogs, we assessed the effect of limb muscle afferents on the peak integrated EMG activities of the genioglossus, alae nasi, costal diaphragm, parasternal intercostal, triangularis sterni, and transverse abdominis muscles. The influence of vagal and baroreceptor afferents were eliminated by vagotomy and perfusion of carotid sinuses at a constant pressure. Muscle afferents were activated by stimulating the central end of the gastrocnemius nerve for 1 min at 40 Hz and at different voltages. Stimulation at voltages equal to 5, 10 and 20 times twitch-threshold increased minute ventilation to 165, 216 and 250% of pre-stimulation values, respectively, which was achieved by increasing breathing frequency (shortening of the inspiratory and expiratory times) and tidal volume. The activity of the parasternal intercostal and alae nasi muscles increased by a similar degree to that of the diaphragm while the activities of the genioglossus and transverse abdominis were augmented to a greater degree than that of the diaphragm. On the other hand, the motor drive to triangularis sterni increased significantly only at 20 times twitch-threshold and to a lesser degree than that to the diaphragm. These results suggest that upper airway, inspiratory and expiratory rib cage and abdominal muscles may be independently regulated. Differences in the sensitivity of these muscles to the activation of limb muscle afferents can be explained by a complex pattern of central projections of these afferents on the central respiratory controllers or by intrinsic properties of the motor output of these controllers.

Animals↗
PubMed1991

Chemical activation of thin-fiber phrenic afferents. 2. Cardiovascular responses.

To assess the effects of groups III and IV (thin-fiber) phrenic afferents on arterial pressure, heart rate, and distribution of cardiac output, we injected capsaicin into phrenic arteries of in situ isolated and innervated left diaphragms of dogs anesthetized with chloralose, vagotomized, and mechanically ventilated. Blood flow in the ascending aorta, common carotid, renal, superior mesenteric, and femoral arteries was measured by electromagnetic and Doppler flow probes. Injection of 1 mg capsaicin into the left phrenic artery produced congruent to 15% increase in mean arterial pressure and congruent to 7% increase in heart rate with no change in aortic flow. Phrenic arterial flow decreased by 64%, renal arterial flow by 16%, and superior mesenteric arterial flow by 10%, whereas carotid flow increased by 13% and flow to the right gastrocnemius muscle did not change. Mean arterial pressure, heart rate, and blood flow distribution (with the exception of the decline in phrenic blood flow) returned to baseline within 60 s of the injection. Injection of 1.5 mg capsaicin into the right isolated and innervated gastrocnemius produced congruent to 35% increase in mean arterial pressure, 17% rise in heart rate, and no change in aortic blood flow. Phrenic and carotid arterial flow rose by 240 and 41%, respectively, whereas renal and superior mesenteric flow declined by 50 and 20%, respectively. In conclusion, thin-fiber phrenic afferents have an excitatory effect on arterial pressure and heart rate. They redistribute blood flow away from the renal and intestinal vascular beds and toward the carotid vascular bed. On the other hand, the cardiovascular reflex from thin-fiber phrenic afferents seems less potent than that from limb muscle afferents.

Afferent Pathways↗
PubMed1990

Assessment of respiratory muscle dysfunction in chronic obstructive lung disease.

In COLD, the inspiratory muscles are severely disadvantaged by virtue of the hyperinflation that accompanies this disorder. Such mechanical disadvantage will lead clinically, in the stable patient, to the active recruitment of the accessory muscles of inspiration and to a pattern of rapid, shallow breathing that may be due to either peripheral (muscle) or central (neurogenic) influences thought to be linked to a critical tension-time index of the inspiratory muscles. This pattern appears to be all the more pronounced in the patient with acute respiratory failure and is frequently accompanied by disordered rib cage-abdominal movements. While these movements may reflect the muscles' attempts to stave off fatigue, they may also imply that if the imposed mechanical stress is unrelieved, muscle failure will ensue. In the laboratory, mechanical disadvantage is marked by diminished inspiratory mouth pressures. Because of wide scatter, a low mouth pressure beyond that which can be explained by hyperinflation alone should be confirmed by an assessment of Pesosniff or by the measurement of transdiaphragmatic pressure. Muscle endurance, also compromised in this condition, can be assessed indirectly by the measurement of MVV or MSVC, or more directly by an invasive assessment of the tension-time index and endurance time of the diaphragm or noninvasively by the Endurance Index of McKenzie and Gandevia. And finally, once muscle failure is pending or has been established, a program of muscle rest, either complete or partial, pharmacotherapy, and goal-specific training should be instituted.

Acute Disease↗
PubMed1990

Chemical activation of thin-fiber phrenic afferents: respiratory responses.

In supine chloralose-anesthetized and mechanically ventilated dogs, we assessed the effects of group III and IV thin-fiber phrenic afferents on cardiorespiratory control by injecting capsaicin into the phrenic artery of an in situ isolated and innervated left diaphragm. Inspiratory motor drive was assessed by measuring the electromyogram of left and right diaphragm, left parasternal, and mylohyoid muscles in five protocols. 1) Three boluses (2 ml) of capsaicin (1, 10, and 50 micrograms/ml) were injected 30 min apart. Only the 50-micrograms/ml injection elicited a significant increase in arterial pressure, heart rate, and inspiratory motor drive. 2) Repeated doses of capsaicin were tested. The pressor and hyperpneic responses were weakened. 3) High doses of capsaicin (100 and 500 micrograms/ml) were given. Hyperpneic and pressor responses were similar to those elicited by the 50-micrograms/ml dose. 4) When the left phrenic nerve was sectioned, the pressor and hyperpneic responses to the 50-micrograms/ml injection were abolished. 5) Capsaicin (50 micrograms/ml) was infused into the arterial supply of the in situ vascularly isolated and innervated gastrocnemius. Arterial pressure, breathing frequency, and inspiratory motor drive to all inspiratory muscles increased significantly and to a greater degree than in the diaphragm. In conclusion, diaphragmatic thin-fiber afferents have an excitatory effect on the inspiratory motor drive and arterial pressure that is similar to that seen in limb muscles.

Animals↗