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Biomedical subjects

A Harf

Publications and source records attributed to A Harf.

At least 253 records · Page 14Linked to original sources
PubMed1979

[Acute respiratory failure: comparison of spontaneous ventilation with continuous positive airway pressure (CPAP) and mechanical ventilation with positive and expiratory pressure (CPPV) in 6 cases (author's transl)].

The hemodynamic and respiratory effects of spontaneous ventilation with continuous positive airway pressure (CPAP) and mechanical ventilation with positive and expiratory pressure (CPPV) were compared in six patients with acute respiratory failure. Arterial and mixed venous gases, cardiac output, oxygen delivery and consumption, airway and oesophageal pressures were measured, with each patient on intermittent positive pressure ventilation (IPPV), CPAP and CPPV with the same level of positive and expiratory pressure (PEEP = 20 cmH2O). CPAP was as efficient as CPPV for improving arterial oxygenation. Cardiac output was higher on CPAP than on CPPV due to a lower intra-thoracic pressure with spontaneous ventilation, thus oxygene transport was higher with this methode. However total oxygene consumption and PaCO2 were slightly increased with CPAP due to a higher breathing's work. So, CPAP is as efficient as CPPV at the same level of PEEP in improving intra-pulmonary shunt and PaO2, without adversely affecting cardiac output.

Heart Rate↗
PubMed1979

Differential ventilation in unilateral lung disease: effects on respiratory mechanics and gas exchange.

Conventional PEEP ventilation has been recently reported to be deleterious in some cases of ARF with unilateral pneumonia. In such respect, two cases of unilateral bacterial pneumonia were intubated with a Carlens tracheal tube. Measurement of tidal volume, static compliance, and functional residual capacity of each lung showed marked inequality. Subsequently, both patients were ventilated with a selective distribution circuit, allowing the introduction of a PEEP valve in the expiratory line of the diseased lung. Evident improvement in blood gases was obtained within 24 hours, as tidal volume, static compliance, and FRC of the diseased lung were markedly improved. In one case equalisation of V/Q ratio was documented using the 81m Kr method. Final recovery was obtained in one case.

Adult↗
PubMed1979

Asbestos risk among full-time workers in an electricity-generating power station.

A matched survey of 55 full-time workers probably exposed to asbestos in an electricity-generating power station (exposed group) and of 53 unexposed workers in an automobile plant has been conducted. The asbestos risk in the power station was confirmed by the presence of airborne fibers in the range 0.1--6000 X 10(-9) g/m3 in the air sampled during the survey period and by the presence of FB in the sputa of 32.7% of the workers. The following parameters were significantly related to asbestos exposure in the study group: FB in the sputa, localized rectitude of the diaphragm, pleural thickening, pleural calcification, and the chest pain. Moreover, for all persons studied, gastrointestinal symptoms and recent hoarsening of the voice were significantly related to the number of FB in the sputa.

Adult↗
PubMed1978

Topographical distribution of VA/Q in elderly subjects using Krypton-81m.

The topography of ventilation-perfusion (VA/Q) ratios was measured in seven elderly (aged 58--69) subjects, seated erect, using the short-life (t1/2 = 13 sec) radioisotope Krypton-81m. 81mKr was inhaled (for ventilation) or infused intravenously (for perfusion) continuously for 1--2 min periods, during spontaneous ventilation, while radio-activity was recorded on a large-field gamma camera interfaced to a computer. The VA/Q ratio was computed for 15 horizontal slices of the left lung. VA/Q distribution was similar to that of young subjects. No decrease of basal VA/Q was seen; thus, if there are any changes of ventilation in the lower part of the lung in the elderly, they are matched by equal alterations of perfusion. There was no significant change when 60% oxygen was breathed. The progressive fall in arterial oxygen tension which occurs in erect subjects with increasing age does not appear to be caused by inter-regional differences of ventilation and perfusion.

Aged↗
PubMed1978

Regional distribution of VA/Q in man at rest and with exercise measured with krypton-81m.

The regional distribution of ventilation-perfusion ratio (VA/Q) in the lung was obtained from the continuous inhalation and infusion of 81mKr. With this short half-life isotope (13 s) serial measurements were made in six young normal subjects during spontaneous breathing, with minimal radiation exposure. At rest in the upright position the apical zone had a high VA/Q, but over the lower two thirds VA/Q distribution was relatively homogeneous. There was a slight increase towards the base. During exercise at 50 and 100 W the distribution became more uniform but there was more obvious than at rest. These distributions are consistent with a zone of reduced basal blood flow (zone IV) which becomes more marked on exercise. Apical blood flow was followed during the transition from rest to exercise and recovery. There was a large (40-150%) increase within 30 s of starting to pedal at 50 W, but little change thereafter.

Adult↗
PubMed1977

[Disturbances of wakefulness, sleep and respiratory function in Steinert's disease].

36 night sleep recordings were carried out on 15 patients suffering from myotonia dystrophica. 9 of these patients complained of diurnal hypersomnia. 10 patients had a disturbance of night sleep with a reduction of REM sleep sometimes associated with interruption of the recording with an increase in the light stages of sleep or alternatively with an increase of REM sleep with a reduction in the latency period of the first paradoxical sleep or with narcoleptic elements. 13 patients had abnormally early abolition of chin EMG activity, almost on falling asleep. 11 cases had pathological apnoeic episodes during sleep and in 9 of the 10 patients who underwent respiratory function studies there was a restrictive airways defect. In addition 9 had frank hypoxia without hypercapnia and 4 a right to left shunt. 3 clinically unaffected patients but with affected relatives were also investigated, 2 were found to have sleep disturbances 1 of which was associated with early abolition of tone.

Adolescent↗
PubMedDate not supplied

[Study of ventilatory mechanics - its application to artificial ventilation (author's transl)].

Study of ventilatory mechanics implies collection of input variables (stresses estimated by pressures) and output variables (strains), from which the parameters (compliance, resistance, etc.) of a model reproducing the functioning system can be computed. From this point of view, patients under artificial ventilation show a twofold difficulty: the one is the collection of variables, very difficult in consideration of the patients' precarious state, the other the type of the model: the first order linear model, used for lack of better solution, can be criticized, on the one hand by severe pulmonary changes in these patients, and by the special mode of applying constraints during artificial ventilation on the other. All these facts explain the methodologic and theoretical difficulties encountered in ventilatory mechanics analysis in resuscitation, which actually leads to the expression of one parameter as representative of the pulmonary parenchymal elasticity: the static compliance, and to the determination of the balancing point of the system: the functional residual capacity.

Airway Resistance↗
PubMedDate not supplied

Intrapulmonary shunt is not increased by 100% oxygen ventilation in acute respiratory failure.

Increase of shunt has been demonstrated during short periods of pure oxygen breathing, mostly in patients with mild acute respiratory failure (ARF). Twenty patients with a large range of venous admixture (12 to 63%) were studied when FIO2 was increased from maintenance to one. Intrapulmonary shunt was measured with both the conventional oxygen method [QS/QT (O2)] and the multiple inert gas elimination technique [QS/QT (IG)]. Mean venous admixture decreased from 29 to 24% when FIO2 was increased and QS/QT (IG) remained unaltered. The pattern of blood flow distribution remained similar in both conditions, even in the eleven patients with ARF secondary to bacterial pneumonia and who had a low V/Q mode, highly liable to collapse with 100% oxygen. As no increase in shunt was documented in these patients, reluctance to measure shunt during 100% oxygen breathing should be re-evaluated.

Acute Disease↗
PubMedDate not supplied

Automated measurement of respiratory mechanics in anaesthetized ventilated patients.

The automated multilinear regression analysis method (MLRA) was recently proposed to measure respiratory mechanics in mechanically ventilated subjects [11]. The method is applicable whatever the inspiratory flow pattern and without any assumption as to the value of the parameter characterizing the non linear term of flow resistance. It was compared here in ten mechanically ventilated patients to the constant flow inflation (CFIM) method described by Rossi et al. [15]. The non linear term of flow resistance was lower in intubated patients than in corresponding isolated endotracheal tubes. When derived from the MLRA method, the values for the elastance of the respiratory system were significantly higher (p less than 0.01) than with the CFIM method, and those for the system resistance, significantly lower (p less than 0.01). These differences might be due to the recruitment of lung units in the early part of inflation. When additional resistances were inserted into the respiratory circuit, both methods proved able to determine their values accurately. They therefore appear suitable for respiratory resistance monitoring in anaesthetized ventilated patients.

Adult↗
PubMedDate not supplied

Gas exchange and haemodynamics during high frequency body surface oscillation in rabbits.

To establish the clinical feasibility of high frequency body surface oscillation (HFBSO) as a mode of controlled ventilation for infants and to examine its effects on basic haemodynamic parameters, we studied twelve intact rabbits in two groups. The animals were placed in a body chamber with their heads remaining outside through a neck-hole. The mean chamber pressure was maintained at -3 to -4 cmH2O and a piston pump, operating at 3, 6, 9, 12 and 15 Hz, created pressure swings in the chamber, thus generating oscillatory tidal volumes. A fresh-airflow of 2 1.min-1 was used over the mouth. In the first group of six rabbits, we obtained the relationship between tidal volume (VT) and frequency (f) which maintained a normocapnic state (PaCO2 = 40 +/- 2 mmHg) when the animals were paralysed. The average tidal volumes required were between 1.36 and 1.78 ml.kg-1 for the 3-15 Hz frequency range, or about 1/4 of the spontaneous tidal volume. The corresponding mean PaO2 was 66.7 mmHg at 3 Hz and 73.4 mmHg at 9 Hz. These results indicate that adequate ventilation and acceptable gas exchange took place in these experimental animals during HFBSO. In the second group, six rabbits were catheterized with catheter-tip pressure transducers in order to obtain the aortic (ABP), central venous (CVP) and intrathoracic pressures. The arterial pressure profile was severely deranged by HFBSO, but, electronic subtraction of the intrathoracic pressure swings from the ABP signal resulted in the return of the normal pressure profile.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

A computerized method for measuring respiratory mechanics during mechanical ventilation.

In order to monitor respiratory mechanics in anesthetized ventilated subjects, an automated method was developed and tested on a physical model. The model was composed of an endotracheal tube (curvilinear resistance) coupled to a rigid air-filled box (elastance). Theoretical resistance was determined during steady-state flow experiments and theoretical elastance was estimated from the dimensions of the box. The physical model was connected to a volume-cycled ventilator. Pressure (P) and air flow (V) were measured at the outlet of the tube, and the time integral V of V was calculated. Elastance (E) and curvilinear resistance (R + K/V/) were identified by multiple linear regression analysis, for each ventilatory cycle, according to equation P = EV + RV + K/V/V. When linear regression analysis of P on V, V and /V/V was performed over the entire ventilatory cycle, E was found equal to its estimate, whereas R and K appeared different from their theoretical values. In order to improve determination of R and K, resistive pressure (Pr = P - EV) was calculated using the previously obtained value of E, and multiple linear regression of Pr on V and /V/V was performed over different fractions of the ventilatory cycle. When determined over the expiratory phase corresponding to decreasing flows, R and K were found close to their expected values. Such a method to calculate elastance and curvilinear resistance should prove convenient and efficient in measuring respiratory mechanics during mechanical ventilation.

Computers↗
PubMedDate not supplied

Correlation between lung structure and respiratory function in hamsters with experimental emphysema.

The correlation between lung structure and respiratory function was studied in normal hamsters and hamsters with elastase-induced emphysema. Four physiological parameters related to the elasticity of the respiratory system were determined from the quasi-static deflation pressure-volume curve: the shape constant (K) of the mono-exponential model fitted to the curve, the inflated volume (VI) taken as the volume change from a tracheal pressure of 0 to 30 cmH2O, the total respiratory compliance (C), determined near the relaxation volume and the normalized compliance (C/VI). The lung structure was morphologically described by the mean alveolar linear intercept (Lm) and the internal surface area (ISA). The correlations between these indices showed that 1) the four physiological parameters correlate better with Lm than with ISA, and 2) a simple index such as the normalized compliance allows to predict the severity of emphysema satisfactorily (r = 0.85; p less than 10(-6)).

Animals↗