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Biomedical subjects

R Farré

Publications and source records attributed to R Farré.

At least 91 records · Page 5Linked to original sources
PubMed1996

Effect of nitric oxide inhalation on respiratory system resistance in chronic obstructive pulmonary disease.

Nitric oxide (NO) has been identified as a neurotransmitter of nonadrenergic noncholinergic bronchodilator nerves. To investigate whether inhaled NO exerts a bronchodilator effect in patients with chronic obstructive pulmonary disease (COPD), we measured the resistance of the respiratory system, using the forced oscillation technique, while breathing NO. Eight patients with COPD (7 men and 1 woman; aged 66 +/- 7 yrs (mean +/- SD); forced expiratory volume in one second (FEV1) 37 +/- 17% of predicted) and eight healthy subjects (7 men and 1 woman; 33 +/- 4 yrs; FEV1 108 +/- 14% pred) were studied. Nitric oxide, at a concentration of 40 parts per million (ppm) in air, was inhaled for 20 min. Total resistance (Rrs) and reactance (Xrs) of the respiratory system, arterial oxygen saturation, heart rate, tidal volume, and breathing frequency were continuously recorded at baseline, and during and after ceasing NO inhalation. Methaemoglobin levels were additionally measured in healthy subjects. At baseline, patients with COPD showed higher Rrs than healthy subjects (Rrs at 10 Hz (Rrs,10) 4.97 +/- 2.19 vs 2.29 +/- 0.65 hPa.L-1.s). During NO inhalation, no significant change in Rrs or in Xrs was observed. Mean variation in Rrs,10 while breathing NO was negligible and similar in the two groups (-0.10 +/- 0.13 hPa.L-1.s in COPD patients and -0.02 +/- 0.13 hPa.L-1.s in healthy subjects). Moreover, there were no differences in oxygen saturation, heart rate, tidal volume and breathing frequency during NO inhalation. Methaemoglobinaemia increased at the end of NO inhalation (from 0.48 +/- 0.18 to 0.81 +/- 0.16%), and this increment remained 10 min later (0.86 +/- 0.31%). From these results, we conclude that inhaled nitric oxide, at a concentration of 40 ppm, exerts no effect on respiratory system resistance in patients with chronic obstructive pulmonary disease or in healthy subjects.

Administration, Inhalation↗
PubMed1996

Selenium and glutathione peroxidase reference values in whole blood and plasma of a reference population living in Valencia, Spain.

In order to assess the reference values for selenium nutritional status, adequate indicators (selenium concentration and glutathione peroxidase activity) were determined in whole blood and blood derivates of a healthy population (n = 287) from the province of Valencia, Spain. The reference population was selected by applying preestablished criteria. Selenium in whole blood and plasma was measured by graphite furnace atomic absorption spectrometry (GFAAS), with a deuterium correction, after addition of Pd/Mg(NO3)2 as the matrix modifier and appropriate dilution. Accuracy was checked by means of a reference material (Seronorm Trace Metals serum and whole blood). The population's reference intervals for selenium content at a 95% confidence level were: 53.03-108.96 and 66.71-119.4 mg/L for plasma and whole blood selenium concentration respectively. GPX activity was measured using a modification of the Paglia and Valentine method, and the reference intervals obtained ranged from 196 to 477 U/L in plasma, from 49 to 93 U/gHb in erythrocytes and from 52 to 96 U/gHb in whole blood. The only statistically significant differences detected between men and women are for to the GPX activity in whole blood. The results obtained are in the range of values found by others authors in healthy populations residing in different European countries.

Adolescent↗
PubMed1995

T model partition of lung and respiratory system impedances.

The aim of this work was to demonstrate that the three compartments of the lung T network and the chest wall impedance (Zcw) can be identified from input and transfer impedances of the respiratory system if the pleural pressure is recorded during the measurements. The method was tested in six healthy volunteers in the range of 8-32 Hz. The impedances resulting from the decomposition confirm the adequacy of the monoalveolar structure commonly used in healthy subjects. Indeed, the T shunt impedance is well modeled by a purely compliant element, the mean compliance [0.038 +/- 0.081 (SD) l/kPa], which coincides within 9.5 +/- 6.3% of the alveolar gas compressibility derived from thoracic gas volume (0.036 +/- 0.011 l/kPa). The results obtained provide experimental evidence that the alveolar gas compression is predominantly isothermal and that lung tissue impedance is negligible throughout the whole frequency range. The shape of Zcw is consistent with a low compliance-low inertance pathway in parallel with a high compliance-high inertance pathway. We conclude that the proposed method is able to reliably identify the T network featuring the lung and Zcw.

Adult↗
PubMed1995

Lung and respiratory impedance at low frequency during mechanical ventilation in rabbits.

We have tested in eight rabbits the feasibility of measuring respiratory (Zrs) and lung (ZL) impedances in the low-frequency domain, including below the breathing frequency (fb), during conventional mechanical ventilation (CMV). The animals were tracheotomized and ventilated with a tidal volume (VT) of 20 ml at a fb of 1 Hz. The excitation signal was provided by a flow generator connected in parallel with the ventilator; it included six components ranging from 0.45 to 14.8 Hz, which met the neither-sum-nor-difference criterion of B. Suki and K. Lutchen (IEEE Trans. Biomed. Eng. 39: 1142-1151, 1992) to minimize the influence of nonlinearities. Zrs and ZL were also measured at the same mean lung volume and with the same excitation signal both during apnea and when the ventilator signal was replaced by a sine wave with the same VT and fb (SMV). The real parts (Re) of both Zrs and ZL, as well as the effective elastances, were significantly larger during apnea than during CMV and SMV over the whole frequency range. Re(Zrs) and Re(ZL) were similar during CMV and SMV above fb but they were lower during CMV at 0.45 Hz. The latter difference seems to be related to the presence of harmonics of fb and of additional frequency components due to pulse amplitude modulation. We conclude that, because of nonlinearities, it is feasible to measure Zrs and ZL during CMV only at and above fb.

Animals↗
PubMed1995

Servocontrolled generator to measure respiratory impedance from 0.25 to 26 Hz in ventilated patients at different PEEP levels.

Assessing respiratory impedance (Zrs) in ventilated patients over a wide frequency band, ranging from breathing rates to typical forced oscillation frequencies, during end-expiratory pauses at different positive end-expiratory pressures (PEEP) is of potential interest to assess a patient's respiratory mechanics. Zrs measurements under these conditions are not possible with the present variants of the forced oscillation technique. The aim of this work was to design a forced oscillation generator operating from spontaneous breathing frequencies whilst withstanding PEEP. To this end, we constructed a generator based on a servocontrolled loudspeaker. This allowed the loudspeaker cone to remain at its resting position regardless of the external PEEP applied. The system was optimized by using a mechanical analogue. The clinical applicability of the servocontrolled generator was assessed by measuring Zrs in mechanically-ventilated chronic obstructive pulmonary disease (COPD) patients during end-expiratory pauses at different transrespiratory pressures. The forced oscillation generator designed may be easily applicable in practice since it is small and light. The system is able to withstand transrespiratory pressures of up to 17 hPa and allows the application of forced oscillation of sufficient amplitude ( > 2 hPa peak-to-peak, 0.25-26 Hz) to obtain reliable respiratory resistance and reactance data. The servocontrolled generator permits the assessment of respiratory mechanics over a wide frequency band ranging from breathing frequencies to the most typical forced oscillation frequencies during end-expiratory pauses at PEEPs within the conventional range.

Equipment Design↗
PubMed1994

GFAAS determination of selenium in infant formulas using a microwave digestion method.

A method for determining the selenium content of infant formulas is proposed. It includes wet digestion with nitric acid and hydrogen peroxide in medium pressure teflon bombs in a microwave oven and determination by graphite furnace atomic absorption spectrometry (GFAAS). The absence of interferences is checked. Values obtained for the limit of detection (19.4 ng/g), precision (RSD = 2.2%) and accuracy by analysis of a reference material show that the method is reliable.

Humans↗
PubMed1994

Determination of Cd, Cu, Pb and Zn content of infant formulas by differential pulse anodic stripping voltammetry (DPASV).

The differential pulse anodic stripping voltammetry (DPASV) method described is based on the one reported by Hasse et al., but adapted to normal laboratory conditions. The values obtained in the estimation of the analytical parameters (linearity, detection and quantification limits, precision and accuracy) show that in the conditions described the method is sensitive enough, reliable and useful for determining these elements in infant formulas. A comparison between DPASV and atomic absorption spectroscopy (AAS) methods in the conditions described here shows that the former is less sensitive but that they are similar in precision. The cadmium, copper, lead and zinc contents of different types of infant formulas marketed in Spain are reported.

Electrochemistry↗
PubMed1994

Human lung impedance from spontaneous breathing frequencies to 32 Hz.

Lung impedance (ZL) was measured from 0.1875 to 32 Hz in spontaneously breathing healthy subjects by spectral analysis of the pressure and flow signals generated simultaneously by the muscular generator of breathing and by a forced oscillation system. This method did not require cooperation from the subject to perform panting or special ventilatory maneuvers and therefore allowed us to analyze the frequency dependence of lung resistance, reactance, and elastance (-2 pi.frequency.reactance) at the physiological conditions of normal breathing. Resistance and elastance parameters were also computed by multiple linear regression of the time-domain pressure and flow data on a simple resistance-elastance model. Resistances and elastances computed at the breathing frequency by spectral analysis and by multiple linear regression were similar (nonsignificant differences < 4 and 10%, respectively). The results obtained when comparing ZL from the breathing component (0.1875-0.75 Hz) of the recorded signals and from the forced oscillation component (2-32 Hz) were fairly consistent. ZL (0.1875-10 Hz) was interpreted in terms of a model consisting of an airway compartment, including a resistance and an inertance, in series with a viscoelastic tissue compartment (J. Hildebrandt. J. Appl. Physiol. 28: 365-372, 1970) characterized by two parameters. The model analysis provided parameter values (resistance 2.49 +/- 0.58 hPa.l-1.s, inertance 1.70 +/- 0.29 Pa.l-1.s2, Hildebrandt parameters 4.87 +/- 2.28 and 0.73 +/- 0.99 hPa/l) consistent with the hypothesis that lung tissue in healthy humans during spontaneous breathing behaves as a viscoelastic structure with a hysteresivity of approximately 0.10.

Adult↗
PubMed1993

Oral intake of cadmium, cobalt, copper, iron, lead, nickel, manganese and zinc in the university student's diet.

A duplicate diet meal study was carried out with a group of university students living in a hostel, in order to estimate the intake of Zn, Cd, Co, Cu, Fe, Mn, Ni and Pb. Zn, Cu, Fe, Mn and Ni were determined by flame atomic absorption spectrophotometry and Cd, Co and Pb by graphite furnace atomic absorption spectrophotometry after a nitric acid wet digestion procedure. The estimated intake values from the contents of breakfast, lunch, dinner and drinks were compared with the values of the Provisional Tolerable Daily Intake (PTDI) in the case of Cd and Pb, Recommended Dietary Allowances (RDA) of Co, Fe and Zn and Estimated Safe and Adequate Dietetic Daily Intake (ESADDI) of Cu and Mn. Neither excessive intake of Pb and Cd nor deficiencies in Zn, Co, Fe, Mn or Ni were observed, but Cu intake was lower than the ESADDI.

Diet↗
PubMed1993

Validity of the esophageal balloon technique at high frequencies.

The reliability of the esophageal balloon technique in measuring high-frequency changes in pleural pressure (Ppl) was investigated in six normal subjects by studying the amplitude ratio (A) and phase angle (phi) of esophageal (Pes) and mouth (Pm) pressures during airway occlusion and while pseudorandom pressure variations (2-32 Hz) were applied to the chest. The measurements were made with a common esophageal balloon-catheter system connected to a high-impedance piezoresistive transducer. When the cheeks were firmly supported, A averaged 1.08 +/- 0.063 at 2 Hz and 1.06 +/- 0.11 at 32 Hz. Pes increasingly led Pm with increasing frequency, and phi averaged 20.8 +/- 4.0 degrees at 32 Hz. Washing the airways with 80% He-20% O2 reduced phi by 50%. When the cheeks were not supported, A exhibited a strong positive frequency dependence, averaging 1.71 +/- 0.34 at 32 Hz, whereas phi increased much faster below 20 Hz and tended to decrease afterward. Because the esophageal transfer function Pes/Ppl = (Pes/Pm)/(Ppl/Pm), we could estimate Pes/Ppl by computing for individual subjects the pressure difference between the pleura and the mouth based on the lung and upper airway wall properties that were measured separately. The results suggest that the ratio of Pes and Ppl remains close to unity from 2 to 32 Hz, but Pes lags slightly behind Ppl (phi equals about -7 degrees at 32 Hz).

Adult↗
PubMed1993

Respiratory input impedance up to 256 Hz in healthy humans breathing foreign gases.

Currently available data concerning respiratory input impedance (Zrs) at frequencies up to 300 Hz indicate that Zrs is determined mainly by the airways and, in particular, the gas compressibility in the airways and the airway wall compliance. Hence, measurements of Zrs when breathing gases with different physical properties would be useful in investigating airway mechanics and the role of acoustic propagation. Zrs measured with a standard generator (Zst) and corrected for the upper airway shunt (Zrs*) were measured in nine healthy subjects breathing air or a gas mixture consisting of 20% O2 and 80% He or SF6. The frequency band was extended up to 256 Hz for air and He-O2 and up to 128 Hz for SF6-O2. Zrs exhibited a similar pattern for the three gases, with a shift toward low frequencies as the gas density increased. Moreover, the resonance peaks tended to be narrower and higher as the gas density increased. The second frequency of resonance for He-O2, air, and SF6-O2 were 220, 180, and 50 Hz, respectively, for Zrs* and were systematically higher for Zst. Zrs* and Zst data were interpreted in terms of a tricompartmental model that partitioned the airways into two segments: a central one featuring the acoustic propagation in the airways and a peripheral one that included bronchial wall elasticity (Farré et al. J. Appl. Physiol. 67: 1973-1981, 1989). The model was able to interpret the gas dependence of Zrs* but not that of Zst. The influence of the gas physical properties on both Zrs* and Zst confirms that total Zrs at high frequencies is basically that of the airways and that the second resonance is related mainly to the gas compressibility in the airways.

Adult↗
PubMed1992

Optimized estimation of respiratory impedance by signal averaging in the time domain.

The spontaneous breathing of a subject during measurements of respiratory impedance (Zrs) by the forced oscillation technique (FOT) induces errors that result in biased impedance estimates, especially at low frequencies. Although in standard measurements this bias may be avoided by using special impedance estimators, there are two applications of FOT for which such estimators are not useful: when a head generator is used and when measurements are made during intubation. In this paper we describe a data-processing procedure for unbiased impedance estimation for all FOT setups. The proposed estimator (Z) was devised for pseudorandom excitation and is based on time-domain signal averaging before frequency analysis. The performance of estimator Z was first analyzed by computer simulation of a head generator setup and a setup including an endotracheal tube to measure (2-32 Hz) a resistance-inertance-elastance model mimicking Zrs of a healthy subject. Second, Z was assessed during real measurements in 16 healthy subjects. The results obtained in the simulation (e.g., error in elastance was reduced from 15.6% with most conventional estimators to 3.3% with Z in simulation of head generator setup) and in the measurements in subjects (differences of less than 1.6% between Z and a reference) confirmed the theoretical lack of bias of Z and its practical suitability for the different FOT setups. In addition to its applicability in the situations in which no other unbiased estimators are available, estimator Z is also advantageous in most conventional applications of FOT, since it requires much less computing time and thus allows on-line Zrs measurements.

Adolescent↗
PubMed1991

Determination of antimony in drinking waters by an inexpensive, reproducible hydride generator for atomic spectroscopy.

A method for determining antimony in drinking waters is described. In order to prevent a substantial error caused by the different oxidation states of antimony, Sb(V) is reduced to Sb(III) with potassium iodide-ascorbic acid. Covalent hydride is generated with a home made device by adding NaBH4. The hydride is then atomized in a flame-heated silica tube and atomic absorption is measured spectrophotometrically. The optimal conditions for this determination are discussed and interference effects are described. Results obtained by determining linearity range (0-200 ng), detection (LOD) and quantitation (LOQ) limits (LOD = 0.347 ng/ml, LOQ = 1.158 ng/ml), precision (instrumental CV 4.08% and method CV 7.74%) and accuracy performed by recovery assays (96.1%) show that the method is useful for antimony determination at the concentration usually present in drinking water.

Antimony↗
PubMed1991

Time-domain digital filter to improve signal-to-noise ratio in respiratory impedance measurements.

The mechanical impedance of the respiratory system Zrs is usually measured by forced excitation while the patient breathes spontaneously. Pressure and flow signals due to breathing contaminate the excitation signals, leading to a poor signal-to-noise ratio (SNR) and thus to errors in impedance estimation, especially at low frequencies (up to 8 Hz). To enhance SNR in the recorded signals we designed an infinite impulse response digital filter for the frequent case in which the excitation is pseudorandom. The algorithm is based on narrowband second-order bandpass elements centred at the excitation frequencies. The performance of the filter was assessed in a simulation study by superposing forced excitation signals (2-32 Hz) from a reference model and the signals of breathing recorded from 16 subjects. When compared with a conventional high-pass filtering, the devised filtering resulted in an increase in SNR which was almost constant over the whole frequency band: 6.30 +/- 0.98 dB (mean +/- SD). This improvement in SNR was reflected in an increase in the number of subjects for which the corresponding coherence y2 attained a value greater than the conventional threshold of acceptability (y2 = 0.95). At the lowest frequency (2 Hz) only two (12.5 per cent) simulated subjects had y2 greater than or equal to 0.95 with the conventional high-pass filtering. By contrast, when using the devised comb filter the number of subjects with y2 greater than or equal to 0.95 increased up to 13 (81 per cent). The results obtained suggest that this filter may be useful to improve SNR and thus Zrs estimation.

Airway Resistance↗