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Biomedical subjects

A Harf

Publications and source records attributed to A Harf.

At least 199 records · Page 11Linked to original sources
PubMed1986

High frequency transthoracic ventilation improves gas exchange during experimental bronchoconstriction in rabbits.

In order to evaluate the efficacy of ventilation by high frequency transthoracic oscillation in obstructive lung disease, we studied 10 anesthetized and paralyzed rabbits during experimental bronchoconstriction. In order to generate body surface oscillation, the animals were placed in a body-box connected to a piston pump. Two frequencies were successively applied in random order: 1 Hz, representing "conventional" ventilation, and 5 Hz for high frequency ventilation. During the control period, the magnitudes of the oscillation were adjusted such that the tidal volumes thus produced yielded normocapnia (PaCO2 = 40 +/- 2 mmHg) for at least 3 min at each frequency. The same tidal volumes were then used after a bronchoconstriction induced by aerosolized carbachol. We obtained a severe and stable bronchoconstriction and oscillated the animals at 1 and 5 Hz at identical tidal volumes as those used during the control period. Identical at the 2 frequencies of oscillation during the control period, the rate of CO2 elimination with bronchoconstriction was significantly higher (p less than 0.05) at 5 Hz (15.9 +/- 3.3 ml/min) than at 1 Hz (14.2 +/- 3.9 ml/min); PaCO2 was also significantly lower at 5 Hz than at 1 Hz. Mean arterial PO2 was significantly higher (p less than 0.01) at 5 Hz (58 +/- 4 mmHg) than at 1 Hz (46 +/- 12 mmHg) during bronchoconstriction. Mean alveolararterial O2 pressure difference was significantly lower (p less than 0.01) at 5 Hz (49 +/- 13 mmHg) than at 1 Hz (59 +/- 11 mmHg). Only a minor increase in lung volume was found during high frequency ventilation, and no significant hemodynamic changes occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1986

Cardiopulmonary effects of a single oral dose of almitrine at rest and on exercise in patients with hypoxic chronic airflow obstruction.

Almitrine, a new triazine derivative, was studied in a double-blind, randomized, parallel study in 16 patients with hypoxic chronic airflow obstruction (eight almitrine and eight placebo). At rest, compared to placebo, a 3 mg/kg single dose of almitrine given orally significantly increased the partial pressure of oxygen (mean increase: +12.0 +/- SEM 2.1 mm Hg, p less than 0.001) and decreased the partial pressure of carbon dioxide (mean decrease: -6.0 +/- 0.7 mm Hg, p less than 0.001); this improvement in arterial blood gases persisted on exercise. The lack of significant change in ventilation and the decrease in the alveolar-arterial oxygen gradient (mean decrease -10.0 +/- 1.9 mm Hg; p less than 0.001) at rest suggests a change in the distribution of the ventilation-perfusion ratio in the lung; such a change was confirmed by a krypton 81m isotopic study. Pulmonary hemodynamic responses were studied at rest and on exercise; a significant but slight increase in mean pulmonary artery pressure at rest (+4.0 +/- 1.5 mm Hg, p less than 0.05) was found.

Administration, Oral↗
PubMed1986

Lung mechanics in growing guinea-pigs treated with growth hormone.

Because growth hormone excess has been reported to accelerate lung growth in acromegalic men and in adult rats, effects of growth hormone were tested in prepuberal guinea-pigs. From week 2 to week 4, five guinea-pigs were injected daily with human growth hormone (0.1 mg/kg) and compared with five injected with saline. At week 4 lung mechanices were measured and the animals sacrificed. Growth hormone-injected guinea-pigs gained more weight than saline ones (P less than 0.01) and had heavier livers (P less than 0.01). However, no difference was observed between both groups for lung weight, volume or distensibility.

Animals↗
PubMed1985

Total respiratory compliance as a function of lung volume in patients with mechanical ventilation.

In normal subjects breathing spontaneously, compliance has been shown to be influenced by the lung volume from which deflation started. We wondered whether this would also be true for patients with acute respiratory failure who required mechanical ventilation and we accordingly studied 15 such patients. Chest inflation was performed using a continuous flow device (ATM-PV 102), and total compliance was measured as the slope of the pressure-volume relationship during deflation. As inflated lung volumes were increased by 10 to 15, 20 and 25 ml/kg body weight above FRC, mean compliance increased to 38.2, 45.5, 52.2 and 59.3 ml/cmH2O respectively. Each of these increases in mean compliance was statistically significant (p less than 0.001). Increasing the inflated lung volume to 30 ml/kg produced no further significant increase in mean compliance. This study showed that, in patients with acute respiratory failure requiring mechanical ventilation, compliance measured during deflation is a function of the inflated lung volume. We recommend that the compliance should be measured from a constant and high lung volume, equal to 25 ml/kg body weight above FRC.

Acute Disease↗
PubMed1985

Pulmonary function after transverse or midline incision in patients with obstructive pulmonary disease.

Atelectasis and bronchopneumonia occur frequently in patients undergoing aorto-iliac reconstructive surgery. Transverse (T) incisions in upper abdominal surgery are thought to be followed by fewer pulmonary complications than midline incisions (M) but reports remain controversial. We studied the incidence of postoperative pulmonary complications and lung dysfunction after T and M incisions for aorto-iliac surgery in 13 patients with chronic obstructive pulmonary disease (COPD) and 13 control patients with normal lungs (C). For all subjects, we evaluated (1) postoperative clinical or radiological pulmonary events; (2) preoperatively and on postoperative days 2 (D2), 5 (D5), 9 (D9) and 12 (D12) - the forced expiratory volume in 1 s (FEV1), vital capacity (VC), alveolar-arterial oxygen difference (AaPO2), and (3) convenience for the surgeon. Operatively, aortic exposure was excellent with both incisions. Bronchopneumonia occurred only after M in five patients (1 C, 4 COPD). In contrast with the control patients in whom no difference was found between T and M incisions, the FEV1 of COPD patients was significantly less impaired with T than with M incisions (p less than 0.005 on D2 and p less than 0.05 on D5). VC decreased similarly with both incisions on D2 but on D5 the improvement was less with M (p less than 0.005). Changes in AaPO2 were more marked on D2 and D5 for the COPD patients with M incisions. We conclude that (1) in patients with chronic obstructive pulmonary disease, laparotomy with a transverse incision was associated with better postoperative lung function and fewer pulmonary complications; (2) in patients without pulmonary disease, midline and transverse incisions were equivalent.

Abdominal Muscles↗
PubMed1985

Bronchorelaxation and plasma histamine after salbutamol inhalation.

Plasma histamine in 8 normal subjects was measured before and after inhalation of carbachol to induce a 50% fall in specific airway conductance (SGaw). The measurements were repeated 5 min after inhalation of salbutamol or placebo. No significant change in plasma histamine occurred after placebo or carbachol inhalation, despite the persistent induced bronchospasm after the latter treatment. In contrast, plasma histamine was significantly increased from 0.25 to 0.43 ng/ml after salbutamol inhalation. Simultaneously, induced bronchospasm was relieved, from 51% to 103% of baseline SGaw. Thus, the relief of carbachol-induced bronchospasm by salbutamol was associated with a rise in plasma histamine. Since salbutamol itself is a potent inhibitor of mast cell degranulation and histamine release, the present findings suggest that histamine may be released and sequestered within the lungs during carbachol-induced-bronchospasm, and also that desequestration of bronchoconstrictor mediators accumulated at the point of contact of bronchial smooth muscle may contribute to the relief of bronchospasm by salbutamol.

Adult↗
PubMed1985

On line determination of airway resistance by plethysmography and microcomputer.

On line determination of airway resistance is carried out by an Apple II connected to a flow body plethysmograph. Recognition of the panting maneuver is performed in real time. Linear drift of plethysmographic volume V is eliminated by taking the derivatives V and Vm of V and mouth flow Vm. Linear regression of V on Vm yields an estimate R of airway resistance, at a volume close to functional residual capacity FRC. The values of FRC is given by linear regression of V on Pm, the derivative of mouth pressure. No significant difference has been found between the estimates of the specific conductance sG calculated by linear regression and by spectral analysis of V and Vm. As variability of sG can be kept below 10%, the regression technique appears to be reliable for routine patient testing and pharmacological studies.

Airway Resistance↗
PubMed1985

A microcomputer-based system for real-time calculation of airway conductance in awake guinea pigs.

Bronchial responsiveness to various drug stimuli is currently studied by constructing cumulative dose-response curves of specific respiratory conductance (SG). Airway conductance can be measured in guinea pigs by the plethysmographic technique, during the rapid transition from expiration to inspiration (TEI). Since the drug action assigns a strict timing to the experiment, conventional methods of measuring SG prove inconvenient and often lack accuracy. A computerized data acquisition system has therefore been developed to recognize TEI and calculate SG in real time. This paper describes the significant features of the program DOREMI, and gives an illustrative example of the system in use.

Airway Resistance↗
PubMed1985

Pressure change and gas mixing induced by oscillations in a closed system.

In an attempt to delineate some mechanical behaviors found in branching airways, pressure transmission, gas motion, and mixing were studied during high-frequency oscillation (HFO) in an idealized system consisting of a large straight tube and a rigid sphere linked together by a small straight tube. Depending on the frequency f, and on the unsteadiness dimensionless parameter alpha, pressure amplitude in the large tube is either strongly attenuated or amplified in the sphere. This finding may provide a theoretical basis for the pressure resonance phenomenon observed in the lung by previous investigators. Gas compression in the closed volume causes convective mixing throughout the system. The measured dispersion was found to be proportional to f(VT/A)2, in agreement with a recent report. However, bulk convective mixing was sufficient to explain the dispersion for oscillatory volumes (VT) as small as 80 percent of the small tube volume, as has been previously suggested.

Biomechanical Phenomena↗
PubMed1985

Respiratory resistance in dogs by the single-breath and the forced oscillation methods.

Total respiratory resistance (Rrs) was measured in six anesthetized dogs with two different methods: the single-breath (SB) method, which provides the time constant of the system during a relaxed expiration and the forced oscillation (FO) method, which uses a pseudorandom noise signal applied at the airway opening. The comparison was made in three conditions: before muscle paralysis (A), after muscle paralysis (B), and after tracheal banding (C). In conditions A and B the two computed resistances correlated very well with each other (r = 0.98). No systematic difference between Rrs values obtained with the two methods was found. In condition C the respiratory resistance was clearly nonlinear from the flow-volume curves during SB and could be described with Rohrer's equation: Rrs = K1 X V + K2 X V2, where K1 and K2 are Kohrer's constant and V is flow. Rrs measured with FO was not frequency dependent during tracheal banding (C) and was virtually equivalent to K1. Since the FO method uses low flows as the input of the respiratory system and K1 could be ascribed to laminar flow, the numerical matching appears reasonable and tends to reinforce the validity of both methods of measurement. We conclude that, for the normal respiratory system, FO and SB methods are approximately equivalent. In the presence of a markedly alinear central airway resistance with normal lungs, the SB method appears to provide a more adequate description of the flow-resistive properties of the system.

Airway Resistance↗
PubMed1985

Mechanical ventilation with 100% oxygen does not increase intrapulmonary shunt in patients with severe bacterial pneumonia.

Pure oxygen ventilation has been shown to increase the right to left shunt QS/QT in both normal and diseased lungs. Nitrogen absorption atelectasis, an explanation of the phenomenon, is likely to occur in lung units with low ventilation/perfusion ratio. In 11 patients with severe unilateral or bilateral bacterial pneumonia, we assessed the effects of increasing FlO2 from maintenance level (m = 0.44 +/- 0.11) to 1.0. Venous admixture (QVA/QT) was calculated using the O2 method, and the distribution of the VA/Q ratios were assessed with the 6 inert gas (IG) technique providing the distribution between the true shunt (QS/QT IG) and the low VA/Q units. Although a large part of perfusion was distributed preferentially to low VA/Q units, ranging from 2 to 43% of cardiac output, thus placing large zones of lung parenchyma at risk of absorption atelectasis, QVA/QT decreased from 31 +/- 13% to 25 +/- 10% and IG shunt did not increase after 30 min of O2 ventilation. In addition, QS/QT IG remained unaltered despite PVO2 increased from 32 to 43 mmHg, suggesting a poor level of hypoxic vasoconstriction in human bacterial pneumonia.

Bacterial Infections↗
PubMed1985

Stable normocapnia during high-frequency body surface oscillation in rabbits.

In order to identify the useful range of frequencies and the effect of lung volume on gas exchange during high-frequency ventilation, particularly during high-frequency body surface oscillation (HFBSO), we studied 12 normal, anesthetized, and paralyzed adult rabbits in 2 groups at 1, 3, 5, 8, 12, and 16 Hz in random order. The rabbits were placed in a body box, and a "bias" flow system different from all previously reported systems was used. For a given animal at a given frequency, the oscillation magnitude was adjusted to ensure normocapnia, defined as PaCO2 equal to 40 +/- 2 mmHg, for at least 5 min. For the first group (n = 6) with a mean tracheal pressure of 0.5 cmH2O, the necessary tidal volumes (mean +/- SD) were 3.7 +/- 0.2, 1.9 +/- 0.2, and 1.5 +/- 0.1 ml/kg at 1, 3, and 5 Hz, respectively. Further increases in frequency resulted in only small decreases in the required tidal volumes: 1.4 +/- 0.1, 1.2 +/- 0.1, and 1.2 +/- 0.1 ml/kg at 8, 12, and 16 Hz, respectively. Arterial PO2 values were very similar at all 6 frequencies, with a mean of 78.6 +/- 3.3 mmHg in this group. For the second group (n = 6) with a mean tracheal pressure of 5 cmH2O, arterial PO2 values were again the same at all frequencies applied but were significantly higher (95.5 +/- 2.6 mmHg) than in the first group. No significant difference was observed in the tidal volumes required to maintain normocapnia between the 2 groups, i.e., at the 2 mean tracheal pressures studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Nitrogen washout during tidal breathing with superimposed high-frequency chest wall oscillation.

In order to assess the efficacy of high-frequency chest wall oscillation (HFCWO) superimposed on tidal ventilation, multiple-breath nitrogen washout curves were obtained in 7 normal seated subjects. To maintain a regular breathing pattern throughout the study, the subjects breathed synchronously with a Harvard ventilator set at a constant tidal volume and frequency for each subject during a trial period. Washout curves were obtained during 3 different maneuvers performed in random order. Series A was the control condition with no superimposed HFCWO. In Series B and C, HFCWO at 5 Hz was superimposed on the regulated tidal breathing; the magnitude of the oscillatory tidal volume measured at the airway opening was 20 ml for Series B and 40 ml for Series C. The nitrogen washout was clearly faster in Series C than in Series A for each subject. In Series B, there was an interindividual variability, with a washout rate either equal to that in Maneuver A or in Maneuver C, or intermediate between the two. When these washout curves were analyzed in terms of a simple monocompartment model, the time constant of the washout was found to decrease by 16 +/- 11% in Series B, and 25 +/- 7% in Series C compared with that in Series A. In this group of normal subjects, the correction of any inhomogeneity in the distribution of the ventilation is unlikely to explain these results because of the close fit of all washout curves to a monoexponential model. It is postulated that during inspiration HFCWO enhances gas mixing in the lung periphery and that during expiration it improves gas mixing in the airways.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Influence of caloric intake on the respiratory mode during mandatory minute volume ventilation.

Mandatory minute volume ventilation has been proposed as a method for weaning patients from ventilators. The purpose of this study was to delineate the influence of caloric intake on spontaneous ventilation in patients receiving mandatory minute volume ventilation. While the value of such ventilation remained unchanged, eight patients were studied at the following three different levels of daily caloric intake: (1) level A, mean of 223 kcal/sq m; (2) level B, mean of 1,380 kcal/sq m; and (3) level C, mean of 2,100 kcal/sq m. We performed gas exchange measurements and a 24-hour recording of ventilation with a monitoring system providing distinction between spontaneous and mechanical cycles. We found that the ventilatory mode was markedly dependent upon the nutritional intake; the percentage of spontaneous ventilation over 24 hours increased from 11 +/- 7 percent (+/- SE) during diet A to 50 +/- 9 percent during diet B and 79 +/- 8 percent during diet C. This increment paralleled the increase in production of carbon dioxide with caloric intake. We suggest therefore that the patient's ability to breathe spontaneously when receiving mandatory minute volume ventilation should be interpreted according to caloric intake.

Aged↗
PubMed1984

[Acute respiratory distress syndrome in the adult. Distribution of the ventilation-perfusion ratio].

Hypoxemia in the acute respiratory distress syndrome may be due to a variety of causes: trùe pulmonary shunt, decreased ventilation/perfusion ratios, impaired diffusion and/or fall of mixed venous oxygen. In order to sort out these different tension mechanisms, 18 patients with acute respiratory distress syndrome were explored by the inert gas method. In 6 of them hypoxemia was due to a true shunt (35 +/- 10%). The remaining 12 patients also had a true shunt (26.5 +/- 9.5%), but 4.5% of the cardiac output was distributed to areas with a ventilation/perfusion ratio between 0.1 and 0.005. Thus, in these 18 patients with acute respiratory distress, hypoxemia could be explained essentially by a true shunt.

Adult↗
PubMed1984

Regional distribution of ventilation-perfusion ratios in acute pulmonary embolism.

Regional ventilation perfusion ratios have been computed in 44 patients with acute pulmonary embolism with a gamma-camera using Krypton 81m, a short-life radionuclide delivered by inhalation and infusion. This noninvasive technique is performed during tidal breathing and can be easily repeated. High V/Q's are detected in the embolic regions and low V/Q's in the nonembolic regions with a shift of the perfusion distribution towards these low values. This pattern disappears with recovery. This technique can be used in clinical practice for diagnostic purposes.

Acute Disease↗