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Biomedical subjects

H Guenard

Publications and source records attributed to H Guenard.

50 records · Page 3Linked to original sources
PubMed1983

Pulmonary capillary blood volume during immersion in water at different temperatures.

Pulmonary capillary blood volume (Qc) was determined for 7 subjects in the standing posture and immersed up to the sternal manubrium at three water temperatures: 34 degrees C +/- 0.5 degrees C, thermally neutral bath; 25 degrees C +/- 0.5 degrees C, cold bath; and 40 degrees C +/- 0.5 degrees C, hot bath. The Qc was calculated from the lung transfer factor DLco measured while breathing two gas mixtures (21.1% O2 and 90.0% O2) during breath holding. Control experiments in a dry air environment show that Qc values for standing posture decrease compared to the sitting values, owing to a redistribution of the intrathoracic blood volume to lower body parts as a result of gravity. Immersion at 34 degrees C in an upright position produces a significant increase in Qc (P less than 0.01). This is a result of the hydrostatic counterpressure: blood shifts from the periphery to the intrathoracic regions. Immersion at 25 degrees C increases Qc compared to the values obtained at 34 degrees C, but the difference is not significant. The contribution of vasoconstriction to blood volume shift in cold water is probably less important than that of hydrostatic counterpressure. During immersion at 40 degrees C, the rise in Qc is very significant (P less than 0.05). This may be explained by an increase in cardiac output and central blood volume when skin temperature is raised at 40 degrees C.

Adult↗
PubMed1982

Effects of oxygen breathing on regional distribution of ventilation and perfusion in hypoxemic patients with chronic lung disease.

Regional distribution of ventilation and perfusion were measured in 17 hypoxemic and 16 normoxic patients using 13N as tracer. The effect of 100% and 50% O2 breathing was tested. No variation was observed in normoxic patients. In hypoxemic patients, perfusion was not modified significantly during O2 breathing. Poorly-ventilated zones hypoventilated even more during O2 breathing. It is suggested that this effect may have been due to (1) a collapse of some alveoli, (2) a variation in the mechanical properties of the surrounding opened alveoli, or (3) a possible modification in tidal volumes and functional residual capacities during O2 breathing.

Blood Gas Analysis↗
PubMed1981

[Simultaneous assessment of intra-pulmonary right-to-left shunting and of aADCO2 in 5 neonates with refractory hypoxemia (author's transl)].

Five neonates with refractory hypoxemia (aortic PO2 less than or equal to 6.7 KPa despite FiO2 = 1 and efficient artificial ventilation) were investigated in order to determine the principal mechanism of hypoxemia. PO2 values were measured (under FiO2 = 1) in a pulmonary vein, the left auricle and the aorta. They were used to distinguish intra-pulmonary shunts from extra-pulmonary shunts (though foramen ovale and/or ductus arteriosus). Simultaneous measurements of PACO2 and PaCO2 were used to assess the percentage of the ventilation output reaching hypoperfused areas. In cases with extra-pulmonary shunt, when this percentage is over 30%, pulmonary hypertension is likely. The use of both methods is useful for selecting those patients who might benefit from tolazoline.

Blood Gas Analysis↗
PubMed1980

A new radioisotope for lung ventilation studies: 19-neon.

Neon 19, 17-second positron-emitting radioelement, is produced continuously by 23MeV alpha particle bombardment of oxygen. For a 12 muA particle current the method of preparation described delivers 14 mCi of neon 19 per min to the functional exploration room. The radiochemically pure radioactive gas is diluted in air and breathed continously by the patient lying under a positron tomographic camera. The regional lung ventilation distribution is obtained on 2 cm thick sections of organ with a transverse resolution of 17 mm. Quantification of the ventilation output per unit lung volume is contemplated.

Heart Ventricles↗
PubMed1980

Respiratory water loss.

Two kinds of studies have been conducted in order to measure respiratory water loss: a single breath study of instantaneous variations in relative gas humidity of air expired during one respiratory cycle and a multibreath study of the average values of water vapor in air expired during several successive cycles of steady state ventilation. In the first case, relative gas humidity is computed from results obtained by thermometry and mass spectrometry; in the second case, average water vapor content of expired air is calculated from plethysmographic spirometry and expired water collection. Both experiments showed that mixed expired gas is not fully water saturated. The multibreath study showed that the mass of water lost per liter of ventilated gas is not a function of ventilation per se but rather increases as tidal volume rises and decreases as respiratory frequency diminishes. The mass of water lost per cycle of steady state ventilation increases with tidal volume so that mean expired gas volume may be considered as a mixture of dry gas and water saturated gas. The single breath study showed that unsaturated gas is expired in the first part of expirate followed by wet saturated gas in the second part. The numerical values given by the two kinds of studies are in close agreement.

Humans↗
PubMed1975

Alveostat, an alveolar PACO2 and PAO2 control system.

In the study of the physiological regulation of respiration through a control system model it is necessary to test the ventilatory response to various forcing functions of either the parrtial pressure of alveolar carbon dioxide (PACO2) or oxygen (PAO2). Since PACO2 and PAO2 are both functions of alveolar ventilation and metabolic rate, such a result cannot be obtained by merely changing the composition of the inspired gases without a feedback control. Thus a servomechanism is necessary. The input to the servomechanism is an instantaneous determination of PACO2 and PAO2. This is accomplished by using the criterion of equality of the exchange ratio in mean alveolar gas and mean expired gas. The servomechanism described has three essential characteristics: rapidity, accuracy, and stability. In experiments of step, ramp, and sinusoidal forcing functions, variations of PACO2 have been obtained without change in PAO2, and step variations of PAO2 have been obtained without change in PACO2.

Carbon Dioxide↗
PubMedDate not supplied

Spirometric reference values in Tunisian children.

BACKGROUND: In Tunisia, there are no normal values of pulmonary function for healthy Tunisian children. OBJECTIVES: The purpose of this study was to set reference values for spirometric lung function in Tunisian children and to compare these results with other data sets. METHODS: Spirometric values were measured with a Minato portable spirometer in 1,114 asymptomatic, nonsmoking Tunisian children (581 boys and 533 girls) 6-16 years of age. Natural logarithmic values of lung function and standing height were used in the final regression model. RESULTS: Prediction equations for forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), FEV(1)/FVC x 100, maximum mid expiratory flow (MMEF 25-75%) and peak expiratory flow (PEF) for both sexes are presented with standing height as the dependent variable. Our data show a significant increase in lung function with standing height in both sexes. Comparing our results with recent data, values of FVC and FEV(1) in both sexes in the present study are close to those in European, white US and Asian children, whereas our values are higher than the Libyan ones. CONCLUSIONS: Healthy Tunisian children showed similar spirometric reference values compared to European, white US and Asian children. Thus, these standards of lung function could also be used in Tunisia.

Anthropometry↗