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Biomedical subjects

R G Loudon

Publications and source records attributed to R G Loudon.

At least 37 records · Page 2Linked to original sources
PubMed1985

Lung sound analysis for continuous evaluation of airflow obstruction in asthma.

We developed a system for monitoring airflow obstruction noninvasively, based on the principle that the proportion of the breath cycle occupied by wheezing (Tw/Ttot) in any one subject corresponds to the severity of airways obstruction. Lung sounds were recorded continuously from the chest wall. Fifty 250 ms sound segments were randomly chosen from five-minute periods and analyzed for the presence or absence of wheezes. The proportion with wheezes was used as an estimate of Tw/Ttot (Est Tw/Ttot). For 12 wheezy patients, there was a good correlation between the Est Tw/Ttot and the forced expiratory volume in one second (r = 0.893, p less than 0.001). The system was used to evaluate nocturnal asthma. Five subjects were studied over eight nights. It was found that there was more wheezing from 4:00 to 4:30 AM than from midnight to 12:30 AM (p less than 0.05). This technique may prove useful in continuous, noninvasive monitoring of wheezy patients.

Adult↗
PubMed1984

Quantitation of wheezing in acute asthma.

Pulmonary sounds were recorded before and after bronchodilator treatment in 20 patients with acute attacks of asthma. Analysis of the sounds showed that improvement in the forced expiratory volume in one second was associated with the following two changes in the sound signal: (1) the proportion of the respiratory cycle occupied by wheeze (Tw/Ttot ratio) was reduced from 86 percent to 31 percent on average; and (2) the sound frequency of the highest pitched wheeze was also reduced, from a mean of 440 Hz to 298 Hz.

Acute Disease↗
PubMed1984

Acetazolamide and cerebral oxygenation in dogs.

Acetazolamide could theoretically impair oxygen delivery to cerebral tissue by inhibiting local acidification of capillary blood. There is considerable evidence, however, that acetazolamide improves cerebral oxygen tension. This experiment was designed to demonstrate increased deep cerebral oxygen tension after acetazolamide. Three groups of dogs were anesthetized with pentobarbital and ventilated with a respirator. A Teflon-coated stainless steel catheter was placed through a craniotomy into the parietal lobe and advanced into the corona radiata to monitor cerebral pO2 and pCO2 with a mass spectrometer. Group one dogs were normoxic and eucapneic. Group two dogs were hypoxemic, and Group three dogs were hypocapneic. After control cerebral and arterial gas tensions had been recorded, acetazolamide (30 mg kg-1) was injected intravenously. Cerebral gas tensions were monitored continuously and arterial gases were analyzed at 30, 60, 90 and 120 min. Cerebral oxygen tension was not decreased by acetazolamide in any of the dogs. Cerebral carbon dioxide tension was increased by acetazolamide in all dogs. We conclude that acetazolamide does not deplete cerebral oxygen tension even in the face of hypoxemia or acute hypocapnea.

Acetazolamide↗
PubMed1983

Quantitation of bronchoalveolar lavage with methylene blue.

Bronchoalveolar lavage yields a return that is composed of lung liquid and lavage liquid in variable and unknown proportions. Concentrations of chemicals and cells in lung liquid have been presented by previous workers in relative terms, sometimes relating them to the albumin content on the assumption that it is comparatively stable. We report here the use of methylene blue in the introduced fluid as an external marker. This allows the dilution, and thus absolute values, to be calculated. We found the concentrations of albumin in lung fluid to be significantly higher in a group of patients with sarcoidosis (0.50 mg/ml +/- 0.40, mean +/- standard deviation) than in a control group (0.15 mg/ml +/- 0.07; p less than 0.02). Absolute cell counts of lymphocytes in lung fluid lavaged from patients with sarcoidosis were higher than those for control patients (154 lymphocytes/ml +/- 98.9 versus 4 +/- 2.6). There was a correlation between the absolute number of lymphocytes and the albumin concentration per milliliter lung liquid (r = 0.71, p less than 0.001).

Adult↗
PubMed1980

Ventilatory response to transient hyperoxia in head injury hyperventilation.

We have measured breath-by-breath instantaneous minute ventilation (VIinst) before, during, and after the administration of 10 breaths of 100% oxygen to seven male patients with head injury hyperventilation. The patients were hypoxemic (PaO2 61.2 +/- 6.3) and hypocapnic (PaCO2 26.6 +/- 5.9) with a respiratory alkalosis (pH 7.53 +/- 0.06) while breathing air. Following the oxygen VIinst fell on the average by 40 +/- 12.7% from 16.06 +/- 3.75 1.min-1 to a minimum of 9.73 +/- 3.20 1.min-1 at 20.4 +/- 2.9 s after the first breath of oxygen. In the majority of our hyperventilating patients, almost all of the resting hyperventilation could be abolished transiently by 100% oxygen. This fall in ventilation represents the peripheral chemoreceptor contribution to resting ventilation and is increased in the head injury patients in comparison with normal subjects breathing air or hypoxic gas mixtures, altitude-acclimatized subjects and patients who are hypoxic because of chronic bronchitis or interstitial lung disease. We suggest that the increased reflex hypoxic drive to ventilation found in our patients is secondary to their cerebral injury, resulting in a reduction of descending cortical inhibitory influences on the medullary respiratory control centers.

Adolescent↗
PubMed1980

Hyperventilation-induced cerebral hypoxia.

Acute respiratory alkalosis decreases cerebral blood flow, increases the affinity of hemoglobin for oxygen, and can result in cerebral hypoxia. This experiment was designed to study this phenomenon in dogs, and to demonstrate the effect of an increased concentration of inspired oxygen. Seven mongrel dogs were anesthetized with pentobarbital and ventilated with a constant volume respirator. A Telfon-coated stainless steel catheter was placed through a craniotomy into the parietal lobe and advanced through the corona radiata to monitor cerebral PO2 and PCO2 with a mass spectrometer. Steady state cerebral and arterial gas tensions were recorded during eucapnic ventilation with air, eucapnic ventilation with 100% oxygen, hypocapnic ventilation with air, and hypocapnic ventilation with 100% oxygen. Decreased cerebral tissue oxygen tension was demonstrated in hypocapnic dogs ventilated with air. When the concentration of inspired oxygen was increased, the relatively small increase in artrial oxygen content was associated with a marked increase in PO2 at the cerebral tissue level. This may be of clinical importance in therapeutic or centrally mediated hyperventilation.

Animals↗
PubMed1979

Pulmonary function studies in acute pulmonary histoplasmosis.

We performed follow-up pulmonary function studies on three patients with acute pulmonary histoplasmosis over a period of several months, and found that the disease is benign and usually responds well to treatment or is self-limiting. There are four major changes in lung function, namely a restrictive defect, an impairment of diffusing capacity, stiff lung, and obstruction in small airways. These changes usually lead to disturbance of ventilation-perfusion ratios and impaired gas transport across alveolar capillary membranes, resulting in arterial hypoxemia. There is also hypocapnia from alveolar hyperventilation commonly found in restrictive and stiff lung syndrome.

Adult↗
PubMed1979

Mechanisms of hyperventilation in head injury: case report and review.

We report the case of a head-injured patient with spontaneous hyperventilation who had recurrent episodes of relative hypoventilation associated with increases in intracranial pressure. Detailed ventilatory studies were performed during the 2nd week after injury. Our findings in this patient prompted us to review the possible mechanisms underlying the observed changes. We suggest that spontaneous hyperventilation in head injury is secondary to a decrease in cortical inhibitory influences on respiratory control mechanisms and that the transient episodes of relative hypoventilation observed in our patient may reflect modified ventilatory responses dependent on the altered state of consciousness. (Neurosurgery, 5: 701--707, 1979).

Adult↗
PubMed1979

Lung sound terminology in case reports.

Terms used to describe lung sounds in published case reports were tabulated, including qualifying adjectives. Seven journals were reviewed, and a total of 663 case reports were included. From the frequency of usage and similarity of qualifying adjectives it appears that "rales" and "crepitations" are equivalent terms. Many authors feel the need to qualify "rales": sixteen descriptive adjectives were encountered. Some authors distinguish between "rhonchus" and "wheeze," but the terms, for most, appear to mean the same thing. It is evident that current usage varies widely, even in the terminology of the basic categories of sounds.

Auscultation↗
PubMed1977

Metastatic pulmonary calcification in primary hyperparathyroidism.

Metastic pulmonary calcification (MPC) developed in a patient with primary hyperparathyroidism. Renal function was only minimally impaired (creatine clearance of 65 ml/min) the day prior to appearance of the lung infiltrate, but deteriorated (creatinine clearance of 14 ml/min) concomitantly with the appearance of MPC. Lung imaging with 99mTc bone-scanning agents helps differentiate MPC from other problems with similar clinical and roentgenographic findings, thus allowing prompt therapy.

Calcinosis↗
PubMed1976

Pulmonary compliance changes after experimental head injury.

Reduced static compliance has been reported in the lungs of experimental animals removed immediately after head injury. To relate these findings to clinical human experience, pulmonary dynamic compliance measurements were continuously made by clinically applicable methods in 18 monkeys subjected to severe head trauma. After a 2-hr control period, the monkeys were given a standard blow on the head and followed for 2 more hours. Two monkeys died immediately after trauma and two during the succeeding two hours. Pulmonary compliance significantly decreased in these animals only at time of death. No change in compliance was noted in animals which did not die during the 2 hours of observation after trauma were killed by further trauma. These animals did not demonstrate decreased compliance. The findings suggest that the mechanical characteristics of the lungs following head trauma in experimental animals can be measured by methods used clincally and may remain unaltered until immediately before the time of death.

Animals↗