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Biomedical subjects

M D Hammond

Publications and source records attributed to M D Hammond.

At least 19 recordsLinked to original sources
PubMed1993

Comparison of diaphragm EMG centroid frequencies: esophageal versus chest surface leads.

Previous work has suggested that diaphragm EMGs recorded from the lower thoracic wall yield spuriously low centroid frequencies (Fc). For this reason we compared EMGs recorded from two anterolateral thoracic wall locations with EMGs recorded simultaneously from a bipolar esophageal electrode in 11 stable quadriplegic patients. Their maximal inspiratory pressures (Pdimax) ranged from 31 to 85, averaging 55 cm H2O. Quadriplegic patients were selected to exclude EMG contamination of surface recordings by intercostal muscle activity. Recordings were made during resting breathing, voluntary hyperventilation, CO2-stimulated hyperventilation, and inspiratory resistance breathing at 50% of Pdimax. Centroid frequencies were consistently lower from surface recordings than from esophageal recordings. Centroid frequencies (Hz) recorded from the esophagus were 86.9 +/- 3.0 (SEM) resting, 93.4 +/- 3.7 during voluntary hyperventilation, 85.8 +/- 4.2 during CO2-stimulated ventilation, and 88.5 +/- 1.4 during inspiratory resistance breathing. Corresponding Fc values from simultaneous thoracic surface recordings were 62.6 +/- 3.6, 62.0 +/- 2.8, 58.6 +/- 3.1, and 58.8 +/- 2.5. On several subjects, decreases in Fc that occurred during sustained maximal inspiratory efforts were present in esophageal recordings but not in surface recordings. We conclude that thoracic surface recordings of the diaphragmatic EMG do not accurately reflect frequency information.

Airway Resistance↗
PubMed1993

Cardiac tamponade due to Nocardia asteroides.

Pericarditis with hemodynamic compromise is a rare manifestation of infection with Nocardia asteroides. To our knowledge, only six cases have been reported previously. In contrast to other cases of pericardial disease due to Nocardia, culture of the pericardial fluid in our case was negative while culture of pericardial tissue led to the diagnosis. Surgical intervention and appropriate antibiotic therapy are essential in the treatment of Nocardia pericarditis.

Cardiac Tamponade↗
PubMed1992

Acute ozone-induced lung injury in rats: structural-functional relationships of developing alveolar edema.

As part of a study on the effects of acute ozone stress on the lung surfactant system, we correlated morphometric, biochemical, and functional indices of lung injury using male rats exposed to 3 ppm ozone for 1, 2, 4, and 8 hr. Evaluation of lung mechanics, using the Pulmonary Evaluation and Diagnostic Laboratory System, revealed a significant decrease in dynamic lung compliance (ml/cmH2O/kg) from a control value of 0.84 +/- 0.02 (SEM) to 0.72 +/- 0.04 and 0.57 +/- 0.06 at 4 and 8 hr, respectively. At 2 hr there was a transient increase in PaO2 to 116 torr (control = 92 torr) followed by a decrease at 4 hr (65 torr) and 8 hr (55 torr). Morphometry of lung tissue, fixed by perfusion of fixative via the pulmonary artery at 12 cm H2O airway distending pressure, demonstrated an increase in the area of the intravascular compartment at 8 hr, in association with a 65 and 39% replacement of the alveolar area by fluid in ventral and dorsal lung regions, respectively. There was a positive correlation (r = 0.966) between alveolar edema and transudated proteins in lavage fluid. A stepwise multiple regression model, with edema as the dependent variable, suggested that pulmonary vasodilatation, hypoxemia, and depletion of surfactant tubular myelin in lavage fluid were indices for predicting alveolar edema. In a second model, with lavage protein concentration as the dependent variable, decreasing dynamic compliance and hypoxemia were predictors of progressive, intraalveolar transudation of plasma proteins. The above structural-functional relationships support the concept that ozone-induced high-protein alveolar edema is pathogenetically linked to pulmonary hyperemia, deficiency of surfactant tubular myelin, and associated lung dysfunctions.

Animals↗
PubMed1992

Adult respiratory distress syndrome: a review for the clinician.

Adult respiratory distress syndrome is a common respiratory problem with a wide array of precipitating causes and an overall mortality rate of more than 50%. Signs on physical examination tend to be nonspecific as do laboratory findings associated with the syndrome. Because of its diverse etiology, there is no one specific treatment for adult respiratory distress syndrome. Therapy is primarily supportive and centers around the use of mechanical ventilator support. The authors discuss the pathogenesis and management of this syndrome together with some of the newer approaches to mechanical ventilation.

Adrenal Cortex Hormones↗
PubMed1991

Effect of mean airway pressure on gas exchange during high-frequency oscillatory ventilation.

We studied the effect of mean airway pressure (Paw) on gas exchange during high-frequency oscillatory ventilation in 14 adult rabbits before and after pulmonary saline lavage. Sinusoidal volume changes were delivered through a tracheostomy at 16 Hz, a tidal volume of 1 or 2 ml/kg, and inspired O2 fraction of 0.5. Arterial PO2 and PCO2 (PaO2, PaCO2), lung volume change, and venous admixture were measured at Paw from 5 to 25 cmH2O after either deflation from total lung capacity or inflation from relaxation volume (Vr). The rabbits were lavaged with saline until PaO2 was less than 70 Torr, and all measurements were repeated. Lung volume change was measured in a pressure plethysmograph. Raising Paw from 5 to 25 cmH2O increased lung volume by 48-50 ml above Vr in both healthy and lavaged rabbits. Before lavage, PaO2 was relatively insensitive to changes in Paw, but after lavage PaO2 increased with Paw from 42.8 +/- 7.8 to 137.3 +/- 18.3 (SE) Torr (P less than 0.001). PaCO2 was insensitive to Paw change before and after lavage. At each Paw after lavage, lung volume was larger, venous admixture smaller, and PaO2 higher after deflation from total lung capacity than after inflation from Vr. This study shows that the effect of increased Paw on PaO2 is mediated through an increase in lung volume. In saline-lavaged lungs, equal distending pressures do not necessarily imply equal lung volumes and thus do not imply equal PaO2.

Animals↗
PubMed1991

Distribution of ventilation and perfusion with different modes of mechanical ventilation.

We compared pulmonary gas exchange during synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), and airway pressure release ventilation (APRV). Nine subjects aged 56 to 75 yr were studied from 4 to 19 h after cardiac operations. When subjects were ready to be weaned from mechanical ventilation their ventilation-perfusion distribution was estimated using the multiple inert gas elimination technique during SIMV. The subjects then received PSV and APRV during alternating periods on a randomized basis, and the gas-exchange measurements were repeated. Vasoactive infusions and inspired oxygen fraction were held constant throughout the investigation. The results indicated that the major characteristics of the main mode of the VA/Q distributions (mean, standard deviation, and skew) were similar during all three modes. Dead space was lower during APRV (30.1 +/- 1.7% [SEM]) than during SIMV (36.2 +/- 1.5%) and PSV (37.1 +/- 2.7%) (p less than 0.05). Right-to-left shunt was significantly greater during APRV (19.9 +/- 2.3%) than during SIMV (15.4 +/- 1.7%) (p less than 0.05). Peak airway pressure (Paw) was higher during SIMV (32.8 +/- 1.3 cm H2O) than both PSV (19.4 +/- 2.1 cm H2O) and APRV (14.3 +/- 1.0 cm H2O) (p less than 0.05). Minute ventilation was lower during APRV (7.5 +/- 0.07 L/min) than during SIMV (9.4 +/- 0.6 L/min) and PSV (9.0 +/- 0.5 L/min) (p less than 0.05). Hemodynamic variables were similar during all three modes. We conclude that all three modes provide acceptable oxygenation and ventilatory support.

Aged↗
PubMed1990

Design, synthesis, and 5-lipoxygenase-inhibiting properties of 1-thio-substituted butadienes.

The synthesis of novel 1-thio-substituted butadienes, designed as mechanism-based 5-lipoxygenase inhibitors, is described. The structure of these compounds closely resembles a proposed high-energy intermediate during the lipoxygenation of arachidonic acid. They demonstrate 5-lipoxygenase inhibition in vitro and in vivo. The most potent compound is 15a with an IC50 of 1.8 microM in vitro. LTC4 release was inhibited by 80% after intraperitoneal administration of 15c at a dose of 2 mg/kg.

Animals↗
PubMed1990

Respiratory muscle strength in congestive heart failure.

In experimental animals, conditions which drastically decrease cardiac output may reduce the strength and endurance of respiratory muscles leading to hypercapnic respiratory failure. Because patients with chronic CHF have reduced cardiac output and vital capacity (FVC), we measured PImax and PEmax and maximal handgrip force in 16 patients with CHF and 18 AMNs. The patients with CHF had a mean left ventricular ejection fraction of 26 +/- 7 percent. Maximal respiratory pressures were significantly reduced; group mean values (+/- SD) for PImax at FRC were 41.4 +/- 5.6 cm H2O (CHF) and 102.1 +/- 27.4 cm H2O (AMN) (p less than 0.001), with PImax values in five patients with CHF as low as 20 to 30 cm H2O. In most patients, PEmax was comparably reduced. Handgrip force was less dramatically reduced, suggesting selective respiratory muscle weakness. Possible explanations include reduction in respiratory muscle blood flow or generalized muscular atrophy and weakness related to cardiac cachexia.

Forced Expiratory Volume↗
PubMed1990

Effect of mild hypoxemia on bronchial responsiveness.

Nonspecific bronchial responsiveness may be influenced by a number of stimuli. A potentially important stimulus with significant clinical implications is hypoxemia. To investigate the effect of hypoxemia on baseline pulmonary function and bronchial responsiveness, 13 subjects (eight with mild asthma and five normal) were tested on two separate days within a 1-week period. Spirometry measured before and after breathing room air through the experimental circuit for ten minutes was not significantly different. Likewise, there was no difference in baseline spirometry during mild hypoxemia (arterial saturation of 90%) compared with air breathing. The eight asthmatic subjects underwent a methacholine bronchoprovocation challenge on each of the two test days. The PC20FEV1 measured on the "hypoxemic" day (3.7 +/- 4.5 mg/mL) was not significantly different from the measured on the "room air" day (2.5 +/- 2.4 mg/mL, P greater than .05). We conclude that mild hypoxemia does not significantly affect baseline spirometry nor bronchial responsiveness.

Adult↗
PubMed1989

Pulmonary disease caused by Mycobacterium terrae complex.

A 64-year-old alcoholic man had a chronic cavitary pulmonary infiltrate. Initial sputum smears and cultures yielded abundant acid-fast organisms subsequently identified as Mycobacterium terrae. Treatment with rifampin and ethambutol resulted in progressive clinical and roentgenographic resolution with an apparent cure after 18 months of therapy.

Chronic Disease↗
PubMed1989

Gas exchange in healthy rabbits during high-frequency oscillatory ventilation.

We examined the effects of oscillatory frequency (f), tidal volume (VT), and mean airway pressure (Paw) on respiratory gas exchange during high-frequency oscillatory ventilation of healthy anesthetized rabbits. Frequencies from 3 to 30 Hz, VT from 0.4 to 2.0 ml/kg body wt (approximately 20-100% of dead space volume), and Paw from 5 to 20 cmH2O were studied. As expected, both arterial partial pressure of O2 and CO2 (PaO2 and PaCO2, respectively) were found to be related to f and VT. Changing Paw had little effect on blood gas tensions. Similar values of PaO2 and PaCO2 were obtained at many different combinations of f and VT. These relationships collapsed onto a single curve when blood gas tensions were plotted as functions of f multiplied by the square of VT (f. VT2). Simultaneous tracheal and alveolar gas samples showed that the gradient for PO2 and PCO2 increased as f. VT2 decreased, indicating alveolar hypoventilation. However, venous admixture also increased as f. VT2 decreased, suggesting that ventilation-perfusion inequality must also have increased.

Animals↗
PubMed1987

Some further properties of human pulmonary mast cells recovered by bronchoalveolar lavage and enzymic dispersion of lung tissue.

The properties of human pulmonary mast cells obtained by bronchoalveolar lavage (BAL) and enzymic dispersion of lung tissue have been compared with those of basophil leucocytes. On challenge with anti-human IgE, the pulmonary cells released both histamine and the newly generated mediators prostaglandin D2 (PGD2) and leukotriene C4 (LTC4). In contrast, the blood leucocytes released histamine but very little leukotriene and no prostanoid. Interestingly, both basophil leucocytes and BAL cells released histamine spontaneously in a hyperosmolar environment whereas dispersed lung (DL) cells showed limited reactivity under these conditions. The possible clinical significance of these findings in human bronchial asthma is discussed.

Adult↗
PubMed1987

Oxygen diffusing capacity estimates derived from measured VA/Q distributions in man.

Data from eighteen subjects, studied in hypoxia (minimum PIO2 = 80 Torr) both at rest and during exercise, were analyzed using computer models which estimate O2 diffusing capacity from measured VA/Q distributions (obtained using the multiple inert gas elimination technique 'MIGET') and measured O2 exchange. Two of these models assigned the distribution of the diffusing capacity (D) in proportion to either the perfusion (DLO2-Qwt) or ventilation (DLO2-Vwt) distributions from MIGET, and thus modeled the effects of VA/Q and D/Q beta (where Q beta is the perfusive conductance) inequalities respectively. The third model (DLO2-3C) assigned all the diffusing capacity to a single homogeneous compartment. At rest DLO2 was 41.1 +/- 4.8, 41.1 +/- 5.4 and 30.2 +/- 2.1 ml X min-1 X Torr-1 for the Qwt, Vwt and 3C models respectively. These rose to 93.7 +/- 2.6, 109.3 +/- 4.5 and 81.1 +/- 1.9 ml X min-1 X Torr-1 respectively at maximal exercise, all significantly different from rest (P less than 0.001 for each). The effects of measured VA/Q and theoretical D/Q beta inhomogeneities on diffusing capacity estimates were significant even in normal lungs. Both types of inequality caused an appreciable underestimation of DLO2. These multi-compartment model estimates, using real data, are consistent with published theoretical predictions of the effects of V, Q and D inequalities. The results during exercise come close to morphometric predictions of maximal oxygen diffusing capacity in man.

Blood Gas Analysis↗
PubMed1987

Some studies on human pulmonary mast cells obtained by bronchoalveolar lavage and by enzymic dissociation of whole lung tissue.

Human pulmonary mast cells were obtained by bronchoalveolar lavage (BAL) and by enzymic dissociation of whole lung. The cells released histamine on immunological stimulation or on exposure to a hyperosmolar environment. Cell suspensions similarly released newly generated products of arachidonic acid metabolism. Increased numbers of mast cells were recovered by BAL of asthmatic subjects and patients suffering from sarcoidosis and these cells were hyperresponsive to immunological challenge. Mast cells recovered by BAL and enzymic dissociation were differentially inhibited by antiasthmatic drugs. These data emphasize the potential role of BAL mast cells in pulmonary diseases of diverse origin.

Adolescent↗
PubMed1986

Pulmonary gas exchange in humans during exercise at sea level.

Previous studies have shown both worsening ventilation-perfusion (VA/Q) relationships and the development of diffusion limitation during exercise at simulated altitude and suggested that similar changes could occur even at sea level. We used the multiple-inert gas-elimination technique to further study gas exchange during exercise in healthy subjects at sea level. Mixed expired and arterial respiratory and inert gas tensions, cardiac output, heart rate, minute ventilation, respiratory rate, and blood temperature were recorded at rest and during steady-state exercise in the following order: rest, minimal exercise (75 W), heavy exercise (300 W), heavy exercise breathing 100% O2, repeat rest, moderate exercise (225 W), and light exercise (150 W). Alveolar-to-arterial O2 tension difference increased linearly with O2 uptake (VO2) (6.1 Torr X min-1 X 1(-1) VO2). This could be fully explained by measured VA/Q inequality at mean VO2 less than 2.5 l X min-1. At higher VO2, the increase in alveolar-to-arterial O2 tension difference could not be explained by VA/Q inequality alone, suggesting the development of diffusion limitation. VA/Q inequality increased significantly during exercise (mean log SD of perfusion increased from 0.28 +/- 0.13 at rest to 0.58 +/- 0.30 at VO2 = 4.0 l X min-1, P less than 0.01). This increase was not reversed by 100% O2 breathing and appeared to persist at least transiently following exercise. These results confirm and extend the earlier suggestions (8, 21) of increasing VA/Q inequality and O2 diffusion limitation during heavy exercise at sea level in normal subjects and demonstrate that these changes are independent of the order of performance of exercise.

Altitude↗
PubMed1986

Pulmonary gas exchange in humans during normobaric hypoxic exercise.

Previous studies (J. Appl. Physiol. 58: 978-988 and 989-995, 1985) have shown both worsening ventilation-perfusion (VA/Q) relationships and the development of diffusion limitation during heavy exercise at sea level and during hypobaric hypoxia in a chamber [fractional inspired O2 concentration (FIO2) = 0.21, minimum barometric pressure (PB) = 429 Torr, inspired O2 partial pressure (PIO2) = 80 Torr]. We used the multiple inert gas elimination technique to compare gas exchange during exercise under normobaric hypoxia (FIO2 = 0.11, PB = 760 Torr, PIO2 = 80 Torr) with earlier hypobaric measurements. Mixed expired and arterial respiratory and inert gas tensions, cardiac output, heart rate (HR), minute ventilation, respiratory rate (RR), and blood temperature were recorded at rest and during steady-state exercise in 10 normal subjects in the following order: rest, air; rest, 11% O2; light exercise (75 W), 11% O2; intermediate exercise (150 W), 11% O2; heavy exercise (greater than 200 W), 11% O2; heavy exercise, 100% O2 and then air; and rest 20 minutes postexercise, air. VA/Q inequality increased significantly during hypoxic exercise [mean log standard deviation of perfusion (logSDQ) = 0.42 +/- 0.03 (rest) and 0.67 +/- 0.09 (at 2.3 l/min O2 consumption), P less than 0.01]. VA/Q inequality was improved by relief of hypoxia (logSDQ = 0.51 +/- 0.04 and 0.48 +/- 0.02 for 100% O2 and air breathing, respectively). Diffusion limitation for O2 was evident at all exercise levels while breathing 11% O2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Grass Conjuvac. II. Pro-inflammatory activity and potential for inducing hypersensitivity.

Treatment of rats with Conjuvac induced no anti-pollen extract (PE) IgE and no sensitization, whereas alum-adsorbed pollen extract induced IgE antibody and marked sensitivity. Conjuvac induced anti-PE IgE in rats treated with Bordetella pertussis organisms but the antibody concentrations were less than those induced by PE with B. pertussis. There was no indication, either in rats injected with B. pertussis and Conjuvac or alginate (ALG), of sensitization to ALG. In guinea pigs, Conjuvac induced immediate hypersensitivity to PE but there was no delayed hypersensitivity. Furthermore, no immediate hypersensitivity and little or no delayed hypersensitivity to ALG was detected in guinea pigs injected with conjuvac or ALG. Histological studies at Conjuvac injection sites in rabbits revealed inflammatory reactions less intense than those produced by aluminium hydroxide.

Adjuvants, Immunologic↗