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Biomedical subjects

J Moxham

Publications and source records attributed to J Moxham.

At least 19 recordsLinked to original sources
PubMed1992

A clinically relevant modification to existing inhaler therapy.

A modified formulation of inhaled salbutamol and a new inhaler device were studied in a group of 11 moderate-to-severe asthmatic patients. Changes in airway calibre (FEV1, Vmax30) were measured before and after inhalation of the new formulation, and compared with changes following inhalation of conventional salbutamol. A standard Rotahaler was used as a reference for the new inhaler. The study was conducted as a two-part randomized, double-blind cross-over trial. We found a significantly greater bronchodilatation of the larger airways using the modified drug in the Rotahaler. The new inhaler did not show any superiority over the Rotahaler, contrary to expectations from in vitro work. A slightly shorter model may better reflect the in vitro results. The study has implications for inhalation therapy in general.

Adult↗
PubMed1992

Detection of HIV in haemopoietic progenitors.

Peripheral blood cytopenias present a major problem in the management of patients with HIV infection. Their pathophysiology is likely to be multifactorial, although there is controversy as to whether haemopoietic progenitors are a target for HIV. In order to investigate the haemopoietic defect in HIV infection, we looked at bone marrow culture characteristics of marrow from eight HIV+ patients compared to normal controls. We performed long-term liquid culture (LTC) and colony forming assays for granulocyte-macrophage (CFU-GM) and granulocyte, erythroid, megakaryocyte, macrophage (CFU-GEMM). In LTC we found normal stromal appearance and haemopoietic focus formation. There was no difference in colony assays of CFU-GM and CFU-GEMM between HIV+ and normal controls. Colonies taken from CFU-GM and CFU-GEMM were analysed for HIV DNA sequences, and we were able to detect HIV DNA in colonies from all HIV+ patients. Our results indicate that despite infection of haemopoietic progenitor cells by HIV, bone marrow function is preserved. This suggests that HIV-related cytopenias may be due to alternative mechanisms not present in our in vitro system.

Adult↗
PubMed1992

Short term effect of oxygen on renal haemodynamics in patients with hypoxaemic chronic obstructive airways disease.

BACKGROUND: Oxygen therapy is effective in the prevention and treatment of oedematous exacerbations of cor pulmonale. As renal blood flow is reduced in cor pulmonale a study was designed to investigate whether one of the beneficial effects of oxygen was to increase renal blood flow. The effect of oxygen therapy on renal haemodynamics measured noninvasively was examined in patients with chronic obstructive airways disease and previous episodes of oedema. METHODS: Renal blood flow waveforms were recorded in a single vessel by colour flow Doppler ultrasound in nine hypoxaemic patients (PaO2) (arterial oxygen tension < 8 kPa while they were breathing air) with chronic obstructive airways disease and previous oedema and eight age matched normoxaemic volunteers (arterial oxygen saturation (SaO2) 97% or more when breathing air) while they were breathing air and oxygen. SaO2 and transcutaneous PaO2 (TcPO2) and PaCO2 (TcPCO2) were monitored. Five renal velocity profile recordings were made from the same segmental vessel with the patient breathing room air for one hour followed by oxygen titrated to achieve an oxygen saturation of 95% or more without a rise in TcPCO2 for 15 minutes. Control subjects breathed 35% oxygen. RESULTS: No significant change in the pulsatility index (a measure of distal vascular resistance) or mean height of the waveform (Tamx, a measure of renal blood flow) occurred in the control subjects while they were breathing air or oxygen. The pulsatility index of the patients with chronic obstructive airways disease was significantly greater than that in the control subjects breathing air (1.44 (SD 0.28) v 1.03 (0.14). Breathing oxygen was associated with an increase in TcPO2 in the patients (from 6.9 (1.9) to 11.5 (0.7) kPa), a fall in pulsatility index (from 1.44 (0.28) to 1.26 (0.14) and an increase in Tamx (from 0.187 (0.055) to 0.234 (0.087) m/s). CONCLUSIONS: The results suggest that renal vascular resistance is increased in patients with chronic obstructive airways disease and hypoxaemia and that short term oxygen therapy reduces renal vascular resistance and increases blood flow. Some of the benefits of oxygen therapy in cor pulmonale may be due to improvements in renal haemodynamics.

Aged↗
PubMed1992

Repetitive stimulation of phrenic nerves in myasthenia gravis.

BACKGROUND: In the investigation of patients with myasthenia gravis, repetitive supramaximal stimulation of an affected peripheral nerve is commonly performed to detect abnormal transmission at the neuromuscular junction. A study was undertaken to determine whether abnormal transmission could similarly be detected during stimulation of the phrenic nerves. METHODS: The phrenic nerves were stimulated supramaximally with surface electrodes in 13 patients with myasthenia gravis and in 16 control subjects (six control patients with diaphragmatic weakness but not with myasthenia and ten normal subjects). The amplitude of diaphragm muscle action potentials was measured with surface electrodes during phrenic nerve stimulation at frequencies of 1-5 Hz for 3-4 seconds. RESULTS: In five patients with myasthenia gravis, a significant decrement (15-43% decrease) occurred in the amplitude of diaphragm muscle action potential during stimulation at 3 Hz. When stimulation frequency was reduced to 1 Hz, diaphragm muscle action potentials returned to their original amplitude within 4-5 seconds. The decrement in the amplitude of the diaphragm muscle action potential was reduced temporarily in three of four patients after the administration of intravenous edrophonium chloride (Tensilon). There was no significant change (< 10% decrease) in the amplitude of diaphragm muscle action potentials during stimulation at increased frequencies either in the 16 control subjects or in eight of the patients with myasthenia gravis. CONCLUSION: A significant reduction in the amplitude of diaphragm muscle action potential occurred in five of 13 patients with myasthenia gravis during phrenic nerve stimulation at 3 Hz but in none of the control subjects. This may be a useful and non-invasive method for identifying patients with myasthenia gravis in whom weakness of the diaphragm is suspected.

Action Potentials↗
PubMed1991

The effects of mild obesity on lung function.

Lung volumes and blood gas tensions were measured in 144 males awaiting coronary artery surgery. Patients were divided into three groups according to their body mass index. Functional residual capacity (FRC), expiratory reserve volume (ERV) and arterial oxygen tension (PaO2) were reduced in the 91 patients with Grade I obesity (mean +/- SD weight, 81.1 +/- 9.0 kg) compared with the results obtained in the 28 patients of normal weight (Grade 0, 70.8 +/- 8.8 kg). The magnitude of the reduction was greater in the Grade II obesity patients (90.1 +/- 8.8 kg, n = 25). Mean values were: FRC 3.45, 3.17, 2.66 l; ERV 1.10, 0.77, 0.59 l and PaO2 11.05, 10.47, 9.99 kPa in patients with Grades 0, I and II obesity respectively. The alveolar-arterial oxygen difference (A-aPO2) was significantly higher in the obese patients. Mean A-aPO2 was 2.47, 3.14 and 3.88 kPa in patients with Grades 0, I and II, respectively. We conclude that obesity, even when mild, significantly impairs lung function.

Adult↗
PubMed1991

Inspiratory muscle relaxation rate after voluntary maximal isocapnic ventilation in humans.

We have investigated whether the capacity of the inspiratory muscles to generate pressure and flow during a ventilatory load is related to changes in inspiratory muscle relaxation rate. Five highly motivated normal subjects performed voluntary maximal isocapnic ventilation (MIV) for 2 min. Minute ventilation and esophageal, gastric, and transdiaphragmatic pressures were measured breath by breath. We observed that ventilation, peak inspiratory and expiratory pressures, and inspiratory flow rate declined from the start of the run to reach a plateau at 60 s that was sustained for the remainder of the exercise. In a subsequent series of studies, MIV was performed for variable durations between 15 and 120 s. The normalized maximum relaxation rate of unoccluded inspiratory sniffs (sniff MRR, %pressure loss/10 ms) was determined immediately on stopping MIV. Sniff MRR slowed as the duration of MIV increased and paralleled the decline in inspiratory pressure and ventilation observed during the 2-min exercise. No further slowing in MRR occurred when ventilation became sustainable. We conclude that, during MIV, the progressive loss of ventilation and capacity to generate pressure is associated with the early onset and progression of a peripheral fatiguing process within the inspiratory muscles.

Adult↗
PubMed1991

Sniff esophageal and nasopharyngeal pressures and maximal relaxation rates in patients with respiratory dysfunction.

Sniff esophageal pressure (Pes) and maximal relaxation rate (MRR, percent pressure loss/10 ms) are useful measurements of inspiratory muscle performance, but they require the passage of an esophageal balloon. We have examined the relationship between sniff esophageal and nasopharyngeal pressures (sniff Pes, sniff Pnp) and maximal relaxation rates (Pes MRR, Pnp MRR) in 13 patients with chronic obstructive pulmonary disease (COPD), five with intrapulmonary fibrosis (IPF), and seven with the "shrinking lung syndrome" of systemic lupus erythematosus (SLE). The ratio sniff Pnp/Pes (mean +/- SD) was 0.65 +/- 0.15 in COPD, 0.76 +/- 0.18 in IPF, and 0.91 +/- 0.03 in SLE. The ratio Pnp/Pes MRR was 1.20 +/- 0.2 in COPD, 1.14 +/- 0.12 in IPF, and 1.07 +/- 0.13 in SLE. We confirm that the transmission of pleural pressure to the upper airways during brief dynamic maneuvers is impaired in the presence of airway obstruction and lung fibrosis. We conclude that measurements of sniff Pnp and Pnp MRR are of limited value in patients with abnormal lung mechanics.

Adult↗
PubMed1991

Maximal relaxation rate of inspiratory muscle can be effort-dependent and reflect the activation of fast-twitch fibers.

We have measured the normalized maximal relaxation rate (MRR, % pressure loss/10 ms) of esophageal and transdiaphragmatic pressures in five normal subjects who performed unoccluded shifts from FRC, with the peak pressure varying between 10 and 100% of each subject's maximum. MRR was computed as the maximal rate of decay of pressure divided by the peak pressure, with units of %pressure loss/10 ms. We observed that MRR became progressively faster as sniff peak pressure increased in amplitude above 10% maximum. In four subjects this trend was most marked for sniffs of less than 40% maximal pressure, with little change as peak pressure increased further. In a fifth subject this trend continued across the full range of pressure. Thus, MRR may be an effort-dependent variable during voluntary inspiratory maneuvers. We postulate that sniff MRR becomes faster with increasing peak pressure because of progressive activation of fast-twitch type II muscle fibers. The findings of this study suggest that erroneous conclusions about the significance of slowing of sniff MRR with fatigue may be made if MRR is determined from voluntary efforts with a peak pressure of less than 60% of control maximum, as may occur with fatigue.

Humans↗
PubMed1991

Domiciliary nocturnal nasal intermittent positive pressure ventilation in COPD: mechanisms underlying changes in arterial blood gas tensions.

The improvement in arterial blood gas tensions following assisted ventilation in chronic obstructive pulmonary disease (COPD) has usually been attributed to the relief of incipient or established respiratory muscle fatigue. The contribution of changes in the load placed upon and the drive to the respiratory muscle pump have not been evaluated. We have investigated the contribution of changes in respiratory muscle strength, the ventilatory response to CO2 and ventilatory function to changes in arterial blood gas tensions in eight patients with severe COPD completing six months domiciliary nasal intermittent positive pressure ventilation. Six patients showed a reduction and two an increase in arterial carbon dioxide tension (PaCO2), median (range) for eight patients, -0.9 kPa (-1.5 to +0.4) (p less than 0.05) and seven showed an improvement in arterial oxygen tension (PaO2), +0.7 kPa (-0.4 to +1.7) (p less than 0.05) during daytime spontaneous breathing. The reduction in PaCO2 was not related to increased inspiratory muscle strength but was correlated with a decrease in gas trapping (Spearman rank correlation coefficient (r(S)) 0.85, p less than 0.05) and in the residual volume (r(s) 0.78, p less than 0.05), suggesting reduced small airway obstruction and, therefore, a reduction in load. The change in PaCO2 also correlated with the increase in ventilation at an end-tidal CO2 of 8 kPa during rebreathing (r(s) -0.76, p less than 0.05) suggesting improved chemosensitivity to CO2. Our data do not support the hypothesis that improvements were due to the relief of muscle fatigue. We suggest that the contribution of changes in load and central drive warrant further investigation.

Female↗
PubMed1990

Effect of chronic airflow limitation on resting oxygen consumption.

The work of breathing in patients with severe chronic airflow limitation is increased even at rest but little is known about the magnitude of this increase. Resting oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient (RQ) were measured in 13 patients with severe chronic airflow limitation (mean FEV1 0.78 1, vital capacity 2.1 1) and compared with those of 13 age, weight, and height matched control subjects. Whereas mean RQ was the same in the two groups (0.82), mean VO2 and VCO2 were higher in the patients (+ 18 ml min-1 and + 15 ml min-1 respectively). When VO2 was standardised for body surface area it was 10.9% higher in the patients (p less than 0.05). If the increased resting VO2 in these patients were solely due to increased activity of the respiratory muscles, it would represent a fourfold increase in the oxygen cost of breathing.

Body Surface Area↗