Biomedical subjects

A D Muir

Publications and source records attributed to A D Muir.

18 recordsLinked to original sources

PubMed1992

Postoperative hypoxaemia after major abdominal vascular surgery.

We have studied the severity and duration of nocturnal hypoxaemia before operation and for the first five nights after operation after elective major abdominal vascular surgery. Oxygen supplementation was almost 100% effective in keeping oxygen saturation greater than 90% during the early postoperative period; however, 50% of patients spent prolonged periods with an SpO2 less than 85% during at least one night after operation. The risk of severe hypoxaemia persists well beyond the current prescription of supplementary oxygen in these high risk patients. A significant association exists between the mean preoperative overnight saturation value and the nocturnal saturation observed subsequently in the later postoperative period.

Adult↗

PubMed1992

Late postoperative nocturnal dips in oxygen saturation in patients undergoing major abdominal vascular surgery. Predictive value of pre-operative overnight pulse oximetry.

Twenty-four patients (23 male) who presented for aortic reconstructive surgery were studied with pulse oximetry on a pre-operative night and during the first five postoperative nights. Patients with five or more dips in oxygen saturation of greater than 4% (with a prompt recovery back toward baseline of 3% or more) per hour of monitoring were classified as having a significant abnormality of respiration. Pre-operatively, four of 24 patients (17%) demonstrated such an abnormality. Postoperatively, 12 patients (50%) met these criteria on at least one of the first five postoperative nights and six of these had two or more nights with severe episodic hypoxaemia. Frequent severe episodic dips in arterial oxygen saturation (to less than 85% saturation) occurred in the late postoperative period at a time when oxygen therapy would usually have been discontinued. Pre-operative overnight pulse oximetry studies fail to predict the development of abnormal respiratory patterns in the postoperative period in the majority of patients.

Adult↗

PubMed1991

Haemodynamic effects of periodic ventilation: abolition with supplementary oxygen.

A 63-yr-old man was noted to breathe with a periodic pattern of ventilation during sleep, both before and after operation for coronary artery grafting, and 6 weeks later after aortic aneurysm repair. Periodic ventilation was associated with cyclic oxygen desaturations and increases in heart rate and arterial pressure. Administration of oxygen was found to abolish consistently the periodic pattern and the associated haemodynamic changes.

Hemodynamics↗

PubMed1991

Preoperative silent myocardial ischaemia: incidence and predictors in a general surgical population.

We have studied before operation 156 patients aged more than 40 yr presenting for elective vascular or non-vascular surgery, using ambulatory ECG monitoring to detect silent myocardial ischaemia (SMI). The prevalence of SMI was 18.2% in the vascular group (n = 102) and 7.6% in the non-vascular group (n = 54). A history of ischaemic heart disease, or an abnormal ECG suggestive of a previous myocardial infarction, predicted a high risk of SMI (28% compared with 9% in the absence of these variables). However, a significant amount of SMI (36% of the total) occurred in patients without one of the defined risk factors. In addition, 24 of the patients with abdominal aortic disease underwent cardiac gated blood pool (MUGA) scans. Abnormal ventricular wall function was observed in 62.5% of the patients. Twenty-nine percent of the patients studied with MUGA scans had SMI and 21% had ejection fractions less than 40%. A significant association (P less than 0.05) existed between the presence of SMI and a ventricular ejection fraction of less than 40%.

Adult↗

PubMed1991

Postoperative myocardial ischaemia: temporal association with nocturnal hypoxaemia.

Three patients presenting for elective aortic surgery were studied before operation and for up to 3 days after operation with ambulatory electrocardiographic monitoring and nocturnal pulse oximetry. Supplementary oxygen was administered for the first 2 days after operation and withdrawn on the 3rd morning after operation. Heart rate remained increased for the first 3 days after operation. Two patients developed episodes of myocardial ischaemia during the first 48 h after operation while their arterial oxygen saturation remained greater than 90%. On the third day, and during the third night after operation, both the severity and duration of myocardial ischaemia increased markedly, associated with arterial hypoxaemia. A temporal relationship between decreases in oxygen saturation and fluctuations in ST segment level were observed in the three patients.

Aged↗

PubMed1991

Postoperative obstructive sleep apnoea. Haemodynamic effects of treatment with nasal CPAP.

A 74-year-old man presenting for aortic reconstructive surgery showed severe, previously undiagnosed obstructive sleep apnoea during overnight oximetry monitoring before operation. Postoperatively, in the first 4 hours following extubation, he suffered 238 episodes of respiratory obstruction. These events were associated with frequent arousals, large fluctuations in systolic and diastolic blood pressure. Administration of nasal continuous positive airways pressure abolished the obstructions and allowed an uninterrupted night's sleep, with a significantly reduced blood pressure. Subsequent dips in oxygen saturation as a result of respiratory obstruction recurred on the fifth postoperative night. We conclude that pre-operative overnight oximetry may be useful in identifying those patients at risk of postoperative upper airway obstruction. Use of nasal continuous positive airway pressure may prevent the occurrence of early postoperative obstruction and the associated haemodynamic changes.

Aged↗

PubMed1988

The effects of controlled oxygen therapy on ventricular function in patients with stable and decompensated cor pulmonale.

We made simultaneous measurements of pulmonary hemodynamics, cardiac output, and right ventricular ejection fraction (RVEF) to assess the right ventricular function in 14 patients with pulmonary arterial hypertension as a result of chronic obstructive pulmonary disease (COPD). From these measurements, the right ventricular end-systolic pressure/volume relationship could be calculated and used to assess right ventricular contractility. Eight of the patients were clinically stable, without edema, and 6 presented acutely with gross edema, indicating decompensated cor pulmonale. Measurements were made at rest, while breathing air and oxygen. Although mean pulmonary arterial pressure (Ppa) was similar in those with (Ppa = 33 +/- 6 mm Hg) and without edema (Ppa = 30 +/- 8 mm Hg, p greater than 0.05), RVEF was lower in edematous (RVEF = 0.23 +/- 0.11) compared with non-edematous patients (RVEF = 0.47 +/- 0.04, p less than 0.01). Cardiac output was normal in both groups. The mean right ventricular end-systolic pressure/volume ratio (P/V) was lower in those patients with edema (P/V = 0.41 +/- 0.27), as compared with those without edema (P/V = 1.69 +/- 0.35, p less than 0.05), as a result of an increase in right ventricular end-systolic volume index. Similarly, left ventricular end-systolic volumes were higher in edematous than in non-edematous patients. Breathing 1 to 3 L/min of oxygen for 30 min decreased total pulmonary vascular resistance (p less than 0.05) in those patients without edema, but not in patients with edema. Oxygen did not change RVEF, left ventricular ejection fraction (LVEF), or the ventricular end-systolic P/V relationships.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗

PubMed1985

Microsporum canis infection of the scalp in an adult.

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Animals↗

PubMed1985

Effect of alcohol and aldehyde dehydrogenase inhibitors on the toxicity of 3-nitropropanol in rats.

The nitrocompounds 3-nitropropanol (NPOH) and 3-nitropropionic acid (NPA) were shown to be equally toxic when injected intraperitoneally into male Wistar rats. The LD50 for NPOH was 0.58 mmol/kg and for NPA it was 0.56 mmol/kg. NPOH was rapidly metabolized to NPA but this conversion was suppressed by prior administration of ethanol or 4-methylpyrazole to inhibit alcohol dehydrogenase. Administration of ethanol or 4-methylpyrazole before NPOH protected rats from intoxication. However, if the alcohol dehydrogenase inhibitors were given after the nitroalcohol, toxicity still occurred. Administration of the aldehyde dehydrogenase inhibitor diethyldithiocarbamic acid had little effect on the conversion of NPOH to NPA and did not alter the toxicity of NPOH. It was concluded that NPOH and NPA are equally toxic to rats but that NPOH is toxic due to its being rapidly converted to NPA.

1-Propanol↗

PubMed1984

Absorption of 3-nitropropanol and 3-nitropropionic acid from the digestive system of sheep.

When 3-nitropropanol (NPOH) was injected into the rumen (30 mg/kg), abomasum (10 mg/kg) or small intestine (10 mg/kg) of sheep, it was rapidly absorbed and converted to 3-nitropropionic acid (NPA). The reticulo-rumen was the major site of absorption for the miserotoxin aglycone but the abomasum and the small intestine also had the capacity to absorb NPOH. When NPA was injected into different regions of the alimentary tract, the reticulo-rumen was also the major site of absorption. Absorption of NPA or NPOH from the small intestine was much more rapid than from the abomasum. Plasma levels of NPA and inorganic nitrite were higher after dosing with NPOH than with NPA indicating a more rapid rate of uptake of the aglycone.

1-Propanol↗

PubMed1984

Absorption of 3-nitropropanol (miserotoxin aglycone) from the compound stomach of cattle.

Miserotoxin, the toxic component of certain Astragalus spp. (Leguminosae), was rapidly hydrolyzed to 3-nitropropanol (NPOH) in the rumen of cattle dosed with timber milkvetch (A. miser var. serotinus). The aglycone showed a rapid rate of disappearance from the rumen with an average half-life of 1.24 h. In contrast to the passage of Co-EDTA, which showed an exponential rate of increase in the abomasum, NPOH was not detected in abomasal fluid collected from dosed cattle. Rapid absorption of NPOH from the rumen was shown by plasma levels of 3-nitropropionic acid (NPA) and inorganic nitrite, but conversion of NPOH to NPA was not observed to any significant extent in the rumen.

1-Propanol↗

PubMed1984

Quantitative determination of 3-nitropropionic acid and 3-nitropropanol in plasma by HPLC.

The separation and determination of 3-nitropropanol (NPOH) and 3-nitropropionic acid (NPA) by reverse-phase high-pressure liquid chromatography (HPLC) is described. The system consists of a Micropak MCH-5 column eluted isocratically with 0.15% orthophosphoric acid (pH 2.0). This technique permits the simultaneous determination of NPA and NPOH in bovine and ovine plasma.

1-Propanol↗

PubMed1984

Conversion of 3-nitropropanol (miserotoxin aglycone) to 3-nitropropionic acid in cattle and sheep.

The metabolism of intravenously administered 3-nitropropanol (miserotoxin aglycone) was examined in cattle and sheep using high-pressure liquid chromatography (HPLC) to determine nitrocompounds in plasma. 3-Nitropropanol (NPOH) showed a rapid rate of decay and simultaneously, 3-nitropropionic acid (NPA) was detected at comparable levels in plasma. In animals dosed with NPOH, the observed NPA decayed at a slower rate than NPOH. Nitrite levels in plasma were more closely related to NPA than to NPOH. Therefore, metabolism of NPOH is linked to NPA and this could provide a common basis for the toxicity of these compounds in cattle and sheep.

1-Propanol↗

PubMed1982